摘要:

Data are presented to show that a previously reported correlation of the strength of the alpha relaxation in annealed solution‐grown crystals of polyethylene with the inverse of lamella thickness is not unique. Nor is a previously reported dependence of relaxation temperature on lamella thickness unique. As the lamella thickness changes with annealing temperature, the unit cell dimensions, the macroscopic density, and the residual solvent content of the crystals also change. Thus, there are apparent correlations between these parameters and the relaxation strength and temperature. Since it is not obvious which, if any, of these correlations is the fundamental one with regard to the alpha relaxation, some caution must be exerted in interpreting them. As an example of this, data are discussed to suggest that there is at least one other presently unknown parameter of importance to the relaxation.

ISSN:0021-8979    

DOI:10.1063/1.1658461

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The unit cell dimensions have been measured at temperatures between 93 and 333 K for linear polyethylene samples with long periods of 385, 220, and 99 Å. The angular positions of 6 x‐ray diffraction lines were obtained at 5–10 K intervals with a powder diffractometer and the positions corrected for beam penetration so as to agree with powder camera results obtained with more lines at 296 and 155 K. At lower temperatures, the cell dimensions are nearly independent of long period, but at higher temperatures, the basal area of the cell appears to vary linearly with the reciprocal of the long period. The value of the slope increases with temperature and at 293 K is nearly the same for sets of data obtained with a number of different molecular weight distributions, crystallization and annealing conditions as well as forn‐paraffins. The specific volume data for all three polymer samples can be represented between 133 and 333 K with a standard deviation of 2.6×10−4cm3g−1by the equationV=0.8341(1055.5−T)/(931.7−T)+(0.12−1.6×10−3T+7.8×10−6T2)/l2in whichVis in cm3g−1,Tis °K andl2is the long period expressed in angstroms. It is concluded that the interaction of the molecules at the surface of the crystal is not as important as the length of the molecular stems between the folds in affecting the dimensions at higher temperatures. The stems probably alter the dimensions through their effect on the thermal energy. The dependence of crystal specific volume on crystal size is estimated to reduce the heat of fusion of small crystals by about 2% in the normal range of long period. Neglecting this in analyzing melting‐temperature‐lamella‐thickness data can lead to errors of the order of 3% in the surface free energy and 0.3 K in the equilibrium melting temperature. The variation of crystal specific volume accounts for about 5% of the variation of macroscopic specific volume and constant pressure specific heat with long period.

ISSN:0021-8979    

DOI:10.1063/1.1658462

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A delay timetdto re‐establish steady‐state neck motion is observed if a partially drawn nylon 6–10 monofilament is aged for a timetaat a stress &sgr;abelow the stress used to propagate the neck in a tensilecreep experiment. The delay time increases ask&sgr;atamfor longta, where 0<m<1, as long as the neck is immobile. The factorkincreases steadily with the aging temperatureTabelow 40°C, the glass transition temperatureTgof amorphous nylon 6–10, but much more rapidly withTaaboveTg. Aging at &sgr;a>0 is necessary to observe a delay time and, in fact, the effects of aging at &sgr;acan be erased by subsequently aging a short time at zero stress. At aging stresses just below the propagation stress &sgr;p, the neck still moves, but at a lower velocity than at &sgr;p. In this regime the delay time increases asc(&sgr;p−&sgr;a), wherecis markedly increased by decreases in temperature. It is proposed that stress aging is caused by the stress‐induced formation of small regions of better interchain packing (microcrystals) in nominally amorphous portions of the nylon and that the delay time is the time necessary to break up the microcrystalline structure induced by stress aging into the structure characteristic of steady‐state flow. The breakup process is thermally activated with an activation enthalpy of 3.85 eV and stress activated with a shear activation volume of approximately 104Å3. A modified Eyring model of flow is developed which assumes that the microcrystals are primary flow units which use up free volume in the amorphous regions as they are formed. This model accounts qualitatively for all, and quantitatively for some, of the features of the dependence of delay time on propagation and aging variables. Other theories, in particular free‐volume collapse and dislocation dynamics theories, cannot be reconciled with all the observed characteristics of stress aging.

ISSN:0021-8979    

DOI:10.1063/1.1658463

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A thin film marker technique is described for determining quantitatively from replicas the nonhomogeneous deformation modes operative in spherulitic polyethylene. Experiments were conducted at temperatures from −20° to 120°C and strain rates of the order of 0.04 sec−1. At −20°C, pronounced deformation at spherulite boundaries is observed. This results in stress concentrations which cause the accompanying nonhomogeneous deformation of the spherulites themselves to occur. At 70°C, corresponding to the &agr; relaxation, the deformation has become almost entirely homogeneous within lamellae. At 120°C, corresponding to the &agr;′ relaxation, lamellar boundary slip is clearly observed in addition to homogeneous deformation.

