N. H. Ladizesky

A study of the adhesion of drawn polyethylene fibre/polymeric resin systems

The effect of plasma etching and chromic acid treatment on the surface adhesion of ultra-high modulus polyethylene fibres to an epoxy resin has been studied. The adhesion was determined from pull-out tests, and showed a significant improvement for both plasma and acid treatments. The mechanism of failure, however, appeared to be different in the two cases. Untreated and acid-treated monofilaments showed a fairly smooth surface and failure of the pull-out samples involved sliding along the monofilament/resin interface. Plasma treatment, on the other hand, produced a remarkable structure on the monofilament surface, into which resin penetrated to produce a mechanical keying between monofilament and resin. Failure in the pull-out test then involved rupture within the monofilament.

Ultra-high-modulus polyethylene fibre composites: I—The preparation and properties of conventional epoxy resin composites

Abstract It has been shown that conventional techniques can be used to prepare epoxy resin composites incorporating ultra-high-modulus polyethylene (UHMPE) fibres as the reinforcing phase, either as continuous filament yarn or woven fabric. These composites showed very satisfactory values of stiffness and strenght, and very good energy absorption in Charpy impact tests. The interlaminar shear strength of the composites could be significantly increased by plasma etching of the fibres in oxygen gas. This treatment reduced resin cracking in flexural and impact tests, but did not reduce the impact energy absorption very greatly because the latter is primarily associated with plastic deformation of the fibres. The composites were also subjected to preliminary environmental tests, with very encouraging results.

Hydrostatically extruded HAPEX

Hydroxyapatite reinforced high density polyethylene composite (HAPEX™) has been developed for bone substitution. To improve its mechanical properties, HAPEX™ was hydrostatically extruded at different extrusion ratios after compression moulding. Substantial increases in the tensile and flexural properties of both unfilled polyethylene and HAPEX™ were achieved. It was evident that the higher the extrusion ratio, the stiffer and the stronger the extruded rods. The ductility of HAPEX™ was also significantly enhanced by hydrostatic extrusion. Hydrostatically extruded HAPEX™ possesses mechanical properties that are within the bounds for human cortical bone, which indicates its potential for load-bearing skeletal implant applications.

Fibre reinforcement of ceramic/polymer composites for a major load-bearing bone substitute material

Abstract A recently developed hot-compaction technology has been used to reinforce hydroxyapatite/polyethylene bone-substitute composites with woven, high-performance polyethylene fibres. The resulting systems have excellent compatibility between the phases, resulting in mechanical properties suitable for pros theses under high physiological loads. The manufacturing techniques allow different arrangements between the components and their relative merits and future possibilities are assessed.

Ultra-high-modulus polyethylene composites. III: An exploratory study of hybrid composites

Abstract Epoxy resin/fibre composites have been prepared by lamination of pre-preg sheets in which the reinforcing phase is glass, carbon or ultra-high-modulus polyethylene (UHMPE) fibres. Hybrid composites have also been produced with a sandwich structure of glass or carbon fibre layers enclosed symmetrically between UHMPE fibre layers. It has been shown that these hybrid composites can provide an unusual and potentially useful combination of mechanical properties, in terms of tensile modulus and strength, compressive strength and high impact energy, including the capability of withstanding high levels of deformation without disintegrating.

Hydroxyapatite/high-performance polyethylene fiber composites for high-load-bearing bone replacement materials

A combination of three technologies, high-performance fiber processing, fiber compaction, and hydrostatic extrusion has been used to produce hydroxyapatite/polyethylene bone analog composites with the highest stiffness and strength yet encountered in these systems, fully matching the values associated with cortical bone. These advantages of the new materials are complemented by satisfactory ductility. Observation of the melting behavior of the composites, together with an analysis of their hydrostatic extrusion characteristics, provides some understanding of the mechanisms leading to their superior mechanical performance.

Ultra-high-modulus polyethylene fibre composites: II—Effect of resin composition on properties

Abstract The mechanical behaviour of thermosetting resin composites reinforced with ultra-high-modulus polyethylene fibres has been studied. Polyester and epoxy resins with a range of chemical composition and different breaking elongations have been used. Although there were no major differences in mechanical behaviour due to resin composition, small but significant changes were observed in the impact energy and compressive strength of the different formulations.

The determination of Poisson's ratio and extensional modulus for polyethylene terephthalate sheets by an optical technique

The extensional compliance parallel to the draw direction, and the Poissons ratio in the plane of the sheet, have been determined for one-way drawn polyethylene terephthalate sheet. The technique was to photograph an electron microscope grid printed on the surface of the sheets and thus measure changes in dimension under load. The results show good internal consistency and those for the extensional compliance agree well with other determinations.

Extensional and shear compliances of polyethylene terephthalate sheets with orthorhombic symmetry

The St Venant relations are applied to obtain the three shear compliances of a polymer sheet with orthorhombic symmetry. The results for one way drawn polyethylene terephthalate sheet taken in conjunction with data for two extensional compliances, suggest that in this material, planar orientation is an important factor in determining the mechanical properties.

Shear strength of highly drawn linear polyethylene sheets

The shear strength of highly drawn linear polyethylene (HDLPE) sheets has been measured using sample shapes suggested by the lap joint technique. Several variables were investigated, including different parent polymers, irradiation dose, draw ratio, drawing methods and geometrical parameters. The lap joint theory has been successfully applied to several qualitative aspects of these experiments.