摘要:

AbstractA simple model, based on an average elongational rate, correctly predicts qualitatively the effects of changes in all spinning parameters on the orientation of fibers spun from viscoelastic melts. The model may be extended to any extrusion process with an elongational character.

ISSN:0032-3888    

DOI:10.1002/pen.760210302

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractMethods of predicting and correlating thermal conductivity of polyethylene resins in solid and melt states are discussed herein. Dependence on crystallinity or density is estimated for the solid state by a form of Maxwell's equation for electrical conductivity. An equation is presented for predicting melt thermal conductivity based upon Bridgman's theory of energy transport and pressure‐volume‐temperature (PVT) data. The effect of pressure on melt thermal conductivity is calculated from the theory. The effect of pigmentation for near spherical particles up to approximately 2.5 volume percent is also correlated by a form of Maxwell's equation. Experimental thermal conductivities of unpigmented and pigmented polyethylene resins from 50 to 300°C are in good agreement with theoretical predictions and with literature

ISSN:0032-3888    

DOI:10.1002/pen.760210303

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractTorsional Braid Analysis (TBA), like many other sample‐supported techniques, measures the transition temperatures of a polymer deposited on an elastic support. It is shown here that any polymer transition found by the location of the maximum in the log decrement Δ (or loss tangent tan δ) of a composite shifts to lower temperatures as the rigidity (or modulus) of the elastic support is increased. The magnitude of this temperature decrease is larger for transitions at which a composite has a larger support‐to‐polymer rigidity ratio. In general the above conclusions hold even with unsupported systems if the rigidity (or modulus) of the sample can be increased without interfering with the polymer domain under investigation, for example, by crosslinking one of two phases of microphase‐separated co

ISSN:0032-3888    

DOI:10.1002/pen.760210304

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractGel Permeation chromatography (GPC) yielded high values for branching frequency. Low polymers persisting long into the reaction and impurities resulted in almost constant number average molecular weights and steeply rising polydispersity. The percent insolubles was low and passed through a maximum attributed to a 1,2,3‐propantriol/isocyanate reaction product which was insoluble and became solubilized by the addition of polybutadiene. The dynamic viscosities of the products rose with conversion. When studied over various shear rates, the curves could be extrapolated to zero shear values. The relationship between zero shear viscosity and molecular weight yielded a slope of 3.5 for linear samples and a lightly branched sample prepared using 1,6‐hexamethylene diisocyanate. The lightly branched samples made using 2,4‐toluene diisocyanate yielded slopes less than 3.5. The highly branched samples yielded slopes well above 3.5. The moduli increased rapidly with reaction time and then levelled off. In the absence of 1,2,3‐propantriol, the loss modulus surpassed the storage modulus. When 1,2,3‐propantriol was added, the moduli increased more rapidly, levelled off at higher values, and the storage modulus exceeded the loss modulus. Studies of the swelling of the final product showed that these measurements yielded abnormally high values for the molecular weight between crosslinks; evidence of poor network

ISSN:0032-3888    

DOI:10.1002/pen.760210305

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThree aspects of the failure of thermoplastics, having a special importance in engineering, are investigated. They are: (a) Transition from linear to nonlinear viscoelasticity; (b) Crazing; (c) Fracture. Energy related criteria, developed from the Reiner‐Weissenberg thermodynamical theory of strength, are used for the characterization and prediction of failure under its different forms, for simple uniaxial loading histories such as creep, stress relaxation and constant rate of strain. The computation of the stored and dissipated parts of the specific stress energy becomes possible in a relatively simple way, if the relaxation modulus and the creep compliance are approximated by Prony‐Dirichlet‐type series with a finite number of terms. Published experimental data, as well as experiments carried out by the author on different thermoplastics are in very good agreement with theoretical results. Further, based on experimental data, the equations obtained can be reduced to very simple and useful relations. The influence of elevated temperatures (below the glassy‐transition point) on failure is also con

