The plastic deformation of ultra-high molecular weight polyethylene

Abstract

Gel-spun filaments of different initial morphologies have been subjected to controlled drawing at elevated temperatures. The drawn samples have been examined by highresolution scanning electron microscopy. The deformation mechanism at temperatures up to 120 ~ C is very similar to crazing, especially in the case of unoriented gel-spun filaments. Filaments exhibiting a shish-kebab morphology offer the opportunity of examining the deformation of elementary fibrils in a quantitative way. The transformation of individual lamellae into fibrils is the initial deformation mode, which is followed by slip of fibrils at a later stage. This is concluded from a comparison of experimental data and model calculations of the maximum draw ratio. Drawing at 144 ~ C results in the formation of globular aggregates of lamellae, with a characteristic long period of 40 nm. This long period persists until all the globules have been converted, by micronecking, into aggregate fibrils of extended-chain character. On a molecular scale, the various processes can be described as the temperature-dependent flow behaviour of an entanglement network.

Structural hierarchy and surface morphology of highly drawn ultra high molecular weight polyethylene fibers studied by atomic force microscopy and wide angle X-ray diffraction

“…While some microfibrils are measured as small as 16 nm and greater than 90 nm, over 70 percent of the fibrils measured are between 20 and 40 nm. These dimensions, consistent with similar measurements via SEM in the literature [43], correlate quite well with the crystallite dimensions calculated from WAXD measurements. This suggests that the majority of microfibrils are arrays of single crystals linked in series.…”

Gel-spun polyethylene fibres

“…melt-spinning or fibres prepared from semi-dilute polymer solutions) and the process variables, as extensively described in the literature [27,29,[30][31][32][33][34][35]. During cold-drawing the lamellar structures are transformed into fibrillar structures by rotation/translation of (parts of) lamellae and/or by local melting of the lamellae due to local high stress concentrations.…”

DSC experiments on gel-spun polyethylene fibers

“…Hot-drawing was possible up to a maximum hot-draw ratio of 80 and this resulted in a fiber with a tensile strength of 3.55 GPa. SEM and SAXS studies of the hot-drawing process of these gel-spun fibers revealed that for high hot-draw ratios the lamellar structure was transformed into a fibrillar structure [32,33]. Hot-drawing to lowdraw ratios resulted in a decrease of the crystallinity and a shift of the peak melting temperature Tm to somewhat lower temperatures due to a recrystallization of the lamellar material into less perfect crystals, due to fast cooling of the thin hot-drawn fibers.…”