1994 рік

The axial creep of a textile fibre produced from a blend of fibre-grade polypropylene with 5 wt% of commercial atactic polystyrene was measured for 4 h over a range of stresses and temperatures. Using a combined time--temperature-stress superposition principle, a master curve was constructed, taking the reference temperature as room temperature. The master curve was found to cover a period of over 120 years, which is the lifetime of some geotextiles used in reinforcing applications, and could be of interest to designers of such products.

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Some problems in the measurement of stress-strain curves for thermoplastics are considered and the importance of measuring true stress-strain curves is emphasized. However, an increasing number of suitable curves have now been published of which the large majority have been found to comply with the following Gaussian equation: Otru? = Y+ Gp(22 - !/,~) where atrue is the true stress, Y is the extrapolated yield stress, Gp is the strain hardening modulus and 2 is the extension ratio. It is shown that the Considere condition for necking requires that Y/Gp> 3 and the available results support the proposition that this is a necessary condition for necking to occur. High values of Gp are observed in polymers with an extended chain conformation.

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Diglycidyl ether of bisphenoi A was cured with aliphatic diols of different chain length. The time to gelation and the end curing time or time to vitrification were determined at different curing temperatures and concentrations of diol, by means of thermal conductivity measurements. From these results Arrhenius activation energies can be obtained

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The electrochemically activated direct introduction of CO2 into poly(vinyl chloride), poly(vinyl bromide) and polybutadiene to form the corresponding acrylic acid copolymers is shown. It is demonstrated that the maximum extent of carboxylation is attained in the case of poly(vinyl chloride), when conducting controlled-potential electrolysis in dimethylformamide using a platinum cathode and sacrificial anode in an undivided cell. Possible pathways for the explored reactions are suggested

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The compatibilizing effect of a new graft copolymer of poly(ethylene glycol) (PEG) on nylon 6 (nylon 6-g-PEG) was investigated for nylon 6/poly(vinyl acetate) (PVAc) blends by using melting-point depression and X-ray diffractograms. It was found that nylon 6-g-PEG exhibits no compatibilizing effect for the nylon 6/PVAc blends, but the graft copolymer itself shows a miscibility window in its blends with PVAc for blend compositions containing less than 50 wt% of the graft copolymer

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This is the first of three papers on a recently discovered melt flow singularity during capillary flow of linear polyethylene, the 'extrusion window' at and close to 150°C. After placing the subject in its historical perspective, the various experiments are described by which the 'extrusion window' is revealed. These are: a minimum in pressure at around 150°C for constant material throughput and a maximum in material throughput at 150°C when a constant pressure level is maintained. In the former case the effect sets in at a critical piston velocity v c (i.e. shear rate ~c) and in the latter case at a critical pressure Pc. The v c value was found to be in a steeply inverse relation to molecular weight (M), obeying a power dependence of precisely - 4, while Pc was practically independent of M. The singularity in melt flow behaviour in question is inexplicable in terms of continuum rheology and points to a thermodynamic origin, more specifically to a phase transition at the particular temperature. In line with previous work, the formation of a transient, hexagonal 'mobile' crystal phase is suggested, here created through flow-induced chain extension. While seemingly the criticality in v c and the low end cut-off in M suggest the agency of elongational flow-induced chain stretching, such as is known to take place at the orifice entrance (a view held in the preceding publications), the newly found invariance of Pc with M now speaks decisively against the orifice being the site of initiation of the window effect. Rather, it points to a yield phenomenon, such as wall slip in the capillary, which itself would be the consequence of a chain-extension-induced phase transformation at the sharply defined temperature of 150°C, the plausibility of which is argued in this paper. Irrespective of the ultimate source of the effect, its potential advantage for certain melt processing operations should be apparent through requiring less energy for a given material throughput and by ensuring distortion-free extrudates under conditions where otherwise such distortions would be present. Other, more specific issues raised by the work include the relation of the newly found power law to the established M dependence of melt viscosity

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A crosslinked, L-histidyl group-introduced polymer catalyst, which was imprinted by a transition-state analogue of phenyl 1-benzyloxycarbonylamino-3-methylpentylphosphonate in the hydrolysis of pnitrophenyl N-carbobenzoxy-L-leucinate, was prepared from poly(2-methyl-2-oxazoline). The catalyst enhanced the hydrolysis of the L-leucine ester, in comparison to the hydrolysis of the L-phenylalanine and L-alanine esters

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Although the dielectric/~ glass-rubber relaxation has previously been observed in dipole-decorated branched polyethylenes and in linear polyethylene containing several mole per cent chlorine, it has not been observed in linear polyethylene containing very low dipole concentrations. Dielectric relaxation has been studied here in a linear polyethylene specimen (containing a few carbonyl groups per 1000 methylene units) in the hope of observing the/? process. The isochronal loss peak for the/~ relaxation is not well resolved from that for the c~ relaxation. However, it is found that the/~ process is very apparent as an increment in the isochronal dielectric constant scans. This was taken advantage of in characterizing the relaxation. In comparing the results with previous work it is found that there is a progression in the/~ relaxation Tmax location towards higher temperature as the degree of crystallinity increases through branched and linear polyethylene specimens

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Compression-moulded sheets of bacterially produced poly(fl-hydroxybutyrate) (PHB) blended with synthetic poly(e-caprolactone) (PCL) were investigated over the complete composition range from pure PHB to pure PCL. These blends are of potential interest because both components are biodegradable. Although PHB and PCL are immiscible, they formed mechanicaly compatible films containing phase-separated partially crystalline domains. The mechanical properties varied considerably with composition. The low melting point of PCL (~60°C) prevented temperature-resistant blends from being obtained for compositions containing less than 60% PHB.

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Two-dimensional wide- and small-angle X-ray scattering (WAXS and SAXS) patterns have been recorded at the Daresbury Synchrotron Radiation Source in time-resolved studies of changes in orientation and crystallinity during annealing of cold drawn samples of poly(aryl ether ether ketone) (PEEK). An amorphous PEEK film drawn uniaxially to a draw ratio of 2.0 was observed to give a well oriented non-crystalline WAXS pattern. The drawn film was then held at constant length and diffraction patterns recorded while the sample temperature was raised at 15°C min 1 from ambient to the glass transition temperature (Tg= 145°C) and beyond. WAXS patterns were recorded with an exposure time of 5 s. Close to Tg there was a sudden loss of orientation so that the diffraction pattern resembled that given by the specimen before cold drawing. This absence of crystallinity and orientation persisted for ~45 s after which the unoriented non-crystalline pattern began to be gradually replaced by a highly crystalline oriented pattern. This loss of orientation within a non-crystalline specimen close to Tg is consistent with a change from a molecular orientation associated with pseudo-affine deformation to an orientation associated with a stretched rubbery network. From parallel studies, the dramatic changes in the WAXS pattern were found to be correlated with changes in the small angle diffraction. Significant features in the SAXS pattern were not observed until the temperature was ~ 150°C when the meridionally oriented central maximum began to develop. With increasing temperature this maximum gradually broadened in the meridional direction until at ~ 160°C it developed into a distinct meridional peak at a spacing of 140 A. During subsequent annealing the intensity of this peak increased but its spacing did not change. Also, the half width of this peak in the direction parallel to the equator did not vary during annealing, suggesting that the lateral dimension of the crystalline regions within the specimen does not change during crystallite growth.

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