Quality and Surface Modification of BC Softwood For Value-Added Products

Transcription

1 Canadian Forest Products Ltd. Research and Development Centre West 75 th Avenue Vancouver, BC V6P 6G2 Quality and Surface Modification of BC Softwood For Value-Added Products by Suezone Chow Team Leader Alice Obermajer Research Technologist Alison Hack Co-op Student Prepared for 2665 East Mall, Vancouver, B.C. V6T 1W5 Recipient Agreement Number: R Research Program Date: March 2003

2 Summary This project explores a new and economical way to improve the properties of BC softwood lumber, generally not considered by the industry. Surface and vacuum pressure polymer treatments of Lodgepole Pine, Subalpine Fir, and White Spruce (SPF) from Northern BC were investigated to assess the effectiveness of polyurethanes of different molecular weights, and several epoxy products. Penetration depth, density, and growth rate were evaluated in relation to treatment efficacy. The low molecular weight polymer generally gave the better penetration and results. Vacuum pressure application was found to be impractical and unsuccessful due to the moisture-reactive nature of the polyurethanes. Results show that a new composite with a useful combination of properties including high MOR, flexibility, hardness, and abrasive resistance could be obtained. The properties are dependent on the polymer interaction with wood species, wood components (sapwood/heartwood) and treatment face (tangential, radial, and longitudinal). The findings are valuable in the designing of new products and utilization of BC softwood lumber (e.g. the underutilized Subalpine Fir species) for value-added products by exploiting these treated product properties. Products with more flexible nature such as flooring and wall panel applications could be developed with underutilized species such as Subalpine Fir. A recommendation of this study is to transfer the findings into the industrial area by examining applications of the modified wood, as well as to investigate further property enhancement through the optimization of penetration and the examination of water soluble thermosetting polymers. As the results with SPF were promising, it would be of value to examine a greater range of BC wood species such as Douglas Fir, Cedar, and Hemlock, found in coastal forests, as their growth rates would generally be much greater than those of the Northern SPF group. 2

3 Table of Contents SUMMARY...2 LIST OF APPENDICES...5 LIST OF TABLES...6 LIST OF FIGURES...7 OBJECTIVES...11 INTRODUCTION...12 MATERIALS AND METHODS...13 Log Procurement...13 Heartwood/Sapwood Identification...13 Log Bolt Breakdown...14 Test Sample Selection...15 Sample Treatment...15 Curing Trials...16 Static Bending Testing...18 Hardness Testing...19 Abrasion Testing...19 Penetration Depth...20 RESULTS: STATIC BENDING...21 Lodgepole Pine - Heartwood...21 Tangential MOR Tangential MOE Radial MOR Radial MOE Pine Heartwood Summary Lodgepole Pine - Sapwood...26 Tangential MOR Tangential MOE Radial MOR Radial MOE Pine Sapwood Summary Pine Summary Subalpine Fir - Heartwood...34 Tangential MOR Tangential MOE

4 Radial MOR Radial MOE Subalpine Fir Heartwood Summary Subalpine Fir - Sapwood...39 Tangential MOR Tangential MOE Subalpine Fir Sapwood Summary Subalpine Fir Summary White Spruce - Heartwood...42 Tangential MOR Tangential MOE Radial MOR Radial MOE Spruce Heartwood Summary White Spruce - Sapwood...47 Tangential MOR Tangential MOE Radial MOR Radial MOE Spruce Sapwood Summary Spruce Summary Species Comparison...53 RESULTS: HARDNESS...65 Lodgepole Pine - Heartwood...65 Lodgepole Pine - Sapwood...72 Subalpine Fir - Heartwood...77 White Spruce - Heartwood...83 Species Comparison...89 RESULTS: ABRASION RESISTANCE...91 RESULTS: GROWTH RATE AND DENSITY...96 DISCUSSION...97 CONCLUSIONS...99 RECOMMENDATIONS LITERATURE REVIEWED ACKNOWLEDGEMENTS

5 List of Appendices A. Static Bending Modulus of Rupture and Modulus of Elasticity Experimental Values B. Static Bending Statistical Results C. Statistical Hardness Data of Pine Heartwood D. Statistical Hardness Data of Pine Sapwood E. Statistical Hardness Data of Subalpine Fir Heartwood F. Statistical Hardness Data of Spruce Heartwood G. Species Comparison of Hardness for all Polymer Treatments H. Hardness as a Function of Growth Rate I. MOR as a Function of Growth Rate J. Rate of Growth as a Function of Density K. Growth Rate of Lodgepole Pine L. Growth Rate of Subalpine Fir M. Growth Rate of White Spruce 5

6 List of Tables Table 1. Hardness for heartwood of Lodgepole Pine Table 2. Hardness for sapwood of Lodgepole Pine Table 3. Hardness for heartwood of Subalpine Fir Table 4. Hardness for heartwood of White Spruce Table 5. Abrasion resistance for Lodgepole Pine heartwood Table 6. Abrasion resistance for Lodgepole Pine sapwood Table 7. Abrasion resistance for White Spruce heartwood and sapwood Table 8. Abrasion resistance of Subalpine Fir heartwood

7 List of Figures Figure 1. Unstained Lodgepole Pine Figure 2. Stained Lodgepole Pine Figure 3. Stained White Spruce Figure 4. Stained Subalpine Fir Figure 5. Cutting map transparency Figure 6. Cutting map on logs Figure 7. Treatment station with nitrogen Figure 8. Vacuum pressure apparatus Figure 9. Vacuum pressured low molecular weight polyurethane sample Figure 10. Bubbles on oven cured sample Figure 11. Pressure cured, air dried samples Figure 12. Han Chang press Figure 13. Carver laboratory press Figure 14. Static bending apparatus Figure 15. Hardness apparatus Figure 16. Abrasion apparatus Figure 17. Pine heartwood tangential face MOR comparison Figure 18. Pine heartwood tangential face MOE comparison Figure 19. Pine heartwood radial face MOR comparison Figure 20. Pine heartwood radial face MOE comparison Figure 21. Pine heartwood MOR/face comparison Figure 22. Pine heartwood MOE/face comparison Figure 23. Pine heartwood MOR and MOE relative to control Figure 24. Pine sapwood tangential face MOR comparison Figure 25. Pine sapwood tangential face MOE comparison Figure 26. Pine sapwood radial face MOR comparison Figure 27. Pine sapwood radial face MOE comparison Figure 28. Pine sapwood MOR/face comparison Figure 29. Pine sapwood MOE/face comparison Figure 30. Pine sapwood MOR and MOE relative to control Figure 31. Pine tangential face heartwood/sapwood MOR comparison

8 Figure 32. Pine tangential face heartwood/sapwood MOE comparison Figure 33. Pine radial face heartwood/sapwood MOR comparison Figure 34. Pine radial face heartwood/sapwood MOE comparison Figure 35. Subalpine Fir heartwood tangential face MOR comparison Figure 36. Subalpine Fir heartwood tangential face MOE comparison Figure 37. Subalpine Fir heartwood radial face MOR comparison Figure 38. Subalpine Fir heartwood radial face MOE comparison Figure 39. Subalpine Fir heartwood MOR/face comparison Figure 40. Subalpine Fir heartwood MOE/face comparison Figure 41. Subalpine Fir heartwood MOR and MOE relative to control Figure 42. Subalpine Fir sapwood tangential face MOR comparison Figure 43. Subalpine Fir sapwood tangential face MOE comparison Figure 44. Subalpine Fir sapwood MOR and MOE relative to control Figure 45. Subalpine Fir tangential face heartwood/sapwood MOR comparison Figure 46. Subalpine Fir tangential face heartwood/sapwood MOE comparison Figure 47. Spruce heartwood tangential face MOR comparison Figure 48. Spruce heartwood tangential face MOE comparison Figure 49. Spruce heartwood radial face MOR comparison Figure 50. Spruce heartwood radial face MOE comparison Figure 51. Spruce heartwood MOR/face comparison Figure 52. Spruce heartwood MOE/face comparison Figure 53. Spruce heartwood MOR and MOE relative to control Figure 54. Spruce sapwood tangential face MOR comparison Figure 55. Spruce sapwood tangential face MOE comparison Figure 56. Spruce sapwood radial face MOR comparison Figure 57. Spruce sapwood radial face MOE comparison Figure 58. Spruce sapwood MOR/face comparison Figure 59. Spruce sapwood MOE/face comparison Figure 60. Spruce sapwood MOR and MOE relative to control Figure 61. Spruce tangential face heartwood/sapwood MOR comparison Figure 62. Spruce tangential face heartwood/sapwood MOE comparison Figure 63. Spruce radial face heartwood/sapwood MOR comparison Figure 64. Spruce radial heartwood/sapwood MOE comparison

9 Figure 65. MOR for heartwood tangential face Figure 66. Heartwood tangential face MOR relative to control Figure 67. MOR for heartwood radial face Figure 68. Heartwood radial face MOR relative to control Figure 69. MOR for sapwood tangential face Figure 70. Sapwood tangential face MOR relative to control Figure 71. MOR for sapwood radial face Figure 72. Sapwood radial face MOR relative to control Figure 73. MOE for heartwood tangential face Figure 74. Heartwood tangential face MOE relative to control Figure 75. MOE for heartwood radial face Figure 76. Heartwood radial face MOE relative to control Figure 77. MOE for sapwood tangential face Figure 78. Sapwood tangential face MOE relative to control Figure 79. MOE for sapwood radial face Figure 80. Sapwood radial face MOE relative to control Figure 81. Hardness of pine heartwood treated with polymer, pressure cured at 120 C/120 psi/2 min Figure 82. Hardness of pine heartwood treated with polymer, oven cured at 100 C for one hour Figure 83. Hardness differences in load force relative to control for polymer treated, pressure cured Lodgepole Pine heartwood Figure 84. Hardness differences in load force relative to control for polymer treated, oven cured Lodgepole Pine heartwood Figure 85. Hardness of pine sapwood treated with polymer, pressure cured at 120 C/120 psi/2 min Figure 86. Hardness differences in load force relative to control for polymer treated, pressure cured Lodgepole Pine sapwood Figure 87. Hardness differences in load force relative to control for one coat of polymer applied to Lodgepole Pine sapwood. Comparison of curing conditions Figure 88. Comparison of polymer treatment in Lodgepole Pine heartwood and sapwood for a one coat oven cure condition Figure 89. Hardness of Subalpine Fir heartwood treated with polymer, pressure cured at 120 C/120 psi/2 min Figure 90. Hardness of Subalpine Fir heartwood treated with polymer, oven cured at 100 C for one hour

10 Figure 91. Hardness differences in load force relative to control for polymer treated, pressure cured Subalpine Fir heartwood Figure 92. Hardness differences in load force relative to control for polymer treated, oven cured Subalpine Fir heartwood Figure 93. Hardness of White Spruce heartwood treated with polymer, pressure cured at 120 C/120 psi/2 min Figure 94. Hardness of White Spruce heartwood treated with polymer, oven cured at 100 C for one hour Figure 95. Hardness differences in load force relative to control for polymer treated, pressure cured White Spruce heartwood Figure 96. Hardness differences in load force relative to control for polymer treated oven cured White Spruce heartwood Figure 97. Hardness response of wood species to low molecular weight polyurethane treatment Figure 98. Abrasion resistance samples for tangential face of pine heartwood, (left to right) untreated control, low molecular weight polyurethane, and high molecular weight polyurethane treatments Figure 99. Abrasion resistance of various treatments and wood species in tangential face Figure 100. Abrasion resistance of various treatments and wood species in radial face. 94 Figure 101. Abrasion resistance of various treatments and wood species in longitudinal face

11 Objectives The objective of this project was to enhance the properties of abrasion resistance, hardness, and strength of BC softwood through polymer treatment. The effects of polymer molecular weight and curing conditions, as well as, SPF species, growth rate, wood type (sapwood/heartwood) and wood face (tangential, radial, and longitudinal) were investigated. 11

12 Introduction The low density nature of BC softwoods limits their uses in many high value applications, in comparison to medium and high-density hardwoods. In addition, the softwood industry now faces competition from denser and stronger Southern Yellow Pine. As such, there is a need to develop new uses to gain maximum benefit from the BC softwood SPF resource. This project was undertaken to provide a database for the mechanical and physical properties obtained from polymer treatments of the pine, fir, and spruce tree species and to then develop new products through applied research. The softwoods were sampled from the mid-northern interior region of BC and are therefore slow growing with narrow ring structure (10 to 50 rings/inch). This slow growth nature of our softwood timber provides lumber with unique properties, in comparison to the fast-growing southern yellow pines (1 to 2 rings/inch). The results indicated that the mechanical properties in response to the polymer treatments were dependent on the anatomical direction. The radial and longitudinal faces generally showed greater enhancement in strength and hardness than the tangential face. This supports the spaced column concept. The effect of ring width however could not be correlated because all the trees were sampled from the same region, resulting in growth rates that were too similar. An investigation to explore these data in comparison to the faster growing coastal BC tree species is not part of this project plan and will be useful to be included in a future study. Another interesting result was the significant enhancement in hardness of the polymer treated softwoods, with insignificant changes in density. Untreated BC softwood lumber is softer than hardwood species such as oak and maple. Our softwoods have a basic density range from 0.33 to 0.55 while the commercial hardwood species of oak and maple are from 0.6 to 0.7. Traditionally, because of this density limitation, our softwood has seldom been used for flooring and high-value furniture applications. Not only can the hardness of polymer treated SPF lumber be increased, but in some conditions, the flexibility and strength are also increased, and in all cases the abrasion resistance becomes very high. These unique properties could be exploited to utilize SPF species such as Subalpine Fir, which to date has very little value-added potential. The data and findings from this project work have the potential to be applied for creating products and diversifying the market applications for BC softwood lumber. 12

13 Materials and Methods Log Procurement Twenty-seven log bolts (nine each of White Spruce, Lodgepole Pine, and Subalpine Fir) of 12 diameter and 18 length were received from Canfor s Prince George sawmill. Upon arrival at Canfor Research and Development, they were placed into plastic bags to maintain moisture content and prevent checking. The cross sectional face was sanded smooth to enable the mapping of the growth rings. Ring width and cumulative ring width were plotted against the ring number to provide information about growth rate of each tree. Heartwood/Sapwood Identification The heartwood, sapwood, and juvenile wood were identified. The moisture content and differential absorption rates of water were used to determine the sapwood/heartwood boundary of the trees. Sapwood showed up clearly as a wet zone and would absorb water when wetted. In some cases, sapwood was attacked by mold and stained blue. As well, it was possible to use chemical staining techniques for pine and spruce. For pine species, in many bolts, the heartwood was already differentiated from the sapwood by its darker colour due to the higher extractives content (Figure 1). A mixture of benzidine hydrochloride and sodium nitrite was applied to the cross sectional face of each pine bolt. The heartwood turned red in colour, due to the reaction with pinosylvin phenols, while the sapwood remained uncoloured (Figure 2). In spruce, there was no natural colour difference between the heartwood and sapwood and another staining technique was used. Bromcresol green was applied and the spruce sapwood became blue/green while in heartwood, the green colour of the stain faded (Figure 3). This reaction is caused by hydrogen ion activity (difference in sapwood/heartwood ph). It was most difficult to determine sapwood/heartwood in Subalpine Fir due to uniformity in colour, lack of mold attack, and presence of moisture pockets in the heartwood (Figure 4). Figure 1. Unstained Lodgepole Pine Figure 2. Stained Lodgepole Pine 13

14 Figure 3. Stained White Spruce Figure 4. Stained Subalpine Fir Log Bolt Breakdown The juvenile wood, heartwood, and sapwood for each log were traced onto transparencies to record the original log shape and characteristics. A cutting plan was mapped out on each transparency to maximize and estimate the samples available from each tree bolt and to document sample location within each bolt (Figure 5). This map was transferred onto the log bolt to be used as a guide for cutting (Figure 6). Attempts were made to obtain pure sapwood and pure heartwood specimens. The specimens were mapped such that faces would be tangential and radial. Figure 5. Cutting map transparency Figure 6. Cutting map on logs The log bolts were cut on a large bandsaw at the Canfor Research pilot plant into specimens (for hardness and abrasion resistance testing) and specimens (for static bending). The bending test specimens were sorted into clear and unclear samples. Only the clear specimens were used. Samples were air dried to between 10% and 20% moisture content and then planed to achieve a smooth surface. 14

15 They were then placed into a controlled temperature and humidity room (23 C and 50% relative humidity) to condition to a moisture content in the range of 10-12%. Test Sample Selection The samples for bending, hardness, and abrasion resistance tests were grouped according to which log bolt that they originated from. They were then separated into treatment sets so that each set contained samples from different logs. The static bending test sample pieces were matched for the tangential and radial face treatment. For each treatment condition in the bending test, five to seven sticks were used for both the tangential and radial face of the wood. Treatment sets for the hardness test consisted of three samples per set. For the abrasion resistance test, four longitudinal face pieces from the same log position were combined to make one sample. The tangential and radial face abrasion samples were cut from the previously tested hardness samples. Moisture contents of the samples were determined by the oven dried (100 C) weight of a half inch sample for bending and a quarter inch sample for hardness. The dimensions and weight, to determine the density prior to treatment, and the rings per inch were also recorded. Except for the treatment face, all of the faces of the samples were taped to ensure chemical application to only the treatment face, as well as to conserve moisture content. Sample Treatment Treatments consisted of low (UL-2054), medium (UL-2055), and high (UL-2056) molecular weight polyurethanes (Dural), as well as epoxy 1032 (Epoxy Tech M.C.S. Inc.). Application rate trials were completed on dummy specimens to determine the behaviour of the polyurethanes and quantify a coating. The high molecular weight polyurethane defined the application rate per coat (0.026 g/cm 2 ) due to its very high viscosity. A handling system, involving the nitrogen purge of headspace, and treatment stations in fume-hoods were set up for the treatment applications (Figure 7). The required chemical load was applied by weight with a brush and included one, two, or three coats, or by vacuum pressure. For the vacuum pressure application, samples were submerged in polymer in a treating tank. A vacuum of 20 to 25 inches of mercury was applied for 30 minutes, followed with a pressure of 75 psi for one hour (Figure 8). This treatment, however, was unsuccessful, possibly due to the reactive nature of these polymers. Many bubbles formed on the surface of the samples and produced a very unfavourable appearance (Figure 9). No significant penetration into the wood was observed. Treatment applications for the tests varied according to the amount of pieces available from the twenty-seven logs. The samples were air dried overnight between faces and coats. It was observed that tiny bubbles formed within the coating in all of the 15

