摘要:

AbstractA method for determining polymer melting temperatures,Tm, based on a simple modification of thermo‐optical analysis is described. The method makes use of a small, highly conducting substrate and a preselectedTm, procedure which results in rapid heating rates (∼1500°C/min) without temperature overshoot or superheating. Accuracies to within ±0.15°C are readily obtained. Application of the method to isothermally crystallized polyoxymethylene (Delrin 100 and 500) shows thatTm, increases with both time and temperature of crystallization as well as with increasing molecular weight. The potential of the method for characterizing polymer thermal history and molecular weight is dis

ISSN:0032-3888    

DOI:10.1002/pen.760180102

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractSimilar thermal expansion instabilities, consisting of isothermal, time‐dependent changes in thermal expansion after a rapid change in temperature, were observed in epoxy resins with different degrees of cross‐linking. Creep experiments performed at different stages of expansion show decreases in tensile creep rate with decreased expansion. The role of changes in moisture content as a possible cause of the dimensional instability is examined for epoxy resins and a highly cross‐linked polyurethane. Results indicate that the state of expansion is the primary cause of changes in creep rate rather than temperature or moisture co

ISSN:0032-3888    

DOI:10.1002/pen.760180103

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractAbsorbed moisture was found to plasticize the type of cross‐linked epoxy resin system investigated, causing a lowering of the Ta and in turn affecting mechanical response, such as by shifting the relaxation moduli to shorter times. The phenomenon is described and quantified in terms of an existing free volume theory relationship. Weight gains greater than equilibrium amounts were observed without accompanyingTgchanges which is attributed to moisture entrapment during microcracking in the resin. Creep studies performed under water at 300° F established an additional mechanism for loss of elevated temperature properties which is characterized by the appearance and growth of cracks in the material. The observed failure processes are described in terms of an existing theory for rupture of cross‐linked rubbers. The process is governed by the synergistic effects of moisture, temperature, and stress. Moisture changes the viscoelastic response of the material so that stress‐induced crack formation and growth is facil

ISSN:0032-3888    

DOI:10.1002/pen.760180104

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractIt is found that the principal normal stress difference,N1, in commercial polystyrene melts is a unique function of shear stress σ12, independent of temperature and molecular weight, An empirical expression representing this relationship is developed. The functional dependence reported does not represent data for narrow molecular weight distribution polystyrenes, generally significantly overpredictingN1values. The basis for this behavior is discussed. The implications of theN1− σ12relationship to some rheological and processing problems are descri

ISSN:0032-3888    

DOI:10.1002/pen.760180105

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe curing reaction of thermosetting polymers is accompanied by exothermal heat which has been measured with a differential scanning calorimeter. The Perkin‐Elmer DSC‐1 B was used for recording the curing behavior of a diallyl phthalate molding compound and two unsaturated polyester molding compounds. The residual heat of reaction has also been determined by a dynamic DSC scan of partly cured products made at various mold temperatures and curing times. It was thus possible to calculate the degree of curing and to dictate the optimum processing conditions for the indicated molding compounds. The interpretation of results leads to the conclusions that the DSC can be used to set specifications and to perform quality control for the molding compounds and that the most significant processing parameter is mold temperat

ISSN:0032-3888    

DOI:10.1002/pen.760180106

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA critical factor in the performance of fillers in plastics composites is the manner in which the particles pack together. This is called the packing fraction; the true volume occupied by a filler divided by its apparent total volume. The means for determining packing fraction and its effect on viscosity and physical, thermal, electrical and economic properties are outlined.

ISSN:0032-3888    

DOI:10.1002/pen.760180107

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe structure and properties of an unusual new polyamide copolymer derived from 2,2‐bis‐(4‐aminoeyclohexyl)propane and a 60/40 molar mixture of azelaic and adipic acids are described. The alicyclic diamine structure, with its cyclohexyl rings and central gem‐dimethyl group, contribute to chain stiffness and amorphous character in the polyamide, and sets it apart from more common polyamides (e.g., nylon 6–6) with their relatively flexible polymer chains, low glass transition temperatures and high levels of crystallinity. The particular combination of dicarboxylic acids employed yields a resin with a high glass transition temperature (185°C). This amorphous, colorless material is exceptionally transparent, with a high luminous transmission (92 percent) and low haze (0.5 percent). The polymer is tough and resistant to scratching and abrasion and to attack by chemicals and solvents. Its high glass transition temperature leads to a high heat deflection temperature (160°C) and excellent retention of its mechanical properties at elevated temperatures. It is an atypical nylon in that its dimensions, mechanical properties and electrical properties are relatively unaffected by changing moist

ISSN:0032-3888    

DOI:10.1002/pen.760180108

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractCreep experiments carried out on transparent and translucent polymers permit the observation of irreversible material damage in the form of crazes or microcracks. The formation of such damage is strongly dependent on the applied stress, temperature and environmental conditions. The first appearance of observable material damage seems to be explicable by an energy criterion. The energy supplied by the external load can be divided into conserved and dissipated parts, each of them causing volume (isotropic) and shape (deviatoric) changes. The different parts of the energy can be computed if the creep‐compliance is approximated by a Prony‐Dirichlet series with a finite number of terms. Computations carried out for experiments with air as the environmental medium under isothermal conditions show the dependence between the appearance of first visible material damage (crazes or microcracks) and the conserved ene

ISSN:0032-3888    

DOI:10.1002/pen.760180109

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractShort glass fiber‐epoxy laminates of controlled fiber orientation and distribution were loaded to failure under uniaxial tension. The mechanical characteristics of specimens with different orientation patterns, which were determined experimentally, were compared with analytical predictions based on “Laminate Analogy” methods. Results show good agreement between empirical data and prediction in the case of stiffness, stress‐strain relationship and strength based on ultimate strain criteria. A methodology is proposed according to which a well‐defined, orthotropic, short fiber reinforced plastic system can be prepared, analyzed, and optimized by tailoring it according to the loading pattern in a similar manner to that of the well‐established, continuous fiber reinforce

ISSN:0032-3888    

DOI:10.1002/pen.760180110

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractAn experimental study of the development of orientation in polystyrene melts during flow and its retention in vitrified parts is described. It is shown on the basis of elongational and shear flow experiments that orientation in vitrified polystyrenes may be predicted from a knowledge of the stress field at the time of vitrification and application of stress‐optical laws. More generally a relationship between birefringence and principal stress difference is found which correlates (1) on‐line isothermal shear flow, (2) on‐line non‐isothermal elongational flow (melt spinning), and (3) vitrified samples formed in both shear and elongational flow. It is further proposed that orientation in polymer chains in deforming melts is uniquely dependent on stress—specifically, that the ratio of the stress‐optical constantCto the intrinsic birefringence Δ° is approximate

ISSN:0032-3888    

DOI:10.1002/pen.760180111

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY