摘要:

AbstractAn experimental study was carried out to investigate the development of stress birefringence patterns of molten polymer during the mold filling and cooling operation. For this study, a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a movie film the changes in stress birefringence patterns in the mold cavity during the molding operation, using a circular polariscope. The mold was equipped with an automatic relay system which closes the shut‐off valve when the pressure in the mold cavity reaches a predetermined value. The mold was also equipped with both heating and cooling devices, so that either isothermal or non‐isothermal injection molding could be carried out. The mold temperature was controlled by thermistor regulated controllers. During the entire cycle of the molding operation, the mold cavity pressure was continuously recorded on a chart recorder, using a melt pressure transducer. The present study shows how molding conditions (namely, injection pressure, melt temperature, mold temperature) influence the distribution of stress birefringence patterns in a molten polymer while it is being injected into, and cooled in, a rectangular mold cav

ISSN:0032-3888    

DOI:10.1002/pen.760180302

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractAn experimental study was carried out to investigate the phenomenon of interfacial instability in multilayer flat‐film coextrusion. For the study, a sheet‐forming die with a feed block was used to coextrude three‐and five‐layer flat films. Polymers coextruded were: (a) low‐density polyethylene with polystyrene, and (b) high‐density polyethylene with polystyrene. It was observed that, for a given polymer system, there is a critical value of wall shear stress at which an irregular (i.e., unstable) interface between the layers sets in, giving rise to a pattern similar to that usually found in a wood panel. Once the instability sets in, the severity of interfacial instability is found to depend on both the total volumetric flow rate (hence wall shear stress) of the combined streams and the ratio of the individual layer thicknesses. An attempt is made to correlate the critical conditions for the onset of interfacial instability in terms of the layer thickness ratio, and the viscosity and elasticity ratios of the two polymers being

ISSN:0032-3888    

DOI:10.1002/pen.760180303

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractMultilayer blown film coextrusion was studied, both experimentally and theoretically. For the experimental study, an annular die with a feed‐port system was designed and multilayer blown films were produced by rotating the inner mandrel with a one horsepower variable‐speed drive at speeds from nearly 2 to 6 rpm, and by inflating the tubular molten film with air. The die has 16 feed slots and melt pressure transducers are mounted along the axial direction of the outer wall of the annular flow channel. The transducers were used to determine the pressure gradient in the annular flow channel, which then permitted determination of the reduction in pressure drop when different combinations of two polymer systems were coextruded. Polymers used for b own film coextrusion were: (1) low‐density polyethylene with ethylene‐vinyl acetate; (2) low‐density polyethylene with high‐density polyethylene; (3) low‐density polyethylene with polypropylene; (4) high‐density polyethylene with ethylene‐vinyl acetate. For the theoretical study, stratified helical flow was analyzed using a power‐law non‐Newtonian model. A computational procedure was developed to predict the number of layers, layer thickness, and the volumetric flow rate as functions of certain processing variables (namely, the pressure drop in the die, and the angular speed of rotation of the inner mandrel of the die) and the rheological parameters of the individual polymers concerned. Comparison was made of the theoretical prediction of volumetric flow rate with experimental ones. Some representative results are presented of the theoretically predicted axial and angular velocity distributions, shear stress profiles, an

ISSN:0032-3888    

DOI:10.1002/pen.760180304

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractSimultaneous interpenetrating networks (SIN's) have been synthesized by simultaneous polymerization of a rubbery polymer based on castor oil and a second plastic forming monomer plus initiator and crosslinking agent. According to the overall composition and synthetic details, SIN's of elastomeric, leathery, or plastic behavior have been obtained. Polymers employed were the crosslinked polyester from castor oil and sebacyl chloride (a castor oil derivative) and polystyrene crosslinked with 1 percent divinyl benzene, simultaneously polymerized. Electron microscopy revealed a complex two phase morphology strongly depending on the relative gelation times of the two polymers, the polymer gelling first becoming the more continuous phase. Stress‐strain curves show a SIN plastic with a well developed yield point, as well us highly toughened elastomers. Both the plastic and the elastomeric SIN's are tougher than the corresponding homopolymers. Modulus‐temperature curves show a glass transition temperature around −60°C for the elastomer component, and +100°C for the polystyrene in th

