Application and Performance of Disperse Dyes on Polylactic Acid (PLA) Fabric

Transcription

1 Application and Performance of Disperse Dyes on Polylactic Acid (PLA) Fabric By Lois E. Scheyer and Annacleta Chiweshe, University of Nebraska, Lincoln Several factors have led to the development of polylactic acid (PLA) fibers for textiles applications. The fiber potential of PLA was established in the 1950s when PLA biodegradable and bioabsorbable surgical sutures were produced. 1 Since then, lower cost processes that eliminate gypsum by-products have catalyzed the use of significant amounts of PLA in an array of new applications that include: biodegradable forks, spoons, and knives; biodegradable and environmentally safe plastic packaging with good mechanical and thermoplastic properties; formulations for paper coatings; adhesives for high quality recycled paper; mold-resistant prosthetic devices; and slow release carriers or capsules for herbicides and pesticides. 2-5 The first textile application for PLA was nonwovens. Then increased emphasis on environmentally benign manufacturing processes in Japan and Europe motivated the production of PLA/ cotton blend t-shirts, golf shirts, and women s lingerie. Currently, PLA carpets ABSTRACT The objectives of this study were to gain more understanding of the application of disperse dyes on Polylactic acid (PLA) with respect to time, temperature, and fiber crystallinity, and to evaluate the fastness of the dyes on PLA fabrics. Nine disperse dyes including anthraquinone, azo, methine, nitro, and quinoline dyes were applied to PLA spunbonded fabrics under low temperature conditions (70C) and high temperature conditions (100C), and the dyebath exhaustion was determined at 10, 20, 30, 40, 50, and 60 minutes. The dyes had good fastness to light, washing, and gas fume fading. Key Terms Disperse Dyes Dye Fastness Polylactic Acid Spunbonded Fabrics with good antimicrobial properties are being developed. An advantage of using PLA in textile fibers is the benign chemicals and processes used in production. PLA is produced from the polymerization of lactic acid (2-hydroxypropionic acid). Lactic acid is produced naturally during metabolism in most living organisms including humans and is used in the manufacture of cheese, pickles, yogurt, and food preservation and acidulation. 2,6 The primary raw materials for commercial production include corn, whey, sweet sorghum, wheat, barley, sugar beets, and sugar cane. Other raw materials for lactic acid include petroleum, coal, and natural gas liquids. 1 The recent focus has been on producing lactic acid through the fermentation of the wet milling products of corn. An understanding of the dyeability of PLA is essential to production of aesthetically pleasing textiles. Kameoka, et al., published a patent on the application of Miketon Polyester Blue RSE on aliphatic polyester filaments derived primarily from PLA. 7 Miketon Polyester Blue RSE contains a mixture of proprietary disperse dyes, and therefore the patent provides no information on the chemical structures of dyes that were used. Also, the amount of PLA in the aliphatic polyester filaments was not disclosed. The data indicated that the optimum conditions for producing the vibrant colors needed for commercial applications were a 60-minute dye application at C at ph 5. A dye exhaustion of 88% was achieved under these conditions. However, the method used for determining exhaustion in the patent was inaccurate. The exhaustion values were calculated from the absorption (optical density) values of the residual dyebaths, and no solvent was used to dissolve the disperse dyes. Beer s law does not hold for dispersions such as disperse dyes in water. The molecular weight lowering ratio was less than 20% with the specified dyeing conditions, but the data clearly showed that increased time, increased temperature, or raised or lowered ph significantly lower the molecular weight. EXPERIMENTAL There are many unanswered questions about the application of disperse dyes on PLA. Therefore, the objectives of this study were to gain more understanding of the application of disperse dyes on PLA with respect to time, temperature, and fiber crystallinity, and to evaluate dye fastness. Dyeing Trials High and low crystallinity spunbonded PLA fabrics were supplied by Cargill Dow Polymers for this study. The results of this study were originally presented at the 1999 AATCC International Conference and Exhibition. 