Structural-mechanical transformations in highly oriented polyethylene fibres in the preparation of very highly reinforced organoplastics

Conclusions -- From analysis of the change in mechanical properties in texture x-ray diagrams and photographs from scanning microscopy, it is possible to state that the reprofiling temperature of polyethylene fibres in the preparation of UROP should be lower than the melting point to the extent of 20–30%.-- For maximum retention of the original fibre properties in the UROP, it is advisable to carry out transverse compression simultaneously with axial stretching.-- Increasing the molecular weight of the starting polyethylene fibres leads to a decrease in the degree of utilization of their elastic-strength properties in the UROP, although the absolute values of the basic mechanical characteristics of the plastics are raised.Translated from Khimicheskie Volokna, No. 4, pp. 42–45, July–August, 1991.     

Thermal conductivity of highly oriented polyethylene

We have measured the thermal conductivity of oriented polyethylene both along and perpendicular to the draw direction for draw ratio λ between 1–25 and in the temperature range of 120 to 320K. The results for λ ? 5 have been analysed in terms of the modified Maxwell model while the further increase of thermal conductivity along the draw direction at higher λ has been explained by the Takayanagi model. The Young's modulus and thermal conductivity along the draw direction for the sample with λ = 25 were found to be 64 GN/m² (at 220K) and 140 mW/cm K (at 300K), respectively, which are extremely high values for polymers. This material, which is a good electrical insulator and yet has a high thermal conductivity, may be useful in electrical applications requiring large dissipation of heat.     

Shrinkage of highly oriented gel-spun polymeric fibres

Summary The melting and shrinking process of gel-spun hot-drawn UHMWPE fibres has been investigated. Instead of being superheated, the highly oriented fibres start to melt at the fibre ends and shear bands, at a temperature near the equilibrium melting temperature of polyethylene. For draw ratios of 40, the fibre transforms into a ribbon shape upon melting. This change in shape could be prevented by constrained heating before shrinkage. Ribbon-like melting was also observed for gel-spun hot-drawn poly(L-lactide) fibres.     

Sorption and diffusion of solvents in highly oriented polyethylene

Measurements have been made of the sorption and diffusion coefficients of various solvents in oriented linear polyethylene pipe produced by hydrostatic extrusion. In all cases the equilibrium sorption is a factor of about ten less than that for isotropic linear polyethylene, and the diffusion coefficients are a factor of about a hundred less.     

The structure of highly oriented high modulus polyethylene

A comparative study of the structure of uniaxially-oriented bulk samples of linear PE of various molecular weights over a wide range of draw ratios has been carried out by means of small and wide angle X-ray analysis, NMR-spectroscopy and DSC. The structure of oriented high molecular weight PE samples, prepared by drawing single crystal mats to draw ratios up to 200, have also been studied. A large number of unfolded tie-molecules have been found to exist in the trans-conformation in PE amorphous regions. These tie-molecules, which connect the adjacent crystallites along the axis of orientation, and are not large crystals, account for the high mechanical properties of these samples. It has been shown that in the course of the orientation process, chain unfolding in the amorphous regions is accompanied by the formation of continuous linear systems consisting of several coherent crystallites and tie-molecules. These are coherently aligned along the macromolecular axis.     

The thermal expansion behaviour of highly oriented polyethylene

The thermal expansion behaviour of oriented polyethylene has been studied over the temperature range ?50°C to +20°C. In general the values for the thermal expansion coefficient in the orientation direction are negative and of a greater magnitude than the c-axis expansion for the crystal, which is approached at ?50°C. This remarkable effect has been quantitatively related to the influence of an internal shrinkage force, and the changes in expansivity with temperature shown to relate primarily to the change in modulus with temperature.     

Dipolar-decoupled carbon-13 NMR study of highly oriented polyethylene films

Summary High-resolution solid-state ¹³C NMR spectra and ¹³C relaxation times T₁ and T₁ have been measured at 40–100° C for uniaxially oriented polyethylene films with the drawing direction parallel to the magnetic field; this sample has a unique morphological structure that the noncrystalline chains are nearly disordered irrespective of the high degree of drawing. A sharp resonance line(line A) appears at the position corresponding to the principal value ₃₃ of the chemical shift tensor for the CH₂ carbons with the trans-trans conformation. Another sharp linedine B) is observed at almost the same chemical shift as for the CH₂ carbons of polyethylene in solution. Although these observations are similar to those for a cold-drawn polyethylene sample reported previously, line B is much enhanced in intensity and the linewidth is narrower in the present sample, reflecting the disorientation of the noncrystalline component. It is found from T₁ measurements that line A contains two components with different molecular mobility, both being assigned to the crystalline components. On the other hand, the line B is composed of a single component assignable to the noncrystalline component with liquid-like molecular mobility.     