16 polyurethanes. This was due to the reaction with the moisture in the wood that liberates CO 2. The low molecular weight polyurethane exhibited the most bubbling whereas the high molecular weight polyurethane showed the least. Figure 7. Treatment station with nitrogen Figure 8. Vacuum pressure apparatus Figure 9. Vacuum pressured low molecular weight polyurethane sample Curing Trials Curing trials were done on dummy samples at 100 C for one hour (air dried coat), 100 C for one hour (wet coat), 120 C and 120 psi for two minutes (air dried coat), and 120 C and 120 psi for two minutes (wet coat). The 100 C (air dried coat) cure resulted in a hard, light coloured coat with bubbles still present (Figure 10). The 120 C and 120 psi for two minutes (air dried coat) cure resulted in a hard, smooth, shiny dark finish without air bubbles (Figure 11). Both the oven cure and the pressure cure trials of the wet coat 16

17 resulted in the absence of bubbles, better penetration, and a very light, transparent finish. Curing of the wet coat may be the optimum condition, however, the problems in the handling of so many samples and so many faces wet, resulted in choosing the oven and pressure cure on air dried samples. Due to the pressure cured samples giving a better finish than the oven cure, where sample quantity was limited, pressure cure was done. The epoxy 1032 cure was done at room temperature overnight. Figure 10. Bubbles on oven cured sample Figure 11. Pressure cured, air dried samples For pressure curing of the bending samples, a Han Chang press was used (Figure 12). Pressure curing of the hardness samples utilized a Carver laboratory press ( Figure 13). In both cases, 120 psi was converted to pounds of force to determine the gauge setting. The masking tape was removed from the untreated faces and the samples were pressed individually to ensure uniform force as slight variations in thickness existed among samples. After pressing, the samples were conditioned in the controlled temperature and humidity room. Figure 12. Han Chang press 17

18 Figure 13. Carver laboratory press Static Bending Testing The bending tests were completed on an Instron 4204 and were carried out according to ASTM method D , section 8. The Instron setup is shown in Figure 14. A semicircular bearing block of 3 radius was used to apply the load. Centre loading and a span length of 14 were used. Pivotal bearing plates supported both ends of the sample to permit adjustment for slight twists in the specimen. The load was applied continuously throughout the test at a crosshead rate of 0.05 in/min. Data was recorded at a sampling rate of 5 points per second. The sample was placed so that the tension from the applied load was subjected on the desired wood and face. The dimensions and weight of the sample were recorded immediately before testing and a half inch section was cut for moisture content determination. The modulus of rupture (MOR) and the modulus of elasticity (MOE) were calculated for each specimen and recorded. Figure 14. Static bending apparatus 18

19 Hardness Testing The hardness tests were also performed on the Instron, according to ASTM method D , section 13. The apparatus setup is shown in Figure 15. Dimensions and weight of the conditioned samples were recorded and the moisture content (one quarter inch section) was determined immediately prior to testing. Force was applied by a rod with a ball end half an inch in diameter and the load was recorded at penetration of one half of the ball diameter (one quarter inch). Two measurements were taken per side and face (tangential, radial, and longitudinal). The load was applied continuously throughout the test at a crosshead rate of 0.25 in/min. Figure 15. Hardness apparatus Abrasion Testing Abrasion resistance testing was completed using a Taber Abraser Tester with calibrase cs-17 wheels (Figure 16). For the tangential and radial faces, two 2 4 pieces were placed together on a sample holder and a hole was drilled in the centre. For the longitudinal face samples, four 2 2 pieces were placed together to comprise the required 4 4 sample dimension. The weight and moisture content of the sample piece was measured prior to testing. The samples were then subjected to 500 cycles on the Taber Abraser. The sample weight was recorded after testing and reported as the Taber Wear Index (TWI), or weight loss in mg per 1000 revolutions. 19

20 Figure 16. Abrasion apparatus Penetration Depth Cross sections of the treated samples were viewed with a stereomicroscope. The observed penetration depth appeared to be limited to surface with a few wood cell layers in all treatment conditions, including the vacuum pressure process. 20

21 Results: Static Bending Lodgepole Pine - Heartwood Tangential MOR An increase in the modulus of rupture (MOR) was achieved for all of the polymer treatments of pine heartwood on the tangential face. As seen in Figure 17 1, the greatest increase in the modulus of rupture was given by one coat of 100 C (oven) cured low molecular weight polyurethane, with a MOR value of 14,637 psi. This was supported by statistical analysis using the t-test 2,3, where t stat was greater than t crit (implying a positive statistical significance) for both the one- and two-tailed distribution analyses. One and two coats of 120 C and 120 psi (pressure) cured low molecular weight polyurethane treatments also showed a positive statistical significance, although not as high as the oven cured samples. One coat of pressure cured medium and high molecular weight polyurethanes indicated no significant increase in the mean MOR value. Pine Heartwood Tangential Face MOR Comparison MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 17. Pine heartwood tangential face MOR comparison 1 Error bars in graphs show maximum and minimum experimental values within the treatment set 2 Experimental MOR and MOE values used for t-test are given in Appendix A 3 All t-test results are shown in Appendix B 21

22 Tangential MOE The modulus of elasticity (MOE) of the tangential face of pine heartwood showed little increase compared to the MOR. Figure 18 shows that the most rigid of the tested samples was obtained using one coat of pressure cured low molecular weight polyurethane (MOE of 1,777,586 psi). However, this increase was not large enough to constitute a significant difference between the mean values. The only other treatment to display an increase in the MOE was one coat of oven cured low molecular weight polyurethane. It was noted that one coat of either the medium or high molecular weight polyurethane produced spongy coatings on the wood, while one coat of the low molecular weight polyurethane did not. However, when two coats of the low molecular weight polyurethane were applied, similar characteristics to the medium and high molecular weight applications were seen. This spongy coating could possibly explain the increase in flexibility of the samples, and hence the decrease in stiffness MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 18. Pine heartwood tangential face MOE comparison Radial MOR Figure 19 shows the modulus of rupture for the radial face of pine heartwood. Once again, one coat of oven cured low molecular weight polyurethane showed the highest increase in strength, rising to a MOR of 15,954 psi. This treatment also showed to be the most significant in the applied t-test. Two coats of pressure cured low molecular weight 22

23 polyurethane also produced a significant increase in strength. One coat of pressure cured low, medium, and high molecular weight polyurethane, and room temperature cured epoxy 1032, resulted in no significant change from the untreated control (12,596 psi) MOR (psi) control low PU, press cure, low PU, press cure, 2 coats medium PU, press cure, high PU, press cure, epoxy 1032, RT cure, Figure 19. Pine heartwood radial face MOR comparison Radial MOE The MOE for the radial face of pine heartwood is shown in Figure 20. It is evident that one coat of oven cured low molecular weight polyurethane gave the best result, with a MOE of 1,895,429 psi. This value also proved to be the only statistically significant MOE value by the t-test. The medium and high molecular weight polyurethane treatments, as well as the epoxy 1032, again showed a decrease in rigidity, with possible reasons described earlier. Two coats of pressure cured low molecular weight polyurethane showed a slight increase in the MOE, perhaps because the radial face of the pine heartwood absorbed some of the lower molecular weight polymer, resulting in a less spongy, two coat surface. Pine Heartwood Summary Figures 21 and 22 summarize the comparison of the MOR and MOE, respectively, between the two faces of pine heartwood. First, observing Figure 21, it is noted that the two untreated controls bear similar MOR values of 12,344 psi and 12,596 psi for the 23

24 MOE (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, press cure, high PU, press cure, epoxy 1032, RT cure, Figure 20. Pine heartwood radial face MOE comparison MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Tangential Figure 21. Pine heartwood MOR/face comparison Radial 24

25 tangential face and radial face, respectively. As stated earlier, one coat of oven cured low molecular weight polyurethane delivered the best treatment for both faces in terms of strength. The tangential and radial strengths seemed to trade off for one and two coats of pressure cured low molecular weight polyurethane: the tangential face strengthened better to the one coat and the radial better to the two coats. The medium and high molecular weight polyurethane treatments produced relatively the same MOR values for both pine heartwood faces. Figure 22 shows the tangential face of the untreated control to be slightly more rigid than that of the radial face. With this in mind, the radial face still gave the highest MOE value with a treatment of one coat of oven cured low molecular weight polyurethane, while the tangential face with the same treatment showed a much smaller, and not significant, increase. As with the MOR, the one and two coat pressure cured low molecular weight polyurethane samples traded off in rigidity according to the applied face: the tangential face was more rigid with one coat whereas the radial face was more rigid with two coats. The medium and high molecular weight polyurethane treated samples indicated to be more flexible than the control for both faces MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Tangential Figure 22. Pine heartwood MOE/face comparison Radial Figure 23 summarizes the above results, plotting the various treatment results relative to their corresponding control. On examination of only the one coat pressure cured treatments of low, medium, and high molecular weight polyurethane, an interesting 25

26 observation was made. For all four cases displayed on the graph, it was noticed that the low molecular weight polyurethane produced the highest results of the three treatments, followed by the high molecular weight and then the medium molecular weight polyurethanes. This trend illustrates consistent behaviour of the individual treatments on pine heartwood. It is also evident from Figure 23 that one coat of oven cured low molecular weight polyurethane produced the highest increase in strength (26.66%) and rigidity (16.21%) overall. As a second choice, either the one or two coats of pressure cured low molecular weight polyurethane could be used, depending on the desired face to be treated. One coat gave better results on the tangential face while two coats on the radial face produced favourable results % Difference Relative to Control coats medium PU, press cure high PU, press cure, epoxy 1032, RT cure, Tang MOR Radial MOR Tang MOE Radial MOE Figure 23. Pine heartwood MOR and MOE relative to control Lodgepole Pine - Sapwood Tangential MOR Likewise as for pine heartwood, the MOR for the tangential face of pine sapwood increased for all of the tested polymer treatments. However, it is two coats of pressure cured low molecular weight polyurethane that gave the best result, with a MOR of 14,720 psi (Figure 24). This increase in strength proved to be even more statistically significant than one coat of oven cured polyurethane on the heartwood tangential face. One coat of 26

27 oven cured high molecular weight polyurethane also showed a significant improvement. It should be noted that only two samples were used in the analysis of this set due to faulty breaks (shear, knots, etc.) within three of the wood pieces, therefore the mean and t-test analysis may be somewhat biased. Previous results with the high molecular weight polyurethane were not favourable. This is an anomaly in this case. All of the other treatments displayed no substantial increase from the untreated control MOR (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, medium PU, oven high PU, press press cure, cure, cure, high PU, oven cure, Figure 24. Pine sapwood tangential face MOR comparison Tangential MOE As seen in Figure 25, two coats of pressure cured low molecular weight polyurethane showed the highest MOE, with a value of 1,737,852 psi, for the tangential face of pine sapwood. However, the applied t-test proved that this increase is not significant. One coat of pressure cured low molecular weight and high molecular weight polyurethane indicated no significant difference as compared to the control. Radial MOR The MOR for the radial face of pine sapwood is shown in Figure 26. A significant increase in strength was seen for the two coat pressure cured low molecular weight polyurethane, although this is only for the one-tailed distribution analysis. All of the 27

28 MOE (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, medium PU, oven high PU, press press cure, cure, cure, high PU, oven cure, Figure 25. Pine sapwood tangential face MOE comparison MOR (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, press cure, medium PU, oven cure, high PU, press cure, high PU, oven cure, epoxy 1032, RT cure, Figure 26. Pine sapwood radial face MOR comparison 28

29 other treatments and cures in this test showed an increase in the MOR, however, none proved to be significant. Radial MOE All except one treatment of the radial face of pine sapwood resulted in a decrease in the MOE (Figure 27). Two coats of pressure cured low molecular weight polyurethane showed a very slight increase, but with insignificant deviation from the untreated control. One coat of oven cured low molecular weight polyurethane actually showed a significant decrease in rigidity MOE (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, press cure, medium PU, oven cure, high PU, press cure, high PU, oven cure, epoxy 1032, RT cure, Figure 27. Pine sapwood radial face MOE comparison Pine Sapwood Summary A graphical comparison of the MOR between the two tested faces of pine sapwood is presented in Figure 28. Overall, the treated tangential face tended to be stronger than the treated radial face. This was apparent for the untreated controls as well. It is evident from the graph, and previous discussion, that two coats of pressure cured low molecular weight polyurethane provided the greatest strength enhancement for the sapwood. Figure 29 displays the comparison of the MOE for the two faces of pine sapwood. On average, the tangential face appeared to deliver a higher rigidity than the radial face. The 29

30 MOR (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, medium PU, oven press cure, cure, high PU, press cure, high PU, oven cure, Tangential Figure 28. Pine sapwood MOR/face comparison Radial MOE (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, press cure, medium PU, oven cure, high PU, press cure, high PU, oven cure, Tangential Figure 29. Pine sapwood MOE/face comparison Radial 30

31 plot shows little deviation between the treated samples and their corresponding controls. In fact, most of the deviation is in the negative direction, suggesting that the treated samples were more flexible. The results for pine sapwood treatments relative to the corresponding control are summarized in Figure 30. Unlike pine heartwood, there was no obvious trend between the one coat treatments of pressure cured low, medium and high molecular weight polyurethanes. Two coats of pressure cured low molecular weight polyurethane delivered the best results, providing both improved strength (24.03%) and improved rigidity (9.53%) for both faces of pine sapwood, the only treatment to do so in this test % Difference Relative to Control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, press cure, medium PU, oven cure, high PU, press cure, high PU, oven cure, epoxy 1032, RT cure, Tang MOR Radial MOR Tang MOE Radial MOE Figure 30. Pine sapwood MOR and MOE relative to control Pine Summary Figures 31 and 32 compare the tangential face of heartwood and sapwood using the MOR and MOE, respectively. It is observed that, for all of the treated samples except for two coats of pressure cured low molecular weight polyurethane, the heartwood provided stronger and more rigid test results. Two coats on the tangential face of sapwood proved to be the greatest enhancement overall, as was seen earlier in Figure 30. A similar comparison is shown in Figures 33 and 34 for the radial face of pine. Once again, heartwood exhibited stronger and more rigid characteristics than sapwood in the 31

32 MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Heartwood Sapwood Figure 31. Pine tangential face heartwood/sapwood MOR comparison MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Heartwood Sapwood Figure 32. Pine tangential face heartwood/sapwood MOE comparison 32

33 MOR (psi) control low PU, press cure, low PU, press cure, 2 coats medium PU, press cure, high PU, press cure, epoxy 1032, RT cure, Heartwood Sapwood Figure 33. Pine radial face heartwood/sapwood MOR comparison MOE (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, press cure, high PU, press cure, epoxy 1032, RT cure, Heartwood Sapwood Figure 34. Pine radial face heartwood/sapwood MOE comparison 33

34 tested samples. With the exception of two coats of pressure cured low molecular weight polyurethane, the treated heartwood also displayed a larger deviation from the control. Overall, the highest MOR, and hence the strongest sample, was produced by one coat of oven cured low molecular weight polyurethane on the radial face of pine heartwood, with a mean value of 15,954 psi. This was followed by two coats of pressure cured low molecular weight polyurethane on the tangential face of pine sapwood, at 14,720 psi. The highest MOE, indicating rigidity, resulted from one coat of oven cured low molecular weight polyurethane on the radial face of pine heartwood, with a value of 1,895,429 psi. The next highest MOE, 1,777,586 psi, was obtained with one coat of pressure cured low molecular weight polyurethane on the tangential face of pine heartwood. Subalpine Fir - Heartwood Tangential MOR The tangential face of Subalpine Fir heartwood increased in strength for all treatment applications (Figure 35). One coat of pressure cured low molecular weight polyurethane, at a mean value of 11,662 psi, resulted in the highest increase and the only significant change in the MOR MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 35. Subalpine Fir heartwood tangential face MOR comparison 34

35 Tangential MOE Figure 36 plots the mean MOE values for the tangential face of Subalpine Fir heartwood. Most of the treatments showed a decrease in stiffness, while others showed only a slight positive deviation from the untreated control. None of the values proved to be statistically significant MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 36. Subalpine Fir heartwood tangential face MOE comparison Radial MOR An increase in the MOR was achieved for all of the treated radial faces of Subalpine Fir heartwood (Figure 37). One coat of pressure cured medium molecular weight polyurethane produced the highest, and most significant, strength, with a MOR of 11,869 psi. One coat of pressure cured low molecular weight polyurethane also resulted in a statistically significant increase from the untreated control. Radial MOE The MOE values for the radial face of Subalpine Fir heartwood are shown in Figure 38. One coat of pressure cured low, medium, and high molecular weight polyurethane all showed very little deviation from the untreated control. A significant decrease in rigidity was seen for two coats of pressure cured low molecular weight polyurethane, dropping to a mean value of 1,279,562 psi. 35

36 MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 37. Subalpine Fir heartwood radial face MOR comparison MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 38. Subalpine Fir heartwood radial face MOE comparison 36

37 Subalpine Fir Heartwood Summary Figures 39 and 40 give a visual comparison of the tangential and radial face using the MOR and MOE results, respectively. It is evident from both graphs that the treated radial face produced higher mean values than the tangential face. The only treatment in which this statement is not true was two coats of pressure cured low molecular weight polyurethane, where the radial MOE value was significantly low. By observing these two figures, it can be concluded that treatment of Subalpine Fir heartwood leads to stronger, yet more flexible, wood. Figure 41 compiles all of the Subalpine Fir heartwood graphs together relative to their corresponding control. The increased strength of the radial face was very noticeable; one coat of pressure cured medium molecular weight polyurethane showed the best improvement, an increase of 17.43% from the untreated control. The radial face of the two coat pressure cured low molecular weight polyurethane sample, however, showed an 18.99% increase in flexibility. There was no apparent trend within the three one coat pressure cured polyurethane samples MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Tangential Radial Figure 39. Subalpine Fir heartwood MOR/face comparison 37

38 MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Tangential Radial Figure 40. Subalpine Fir heartwood MOE/face comparison % Differece Relative to Control coats medium PU, press cure, high PU, press cure, Tang MOR Radial MOR Tang MOE Radial MOE Figure 41. Subalpine Fir heartwood MOR and MOE relative to control 38

39 Subalpine Fir - Sapwood Tangential MOR A comparison of the MOR values for the tangential face of Subalpine Fir sapwood is given in Figure 42. It is evident that one coat of pressure cured low molecular weight polyurethane produced the strongest wood, with a mean value of 12,562 psi. This increase, however, was not great enough to constitute a significant difference from the untreated control. Two coats of pressure cured low molecular weight polyurethane was visibly less than the untreated and other treated samples, and came close to deviating significantly in the negative direction MOR (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, press cure, high PU, press cure, epoxy 1032, RT cure, Figure 42. Subalpine Fir sapwood tangential face MOR comparison Tangential MOE Every treatment of the tangential face of Subalpine Fir sapwood achieved a decrease in the MOE (Figure 43). One coat of pressure cured low and high molecular weight polyurethanes showed very little deviation from the untreated control. Once again, two coats of pressure cured low molecular weight polyurethane produced the lowest mean of the tested treatments. 39

40 MOE (psi) control low PU, press cure, low PU, press cure, 2 coats low PU, oven cure, medium PU, press cure, high PU, press cure, epoxy 1032, RT cure, Figure 43. Subalpine Fir sapwood tangential face MOE comparison Subalpine Fir Sapwood Summary Figure 44 displays the tangential MOR and MOE values relative to the untreated control. As stated earlier, one coat of pressure cured low molecular weight polyurethane showed the highest improvement in strength, increasing 10.15%. There was no increase in the MOE, and two coats of pressure cured low molecular weight polyurethane actually decreased in strength by 14.52%. Subalpine Fir Summary Figures 45 and 46 compare the strength and rigidity, respectively, of heartwood and sapwood for the tangential face of Subalpine Fir. In both cases, treated sapwood tended to produce higher mean values than heartwood. Two coats of pressure cured low molecular weight polyurethane was an exception, as the treated heartwood outperformed the sapwood in both the MOR and MOE. Both figures show that the untreated sapwood was also stronger and more rigid than the untreated heartwood. Therefore, the actual improvements provided by each treatment on the heartwood and sapwood were not so different. Overall, one coat of pressure cured low molecular weight polyurethane appeared to deliver the best improvements in strength and rigidity for Subalpine Fir. As well, even though heartwood provided larger deviations from the untreated control, sapwood produced the higher mean values. 40

41 % Differece Relative to Control coats medium PU, press cure, high PU, press cure, epoxy 1032, RT cure, Tang MOR Tang MOE Figure 44. Subalpine Fir sapwood MOR and MOE relative to control MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Heartwood Sapwood Figure 45. Subalpine Fir tangential face heartwood/sapwood MOR comparison 41

42 MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Heartwood Sapwood Figure 46. Subalpine Fir tangential face heartwood/sapwood MOE comparison White Spruce - Heartwood Tangential MOR No significant increase in MOR was seen for the tangential face of spruce heartwood, shown in Figure 47. The treatment that gave the highest MOR was one coat of oven cured low molecular weight polyurethane, at a value of 13,432 psi. One coat of pressure cured low molecular weight polyurethane followed closely behind the oven cured mean, but the variation between the individual tests was much greater. Tangential MOE Every treatment tested on the tangential face of spruce heartwood resulted in a decrease in the MOE (Figure 48). However, none of these reductions in rigidity proved to be statistically significant. Two coats of the pressure cured low molecular weight polyurethane gave a visibly lower MOE than all of the other treatments. Radial MOR The MOR results of the various treatments of the radial face of spruce heartwood displayed insignificant deviation from the control (Figure 49). One coat of pressure cured high molecular weight polyurethane showed to be slightly less than the control 42

43 MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 47. Spruce heartwood tangential face MOR comparison MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 48. Spruce heartwood tangential face MOE comparison 43

44 value, where as all of the other treatments demonstrated an increase in strength. The highest MOR value, 13,548 psi, in this test was given by one coat of oven cured low molecular weight polyurethane MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 49. Spruce heartwood radial face MOR comparison Radial MOE A decrease in the MOE was observed for every treatment but one for the radial face of spruce heartwood (Figure 50). One coat of pressure cured low molecular weight polyurethane produced the most rigid MOE of the set, at a value of 1,957,479 psi. However, it was by no means large enough to constitute a significant difference from the control. Spruce Heartwood Summary Figures 51 and 52 display a graphical comparison of the two tested faces in terms of the MOR and MOE, respectively. Examining Figure 51 first, it is noted that, for all of the treatments, the radial face resulted in higher mean strength than the tangential face. It is not visibly obvious which treatment produced the best results, as the deviation between the means was very small. On inspection, both the pressure and oven cured one coat treatments of the low molecular weight polyurethane produced somewhat stronger wood. In Figure 52, it is seen that the radial face was also more rigid than the tangential face for 44

45 MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 50. Spruce heartwood radial face MOE comparison MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Tangential Figure 51. Spruce heartwood MOR/face comparison Radial 45

46 most treatment cases. The most rigid of the treated samples, one coat of pressure cured low molecular weight polyurethane, did not appear to deviate from the untreated control. However, all of the other treatments showed a decrease in rigidity on both faces MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Tangential Figure 52. Spruce heartwood MOE/face comparison Radial The treatment results relative to the untreated control are shown in Figure 53. The same trend for the pressure cured one coat of low, medium, and high molecular weight polyurethanes was seen in the spruce heartwood as was observed in the pine heartwood. As stated before, the low molecular weight polyurethane produced the highest results of the three treatments, followed by the medium and then the high molecular weight polyurethane. By observing Figure 53, there was no obvious choice for an enhanced coating treatment. The greatest increase in the MOR, given by one coat of oven cured low molecular weight polyurethane on the tangential face, was a mere 7.87%. The only increase in the MOE, an insignificant 1.50%, resulted from one coat of pressure cured low molecular weight polyurethane on the radial face. Due to the lack of statistically significant changes amongst the various treatments, spruce heartwood may not be the most suitable wood for strengthening purposes using polyurethane. 46

47 % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Tang MOR Radial MOR Tang MOE Radial MOE Figure 53. Spruce heartwood MOR and MOE relative to control White Spruce - Sapwood Tangential MOR An increase in the MOR was seen for all of the treatments on the tangential face of spruce sapwood (Figure 54). The strongest set was given by one coat of oven cured low molecular weight polyurethane, at a mean value of 13,143 psi. This MOR, however, was slightly too low to be significantly different from the untreated control. One coat of the pressure cured medium molecular weight polyurethane showed very little deviation from the untreated control. Tangential MOE The MOE for the tangential face of spruce sapwood is shown in Figure 55. None of the tested treatments proved to be statistically significant. One coat of pressure cured low and high molecular weight polyurethanes appeared to produce the most rigid samples, having values of 1,961,009 and 1,963,559 psi, respectively. Two coats of pressure cured low molecular weight polyurethane displayed a visibly lower rigidity than the other treated and untreated samples. Both treatments of one coat of oven cured low molecular weight polyurethane and one coat of pressure cured medium molecular weight polyurethane resulted in only minor deviations from the untreated control. 47

48 MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 54. Spruce sapwood tangential face MOR comparison MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 55. Spruce sapwood tangential face MOE comparison 48

49 Radial MOR Figure 56 plots the MOR for the various treatments of the radial face of spruce sapwood. Every treatment in this case resulted in an increase in strength. One coat of pressure cured low molecular weight polyurethane gave the highest significant mean value, 12,556 psi. One coat of pressure cured medium molecular weight polyurethane also increased significantly from the control MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 56. Spruce sapwood radial face MOR comparison Radial MOE The mean MOE values for the radial face of spruce sapwood are plotted in Figure 57. There were no significant increases in the stiffness of the treated wood. The largest MOE (1,791,444 psi) was given by one coat of pressure cured medium molecular weight polyurethane. One coat of oven cured low molecular weight polyurethane resulted in a statistically significant decrease in rigidity. Spruce Sapwood Summary Figures 58 and 59 display a MOR and MOE comparison of the two faces of spruce sapwood, respectively. In both graphs, it is visible that the tangential face was stronger than the radial face. For the MOR, however, the radial face produced the largest increase overall, as its mean value was much lower than the tangential value for the untreated 49

50 MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 57. Spruce sapwood radial face MOE comparison MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Tangential Figure 58. Spruce sapwood MOR/face comparison Radial 50

51 control. Where increases are seen in the MOE, the tangential face produces the larger changes of the two faces MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Tangential Figure 59. Spruce sapwood MOE/face comparison Radial A summary plot of the two faces relative to their corresponding control is shown in Figure 60. The largest improvement (17.55%) in the MOR was given by one coat of pressure cured low molecular weight polyurethane on the radial face. One coat of pressure cured high molecular weight polyurethane produced the greatest increase (9.55%) in MOE. It is obvious that one coat of pressure cured low molecular weight polyurethane produced the greatest increases overall. Spruce Summary The tangential face of spruce heartwood and sapwood is compared in Figures 61 and 62 in terms of MOR and MOE, respectively. It is not immediately obvious which of the two woods was stronger. The deviation between the all of the treated and untreated MOR values was quite small and therefore no obvious enhancement in strength is immediately evident. Every treatment of spruce sapwood produced a higher MOE than the same treatment on heartwood. However, in the case of the untreated control, the heartwood showed to be more rigid. Therefore, polyurethane treatment on sapwood, rather than heartwood, was more effective in increasing the stiffness of the wood. Overall, for the tangential face of spruce heartwood and sapwood, one coat of oven cured low molecular 51

52 % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Tang MOR Radial MOR Tang MOE Radial MOE Figure 60. Spruce sapwood MOR and MOE relative to control MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Heartwood Sapwood Figure 61. Spruce tangential face heartwood/sapwood MOR comparison 52

53 weight polyurethane gave the highest MOR of the treated samples and one coat of pressure cured low molecular weight polyurethane gave the highest MOE MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Heartwood Sapwood Figure 62. Spruce tangential face heartwood/sapwood MOE comparison Figures 63 and 64 compare the radial face of spruce heartwood and sapwood by means of the MOR and MOE, respectively. The heartwood noticeably dominated over the sapwood in strength and rigidity for the treated samples. However, this was also the case for the untreated control, therefore the actual increase in strength and rigidity of the treated heartwood was small. On inspection, all of the sapwood MOR values were lower than the least heartwood MOR value, indicating that the radial face of spruce heartwood was much stronger than that of the sapwood, even with treatment. The radial face MOE for both heartwood and sapwood displayed very little increase and a much larger decrease, respectively. One coat of pressure cured low molecular weight polyurethane provided the best overall enhancement in strength and rigidity for both the heartwood and sapwood. Species Comparison Figures 65 and 66 display the MOR values and MOR percent relative to the untreated control, respectively, for the tangential face of heartwood. From the first plot, it is evident that Subalpine Fir was not as strong as the other woods. One coat of oven cured low 53

54 MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Heartwood Sapwood Figure 63. Spruce radial face heartwood/sapwood MOR comparison MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Heartwood Sapwood Figure 64. Spruce radial heartwood/sapwood MOE comparison 54

55 MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 65. MOR for heartwood tangential face Pine Alpine Fir Spruce % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Pine Alpine Fir Spruce Figure 66. Heartwood tangential face MOR relative to control 55

56 molecular weight polyurethane, applied on pine, resulted in the highest MOR (14,637 psi) and also the highest improvement (18.57%) overall. The same plots as above, but for the radial face, are shown in Figures 67 and 68. Subalpine Fir again showed to be much weaker than the pine and spruce. As in the tangential face, one coat of oven cured low molecular weight polyurethane, applied on pine, proved to be the strongest treatment. The mean MOR value in this case was 15,954 psi with an increase of 26.66% from the untreated pine control. Considering that the tangential and radial pine heartwood controls had roughly the same mean value, it can be concluded that one coat of oven cured low molecular weight polyurethane on the radial face of pine produced the strongest treatment, and best improvement, of the three tested heartwood MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 67. MOR for heartwood radial face Pine Alpine Fir Spruce The MOR plots are given in Figures 69 and 70 for the tangential face of sapwood. In general, the Subalpine Fir MOR increased and the pine and spruce sapwood decreased from the corresponding heartwood values. Two coats of pressure cured low molecular weight polyurethane, applied on pine, produced the highest MOR (14,720 psi) as well as the largest increase from the untreated control (24.03%). This MOR value came within 100 psi of the highest tangential face heartwood value, stated earlier. Therefore, it can be generalized that one coat of oven cured low molecular weight polyurethane on the 56

57 % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Pine Alpine Fir Spruce Figure 68. Heartwood radial face MOR relative to control MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 69. MOR for sapwood tangential face Pine Alpine Fir Spruce 57

58 tangential face of pine heartwood is equivalent to two coats of low molecular weight polyurethane on the tangential face of pine sapwood % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Pine Alpine Fir Spruce Figure 70. Sapwood tangential face MOR relative to control Figures 71 and 72 show the MOR results for the radial face of the tested sapwood. As in the tangential face, the mean MOR values for pine and spruce sapwood were lower compared to that of the heartwood. Two coats of pressure cured low molecular weight polyurethane was again the strongest (13390 psi) of the set, and improved the most over the untreated control (18.65%). This MOR value differed from the heartwood radial face by over 2,700 psi. Overall, the low molecular weight polyurethane seemed to improve the various wood samples better than the medium and high molecular weight polyurethanes. As well, pine seemed to take best to the polyurethane, showing the greatest increases in strength. In particular, the radial face of pine, treated with one coat of oven cured low molecular weight polyurethane resulted in the highest strength. The MOE heartwood tangential face values and percent differences to the untreated control are shown in Figures 73 and 74, respectively. Subalpine Fir was evidently much more flexible than both pine and spruce. The most rigid sample was the untreated spruce control (1,857,630 psi) while one coat of oven cured low molecular weight polyurethane, applied on the tangential face of Subalpine Fir, was the least rigid (1,339,001 psi). In this 58

59 MOR (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 71. MOR for sapwood radial face Pine Spruce % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Pine Spruce Figure 72. Sapwood radial face MOR relative to control 59

60 MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 73. MOE for heartwood tangential face Pine Alpine Fir Spruce % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Pine Alpine Fir Spruce Figure 74. Heartwood tangential face MOE relative to control 60

61 case, the highest and lowest MOE values did not correspond to the greatest increase and decrease, respectively. Figures 75 and 76 present the MOE of the radial face of heartwood. Once again, Subalpine Fir appeared, in general, to be more flexible than the other two species. One coat of pressure cured low molecular weight polyurethane, applied on spruce, produced the most rigid of the tested sample (1,957,479 psi) and two coats of pressure cured low molecular weight polyurethane, applied on Subalpine Fir, produced the most flexible (1,279,562 psi). This most flexible treatment also coincided with the largest decrease ( %) relative to the control MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 75. MOE for heartwood radial face Pine Alpine Fir Spruce The MOE results for the tangential face of sapwood are shown in Figures 77 and 78. Unlike the heartwood, pine sapwood as well as Subalpine Fir sapwood, were shown to be the more flexible of the three tested wood species. One coat of pressure cured low and high molecular weight polyurethane, applied on spruce, showed to be the most rigid applications (1,961,009 and 1,963,559 psi, respectively). The most flexible treatment was given by two coats of pressure cured low molecular weight polyurethane, applied on Subalpine Fir (1,386,313 psi). These rigid and flexible values also coincided with the largest increase and decrease relative to the control. 61

62 % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Pine Alpine Fir Spruce Figure 76. Heartwood radial face MOE relative to control MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 77. MOE for sapwood tangential face Pine Alpine Fir Spruce 62

63 % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Pine Alpine Fir Spruce Figure 78. Sapwood tangential face MOE relative to control Figures 79 and 80 plot the MOE for the radial face of sapwood. A decrease in the rigidity was seen in both pine and spruce when compared to the radial face of heartwood. The highest rigidity was a result of treating spruce with one coat of pressure cured medium molecular weight polyurethane (1,791,444 psi) followed closely by one coat of pressure cured low molecular weight polyurethane on the same species (1,777,652 psi). The most flexible sample was produced by one coat of oven cure low molecular weight polyurethane on pine (1,288,412 psi). In terms of MOE, spruce tends to produce the most rigid samples with one coat of pressure cure low molecular weight polyurethane. Subalpine Fir tends to produce the most flexible samples, with either one coat of oven cure low molecular weight polyurethane or two coats of pressure cured low molecular weight polyurethane. 63

64 MOE (psi) control 2 coats medium PU, press cure, high PU, press cure, Figure 79. MOE for sapwood radial face Pine Spruce % Difference Relative to Control coats medium PU, press cure, high PU, press cure, Pine Spruce Figure 80. Sapwood radial face MOE relative to control 64

65 Results: Hardness Lodgepole Pine - Heartwood Table 1 shows the mean hardness data with coefficient of variation and % difference relative to control for each face of polymer treated heartwood samples of Lodgepole Pine. Sample sizes ranged between 12 to 24 data points. Data that are in bold are significantly different relative to the control. Significance was confirmed by t-test (one-tailed, two sample, assuming equal variance) as wood itself is so variable. The performance of the polymers is summarized in Figures 81 and 83 for the pressure cure process and Figures 82 and 84 for the oven cure process. In order to put the mean data trends into perspective, the scale for the graphs was chosen to include the range of all the data points. Please refer to Appendix C to view the statistical data and the variabilities within the sample sets. In Figure 81, what is striking is the vacuum pressure result, particularly when the uptake of polymer determined by weight, was found to correspond to an average of only one and one-half coats or 0.039g/cm 2. Just to remind the reader that in the brush treatments, application rate was carefully controlled to g/cm 2 per coat, which corresponds to 0.052g/cm 2 for two coats and g/cm 2 for three coats. The vacuum pressure treatment data for the low molecular weight polyurethane was indicative of the lack of wood surface penetration in the tangential and radial faces and the enhanced penetration in the longitudinal face. It is also indicative of a difference in reaction chemistry in comparison to the brush treatments, as a significant softening effect (decrease in hardness by 22% in tangential, and decrease of 14% in radial) was observed when the vacuum pressure treated polymer is acting on the surface as compared to no significant differences seen at the higher dosages under surface treatment. Table 1 and Figures 81 and 83 illustrate the trends for polymer treated heartwood undergoing pressure cure. In the tangential face, significant increases, 9% and 8%, were seen in the low and medium molecular weight polymers at the two coat application, respectively. In the radial face, an increase of 9%, 7% and 7% was seen at the one coat application for medium molecular weight polyurethane, high molecular weight polyurethane, and epoxy, respectively. The trendlines show that the maximum gain was from the medium and high molecular weight polyurethanes. At the two coat application, the low molecular weight polyurethane treatment showed a gain of 8% as well. The application of three coats of polymer did not show any significant increase in the heartwood hardness (tangentially and radially). For the longitudinal face, low molecular weight polyurethane and epoxy treatments did not show significant effect at the one coat application. The maximum effect for medium and high molecular weight polyurethanes was seen at the one coat application with increases of 7% and 11%, respectively. At the higher application rates there was no effect seen for the medium molecular weight polyurethane and a significant softening of 11% and 7% in the two and three coat applications of high molecular weight polyurethane. In the low molecular weight polyurethane, the maximum effect of 7% was seen at two coats, with surface treatment plateau confirmed by three coat application. The significant increase of 23% observed in vacuum pressure treatment likely reflects the increased penetration of this face and 65

