DSC experiments on gel-spun polyethylene fibers

Abstract

The tensile strength of gel-spun polyethylene fibers obtained after hot-drawing depends on spinning conditions such 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 hotdrawing lead to fibers with poor properties. This is in contrast to hot-drawn fibers obtained from gel-spun fibers with a lamellar structure. Lamellar or shish-kebab structures in the gel-spun fibers can be distinguished by means of DSC experiments on strained fibers. On the basis of these experiments a qualitative prediction of the final tensile properties can be made. DSC experiments on (un)strained hot-drawn fibers show that in the case of shish-kebab structures an incomplete transformation into a fibrillar structure takes place which partly explains the low tensile strength. Chain slippage which becomes possible after the orthorhombic-hexagonal phase transition is involved in the fracture mechanism. The shift of the orthorhombic-hexagonal phase transition to higher temperatures with increasing tensile strength indicates that the increase in strength corresponds 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 into a fibrillar structure is more complete in the latter case.

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

“…Tensile strengths (GPa) The mechanical properties of the drawn specimens are generally believed to depend mainly on the degree of orientation of the drawn specimens, as their molecular weights are constant [48,49]. As evidenced by the orientation analysis, at a fixed draw ratio, the orientation factor values of the drawn F 100 A 0.05 and F 100 A xM-0.025 fiber specimens prepared at the optimal purified and acid treated ATP contents are always higher than those of other F 100 A y and/or F 100 A xM-y fiber specimens prepared at ATP and/or acid treated ATP contents deviating from their optimal values, respectively.…”

SAXS experiments on voids in gel-spun polyethylene fibres

“…For example, for a crystallinity of the polyethylene of 60%, this contribution to the total scattering is 35.4% and 4.5% for void volume fractions of 1% and 10% respectively. The crystallinity of the extracted fibres is of the order of 60% to 70% as shown previously in our differential scanning calorimetry (DSC) study of gel-spun polyethylene fibres [25]. For a fibre with known crystallinity the volume fraction of voids can be calculated from the scattering 1 552 power t/2.…”

“…Its high scattering contribution complicates the study of the morphology of the extracted fibres [23,24]. The formation of porous structures can be ascribed to two facts.…”

“…The formation of porous structures can be ascribed to two facts. In the first place, the use of the volatile n-hexane for the extraction process results in a very fast, but incomplete, lateral shrinkage during the evaporation of hexane [23]. This process is, in particular, of interest for fibres containing a lamellar structure.…”

“…This process is, in particular, of interest for fibres containing a lamellar structure. For fibres with a shish-kebab structure the lamellar overgrowth prevents a close packing of the fibrils [23]. The porous fibres may be considered as a threephase system consisting of amorphous polyethylene, crystalline polyethylene and voids with electron densities, 0, of 0.489, 0.571 and 0 mol electron cm 3, respectively.…”