Model description of the nonlinear viscoelasticity of oriented polyethylene terephthalate and polycaproamide fibres

The possibility of quantitatively describing and predicting the nonlinear viscoelasticity of fibres in the region of low strains based on a mechanical model is demonstrated. __________ Translated from Khimicheskie Volokna, No. 3, pp. 12–15, May–June, 2006.     

Photoinitiated grafting of methyl methacrylate on highly oriented polyethylene: Effect of draw ratio on grafting

Modification of highly oriented polyethylene was performed using a photoinitiated grafting technique. The samples were first coated with photoinitiator and then exposed to methyl methacrylate vapor under UV light (λ > 290 nm) at 60°C. The extent of grafting was studied as a function of draw ratio. It was found that the extent of grafting decreased significantly as the draw ratio was increased. Control samples of undrawn samples with different thermal histories suggested that there was another factor in addition to crystallinity that influences the extent of grafting. It is proposed that amorphous orientation or taut-tie molecules reduce the photoinitiation process. Gravimetric and attenuated total reflectance-IR measurements indicated that the grafting reaction can occur below the sample surface (or internal grafting) and that the proportion of surface grafting increases with increasing draw ratio. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 465–470, 1998     

SEM studies on helically oriented polypropylene fibres

The surface morphology of the PP fibres with internal helical texture were studied. The studies were carried out by the direct observation of the untreated fibre surface, and by the ‘marked deformation’ method of microscopical objects using a ‘JEOL’ scanning electron microscope. The results showed the helical internal texture of these fibres.     

Irradiation of highly oriented polyethylene fibers in the atmosphere of some vinyl monomers: Effect on compressive strength

Highly oriented polyethylene fibers have been modified by γ‐irradiation in the presence of some vinyl monomer vapors, followed with further annealing in the atmosphere of the same monomer. Two types of vinyl monomers that are known to produce polymers with different glass transition temperatures, namely methyl methacrylate and vinyl acetate, were studied for their effect on the compressive strength of the fiber. It was found that a significant improvement in compressive strength, measured by tensile recoil test, was obtained. The level of improvement was affected by heat treatment and the presence of monomer during irradiation. Modification with vinyl acetate was found to be more effective than methyl methacrylate. These facts suggest that the improvement in compressive strength was attributable to several factors, including structural relaxation, the presence of graft copolymer, and energy dissipation ability of the graft copolymer. It is speculated that lateral integrity of the fiber is one of the key factors that prevents sliding of microfibril and possibly lateral or circumferential expansion of the fiber to accommodate kink band. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2494–2502, 2001     

Basic directions of research in the area of preparing carbon fibre materials based on hydrocellulose fibres

Conclusions -- A wide assortment of CFM based on viscose technical yarn has been developed in the VNIIPV and introduced into industry.-- Basic trends of studies in the area of preparing CFM based on HCF have been defined: improvement in the quality of viscose technical yarn; solution of ecological problems in its manufacture; optimization of technology with the purpose of improving characteristics and reducing costs; the development of CFM with qualitatively new characteristics; and the search for new regions of application.VNIIPV. Translated from Khimicheskie Volokna, No. 3, pp. 8–10, May–June, 1991.     

Preparation of highly filled ferrite-containing fibres based on fluororesin and their properties

Institute of Synthetic Polymeric Materials, Moscow. Siberian Physico-Technical Institute, Tomsk. Institute of Radio Techniques and Electronics, Moscow. Moscow State Textile Academy. Translated from Khimicheskie Volokna, No. 3, pp. 52–54, May–June, 1992.     

Microstructure control of highly oriented short carbon fibres in SiC matrix composites fabricated by direct ink writing

A novel method is proposed for fabricating highly oriented carbon fibre reinforced SiC ceramic composites (C_f/SiC) by direct ink writing (DIW). For the first time, the control of carbon fibers’ orientation in DIW was studied by numerical simulation. An interfacial layer was prepared by chemical vapor infiltration (CVI). The microstructure and phase composition of C_f/SiC were studied by scanning electron microscopy and X-ray diffraction, respectively. The results showed that fibers of different interfacial thicknesses could be obtained effectively by varying the CVI time. The breakage of short fibres remarkably improved the fracture toughness of the parts. The specimens showed excellent mechanical properties with bending strength of 274 ± 13 MPa and fracture toughness of 5.82 ± 0.25 MPa m^1/2. This method could be extended to the preparation of other resin and ceramic composites.