Combination of a Viscoelastic and a Tribological Analysis of a Low-Density Polyethylene with a High Degree of Cross-linking

Cross-linking of polymers is an efficient method to tailor the end-use properties of polymer materials. Cross-linking using a chemical agent, e.g., dicumyl peroxide (DCP), allows for a spatially uniform network formation in the melt state. In addition, it is also associated with side reactions which influence the final properties of the plastic part. This work investigates the influence of DCP concentration on the tribological properties of a cross-linked low-density polyethylene (LDPE) grade. In particular, high DCP concentrations up to 20 phr are chosen in order to explore the effect of a high degree of cross-linking. The viscoelastic properties below and above the melting temperature are studied in detail to support the interpretation of the tribological results. Rheological investigations allow one to monitor the cross-linking of the long-chain branched LDPE. The data and the subsequent optical analysis show that wear already is significantly reduced at a low DCP concentration of 1 phr because of the covalent bonds caused by cross-linking. A high DCP concentration of 20 phr yields an increase of coefficient of friction which can be explained by the low stiffness and the resulting high contact area in the case of highly cross-linked LDPE. Cross-linking of a low-density polyethylene (LDPE) using dicumyl peroxide (DCP) strongly influences the crystallinity and as a consequence the tribological properties. Wear can be effectively reduced already at a low peroxide concentration of 1 phr because of the covalent network. A high peroxide concentration of 20 phr and the resulting higher contact area significantly increase the coefficient of friction of LDPE. image