摘要:

AbstractThe present study reports on the results of an integrated experimental program to determine some of the important interactions between resin properties, moldability, and the microstructure and ultimate properties of molded articles. As part of the program, resins are characterized as to their rheological, thermal, and crystallization behavior. Then, the resins are injection molded in a laboratory machine employing simple, but highly instrumented molds in order to evaluate moldability and to produce moldings for testing and analysis. Microstructural analysis to determine morphology and orientation of the moldings is carried out utilizing polarized light microscopy and differential scanning calorimetry. Finally, shrinkage and tensile properties of the moldings are determined experimentally. To illustrate the utility of the proposed techniques, results are reported for two polyethylene resins' that exhibit superficially similar properties but, according to tests, show significant differences in moldability and product properties.

ISSN:0032-3888    

DOI:10.1002/pen.760201702

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractAn experimental study is reported of the origins of fluted void structures in wet spun fibers. Optical microscopy studies of the interaction of spinning solutions and coagulating bath liquids suggest these voids originate in a fingering phenomenon occurring at the interface. Further studies show that this fingering effect is generally independent of the presence of the polymer and dependent on the two low molecular weight liquids alone. In the systems investigated it is found that the occurrence of the fingering is associated with a critical value of the heat of solution. It is argued that the fingering and associated fluted void structures in wet spun fibers are due to a “Thomson‐Marangoni” type interfacial instability. This can be justified using the theory of hydrodynamic stability. Fluted void structures produced in asymmetric membranes probably have a similar o

ISSN:0032-3888    

DOI:10.1002/pen.760201703

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractUsing prepared and commercial two‐step phenolic molding compounds, the influence of moisture on their curing behavior was examined by the disk cure test and the solvent extraction method for the early and middle stages of the curing process, respectively. It was determined that moisture in the compounds could enhance the curing rate and the degree of cure as well as flowability. A possible mechanism explaining the acceleration of curing was proposed, suggesting that moisture might facilitate catalytically the decomposition of hexamine or hexamine‐novolac adduct into reactive low molecular weight materials, which could then easily react with a resin even in a state of fairly advanced cure due to their facile diffus

ISSN:0032-3888    

DOI:10.1002/pen.760201704

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe experimental results of the Viscoelastic properties of linear polymers of narrow molecular weight distribution (MWD) and of their mixtures have been analyzed and generalized. Based on the study of the properties of polymers of narrow MWD, we propose a classification of high molecular weight compounds. It specifies a distinct boundary between oligomers and polymers, assuming that the most important feature of polymers is the manifestation of large high‐elastic recoverable deformations of entropy character. For polymers to be characterized, not the absolute molecular weight is essential, but the molecular weight referred to the boundary values. The corresponding state for polymers is attained at temperatures 100°C away from the glass temperature. The transition from the fluid to the high‐elastic state with increasing deformation rate (or frequency for cyclic deformation) has been studied. Transition to the high‐elastic state takes place over a narrow stress range (0.1‐1.0 dynes/cm2), independent of molecular weight, whereas the critical deformation rates (frequencies), like viscosity, depend greatly on molecular weight. An increase in the amount of deformation shifts, to u certain extent, this transition to lower Kites of deformation (frequencies). In the region of deformation rates (frequencies) corresponding to the high‐elastic state, the effect of large deformations during shear manifests itself largely in the tear‐off of polymers Iron, the confining surfaces and in specimen rupture. Polydispersity has a strong effect on the properties of polymeric systems. As the rate of deformation is increased, the transition proceeds successively from the higher molecular weight components. This relaxational transition is tantamount to a change of the structure for polymeric systems. It is responsible for non‐linear, particularly, non‐Newtonian behavior of such systems. The transition to the high‐elastic state and all the related phenomena are observed also in concentrated solutions of high molecular weight polymers. The long‐term durability of un‐cured rubbers in the high‐elastic state is described b

