Study On Interfacial Compatibility And Extrusion Rheological Properties Of High Density Polyethylene/Bamboo Flour Composites

Bamboo plastic composite has the double properties of both wood and plastic as a new type of environmentally friendly materials. It offers various benefits such as good corrosion resistance, low cost, high strength, long life, etc so that it has achieved applications in construction, transportation and automobile, etc. However, there is poor compatibility between the wood fillers and the matrix resin interface, and packing not easily dispersed in the matrix, resulting in their difficulty in production molding, extrusion speed is slow, easy to melt fracture, thus limiting its application and development. In this study,the rheological properties, microstructures and processing characteristics were researched by rotational rheometer, torque rheometer, scanning electronic microscopy and energy disperse spectroscopy(SEM-EDS) on the basis of good comprehensive performance of the samples so as to provide theoretical basis for production. The main contents and results of the experiments are described as follows:The silane coupling agent, ethylene-methylacrylate copolymers(EMA) and amphiphilic dendritic polymers(PAMAM) were choosed to improve the interfacial compatibility for the composites. The results show that PAMAM were more effective in improving the interface compatibility between bamboo flour and the matrix, the tensile strength and impact strength increased by 33.63% and 38.9%, respectively.Rheological test results show that the viscoelastic behavior of the blends are significantly different from HDPE matrix and show “solid-like” features at low frequency. The contribution of the network structure and interface for the blends increase with the contents of bamboo flour so as to the increase of modulus, viscosity, stress and the degree of stress overshoot. The presence of PAMAM reduced the interaction of bamboo flour particles, thus lowering the elastic storage and relaxation time.The structure evolution of the composites were investigated through tracking the distribution of silicon with scanning electronic microscope-X-ray energy dispersive spectrometer(SEM-EDS) and combining with dynamic rheological testing. It is founded that the content of interface silicon and dynamic modulus and viscosity increase with processing time. These phenomena reflect the increase of interaction between bamboo flour and HDPE molecular-chains and interface layer thickness. It’s stated that the HDPE molecular chains gradually transfer into the bamboo flour and form tangles structure under shear, which resulted higher modulus. Since the enhancement of shearing, the composite systems gradually deviate from the equilibrium state and the decrease of modulus, viscosity and first normal stress difference.The extrusion processability of the composites was studied by torque rheometer extrusion platform. Results indicate that the elastic energy storage of the composites increase with the increasing of bamboo flour content and it is inclined to characteristic relaxation time, so as to exhibit flow instability such as melt fracture under the same shear rate. The flow behavior of filled system is instable and the surface of extrudates gradually become smooth and turn up "the second smooth area" under high shear rate, which is significantly different from that of HDPE matrix. Undering high shear rate, the filling systems do not obey the Cox- Merz rules owing to the blends deviate from the equilibrium state and the appearance of wall slip. With small amount of PAMAM can improve the melt fluidity and lower the critical shear rate which correspond the second smooth area. It can be seen that the shear viscosity and temperature accord with Arrhenius equation and extrudate with smooth surface can be obtained under high temperature. The extrudates emerge from short die with much smoother surface in that the short during time and less elastic energy storage.