Showing papers by "DSM published in 1979"

Ultrahigh-strength polyethylene filaments by solution spinning/drawing, 2. Influence of solvent on the drawability†

Abstract: High-modulus structures of linear polyethylene with Young’s moduli of 70 GPa may be generated, for example, by drawing meltspun fibers to very high draw ratios’), solid-state extrusion (e. g., cf.’)) and by the solution-crystallization technique referred to as surface growth3). The tensile strength of the drawn and extruded materials is usually found below 1 GPa, whereas the longitudinal crystals of Zwijnenburg and Pennings may have a strength as high as 3 GPa. The superior strength of the latter filaments, which have comparable Young’s moduli, is due to the high molecular weight of the polymer sample used4*’). Previous attempts to draw or extrude polyethylene of similar molecular weight to high draw ratios only succeeded at relatively high temperatures, in fact above the melting point, where the effectiveness of the chain-extension process is known to be low (see6)). The structures thus produced, therefore, exhibited but moderately improved mechanical properties6). In a wide-ranging study on the processability of high molecular weight polymers it has been found that the effective drawability of these materials is drastically enhanced by spinning” or casting from dilute solutions. This effect will be illustrated in the present paper for polyethylene, and this improved drawability will be discussed in terms of a favourable intermolecular topology of the polymer.

Ultrahigh-strength polyethylene filaments by solution spinning and hot drawing

Abstract: 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 Young's 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 Young's 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 Young's 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.

A small angle X-ray scattering study of polyethylene fibres, using the two-dimensional correlation function

Abstract: By Fourier transformation of the intensity distribution in the small angle X-ray scattering diagram of a polymer fibre one obtains the corresponding two-dimensional correlation function. This is compared with correlation functions calculated on the basis of different models of the semi-crystalline morphology. Here, two steps may be distinguished: in the first, the correctness of a model may be checked with the aid of qualitative features, such as the relative positions and sizes of positive and negative areas; in the second a quatitative agreement is pursued by fixing the various parameters involved. This method was applied to cold drawn low density polyethylene before and after annealing at different temperatures. In the case of the non-annealed sample, the microparacrystalline model, discussed byHosemann andLoboda-Cackovic (J. Appl. Cryst.11, 540 (1978)) was found to give the best fit. Annealing at 80 °C or higher temperatures seems to lead to what has been indicated as a three-dimensional chess-board structure; it consists of fibrils in which crystalline and amorphous regions alternate in such a way that the crystalline regions in a fibril are adjacent to amorphous regions in neighbouring fibrils.

Metal Surface Area and Metal Dispersion in Catalysts

Abstract: A survey is presented of a number of methods for the determination of free-metal surface areas. The following metals are dealt with: iron, copper, silver, gold, nickel, cobalt, palladium and platinum. Alloy catalysts are not considered. Recommendations are made with respect to the choice of the adsorbate, the measuring technique and data interpretation.

Phase equilibria in multicomponent polymer mixtures

Abstract: In recent years thermodynamic equilibrium properties of amorphous polymer blends have been the subject of increasing interest. Experimental techniques, known in the study of polymer solutions, have been applied to blends and have been modified to deal with highly viscous systems. Determination of critical points, spinodal and cloud-point curves are now well possible by means of a low-speed centrifuge, pulse induced critical scattering and the centrifugal homogenizer. The classic Flory-Huggins model cannot describe the experimental results. Improvements can be made by the introduction of the contact surface areas of the segments, and by correcting the combinatorial entropy of mixing for orientational effects related to chain flexibility. Two-peaked spinodals may furthermore be described with a model accounting for three concentration ranges in the blend, the two dilute solutions of one polymer in the other and an intermediate range of uniform segment density. As a third possibility the introduction of holes in the lattice (simple lattice gas) can also lead to qualitatively correct descriptions, even in those cases where the phase diagram is still more complex (system poly(styrene-co-acrylonitrile)/polymethylmethacrylate) and shows three miscibility gaps. Strictly-binary polymer mixtures with a bimodal cloud-point curve should show two stable critical points. The fact that we did not find more than one may be attributed to polydispersity which easily shifts one of the critical points into the experimentally inaccessible meta-stable region.

A simple procedure of accounting for physical aging in the prediction of the modulus of glassy plastic materials

Abstract: The basic relationships are presented for predicting the creep and stress relaxation as a function of physical aging, loading time, and temperature of amorphous polymers processed under such conditions that their thermal treatment amounts to a quench from the melt to the glassy state. A nomogram construction, based on these relations, is proposed and developed for a particular polymer, namely an extrusion type acrylonitrile-butadiene-styrene (ABS), RONFALIN EST. The applicability of the procedure is restricted to the isothermal viscoelastic behavior at low stresses and strains of unplasticised amorphous plastic materials quenched from the melt to the glassy state.

Preparation of tris-(beta-hydroxypropyl) isocyanurate

Abstract: The invention concerns a process for the preparation of tris-(β-hydroxypropyl)-isocyanurate through reaction of propylene oxide with cyanuric acid. According to the invention the reaction is effected in a polyol, which is liquid under the process conditions and in which tris-(β-hydroxypropyl)-isocyanurate is soluble or miscible, in the absence of a catalyst. Preferably a polyol is used which may be used in admixture with tris-(β-hydroxypropyl)-isocyanurate in polyurethane synthesis. The advantages of the process are that the propoxylation does not proceed too far, and that there is no need to remove catalyst residues or solvent.