8 After the conference Lowe and Negulescu conducted a study on the effects of disperse dye application procedures used in this study on the crystallinity of the high and low crystallinity spunbonded PLA fabrics. 9 They reported that the percent crystallinity of the high and low crystallinity undyed fabrics were 50% and 21%, the glass transition temperatures for both fabrics were 58-62C, and the melting temperatures for both fabrics were C. Woven fabrics could not be obtained at the commencement of this study. That the dyeability of woven fabrics would differ is recognized. The initial dyeing experiments were conducted with high crystallinity spunbonded fabrics. When questions arose about the results with the high crystallinity spunbonded fabrics, experiments were conducted with low crystallinity spunbonded fabric. All the experiments with disperse dyes were performed with 44

2 Fig. 1. Exhaustion of C.I. Disperse Yellow 42 on high crystallinity PLA spunbonded fabrics at 70, 80, 90, and 100C. Fig. 2. Exhaustion of C.I. Disperse Violet 93 on low crystallinity PLA spunbonded fabrics at 70, 80, 90, and 100C. 0.5 g pieces of fabric in 25 ml dyebaths using 2% owf dye and one drop of Basol WS LIQ dispersing agent. For these experiments the fabrics were wet out in distilled water and two stainless steel balls were added to each dyebath to agitate the fabric during dyeing. When C.I. Disperse Yellow 42 was applied to high crystallinity spunbonded fabric at 70, 80, 90, and 100C, the exhaustion increased fourfold between 90 and 100C (Fig. 1). Based on these preliminary results, two sets of six dyeings were conducted in an Atlas Launder-Ometer with nine disperse dyes. Different dyebath temperatures were used for the two sets: 70C was used for low energy dyeing of one set, and 100C was used for high energy dyeing of the other set. With the low temperature dyeings, 70C was used because it was just above the glass transition temperature of 57C. The 100C temperature was used for the high temperature dyeings because of the significant increase in dye exhaustion between 90 and 100C. Within each set, six dyeings were performed that differed in duration (i.e., 10, 20, 30, 40, 50, and 60 minutes). The following nine disperse dyes were selected for the study based on commercial availability and chemical class: C.I. Disperse Blue 3 (anthraquinone); C.I. Disperse Brown 1 (monoazo); C.I. Disperse Orange 29 (azo); C.I. Disperse Violet 26 (anthraquinone); C.I. Disperse Yellow 42 (nitro); C.I. Disperse Yellow 82 (methine); C.I. Disperse Yellow 54 (quinoline); C.I. Disperse Violet 93 (azo); and C.I. Disperse Blue 356 (azo). Dyebaths were saved at the end of each dyeing cycle for later analysis. The dyed fabrics were rinsed in warm tap water and air dried. Experiments were performed with low crystallinity PLA spunbonded fabric when low exhaustion values were obtained in dye experiment with high crystallinity spunbonded fabric. In the first experiment, Disperse Violet 93 was applied to low crystallinity PLA spunbonded fabric. Dyeings were performed at 70, 80, 90, and 100C for 10, 20, 30, 40, 50, and 60 minutes (Fig. 2). Disperse Violet 93 was used to dye low crystallinity fabric at progressive temperatures instead of Disperse Yellow 42 (used to dye high crystallinity PLA). Although Disperse Violet 93 did not exhaust well on high crystallinity fabric it had potential to show gradations in exhaustion because it had a slightly higher exhaustion at 100C than at 70C on the high crystallinity fabric. After the experiments were completed with Disperse Violet 93, the other eight disperse dyes were applied to low crystallinity PLA spunbonded fabric at 100C. Six dyeings that differed in duration (i.e., 10, 20, 30, 40, 50, and 60 minutes) were performed with each dye. Dyeings were not conducted at 70C with the other dyes on low crystallinity fabric because of the low exhaustion of Disperse Violet 93 at 70C. All of the experiments with the nine dyes were replicated three times. Dyebath Exhaustion Dyebath dilutions equivalent to 0, 20, 40, 60, and 80% exhaustion were prepared with each of the nine disperse dyes. One milliliter aliquots of each of these solutions were diluted with 20 ml of acetone. Absorbiometric readings were taken at the wavelengths of maximum absorbance for each of the solutions (i.e., nm for Disperse Blue 3, nm for Disperse Blue 356, nm for Disperse Brown 1, nm for Disperse Orange 29, nm for Disperse Violet 26, nm for Disperse Violet 93, nm for Disperse Yellow 42, nm for Disperse Yellow 54, and nm for Disperse Yellow 82). Absorbiometric calibration curves were prepared with the absorbance on the y-axis and exhaustion on the x-axis. Separate calibration curves were prepared for each of the three replications. Acetone (20 ml) was mixed with residual dyebath samples from saved dyebaths (1 ml). The solutions were evaluated spectrophotometrically, and the exhaustions of the dyebaths were calculated using the calibration curves. The correlation coefficients for the calibration curves ranged from to The mean of the correlation coefficients was The absorbencies were measured, and the standard exhaustion curves were used to calculate the percent exhaustion values. Exhaustion curves were prepared with the percentage exhaustion on the y- axis and time (10, 20, 30, 40, 50, and 60 minutes) on the x-axis. Evaluation of Colorfastness The fastness of the disperse dyes to laundering, light, and gas fume fading were evaluated using standard test methods. PLA high crystallinity spunbonded fabrics that were dyed for 60 minutes at 100C were used in these tests. Colorfastness tests were not performed on the fabrics FEBRUARY

3 Fig. 3. Exhaustion of disperse dyes on high crystallinity PLA spunbonded fabric at 70 and 100C, and on low crystallinity PLA spunbonded fabric at 100C. dyed at 70C because the exhaustion was too low to recommend low temperature application procedures. Fastness to laundering was evaluated according to Test 2A in AATCC Test Method (Colorfastness to Laundering, Home and Commercial: Accelerated). 10 An Atlas Xenon Weather-Ometer (model Ci65A) was used to evaluate the colorfastness to light according to AATCC Test Method 16E Fabric specimens were subjected to three light exposures. The effect of sunlight passing through window glass (i.e., indoor light), was simulated using a soda lime outer filter and a borosilicate inner filter. The test method was modified to simulate natural outdoor sunlight at the earth s surface by using borosilicate inner and outer filters. Fabrics for both indoor and outdoor exposures were exposed for 80 AFUs (AATCC Fading Units). Another set of fabrics was exposed to sufficient simulated indoor light to determine the AATCC Blue Wool lightfastness standard classifications. Testing Services Inc. (TSI) evaluated the fastness of the disperse dyes to gas fume fading according to AATCC Test Method (Colorfastness to Burnt Gas Fumes). 10 The fastness of the disperse dyes to laundering, light, and gas fume fading were evaluated using an AATCC Gray Scale for Color Change. 10 The staining of the disperse dyes on multifiber cloth #10 (Test Fabrics Inc.) in the laundering test was evaluated using an AATCC Gray Scale for Staining. Analysis of variance (ANOVA) tests were performed on fastness to laundering, light, and gas fume fading by dye type. When the ANOVA showed significant color change differences among the dyes, Duncan s Multiple Range Test was performed to determine the dyes with significant differences in color change. RESULTS AND DISCUSSION Dye Exhaustion Fig. 3 shows exhaustion curves for the nine disperse dyes applied on high crystallinity PLA fabrics at 70C and 100C dyeing temperatures. Temperature increases caused dramatic increases in the exhaustion values for Disperse Brown 1 and Disperse Yellow 42, while the increases in the exhaustion values for the other dyes were limited. Since high crystallinity spunbonded PLA was used in these experiments, and since dyes must diffuse into fibers to achieve high exhaustion values, the results suggest that the three dyes with high exhaustion values were able to diffuse into the interiors of the fibers. Additional experiments were conducted to determine if the fiber crystallinity hindered dye exhaustion on the fibers and if the fibers had limited affinity for PLA. The hindering affects of limited interstices between polymer chains on dye diffusion were investigated by measuring the exhaustion of the nine disperse dyes on low crystallinity PLA (Table I). The crystallinity values for PLA in this study were determined by differential scanning calorimetry. Maximum crystallinity for PLA fibers is about 58%. 9 The crystallinities for the high and low crystallinity PLA were 50% and 21% respectively. The percent exhaustion values of four of the nine dyes (i.e., Disperse Violet 26, Disperse Violet 46

4 TABLE I. Percent Exhaustion Values for Disperse Dyes Applied at 70C and 100C to High Crystallinity PLA and Low Crystallinity PLA Spunbonded Fabrics Dye High Crystallinity PLA Low Crystallinity PLA 70C 100C 100C Disperse Blue Disperse Blue Disperse Brown Disperse Orange Disperse Violet Disperse Violet Disperse Yellow Disperse Yellow Disperse Yellow , Disperse Yellow 82, and Disperse Brown 1) increased at least 20% when they were applied to low crystallinity fibers. Thus, the crystallinity of the high crystallinity fibers limited the dye saturation capacities of the fibers. 12 The high crystallinity fibers had fewer interstices that dye molecules could penetrate than the low crystallinity fibers. Interestingly, the exhaustion increased prior to 30 minutes with six of the nine disperse dyes and decreased significantly after 30 minutes for three of the dyes. Lowe and Negulescu demonstrated that the decreases in exhaustion resulted from cold crystallization of the fibers in the dyebaths. 9 The dyeing process also caused the low crystallinity fibers to become brittle. Lowe and Negulescu examined the effects of dyeing on the elasticity of the low crystallinity fibers. 9 The crystallinity values for PLA that are reported here (20-60%) are equivalent to the crystallinity values that have been reported for polyester. 12 However, no comparisons are made between the effects of the crystallinity of PLA and polyester on dyeing because many factors influence the interpretation of the effects of fiber crystallinity on dye exhaustion. The various methods of determining crystallinity including x-ray analysis, density, and differential scanning calorimetry yield different crystallinity values. The variation in the degrees of amorphous/crystalline order in polymers contributes to the differences in results. Treatments such as heat setting, drawing, and cooling rate affect the degrees of order in fibers. The fact that only four of the disperse dyes had exhaustions values greater than 60% on low crystallinity fibers indicates that PLA has a moderate affinity for disperse dyes. The affinity was high enough to achieve good colors on PLA. However, a considerable amount of color remained in the effluent. Several things were observed about the chemical structures of the dyes that had high exhaustion values. The two dyes (Disperse Brown 1 and Disperse Yellow 42) that exhausted the best on the PLA had linear configurations. Disperse Brown 1 was one of the four azo dyes in the study and Disperse Yellow 42 was a nitrodiphenylamine dye. Notably, the exhaustion of the dyes with multiple carbonyl groups did not exhaust well on the high crystallinity PLA, but their exhaustion increased significantly on low crystallinity PLA. This tendency includes both of the anthraquinone dyes (Disperse Blue 3 and Disperse Violet 26) and the methine dye (Disperse Yellow 82). However, further experiments are needed to determine if this is true for other anthraquinone and methine dyes. Maximum dye exhaustion occurred within 30 minutes for most dyes on high and low crystallinity PLA. Thus disperse dyes can be applied in short periods of time on both high and low crystallinity PLA fabrics. Washfastness All of the disperse dyes in this study except Disperse Orange 29 had acceptable washfastness gray scale ratings of 4 or greater, but some dyes had unacceptable staining on nylon, gray scale ratings of 3 or less (Table II). 14 Thus, most disperse TABLE II. dyes on PLA would maintain their color during laundering, but they might stain other items in the laundry. Lightfastness The lightfastness data are given in Table III. Disperse dyed PLA fabrics were exposed to 80 AFUs of xenon radiation simulating indoor and outdoor light. This exposure is greater than most apparel fabrics receive in their lifetimes. Disperse Violet 26 exhibited excellent lightfastness properties on PLA, with an AATCC Gray Scale for Color Change rating of 4.6 for indoor exposure. Disperse Orange 29 and Disperse Yellow 42 had good lightfastness with ratings of 3.8 and 3.9, respectively. Disperse Yellow 82 had the poorest lightfastness with a rating of 1.3. Fabrics exposed to outdoor light faded slightly more than those subjected to indoor exposure because of the difference in the wavelength distribution of the light Fastness to Washing and Staining Ratings a for Disperse Dyes Applied on High Crystallinity Polylactic Acid Spunbonded Fabric at 100C Staining Dye Washing Wool Acrylic Polyester Nylon Cotton Acetate Mean Disperse Blue Disperse Brown Disperse Orange Disperse Violet Disperse Violet Disperse Yellow Disperse Yellow Disperse Yellow a AATCC gray scale for color change rating and AATCC gray scale for staining ratings where: 5 denotes no change, 4 denotes slight change, 3 denotes noticeable change, 2 denotes considerable change, and 1 denotes heavy change in color. FEBRUARY

