Design and process for producing silance-crosslinked polyolefin compound

Abstract

A formulation was designed to produce silane crosslinkable HDPE compound suitable for extrusion blow molding by melt blending technique on Magic extrusion blow molding machine. The formulations consist of HDPE as the base polymer, a carrier chemical pack containing an organic unsaturated silane and a free radical generating agent and condensation catalyst. In designing and formulating silane crosslinkable blow molded HDPE compounds with satisfactory properties, ASTM D 2647 was used as the reference. Grafting and crosslinking reaction was proposed for the formulated system. The product was characterized for the chemical, thermal, physical and mechanical properties. The chemical reactions during grafting and crosslinking involved a three step mechanisms. Extrusion blow molded bottle were stored in water for curing at various temperature and time. DSC, FTIR and TGA were used to determine the chemical groups involved in the reactions and gel contents were determined in parallel. The results from curing showed that a further formation of Si-O-Si crosslink’s took place after the point at which maximum gel contents has been reached. Mechanical measurements indicated that further crosslink’s were formed within the existing gel. Suitable range concentration relating to 100 parts of base polymer was found for vinyltrimethoxysilane (VTMO) to be between 1.6 to 2.0 phr. The concentration of dicumyl peroxide (DCP) initiator was between 0.1to 0.5 phr. The concentration of dibutyltin dilaurate (DBTL condensation catalyst) was being 0.005 to 0.02. When the DBTL amount was less than 0.005 phr, the crosslinking reaction did not proceed sufficiently. When the DBTL amount was larger than 0.02 phr, local crosslinking proceeds in the extruder at the time of extrusion, resulting in a greatly deteriorated appearance of the product. The selected components used in the formulation are HDPE grade HB6200, vinyltrimethoxysilane (VTMO) as the crosslinking agent, dicumyl peroxide (DCP) as the initiator, dibutyltin dilaurate (DBTL) as the condensation catalyst and Irganox 1010 as the antioxidant. The blow molded bottle properties and processability of the compound depends on the formulation and process parameter.