摘要:

AbstractWhen polymers are subjected to sheer, macroalkyl radicals are formed which lead to accelerated oxidation. This may occur in the polymer melt during processing or under conditions of mechanical fatigue at lower temperatures (e.g., in cross‐linked rubbers). Under these conditions, chain‐breaking electron acceptor (CB‐A) antioxidants are found to be relatively more effective than under conditions of thermal oxidation and the evidence suggests that the reduced and oxidized couples of some antioxidants, for example, phenol/phenoxyl or hydroxylamine/nitroxyl, can deactivate radicals catalyti

ISSN:0032-3888    

DOI:10.1002/pen.760241302

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760241303

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractDynamic and static mechanical properties of a soluble aromatic polyimide (PI 2080) were investigated. It, unlike poly(pyromellitimide) (PI), was essentially amorphous in X‐ray diffraction and did not exhibit any heterogeneous two‐phase structure having ordered phases after annealing at temperatures around its glass transition temperature. The mechanical properties including thermal‐distortion temperature and elastic recovery were not much affected by the annealing. The difference in molecular aggregation and mechanical properties between PI 2080 and PI may be due to their different chemical structures. The flexible carbonyl group and the statistical distribution of copolymeric repeating units in the main chain of PI 2080 seem to prevent the formation of molecular

ISSN:0032-3888    

DOI:10.1002/pen.760241304

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760241305

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA mathematical analysis of bubble growth in an expanding foam is presented. The analysis is based on a cell model whereby the foam is divided into spherical microscopic unit cells of equal and constant mass, each consisting of a liquid envelope (or shell) and a concentric spherical gas bubble. Expansion occurs by diffusion of a dissolved gas from the supersaturated envelope into the bubble. This cell model is capable of describing important qualitative features of a real system of numerous bubbles growing in close proximity to one another, and is intended as the building block of a global analysis of macroscopic foam expansion. The coupled algebraic and differential equations governing the growth of a cell are derived and solved numerically. Five dimensionless parameters are identified for the case of constant temperature and pressure outside the cell, and their effects are demonstrated through computer simulations of the system. Of these parameters, surface tension and initial radius prove to be of relatively little importance in the practical cases considered. The other parameters are the thermodynamic driving force, the cell mass (inversely proportional to the number density of bubbles), and the ratio of characteristic times for mass and momentum transport.

ISSN:0032-3888    

DOI:10.1002/pen.760241306

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA study of the crystalline orientation, light transmission, and surface roughness of polyethylene tubular film prepared in our laboratories is presented. The present studies were primarily carried out on low‐density (LDPE) and linear‐low‐density (LLDPE) polyethylene films. The optical properties of a few films of high‐density polyethylene (HDPE) prepared for a previous study of morphology were characterized for comparison to the LDPE and LLDPE films. Wide angle X‐ray diffraction and birefringence were used to characterize orientation. Both the LDPE and LLDPE films exhibited crystalline texture in which theb‐axes tended to be perpendicular to the film surface and thea‐axes had some tendency to align with the machine direction. Thec‐axes tended to be concentrated in the plane of the film with nearly equal biaxial orientation with respect to the machine and transverse directions. Little variation in the crystalline orientation was found with changes of process conditions in the range studied. Birefringence results indicate that the amorphous regions developed an orientation in which the chains tend to be normal to the film surface. The majority of light scattering from these films and a series of HDPE films was from the surface and not from the film interior. The transmission coefficient for the surface contribution was found to be a monotonic decreasing function of the standard deviation of the surface height obtained from surface profiles measured by profilometer. The surface asperites were largest for the HDPE and smallest for the LDPE samples. The intensity of both the surface and interior contributions to the scattering increased with increasing frostline height, i.e., a slower cooling rate. As draw‐down ratio and blow‐up ratio increase the scattering contribution from the film interior decreases but the contribution from the surface increases somewhat. These effects are discussed in terms of the changes in crystalline morphology and surface roughness produced by flow defects generat

ISSN:0032-3888    

DOI:10.1002/pen.760241307

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe effect of temperature and humidity on polymer aging is well recognized. Gardner and Martin and Kelleher,et al., have collected extensive data on the effect of temperature and humidity during the course of aging of poly(butylene terephthalate) (PBT). They proposed an empirical equation to predict the half‐life of aging. In the present work the data of Gardner and Martin have been reanalyzed to evolve an empirical equation which is applicable to the entire range of changes during agin

ISSN:0032-3888    

DOI:10.1002/pen.760241308

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA quasi‐three‐dimensional model was applied to the composite of ionomer and isotropically oriented discontinuous poly(p‐phenylene terephthalamide) (PPTA) fibers having the surface modified by carboxymethyl groups in order to predict the Young's modulus from the properties of the constituent materials over a wide temperature range. The model in which the modified PPTA fibers are dispersed in ionomer matrix in a three‐dimensional network is composed of series and parallel models. A good agreement between calculated and experimental values was eventually obtained. For comparision, the complex modulus of the composite was also evaluated by application of the Halpin‐Tsai equation modified by Nielsen. The calculated values agreed with the observed values below 240 K, whereas the calculated values above 260 K were significantly lower than the observ

ISSN:0032-3888    

DOI:10.1002/pen.760241309

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA method of determining fiber orientation in composites using wide‐angle X‐ray diffraction (WAXS) is described. Oriented crystalline fibers are suspended in an amorphous polymer matrix. The WAXS reflects characteristics of the fiber are used to determine the mean orientation and orientation distribution of the crystallographic axes representing the polymer chain relative to preferred axes located in the test specimen. The chain direction crystallographic axis is taken as representing the fiber axis, and the orientation of this axis to represent the orientation of the fibers. Experimental studies were carried out using Kevlar (poly(p‐phenylene terephthalamide)) fibers suspended at a 20 volume percent loading in a polymethyl methacrylate matrix. The Kevlar fibers had Hermans orientation factors of 0.92. Specific attention is given to how through circular dies. We have examined both extrudates and the material frozen‐in when the composite in the reservoir and die is cooled to room temperature. Fiber orientation factors, corresponding to Hermans orientation factors, 0.3 to 0.38 were obtained for the extrudates. Orientation factors for fibers within the die is about 0.45. Specially prepared completely oriented samples had orientation factors of 0.93, which closely corresponds to the orientation of th

ISSN:0032-3888    

DOI:10.1002/pen.760241310

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe kinetics of thermal and thermal‐oxidative degradation of polyethylene terephthalate (PET) have been investigated as a function of melt temperature, melt residence time, melt environment, and drying environment. Rates of thermal and thermal‐oxidative degradation were measured in terms of: weight loss of volatile degradation products, decreasing inherent viscosity, and increasing carboxyl end group concentration. Thermal‐oxidative degradation was also investigated by Differential Scanning Calorimetry. Calorimetric results show that thermal‐oxidative degradation of PET is an exothermic reaction, with an apparent activation energy of 117 kJ/mol. Melt temperature, melt residence time, melt environment, and drying environment have all been found to affect the degradation of PET. Analysis of inherent‐viscosity kinetic data has been carried out, utilizing existing theories based on a random chain scission mechanism. Activation energies of 117 and 159 kJ/mol have been calculated for air‐dried and vacuum dried samples r

ISSN:0032-3888    

DOI:10.1002/pen.760241311

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY