摘要:

The measurements of time-dependent thermally stimulated shrinkage forces were employed for investigating the initial stages of shrinkage in oriented and aged polycarbonate (PC). It was found that the observed induction effect results from the high localization of shrinkage processes and that it significantly depends on thermal history of oriented samples. The activation energy of shrinkage, derived on the basis of a simple mechanical model, remains approximately constant during the aging process, indicating that the major effect of aging is confined to the gradual relaxation of internal stresses “frozen-in” after the deformation. A simple relation t0/ta0.64= const was found between the induction time t0and aging time taof oriented PC.

ISSN:0022-2348    

DOI:10.1080/00222348908215224

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A change of Gibb's free energy in mixing of polymer and solvent, ΔFm, is often expressed in the following form:

ISSN:0022-2348    

DOI:10.1080/00222348908215225

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The fatigue behavior of segmented polyurethane and the effect of aging following fatigue were investigated by a combination of thermoluminescence (TL) and pulse NMR. It was found that the peak at 405 K, related to the segmental motion in the interfaces around the hard domains, decreased in intensity in the early stage of fatigue and disappeared at 1.0 × 105cycles. Meanwhile a new TL peak near 390 K (peak I) appeared and increased in intensity sharply during fatigue up to 1.0 × 105cycles. In this process the peak at 440 K (peak H) decreased in intensity correspondingly. The maximum temperatures of both peaks remained almost unchanged during fatigue. On the other hand, in the aging process following fatigue, this newly appeared TL peak decreased in intensity and the higher TL peak regained intensity accordingly. The TL and NMR results showed that the enhanced lower TL peak during fatigue is related to a fatigue-induced phase-mixed phase, which has a segmental mobility higher than the interfaces around the hard segment domains, and that this phase-mixed intermediate phase increases in volume fraction as the fatigue proceeds but decreases and is transferred partly to the hard segment domains during aging following fatigue.

ISSN:0022-2348    

DOI:10.1080/00222348908215226

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Strain-induced crystallization (SIC) was studied in blends of cis-l,4-polyisoprene (hevea rubber) and synthetic trans-1,4-polyisoprene (t-PI) using the wide-angle x-ray scattering technique. Uncrosslinked solution blends were uniaxially stretched at room temperature, and the dependence of the apparent crystallinity on elongation and t-PI content was analyzed. With increasing amounts of t-PI, both the onset of SIC phenomenon and the rupture occur at smaller elongations. These results are in accord with those obtained previously on true stress and birefringence.

ISSN:0022-2348    

DOI:10.1080/00222348908215227

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The axial and radial dimensions of a fiber are known to be key factors with respect to the mechanical stress necessary to promote failure, this being known as the size effect. Usually different methods are used to quantify the two types of size effects: Linear elastic fracture mechanics (lefm) and related schemes provide the theoretical basis for the effect of diameter variability upon strength whereas statistical theories, generally based upon the Weibull probability distribution combined with the weakest-link theorem, describe length effects. Here we show that simple modifications of the classical Poisson/Weibull form yield a new failure probability function which provides a more adequate explanation for diameter effects on strength in polydiacetylene fibers, and also resolves in a satisfactory way a current problematic issue inherent to the Weibull/weakest-link model. A maximum likelihood estimation procedure is presented for the evaluation of the most appropriate parameters of the proposed failure probability function.

ISSN:0022-2348    

DOI:10.1080/00222348908215228

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The solid-state morphology of poly(hexamethylene p,p'-bi-benzoate) (BB-6) and its dependence on the texture of the smectic liquid crystal state from which it crystallized were studied using electron microscopy, polarizing optical microscopy, and small-angle x-ray diffractometry. Thin films of BB-6 suitable for the microscopy were prepared by casting a hot solution of the polymer in tetrabromoethane onto mica at 150°C. The as-cast film of BB-6 was first heated to 260°C, maintained in the smectic range (210°C), and then cooled gradually to room temperature. A number of types of defect structures—such as Dupan cyclides, edge dislocation, tilt walls, and disclinations — were observed in the solid BB-6 formed from the smectic melt. On the basis of the electron microscopy and small-angle x-ray diffractometry, it is suggested that folded-chain crystals are formed during the crystallization from the smectic melt. Electron microscopic observations of the solid BB-6 and its orientation behavior under shear can be reasonably explained by assuming the presence of a precursory chain-folded layer structure in the smectic liquid crystal of BB-6.

ISSN:0022-2348    

DOI:10.1080/00222348908215229

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Colloidal, aqueous dispersions of certain acrylate-methacrylate copolymers with cationic groups have been prepared by a coacervation technique using ethanol as solvent and water as nonsolvent. Stability of the dispersions to electrolytes (sodium chloride, sodium sulfate, and sodium carbonate) increased markedly (up to 10 times) with a small (2-fold) increase in polymer cation content. The polymer dispersions were most sensitive to sodium sulfate and least sensitive to sodium chloride. Sodium carbonate was, in turn, less effective than the sulfate in flocculating the dispersions; this observation relates to the partial hydrolysis of the CO32-anion to less readily adsorbed OH−and HCO3−anions.

ISSN:0022-2348    

DOI:10.1080/00222348908215230

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The elastic and viscoelastic properties of nylon-6 films with different structural forms and different degrees of crystallinity, obtained by heat setting nylon-6 films at various temperatures, without constraint, have been investigated. The elastic modulus increases with increasing degree of crystallinity. The values of the transverse elastic moduli for completely amorphous and completely crystalline samples have been calculated on the basis of these results. The measurements of dynamic mechanical properties were carried out at two different frequencies, viz., 11 Hz and 110 Hz, over a range of temperature from room temperature to 150°C under ambient conditions of humidity. It is observed that the moisture content increases whereas the glass transition temperature decreases with increasing temperature of pretreatment. The activation energy of the α transition has also been calculated.

ISSN:0022-2348    

DOI:10.1080/00222348908215231

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A method is presented to describe quantitatively the influences of electrostatic interactions on local conformational changes and to demonstrate their effect on the static chain flexibility. This was done within the rotational isomeric state scheme (RIS) by incorporating Coulomb interaction energies and introducing electrostatic statistical weights in the matrices of the conformational partition function. As a main result we found constant flexibilities for a wide range of counterion concentrations. The screening effect of counterions surrounding the individual charge carriers on the chain backbone starts only at concentrations where intercharge distances and the screening length of the ionic atmospheres are of the same order of magnitude. Electrostatic interactions between polyion charges are mainly determined by bare Coulomb forces.

ISSN:0022-2348    

DOI:10.1080/00222348908215232

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

It is shown that motional averaging of the g and the A tensor of the electron paramagnetic resonance spectrum of such transition metal complexes as copper benzoyl acetonate (CuBA) and vanadyl acetonate (VAA) doped into polymers provides a sensitive probe of motion during the glass-to-rubber transition. Because of the larger and more anisotropic g and A tensors these probes are more sensitive to motional effects than the more commonly used nitroxide paramagnetic probes. The relationship between probe motion and intrinsic chain motion is examined.

ISSN:0022-2348    

DOI:10.1080/00222348908215233

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor