Comparison of the Mechanical Properties Between 2D and 3D Orthogonal Woven Ramie Fiber Reinforced Polypropylene Composites Comparison of the Mechanical Properties Between 2D and 3D Orthogonal Woven Ramie Fiber Reinforced Polypropylene Composites Qian Zhang, Xiaomeng Fang, Xiaojuan Sun, Baozhong Sun, and Yiping Qiu Key Laboratory of Textile Science and Technology Ministry of Education, College of Textiles, Donghua University, Shanghai, China, 201620 Summary Polypropylene (PP) composites reinforced with ramie 2D plain fabric is widely developed recently. In this paper, PP composites reinforced by using 3D orthogonal woven ramie fabric under hot-press molding process were made. The tensile and flexural strength of reinforced composites were tested and discussed. The results showed that the normalized tensile strength and the normalized tensile Young's modulus of 3D composite were significantly improved compared with that of 2D composites. The normalized flexural strength and the normalized flexural Young's modulus of 3D composite were also greatly improved. Overall results indicating that compared with 2D composite the 3D orthogonal woven ramie fabric could significantly improve the mechanical property of PP composites. Keywords: Green composites, 3D orthogonal woven, 2D plain fabrics, Ramie yarns, Polypropylene 1. Introduction Green composites with molding ability and recyclable characters combined with cellulose fiber and biodegradable or thermoset/ thermoplastic resin has been a focus in new material fields. Cellulose fiber including ramie, flax, jute, kenaf etc, are commonly used as reinforcing materials as the specific strength and stiffness approached the level of glass fiber. Furthermore cellulose fiber is environmental friendly from growth to processing 1,2. Referring to the main type of textile structure used as reinforce material in green composites, randomly arranged staple fiber in the composites is widely used. As the length and weight content of fibers raise, fracture strength and Young s modulus of staple fiber reinforced composites obviously increase 3,4. Woven fabrics as preforms of composites was also investigated 5, whereas studies on 3D orthogonal woven fabrics with tie yarns in the thickness direction are Smithers Rapra Technology, 2014 limited in cellulose fibers reinforced composites. This paper focuses on the mechanical properties of the 3D orthogonal ramie woven fabrics reinforced polypropylene composites. 2. Experimental procedure 2.1 Preform Fabrication Textile fabrics as the preforms contain two types: 2D and 3D. 2D stands for laminates of plain woven fabrics; 3D orthogonal woven fabrics differ from 2D in the thickness direction, the z-yarns in 3D fabrics tie the warp and weft yarns together into a integer structure. In addition, warp and weft yarns in 3D fabrics align in 0 and 90 direction respectively without crimp. 2D fabrics were laid up with 4 layers of plain fabrics and 3D fabrics were fabricated with 3 layers of warp yarns and 4 layers of weft yarns (Figure 1). The parameters of fabrics of perform as Table 1. 2.2 Preparation and Heat-press Polypropylene was used as thermoplastic matrix and heat-press were conducted on a plate vulcanizing machine. Before heat-press mold, PP master batch was molded into two films. Then PP films were laid on the upper and bottom of fabric in order to build a sandwich structure. Then the three layer were heat-press in 180 C and 7 MPa for 5 minutes. 2.3 Composite Parameters Design The fiber volume fractions were calculated in corresponding to the different weft densities of fabric preforms. A hollow square steel frame with the same size of the performs (30 cm 30 cm) was placed surrounding the fabric and matrix in heat-press process so as to fix the thickness of composites as the thickness of frame (3 mm). As the 3D fabrics were non-crimped and fabricated with 3 layers warp yarns and one system of Z yarns, so the fiber volume friction was less than 2D composites with same thickness either in warp yarns and weft yarns. Polymers & Polymer Composites, Vol. 22, No. 2, 2014 187
Qian Zhang, Xiaomeng Fang, Xiaojuan Sun, Baozhong Sun, and Yiping Qiu Table 1. Parameters of fabrics Yarns Fineness Material Densities of fabric Warp 560 tex Ramie 40 lines/10 cm Weft 560 tex Ramie 40 lines/10 cm Z 560 tex Ramie 40 lines/10 cm Table 2. Parameters of fabrics Yarns Warp density (lines/10 cm) Weft density (lines/10 cm) Z Densities (lines/10 cm) 2D-40 40/layer 40/layer -- 2D-60 40/layer 60/layer -- 3D-40 40/layer 40/layer 40 3D-60 40/layer 60/layer 60 Figure 1. Construction diagram of 2D (a) and 3D (b) orthogonal woven fabric, coordinate, and directions of yarns (a) (b) 2.4 Sample Preparation and Test In order to compare the performance of 2D and 3D orthogonal ramie woven fabrics reinforced polypropylene composites under different fiber densities, samples listed in Table 2 were prepared. Regard the difference between structures of fabric preforms, fiber volume fractions were calculated with weigh method. In tensile tests, specimens shaped in dog-bone form were loaded along warp and weft directions in a constant speed of 5 mm/ min on MTS810. Test clamp length was 115 mm. Impact tests were conducted on Intron Dynamic weight impact tester, and test speed was 2 m/s. Each sample included 5 specimens; the result was averaging from all single test results. 