ISSN:0032-3888    

DOI:10.1002/pen.760210306

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractRecovery experiments aboveTghave been performed on glass bead and short glass fiber polystyrene composite sheets obtained from extrusion and subsequent hot drawing. A shift procedure has been applied to recoil data using the Williams‐Landel‐Ferry (WLF) equation with the same values ofC1andC2used for unfilled polystyrene. The data reported show that an improvement of the dimensional stability of a drawn thermoplastic material can be obtained by adding very low volume percentage of fibers. Moreover, all the recoil data have been reduced to a unique generalized master curve which takes into account the draw ratio, the filler content, and geometry, using a fractional distance from equilibrium as a measure of the recovery. These results indicate that the presence of the filler does not affect the recoil kinetics of the polymeric mat

ISSN:0032-3888    

DOI:10.1002/pen.760210307

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractCold working (rolling) of polycarbonates introduces residual stresses and molecular orientation both of which can improve, the notched Izod impact value. Annealing relieves both residual stresses and orientation. Annealing for various time periods established the critical level of residual stress necessary for the ductile failure mode of polycarbonate in the Izod impact test. The relaxation of both residual stress and molecular orientation was measured as a function of annealing temperature, for annealing times of 2 hs, and the relative changes have thus been determined. It is shown that residual stresses cannot be entirely removed without significantly influencing orientation for 2 h annealing times.

ISSN:0032-3888    

DOI:10.1002/pen.760210308

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractA series of segmented polyurethanes based on hydroxylterminated polybutadienes (HTPBD) and their hydrogenated derivatives (HYPBD) has been synthesized. Thermal, mechanical, and spectroscopic studies were carried out over a wide temperature range to elucidate the structure‐property relationships existing in these polymers. Both thermal and dynamic mechanical response showed a soft segmentTgat −74°C for the unsaturated polyurethanes and at −69°C for the hydrogenated samples. In addition, two hard segment transitions are observed by differential scanning calorimetry (DSC) at 40 and 75°C and a softening region by thermal mechanical analysis (TMA) at 190°C. The lowTg, very close to that of the free HTPBD and HYPBD and independent of hard segment content, indicated that these polymers were well phase separated. Results of infrared analysis revealed that at room temperature, 90‐95 percent of the urethane N‐H groups formed hydrogen bonds. Since hydrogen bonding resides only within the hard segment domain in these butadiene‐containing polyurethanes the extent of H‐bonding served as additional evidence for nearly complete phase segregation. From dynamic mechanical studies, the plateau modulus above the soft segmentTgand stress‐strain behavior depended upon the concentration of hard segments. A slight increase in the modulus, a moderate increase in stress (σb), and decrease in elongation accompanied a higher hard segment content. The thermal and mechanical response of these polyurethanes appears to be consistent with behavior observed for other phase segregated systems. Variations in behavior resulting from hydrogenation of the precursor prep

ISSN:0032-3888    

DOI:10.1002/pen.760210309

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractIt is shown that the annealing of a high molecular weight, high density polyethylene at different temperatures ranging from 393.2 to 405.2 K influences the density of the material, the lamellar structure as studied by differential scanning calorimetry and transmission electron microscopy, and the necking and fracture behavior at constant uniaxial tensile loading in air at 313 K. In previous reports, a marked transition in the necking and fracture behavior of high density, high molecular weight polyethylene under constant uniaxial tensile loading has been reported. The nominal stress and the maximum strain rate of this transition show minima for polyethylenes annealed at temperatures of about 401 K. By combining these data with data for the lamellar structure a hypothesis that explains the necking/fracture behavior is set up. The heat treatment at temperatures from 393.2 to 403.2 K of the original non‐equilibrium lamellar structure causes a molecular fractionation preferentially of low molecular weight and branched material. These segregated parts may then act as fracture initiators and thus lower the resistance towards fracture. Other structural effects such as those proposed by McCready and co‐workers may also be of importance. The fracture curves at nominal stresses below transition of the materials annealed at 396.7 and 401.2 K for 24 h are shifted to shorter times in comparison with that of the non‐annealed material and this can also be explained by molecular fractionation. The time to necking at 14 MPa nominal stress seems to be related to the lamellar thickness of the sa

ISSN:0032-3888    

DOI:10.1002/pen.760210310

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760210301

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY