New biomedical polyurethane ureas with high tear strengths

Biodegradable polyurethanes ureas (PUU) were synthesized by a two step polymerization. First a poly (ε-caprolactone) prepolymer was terminated with three different diisocyanates: lysinediisocyanate (LDI), 1,6-hexanediisocyanate (HDI) and 1,4-butanediisocyanate (BDI). Second the prepolymers were chain extended with 1,4-butanediamine. The degradation products of these polymers are non-toxic. The mechanical properties of the PUU are compared with those of three PU's. Compared to these PU's, the HDI and BDI based PUU showed a very high resistance to tearing. Received: 9 September 1996/Revised: 14 November 1996/Accepted: 18 November 1996     

Ultra-high strength polyethylene by hot drawing of surface growth fibers

Summary Hot drawing at 150°C has been applied to high molecular weight polyethylene fibers produced by flow induced crystallization in a Couette apparatus, referred to as the surface growth technique. A distinct improvement of the tensile properties of the fibers was noticed upon drawing. A tensile strength at break of 4.7 GPa was reached. Drawability is discussed in relation to fiber morphology. The shish-kebab like structure of the surface growth fiber was transformed into a morphology consisting of smooth fibrils upon drawing.     

SAXS experiments on voids in gel-spun polyethylene fibres

The morphology and properties of extracted gel-spun polyethylene fibres depend on the spinning conditions. The main structures in the extracted fibre are shish-kebabs and lamellae. Equatorial small-angle X-ray scattering (SAXS) experiments show that the former structure is very porous due to the presence of lamellar overgrowth preventing a close package of the backbone fibrils, whereas the latter structure is relatively dense. After hot-drawing, due to melting/recrystallization, both structures are transformed on a 100 nm scale into a dense structure consisting of shish-kebabs or fibrils containing a void volume fraction of about 1%, as revealed by the scattering power of equatorial SAXS experiments. Moreover, a slight decrease of the equatorial intensity especially at the smallest angles after treating the hot-drawn fibres with paraffin oil, points to a small contribution of multiple scattering to the equatorial scattering. This implies the presence of a superstructure of not too closely packed macrofibrils. SAXS measurements of strained ultra-high-strength polyethylene fibres show that no or very little void formation is involved in the fracture mechanism. Most probably this is due to the (partly) fibrillar structure.     

Short aramid-fiber reinforced ultra-high molecular weight polyethylene

Summary Ultra-High Molecular Weight Polyethylene (UHMWPE) is frequently used in artificial joints because of its high wear resistance. To extend the lifetime of these joints even further, it is necessary to decrease the wear rate. The wear rate may be decreased by blending UHMWPE with short aramid fibers. On account of the extremely high viscosity of UHMWPE mixing was accomplished by swirling the UHMWPE powder and the chopped fibers with compressed dry nitrogen, and a composite with fairly uniformly distributed and randomly oriented fibers was obtained by compression moulding. The failure behaviour of the composite changes from ductile for low fiber content to brittle failure for higher fiber content. The deviation of the experimental Young's modulus from the theoretical value can be explained by, among others, the void content. Preliminary results show that the wear rate of UHMWPE indeed decreases with incorporation of the aramid fibers.     

Suspension spinning of ultra-high molecular weight polyethylene

Summary This note deals with the preparation of ultra-high strength polyethylene filaments by suspension spinning and subsequent hot-drawing at 148 °C. Suspension spinning involves the flow of stabilized suspensions of high molecular weight polyethylene powder in a solvent mixture through a long heated tube. In the tube, which acts as the spinning apparatus, the polyethylene is dissolved after which the polymer solution is spun in air. Under appropriate conditions of spinning and hot-drawing monofilaments were produced with a tensile strength at break of 3.8 GPa and a Young's modulus of 124 GPa.     

Crosslinking of ultra-high strength polyethylene fibers by means of γ-radiation

Summary An ultra-high strength polyethylene fiber with an initial tensile strength at break of 3.0 GPa, was irradiated at room temperature under vacuum by means of ⁶⁰Co -radiation.Gelcontent and equilibrium volume degree of swelling of the gelfraction, were determined as a function of dose. From a plot of the effective network chain density versus dose, it was concluded that the fiber contained about 2 entanglements per number average molecule. Furthermore, a crosslinking efficiency of 0.33 crosslink per 100 eV of absorbed energy was found.Part 1 : cf⁵ It is a pleasure to acknowledge the support by the Netherlands Foundation for Chemical Research (S.O.N.) with financial aid from the Netherlands Organization for the Advancement of Pure Research (Z.W.O.).