66 possibly different reaction chemistry. In the surface treatments of pine heartwood, the longitudinal face was the most permeable, followed by radial, and then tangential. The tangential face was not permeable to the high molecular weight polyurethane. For the pine polymer treated heartwood, the low molecular weight polyurethane gave about 8% increase in all three anatomical directions at g/cm 2 application. The medium and high molecular weight polyurethanes gave similar gains, however their performances were much more dependent on the wood face. Refer to Table 1 and Figures 82 and 84 for a similar analysis of the polymer treated pine heartwood that was cured at 100 C for one hour. The best overall performances were seen in the medium molecular weight polyurethane at 0.026g/cm 2 with gains of 8%, 17%, and 8% in the tangential, radial, and longitudinal faces, respectively, and in the low molecular weight polyurethane at 0.078g/cm 2 with gains of 7%, 14%, and 16% for the tangential, radial, and longitudinal faces, respectively. Figures 83 and 84 show the comparison between oven and pressure cure. Less softening at the higher molecular weight polyurethanes and higher coating applications was seen in the oven cure condition. Higher gains in hardness were seen for oven cured samples, particularly in the radial face. In fact, in the oven cure treated polyurethanes, the radial face seemed to be the most permeable followed by longitudinal, and then tangential. The epoxy 1032 product, which has been formulated to cure at room temperature, showed a very significant effect in the longitudinal face with hardness gains of 21% and 26% for one and two coat applications. In the radial face, a 12% gain was seen at two coat application. No effect was seen in the tangential face. 66

67 Table 1. Hardness for heartwood of Lodgepole Pine. tangential face radial face longitudinal tangential face radial face longitudinal average lbf average lbf average lbf % difference % difference % difference and cv(%) and cv (%) and cv (%) relative to control relative to control relative to control control C cure Epoxy C cure 2 coat Epoxy C cure low PU medium PU high PU C cure 2 coat low PU medium PU high PU C cure 3 coat low PU medium PU high PU C/120psi epoxy C/120psi low PU medium PU high PU C/120psi 2 coat low PU medium PU high PU C/120psi 3 coat low PU medium PU high PU C/120psi vac/pressure low PU Data in bold is significantly different relative to control. Significance confirmed by t-test. Sample sizes range from 12 to 24. cv is the coefficient of variation. 67

68 Tangential Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush 3 coat brush vacuum /pressure Radial Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush 3 coat brush vacuum /pressure Longitudinal Face Load at mm (lbf) Low PU Medium PU High PU Epoxy untreated brush 2 coat brush 3 coat brush vacuum /pressure Figure 81. Hardness of pine heartwood treated with polymer, pressure cured at 120 C/120 psi/2 min. 68

69 Tangential face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush 3 coat brush Radial face Load at mm (lbf) lo w P U medium PU high PU epoxy untreated brush 2 coat brush 3 coat brush Longitudinal face Load at mm (lbf) Low PU Medium PU High PU Epoxy untreated brush 2 coat brush 3 coat brush Figure 82. Hardness of pine heartwood treated with polymer, oven cured at 100 C for one hour. 69

70 polym er % Difference of Load at mm low PU m edium PU high PU epoxy ta n g e n tia l radial lo n g itu d in a l coat polym er % Difference of Load at mm low PU m edium PU high PU tangential radial lo n g itu d in a l coat polym er % Difference of Load at mm low PU medium PU high PU tangential radial longitudinal -15 Figure 83. Hardness differences in load force relative to control for polymer treated, pressure cured Lodgepole Pine heartwood. 70

71 polym er % Difference of Load at mm low PU medium PU high PU epoxy 1032 tangential radial lo n g itu d in a l coat polym er % Difference of Load at mm low PU m edium PU high PU epoxy tangential rad ial lo n g itu d in a l coat polym er % Difference of Load at mm low PU m edium PU high PU ta n g e n tia l radial lo n g itu d in a l Figure 84. Hardness differences in load force relative to control for polymer treated, oven cured Lodgepole Pine heartwood. 71

72 Lodgepole Pine - Sapwood The untreated sapwood of Lodgepole Pine was found to be softer than untreated heartwood by 7%, 9%, and 18% in the tangential, radial, and longitudinal faces, respectively. Table 2 shows the sapwood hardness results. Refer to Appendix D for individual data and statistical analysis. Figures 85 and 86 showed the treatment trends under pressure cured conditions and can be compared against heartwood Figures 81 and 83. The sapwood was the more treatable wood component as the gains seen were much higher than in heartwood. For example, a one coat application of low molecular weight polyurethane showed a 22% gain in radial sapwood versus a 4% gain in radial heartwood. At the two and three coat applications, the gains were much higher for sapwood, compared to heartwood (Figures 83 and 86). No softening was seen in the treated sapwood samples. At pressure cure conditions, the low and medium molecular weight polyurethanes gave the best results at two coat application. This was the same trend as in heartwood. Figure 87 shows the comparison of oven cure to pressure cure in treated sapwood at one coat polymer application and shows that the oven cure condition is preferred, particularly for medium molecular weight polyurethane where a gain of 17%, can be attained in the tangential face, along with 15% in radial and 18% longitudinal. The high molecular weight polyurethane showed an impressive gain of 29% in longitudinal, 15% in radial, but no effect in tangential. The room temperature cured epoxy product showed very high gain of 42% in longitudinal, 15% in radial and no effect in tangential. Figure 88 shows a comparison of polymer treated pine sapwood and heartwood for one coat oven cure condition. Pine heartwood results were generally higher than sapwood, except where gains in the order of 20% are seen in sapwood. Table 2. Hardness for sapwood of Lodgepole Pine. tangential face radial face longitudinal tangential face radial face longitudinal average lbf average lbf average lbf % difference % difference % difference and cv (%) and cv(%) and cv (%) relative to control relative to control relative to control control C cure Epoxy C cure low PU medium PU high PU C/120psi low PU medium PU high PU C/120psi 2 coat low PU medium PU high PU C/120psi 3 coat low PU medium PU high PU Data in bold is significantly different relative to control. Significance confirmed by t-test. Sample sizes range from 12 to 24. cv is coefficient of variation. 72

73 Tangential Face Load at mm (lbf) lo w P U m edium PU high PU untreated brush 2 coat brush 3 coat brush Radial Face Load at mm (lbf) lo w P U m edium PU high PU untreated brush 2 coat brush 3 coat brush Longitudinal Face Load at mm (lbf) lo w P U m edium PU high PU untreated brush 2 coat brush 3 coat brush Figure 85. Hardness of pine sapwood treated with polymer, pressure cured at 120 C/120 psi/2 min. 73

74 1 co at p olym er 30 % difference of load at mm low PU medium PU high PU 20.5 tangential radial longitudinal coat polym er % difference of load at mm low PU medium PU high PU 5.3 tangential radial longitudinal coat polym er % Difference of Load at mm low PU medium PU high PU 11.0 tangential radial longitudinal Figure 86. Hardness differences in load force relative to control for polymer treated, pressure cured Lodgepole Pine sapwood. 74

75 polymer, press cure % difference of load at mm tangential radial longitudinal low PU medium PU high PU polymer, oven cure % difference of load at mm tangential radial longitudinal -5 low PU medium PU high PU epoxy Figure 87. Hardness differences in load force relative to control for one coat of polymer applied to Lodgepole Pine sapwood. Comparison of curing conditions. 75

76 Sapwood Load at mm (lbf) Tangential Radial Longitudinal control low PU medium PU high PU Epoxy Heartwood Load at mm (lbf) Tangential Radial Longitudinal control low PU medium PU high PU epoxy 1032 Figure 88. Comparison of polymer treatment in Lodgepole Pine heartwood and sapwood for a one coat oven cure condition. 76

77 Subalpine Fir - Heartwood Table 3 shows the hardness results for the polymer treated heartwood of Subalpine Fir. Refer to Appendix E for individual data and statistical analysis. Of the surface treatment conditions that underwent pressure cure, the one coat application of low molecular weight polyurethane in the tangential face was the only treatment that resulted in significant improvement in hardness. The increase was 12% and the samples were examined and no unusual aspects were found. Growth rates of the samples in the set were 11, 22, and 12 rings per inch, which is not in the range for the effect of growth rate to cause hardness increase. The only significant gain took place in what was determined in pine as the least treatable face. Figure 89 shows the performance of the polymers relative to each other for the three different anatomical directions. Although none of the polymers showed very positive results, the low molecular weight polyurethane was the best of the set evaluated. The vacuum pressure treatment results showed the same trends as in pine, indicating that this process is not suitable for the polyurethane. Figure 91 plots the percent differences of hardness relative to the control for each face and polymer. These graphs show the lack of effect of the polymer treatments at one coat application and the very significant negative or softening phenomena of the higher molecular weight polymers at multiple coatings. Of the surface treatment conditions that underwent oven cure, again the one coat application of low molecular weight polyurethane in the tangential face was the only polyurethane treatment that resulted in significant improvement in hardness. The increase was 24% and again nothing unusual was found within the samples tested. They were all from different logs than those in the parallel pressure cure set and growth rates were around 20 rings per inch. Figures 90 and 92 show that the trends were accentuated in the oven cure condition. The one positive effect was doubled, and the softening effect, at the three coat application, particularly for low and medium weight polyurethanes, was increased. The epoxy 1032 product that is formulated to cure at room temperature, showed positive effect in the longitudinal face only, at 20% for one and two coats and 30% for three coats. 77

78 Table 3. Hardness for heartwood of Subalpine Fir tangential face radial face longitudinal tangential face radial face longitudinal average lbf average lbf average lbf % difference % difference % difference and cv(%) and cv (%) and cv (%) relative to control relative to control relative to control control C cure Epoxy coat coat C cure low PU medium PU high PU C cure 2 coat low PU medium PU high PU C cure 3 coat low PU medium PU high PU C cure vac/pressure low PU C/120psi epoxy coat C/120psi low PU medium PU high PU C/120psi 2 coat low PU medium PU high PU C/120psi 3 coat low PU medium PU high PU C/120psi vac/pressure low PU Data in bold is significantly different relative to control. Significance confirmed by t-test. Sample sizes range from 12 to 24. cv is coefficient of variation. 78

79 Tangential Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush 3 coat brush vacuum/pressure Radial Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush 3 coat brush vacuum /pressure Longitudinal Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush 3 coat brush vacuum /pressure Figure 89. Hardness of Subalpine Fir heartwood treated with polymer, pressure cured at 120 C/120 psi/2 min. 79

80 Tangential Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush 3 coat brush vacuum /pressure Radial Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush 3 coat brush vacuum /pressure Longitudinal Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush 3 coat brush vacuum /pressure Figure 90. Hardness of Subalpine Fir heartwood treated with polymer, oven cured at 100 C for one hour. 80

81 polym er % Difference of Load at mm low PU m edium PU high PU epoxy tangential radial longitudinal coat polym er % Difference of Load at 5.625mm low PU -0.2 m edium PU high PU epoxy tangential radial longitudinal coat polym er % Difference of Load at 5.625mm low PU m edium PU high PU tangential radial longitudinal Figure 91. Hardness differences in load force relative to control for polymer treated, pressure cured Subalpine Fir heartwood. 81

82 polym er % Difference of Load at mm low PU m edium PU high PU -1.5 epoxy tangential radial lo n g itu d in a l coat polym er % Difference of Load at 5.625mm low PU m edium PU high PU epoxy tangential radial longitudinal coat polym er % Difference of Load at 5.625mm low PU m edium PU high PU epoxy ta n g e n tia l radial lo n g itu d in a l Figure 92. Hardness differences in load force relative to control for polymer treated, oven cured Subalpine Fir heartwood 82

83 White Spruce - Heartwood Table 4 shows the hardness data for polymer treated heartwood of White Spruce. Refer to Appendix F for individual data and statistical analysis. The pressure cured treatments are shown in Figures 93 and 95 and indicate that the low molecular weight polyurethane at one coat application gave very significant improvement in all three anatomical directions. Hardness improvements were 16%, 19%, and 10% in the tangential, radial, and longitudinal faces, respectively. The epoxy 3202 also performed well on spruce heartwood, with hardness gains of 17%, 20%, and 21% in the tangential, radial, and longitudinal faces, respectively. The higher application rate of polyurethanes improved hardness in the longitudinal face only, with increases of 14% for low polyurethane, 13% medium molecular weight polyurethane, and 7% high molecular weight polyurethane. In the oven cured treatments (Figures 94 and 96), significant improvements were seen in the medium molecular weight polyurethane (one coat) at 14%, 18%, and 16% in the tangential, radial, and longitudinal faces respectively. The hardness of the longitudinal face was improved by polyurethane treatments of one coat by 17%, 16%, and 17% in low, medium, and high molecular weight polyurethanes, respectively. Higher application rate of polyurethane did not cause significant further improvements in hardness. The room temperature cured epoxy 1032, only showed significant improvement in the longitudinal face, by 20%. The results of spruce heartwood to polyurethane treatment were interesting in that all three faces showed similar response. 83

84 Table 4. Hardness for heartwood of White Spruce. tangential face radial face longitudinal tangential face radial face longitudinal average lbf average lbf average lbf % difference % difference % difference and cv(%) and cv (%) and cv (%) relative to control relative to control relative to control control C cure epoxy C cure low PU medium PU high PU C cure 2 coat low PU medium PU high PU C/120psi epoxy C/120psi low PU medium PU high PU C/120psi 2 coat low PU medium PU high PU

85 Tangential Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush Radial Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush Longitudinal Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush Figure 93. Hardness of White Spruce heartwood treated with polymer, pressure cured at 120 C/120 psi/2 min. 85

86 Tangential Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush Radial Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush Longitudinal Face Load at mm (lbf) lo w P U m edium PU high PU epoxy untreated brush 2 coat brush Figure 94. Hardness of White Spruce heartwood treated with polymer, oven cured at 100 C for one hour. 86

87 polymer % Difference of Load at mm low PU medium PU high PU epoxy 3202 tangential radial longitudinal coat polymer % Difference of Load at mm low PU medium PU high PU 7.1 tangential radial longitudinal Figure 95. Hardness differences in load force relative to control for polymer treated, pressure cured White Spruce heartwood. 87

88 polymer % Difference of Load at mm low PU medium PU high PU epoxy 1032 tangential radial longitudinal coat polymer % Difference of Load at mm low PU medium PU -0.1 high PU tangential radial longitudinal Figure 96. Hardness differences in load force relative to control for polymer treated oven cured White Spruce heartwood. 88

89 Species Comparison The low molecular weight polyurethane, pressure cured treatment results showed significant improvement in hardness in all the wood species in this study. Therefore, the discussion of this treatment condition is given and the results are shown below in Figure 97. The interspecies comparisons for all polymers are shown in Appendix G for reference. The data shows that pine heartwood generally had the highest hardness profile. In the tangential face, spruce and Subalpine Fir had very similar treatment profiles and although show greater enhancement by polymer treatment, remain 12% softer than pine heartwood. The pine sapwood had a very similar treatment profile to pine heartwood, but remained at 5% lower at the maximum effect. In the radial face, Subalpine Fir was the softest and there was little effect with polymer treatment. The pine sapwood was the most treatable in this face and gave the highest hardness. Spruce had a similar profile to pine sapwood, but remained 12% softer. The treated spruce hardness was as good as the untreated heartwood pine hardness. In the longitudinal face, pine heartwood and Subalpine Fir heartwood had the highest initial hardness. Pine responded well to the polymer treatment, while Subalpine Fir did not. Pine sapwood and spruce had similar treatment profiles and initial hardness. After one coat of treatment, all species possessed similar hardness. At two coat treatment, spruce, Subalpine Fir, and pine sapwood had similar hardness, and pine heartwood was 12% greater. 89

90 Tangential Face, Low PU, press cure Load at mm (lbf) Pine Heartwood Pine Sapwood Subalpine Fir Heartwood Spruce Heartwood untreated brush 2 coat brush 3 coat brush vacuum pressure Radial Face, Low PU, press cure Load at mm (lbf) Pine Heartwood Pine Sapwood Subalpine Fir Heartwood Spruce Heartwood untreated brush 2 coat brush 3 coat brush vacuum pressure Longitudinal Face, Low PU, press cure Load at mm (lbf) Pine Heartwood Pine Sapwood Subalpine Fir Heartwood Spruce Heartwood untreated brush 2 coat brush 3 coat brush vacuum pressure Figure 97. Hardness response of wood species to low molecular weight polyurethane treatment. 90

91 Results: Abrasion Resistance Table 5 to Table 8 summarize the abrasion resistance results for the polymer treatments of Lodgepole Pine, Subalpine Fir, and White Spruce. The Taber Wear Index (TWI) is a measure of the weight loss of the sample and the lower the value, the more abrasion resistant the material. At one coat application, the polyurethane treatments showed very high abrasive resistance, with TWI values ranging from 0 to 50 for low, medium, and high molecular weight polyurethane. This was a significant improvement in relation to the untreated softwood controls whose TWI were in the order of 300. The results are shown graphically in Figures 99 to 101, detailing the effect occurring in each sample face. The polyurethane treatments have been pressure cured. The retail polyurethane, which is formulated to cure at room temperature, had a TWI of 177 that was similar to the epoxy products. Oven cured sample condition results indicated similar trends to pressure cured samples for the polyurethane treatments. Note that the low and medium molecular weight polyurethane treatments displayed zero weight loss and the high molecular weight polyurethane tended to show some weight loss. An interesting phenomenon was observed. The low and medium molecular weight polyurethanes tended to absorb the particles from the wheels of the abrasion tester. Therefore there was some weight gain rather than weight loss. The only time this did not occur was in the low molecular weight polyurethane vacuum pressure, pressure cured, treatments. The high molecular weight polyurethane also did not possess this absorption effect. In order to relate visually to the TWI values, the levels of abrasion are shown below in Figure 98. It was suspected that two and three coat application would improve abrasive resistance, and this was confirmed with testing on Lodgepole Pine showing zero abrasion. Figure 98. Abrasion resistance samples for tangential face of pine heartwood, (left to right) untreated control, low molecular weight polyurethane, and high molecular weight polyurethane treatments. 91