Pj Piet Lemstra

Ultra-high-strength polyethylene filaments by solution spinning/drawing

This paper deals with ultra-high-strength monofilaments of linear polyethylene that are produced by solution spinning and subsequent hot drawing at 120° C. The influence of the draw ratio on the mechanical and thermal properties of the fibres was investigated. Some salient features of a polyethylene filament with a draw ratio of 31.7 are: tensile strength at break=3.0 GPa, Youngs modulus=90 GPa and DSC-melting point at a scan speed of 10° C min−1=145.5° C. The modulus was found to depend linearly on the draw ratio. The tensile strength tended, by contrast, to approach an upper limit at high draw ratios. Additional morphological and X-ray studies revealed an extremely good orientation of the macromolecules in the fibre direction of the highly drawn polyethylene monofilaments.

Ultrahigh-Strength Polyethylene Filaments by Solution Spinning and Hot Drawing

The past decade has seen a rapidly growing interest in highmodulus and high-strength polymeric fibers (see e.g. CIFERBI, WARD 1979). The methods to prepare these filaments are based on cold/ hot drawing (CAPACCI0, WARD 1974), two-stage drawing (CLARK, SCOTT 1974), hydrostatic (GI~SON et al. 1974) and direct (SOUTHERN, POR~ER 1970; TAKAYANAGI et al. 1966) extrusion, elongational flow (PENNINGS et al. 1972; ZWIJNENBURG, PENNINGS 1976) and on the intrinsic rigidity of particular macromolecules in solution (e.g. CIFERRI 1975). High-modulus polyethylene filaments with Youngs moduli of about 70 GPa have been produced by CAPACCI0 and WARD (1974) through drawing. PORTER et al. (1970) performed solid-state extrusion to obtain polyethylene structures with similar mechanical properties. The tensile strength of these materials is usually found below I GPa (CAPACCI0, WARD 1975; KOJIMA, PORTER 1978). Longitudinal crystals of polyethylene with a Youngs modulus of 100-120 GPa and a tensile strength of 3-4 GPa have been obtained from solution by ZWIJNEN~JRG and P~NNINGS (PENNINGS 1977) in a Couette-type apparatus employing a crystallization technique referred to as surface growth. This short communication describes some preliminary results on alternative routes to produce high-strength and high-modulus polyethylene filaments with a uni-axial Youngs modulus of 90 GPa and a tensile strength of 3 GPa. The method is based on a simple solution-spinning and drawing process that can be performed continuously.

Ultra-high strength polyethylene filaments by solution spinning/drawing. 3. Influence of drawing temperature

Abstract The influence of the temperature on the drawing behaviour of gel-fibres, which were obtained by spinning of a 2% w/w solution of high molecular weight polyethylene ( M w = 1.1 × 10 6 ) in decalin, was studied in the range from 70 to 143°C. It was found that the drawing temperature, like the presence of solvent in the gel-fibres, affected the maximum attainable draw ratio, but did not influence the effectiveness of the hot drawing below the melting point of the polymer.

Speciality products based on commodity polymers

Abstract Synthetic polymers constitute an established class of materials. The distinction often made between the mass-produced commodity polymers and speciality polymers is less clearly defined, since with novel preparation techniques bulk polymers are now increasingly used in speciality applications. Such new applications of commodity polymers often compete with the classical inorganic materials: metals and glasses. In this respect synthetic polymers often suffer from inferior performance with respect to strength/stiffness, barrier properties etc. These deficiencies are not necessarily intrinsically related to commodity polymers, as will be demonstrated with some examples: high-modulus/high-strength polyethylene fibres and barrier films based on polypropylene.

Nuclear magnetic resonance studies on sequence distributions in vinyl alcohol-vinyl acetate copolymers

Abstract The microstructure of vinyl alcohol-vinyl acetate copolymers was studied using both 13C n.m.r. and 1H n.m.r. techniques. The sequence lengths of vinyl acetate units calculated respectively from the compositional dyads, from the methylene absorptions and feom the triple carbonyl absorptions in the 13C n.m.r. spectrum were not identical, and moreover the dyad-triad relationship showed a large discrepancy. 1H and 13C n.m.r. spectra of a 5 mol% re-acetylated random sample, containing mainly isolated acetate units, indicate that configurational splitting complicates the assignment of the triple carbonyl absorption, which originally was interpreted as a compositional triad. After correcting for tacticities the results could be brought in line and the C=O resonances proved to be useful in obtaining information on the percentage of isolated vinyl acetate units and the sequence length nA2+ (the average length of vinyl acetate units ≥2).

Extended-chain structure for isotactic polystyrene: additional x-ray diffraction and calorimetric results

Abstract The recently discovered extended-chain structure in isotatic polystyrene gels opens new horizons on the stereochemistry of the polyolefins and molecular organization in polymeric gels. New X-ray fibre diffraction patterns obtained from stretched gels formed in different solvents support the contention that the structure is produced by intramolecular forces between continguous units probably via adjacent aromatic appendages.

High-strength/high-modulus structures based on flexible macromolecules : gel-spinning and related processes

Amongst the various developments in the area of high-performance fibres, two major routes can be discerned which are completely different in respect of the starting (base) materials, respectively intrinsically rigid as opposed to intrinsically flexible macromolecules.

Ultra-drawing of High-Molecular-Weight Polyethylene Cast from Solution IV. Effect of Annealing/Re-Crystallization

The ultra-drawability of spun/cast UHMW (ultra-high-molecular-weight)-Polyethylene is lost gradually upon annealing, but almost instantaneously upon melting/re-crystallization. This phenomenon poses severe limitations on processing of so-called “dis-entangled” polyethylene, as will be discussed below.