5 sources. Outdoor light has more wavelengths in the UV region which causes more fading. Gas Fume Fading Results for gas fume fading are presented in Table III. The tendency of disperse dyes on PLA to gas fume fade was evaluated because of the tendency of disperse dyes on acetate to gas fume fade. According to the Colour Index, the disperse dyes that were included in this study that have a tendency to gas fume fade on acetate are Disperse Yellow 82 (ISO gray scale rating of 2) and Disperse Blue 3 (AATCC gray scale rating of 2). 13 However, gas fume fading ratings were not given in the Colour Index for Disperse Orange 29, Disperse Violet 26, and Disperse Violet 93. In this study all of the disperse dyes on PLA had good resistance to gas fume fading. 13 A slight change appeared in the color of Disperse Blue 3 (gray scale rating was 3.8), but this change was minimal compared to the noticeable change on acetate (gray scale rating was 2.0). Thus, disperse dyes on PLA had good resistance to fading by nitrogen gas fumes, and gas fume fading should not be a problem in apparel applications. The classifications of the dyes by AATCC Blue Wool Lightfastness Standards were determined and compared to the ISO daylight ratings for dyes on acetate, triacetate, polyester, and nylon in the Colour Index. 13 In comparison to the ratings for dyes on polyester, the ratings for dyes on PLA were generally one half to one classification lower. CONCLUSIONS This study demonstrated that good color depth on PLA can be achieved with disperse dyes. Maximum levels of exhaustion were achieved at 100C in 30 minutes. The two dyes that had exhaustions greater than 50% on the high crystallinity PLA were linear dyes. Other disperse dyes that exhaust well on PLA need to be found through extensive dye trials. Additional ways of improving the dye exhaustion and additional research that addresses the TABLE III. Fastness to Light and Gas fume Fading Ratings for Disperse Dyes Applied on High Crystallinity Polylactic Acid Spunbonded Fabric at 100C Classification by Visual Gray Scale for Color Change Ratings a AATCC Blue Wool Dye Indoor Light Outdoor Light Fume Fading Lightfastness Standards Disperse Blue Disperse Blue Disperse Brown Disperse Orange Disperse Violet Disperse Violet Disperse Yellow Disperse Yellow Disperse Yellow a AATCC gray scale for color change rating where: 5 denotes no change, 4 denotes slight change, 3 denotes noticeable change, 2 denotes considerable change, and 1 denotes heavy change in color. problem of fiber embrittlement are needed. Acknowledgments This study was made possible by research funds provided by the Institute of Agriculture and Natural Resources at the University of Nebraska (Journal Contribution No ) and the Nebraska Corn Board. Further appreciation is extended to the following: Cargill Dow Polymers for providing fabrics for this study; Albanil Dyestuffs International, D & G Dyes Inc., Dyerich Chemical Corp., and BASF Corp. for providing dyes and Basol WS LIQ dispersing agent for this study; and Ioan Negulescu for crystallinity data. References 1. Lipinsky, E. S. and R. G. Sinclair, Chemical Engineering Progress, Vol. 82, No. 8, August 1986, pp Demirci, A., A. L. Pometto III, and K. E Johnson, Applied Microbiology and Biotechnology, Vol. 38, No. 6, March 1993, pp Ajioka, M., K. S. Enomoto, and A. Yamaguchi, Journal of Environmental Polymer Degradation, Vol. 3, No. 4, October 1995, pp Shon, M., Chemical Marketing Reporter, Vol. 240, No. 17, October 1991, pp9, Anonymous, Feedstuffs, Vol. 63, No. 25, June 1991, p9. 6. Datta, R., et al., FEMS Microbiology Reviews, Vol. 16, No. 2-3, February 1995, pp Kameoka, T. et al., U.S. Patent No. 5,630,849, Scheyer, L. E., and A. Chiweshe, Book of Papers, AATCC International Conference and Exhibition, Charlotte, 1999, pp Lowe, N. E., and I. I. Negulescu, Book of Papers, AATCC International Conference and Exhibition, Winston-Salem, AATCC Technical Manual, Vol. 73, Rudin, A. The Elements of Polymer Science and Engineering, Academic Press Inc., Orlando, Fla., Peters, L., The Theory of Coloration of Textiles, edited by C. L. Bird and W. S. Boston, Society of Dyers and Colourists, Bradford, England, 1975, pp Colour Index, The Society of Dyers and Colourists and AATCC, Bradford, England, Annual Book of ASTM Standards, Vol. 7.01, Philadelphia, Pa., Author s Address Lois Scheyer, University of Nebraska-Lincoln, 234 Home Economics Building, Lincoln, Nebr ; telephone ; fax ; lscheyer@unlnotes.unl.edu. 48