Preparation and characterisation of biodegradable starch-based nanocomposite materials

Different formulations of biodegradable starch-polyester blend nanocomposite materials have been film blown on a pilot scale film blowing tower. The physical properties of different films have been examined by thermal and mechanical analysis and X-ray diffraction. The results show that the addition of an organoclay (from 0 to 5 wt%) significantly improves both the processing and tensile properties over the original starch blends. Wide angle X-ray diffraction (WAXD) results indicate that the best results were obtained for 30wt% starch blends, and the level of delamination depends on the ratio of starch to polyester and amount of organoclay added. The crystallisation temperature of the nanocomposite blends is significantly lower than the base blend. This is probably due to the platelets inhibiting order, and hence crystallisation, of the starch and polyester. The mechanical and thermal properties of the blends are also sensitive to the way the clay particles are dispersed. (C) 2003 Society of Chemical Industry.

Polyethylene-layered silicate nanocomposites for rotational moulding

A series of polyethylene-layered silicate nanocomposites has been studied as possible new candidates for rotational moulding. Two organically treated layered silicates were melt-compounded into a maleated linear low-density polyethylene host polymer at loadings of 6 and 9%, by weight. The morphology and properties of the nanocomposites were assessed by using dynamic mechanical thermal analysis, parallel-plate rheometry, wide-angle X-ray diffraction and transmission electron microscopy. The sintering behaviour of the nanocomposites was qualitatively assessed via hot-stage microscopy, indicating that the choice of nanofiller will play an important role in terms of producing nanocomposite materials with acceptable processability for rotational moulding. (C) 2003 Society of Chemical Industry.

Simultaneous observations of ionospheric quasiperiodic scintillations from short and long meridional baselines using VHF transmissions from transit satellites

For the first time it was possible to observe regular quasiperiodic scintillations (QPS) in VHF radio-satellite transmissions from orbiting satellites simultaneously at short (2.1 km) and long (121 km) meridional baselines in the vicinity of a typical mid-latitude station (Brisbane; 27.5degreesS and 152.9degreesE geog. and 35.6degrees invar.lat.), using three sites (St. Lucia-S, Taringa-T in Brisbane and Boreen Pt.-B, north of Brisbane). A few pronounced quasiperiodic (QP) events were recorded showing unambiguous regular structures at the sites which made it possible to deduce a time displacement of the regular fading minimum at S, T and B. The QP structure is highly dependent on the geometry of the ray-path from a satellite to the observer which is manifested as a change of a QP event from symmetrical to non-symmetrical for stations separated by 2.1 km, and to a radical change in the structure of the event over a distance of 121 km. It is suggested the short-duration intense QP events are due to a Fresnel diffraction (or a reflection mechanism) of radio-satellite signals by a single ionospheric irregularity in a form of an ellipsoid with a large ionization gradient along the major axis. The structure of a QP event depends on the angle of viewing of the irregular blob from a radio-satellite. In view of this it is suggested that the reported variety of the ionization formation, responsible for different types of QPS, is only apparent but not real. (C) 2003 Elsevier Science Ltd. All rights reserved.

Cross-linking of PFA by electron beam irradiation

The effect of electron beam radiation on a perfluoroalkoxy (PFA) resin was examined using solid-state high-speed magic angle spinning F-19 NMR spectroscopy and FT-IR spectroscopy. Samples were prepared for analysis by subjecting them to electron beam radiation in the dose range 0.5-2.0 MGy at 633 K, which is above the crystalline melting temperature. The new structures were identified and include new saturated chain ends, short and long branches, unsaturated groups, and cross-links. The radiation chemical yield (G value) of new long branch points was greater than the G value of new chain ends, suggesting that cross-linking is the net radiolytic process. This conclusion was supported by an observed decrease in the crystallinity and an increase in the optical clarity of the polymer.

Pseudo-randomness of round-off errors in discretized linear maps on the plane

We analyze the sequences of round-off errors of the orbits of a discretized planar rotation, from a probabilistic angle. It was shown [Bosio & Vivaldi, 2000] that for a dense set of parameters, the discretized map can be embedded into an expanding p-adic dynamical system, which serves as a source of deterministic randomness. For each parameter value, these systems can generate infinitely many distinct pseudo-random sequences over a finite alphabet, whose average period is conjectured to grow exponentially with the bit-length of the initial condition (the seed). We study some properties of these symbolic sequences, deriving a central limit theorem for the deviations between round-off and exact orbits, and obtain bounds concerning repetitions of words. We also explore some asymptotic problems computationally, verifying, among other things, that the occurrence of words of a given length is consistent with that of an abstract Bernoulli sequence.