DSC experiments on gel-spun polyethylene fibers

Abstract: The tensile strength of gel-spun polyethylene fibers obtained after hot-drawing depends on spinning conditions uch as spinning speed, spinning temperature, spinline stretching, polymer concentration, and molecular weight/molecular weight distribution. High deformation rates in the spinline result in shish-kebab structures which after hot-drawing lead to fibers with poor properties. This is in contrast o hot-drawn fibers obtained from gel-spun fibers with a lamellar structure. Lamellar or shish-kebab struc-tures in the gel-spun fibers can be distinguished by means of DSC experiments on strained fibers. On the basis of these xperiments a qualitative prediction of the final ten-sile properties can be made. DSC experiments on (un)strained hot-drawn fibers show that in the case of shish-kebab structures an incomplete transformation i to a fibrillar structure takes place which partly explains the low tensile strength. Chain slippage which becomes possible after the orthorhombic-hexagonal ph se transition is involved in the fracture mechanism. The shift of the orthorhombic-hexagonal ph se transition to higher temperatures with increasing tensile strength indicates that he increase in strength corre-sponds to an increase in length of the crystal blocks. Consequently, creep failure also occurs at higher stresses. The melting behavior of cold-drawn and hot-drawn fibers is qualitatively similar, but the transformation i to a fibrillar structure is more complete in the latter case