Photoinitiated crosslinking of low density polyethylene. V: Orientation in stretched samples

Low density polyethylene (LDPE) is extruded, stretched, and photocrosslinked at different temperatures with different stretch rations in a continuous production line. Three different sequences are adopted: crosslinking before drawing, crosslinking after drawing, and crosslinking during drawing. The effect of drawing is studied by measuring the tensile properties. The increase of tensile strength and the decrease of elongation at break after stretching are related to chain orientation in crystalline morphology measured by X-ray diffraction. Thermal analysis by differential scanning calorimetry (DSC) supports these results. Owing to chain relaxation, the effects of orientation by stretching are significant only when the samples are drawn at a temperature not much higher than the melting point. Annealing of the drawn samples at a temperature above the melting point shows that the orientation in a crosslinked sample is retained for a much longer time than in an uncrosslinked sample. For the crosslinked samples, it is found that crosslinking after or during drawing gives a material with lower shrinkage upon heating; however, crosslinking before drawing gives a heat-shrinkable material.     

Inflammation as a cause of malnutrition, atherosclerotic cardiovascular disease, and poor outcome in hemodialysis patients

Cardiovascular disease (CVD) remains the major cause of morbidity and mortality in end‐stage renal disease (ESRD) patients treated by hemodialysis (HD). Although traditional risk factors are common in dialysis patients, they may not alone be sufficient to account for the unacceptable high prevalence of CVD in this patient group. Recent evidence demonstrates that chronic inflammation, a nontraditional risk factor that is commonly observed in HD patients, may cause malnutrition and progressive atherosclerotic CVD by several pathogenetic mechanisms. The cause(s) of inflammation in HD patients is multifactorial and includes both dialysis‐related (such as graft and fistula infections, bioincompatibility, impure dialysate, and back‐filtration) and dialysis‐unrelated factors. Although inflammation may reflect underlying CVD, an acute‐phase reaction may also be a direct cause of vascular injury. Available data suggest that proinflammatory cytokines play a central role in the genesis of both malnutrition and CVD in ESRD. Thus, it could be speculated that suppression of the vicious cycle of malnutrition, inflammation, and atherosclerosis (MIA syndrome) would improve survival in dialysis patients. As there is not yet any recognized, or even proposed, targeted treatment for ESRD patients with chronic inflammation; it would be of considerable interest to study the long‐term effect of various anti‐inflammatory treatment strategies on nutritional and cardiovascular status as well as outcome in these patients.     

Application of computed X-ray tomography scanning in the study of thermo-oxidative degradation of thick-walled filled natural rubber vulcanizates

The aging of five thick-walled natural rubber compounds has been studied by computed X-ray tomography scanning and crosslink density measurements. The compounds were compouded as ordinary carbon-black-filled rubbers with sulfur and peroxide as curing agents. The rubber samples were aged in air at 70, 100, and 150°C for 1000h. The relatively new technique of computed X-ray tomography scanning proved to be a good method for studying the aging procedure, and especially for following the crack propagation in the surface. Antioxidants (TMQ and 6PPD) had a low effect on the resistance toward oxidative degradation and crosslinking under these conditions. Surprisingly, the efficient sulfur-vul-canized material had a poor resistance toward thermal degradation. When the crosslink density and the computed X-ray tomography scanning results were compared, it was assumed that the computed X-ray tomograph detected oxygen in the surface, both as elementary oxygen and as oxygen in degradation products, i.e., in carbonyls. The results agree well with the theory that oxidative aging is limited by the ability of the oxygen to diffuse into the material.     

Thermal destruction of PCB and hexachlorobenzene

PCB and hexachlorobenzene are considered to be two environmental compounds of concern that are most difficult to destroy. This report describes experiments that have been carried out in order to obtain basic data for appraisal of the risks involved in the thermal destruction of PCB and hexachlorobenzene.The investigation indicates that it is possible to destroy PCB by incineration provided that the transit time is sufficiently long. In the pilot scale incinerator used, a transit time of more than two seconds was required to obtain a residue of PCB that was less than 100 mg/kg PCB fed into the incinerator. It was not possible to determine any fixed relationship between the temperature and the PCB residue within the temperature range examined (675–1000°C). The investigation also shows that hexachlorobenzene is formed in association with the combustion of PCB and that the rate of formation increases at high temperatures (35 mg HCB/kg PCB at 1000°C).A temperature of 950°C is needed for the destruction of hexachlorobenzene if the residue is to be less than 100 mg HCB/kg HCB. At 800°C, with a transit time of about 2 s, there is a residue of approximately 1200 mg/kg.     

Graft copolymerization onto starch. II. Grafting of acrylonitrile to granular native potato starch by manganic pyrophosphate initiation. Effect of reaction conditions on grafting parameters

The effect of reaction conditions on the composition of native potato starch–polyacrylonitrile graft copolymers initiated by manganic pyrophosphate onto starch slurries at 30°C has been examined. In general, when the Mn³⁺ ion concentration was increased from 0.15 × 10^?3M to 3.0 × 10^?3M (other conditions kept constant), an increase in conversion of monomer to polymer and % add-on was observed, whereas frequency of grafts (anhydroglucose units, AGU, per grafted chain) decreased. Also, the average molecular weights of grafts showed a decrease from 2.2 × 10⁵ to 1.5 × 10⁵. Increasing the concentration ratio of starch to monomer during polymerization by a factor of 3 produced an increase in the conversion of monomer to polymer, whereas an increase in frequency of grafts (AGU/chain) was obtained. Values of % add-on and average molecular weights of the grafts showed, however, a decreasing tendency. It was observed that grafting onto starch took place readily even at acid additions as low as 10 × 10^?3M H₂SO₄ (pH ?1.8). Selective solvent extraction of homopolymer and extremely low conversions of monomer to polymer (0.1%–1.5%) in duplicate runs without addition of starch indicated that grafting efficiencies were high in all cases. An attempt has been made to interpret the results in terms of variations in factors such as initial ratio of (Mn³⁺)/(AGU), termination rate of acrylonitrile chain radicals by oxidation by Mn³⁺ ions, oxidation rate of radicals formed on anhydroglucose units by Mn³⁺ ions, and physical factors such as diffusion rate of Mn³⁺ ions through the polyacrylonitrile-grafted starch granules for terminating the radicals.     

Photoinitiated crosslinking of low density polyethylene: II. Morphology and properties

The crystalline morphology and physical properties of photocrosslinked polyethylene in a low density polyethylene (LDPE)-benzophenone (BP)-triallyl isocyanurate (TAIC) system have been studied. The results of X-ray diffraction and DSC thermal analysis indicate that the effect of crosslinking on the degree of crystallinity of the material is quite limited, but the presence of crosslinks can affect the regularity of the crystal regions. This is proposed to be responsible for the slight variation in properties of the crosslinked material at room temperature, such as the decrease of modulus and the changes of yield behavior. The main improvements in properties of the photocrosslinked polyethylene are found at high temperatures, especially above the melting point. The strength is increased, and the heat distortion temperature is enhanced significantly, as previously reported in the literature.     

Wobbling in modern motorcycles

Serious personal injuries have been reported, caused by motorcycles which suddenly began to wobble when ridden at moderate to high speed. A random sample of 1043 owners of 1978–1982 model year motorcycles was interviewed concerning their experience of wobbling in 1982. The response rate was 95%. Wobbling was reported by 45% of the owners, 8% reported at least one incident of severe wobbling. This figure indicates that about 6000 riders in Sweden experienced severe wobbling during 1982. Wobbling increased proportionately both with the distance ridden and engine displacement and was highest among those riders who make heavy use of the engine's power. A statistically significant difference in wobbling was found between Japanese and other manufacturers. The reported average speed where wobbling occurred was 118 .