This thesis deals with the low temperature processing behavior of ultrahigh molecular weight polyethylene (UHMWPE)/mineral oil blends. The addition of mineral oil is to enhance processability and interfacial cohesion of UHMWPE powders . Besides, it promotes heat conduction throughout the polymeric material. Precision extrudates with a stiffness of ~ 10 GPa and a tensile strength of 83 MPa have been achieved using a single stage ram extrusion process....[ Read more ]

This thesis deals with the low temperature processing behavior of ultrahigh molecular weight polyethylene (UHMWPE)/mineral oil blends. The addition of mineral oil is to enhance processability and interfacial cohesion of UHMWPE powders . Besides, it promotes heat conduction throughout the polymeric material. Precision extrudates with a stiffness of ~ 10 GPa and a tensile strength of 83 MPa have been achieved using a single stage ram extrusion process.

Capillary rheometer was employed to study the processability of the blend. It was observed that the material could be readily processed into precision extrudates below its melt transition temperature for extrusion draw ratios (EDRs) up to nine. Strong shear thinning characteristic was observed for an EDR of nine. Such kind of flow behavior guarantees processability enhancement at the price of a slowly rising extrusion pressure.

Differential scanning calorimetry (DSC) measurements on extrudates with different EDRs show two melting peaks for both skin and core samples of extrudates with EDRs less than four, indicating occurrence of partial melting and uniform distribution of the partially molten polymer throughout the sample. Such partial melting, therefore, demonstrates a blend of molten UHMWPE with solid UHMWPE powders which is expected to enhance toughness of the extrudates.

Wide angle X-ray diffraction (WAXD) measurements on the extrudates show likely skin and core structures where the skin shows a slightly higher orientation function than the core. The overall orientation, however, is close to the orientation function values measured for the skin and is found to increase with increasing EDR.

Scanning electron microscopy (SEM) studies support DSC results by showing good cohesive structure in inter-facial regions of UHMWPE powders up to EDR of four. Meanwhile, they agree well with the WAXD data with respect to increasing anisotropy with increasing EDR.

Mechanical property measurements show that stiffness increases with increasing EDR. Toughness, however, begins to decline when the EDR is greater than four. The highest toughness value thus obtained is ~10x10⁶Jm^-3.