| With the environment pollution and the petroleum shortage becoming serious,the disadvantages of traditional fibers reinforced resin extracted from petroleum are getting more and more obvious.The development of biodegradable composite materials has become a hot area of research for researchers.Sisal fiber(SF)has the advantages of low cost,high ratio of strength,reproducibility and biodegradability.PLA also has the advantages of reproducibility and biodegradablility,besides that its raw materials have a wide range of sources.However,its application fields are limited for the high cost and brittleness.Preparation of completely biodegradable composites through sisal fiber reinforced PLA,can not only improve the PLA's comprehensive performance,lower the price and expand the application fields,it is also of great significance for alleviating environmental pollution and promoting the sustainable development of economy.Considering the bad interface compatibility between untreated sisal fiber(USF)and PLA,this paper introduces bisoxazoline(BO)which has high reaction activity with hydroxyl and carboxyl in the mixing process.BO can connect the PLA on the surface of plant fiber as a bridge,which reduces the polarity of the fibers and improves the interface bonding performance of the composites.In addition,BO as the chain extender can also connect different PLA molecular chains together to improve the molecular weight of the PLA,thus promoting the performance of the composites.Through the contrast with USF,this paper studied the changes of chemical composition,thermal stability and microstructure changes of alkali-treated sisal fiber(ASF)and BO modifying ASF(BO-ASF).Then different sisal fibers were mixed with PLA to prepare three kinds of composites,which were called PLA/USFs,PLA/ASFs and PLA/BO/ASFs,respectively.The crystallization properties,mechanical properties and rheological properties of composites were studied.Finally the GPC was used to study the change of molecular weight of composites before and after the alkali treatment and the effect of BO content on the molecular weight of PLA/BO/ASFs.Results show that:After alkali treatment,the diameter of the fiber becomes smaller,the fiber gets more rough and its thermal stability improves a lot.After the modification of BO,the PLA molecular chains are successfully grafted onto some fiber surfaces.Compared with the ASF,the fiber fibrillation degree increases,and the thermal stability is slightly lower but still better than USF.It is found that BO content has no obvious influence on the thermal stability of sisal fiber.Compared with pure PLA,the tensile modulus,flexural modulus and impact strength of the composites are higher and other mechanical properties decrease a lot.In general,when the fiber content is the same,the mechanical and interfacial properties of the PLA/BO/ASFs are the best,the PLA/ASFs' s are the second and the PLA/USFs' s are the worst.The thermal stability of PLA/USFs and PLA/ASFs is a little lower than that of PLA.The thermal stability of PLA/BO/ASFs increases first and then decreases with the increase of the content of BO.The addition of fiber improves the crystallization ability of composites.The addition of BO improves the cold crystallization temperature of PLA/BO/ASFs and reduces the degree of crystallization of PLA/BO/ASFs.With the improvement of fiber content,the cold crystallization temperature of the PLA/ASFs and PLA/BO/ASFs gradually decreases,and the crystallinity of them gradually increases.The addition of BO reduces the liquidity of PLA/BO/ASFs and raises its viscoelasticity,the complex viscosity,storage modulus and loss modulus of PLA/BO/ASFs increases first and then decreases with the increase of the content of BO.The addition of fibers results in the degradation of composites.The degradation of the PLA/ASFs is more obvious than that of the PLA/USFs.After adding BO,the molecular weight of the PLA/BO/ASFs increases first and then decreases with the increase of BO content,but is higher than that of the PLA/ASFs as a group. |
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