Ultrahigh molecular weight processing

In spite of processing difficulties, some higher-molecular-weight polymers, such as ultrahigh-molecular-weight polyethylene (uhmwpe), are used because of their superior toughness. 

K.A. Saum, W.M. Sanford, W.G. Dimaio, Jr., and E.G. Howard, Jr., Process for medical implant of cross-linked ultrahigh molecular weight polyethylene having improved balance of wear properties and oxidation resistance, US Patent 6017 975, January 25, 2000. 

Ultrahigh-molecular-weight polyethylene (PE) can be processed into a gel. Blends of such a PE with polyoctylthiophene were prepared, and conductivities above 10 4 S/cm were measured for POT volume fractions < 1%. Data at even lower POT content suggest a percolation threshold below a volume fraction of 3 x 10 4. Presumably, POT is rejected by PE and adsorbs on the threads forming the gel. 

As illustrated above, selection of cocatalyst is often predicated on cost. In some cases, however, use of an alternative cocatalyst may transcend the cost factor. This could be because the alternative cocatalyst provides enhanced polymer properties or improved process performance. For example, use of TMAL as cocatalyst in place of TEAL in a gas phase process has been shown to provide linear low density polyethylene with lower hexane extractables and superior film tear strength (14). Ultrahigh molecular weight polyethylene and polyethylene with broader molecular weight distribution can be produced using "isopre-nylaluminum" as cocatalyst (15-17). 

As shown in Table 12.1 the impact resistance and tensile strength of ultrahigh-molecular weight polyethylene (uhmwpe) are superior to those of HOPE, but UHMWPE is mort difficult to process, uhmwpe is also slightly harder than hope. 

The wear behaviour of polytetrafluoroethylene (PTFE), carbon-filled PTFE, high density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMPE), low density polyethylene (LDPE) and polymethyl methacrylate (PMMA) was studied. To ensure consistent and controlled properties of the samples, many of the materials were processed in the authors laboratory. The details of sample preparation and processing techniques are reported elsewhere ( ). ... 

J.-G. Gai, Y. Zuo, Metastable region of phase diagram optimum parameter range for processing ultrahigh molecular weight polyethylene blends. J. Mol. Model. 18, 2501-2512... 

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