3. Results and discussion 3.1 Tensile Properties Figures 2 to 4 show the tensile test results in warp and weft directions. Normalized strength is calculated with below equation: normalized strength = strength (MPa)/fiber volume fraction (%) Figure 2 and Figure 3 are the normalized tensile Young's modulus and normalized tensile strength for 2D and 3D orthogonal ramie woven fabrics reinforced polypropylene composites. The data indicates that the 3D composites demonstrated much higher normalized tensile Young s modulus and normalized tensile strength than 2D composites. The main reason for the higher Young s modulus is that the warp and weft yarn in 3D composites were fabricated in a flat and straight manner. When doing the initial stretch all the fibers were under tension. While the warp and weft yarn in 2D composites were fabricated in a crimped manner. When doing the initial stretch, the clamp are basically measuring the strength to stretch the crimped fibers into flat and straight fibers. The other reason maybe from the sample preparation. The 2D composition are prepared by heat press molding of flat woven fabrics. It was very challenge to keep all the fiber at the same direction for either warp or weft direction. So part of the fiber in either warp or weft direction were not fully utilized during tensile test which generates no tensile strength. Figure 2 and Figure 3 also showed the differences between 2D and 3D composites for mechanical property impacted by weft yarns density change. For 3D composite with the increase of weft yarns density there was no big changes on normalized tensile strength and Young's modulus in warp direction. Mainly because the change of weft yarns density didn't have big impact to the wrap yarn. However at the weft 188 Polymers & Polymer Composites, Vol. 22, No. 2, 2014
Comparison of the Mechanical Properties Between 2D and 3D Orthogonal Woven Ramie Fiber Reinforced Polypropylene Composites direction with the increase of weft yarns density the normalized Young's modulus were increased, mainly because of the higher fiber density improved the stiffness of composition in weft direction. While the normalized tensile strength were reduced with increase of weft yarns density. Mainly because the improve of tensile strength by higher weft density was offset by the increase of fiber volume fraction. For 2D composite the normalized tensile strength and Young s modulus were reduced in wrap direction. Mainly because the increased weft yarns density created more crimp of wrap yarn which resulted in more strain from relaxation of crimped fibers. However in weft direction increased weft yarn density did help improves the modulus but the normalized tensile strength was not improved mainly because of the same reason that improve of tensile strength by higher weft density was offset by the increase of fiber volume fraction. Figure 2. Normalized tensile Young s modulus of 2D and 3D composites Figure 3. Normalized tensile strengths of 2D and 3D composites The ultimate tensile strains of 2D and 3D composites were shown in Figure 4. The tensile strength of 3D composition is lower than 2D composition. The major reasons to the lower tensile strength comes from two different factor. Firstly the 3D composites only have 3 layer warp yarns and 4 layer weft yarns while 2D composites has 4 layers of both waft and warp yarns. Secondly the flat straight structure of 3D composition in both wrap and weft direction also result in less fiber friction which reduces the ultimate tensile strength. Figure 4. Ultimate tensile strains of 2D and 3D composites Figure 5 presents the typical stressstrain curves of 2D and 3D composites. For 3D composites, from the initiation point A to damage point B, the slope of curve was very constant. After the damage point B, it showed a ladder like curve from point B to point G. The 3D orthogonal woven fabric contained 3 layers of warp yarns, differences on weaving and straightness of yarns Polymers & Polymer Composites, Vol. 22, No. 2, 2014 189
Qian Zhang, Xiaomeng Fang, Xiaojuan Sun, Baozhong Sun, and Yiping Qiu Figure 5. Stress-strain curves of 2D and 3D composites in warp direction for tensile tests. (a) Stress-strain curve of 3D-40 composites; (b) Stress-strain curve of 2D-40 composites Figure 6. Normalized flexural Young s modulus of 2D and 3D composites It is obvious that the normalized flexural strengths and flexural Young s modulus of 3D composites are higher than 2D composites in both warp direction and weft direction. The reasons are as follows: firstly the Z yarn in the thickness direction of the 3D composites helps to avoid delamination, secondly yarns in the fabric interlaced in 2D fabrics slip easily than parallel yarns arranged in the 3D fabrics. Figure 6 and Figure 7 also showed the differences between 2D and 3D composites for flexural property impacted by weft density change. For 3D composite with the increase of weft yarn density there was no improvement on normalized flexural strength and flexural Young s modulus in warp direction. Mainly because the same reason as tensile property, the change of weft yarn density didn t have big impact to the wrap yarn. However at the weft direction with the increase of weft yarn density the normalized flexural Young s modulus were increased, mainly because of the higher fiber density improved the stiffness of composition in weft direction. While the normalized flexural strength were reduced with increase of weft yarn density. Mainly because the improve of tensile strength by higher weft density was offset by the increase of fiber volume fraction. between different layers would demonstrate different tension. As a result, the respective damage point of 3 layers are not at same time. The slope of stress-strain curve of 2D composites changed in point H. There is a short higher modulus area from starting point to point H owing to the inter-yarns and inter-fibers friction resistance force produced by changing of crimp of the yarns and fibers in fabrics. After point H the crimp degree of warp yarns is decreased and yarns are compressed at the interlacing points. Until the load reaches the break point, the fabrics break immediately. 3.2 Flexural Tests Figures 6 and 7 show the flexural test results of 2D and 3D composites. For 2D composite the normalized flexural strength and flexural Young s modulus were reduced in wrap direction. Mainly because the increased weft yarn density created more crimp of wrap yarn which resulted in more strain from relaxation of crimped fibers during flexural test. In weft direction the normalized tensile strength was not improved by increased weft yarn density mainly because of the same reason that improve of tensile strength by higher weft density was offset by the increase of fiber volume fraction. In addition, one thing worth mention is that the normalized flexural strength in 190 Polymers & Polymer Composites, Vol. 22, No. 2, 2014
Comparison of the Mechanical Properties Between 2D and 3D Orthogonal Woven Ramie Fiber Reinforced Polypropylene Composites Figure 7. Normalized flexural strengths of 2D and 3D composites Development Program of China (No.2007AA03Z101), the State Key Program of National Natural Science of China (No.51035003), Natural Science Foundation for the Youth (No. 50803010 and 60904056), National Science Foundation for Post-doctoral Scientists of China (No.20100470664), Shanghai Post-doctoral Research Funded Project (No.09R21410100), the Program of Introducing Talents of Discipline to Universities (No. B07024). the warp direction was always higher than in the weft direction indicated by data from Figure 7. As regarding PP matrix, the viscosity is relative high for full penetration in the woven fabrics. The increase of weft yarn density also created some challenges for PP matrix to fully penetrated into the woven fabrics. The soakage rate and the surface compatibility between ramie and PP are critical factors for mechanical properties of composites. 4. Conclusions 3D orthogonal woven ramie fabric is a new configuration type of preform of green composites. The tensile and flexural performances of 3D composites are distinctly superior to 2D composites. With the weft densities of the fabrics change, the mechanical properties of 3D and 2D composites was quite different owing to the different configurations of the fabrics. Test results show that 3D orthogonal woven ramie fabric composition demonstrated the most attractive properties in terms of higher normalized tensile strength, higher young s modulus and higher flexural modulus Acknowledgment This study was supported by the Fundamental Research Funds for the Central Universities (No. KLTST201201), the National Level Teaching Groups for Textile Materials Science grant, the National High Technology Research and References 1. John M.J. and Thomas S., Biofibres and Biocomposites. Carbohyd Polym., 71 (2008) 343-364. 2. Bledzki A.K. and Gassan J., Composites reinforced with cellulose based fibres. Prog Polym Sci., 24 (1999) 221-274. 3. Lodha P. and Netravali A.N., Characterization of interfacial and mechanical properties of "green" composites with soy protein isolate and ramie fiber. J. Mater. Sci., 37 (2002) 3657-3665. 4. Wollerdorfer M. and Bader H., Influence of natural fibres on the mechanical properties of biodegradable polymers. Industrial Crops and Products, 8 (1998) 105-112. 5. Herrmann A.S., Nickel J., and Riedel U., Construction materials based upon biologically renewable resources from components to finished parts. Polymer Degradation and Stability, 59 (1998) 251-261. Polymers & Polymer Composites, Vol. 22, No. 2, 2014 191
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