The effect of high-energy electron beam on drawn and undrawn high density polyethylene fibers

HDPE monofilaments were obtained using different extruders and drawn by post-extruder equipments. After solidification, drawn and undrawn monofilaments (draw ratio 7:1) were irradiated with 10 MeV electron beams in air at room temperature at 25, 50, 75, 100 and 125 kGy doses to induce a network structure. The phenomenon of the HDPE crosslinking was studied on the basis of gel content measurements. The fibers were examined by differential scanning calorimetry (DSC) and mechanical properties measurements. It was noted that the gel fraction increased with the irradiation dose up to 75 kGy and showed a significant increase with draw ratio, but at higher doses remained without considerable change. Melting temperature of drawn fiber increased with raising irradiation dose but decreased in undrawn sample. Also a bimodal endotherm peak was observed for drawn polyethylene irradiated in air. The changes in melting temperature and appearance of bimodal endotherm were related to the radiation chemistry of polyethylene in the presence of oxygen and interlamellar interactions. Heat of fusion and degree of crystallinity slightly increased for undrawn and drawn samples but, heat of crystallization was reduced by increasing irradiation dose due to the increase in the degree of crosslinking. The results of mechanical properties revealed that no significant changes occurred in Young’s modulus by increasing irradiation dose. As a result of oxidative degradation happened by the presence of the oxygen molecules during the irradiation process, the tensile properties of irradiated fibers decreased but elongation-at-yield for undrawn and elongation-at-break for drawn fibers boosted by increasing irradiation dose up to 125 kGy.