Study On The Process Of EVOH Modified Bagasse And The Properties Of PVC Composites

In order to improve the interfacial compatibility of polyvinyl chloride(PVC)/bagasse composites and improve the properties of the composites,ethylene-vinyl alcohol copolymer(EVOH)was used as the interfacial modifier in wood-plastic composites in this thesis.Because EVOH is a polymer and its melt viscosity is large,it is difficult to make the EVOH evenly distributed on the bagasse surface by conventional modification methods,and the modification effect is not good.For this reason,EVOH was formulated into a glycerol solution for the modification of bagasse to improve the performance of the PVC/bagasse composite in the first chapter of the thesis.We studied the process of EVOH modifying bagasse and the modification effect of three kinds of EVOH by judging the data changes of the contact angle and surface tension of bagasse before and after modification,and the interfacial tension and adhesion work between PVC and bagasse before and after modification.The results showed that the temperature had no obvious effect on the modification bagasse.Washing and standing for a period of time both can reduce the excessive glycerin on the surface of modified bagasse,so that the surface polarity of modified bagasse is reduced.The proper amount of glycerol can promote the uniform dispersion of EVOH on the bagasse surface.When the mass ratio of EVOH to glycerol is 1:0.8,the modification effect of EVOH is best.The optimal amount of EVOH,which is with ethylene fractions of 24,35,and 48 mol%(marked as E24,E35,E48),modifying bagasse was 3,7.5,and 9 wt%of bagasse,respectively;and the optimum dosage increases with the increase of ethylene structural unit content of EVOH.In the second chapter of this thesis,the bagasse was modified under the optimal dosage of EVOH,and PVC/modified bagasse composites were prepared by high-mixing,milling,and compression molding to examine their actual modification effects.It is found that the mechanical properties and water absorption of composites is greatly volatile,which is inconsistent with the theoretical predictions.And repeated test data is still irregular.The analysis found that the thickness of the plasticised sample during the compression molding process can lead to the difference in the density of the final sample,which will greatly affect the mechanical properties of PVC composites.Therefore,in the scientific research of compress-molded composites,controlling the density of composite to ensure its consistency is of great significance for drawing correct conclusions.This finding has universal guiding significance.In the third chapter of this thesis,PVC/modified bagasse composites were prepared on the basis of optimal dosage of EVOH and controlling density uniformity,and we studied the effects of three EVOHs on the performance of PVC/bagasse composites.The mechanical properties and processing properties of composites,which modified with three kinds of EVOH,are improved,and the water absorption and linear thermal expansion coefficient are reduced.Among the modified systems,E35 modified bagasse has the best effect.Compared with the simple mixing method,the treatment method,which was formulating EVOH into a glycerol solution,is better,indicating that the method has high industrial application value.The change in the position of the infrared absorption peak of the hydroxy group of the EVOH resin and its use as a compatibilizer in the composite material provides evidence of hydrogen bonding between EVOH and bagasse.SEM shows that EVOH improves the interface and uniform dispersion of bagasse and PVC matrix.This inferred the modification mechanism of EVOH:bagasse after EVOH modification,part of hydroxyl groups in EVOH can form hydrogen bonds with hydroxyl groups on the bagasse surface,so that the EVOH is covered on the bagasse,which reduces the surface polarity of bagasse and promotes the dispersion of bagasse.At the same time,hydrogen bonds are formed between EVOH covered on the surface of bagasse and PVC matrix,so that the intermolecular force between the two phases becomes strong.the hydroxyl group in E35 exactly satisfies the requirements of the bagasse dispersion and interphase force,so its modification effect is best.