摘要:

Small-angle x-ray scattering curves of isotropic “sponge-like” structures can be analyzed by reducing the problem to one dimension; that is, by calculating the intersections of a chord. The projection of the interference function is then evaluated, and the desmearing procedure for slit-smeared scattering curves is no longer necessary.

ISSN:0022-2348    

DOI:10.1080/00222348408229359

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Crystallization behavior of high-density polyethylene blended with polypropylene was investigated in the oriented system, using wide-angle and small-angle x-ray diffractometries and electron microscopy. When polypropylene/polyethylene (PP/PE) drawn blends were heat treated in the temperature range above the melting point of PE, a new orientation texture of PE was produced during melt-recrystallization in the PP matrix. The majority of PE crystallites are aligned with their (110) planes perpendicular to the draw direction of the film specimen. Furthermore, well-developed lamellar structure is formed in the PE phase, along the crystallite b axes oriented preferentially at angles of 30-40° to the draw direction. The reason that such a distinctive orientation texture of PE develops in the blend with PP is discussed in some detail. As a possible explanation, it is suggested that thermal shrinking stress greatly affects the crystallization behavior of PE.

ISSN:0022-2348    

DOI:10.1080/00222348408229360

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Reliable data published in the literature on the nonlinear relaxational behavior of amorphous polymers in the rubbery range (T > Tg) are reanalyzed according to the “double-shift” procedure. The purpose of this study is to investigate the existence of a low strain-middle strain transition at around 40—50% of strain when an amorphous polymer is pulled in the rubbery state. This critical strain transition separating two distinct regimes of deformational behavior has already been reported in tensile experiments at constant pulling speed. In the work which is reanalyzed here, cross-linked or un-cross-linked amorphous elastomers are suddenly deformed at a constant temperature to a certain finite strain level and then allowed to relax. We replot the original relaxation data in a manner which is compatible with the double-shift superposition technique. Then we determine the best value of the horizontal and vertical shift factors so the curves obtained at different relaxational strains can superimpose. The analysis of the strain dependence of the shift factors confirms the existence, for the elastomers studied (PDMS, PBD, PIB), of a critical strain transition at around 40—50% of strain.

ISSN:0022-2348    

DOI:10.1080/00222348408229361

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The total radical decay in γ-irradiated polyethylene, measured by EPR, is discussed. By using the model of broad distribution of reaction constants and by an improvement of the estimate of radical concentrations, it is proved that radical-generating reactions occur during the temperature increase after γ-irradiation. The number of total radicals produced that are generated during the temperature increase is of the same order of magnitude as the radicals initially produced by the γ-irradiation. Some arguments are summarized to support the applicability of the model of broad distribution.

ISSN:0022-2348    

DOI:10.1080/00222348408229362

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The binding isotherms of C.I. Basic Red 18 with carboxy-methyl cellulose having various degrees of substitution have been determined in an acetate buffer at pH 4.2 and 30°C by a dynamic dialysis technique. The isotherms show a sigmoidal increase of binding with increasing free dye concentration in solution. The results strongly suggest a cooperative mode of binding. In the interpretation of the results, McGhee and von Hippel's theory considering cooperativity in binding was used. The intrinsic binding constant K, the number of consecutive polymer residues occupied by a single dye molecule n, and the cooperativity parameter were determined. A molecular mechanism of binding is proposed.

ISSN:0022-2348    

DOI:10.1080/00222348408229363

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The glass transition temperatures Tg, sub-glass transition temperatures sub-tg, melting points Tm, and apparent melting enthalpies δHfhave been measured for poly-N-(n-octadecyl)maleimede (PMI-18) fractions having number-average molecular weights between 1.25×103and 1.9×105by using differential scanning calorimetry. The results showed a dependence of the galss transition temperature on molecular weight similar to that observed for conventional linear polymers. The variation of Tgof PMI-18 fractions with molecular weight cannot be conveniently represented by any of the usual equations. On the other hand, the variation of Tgwith molecular weight can be described very precisely by means of the Ellis equation, which leads to a value of Tg(∞)=387.6 K. An analysis of the present data on Tg, in conjuntion with a similar treatment due to Cowie, has shown that a plot of Tgagainst logXn(whereXnis the number average bacbone bond number of main chain segments, namely, number of backbone carbon atoms or backbone carbon-carbon bonds) may be delimited into three well-differentiated regions. The boundary conditions, however, do not agree with the limits given by Cowie for typical linear polymers. However, the nalysis of the data as a function of the number of free bonds = virtual bonds = degree of polymerization also shows three well-differentiated regions. Their boundary condi6tions now agree with those given by Cowie for some other polymers. This alternative treatment suggests the importance of the backbone chain complexity effect on the glass transition temperature as well as its molecular weight dependence. The sub-Tg= Tgtransition, due to the local motion of the n-alkyl side chains, seems to be independent of molecular weight. The lack of a dependence of both the melting point temperature Tmand the apparent melting enthalpy δHfon molecular weight confirms that this motion is an internal one within the n-alkyl side chain of PMI-18 but without any interaction with the main chain. Fractions with molecular weights lower than 5.4×103(DPn= 15.5), however, show the characteristic dependence of Tmon molecular weight of low molecular weight susbstances.

ISSN:0022-2348    

DOI:10.1080/00222348408229364

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The crystal structure and helical conformation of polybutene-1 crystallized from dilute solution is shown to be a function of the crystal structure before dissolution, the maximum temperature in solution attained before cooling to the crystallization temperature, and the time at that maximum temperature. The effect is, in general, reversible if the solution is held for sufficient time (on the order of 1 hr) before crystallization. The results suggest a temperature-dependent equilibrium helix conformation in solution, which only slowly approaches equilibrium and which determines the helical conformation of the resulting nuclei during crystallization. Solution viscosity measurements indicate a substantial difference in molecular size corresponding to the variation in thermal history. The results indicate that the prior history of a polymer may not be removed by solution.

ISSN:0022-2348    

DOI:10.1080/00222348408229365

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The speckle photography method (single-beam speckle interferometry) was used to study the deformation of a high-density polyethylene film by determining the detail field of displacements in an enlarged image of the sample. The method is based on the analysis of changes in speckle patterns corresponding to two different deformation states, as the changes in the speckle patterns contain information about the change of the object. The displacement vector and Poisson ratio have been determined with an accuracy of 10% in the small deformation range (displacements of several microns). Limitations of the method, such as the range of measurable displacements, effect of image defocusing, and tilt of the sample, are discussed. Among advantages of the method are comparative simplicity (it does not require grating on the object surface) and the possibility of its application to larger deformations while maintaining the small deformation steps between two deformation states.

ISSN:0022-2348    

DOI:10.1080/00222348408229366

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor