| Polylactic acid (PLA) is a kind of thermoplastic polyester prepared by lactic acid condensation or lactide ring opening polymerizaton, it has a good biological compatibility and degradation. After the biodegradation, it will eventually become water and carbon dioxide as the product of the existence and will not pollute the environment. Although PLA has many advantages, it has many significant disadvantages, such as large brittleness, poor impact resistance, poor hydrophilicity, low thermal deformation temperature, also the fact that degradation cycle is difficult to control which limit its applicability and production capacity. In order to improve the applicable properties of PLA, a variety of fillers were usually added to adjust the properites. In this paper, PLA was used as the matrix and two kinds of wood fibers were as reinforcement. This study focused on the influence of chemical modifications of wood fiber on the composite effect with biodegradable polylactide. After being modified WF was blended with PLA by melt compounding and injection molding. The properties of WF/PLA composites were characterized by techniques of DSC, SEM, tensile testing, impact testing and DMA. The effect of different modification methods (base, anhydride, hyper branched polyester, and organosilanes processing) on interface morphology, thermal properties and mechanical properties were discussed.In this paper, two kinds of wood fibers were composited with PLA. Before blending, the two kinds of wood fiber were chemical processed with different modifiers, and the overall performance of the composites was compared and analyzed:(1) Powdered cellulose and PLA were blended to prepare WPF/PLA composites. Modified WPF/PLA composites have improved crystallization ability and interface compatibility. DMA analysis showed that the storage modulus has also been increased. The mechanical property of alkali processed AWPF/PLA has been inproved, tensile strength, Young’s modulus and elongation at break were respectively increased by 35.7%,10.2% and 76.4%. The tensile strength, Young’s modulus and elongation at break of MAWPF/PLA (povdered cullulose was co-treated by alkali and maleic anhydride) were increased respectively by 35.7%,22.3% and 48.0%; meanwhile, the impact strength of AWPF/PLA and MAWPF/PLA were decreased by 10.0% and 7.6% respectively.(2) Fiber wood cellulose and poly lactic acid were composited to prepare WF/PLA composites. The pores on the fracture surface of the modified WF/PLA were significantly reduced, the surface of the fibers is smoother and the crystallization capacity. Compared with the untreated WF/PLA composite, AAWF/PLA, DMPA/PLA and SAWF/PLA(treated by acetic anhydride, hyper branched polyester and silane coupling agent) composites, tensile strength was increased by 2.0%,2.8% and 2.7% respectively and impact strength was increased by 3.8%,1.4% and 13.6% respectively. DMA results showed that modified SAWF/PLA composites had increased storage modulus and loss modulus, corresponding to the decreased tanδ.(3) Compared with MAWPF/PLA and SAWF/PLA. In terms of thermal properties, MAWPF/PLA ratio is 3.8% as lower as that of SAWF/PLA. In terms of mechanical properties, tensile strength and Young’s modulus of MAWPF/PLA composite are respectively 2.6% and 7.1% as higher as those of SAWF/PLA composite, while the elongation-break ratio and impact strength of SAWF/PLA are reduced by 12.5% and 8.8% respectively. In terms of dynamic mechanics, compared with SAWF/PLA composites, the initial storage modulus of WPF/PLA composite is increased by 4.2%, while its loss modulus and tan8 peak value are decreased 17.9 % and 70.4%.In general, the incorporation of wood fiber resulted in enhanced thermal dynamics and mechanical property in composites especially with modified wood fiber. The above results showed that MAWPF/PLA had a superior performance in the respect of strength and SAWF/PLA had an improved overall properties of the composites and especially significant stiffness. |
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