ISSN:0021-8979    

DOI:10.1063/1.1658464

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Previous work has shown that the creep data of a slow‐cooled polyethylene can be superposed by means of a series of horizontal and vertical shifts to give a creep master curve at room temperature. The curve is smooth and regular with the exception of a discontinuity in the region of 2000 sec. In the time and temperature range of the measurements, polyethylene has two overlapping relaxation mechanisms, the &agr; and &agr;′. If it is assumed that the logarithmic decrements of the two relaxations are additive, the theory of linear viscoelasticity can be simply extended to cover this case, and it is shown that the discontinuity in the master creep curve arises quite naturally as a result of the differing activation energies of the two relaxations. This is a general conclusion and is independent of the nature of the relaxation mechanisms involved.

ISSN:0021-8979    

DOI:10.1063/1.1658465

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The statistical theory of rubber‐like elasticity requires the energy contribution (fe/f) to be independent of the applied strain. We have in recent publications demonstrated that this stipulation is satisfied within the framework of the statistical theory. However, since this theory is only valid up to moderate strains (∼30%), the question then arises as to howfe/fbehaves at large deformations. In this paper we have examined this problem in the context of phenomenological theories of finite elasticity. It is shown that only for neo‐Hookean strain energy function, which is equivalent to the statistical‐theory free‐energy function, is the value offe/fa constant. For other strain energy functions, such as the Mooney‐Rivlin and Valanis‐Landel functions,fe/fmust decrease with increasing strain. The implication is that in the elasticity of most real rubbers the intermolecular energies play a more important role than previously realized.

ISSN:0021-8979    

DOI:10.1063/1.1658466

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The dielectric relaxation of amorphous bulk poly(2, 6‐dimethyl phenylene oxide) (PPO) has been measured between −160° and 260°C over a frequency range extending from 0.1 to 10 kHz. Two broad loss peaks of comparable intensities are observed‐a high‐temperature &agr; relaxation identified with the glass transition and a low‐temperature &ggr; relaxation of uncertain origin. The intensity of the &agr; relaxation can be well accounted for in terms of a loss of orientational dipolar correlation in a calculation based on a consideration of a rotational isomeric model and of the geometry of the PPO chain.

ISSN:0021-8979    

DOI:10.1063/1.1658467

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The strain‐optical coefficient of ethylene‐methacrylic acid copolymers is measured in static and dynamic experiments as a function of temperature and degree of ionization. An alpha optical loss peak which corresponds to a mechanical loss peak is found for the ionized salt but not for the un‐ionized acid. This peak is associated with mobility of an ionized domain. Birefringence relaxation curves are found to be superposable using horizontal and vertical shift factors. A plot of the logarithmic shift factor against (1/T) gives a broken curve exhibiting two activation energies for the salt indicating contributions by two processes.

ISSN:0021-8979    

DOI:10.1063/1.1658468

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

This paper reports results of studies of birefringence (&Dgr;) in ABS systems and in two component materials, measurements which reveal information about the orientation and response of these materials to deformation. Continuous measurements of (&Dgr;) at strain rates (&egr;˙) from 8.5×10−5to 3.3×10−3sec−1were carried out with a He&sngbnd;Ne laser light source on polystyrene (PS), poly(styrene‐acrylonitrile) (SAN), and two clear ABS polymers. Measurements at constant &egr;˙ were related to mechanical response of the materials in creep, and two tests for the invariance of the stress optical coefficient were developed. These were achieved through comparison of computer‐generated plots of appropriate rheo‐optic functions with rheological counterparts derived from previous creep measurements via the convolution procedure of Hopkins and Hamming. Such comparisons indicated nearly identical constant time dependences for the respective logarithmic plots of (&Dgr;/&egr;˙) and (stress/&egr;˙) vs time (t) for the PS and SAN polymers. Comparison of other functions confirmed the constant value of thestressoptical coefficient (SOC) implied above, |(SOC)| being 1.0×10−12cm2/dyn. This paper also presents results which indicate that the onset of yielding in the ABS systems can be studied by these optical techniques. It was observed that the increase in &Dgr; in the two ABS systems was followed by the onset of a high degree of scattering which produced a maximum (M) in each plot of apparent &Dgr; vst, the height ofMdecreasing with increasing &egr;˙. The relevance of this latter phenomenon to the study of impact strength and yielding in ABS systems is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658469

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Comparison of the laser‐Raman spectra with the polarized infrared spectra of native cellulose from the cell walls of the algaeValonia ventricosahas allowed greater confidence to be placed on the vibrational assignments than was possible previously from infrared data alone. The major details of the chain conformation and packing are already known from x‐ray and electron diffraction studies, but the relative chain polarities and the nature of the intra‐ and intermolecular hydrogen bonding remain unknown. The present work indicates that only one rotational conformation is present for the −CH2OH side chains, which reduces considerably the number of structural possibilities.

ISSN:0021-8979    

DOI:10.1063/1.1658470

出版商:AIP    

年代:1970

数据来源: AIP