Melting of ultrahigh molecular weight polyethylene

Abstract

SynopsisOn heating in DSC, samples of UHMWPE show a single, fairly sharp, melting endotherm which may be increased to a peak temperature of 147°C and 77% crystallinity by annealing at elevated temperatures. An irreversible conversion of nascent to folded crystals, between 134 and 142"C, was observed by heating nascent UHMWPE powder in the calorimeter. In the presence of n-hexatriacontane, the melting endotherm of UHMWPE was depressed and broadened and the conversion of nascent to melt-crystallized polyethylene facilitated on heating. A melt-crystallized mixture of ordinary linear polyethylene (HDPE) and UHMWPE was not resolved on remelting. After annealing this mixture for 12 h at 130°C, HDPE was fractionated and the melting of UHMWPE was sharpened. Crystals of UHMWPE, prepared from dilute solution in xylene, show a single sharp melting endotherm and high crystallinity, but the melting peak is reduced in temperature compared to nascent crystallized powder.

Blend membranes of chitosan and poly(vinyl alcohol) in pervaporation dehydration of isopropanol and tetrahydrofuran

“…Müller et al demonstrated that adding a semicrystalline polyethylene block to P3HT is an efficient approach to enhance the mechanical property of the resulting block copolymer and obtain excellent charge transporting characteristics even at a P3HT content as low as 10 wt % 16. However, semicrystalline polyethylene requires a relatively high processing temperature in the range from 110 to 145 °C, depending on its molecular weight and branching,42, 43 restricting the window of processing parameters and substrates. To reduce the processing temperature, comb‐like crystalline poly(stearyl acrylate) (PSA) may be an appealing candidate to develop a P3HT‐based block copolymer for device applications.…”

Effect of Mechanical Constraint on Tearing Energy of Polymer Membranes

“…The temperature of the oven was ramped at a rate of 0.5 °C min –1 from 25 to 140 °C for PFSA, 110 °C for LDPE, and 134 °C for UHMWPE. The temperatures corresponded to the polar cluster transition temperature for PFSA, and the melting temperature for the polyethylene . After 1 h, the temperature was ramped back to 25 °C at a rate of 0.5 °C min –1 .…”

Morphology and melting behavior of nascent ultra-high molecular weight polyethylene

“…Thin point which approaches the equilibrium value dispersions of flake on a quartz zero background (T 0 m ) for polyethylene, but is irreversibly lowered plate assured that sample transparency broadenfollowing a melt crystallization cycle. 28,29,30,33,34,38,41,42 ing was minimized. Scans in 0.025Њ increments In this sense, the nascent morphology of UHMW were run from 5-51Њ 2u (10 s/step) and, for se-PE represents a unique combination of morphollected samples, 70-85Њ 2u (45-65 s/step).…”

“…Similar characteristics have been observed in other studies of nascent polyethylene. 28,29,44 As the nascent structure is partially disordered with increasing temperature, molten material which is unable to recrystallize following melting at the annealing temperature crystallizes on cooling. This gives rise to Endotherm I in the DSC scan at a position consistent with a melt crystallization.…”