摘要:

AbstractThe present state of knowledge of the manner in which small molecules dissolve and diffuse in plastic materials is briefly described. The advantages and disadvantages of these phenomena are outlined. Two aspects, one positive and one negative, are reviewed in more detail. The use of plastic materials as barriers to gas and vapor transport particularly in packaging applications is described and illustrated by examples. Typical permeability values for water vapor, oxygen and carbon dioxide in various polymer films are given. Values for hydrogen and helium are included to illustrate the possible use of plastic films for gas separations. On the negative side, the migration of residual monomers and other, possibly toxic, substances out of plastic materials can be a serious problem. Some of the basic considerations and practical solutions to the migration problem are discussed in more detail.

ISSN:0032-3888    

DOI:10.1002/pen.760181502

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe chemorheology of polymers prepared by peroxide curing terpolymers of ethylene propylene and diene monomer (EPDM) was studied at 375°F in air. Measurements were conducted on terpolymers containing dicyclopentadiene (DCPD), ethylidene norbornene (ENB) or 1,4‐hexadiene (HD) and also on copolymers. Effects of the level of dicyclopentadiene were investigated. A linear relationship is found between crosslinks formed during oxidation and chain scissions. At low termonomer level and in copolymers, this relationship is linear only during the early stages of oxidation. Results are consistent with a kinetic model in which crosslinking sites and scissioning sites on the polymer compete for free radicals which propagate the oxidative chain reaction. Termonomer units apparently act primarily as crosslinking sites with the tendency to crosslink being substantially greater in DCPD than ENB and HD. The number of crosslinks per scission derived from stress relaxation correlates well with elongation to failure retained after air aging 3 days at 350°F. Adjustment of termonomer level can lead to a ratio of crosslinking to scission which strikes a balance between softening of copolymer and embrittlement of some terpolymers at elevated temperat

ISSN:0032-3888    

DOI:10.1002/pen.760181503

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractAmorphous homopolymer blends were differentiated from the corresponding random copolymers with wide angle X‐ray diffraction (WAXRD) using the diffraction angle and the band width at one‐half peak maximum. The diffraction angle was also used to determine the composition of copolymers and of mixtures of homopolymers. A procedure has been developed to predict the WAXRD patterns of polyblends and/or random copolymers based on those of the corresponding homopolym

ISSN:0032-3888    

DOI:10.1002/pen.760181504

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA theoretical and experimental study of heat transfer to polymer melts flowing through circular tubes is presented. The mathematical model provides for shear heating and expansion cooling effects, and also heat of reaction during flow for various wall boundary conditions. Experimental results, obtained using low density polyethylene, show reproducible temperature and velocity profiles. The measured inlet melt temperature profile and the axial wall temperature profile provide the boundary conditions for the calculations. The experimental data confirm the predictions of the magnitude of the shear heating and expansion cooling effects during tube flow.

ISSN:0032-3888    

DOI:10.1002/pen.760181505

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA theoretical treatment is presented for the prediction of the rate at which a liquid is entrained by a roll which is rotating partially submerged in a Newtonian liquid, and also for the prediction of the variation in the thickness of the film around the roll. The method involves the integration of the momentum equation after neglecting inertia forces in the dynamic meniscus region and the matching of the surface curvature with that derived for the static meniscus region near the liquid surface. The resulting equation allows the prediction of the relationship between a dimensionless film thickness parameter,T, and the capillary number,Ca, as a function of the radius of the roll, the withdrawal angle and the position of the roll periphery. The liquid flux on the roll can also be predicted.

