Study On Processing And Mechanical Properties Of Three Dimensional Orthogonal Woven Ramie Fabric Reinforced Polypropylene Composites

Low price, high specific strength and biodegradability are well known as the advantages of natural plant fibers which are widely used for reinforcing thermoplastic resin, and the composites is environment friendly with recycling and remolding abilities. Based on ramie fabrics reinforced polypropylene (PP) composites, an investigation was undertaken in this thesis to compare the mechanical properties of 2D plain woven ramie fabrics reinforced PP composites (2D composites) and 3D orthogonal woven ramie fabrics reinforced PP composites (3D composites), and then this work focused on the mechanical properties of the composites combined with PP and 3D ramie fabrics impregnated by PP solution (organic solvent). And then modified PP with itaconic acid by melting grafting method, and applied the modified PP as compatibilizer of 3D orthogonal ramie reinforced PP composites, then tested and analyzed the mechanical properties of the composites. The results of this work contribute to providing new approaches and laying foundation for structure designing and processing technologies of plant fiber reinforced thermoplastic composites.The details of this thesis are described as follows:At first, an investigation was undertaken to compare the mechanical properties of 2D plain woven ramie fabrics and 3D orthogonal woven ramie fabrics reinforced PP composites. Nowadays many researchers focus on short fibers and two dimensional fabrics reinforced composites in the field of plant fibers reinforced thermoplastic resin composites. As the mechanical properties of this kind of composites are not good enough, or composites are easy to be delaminated, in this work three dimensional orthogonal woven fabric was employed to reinforced composites for investigating the effects of this kind of structure to mechanical properties. And different weft densities leaded to varied mechanical properties. In this thesis, in order to compare the mechanical properties more objectively, tested values were normalized by fiber volume fraction of the composites. The results indicated that normalized stress and modulus of tensile and flexural tests of 3D composites were higher then 2D composites which thicknesses were close, and normalize impact strength and absorbing energy of 3D composites was higher also.Secondly, the melting viscosity of PP is high and the flowability is poor, so PP resin is difficult to infiltrate into ramie fabrics. In addition, the ramie yarns are stable yarn which are processed by twisting the fibers together, so fibers in yarns are holding tightly which makes the infiltration more difficult, as a result, the poor interface will leads a unsatisfactory mechanical performances. As a result, PP can be dissolved by some hot organic solvent and will be separated out from the solution in small particles form when temperature reduces or add precipitant, so this characteristic of PP could be used in impregnating fabrics by solution which can separate the resin evenly. This thesis investigated the mechanical properties of the impregnated fabrics reinforced composites. The results demonstrated that the normalized strength and modulus of tensile, flexural and impact and total impact absorbing energy of impregnated fabrics reinforced composites were obviously exceeding the untreated fabrics reinforced composites. Due to improvement of interface, resin and fibers could transfer load to each other more efficiently.Finally, PP is a kind of non-polar polymer, and the surface energy is very low, the molecules of PP arrange neatly, so cohesion ability of PP is not good enough. Otherwise the plant fibers are polar and hydrophilic, so the interface is very poor that is a main problem for plant fibers reinforced PP composites. This thesis modified PP with itaconic acid by melting grafting method, so the polar monomers of the itaconic acid grafted on the PP molecule chain, and applied the modified PP as compatibilizer of 3D orthogonal ramie reinforced PP composites. The result showed the normalized tensile strength and modulus were improved obviously, thus the ultimate tensile strain reduced dramatically by impregnating the ramie fabrics with PP solution. For flexural properties, the normalized flexural strength and modulus were improved distinctly, also the ultimate flexural strain reduced obviously. For the impact performance, the maximum load and yield load were enhanced, but the absorbing energy at maximum load and yield load reduced.