摘要:

AbstractThe effect of various diol chain extenders on the thermal, mechanical, electrical and viscoelastic properties of polyurethanes is discussed. Prepolymers were prepared using a polyester (polyethylenepropyleneadipate) and toluene‐2,4‐diisocyanate. Diol chain extenders were of three types in order to investigate structure–property relationships: (a)α,ω‐aliphatic diols; (b) diols with unsaturation present in the chain; and (c) diols with an oxygen atom present in

ISSN:0007-1641    

DOI:10.1002/pi.4980190102

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe amorphous and crystallite orientation in a number of films produced from characterised grades of high density polyethylene has been examined and some tensile properties measured. The films were produced under commercial production conditions with various blow ratios, freeze line heights and thicknesses.Orientation was assessed using optical and X‐ray methods. The relative contributions of the crystallite and amorphous components were calculated for a limited number of the films produced.Amongst the properties measured the ultimate tensile strength and elongation at break appeared to be the most variable. Birefringence was more affected by variation in blow ratio and film thickness than by freeze height changes.Attempts have been made to correlate these variations with crystallite and amorphous orientation as well as the individual behaviour of the polyethylene grades. In carrying out this correlation it became clear that the films could not generally be described by established low or high stress models of crystallite orientation. For these films produced on full‐scale commercial equipment it appears that transcrystallisation behaviour is frequently observed, with a tendency towards the low stress mo

ISSN:0007-1641    

DOI:10.1002/pi.4980190103

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractResults are reported for (a) the reproducibility of styrene–acrylic acid emulsion copolymerisations using (i) sodium lauryl sulphate and (ii) sodium dodecylbenzenesulphonate as stabiliser, and (b) the effect of small amounts of isopropanol upon the emulsion copolymerisation of styrene and acrylic acid using sodium dodecylbenzenesulphonate as stabiliser. Lack of reproducibility of the conversion–time results when sodium lauryl sulphate was used as stabiliser is attributed to partial hydrolysis of the stabiliser brought about by the low pH of the reaction sys

ISSN:0007-1641    

DOI:10.1002/pi.4980190104

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractPreviously reported work showed that high negative birefringence Type III polypropylene spherulites can occur in the weld zone of butt‐welded injection mouldings. Their occurrence under conditions not normally associated with their formation has been investigated further using a variety of thermal treatments. The behaviour proves to be complex but clear evidence emerges that β‐form nuclei remain active in the material for thermal treatments up to 200°C, although this is time dependent and the number of Type III spherulites steadily re

ISSN:0007-1641    

DOI:10.1002/pi.4980190105

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe curing reactions of epoxy resins with aliphatic amine are investigated using the differential scanning calorimetry technique with a single dynamic scan. The rate of the reaction was followed over the temperature range 30–250°C, and the activation energy and the order of the reaction are determined using four different computational methods. The activation energy for the various epoxy systems is observed in the range 40–76 kJ mol−1and the order of the reaction is observed to be

ISSN:0007-1641    

DOI:10.1002/pi.4980190106

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThermoplastic rubbers on heating show a melt rheological transition which is interpreted as the onset of breakdown in the long‐range order of the domain structure. This is mainly due to the mobility of the PS end‐blocks which, from this temperature upwards, can be removed from their base‐phase by forces exerted by the attached rubbery chain. The transition temperature is detected by a change in the slope of an Arrhenius plot of the Melt Flow Index values at various temperatures, for a wide range of samples. The transition temperature is shown to be directly related to the molecular weight of the hard‐block segments (PS), supporting the molecular model proposed pre

ISSN:0007-1641    

DOI:10.1002/pi.4980190107

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractA range of treatment protocols have been used to process the brown algal speciesDurvillea potatorum. The ease of extraction of the treated alginate and associated carbohydrates has been examined as has the composition of the resulting extracts. Extracts have been assessed by viscosity measurements and analysed for their colour, calcium, sodium, ash, amino acid and carbohydrate contents. Extensive investigations have shown that a range of treatments involving chloroethanoic and ethanoic acid produce products of useable viscosity and quality and that the carboxymethylation of seaweed sludge can be achieved.

ISSN:0007-1641    

DOI:10.1002/pi.4980190108

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractInitial rate and degree of conversion in enzymatic hydrolysis of cellulosic materials (CM—cotton linter and bagasse) have complicated dependencies on dosage of γ‐irradiation. The decrease in reactivity at low doses is explained by a decrease in the CM surface caused by radiation‐induced crosslinkages. Doses higher than 0·5 MGy increased reactivity; at 2 MGy the degree of conversion (48 h hydrolysis) was about 5 times higher than in controls. Increased reactivity was caused by depolymerization, increased solubility and decrease of crystallinity inde

ISSN:0007-1641    

DOI:10.1002/pi.4980190109

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractA series of partially neutralized poly(acrylates) has been prepared, and reactions occurring on heating them at 250°C have been studied. It was found that different chemical processes occurred at this temperature, depending on the nature of the counter ion. Univalent cations gave films of excellent chemical resistance in which anhydride formation had occurred, followed by rapid and substantial decarboxylation. Polyvalent cations, by contrast, gave films which, though water insoluble, were of inferior chemical resistance. They were found to have undergone anhydride formation, but not subsequent decarboxylation

ISSN:0007-1641    

DOI:10.1002/pi.4980190110

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper reports the development of a torsional braid analyser equipped with a gas lubricated bearing to minimise undesirable lateral oscillations of the sample, and its interface to a microprocessor for automatic data acquisition and reduction. The contribution of the glass braid substrate to the recorded dynamic mechanical behaviour is examined and some factors (polymer concentration in impregnating solution, braid structure) for the optimisation of the technique are discussed.

ISSN:0007-1641    

DOI:10.1002/pi.4980190111

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY