The effect of temperature and deformation rate on the hot-drawing behavior of porous high-molecular-weight polyethylene fibers

Abstract

SynopsisThe nature of the deformation process involved in hot drawing of porous high-molecular-weight polyethylene was examined by apparent elongational viscosity measurements at drawing temperatures between 100°C and 150°C and deformation rates in the range of 10-6-10-3 m/s. The temperature dependence of the apparent elongational viscosity revealed three distinguishable intervals with different activation energies. In the range of 100-133"C, the activation energy amounted to 50 kJ/mol, indicating that hot-drawing in this region proceeds by a sliding motion of separate fibrillar units. The interval between 133°C and 143°C was characterized by an activation energy of about 150 kJ/mol. Moreover, the porous character of the polyethylene fibers was found to decrease in the drawing process above 133OC. These observations were ascribed to an aggregation of the elementary fibrils upon hot-drawing due to partial melting at the surface of the fibrils. At temperatures above 143°C the activation energy was strongly affected by the initial morphology and the draw ratio of the fibers and amounted to values in the range of 200-600 kJ/mol. Molecular orientation in this region is accomplished by a slippage of individual chains, with entanglements acting as semipermanent crosslinks. Decreasing of the rate of elongation in the drawing process resulted in premature fiber breakage, indicating that the crosslinking action of the entanglements is limited by the time scale of the process.

The plastic deformation of ultra-high molecular weight polyethylene

“…A completely different mechanism at 144 ~ C, as previously suggested [18], is clearly demonstrated in Figs. 5 and 6, although a more or less isotropic filament was used in our case.…”

“…In a subsequent series of experiments on the filament A, the drawing temperature was increased to 144 ~ C. This temperature can be considered to b e close to the lower bound of the optimum hotdrawing range established for the preparation of ultra-strong polyethylene fibres [18]. Drawing in this range is accompanied by migration and removal of defects and by an increase in crystal continuity [19].…”

“…The optimum temperature range for hot-drawing was demonstrated to be 143 to 150 ~ C. In the first investigation into the 1568 underlying mechanism, Smook and Pennings [18] have presented data on the elongational viscosity r~ of gel-spun filaments during hot-drawing, in a range of temperatures between 110 and 148~ and draw ratios between 7 and 36. Some important findings will be summarized here.…”

Ultradrawing properties of ultra-high molecular weight polyethylene/hydrochloric acid treated attapulgite fibers

“…Several authors [16,[18][19][20][21][22] reported that the drawing temperature and rate could markedly affect the maximal achievable draw ratio and tensile properties of solution-grown UHMWPE samples. In addition to the gel solution compositions and drawing conditions, it is generally recognized that the conditions used in the formation process after spinning and/or solution casting of gel solutions can also have a significant influence on the morphology, microstructure and drawing properties of the specimens formed during the above mentioned processes [2,19,[23][24][25][26][27][28][29][30].…”

SAXS experiments on voids in gel-spun polyethylene fibres

“…These fibrillar structures may be more or less closely packed depending on, for example, molecular weight and drawing conditions. For relatively low drawing temperatures, very loosely packed fibrillar structures are obtained, whereas higher draw- ing temperatures result in more dense structures due to melting/recrystallization [28][29][30][31][32]. The drawing temperature commonly used in our laboratory is in the range 144 to 148~ During drawing at these temperatures the porosity on a 100rim scale is largely eliminated [24,30,33].…”