The structure of high-strength ultrahigh-molecular-weight polyethylene fibres fabricated by the gel-spinning method

Abstract

In orientation drawing of UHMPE (ultrahigh-molecular-weight polyethylene) fibres, conformational rearrangements take place that enrich the conformation set of the polymer with T-isomers and impoverish it in G-isomers. The basic increase in the orientation of T-isomers is observed in the initial stages of drawing. In orientation drawing of UHMPE gel fibre, no significant increase was found in the concentration of molecular breaks, a necessary condition for effective strengthening of the fibre. Two types of crystallites (crystallites in folded and straightened chains) and a mesophase were found in samples of multifilament UHMPE fibres. There is a smooth transition from the structure of the foldedchain crystallite (FCC) type to a structure of the straightened-chain crystallite (SCC) type with an increase in the draw ratio due to formation of a rigid amorphous phase of straightened segments of the polymer chains.One of the main problems of polymer technology is to develop new and to improve existing methods of obtaining polymeric materials with extreme properties, particularly with high strength indexes. Gel spinning is currently used as the most effective and industrially feasible method of strengthening flexible-chain polymers [1,2]. It is possible to increase the strength of ultrahighmolecular-weight polyethylene (UHMPE) fibres by one order of magnitude in the stage of orientation drawing of spun gel fibres (the most important stage of gel spinning). However, the strength values attained are no greater than 10% of the theoretical limit [3]. It is important to study the rearrangement of the molecular and supramolecular structure of the polymer that take place during drawing and to establish their correlation with the mechanical properties for further orientation strengthening of fibres.We investigated the effect of orientation drawing on the structure of UHMPE fibres obtained by gel spinning and their elastic-strength properties. Comprehensive studies were conducted with such physical methods as Fourier IR spectroscopy, wide-angle x-ray diffraction, differential scanning calorimetry, and mechanical tests.We studied multifilament fibres (280 filaments) made from UHMPE with a molecular weight of M w = 1.9⋅10 6 drawn at different ratios and at different temperatures. The fibres were fabricated from a 3% spinning solution of UHMPE in paraffin oil in the conditions of the experimental setup at the All-Russian Scientific-Research Institute of Synthetic Fibres [4]. Drawing of the fibres was divided into three stages. The fibre was initially drawn at a temperature of 110°C to ratio λ = 3. In the second stage, after shrinkage, the fibre underwent one-stage thermal orientation drawing at 125-128°C. Both drawing stages were conducted in solvent medium. The third drawing stage was conducted in air at 140-145°C.The IR spectra of filament fibres laid in a monolayer parallel to each other on the frame holder were recorded in polarized light on an Equinox 55 Fourier IR spectrometer.The molecular structure and rearrangements in the...

Investigation of MWCNT Reinforcement on the Strain Hardening Behavior of Ultrahigh Molecular Weight Polyethylene

“…Strong Weissenberg effects [11] have to be overcome during the solution preparation and extrusion phases. Gel-spinning process has been used by many researchers to produce UHMWPE filaments [11][12][13][14]. In this process polymer is dissolved in a solvent and spun through a spinneret.…”

Change in the structure of a polyethylene fiber, obtained by the gel-formation method, during its orientational drawing

“…Information on the relative content of SSCs (T m -conformers) in the nanofi brils of a fi lament with a large stretch ratio can be obtained by Fourier-transform infrared spectroscopy [10]. Figure 4 shows the changes that occur in the conformational composition of PE macromolecules during the drawing of a fi lament to  = 80.…”

“…The extent of the molecular orientation <cos 2 > of the straightened and convoluted segments of chains was determined in specimens of fi laments with different stretch ratios by the method of infrared dichroism [10]. Figure 5 shows the dependence of the degree of orientation of TM-conformers and GTG-conformers on the value of .…”

Carbon Nanotubes and Graphene as Additives in 3D Printing

“…However, it is not feasible to produce UHMWPE filaments by conventional extrusion due to the high Weissenberg effects [25] that would likely affect the flux during extrusion both for filament production and 3D printing. An alternative would be to use the gel-spinning technique [26] in which the polymer is dissolved and spun. The addition of MWCNTs can be problematic as they tend to aggregate during the solvent evaporation stage, but the problems were addressed by using a range of techniques including sonication, melt mixing, and extrusion [24].…”