Reprocessable silane-crosslinked polyethylene: property and utilization as toughness enhancer for high-density polyethylene

Silane-crosslinked polyethylene (Si-XLPE) has been increasingly used as a replacement of polyvinyl chloride for use as residence water pipes and hydronic heating systems. Unfortunately, good management of Si-XLPE wastes originated in the manufacturing processes or from already used products is limited. This article presents a melt-recycling (remelting and remolding) of waste Si-XLPE and its use to produce the high-density polyethylene (HDPE) composition of improved thermal endurance, along with attractive balance of stiffness and toughness. Experiments were carried out with a series of Si-XLPE of different gel fraction and crosslink structure, either loose or tight, aiming at understanding the factors which dictate the reprocessability and properties of crosslinked waste. Tensile and impact properties, crystallization, and heat stability of the HDPE and waste blends were investigated. It is found that waste Si-XLPE materials of loosely network structure can be remelting and remolding as thermoplastic PE. Interestingly, the results showed that crosslink gel in the wastes could be as high as 70 %. Both tensile modulus and impact strength of the HDPE systematically increased with increasing loading and content of gel in the crosslinked materials. The addition of 50 % crosslinked waste led to a rise of heat distortion temperature of HDPE by 20 °C, without evitable change in the melting and crystallization temperatures.