The Study On The Preparation And Rheological Properties Of Polypropylene As The Matrix Of Wood-plastic Composites Materials

The Wood plastic composite materials are widely used because of itshigh specific strength, low cost and biodegradability. However, theinterface compatibility together with mechanical properties decreased andthe viscosity became too high for processtion when more wood powdersare added. Meantime, there are not so much rheology theory for formuladesign and preparation of wood plastic, thus it’s of urgent need to studyon the rheology theory, processing technic and how to improvemechanical properties of the composites when high amount of woodpowder are added.This paper studied on the preparation, structure and properties ofPP/Poplar powder composites. The main subjects are: PP-based woodplastic composites were prepared by melt blending and then characterized.The rheology property was studied with RH7-D Capillary rheometry andthe relationship between each single parameter and the viscosity of thecomposites was ascertained and the mathematical model of apparentviscosity was established in steady state. The influence of vibrationstrength on the apparent viscosity and structure of the compound systemwere studied under vibration force field on self-made multifunctionalall-electric rheometer. Orthogonal tests were carried out on synergy oftoughening and compatibilizing with different elastomers andcompatibilizers. The optimal formula for toughening and comparibilizingwere established by the range analysis and the consolidated balancemethod. The influence of synergy of toughening and compatibilizing onthe structure and properties of the composites were also discussed.The results show that: the crystalline property, the impact andflexural strength were improved because of the fibre reinforcement andheterogeneous nucleation ability of Poplar powders, but with the amountaddition of wood powder, the tensile strength, elongation at break andthermostability decreased promptly, the crystallinity decreased because ofthe steric effect of the PP molecular chain segment motion space wasincresead, The Tensile strength, bending strength, bending modulus of thecomposites went down-up-down change and the impact strength went up-down-up-down change as the size of wood powder decreased. Theresults of rheology property under steady stable and vibration force fieldstate showed that the composites system is pseudoplastic fluid andpower-law fluid which strongly depended on the temperature andpossessed the behavior of shear thinning. when more woodflour wereadded and the temperature declined, the apparent viscosity aand theshear stress of the composites system increased, the dynamic viscositydropped and the woodflour were more dispersed as the vibrationstrengthened; a mathematical model of the apparent viscosity with thecomposites system in steady state was established under reasonablehypothesis; The interface compatibility of composites were significantlyimproved with SBS、EVA-g-MAH、PP-g-MAH、SEBS-g-MAH by theSEM analysis, Meanwhile, the macroscopic mechanical properties, theappearent viscosity and thermal stability of the system increased as wellas the crystallization performance degradation, the best compatibilizationand toughening formula was obtained through the range analysis and theconsolidated balance method, that is SBS:5wt%, EVA-g-MAH:3wt%,PP-g-MAH:10wt%, SEBS-g-MAH:2wt%.