The straight‐chain segment length distribution in xerogels of UHMWPE, which provide high drawability of gel‐derived fibers

Abstract

A series of ultra-high-molecular-weight reactor powders with different technological prehistory were utilized for obtaining fibers through the gel technology. The fibers prepared from some powders exhibited high draw ratios and good mechanical properties (Young's modulus and tensile stress) but other powders yielded fibers of very low drawability. The low-frequency Raman study revealed that the straight-chain-segment (SCS) length distributions in dried gels prepared from powders of ''drawable'' group are bimodal, while the gels issued from powders unsuitable for fiber drawing have unimodal length distributions of SCS.

Structure of the crystalline phase in gelled polyethylene and its effect on the orientational ability of gel fibers

“…As was noted in [20], during gel formation of highly oriented fibers, the strongest and most high modulus products can be obtained from gels with the bimodal SCS length distribution. However, in [20], films were formed from gels via solvent removal.…”

“…(Note that the stack may contain more than two crystallites, but the folds of doubled length join only adjacent crystal lites). The existence of double (bounding two adjacent crystallites) folds was reported in a number of DSC [25] and low frequency Raman spectroscopy [16,20] studies. A "quantum" 2 to 4 fold increase in the length of folds of macromolecules during crystalliza tion of PE from very narrow weight fractions was observed with the use of small angle X ray scattering [26].…”

“…However, in [20], films were formed from gels via solvent removal. The drying pro cedure could distort the result because fibers were drawn from as prepared gels rather than from dry films, in which the gravitational setting could distort the polymer structure.…”

“…This finding was interpreted as a manifestation of crystallite clustering into stacks of lamellar crystallites linked by a certain number of extended tie molecules. It was found that the gels fea turing the bimodal SCS length distribution (i.e., those presumably containing stacks of crystallites) can be formed and that fibers with the best mechanical prop erties can be drawn [20]. Vibrational spectroscopy data indicating the pres ence of crystalline structures in the gels of ultrahigh molecular weight PE were supported by small angle X ray scattering data [16].…”

The Effect of Pressure-Induced Flow (PIF) Processing on the Thermal Stability and Mechanical Properties of Ultra-High Molecular Weight Polyethylene (UHMWPE) Gel

“…Weiss et al (2006) highlighted that any method used to measure the yield stress can also be utilized to devise a rheological criterion for gelation. Pakhomov et al (2007) studied the correlation between the parameters of crystallites in gels and the drawability of gel-derived fibers.…”