摘要:

AbstractFree‐radical reactions, which are relevant in the chemical modification of polymeric materials, are discussed in relationship to their influence on random chain scission. A mathematical model is developed to calculate the entire molecular weight distribution (MWD) with the degree of chain scission as the sole parameter. This expression is identical to the one derived by Saito for the case of scission initiated by irradiation. An expression for the variation of molecular weight averages with the degree of chain scission is derived and compared with those calculated with the methods of moments found in the literature. The validity of empirical closure conditions used with moment methods is discussed. Experimental data for polypropylene (PP), degraded with organic peroxides in a single screw extruder, are compared with predictions when fitting the degree of chain scission. For a specific degradation process, the degree of chain scission is found to be proportional to the initiator leve

ISSN:0032-3888    

DOI:10.1002/pen.760330802

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe objective of this work is to combine reaction, extrusion, and orientation together in a process so as to provide product in a form which is not limited to fiber or film. Three coupled problems form the focus of the work: (i) devising a practical, continuous extrusion‐orientation method; (ii) generating low concentrations of free radicals in the polymer to tailor molecular weight distribution before orientation; (iii) generating high concentrations of free radicals in the polymer to form a network in the oriented polymer without destroying its superior properties after orientation. A continuous extrusion method for orienting polymer in forms other than fibers and films was devised based upon two melt pullers. Operation of a prototype of the equipment showed it capable of providing draw ratios of greater than ten. Injection of low initiator concentrations during extrusion (i.e., before orientation) directed at solving the second problem had an effect which depended upon the degree of branching, the molecular weight, and the degree of unsaturation of the polyethylene. Large increases in molecular weight could be obtained. However, in agreement with previous work, formation of branched molecules drastically limited draw ratios attainable by the extrusion‐orientation process. To obtain high concentrations of free radicals, bench scale experiments demonstrated that a recently published method involving the use of a UV sensitizer and crosslinker followed by irradiation was directly adaptable to this process (with the irradiation applied after orientation) and provided significant improvements in creep resistance. Various attempts involving die design to obtain orientation and high initiator concentrations as well as gamma radiation to induce crosslinking after orientation were attempted and appear far less promising than the above meth

ISSN:0032-3888    

DOI:10.1002/pen.760330803

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractBlends of unsaturated polyester resin and polyvinylacetate (PVAc) were molded with a new instrument called the Plastoreactomat (PRM). The shrinkage and exothermic peak of polymerization were recorded during moding, and the influence of the processing conditions (pressure and temperature) on these phenomena and on the morphology was investigated for various PVAc contents. Within the limits of this study, it was found that shrinkage increases as the temperature and pressure increase. These results are discussed in terms of a competition between the phase separation and the reaction rates. In addition, it was verified that a co‐continuous two‐phase system consisting of the PVAc and the polyester network enhances the low‐profile beh

ISSN:0032-3888    

DOI:10.1002/pen.760330804

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractWe have detailed the effects of annealing and temperature on the residual microstress at the matrix interface in rubber‐filled and glass bead‐filled epoxy resin systems. We found that annealing renders changes in residual microstress. The closer the annealing temperature to the glass transition temperature of the sample, the more pronounced the annealing effect on the stress. Also, we examined the interfacial residual microstress and found a linear relationship with annealing temperature. A description of the mechanism of the interfacial microstress buildup is propo

ISSN:0032-3888    

DOI:10.1002/pen.760330805

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractLiquid‐liquid equilibrium data for the polystyrene‐cyclopentane binary system and the polystyrene‐cyclopentane‐cyclohexane ternary system were measured by observing the cloud points at the temperature range in which the systems showed their lower critical solution temperature. The experimental liquid‐liquid equilibria were correlated successfully by the UNIFAC‐FV model with adjustable

ISSN:0032-3888    

DOI:10.1002/pen.760330806

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe generalization of a multiordering parameter model to treat physical aging in polymeric glasses is more fully explored. In the past, this model has successfully rationalized most aspects of time dependent volume and enthalpy behavior; however, only qualitative agreement between predictions of the generalized model and experiment were previously achieved for physical aging. Now, by paying strict attention to the specific analytical form of the shift factor expression, quantitative predictions have been realized for physical aging behavior based on evaluations of the shift factor parameters using volumetric data. The model also reproduces the observed behavior of glasses subjected to more complex thermal treatment such as those which evoke “memory” in glasses, e.g., shift reversal and nonmonotonic variations of the steepness of relaxation curves in the primary transition reg

ISSN:0032-3888    

DOI:10.1002/pen.760330807

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe use of polymeric materials in building or construction applications is steadily increasing. Therefore, the potential for these materials to be exposed to fire is also increased. The understanding of the pyrolysis characteristics of these materials is thus a necessity. There are many standard tests used to evaluate materials. Unfortunately, the correlation between these tests and large scale fire is less than desirable. A new bench scale rate of heat release apparatus, the Cone Calorimeter, is now being used more frequently in pyrolysis testing of polymeric materials. This apparatus has been shown to correlate much better between room scale testing and large scale fire testing. The cone Calorimeter provides a pyrolysis profile of a material under ambient oxygen conditions. Characteristics such as ignition time, total heat release, maximum rate of heat release, mass loss during pyrolysis, CO2, CO, and smoke production are determined. In this work several almost neat polymers are examined and the general pyrolysis characteristics of these polymers are discussed. The objective of this work is to provide information of basic polymeric pyrolysis properties of these materials. Variations in the material, i.e., molecular weight, polydispersity, and residual catalysis, along with changes in testing procedures, can have dramatic effects on results. Obviously the addition of flame retardant and flame retardant packages to any of these materials will have dramatic effects on results.

ISSN:0032-3888    

DOI:10.1002/pen.760330808

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractDC dark conductivity (σ) has been measured in thin films of poly(N‐vinyl carbazole) (PVK). The dependence of σ on temperature (T) followed a typical Arrhenius relation but at the same time a relation σ(T)α exp(‐[T0/T]2) could be fitted to the experimental points. To reconcile this observation, it is suggested that the expression for the conductivity then is expected to contain in addition to the activation term, the factor exp[‐(T0/T)2] which is the behavior expected in a trap‐free molecular hopping system with a Gaussian distribution of sites energy, so that the DC dark conductivity would be of the functional form\documentclass{article}\pagestyle{empty}\begin{document}$$ \sigma (T)\alpha {\rm exp} - [\Delta \varepsilon /\kappa T + (T_0 /T)^2] $$\en

ISSN:0032-3888    

DOI:10.1002/pen.760330809

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe bursting strength and inflated deflection of linear low density polyethylene (LLDPE), oriented polypropylene (OPP), flexible poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), and polyurethane (PUR) films of different thicknesses were investigated with the pneumatic bursting method. The study showed the bursting air pressure is directly proportional to the thickness of LLDPE, OPP, and PET films. The effect of different membrane diameters on the change of the bursting properties in OPP and PUR film was also investigated. The results showed that the bursting properties are inversely proportional to the membrane diameter. Furthermore, biaxial stress‐strain exerted on the pole region of the tested films was studied. The results denoted that the relationship between the biaxial and uniaxial tensile stress‐strain was considered for two types of film: (1) Film that presented an isotropic tensile behavior showed that the tangential stress‐strain is higher than the tensile stress‐strain. (2) Film that presented an anisotropic tensile behavior showed that the tangential stress‐strain is determined by the weaker tensile stress‐strain values between two

ISSN:0032-3888    

DOI:10.1002/pen.760330810

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760330801

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY