STATIC FATIGUE BEHAVIOR OF LINEAR LOW-DENSITY POLYETHYLENES

Various thermal histories were utilized to generate samples with the s ame crystalline microstructure (i.e. degree of crystallinity, supermol ecular structure, tie molecule density and lamellar thickness) for lin ear low-density polyethylenes (LLDPEs) with the same molecular weight, molecular weight distribution and branch frequency but different bran ch length. The static fatigue properties were found to improve with de creasing applied load for samples with the same type of short-chain br anches. The failure time of static fatigue (t(f)) was found to increas e dramatically as the branch length increased. An equation was used to predict tf from the stress, the branch length and other material para meters. In addition, the initial growth rate of the crack opening disp lacement and the time required to reach the critical opening displacem ent at the notch roots of the specimens were observed to decrease and increase, respectively, with increasing branch length. This dramatic i mprovement in static fatigue properties is attributed to the increasin g sliding resistance of the polymer chains through the crystal and thr ough entanglements in the amorphous region as the branch length of LLD PEs increases.