ISSN:0007-1641    

DOI:10.1002/pi.4980180202

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractStresses which have been frozen into a polymer by cooling to below its glass transition temperature (Tg) are relieved when the polymer is reheated above itsTg. Polymers which have been elongated will contract aboveTg. This sudden contraction just aboveTg is detected as a sharp drop in the differential scanning calorimetric curve. This is the reverse of the well known superheating endotherm accompanying the expansion of annealed polymers. The decrease in the differential scanning calorimetric curve immediately after theTg inflection can be quantitatively related to the residual strain in poly(vinyl chloride) and polycarbonate.

ISSN:0007-1641    

DOI:10.1002/pi.4980180203

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe rate of thermal ageing has been found to decrease when a polymer is adsorbed onto a filler. The retardation of this glassy state relaxation has been found to be dependent on the type and amount of filler present. Comparison with values for the glass transition temperature and melt rheology parameters shows that the same factors are determining each of these properties. Each of these properties is determined by the mobility of the polymer molecules and this is restricted by adsorption onto a filler.

ISSN:0007-1641    

DOI:10.1002/pi.4980180204

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe change of shape patterns of the oxidation peak on differential thermal analysis curves of a series of formulations of polyethylene has been investigated. The unstabilised sample exhibits two oxidation peaks. When a chain‐terminating antioxidant and dilaurylthiodipropionate were added to polyethylene, it was found that as the concentration of dilaurylthiodipropionate increases, the second oxidation peak reduces in size. In many instances when the amount of dilaurylthiodipropionate reaches 0.3% (by weight), the second oxidation peak disappears. The influences of processing method and outdoor exposure on the peak shape have also been examined. The effectiveness and consumption of antioxidants during weathering is clearly shown by the shape change of the oxidation peak on the differential thermal analysis curve

ISSN:0007-1641    

DOI:10.1002/pi.4980180205

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe contribution of entanglements to the modulus of a time independent polymer is satisfactorily accounted for by the C2/λ term in the Mooney‐Rivlin equation. On the other hand, the role of entanglements in time dependent polymers is less evident and seems to give rise to a non‐linear Mooney plot. A model is introduced which considers an entanglement as a topological knot that tightens with initial deformation and subsequently inhibits chain slippage. The observed maximum in a Mooney plot at small values of λ is predicted, and the experimental data of plasticised PVC polybutadiene and styrenebutadiene copolymer are fitted reasonably

ISSN:0007-1641    

DOI:10.1002/pi.4980180206

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractBlends of linear low density and high density polyethylene are examined by x‐ray diffraction and differential scanning calorimetry in order to characterise the crystalline morphology and to investigate the compatibility of the polymers. The polymers are found to form a co‐crystalline phase under a variety of conditions, and can thus be regarded as compatible. The lamellar distributions obtained from the differential scanning calorimetry melting thermograms are found to be dominated by the presence of the high density polyethylene, and this is attributed to the higher mobility of the high density molecules. The lattice parameters of the crystalline phases are found to increase with increasing side branch cont

ISSN:0007-1641    

DOI:10.1002/pi.4980180207

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe fusion process of a PVC dryblend, both with and without a PMMA processing aid, was studied in a Brabender Plasticorder over a range of mixer temperatures. charge masses and rotor speeds. The progress of fusion was monitored by the examination of the morphology of the PVC samples taken during different stages of the fusion process. The technique of examining the acetone‐swollen samples by optical microscopy before and after shearing,1provided an insight to the mechanism of action of the PMMA processing aid. The study established that the PMMA processing aid modified both the inter‐grain coefficient of friction and the packed density which had a significant effect on the initiation of the fusion process. The fusion process of both PVC compounds, i.e. with and without PMMA processing aid, was shown to proceed via a comminution mechanism, where the PVC grains were randomly broken into sub‐grains and primary particle agglomerates. Concurrent with this breakdown, the cohesion of PVC agglomerates was obs

ISSN:0007-1641    

DOI:10.1002/pi.4980180208

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractContour maps of complex relative permittivity within the range ‐ 175°C to 195°C and 0.1 Hz to 3 MHz are presented for basic and ultraviolet resistant grades of a commercial poly(dian carbonate). Several dispersion regions common to both materials are identified, together with an additional region at high temperatures in the ultraviolet resistant material. Comparisons are made with earlier investigations, and possible sources are suggested for each dispers

ISSN:0007-1641    

DOI:10.1002/pi.4980180209

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe effect of uncertainties in Kuhn‐Mark‐Houwink‐Sakurada (KMHS) constants on weight average and number average molecular weights and molecular weight distributions of some poly(ethyl methacrylate) samples have been investigated. Parameters were computed by the Weiss and Cohn‐Ginsberg method. Whereas errors introduced inMw,Mnand HI values due to uncertainty in theKvalue are insignificant, uncertainties in the KMHS exponent present a serious problem. Deviations of ± 3% around a particularavalue cause a ± 20% error inMwand ± 15% error inMn, values. The effect of deviations in the KMHS exponent on the HI values is dependent on the polydisperity of the sample in

ISSN:0007-1641    

DOI:10.1002/pi.4980180210

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractResidual 740 cm−1absorption, a signature of thecisisomer, is always observed to the extent of ± 5% in ‘trans’‐polyacetylene prepared thermally from the Shirawakacisisomer, regardless of the temperature or duration of treatment. The view that a significant fraction of the ‘remnantcisbonds’ is in the form of or can be converted tocisoidsingle bonds is supported by the results of a Diels‐Alder trapping experiment with maleic anhydride. The presence of the remnantcislinkages leads to simple rationalisation of free radical (soliton) generation and diffusion, conjugation lengths determined by Raman spectroscopy, x‐ray structural evolution and electri

ISSN:0007-1641    

DOI:10.1002/pi.4980180211

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY