ISSN:0032-3888    

DOI:10.1002/pen.760290102

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe aging and lifetimes of polymeric materials depend on the reaction of these materials to the particular stresses which are applied. In many cases the molecular weight of the polymer is changed and this affords a way to follow aging phenomena. In the simplest case a homopolymer is subjected to a stress which increases or decreases its molecular weight without any chemical changes. As the situation becomes more complicated, changes in chemical composition occur and different sized molecular species are generated. These new species may be of extremely low molecular weight or they may be in the form of crosslinked gel. This paper reviews methods which are available for the determination of molecular weight and molecular weight distribution of polymeric materials. Recently developed or modified techniques are treated in more detail. Techniques which may be used to characterize the oligomer region or analyze for the presence of crosslinked gel are included.

ISSN:0032-3888    

DOI:10.1002/pen.760290103

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper provides a summary of four EPRI‐sponsored contracts that studied the physico‐chemical characteristics and thermal and electrical behavior of unaged and service‐aged crosslinked polyethylene (XLPE)—insulated cables, and sections of the insulation obtained from this extruded cable. It has been demonstrated that volatile components generated primarily from the peroxideinduced crosslinking process can be defined and quantitatively measured. The morphology of the aged and unaged XLPE extruded insulation can be defined, and the thermal behavior on a micro (morphology changes) and macro (cable aging) level compared. Changes in microvoid level due to melting and recrystallization during cable operation appear to correlate with the limited amount of ac breakdown strength data obtained, and thermal overload of the cable conductor causes complete melting (and recrystallization on cooling) reducing the microvoid level. A single thermal overload alters the morphology but many thermal overloads are required to drive off the vo

ISSN:0032-3888    

DOI:10.1002/pen.760290104

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe kinetic parameters of the thermal decomposition of poly(aryl‐ether‐ether‐ketone) (PEEK) in a nitrogen atmosphere have been obtained using an isothermal weight‐loss method. Several mathematical approaches have been used to obtain the Arrhenius parameters based upon the use of different reaction models. The values obtained for the activation energy (E= 198.4 to 219.7 kJ/mol) and preexponential factor (logA= 11.1 to 12.3 min−1) fall within a narrow range, irrespective of the method of calculation. Although the kinetic data most closely fits an Avrami two‐dimensional nucleating model, the data can be just as easily described by a first‐o

ISSN:0032-3888    

DOI:10.1002/pen.760290105

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractMost polymers are eroded rapidly (>0.1 μm/h) in the low earth orbit (LEO) environment when facing the direction of flight. The rate of erosion varies little with the polymer type, except for fluoropolymers and silicones. Methods for simulating such an environment are reviewed. Secondly, the oxidation lifetime of stabilized and unstabilized polyolefins can be reduced 50 to 90 percent, with a, high yield of carboxylic acid (i.e. chain scission) oxidation products, when thermal oxidation at 70 to 90°C takes place in 0.01 to 0.1 molar sodium chloride solutions, as compared to thermal oxidation in air. Both sets of observations illustrate the need for detailed mechanistic investigations before accelerated test procedures can be developed to predict material lifetim

ISSN:0032-3888    

DOI:10.1002/pen.760290106

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA recently developed analytical technique, modulus profiling, conveniently allows the mechanical properties of elastomers to be mapped with spatial resclutions approaching 0.05 mm. Thus, spatial heterogeneities in modulus caused by processing and aging phenomena can be easily monitored. This paper describes some typical results from polymer aging studies, which Indicate the insights available from this technique. These include application of modulus profiling to understanding (1) mechanical property deterioration of Viton in an elevated temperature, gamma‐radiation environment, (2) recent continuous stress‐relaxation results, and (3) the role of ozone for non mechanically‐stressed materials in high energy radiation environ

ISSN:0032-3888    

DOI:10.1002/pen.760290107

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe effect of polymeric molecular weight and molecular weight distribution on pressure‐sensitive adhesive performance was studied in a model system of commercial polyisobutylenes. Molecular weight was characterized by size exclusion chromatography and membrane osmometry. Pressure sensitive adhesive performance was assessed by shear, peel, and probe tack testing based on standardized test methods. Lower molecular weight polyisobutylenes (Mw<600,000) are successful in peel and probe tack testing due to their ability to flow quickly and wet the substrate test surface. They do not function as well in shear, however, where the polymer must resist flow under a load. High molecular weight species, by contrast, perform well in shear resistance tests and less successfully in peel and probe tack testing. Where high and low molecular weight polyisobutylenes are blended to broaden the molecular weight distribution while maintaining constant weight average molecular weight, adhesive performance in shear, peel, and probe tack are improved. All of the adhesive properties tested were found to have their foundation in some fundamental rheological properties of the polymers (e.g., shear viscosity and tensile creep compliance). This suggests the use of fundamental rheological characterization for screening of adhesive formulations over more empirical adhesive testing method

ISSN:0032-3888    

DOI:10.1002/pen.760290108

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractPoly[1‐(trimethylsilyl)propyne] (PTMSP) is an unusual polyyne material which is optically clear, exhibits high solubility in nonpolar organic solvents, and good oxygen compatibility. By contrast, polyacetylene is black, insoluble, and is unstable in oxygen. The long term stability of PTMSP has been determined by a combination of thermal gravimetric analysis (TGA) and permeability test procedures under a number of different isothermal aging conditions. The use of commercial antioxidants at up to 2 weight percent improves the long term stability of PTMSP. The presence of the antioxidant has no effect on the surface fluorination of PTMSP. Testing of PTMSP films for over eight months shows no change in either permeability or selectivity in contrast to previously reported dat

ISSN:0032-3888    

DOI:10.1002/pen.760290109

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThermal and mechanical studies on many linear polyesters have revealed their behavior in crystalline, liquid crystalline, and amorphous phases. Their phase behavior in binary compositions has also been studied by a range of additional techniques and in combinations including the polycarbonate of bisphenol‐A. Regions of amorphous compatibility and incompatibility have been identified and measures made of transition temperature changes with composition. The conditions for transreaction have also been determined and the properties measured for the resultant new copolymer

ISSN:0032-3888    

DOI:10.1002/pen.760290110

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA series of polyimides based on 4.,4′‐isophthaloyldiphthalic anhydride (IDPA) was prepared and characterized by inherent viscosity, differential scanning calorimetry (DSC), solubility, wide‐angle X‐ray scattering (WAXS), and isothermal thermogravimetric analysis (ITGA). Film forming, tough, insoluble polyimides were obtained with most of the 11 diamines used for evaluation. Two materials were semicrystalline. Several compositions showed excellent thermooxidative stability by ITGA at 300 and 350°C in air, as compared to Kapton‐H (Du Pont) film. The IDPA‐m‐phenylenediamine (m‐PDA) composition, for example, gave a flexible, amorphous film having aTgof 259°C (identical with LARC‐TPI) and insoluble in a wide range of solvents. It is based on a potentially low‐cost dianhydride (IDPA) and, unlike LARC‐TPI, a low‐cost, domestically available diamine which g

ISSN:0032-3888    

DOI:10.1002/pen.760290111

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY