摘要:

AbstractHeat effects and structural transformations in amorphous crystallizable poly(ethylene terephthalate) (PET) during uniaxial stretching accompanied by neck formation, have been investigated by calorimetric and x‐ray methods over a wide range of temperatures and deformation rates. At small deformation (not exceeding 1–2%) and at temperatures below the glass transition temperature of the polymer, PET behaves as an elastic body. Upon stretching at a constant rate, constant heat power is absorbed, heat effects during loading and unloading coincide completely, and no hysteresis is observed. At large deformations (of the order of 50%), cold drawing develops in this temperature range. The internal energy change in cold drawing is zero within experimental error. A periodic heat release during the self‐oscillation regime of drawing PET corresponds to periodic changes in stress, in the rate of the neck formation, and in the appearance of the sample. The temperature limits of the region where crystallization resulting from an uniaxial drawing of the polymer is possible, have been determined, and the heat effect of this phase transition has been measured. Orientation crystallization develops only from 70 to 94°C. These limits are insensitive to changes in deformation rate within one decimal order. The structure of PET in this temperature range has been investigated. The heat of phase transition of orientation crystallization of PET has been determined from the relationship between the measured values of the internal energy change during this process and the limiting degree of crystallinity for the stretched samples. This heat proves to be 5.5 ± 0.

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160701

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe induction period for the onset of crystallization was determined in poly(ethylene terephthalate) in the presence and absence of small metallic particles. Two kinds of substrates were used: single microcrystals “transplanted” from the water‐soluble inorganic polymer (NaPO3)xand powders of the same metals (Au, Pt, and Ir). The nucleating activity ϕ of the substrates was determined on the basis of classical nucleation theory. Values of ϕ obtained for PET are compared with the corresponding values in the (NaPO3)xmelt and with theoretical c

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160702

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA craze may fracture either by the breaking of covalent bonds or by a process of “viscous rupture” involving the movement of bulk material in the craze. In the latter case it is necessary that the majority of the chain ends of the polymer molecules passing through the craze‐matrix interface terminate within the craze. We have therefore calculated the probability of a polystrene macromolecule spanning a thin craze and shown that for viscous rupture a craze in a normal commercial polystyrene must be something more than 40 nm thick. As the measured craze thicknesses have generally exceeded 100 nm, a viscous fracture process is clearly possible, though, of course, chain rupture is not excluded by the argument. More difficulties arise when fracture occurs within a specified region of the craze and the possibility of a bond fracture under these circumstances is briefly disc

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160703

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe Raman spectrum of partially crystalline polyethylene can be described as a superposition of three components, which originate from the orthorhombic crystalline phase, a meltlike amorphous phase, and a disordered phase of anisotropic nature, where chains are stretched but have lost their lateral order. The mass fractions involved in the three phases can be derived directly from the integral intensities of characteristic bands without an additional calibration procedure. A comparison of the results obtained for a variety of samples shows agreement with the crystallinities derived from the density, and the small‐angle and wide‐angle x‐ray diagrams. Data indicate that the disordered anisotropic phase is located at a transition zone between crystalline and amorphous layers. Application of the method in a temperature‐dependence experiment permits a detailed examination of partial

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160704

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe kinetics of craze growth from sharp cracks in polystyrene (PS) and poly(methyl methacrylate) (PMMA) in contact with liquid methanol were measured with time‐lapse photography as a function of the stress intensity factorKI. At highKIthe craze length in both systems increases as √tif the sides of the craze are protected from methanol and astif they are not, wheretis the elapsed time after loading. If such a side‐protected craze is dried under load and then methanol is reintroduced to the crack tip, the methanol front advances with the same kinetics as the original craze growth. This experiment Proves that solvent crazing velocities are limited by the hydrodynamic transport of solvent through the porous craze structure under a capillary pressure driving force (which can be as high as 100 atm). An improved model of fluid flow through the craze is developed and shown to predict craze growth kinetics in good agreement with those observed. The hydraulic permeability of methanol crazes in PS was found to be independent of craze length at small craze length and to be independent ofKIexcept at very lowKI. Although increases in molecular weight in the rangeMw= 200,000 toMw= 670,000 do not markedly affect the crazing kinetics, they greatly increase the time to fracture of the

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160705

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe electron density of the polyoxymethylene molecule was calculated in cylindrical coordinates by a newly derived Fourier method. The density due to hydrogen could be obtained in addition to that from carbon and oxygen. This method is generally applicable to a helical polymer whose unit cell contains only one molecule composed of a number of chemical repeat units in the fiber identity period.

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160706

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractConformational energy calculations are used to investigate molecular motions in polyethylene crystals. From these a model is derived for the motion that accomplishes the net rotation translation that is believed to underlie the nuclear magnetic resonance (NMR) and dielectric α processes in polyethylenes and paraffins (and their dipole decorated derivatives). The resulting model is found to incorporate features of a number of previous models but differs significantly from all of them. The rotation is accomplished by means of a twisted (by 180°) region that propagates smoothly along the chain across the crystal. It differs from previous rotational models in that the twisted region is found to be rather localized (to ∼12 CH2units). A dependence of activation energy on chain length (paraffins) or crystal thickness (polyethylenes), with the activation energy becoming independent of thickness in thick crystals, results not from therotationallattice mismatch of the twisted regionper sebut from thetranslationallattice mismatch induced by the 180° rotation of one stem relative to the other. The twist differs from a stable point‐defect twist previously proposed (Reneker defect) in that the chain torsion is relatively uniform through the twist and there is no shortening of the chain accompanying it. Further, the twist propagates smoothly without local barriers to its advance. Thus the propagating twist is to be through of as a transition state rather than a hopping defect. Detailed atomistic conformational energy calculations on C22H46crystals were combined with a simplified elastic theory for translational stem mismatch in longer chains. From the combined calculations the activation parameters for twist propagation as a function of chain length or crystal thickness could be calculated. The results were compared with experiment for the dielectric α relaxation in paraffins containing dissolved ketones and polyethylenes containing carbonyl groups. The agreement is quite good, especially considering the paucity of adjustable parameters in the model. There is only some slight uncertainty in the calculated entropy of activation and a scattering correction was madea posteriorito account for a slow continued drop‐off in relaxation rate in very thick

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160707

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA complex fine structure in the CH stretching region of the infrared spectrum of deformed polyethylene single crystals is reported. The deformed crystals are shown to be transformed from the orthorhombic crystal form to a monoclinic structure. The previously deducedC2/mmonoclinic structure does not account for the appearance of the new bands. An alternative but similar monoclinic structure is proposed. The symmetry of this structure is consistent with the Fermi resonance interactions required for the observation of these band

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160708

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe pressure–volume–temperature (PVT) properties of a commercial polysulfone derived from bisphenolAand 4,4′‐dichlorodiphenylsulfone are studied experimentally and theoretically in the temperature range 30–370°C and for pressures to 2000 kg/cm2. PVT surfaces are determined for an annealed glass, formed under zero pressure, and for the melt. Two glass‐transition lines must be distinguished:T *g(P) which is the intersection of the glass and melt PVT surfaces, andTg(P), which is obtained by pressurizing the melt isothermally. The application of Ehrenfest‐type equations to these transitions are discussed. The Prigogine–Defay ratior= ΔkΔCp/T *gV *g(Δα)2atP= 0 is found to be equal to 0.95 (±20%), using ΔCpdata determined on identical samples. The melt data is compared with the Simha–Somcynski hole theory, using the reducing parametersV*= 0.788 cm3/g,T*= 12,560°K,P*= 10,875 bar. The hole fraction appearing in the theory is found to be constant alongT *g(P), but the glass PVT relationship cannot be reproduced by using the Simha–Somcynsky theory together with the assumption that the hole fraction remains constant in the glass. AtP= 0 the hole fraction must be allowed to decrease with decreasing temperature, bu

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160709

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe thermoelastic effect has been measured in compression on four glassy polymers; namely, polystyrene, poly(methyl methacrylate), polycarbonate, and epoxy resin. Quantitative results have been obtained for the first time on three of these polymers. It has been shown that by paying attention to specimen geometry and instrumentation results can be obtained to a high degree of accuracy (better than ±1.5% on a given set of measurements). The polymers are shown to obey the classical Thompson equation for thermoelasticity in solids over the temperature range studied (ca. 220–350°K). By inference such materials can be expected to behave classically in general. The results have been used, as first suggested by Trainor and Haward, to obtain values for the linear thermal expansion coefficient and the values so obtained are shown to be in excellent agreement, in general, with literature values obtained by more conventional methods. Results are given for a range of stress from 5 MN m−2to between 25 and 50 MN m−2according to ambient temperature. The method affords a measurement of parameters, in particular, linear thermal expansion coefficient. Values of specific heat for the four plastics have been measured by differential scanning calorimetry and the results compared with publish

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160710

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY