Extrusion foaming behavior of wood plastic composites based on PP/POE blends

The foamed wood-polymer composites with polypropylene (PP) and polyolefin elastomer (POE) blends as matrix were prepared by a co-rotating twin-screw extruder and a single-screw extruder foaming system in this paper. To improve the dispersion uniformity of materials in the samples, a cavity transfer mixer was introduced to the single-screw extruder foaming system. Besides, the effects of both the nucleating agent and the coupling agent on the melt flowability, cell morphology and mechanical properties of the samples were investigated. The nanoparticles were also added to study the effect of nano-nucleating agent on the properties of the foamed samples. The experimental results show that the addition of talc and maleic anhydride grafted polypropylene (MAH-g-PP) resulted in the decrease of the melt flow rate and the increase of the Vicat softening temperature. But the addition of nanoparticles improved the melt flowability and reduced the softening temperature of the samples. Compared with talc, the addition of nanoparticles increased the impact strength of the samples by 6%. Moreover, the minimum cell size and the maximum cell density were obtained with the value of 62 μm and 2.8 × 104 cells cm−3, when the content of both talc and MAH-g-PP were 10 phr. Affected by the cell morphology, the maximum impact strength, tensile strength and flexural strength of the samples were also obtained with the value of 6.6 kJ m−2, 8.3 MPa and 22.6 MPa.