ISSN:0032-3888    

DOI:10.1002/pen.760201705

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractDeterioration or spoilage of dehydrated food products stored in flexible packaging materials depends on the partial pressure of water vapor in the environment of the stored food. Mathematical analysis of the diffusion of water vapor through semipermeable polymer films using Nernst‐Planck equations is combined with non‐liner water sorption isotherms on food to establish criteria and optimum conditions for storage stability of dehydrated food. Langmuir, Brunauer‐Emmet‐Teller (BET), Halsey, Oswin and Freundlich isotherms are used for various ranges of water activity. It is shown that a single parameter, the permeability‐sorption constant, based on the physical properties of the polymer and the sorptive properties of the food, accounts for both diffusion and adostption and can be used to accurately determine maximum storage times and can be used to accurately determine maximum storage times and to optimize the selection of packaging films. The theory is extended to thermodynamically compatible solute‐polymer systems, where the polymer film is swollen appreciably by the diffus

ISSN:0032-3888    

DOI:10.1002/pen.760201706

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractAmong different fluid parameters having some effect on the environmental stress cracking of plastics, the surface tension and the solubility parameter are generally accepted as dominant ones. However, experimental evidence to date indicates that one single parameter can not be used as an index for predicting failure in all cases and a distinction of the conditions of their importance has not been made. This paper presents the results obtained from the creep and fatigue response of high impact polystyrene in different environments, especially those environments that do not show any effect on the unstressed polymer. The results indicate that at high stresses, the mobility of the fluid in penetrating into the polymer craze networks is more important and that at smaller stresses, the solubility parameter is more important.

ISSN:0032-3888    

DOI:10.1002/pen.760201707

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractExperimental data and theoretical considerations on the shape of the temperature‐surface tension coexistence curve are presented for binary mixtures. It is found that the interfacial tension is proportional to the difference between the surface tensions raised to thenth power wherenis of the order of 4.

ISSN:0032-3888    

DOI:10.1002/pen.760201708

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe Gibb's adsorption equations for a multicomponent multiphase system are used to discuss the relationship between the surface tensions and interfacial tension. It is shown for binary systems that when the terms involving the surface excesses vanish, Antonow's rule is obtained.

ISSN:0032-3888    

DOI:10.1002/pen.760201709

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractAn experimental study of steady shear and elongational flow Theological properties of a series of polypropylene melts of varying molecular weight and distribution is reported. Broadening the molecular weight distribution increases the non‐Newtonian character of the shear viscosity function and increases the principal normal stress differences at fixed shear stress. The behavior is compared to earlier rheological property‐molecular weight studies. Correlations are developed for these properties in terms of molecular structure. Elongational flow studies indicate that for commercial and broader molecular weight distribution samples, ready failure by neck development occurs and the elongational viscosity appears to decrease with increasing elongation rate. For narrower molecular weight distribution samples, the elongational viscosity is an increasing function of elongation rate, The implication of these experimental results to viscoelastic fluid constitutive equations and polymer melt processing is develo

ISSN:0032-3888    

DOI:10.1002/pen.760201710

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA simple equation is proposed to calculate the shear‐rate‐dependent viscosities of entangled polymers and particle suspensions. The rate‐dependence of the viscosities is attributed to changes in certain structural parameters associated with the fluids, such as entanglement density or degree of particle agglomeration. The state of these structural parameters for fluids subjected to a given shear flow is determined by two competing process, i.e., structural breakdown and reformation, which in steady How arc in a state of dynamic equilibrium. For the polymer systems structural degradation and reformation are tantamount to entanglement loss and creation, whereas for the suspensions they are correlated with the particle breakup and flocculation. The regeneration process is driven by thermal diffusion and is assumed to be independent of shear rate. The degradation process is caused primarily by the imposed shear and is assumed to be proportional to the shear rate to a powerm(0

ISSN:0032-3888    

DOI:10.1002/pen.760201711

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY