Research On Properties Of Plant Fiber Reinforced Poly(Lactic Acid) Composites

Poly(lactic acid)(PLA)is a completely biodegradable thermoplastic polymer with high strength,high modulus,good processing property comparing with other degradable resins.However,due to PLA with the higher price,brittleness and poor heat resistance,its application in a wider field is limited.In this paper,two kinds of plant fibers were used as reinforcing fibers,and the coir/PLA and C-flax/PLA composites were prepared respectively,and the preparation process and properties of the composites were studied.Firstly,coir was used as the reinforcing material,which was treated with alkali,and coir/PLA composites were prepared by the torque rheometer.The effects of processing temperature,fiber and compatibilizer content on the properties of composites were studied.Mechanical properties tests show that,with 30 wt%coir fiber and 200? processing temperature,the mechanical properties of coir/PLA composites were optimal,of which tensile strength were increased by 20%than pure PLA.DMA results show that,the storage modulus of the PLA material increased after adding coir,and the Tg of material moved to the high temperature,indicating that the capability of deformation resistance of composites were improved.The DSC results and POM images indicate that,the crystallization ability of the PLA material was significantly improved after the addition of coir,which played a promotion role on improvement of the mechanical properties of the composite.After adding self-made MAH-g-PLA compatibilizer,the mechanical properties of the composites were significantly improved,and the tensile strength of composites performed best when the compatibilizer content was 10%,which was increased by 28%than pure PLA.SEM images indicate that,the interface properties of the composites were significantly improved after the addition of the compatibilizer.Unidirectional C-Flax/PLA prepreg tapes were prepared by melt impregnation method.And the structure and properties of prepreg tapes with different fiber content and compatibilizer content were tested.The mechanical properties show that,when the fiber content was 55 wt%,the tensile strength of the prepreg tapes reached 235.75 MPa,which was improved by 300%than pure PLA and had entered the ranks of carbon structural steel.The DSC test show that,the crystallization ability of the PLA material was obviously improved after the addition of flax fiber,and the crystallinity of PLA was increased from 9.6%to 30.75%at maximum degree,which was due to the heterogeneous nucleation of the flax fiber in the PLA material.After adding MAH-g-PLA compatibilizer,the tensile properties,dynamic mechanical properties and interfacial compatibility of the prepreg tapes were significantly improved,which were confirmed by mechanical properties,DMA and SEM image.When the content of compatibilizer was 10%of the weight of resin,the tensile properties of prepreg tape were the best,which was increased by 75%than without compatibilizer.The composites laminates were prepared by hot pressing molding with the braiding C-Flax/PLA prepreg tapes,and the mechanical properties,water absorption and sub microscopic morphology of C-Flax/PLA composite laminates were tested.The mechanical properties show that,the tensile strength of C-Flax/PLA composite sheets were decreased comparing with prepreg tapes,however,it was much higher than pure PLA,and its flexural performance and impact performance were significantly increased than pure PLA.The water absorption performance indicate that the water absorption of PLA material increased obviously after adding flax fiber,but it decreased with the addition of compatibilizer.Sub microscopic morphology indicates that,the flax fibers and PLA matrix bonded were improved obviously after adding compatibilizer.The effect of continuous flax fiber on crystallization behavior of PLA material was analyzed by non-isothermal cold crystallization kinetics.It was found that Jeziorny 's modified Avrami equation,which can better describe the non-isothermal crystallization properties of PLA and composites.Combining the fitting data with the POM image,it was found that the main reason for the crystallization ability of PLA resin improving by flax fiber was that promoted the heterogeneous nucleation of PLA materials.Finally,the biodegradation characteristics of C-Flax/PLA composites were studied by composting process.It was found that the degradation rate of PLA materials was significantly accelerated after adding flax fibers.When buried for 40 days,the weight loss rate of the material was increased from 1.03%of PLA to 9.10%.On the one hand,the hydrolysis and biodegradability of flax fiber were faster than PLA;On the other hand,there was the gap between the fiber and the PLA,which made water molecules or microorganisms enter the interior of the composite accelerating the degradation of the material.