Effect of chemical cross-linking on polyolefin syntactic foam extrudate for cable jacketing

The two objectives of this study were to (1) determine the feasibility of chemically cross-linking a syntactic polyolefin foam via peroxide, and (2) evaluate the effects of cross-linking on physical and mechanical properties of the foamed rod extrudate. A metallocene catalyzed polyolefin plastomer, with 8% Expancel concentration, was extruded on a single screw extruded with various concentrations of dicumyl peroxide at a high and low processing temperature and screw speed. Peroxide concentrations ranged for 0–3.0% for the low temperature range, and 0–1.5% for the high temperature range; all formulations were processed at both 15 and 25 rpm. Selected samples underwent a pressurized heat treatment to further increase the degree of cross-linking. The process conditions as well as physical and mechanical properties were evaluated, and percentage of decomposed peroxide was approximated. Process conditions such as melt temperature and head pressure both increased with the addition of peroxide as did sample density, confirming the presence of cross-linking during the extrusion process. Modulus showed slight improvements at higher peroxide concentrations, and tensile creep resistance was improved with the addition of peroxide. The pressurized heat treatment decreased modulus, and increased density due to degradation of the microballons. Based on decomposed peroxide calculations, the peroxide reaction was found to be most effective at the high processing temperature and lower screw speed.