Morphology of chemically crosslinked ultrahigh molecular weight polyethylene

Morphological characterization of chemically crosslinked ultrahigh molecular weight polyethylene was performed by differential scanning calorimetry and scanning electron microscopy. The lamellar thickness of nascent UHMWPE inferred from DSC endotherms showed a very broad distribution, which was reduced significantly after melting and recrystallizing in DSC. Peroxide crosslinking further reduced the lamellar thickness distribution compared to uncrosslinked samples. After gamma-irradiation, a slowly cooled peroxide-free sample showed a greater increase in lamellar thickness distribution. Examination of the morphology of freeze-fractured surfaces by SEM showed that a slowly cooled peroxide-free UHMWPE exhibited a rougher fracture while chemically crosslinked samples showed a smoother fracture. After compression molding at 300 degrees C for 2 h, the grain boundaries between particles disappeared for all UHMWPE samples, indicating a complete fusion of the original flakes.