ISSN:0032-3888    

DOI:10.1002/pen.760191402

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractA theoretical “two wall” model of polymer chains confined between a pair of infinite parallel walls is developed to represent the amorphous regions in filled or reinforced elastomers, block copolymers and semicrystalline polymers. The free energies of the various types of confined chains are determined using statistics which incorporate nearest‐neighbor interactions. The stress‐strain, tensile ii odulus and swelling properties of the individual chains as a function of chain contour length and temperature are discussed. A mean field, free energy expression is used to account for interactions between confined chain segments: The free energy due to the direct interaction between the walls is given by a van der Waals potential. The equilibrium wall separation of the two wall model is determined as a function of the number of each type of chain, chain contour length and temperature. The two wall model is shown to display several deformation phenomena, including: yield, stress softening; draw; stress hardening; the Mullins effect; set; and crack or craze prop

ISSN:0032-3888    

DOI:10.1002/pen.760191403

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe mechanical properties of polymers are influenced strongly by the structure of the noncrystalline regions. The different methods for characterization of these regions are reported and the results obtained on polyethylene terephthalate, are discussed. The orientation function of the noncrystalline chains can be determined by measurements of the X‐ray scattering and the birefringence. The fraction of taut noncrystalline chains is obtained from NMR measurements combined with a determination of the degree of crystallinity. For a further evaluation of the results it is also necessary to use calculations of the NMR‐ line‐width and the birefringence of chains with fixeu ends. With help of such calculations the end‐to‐end distance of the taut and mobile non‐crystalline chains can be determined, It is also possible to distinguish between tie molecules and loops. With increasing orientation, the amount of taut noncrystalline chains increases. The taut chains are tie molecule rather than taut loops. The end‐to‐end distances increase with increasing crystallizat

ISSN:0032-3888    

DOI:10.1002/pen.760191404

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe modules and birefringence of oriented polymers are known to couple through the structural and intrinsic properties of the polymer. Recent developments in both optical and mechanical theories have allowed this coupling to be expanded so that it includes predictions of modulus and refractive indices of uniaxially‐oriented polymer films at various angles to the draw direction. The validity of these theories has been tested in this study by predicting the angular dependence of the optical and mechanical properties of seven uniaxiallyoriented films of isotactic polypropylene. The present study also provides intrinsic material properties associated with the crystalline and noncrystalline components of the polymer, and consequently allows the identification of the structural parameters that control the properties of ultra‐high oriented isotactic polypropyl

ISSN:0032-3888    

DOI:10.1002/pen.760191405

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe current, and rather incomplete, understanding of the role of amorphous contribution to the Grüneisen functions of semicrystalline polymers is reviewed. There are two kinds of Grüneisen functions. The microscopic mode Grüneisenr parameter is a measure of the volume dependence of lattice frequencies in a solid. Their magnitudes vary with the specific mode. The macroscopic Grüneisen constant relates the mechanical and thermal parameters in solids. It is a weighted average of mode Grüneisen parameters. At a given temperature there is only one Grüneisen constant for a material. Because the various experimental techniques often favor certain lattice modes, there is a great variation in the literature values of Grüneisen functions for polymeric solids., For semicrystalline polymers, the degree of crystallinity and thermal history also affect the measured magnitudes. In this work a unified derivation of the existing equations will be given. Current theoretical models for the Grüneisen constants are described. The available literature data on Grüneisen constants of semicrystalline polymers, principally polyethylene, will be d

ISSN:0032-3888    

DOI:10.1002/pen.760191406

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractAmong the increased structural demands now being made on both unfilled and reinforced plastics is that of dimensional stability under various performance environments. Crystalline polymers are heterogeneous materials consisting of two distinct phases and, as such, can be treated as molecular versions of engineering composites. This paper first outlines the general physical model whereby a crystalline polymer is considered to be a multi‐ply laminate of unidirectionally reinforced plies. The calculational format is then detailed for the prediction of the stiffness and thermal expansion coefficient of an isotropic sheet of crystalline polymer and a sample calculation is given for quenched high density polyethylene. A data base is presented for the stiffness and thermal expansion coefficient of low and high density polyethylene having quenched, slowcooled, and annealed thermal histories. Comparison between experimental and predicted results yields good agreement in all cases to better than 25 percent. Implications and limitations of the predictive technique are discusse

ISSN:0032-3888    

DOI:10.1002/pen.760191407

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractVarious approaches to representing the modulus of a semicrystalline polymer as a composite crystal‐amorphous material are applied to the extensive data of Illers on the shear modulus of linear and branched polyethylenes as a function of crystallinity and temperature. It is found that the modulus of linear polyethylene is fit very well over the range of 47‐96 percent crystallinity from − 180 to 100°C by the Tsai‐Halpin equation with a single value of the contiguity factor, ζ, and crystallinityindependent phase moduli. A value of ζ ≃ 1(near lower bound behavior) is found. In branched polyethylene the behavior below the β relaxation (T

ISSN:0032-3888    

DOI:10.1002/pen.760191408

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractIn this study we investigate the effect of crystallization rate on the extensibility (draw ratio) of spherulitic polyethylene film uniaxially deformed at room temperature. Draw ratios for deformed films increased with increasing crystallization temperature. Transmission electron microscopy of the microfibrillar structures revealed and interconnected network of fibrils. The degree of connectivity between microfibrils was found to decrease with increasing‐crystallization temperature. A model of the deformation process is developed in which inter‐ and intra‐link (extended chain fibers formed during crystallization) distribute the applied stress, initiate the micronecking process and influence the amount of chain unfolding during dr

ISSN:0032-3888    

DOI:10.1002/pen.760191409

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractPolyethylenes have relaxation processes separately assignable to the crystal and amorphous components. The possibility thus presents itself for studying the interaction between the two phases by investigating the anisotropy of the separate relaxation processes induced by overall orientation of the material. Such a study was carried out here by the dielectric method on samples rendered dielectrically active by the introduction of a few carbonyl groups by oxidation. In addition to the usual advantage of ease of frequency variation, the dielectric method in this case has a very great advantage in interpretation resulting from the similarity of dielectric constants of the two phases. In specimens oriented by solid‐state extrusion, it was found that the crystalline relaxation process (α) develops the expected anisotropy resulting from dipoles normal toC‐axis alignment in the extrusion direction. In branched polyethylene (BPE) no accompanying anisotropy of the amorphous β and γ processes was observed. Since the extrusion was carried out well above the glass temperature of the amorphous component, this indicates that constraints from the crystal phase are not sufficient to prevent dissipation of amorphous orientation by segmental motion. However in linear polyethylene (LPE) (where there is no well‐developed β process) some anisotropy of the γ process was observed. It is proposed that a higher degree of constraint of the amorphous component by the crystals in LPE results in suppression of the glass‐rubber (β) relaxation and permits amorphous orientation to accompany crysta

ISSN:0032-3888    

DOI:10.1002/pen.760191410

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe influence of amorphous chains on bulk structure and material properties is examined in block and segmented copolymer systems whose components are in a variety of morphological states including: rubber‐rubber; rubber‐glass; glass‐glass; rubber‐crystalline glass‐crystalline; and, crystalline‐crystalline. The effects of external variables, such as temperature, time, and internal variables, such as molecular weight and composition ratio on the magnitude of the role played by the amorphous chains in these systems ar

ISSN:0032-3888    

DOI:10.1002/pen.760191411

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY