Ion bombardment of polyethylene—influence of polymer structure

Abstract

Polyethylenes of various macromolecular and supermolecular structures were studied from the point of view of their susceptibility to an ion beam treatment. An influence of molecular weight ( M w), molecular weight distribution ( M w/ M n) and the degree of branching were compared within the set of low-density polyethylenes (LDPE) studied. An influence of the length of branches was compared between LDPE, linear low-density (LLDPE) and high-density (HDPE) polyethylenes. An influence of the degree of crystallinity and the morphology of a crystalline phase were compared for HDPE samples solidified under various thermal conditions and ultra-high molecular weight polyethylene (UHMWPE). Plate polymer targets ∼2 mm were bombarded with 100 keV He + or 130 keV Ar + ions (dose of 10 14–10 16 ions/cm 2; ion energy stream density <0.1 μA/cm 2), micromechanical properties of their surface layer (hardness, mechanical modulus and elastic recovery) determined and compared to the virgin materials. Ar + ion beam bombardment generally lowers micromechanical properties of the polyethylenes, whereas He + ion beam treatment makes them higher. The effect is the stronger the higher the molecular weight of polyethylene. However, a long chain branching adversely affects the modification. The degree of crystallinity facilitates an ion beam bombardment from the point of view of micromechanical properties of the materials, however, also the morphology of a crystalline phase was found to play a role.