Process for preparing polyolefin gel articles as well as for preparing herefrom articles having a high tensile strength and modulus

A process is described for the preparation of highly stretchable high-molecular weight polyolefin gel articles and polyolefin gel articles prepared therefrom having combined high tensile strength and high modulus, wherein an initial shaped article of the polyolefin is exposed to or contacted with a swelling agent to form an intermediate swollen article, which is then converted to the gel state and then subsequently subjected to stretching at up to relatively high draw ratios

Study of Percolative Transitions with First-Order Characteristics in the Context of CMR Manganites

The unusual magneto-transport properties of manganites are widely believed to be caused by mixed-phase tendencies and concomitant percolative processes. However, dramatic deviations from "standard" percolation have been unveiled experimentally. Here, a semi-phenomenological description of Mn oxides is proposed based on coexisting clusters with smooth surfaces, as suggested by Monte Carlo simulations of realistic models for manganites, also briefly discussed here. The present approach produces fairly abrupt percolative transitions and even first-order discontinuities, in agreement with experiments. These transitions may describe the percolation that occurs after magnetic fields align the randomly oriented ferromagnetic clusters believed to exist above the Curie temperature in Mn oxides. In this respect, part of the manganite phenomenology could belong to a new class of percolative processes triggered by phase competition and correlations.Comment: 4 pages, 4 eps figure

Chondroprotective actions of selective COX-2 inhibitors in vivo: A systematic review

Knee osteoarthritis (OA) is a condition mainly characterized by cartilage degradation. Currently, no effective treatment exists to slow down the progression of OA-related cartilage damage. Selective COX-2 inhibitors may, next to their pain killing properties, act chondroprotective in vivo. To determine whether the route of administration is important for the efficacy of the chondroprotective properties of selective COX-2 inhibitors, a systematic review was performed according to the PRISMA guidelines. Studies investigating OA-related cartilage damage of selective COX-2 inhibitors in vivo were included. Nine of the fourteen preclinical studies demonstrated chondroprotective effects of selective COX-2 inhibitors using systemic administration. Five clinical studies were included and, although in general non-randomized, failed to demonstrate chondroprotective actions of oral selective COX-2 inhibitors. All of the four preclinical studies using bolus intra-articular injections demonstrated chondroprotective actions, while one of the three preclinical studies using a slow release system demonstrated chondroprotective actions. Despite the limited evidence in clinical studies that have used the oral administration route, there seems to be a preclinical basis for considering selective COX-2 inhibitors as disease modifying osteoarthritis drugs when used intra-articularly. Intra-articularly injected selective COX-2 inhibitors may hold the potential to provide chondroprotective effects in vivo in clinical studies

Chain-extended flexible polymers

High‐strength/high‐modulus structures such as fibres, tapes and rods can be produced currently on the basis of intrinsically flexible macromolecules. The prime example amongst these new developments is gelspinning of high‐molecular‐weight polyethylene resulting in fibrous structures possessing tenacities of 3–4 GPa and corresponding moduli up to appr. 150 GPa. The basic aspects of chain‐extension for polyethylene will be discussed in relation to the various routes toward oriented/extended PE structures as well as recent developments concerning the utilization of other flexible polymeric systems for the production of high‐strength/high‐modulus fibres

Memory effects in polyethylenes : influence of processing and crystallization history

The experimental timescale of memory effects related to restoring equilibrium viscoelastic properties in solution-cast linear and long-chain branched polyethylenes has been investigated. It was found that the crystallization history of low-density polyethylene and ultra-high-molecular-weight polyethylene, with respect to solid-state and melt properties, is lost after heating into the melt after a short period of time. The experimental timescale of memory effects is at least one order of magnitude shorter than the longest relaxation times in these materials, which correspond to reptative motion of macromolecules. The experimental results indicate that long-term memory effects related to the physical entanglement network in polyethylenes are absent and that equilibrium viscoelastic properties of polyethylene melts and solids and the concept of entanglement coupling are related to segmental rather than to macromolecular mobility

Basic aspects of solution (gel) spinning and ultra-drawing of ultra-high molecular weight polyethylene

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