Wood Flour/EVA/HDPE And Starch/EVA/HDPE Composite Foams For Shoe Sole Applications

As a project aimed at environmental-friendly composite foamed sole materials, EVA/HDPE/wood flour, EVA/HDPE/starch composite foams and starch/wood flour composites were prepared through melt blending and compression molding. The composites were characterized by means of mechanical property measurements, FT-IR, thermal properties analysis, scanning electron microscopy and water absorption studies.The thermo-gravimetric and differential scanning calorimetry analyses indicates that the EVA/HDPE/wood flour and EVA/HDPE/starch composites have good thermal stability at processing temperature, and the thermal stability of EVA/HDPE/wood flour composites is better than EVA/HDPE/starch composites. The influence of WF and starch on the crystallinity of blends was examined via X-ray diffraction, and it is found that the crystallinity of EVA/HDPE reduces to the extent that is slightly higher than EVA in the presence of wood flour or starch. Low crystallinity of composite facilitates the gas (produced from the decomposition of blowing agent) solubility and diffusion. For EVA/HDPE/wood flour composite, The micro-morphology of composites was observed by a scanning electron microscope. It is found that the combined effect of high-density polyethylene and wood flour makes cell structures larger in quantity and smaller in size which were then calculated by images analysis. This highlights the nucleation effect of wood flour. Titanate coupling agent enhances the interaction between wood flour and polymer matrix. The data of physical properties suggests that the optimum amounts of high-density polyethylene, wood flour and titanate are 30 phr,10 phr and 2% respectively. The size of wood flour has a great influence on the properties of EVA/HDPE/wood composites. With the decrease of wood flour size, the melting flow rate and compression set decrease, the tensile strength, elastic and density increase. For EVA/HDPE/starch composites, the FT-IR shows that the adsorption peak of hydroxy became weaker and wider, which indicates that glycerin damages and weakens the hydrogen bond between the intermolecular of starch. The SEM shows that starch exhibits better compatibility with plastic phases than wood flour. The unified size of starch granule results in finer cell structures of EVA/HDPE/starch. The mechanical properties measurements show thatEVA/HDPE/starch composite foams have a better performance than EVA/HDPE/wood flour composite foams, the optimum amounts of HDPE and starch are both 20 phr.For starch/wood flour composite, the test results show that the addition of wood flour to thermoplastic starch significantly increases the tensile strength, elongation and thermal stability and decreases water absorption of the composites. The impact gets enhancing with increasing wood flour content and decreasing particle size of the flour. Tensile strength increases up to 30% wt but decreases at 60% wt content of wood flour. The SEM pictures prove the good compatibility of starch and wood flour.