ISSN:0032-3888    

DOI:10.1002/pen.760181506

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractFlow properties of four molten epoxide prepolymers of number average molecular weight 900(I), 1,500(II), 2,100(III) and 4,000(IV), were measured at temperatures ranging from 361 to 463K, and shear rates from 500 to 10,000 s−1. Apparent shear viscosities showed that all prepolymers used have Newtonian behavior up to shear rates of 2,000 s−1. Shear thinning occurs at higher shear rates. Flow activation energies at constant shear rates in the range of 500 to 7,000 s−1vary for prepolymer III from 5 to 24 kcal/mol, and for prepolymer IV from 9 to 25 kcal/mol. Flow indices in the same shear rate range vary for prepolymer III from 1.0 to 0.7 and for prepolymer IV from 1.0 t

ISSN:0032-3888    

DOI:10.1002/pen.760181507

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractPolymeric films are used to enclose other materials (as for packaging), to carry information (as for magnetic tapes), and as an engineering material (as for capacitor dielectrics). There is an appropriate combination of the bulk and the surface properties engineered to fit each particular use. This duality is illustrated by the “processing for properties” of poly(ethylene terephthalate) films. An overview is presented of stretching, stabilization and relaxation methods of manufacture. These processing techniques, in conjunction with changes in the polymer composition, provide the property levels that are commercially signific

ISSN:0032-3888    

DOI:10.1002/pen.760181508

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractMorphology of poly(vinyl chloride) resin particles formed by suspension polymerization was investigated by a combination of several techniques. Significant differences were found in the internal structure of resins obtained under different polymerization conditions. Five main types of resin particles with different porosity and absorptivity were identified by scanning electron microscopy. Three methods were employed to characterize porosity and structural heterogeneity of resin particles: density fractionation of resin particles in mixtures of methanol and carbon tetrachloride; absorption of silicone oil and dioctyl phthalate by resin particles; and examination of fractured particles embedded in epoxy resins. All three methods gave consistent results and can be used for semiquantitative characterization of resin structural heterogeneity. Different particle structure and degree of resin heterogeneity: can profoundly affect compounding and processing operations.

ISSN:0032-3888    

DOI:10.1002/pen.760181509

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractCharacterization of a heterogeneous latex polymer synthesis requires quantifying the association of successive stage compositions with the previous stage latex seed particles. A new method for performing this analysis is presented for uniform sized latex particles by use of a Joyce Loebl disc centrifuge photosedimentometer. An iterative procedure is employed to solve a problem of unknown particle density when a successive polymerization produces new latex particles. The procedure is applicable regardless of the monomer compositions of the various stages and eliminates problems encountered with electron microscopy of soft deformable latex particles.

ISSN:0032-3888    

DOI:10.1002/pen.760181510

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractMaterials and conditions required for constant rate absorption of a liquid into a glassy polymer (Case II transport) have been exploited to produce prototype devices for constant rate delivery of a solute, molecularly dispersed within the polymer, to the surrounding liquid environment. Absorption of n‐hexane in polystyrene films, containing between one and two percent of Sudan Red IV dye, resulted in constant rate liberation of the colored solute to the surrounding fluid. The rate of dye release was controlled by the constant rate absorption of n‐hexane in these dye‐containing films. Companion experiments involving microtome sectioning and photomicrographic recording of dye‐loaded films, consequent to immersion in n‐hexane for various time intervals, revealed that the unpenetrated central core retained the dye originally dispersed within the film sample and, conversely, the swollen outer regions were completely denuded of dye consequent to n‐hexane penetration. The constant rate advance of the microscopically observable sharp boundary, between dye‐containing and dye‐denuded polymer, was quantitatively consistent with the independently determined kinetics of dye accumulation in the supernatant n‐hexane. These results indicate that diffusion of invading n‐hexane to the relaxing boundary and back diffusion of dye in the previously swollen outer shell are both rapid compared with the rate‐determining Case II transport of n‐hexane in these dye‐containing films. The delivery of Sudan Red IV to the n‐hexane was not confounded by an initial burst of solute, typically common to so‐called membrane‐reservoir controlled delivery devices. Swelling‐induced delivery from glassy matrices appears useful, therefore, for the design of monolithic devices for constant rate delivery over the entire course of the delivery cycle. The concept is not limited to monolithic devices; membrane‐reservoir devices could be constructed involving a glassy, solute‐containing reservoir which could be activated by penetration of invading liquid consequent to placement in a suitable fluid environment. Development of devices, suitable for swelling‐controlled release of drugs to target organs, will be based u

ISSN:0032-3888    

DOI:10.1002/pen.760181511

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY