摘要:

AbstractWith respect to molecular masses, polymers are polydispersive. Since many of their properties depend on the distribution of molecular masses, to study this correlation it is necessary to have samples of narrow molecular mass distribution or samples with accurately defined distribution. In spite of the developmental progress of fast instrumental methods (analytical and preparative gel chromatography) used to determine the molecular mass distribution curve and to obtain higher amounts of fractions of narrow molecular mass distributions, there still exists an interest in classical methods of fractionation. On the basis of a survey of monographs on polymer fractionation, numerous publications and personal experience, this review describes primarily what is an efficient fractionation. Afterwards, factors that affect fractionation efficiency according to the type of effects arc given and causes of their action are described. Conditions under which efficient fractional precipitation and fractional solution methods are applied are considered separately. At the end of the review, criteria on the basis of which fractionation efficiency is evaluated are considered in detail.

ISSN:0032-3888    

DOI:10.1002/pen.760280802

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractIn this work, creep induced buckling was studied for a number of thermoplastic materials. The effect was observed by monitoring top displacements of thermoplastic bars as a function of time under static loading conditions. The recorded times to failure were averaged and correlated with the applied loads. The experiments, conducted for different materials, established an exponential dependence between the critical time and the load. The evolution of the buckling eigenvalues was modeled numerically. The simulations of eccentric columns behavior under compressive loads were coupled with the eigenvalue analyses. The correlation of the time‐load predictions obtained from the numerical simulations followed the experimental results within acceptable limits. The observed phenomenon of creep induced buckling was explained by damage accumulation leading to an effective reduction of the load carrying capabilit

ISSN:0032-3888    

DOI:10.1002/pen.760280803

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractFor linear copolymer molecules, the refractive index increment depends on the chemical composition of the molecules. However, the polydispersity in chemical composition of the sample introduces a great complexity in the data analysis in order to obtain a true molecular weight distribution. Even when the mean chemical composition does not depend on the molecular weight, a correction has to be applied when the output of an instrument depends quadratically on the refractive index Increment of the sample, such as in a light‐scattering measurement. For that purpose, the light‐scattering expressions are written in terms of polydispersity in chemical composition, which in turn is modeled using linear copolymerization equations. The microstructure effects, which are related to the order in which two different kinds of monomers appear along the chain, are not as yet taken into account in this appro

ISSN:0032-3888    

DOI:10.1002/pen.760280804

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractWhen blown films of low‐density polyethylene are heated above their melting point (Tm) they shrink to an unoriented state at a conveniently measurable, rate. Curves of contraction as a function of time have been measured at different temperatures ranging from 120°C to 200°C. The contraction curves for shrinkage in the machine direction obtained at different temperatures are superimposable by a lateral shift along the log‐time axis. A master contraction curve, a portion of the retardation spectrum, and the activation energy are obtained. Shrinkage data for low‐density polyethylene films with different thicknesses were analyzed and a correlation was found between contraction and dichroic ratio. This correlation indicates that thermal contraction data can be used as a qualitative measurement of orientation in low‐density polyethy

ISSN:0032-3888    

DOI:10.1002/pen.760280805

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA method for predicting the stress‐strain and volumetric behavior of particulate composites from constituent properties has been developed for large values of strain. This approach allows a simple model for systems in which damage occurs without resorting to complicated constitutive equations. An energy balance derived from the first law of thermodynamics and the equations of linear elasticity calculates critical strain values at which filler particles will dewet when subjected to uniaxial tension and superimposed pressure. Calculations of critical strains over the entire strain history using reevaluated material properties accounting for the damage yield highly nonlinear stress‐strain and volumetric curves. Experimentally observed dependences on particle size, filler concentration, matrix and filler properties, and superimposed pressure are correctly predicted. The method has no adjustable parameters, and allows several idealized models of the dewetting process to be examined. Comparisons of model predictions to experimental data show good agreem

ISSN:0032-3888    

DOI:10.1002/pen.760280806

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe thermal dependence of the parameters of the Carreau A model of viscosity has been investigated for 13 polymeric resins. It was shown that the zero‐shear viscosity and the time constant obey an Arrhenius‐type law and that, for these parameters, compensation effects are exhibited. The shear‐thinning index was found to be fairly independent of temperature. An important consequence of a compensation effect is that only one determination of a parameter at a given temperature gives the complete temperature‐dependence of this pa

ISSN:0032-3888    

DOI:10.1002/pen.760280807

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA model solvent technique is presented according to which polystyrene (PS) foam scrap is recovered in the form of small grains. The process mainly comprises dissolution of the waste into benzene or toluene, filtering, dispersion of the solution into water, and subsequent distillation. The alternative solvent/non‐solvent systems have been studied on the basis of solution rheology, operating conditions during the recycling procedure, and extents of recovery of PS and solvent. Eventually, the toluene/water system has been chosen for a larger scale experiment (LSE), the product of which was used for characterization work. No influence on critical properties was detected due to the solvent technique followe

ISSN:0032-3888    

DOI:10.1002/pen.760280808

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe relationship between the relaxation time spectrumH(τ) in the terminal zone and the volume‐fraction differential molecular‐weight‐distribution functionP(M) is derived by considering binary chain contacts for stress transmission,where β and λ are constants for a given chemical type. This is used to determine the molecular‐weight‐distribution curves from the stress relaxation modulus spectrum (above the crystal melting point) at 370°C for a number of commercial and experimental poly(tetrafluoroethylenes) (PTFEs). It is found that PTFEs typically have bimodal molecular‐weight distributions. The lower‐molecular‐weight peak conforms essentially to the “most‐probable” distribution, and the higher‐molecular‐weight peak to the binary coupling distribution. The entanglement molecular weightMeis 5490, and the number of main‐chain atoms between entanglement points is 110, consistent with a flexible chain. The zero‐shear melt viscosity at 370°C is η0= 1.79 × 10−13Mw2.94±0.13, where η0is in Pa.s andMw/Me= 2,000 to 12,000. The monomeric

ISSN:0032-3888    

DOI:10.1002/pen.760280809

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractStress‐strain relationship of 2,6 dimethyl poly(phenylene oxide)(2,6 MPPO) was established simultaneously with optical micrographic examination as a function of thermal history. Films (5–7 μm) were solvent cast and annealed below their glass transition and melting point. As‐cast film showed ductile behavior associated with shearband formation, whereas thermally treated material exhibited marked embrittlement; the slower it cooled the more brittle it became. Thermally treated material showed mixed mode deformation: crazing and shearbanding. The correlation between the deformation mechanism and its solid state structure was studied using differential scanning calorimetry, wide angle x‐ray diffraction, and density mea

ISSN:0032-3888    

DOI:10.1002/pen.760280810

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760280801

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY