Compatibilization And Characterization Of Bamboo Fibre Reinforced Poly (Lactic Acid) Composites

Poly (lactic acid)(PLA) is a kind of high performance biodegradable polymer, which is synthesized by polymerization of lactic acid from renewable plant resourees. Compared with other biodegradable polymers, PLA has advantages such as high strength, thermoplastic formation, hydrophobicity and good fabricability. But because of its high price, the application of PLA is usually limited in the biomedical area with few commodity applications. In this paper, bamboo plastic composites were fabricated with PLA and bamboo fibre (BF) from bamboo processing industry, taken a balance between the high performance of PLA and the low-cost of bamboo fibre to develop new biodegradable polymeric materials and partly replacement of petroleum-based chemicals for the synthesis and manufacture of commodity polymers. The main research contents and results were as the following.(1) PLA/BF composite mechanical properties and optimization based on universal rotatory experimental design method.Through SAS8.2software, four-variable quadratic mathematical models were formulated by selecting tensile strength(TS), flexural strength(FS), and impact strength(IS) of PLA/BF composites as dependent variables, choosing mixing ratio of PLA/BF, size of bamboo fiber, hot pressing temperature and time as independent variables. The lack of fit of the models were not significant, and the fit of the models were significant.Principal components factor analysis showed that mixing ratio was the most significant impact factor on the TS, FS and IS, while the size of bamboo fiber had the least effect on the TS, FS and IS. Interaction terms between hot pressing temperature and time had significant effect on the TS and FS. The effect of interaction terms between mixing ratio and size of bamboo fiber on the IS was remarkable.The optimal hot pressing parameters of PLA/BF composite about tensile strength under these experimental conditions were mixing ratio of90/10(wt%), size through100mesh standard sieve, temperature at160℃, and time of25mins. The optimum parameters about flexural strength were mixing ratio of90/10(wt%), size through100mesh standard sieve, temperature at200℃, time of5mins. In the end, the optimum parameters about impact strength were mixing ratio of90/10(wt%), size through100mesh standard sieve, temperature at200℃, time of5mins. (2) Effects of alkali treatment on the properties of bamboo fibre/poly(lactic acid) eco-compositesBamboo fiber, after different treatment times with0.30mol/L NaOH solution, was added in PLA matrix as reinforcement. After melt-mixing, PLA/BF composites were prepared through thermo-compression. By comparing the morphology of fiber surface, specific surface area, chemical analysis, mechanical properties and thermal properties of the composites, the effect of alkali treatment time on the performance of the composites was carried out.With the extension of the alkali treatment, the surface of bamboo fibre gradually mercerized under SEM. Infrared spectroscopy results showed that the hydroxyl absorption peaks of bamboo fiber declined after alkali treatment. Specific surface area of bamboo fibre increased significantly after alkali treatment, and reached up to376.92m2/g at3.Oh of NaOH treatment. Meanwhile, loss in weight was observed after the alkali treatment of the fibres, due to dissolution of the hemi-cellulose content, the loss occurred primarily within3.Oh of treatment. DSC analysis showed that there was a significant endothermic peak of alkali treated bamboo fibre between174.4℃and183.0℃.The results of mechanical test showed that when alkali treatment time increased from0to3.Oh, the tensile strength of PLA/BF composites increased from36.67MPa up to44.21MPa, elongation at break increased from4.51%to6.22%, flexural strength growed from61.07MPa to83.85MPa, and flexural modulus of elasticity gradually rised from3.49GPa to4.50GPa. However, the mechanical properties of PLA/BF composites began to decline while more than3.Oh of alkali treatment. Thermal analysis of the composites by using DSC showed that the crystallinity of the PLA matrix increased from3.13%to10.70%, the melting enthalpy from3.19J/g to20.01J/g after3.Oh alkali treatment.(3) Preparation and characterization of PLA/BF composites with maleic anhydride compatibilizerDifferent levels of maleic anhydride(MAH) was added in bamboo fibres which had been treated with0.30mol/L NaOH solution by3.Oh, then melt-mixing with PLA matrix. Through thermo-compression, PLA/BF composites were prepared. By comparing the chemical groups changes, melt flow rate, mechanical properties and thermal properties of the composites, the effect of compatibilizer on the performance of the composites was studied.With the addition of maleic anhydride, the melt flow rate of PLA/BF composites increased in cubic function. The composites of PLA/BF/MAH(70/30/1.0, wt%), from infrared spectroscopy, had a significant hydroxyl stretching vibration peak at3426cm-1, appeared a new one at1508cm-1. While the absorption peaks at869cm-1and756cm-1weakened significantly. There was better tensile strength and elongation at break (47.6MPa,6.22%) when1.0wt%MAH was added in the composites. However, the tensile properties of continuously declined when MAH%increased. The flexural modulus of elasticity reached maximun when the composites added0.5wt%MAH, while the flexural strength continuously decreased remarkably from83.85MPa to56.45MPa.The glass transition temperature of the composites increased in the presence of MAH of0.5%under differential scanning calorimeter, even reduced in the degree of crystallinity and melting enthalpy. However, the glass transition temperature of the composites appeared to decrease significantly and had a much higher crystallinity when MAH%in the composites was greater than0.5%.