Study On Preparation And Properties Of Poly(Lactic Acid)/Natural Fiber Composite Materials

By means of solvent casting process, the composite materials of poly (lactic acid)(PLA)/ramie fiber (RF), PLA/nano hydroxyapatite (n-HA) and PLA/bacterial cellulose (BC) were prepared. The effect of RF coupling agent treatment and soakage processing on PLA/RF mechanical properties, water absorption ability were evaluated. Meanwhile, the effect of n-HA and BC coupling treatment on composite materials mechanical properties and water absorption ability were tested. By using electronic scanning microscope (SEM), the micro structure of composites and surface of ramie fiber were analyzed. The spherocrystal morphology of PLA composites was observed via polarized light microscopy (POM). By using differential scanning calorimetry (DSC), the melting curve of PLA/BC composites were investigated.The results show that the tensile strength of PLA/RF composite materials is enhanced by RF. When the RF treated by coupling agent at around80℃, the reinforcement effect of coupling treated RF on PLA composites is better than that at room temperature. The water absorption rate of RF declines after soakage processing. Comparison with the other two kinds of coupling agent (KH5501, KH570), the enhancement effect of RF treated by coupling agent of A151on PLA/RF is superior. Compared with the no coupling treated RF, the SEM observation results show that the surface of RF treated by coupling agent has more shallow veins and wrinkle, which can enhance the interface bond properties between RF and PLA.By RF soakage processing, the absorption ability of RF is reduced and its water resistance is improved. Along with the content of TBC increasing in the soakage processing solution, the tensile strength of PLA/RF composite materials is reduced and elongation at break is increased.Among the four coupling agents (KH5501. KH570. A151. A171). the treatment effect of KH570on n-HA is best, that is. the tensile strength and elongation at break of PLA/nHA composite coupling treated by KH570are superior to the other three kinds of coupling agent. With the n-HA content (less than10%) increasing, the tensile strength and elongation at break of PLA/n-HA composite are tending to decline.Among the four coupling agents (KH5501,KH57O, A151,A171), the tensile property of PLA/BC composite coupling treated by KH5501and KH570is better than the other two kinds of coupling agent. But the water resistance of PLA/BC composite is reduced by the coupling processing. With the BC content increasing, the tensile strength of PLA/BC composite materials is increased initially and then declined. When the BC content is around5%, it reaches the maximum. The elongation at break is a rising trend.The POM observation results show that the spherocrystal morphology dimension of PLA becomes larger with the TBC content increasing, and the spherocrystal dimension of PLA around RF is smaller than that at the other part. The spherocrystal dimension of PLA/n-HA composite changes unconspicuously when the content of n-HA changes from5%to20%, and it increases obviously when the n-HA content is at25%. With the content of BC increasing, it is observed obviously that spherocrystal dimension becomes decrescent and the quantity of spherulite increases.By means of DSC analysis, it obviously shows that there is Tg in the heating process of PLA and PLA/BC composite materials after the crystallization process at the constant cooling speed. Compared with the PLA, at the same condition of crystallization process, there is the secondary crystallization phenomenon in PLA/BC composite materials during the melting process. The BC is dispersed in the PLA matrix, there are the interactions between the interface of PLA and BC, which bring on higher the specific heat capacity of glass transition process.