Preparation Of Compatibilizer And Interfacial Compatibility Of HDPE/wood Flour Composites

Nowadays, plastics have become an important material in our daily lives because of its applications in many fields. But a lot of waste plastics have been causing the serious environmental problem that it's hard to decompose at ambient temperature. Wood flour that is a waste material has advantages of low density, renewability, biodegradability and nontoxicity. It can be added in thermoplastics as an inexpensive filler to form new composites called Wood plastic composites (WPC).However, a key problem in WPC is the weak compatibility between hydrophobic thermoplastic and hydrophilic wood flour, which destroys the mechanical properties to a large content and furthermore limits applications of WPC. In this paper, High density polyethylene/styrene-ethylene butylene-styrene block copolymer blends (HDPE/SEBS) grafted by maleic anhydride (HDPE/SEBS-g-MAH) which is an effective compatibilizer for HDPE/Wood flour composites was prepared by means of torque rheometer with different contents of maleic anhydride (MAH). The experimental results indicated that MAH indeed grafted on HDPE/SEBS by FTIR analysis due to absorbance peaks of 1867 and 1791 cm^-1 which were asymmetric and symmetric carbonyl vibration of maleic anhydride. The torque increased with increasing the content of maleic anhydride and dicumyl peroxide (DCP). Styrene may increase the graft reaction rate of MAH onto HDPE/SEBS.The isothermal crystallization kinetics of HDPE, HDPE/SEBS and HDPE/SEBS-g-MAH at different cooling rates have been investigated by differential scanning calorimetry (DSC). The methods of Mo Zhishen and Kissinger for isothermal crystallization kinetics were used to analyze the crystallization characteristics of HDPE, HDPE/SEBS and HDPE/SEBS-g-MAH. The experimental results demonstrated that the crystallization rate of HDPE was highest and that of SEBS/HDPE was higher than that of HDPE/SEBS-g-MAH with the aid of Mo Zhishen method and DSC curves. It was found that the enthalpy of HDPE was decreased with adding SEBS due to partial destruction of crystal region and the enthalpy of HDPE/SEBS-g-MAH was lowest because of stronger effect among polar branch groups. According to the analysis of Kissinger method, the crystallization activation energies of HDPE, HDPE/SEBS and HDPE/SEBS-g-MAH were 446.50KJ/mol, 476.03kJ/mol and 407.85kJ/mol, respectively.When 4% HDPE/SEBS-g-MAH was added to HDPE/Wood flour composites, tensile strength and flexural strength of composites can reach 27.35 MPa and 35.3 MPa in comparison of 16.56 MPa and 23.83 MPa (without HDPE/SEBS-g-MAH), increasing by 165% and 148%, respectively. Due to incorporation of thermoplastic elastomer in HDPE/SEBS-g-MAH, The Notched Izod impact strength reached 5.5 kJ.m^-2, increasing by 157% in comparison of system without compatibilizer. To confirm that HDPE/SEBS-g-MAH can obviously enhance the mechanical properties, the mechanical properties of the composites with different compatibilizers that are HDPE/SEBS-g-MAH, HDPE-g-MAH and HDPE-g-MAH/SEBS were compared. The results showed that HDPE/SEBS-g-MAH as the compatibilizer obviously increased the mechanical properties of the composites.The curves of temperature dependence on the dynamic mechanical properties showed that when the compatibilzer was added into the composites, the peak amplitude was decreased and the storage modulus was increased. This is can be explained that strong interaction between wood flour and HDPE led to decrease of the number of molecular segments, due toimproved adhesion between wood flour and HDPE.That HDPE/SEBS-g-MAH improved the compatibility was also conformed by scanning electron micrographs (SEM). When the compatibilizer was not added into the composites, the interphase region between the wood flour and HDPE matrix was clean, and gaps in the interphase region was very obvious which indicates poor adhesion between the surfaces. When adding 4 wt% HDPE/SEBS-g-MAH to the composites system, wood flour was tightly embedded into the HDPE matrix and no obvious gaps could be seen in the interphase region and some wood flours were torn up. This phenomenon can be explained that HDPE/SEBS-g- MAH improved the adhesion between wood flour and HDPE matrix.The surface property of wood flour and wood flour modified by HDPE/SEBS-g-MAH were characterized by inverse gas chromatography. It was showed that the retention time of wood flour modified by HDPE/SEBS-g-MAH and dispersive component of surface free energy increased, compared to wood flour. It demonstrated that HDPE/SEBS-g-MAH indeed reacted with wood flour and the polar property of wood flour decreased.