ISSN:0032-3888    

DOI:10.1002/pen.760180305

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA polybenzimidazole having the structural repeat unitand designated AB‐PBI was formed into films by casting or precipitating from dilute solutions. Selected films were swollen in a plasticizing medium arid drawn about 2X. All films were dried in a vacuum oven to aid in the removal of residual solvent and moisture. Wide angle X‐ray scattering (WAXS) was used to show the type of ordering found in this material and to indicate the extent of molecular orientation. Neither a glass transition nor a crystalline melting point has been observed for this polymer, A Perkin‐Elmer DSC was used to scan the temperature range from −150 to H‐400°C in search of secondary transitions. The rheovibron proved more sensitive and a transition was located in the vicinity of −60°C. An activation energy‐was determined. The morphology of this polymer is subject to speculation. The ability of the chain to adopt a linear conformation leads to the possibility of a liquid‐crystalline nature in solution. A model based on the data in hand is suggested. Stress‐strain data was used to compare the mechanical properties of films prepared by several methods as well as to demonstrate the effect of orie

ISSN:0032-3888    

DOI:10.1002/pen.760180306

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA finite difference procedure was used to solve the equation of conservation of energy with the lubrication approximation. The temperature profiles due to viscous dissipation in the gap formed by a pair of equal sized rolls rotating at the same speed exhibit two maxima in the vicinity of the roll surfaces. The maximum temperatures also exhibit two local maxima and a minimum in the direction of flow. The calculated temperature distributions across and along the flow field reveal the possibility of excessive local heating which might be detrimental for certain temperature sensitive materials such as poly(vinyl chloride) and rubbers.

ISSN:0032-3888    

DOI:10.1002/pen.760180307

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA semiquantitative procedure has been developed for analyzing crystal nucleation in undercooled polymer melts that are undergoing flow. This analysis was applied to the specific ease of molten high density polyethylene experiencing low levels of shearing flow. A custom‐made concentric cylinder viscometer, which could be operated by the Rheometrics mechanical spectrometer instrument, was used to make simultaneous measurements of transmitted torque and optical anisotropy in isothermal melts, The result of the analytical procedure developed here was molecular Size‐dependence of chain distensions caused by prevailing shear. This distribution function was verified by testing against experimentally obtained values of birefringence. Total entropy reduction resulting from this distorted state was then calculated, and the corresponding increase in free energy was found to be at least enough to account for comparable crystal nucleation rates in flowing melts at higher temperatures and in quiescent melts at lower temperatu

ISSN:0032-3888    

DOI:10.1002/pen.760180308

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThis paper aims to review recent studies of the flow of non Newtonian (temperature and shear rate dependent) viscous fluids and to relate them to commonly encountered difficulties in polymer processing. The flows considered take place in narrow channels or pipes, and are dominated by viscous forces. Heat generation and temperature variations are taken to be the most significant aspects. A dimensionless formulation of the energy and stress equations is employed, thus bringing out the role of Graetz, Nahme‐Griffith and Brinkman numbers. These latter are introduced as ratios of temperature differences. Special consideration is given to the question of the stability of such flow

ISSN:0032-3888    

DOI:10.1002/pen.760180309

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe influence of artificial weathering on three general properties of films of high‐impact polystyrene (HIP), poly(ethylene terephthalate) (PET), and poly(vinyl chloride) (PVC) was investigated, Degradation resulting from weathering was investigated in terms of changes in the water vapor permeation, mechanical properties, and optical transmission. The diffusivities and permeabilities of these three materials were significantly altered by weathering at two levels of exposure. Films of HIP were embrittled at both levels of exposure, whereas the PET films were embrittled only at the high level of exposure. Films of PVC showed embrittlement at the highest level of exposure and the lowest test temperature. Changes in the optical properties were less significant, amounting to a relatively small decrease in the transmission of the films in the visible rang

ISSN:0032-3888    

DOI:10.1002/pen.760180310

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe volume of cis‐1,4‐polybutadiene between 5 and 55°C and 1 and 3000 atmospheres was measured to within a relative error of 0.1 percent with an especially developed, bellows‐type dilatometer. The presence of a small transition near 55°C was indicated by analysis of the data and confirmed by differential thermal a

ISSN:0032-3888    

DOI:10.1002/pen.760180311

出版商:Society of Plastics Engineers, Inc.    

年代:1978

数据来源: WILEY