Enhanced Foaming Behavior of Ultrahigh Molecular Weight Polyethylene by Blending Silicone Powder in Microcellular Foaming

Microcellular foaming with CO2 as the blowing agent is developed to prepare low-density ultrahigh molecular weight polyethylene (UHMWPE) foams. To improve the foaming behavior of UHMWPE, silicone powder is used to modify UHMWPE by twin-screw compounding. The silicone powder contents, foaming temperatures, and foaming pressures are varied to investigate their effect on the foaming behavior of UHMWPE in a one-step microcellular foaming process. The results show that the addition of silicone powder leads to significantly improved foaming behavior of UHMWPE by simultaneously increasing the expansion ratio and refining cellular morphology. With the presence of silicone powder, UHMWPE with an expansion ratio up to 34-fold is prepared, while the maximum expansion ratio of pure UHMWPE foam that can be achieved is only 15-fold. Moreover, for the foams with the same expansion ratio, the presence of silicone powder leads to significantly refined cellular morphology. The improved melt flowability and accelerated crystallization by adding silicone powder are responsible for the significantly enhanced foaming ability of UHMWPE. The heterogeneous nucleation effect of silicone powder plays a critical role in refining the cellular morphology by promoting cell nucleation and reducing cell collapse.