摘要:

AbstractIt is shown that the birefringence of a polyethylene crystal can be severely shape dependent via the internal field. Using the cluster model it is concluded that this dependence plays an important role in the structural transition in the uniaxial stretching process.

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180211

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractPolymorphism in nylon‐12 film, which appears on casting from a phenol‐ethanol solution, has been investigated by x‐ray diffraction and infrared absorption. The casting temperature was varied from 30 to 130°C and the ambient atmospheric pressure from 50 to 760 Torr. Casting at 30°C gives only the α form, while casting above 90°C yields only the γ form. At intermediate temperatures, both α and γ forms are obtained, with the γ content increasing as the casting temperature and/or the rate of evaporation of solvent are increased. The ethanol component of the casting solvent appears to act only as a melting‐point depressant for phenol. In contrast, nylon‐6 film cast from the same solvent system between 30 and 160°C gives only the α form. It is proposed that the difference in polymorphism of nylons‐12 and ‐6 is caused by differences in molecular flexibility due to the length

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180212

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe drawing behavior of linear polyethylene homopolymers with weight‐average molecular weights (M̄w) from 101,450 to ca. 3,500,000 has been studied over the temperature range 75°C to the melting point. In all cases 1‐cm gauge length samples were drawn in an Instron tensile testing machine at a constant cross‐head speed of 10 cm/min. With the exception of the lowest molecular weight polymer, it was found that increasing the draw temperature led to substantial increases in the maximum draw ratio which could be achieved, and that this increased monotonically with increasing draw temperature. Measurements of the Young's modulus of the drawn materials showed, however, that the unique relationship between modulus and draw ratio previously established for drawing at 75°C was not maintained to the highest draw temperatures. The highest draw temperature at which this relation held was found to be strongly molecular weight dependent, increasing from ca. 80 to ca. 125°C when M̄wincreased from 101,450 to 800,000. In all cases conditions could be found for drawing samples to draw ratios of 20 or more with correspondingly large values of the Young

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180213

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA thermodynamic analysis of the thermally activated yielding of glassy atactic poly(methyl methacrylate) has been carried out. Samples were deformed in compression at a constant strain rate in the temperature range 150–330 K. Two different deformation modes are rate controlling below and above a critical temperatureTcof the order of 200 K. The low‐temperature mode is characterized by a purely exponential stress dependence of the strain‐rate, and thus defines a true stress‐activation volume. The higher‐temperature mode reveals a stress dependence of the strain rate in the form of a power law with a constant activati

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180214

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe morphology of poly(butylene terephthalate) (PBT) crystallized from the melt at various temperatures was studied by small‐angle light scattering, polarizing microscopy, and wide‐angle x‐ray diffraction. Spherulites with a maltese cross at 45° to the polars formed at lower temperatures while spherulites having an apparently higher melting point with a maltese cross along the polars (0°–90°) formed at higher temperatures. The spherulite size and crystallinity increased with increasing crystallization temperature. TheHvscattering patterns arising from the spherulites formed at lower temperature showed intensity maxima at azimuthal angles of 0° and 90°, while those obtained at higher temperatures showed the more common 45° intensity maxima. Microtomed samples from molded PBT bars showed spherulites with a 45° maltese cross which changed to a 0°–90° maltese cross upon heating just prior to melting. The skin‐core effect due to varying thermal histories in these molded bars was clearly observed. Solvent crystallized films contained positive 0°–90° spherulites. Some changes occurring upon uniaxial stretching of PBT

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180215

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe effects of pressure on the compressibility and crystallization of poly(ethylene terephthalate) (PET) have been investigated. The Instron capillary rheometer was adapted as a high‐pressure dilatometer to perform experiments up to 40,000 psi. Compressibilities of solid and molten PET were measured. The increases in compressibility with increase in temperature for the solid state are discussed in terms of free‐volume theory. Results obtained for the melt are explained by invoking the second law of thermodynamics and the effect of pressure on the Gibbs free energy. The effects of temperature and compression rate on the pressure of crystallization (Pc) were also studied. As the crystallization temperature was increased from 240 to 286°C,Pcincreased by about 16,000 psi. As the compression rate was raised from 1%/min to 8%/min,Pcincreased 10,000 psi. At some undetermined compression rate above 8%/min it seemed impossible to induce crystallization in the melt, even with pressures up to 40,000 psi. Analysis of data on the kinetics of crystallization of PET melt under high pressures revealed low Avrami exponents, for which no unequivocal explanation is offered. It is possible, however, that crystallization at high pressure promotes the formation of a morphology made up of a certain percentage of “extended chains.” The alteration in the attendant spatial geometry involved in the crystallization might explain the lower Avrami exponents found. In another set of experiments, crystallization temperatures (Tc) were measured by slowly cooling PET melt under high pressures. As the pressure was raised from 3000 to 15,000 psi,Tcincreased from about 246 to 282.5°C. These results are consistent with thermodynam

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180216

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractRheological studies were carried out on concentratedm‐cresol solutions of two helical synthetic polypeptides; poly‐γ‐benzyl‐L‐glutamate (PBLG; molecular weight, 150,000) and poly‐ϵ‐carbobenzyloxy‐L‐lysine (PCBZL; molecular weight, 200,000). Steady shear measurements were made over a range of 0.01–16,000 sec−1to obtain steady shear viscosity and first normal stress difference. Dynamic viscosity and dynamic storage modulus were measured both by oscillatory shear between cone and plate and also by an eccentric rotating disk device over frequency ranges of 0.1–400 and 0.1–63 rad/sec, respectively. The concentration ranges were such that both liquid crystalline and isotropic solutions were investigated. The previously reported observations of an apparent negative first normal stress difference within a defined range of shear rate for liquid crystalline solutions were confirmed for the PBLG and PCBZL solutions. At high shear rates the peaks in plots of steady shear viscosity against concentration were profoundly suppressed but peaks in first normal stress difference versus concentration were not. The observation of liquid crystalline order in PCBZL/m‐cresol solutions at room temperature constitutes evidence that the inverse coil‐helix transition temperature is lower in concentrated solutions than in dilute solutions. The critical concentration for formation of the liquid crystalline phase was higher for PCBZL than for PBLG, despite a higher axial

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180217

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180218

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180219

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

ISSN:0098-1273    

DOI:10.1002/pol.1980.180180220

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY