Showing papers in "Polymer Engineering and Science in 1980"
TL;DR: In this paper, the authors define Fickian diffusion in rubbery polymers and present a review and classification of various theoretical models which have been proposed to account for these phenomena.
Abstract: After defining Fickian diffusion in rubbery polymers an overview of transport behavior in polymers is presented. Diffusion and sorption below the glass transition are discussed, followed by a review and classification of the various theoretical models which have been proposed to account for these phenomena. A short list of recommendations for future work is included.
315 citations
TL;DR: In this article, a prediction technique for gas permeability from polymer structure has been developed on the basis of a specific free volume diffusion theory, which predicts a linear relationship between log (permeability) and (−1/specific volume).
Abstract: A prediction technique for gas permeability from polymer structure has been developed on the basis of a specific free volume diffusion theory. In this theory, the free volume available per unit mass in a polymer structure controls the rate of gas diffusion and, hence, its rate of permeation. The smaller this specific free volume is, the more difficult the gas diffusion and, thus, the better its barrier to gases becomes. Specifically, the theory predicts a linear relationship between log (permeability) and (−1/specific volume). A number of existing polymers covering six orders of magnitude in CO2 permeability and O2 permeability were found to follow this correlation. The specific free volume in a polymer was obtained from group contribution calculations. As a result, the gas permeabilities become predictable from the specific volume in a polymer which, in turn, varies with its molecular structure. The advent of this specific free volume theory for gas permeation simplifies greatly the selection of barrier materials for packaging applications. For a given barrier application, a critical specific free volume is first defined from its gas barrier requirement. The polymer structures having specific free volumes smaller than the critical value are then identified. These are the polymers that would have the necessary barrier performance. By this theory, molecular structures, with string polar-to-polar interactions and hydrogen-bonding forces are found to be good barriers to CO2 and O2.
303 citations
TL;DR: In this article, the equilibrium sorption and diffusion of water in a high Tg epoxy was examined using various analytical techniques including differential scanning calorimetry, infrared spectroscopy, electron microscopy and nuclear magnetic resonance.
Abstract: It has been shown that sorbed moisture plasticizes epoxy resins with a resultant depression in the glass transition temperature of the polymer. The nature of the epoxy-water interaction still requires further investigation. The equilibrium sorption and diffusion of water in a high Tg epoxy is examined. Other analytical techniques including differential scanning calorimetry, infrared spectroscopy, electron microscopy and nuclear magnetic resonance are applied to the system. Experimental results suggest that the sorbed water at low concentrations is strongly localized at specific segments or groups in the polymer. Discussion is given relative to the structure-properties of the epoxy and its possible correlation to the experimental data obtained.
212 citations
TL;DR: In this article, shear and elongational flow measurements on polystyrene melts reinforced with small particles were carried out, and the influences of loading level, particle size, and surface treatment on shear viscosity, principal normal stress difference, and length of elongation were discussed.
Abstract: Shear and elongational flow measurements on polystyrene melts reinforced with small particles were carried out. The influences of loading level, particle size and surface treatment on shear viscosity, principal normal stress difference, and elongational viscosity were discussed. These systems exhibited yield values for both shear and elongational flow. Experimental values for the ratio of the tensile to the shear yield stress give satisfactory agreement with the predictions of the von Mises yield criterion. The yield value appears to increase with decreasing particle size and may be varied with surface treatment. The principal normal stress difference at fixed shear stress decreases with volume loading of particulates. The results are interpreted in terms of a system forming a gel due to interparticle forces, which is disrupted by a critical distortional strain energy.
184 citations
TL;DR: In this article, morphological changes induced in segmented elastomers by annealing and quenching are reported. But the effect is much smaller for those samples having crystalline hard segments.
Abstract: Investigations of morphological changes which are induced in segmented elastomers by annealing and quenching are reported. Four different polymers were studied each based on the same soft segment—1000 or 2000 molecular weight poly(tetramethylene oxide). The hard segments were 4,4′-diphenylmethane diisocyanate (MDI) chain extended with 1,4-butane diol (ET series), piperazine coupled with 1,4-butane diol bischloroformate (BN-1,4), or dimethyl terephthalate condensed with 1,4-butane diol (H-50). Following annealing at various temperatures (120, 150, 170, or 190°C), the polymers were quenched to ambient conditions, and their properties measured by differential scanning calorimetry (DSC) as a function of time following the quench. DSC measurements taken immediately after the quench show that the soft segment Tg is higher than that of the control, suggesting that the applied thermal history promoted increased mixing of hard and soft segments. As time passes after quenching, the Tg values decrease and approach an equilibrium value. This effect is much smaller for those samples having crystalline hard segments. Endotherms attributed to the disruption of long range ordering in the hard segment domains resulted from the annealing process. These endotherms appeared at higher temperatures for higher annealing temperatures. The positions of crystalline melting endotherms were independent of the annealing/quenching conditions investigated.
174 citations
TL;DR: The thermal properties of poly(ethylene terephthalate) (PET) are sensitively affected by polycondensation catalysts and temperature, and the kinetics of thermal degradation were investigated by determining the rates of formation of carboxyl groups on isothermal heating as mentioned in this paper.
Abstract: The thermal properties of poly(ethylene terephthalate) (PET) are sensitively affected by polycondensation catalysts and temperature. The kinetics of thermal degradation were investigated by determining the rates of formation of carboxyl groups on isothermal heating. Carboxyl groups in PET were not only a result of thermal exposure but they were also an influence on hydrolytic stability. The hydrolytic cleavage of polyester chains, i.e., the formation of carboxyl groups, was found to be an autocatalytic reaction.
148 citations
TL;DR: In this paper, the relative rates of polymer removal in an oxygen plasma have been measured for 40 polymer samples and the rates of removal are correlated with structural factors which enhance or retard removal.
Abstract: Relative rates of polymer removal in an oxygen plasma have been measured for 40 polymer samples. The rates of removal are correlated, with structural factors which enhance or retard removal. Strong backbone bonds, aromatic and polar functional groups, and metallic atoms decrease the removal rates. Weak bonds not attached to the- polymer backbone have little affect while weak bonds attached directly to the chain or in the chain greatly accelerate removal. Chlorine present in the polymer catalyzes removal. This can be mimicked by mixtures of CF4, and O2 for which much enhanced removal rates are observed.
145 citations
TL;DR: In this article, a study of the fiber orientation in short glass fiber-filled thermoplastics resulting from convergent, divergent and shear flows has been made and the data are consistent with a pressure dependent viscosity.
Abstract: A study has been made of the fiber orientation in short glass fiber-filled thermoplastics resulting from convergent, divergent and shear flows. Convergent flow results in high fiber alignment along the flow direction, whereas diverging flow causes the fibers to align at 90° to the major flow direction. Shear flow produces a decrease in alignment parallel to the flow direction and the effect is pronounced at low flow rates. Non-linear Bagley plots have been observed, under some conditions, during rheological measurements. The data are consistent with a pressure dependent viscosity.
143 citations
TL;DR: In this paper, a mathematical model for isothermal flow of a Newtonian liquid through corotating twin screw equipment is derived for two different flow regimes: the first regime is completely filled with liquid, and the second regime is partly full.
Abstract: A mathematical model is derived for isothermal flow of a Newtonian liquid through corotating twin screw equipment. Two different flow regimes are studied. In the first, channels of twin screw equipment are completely filled with liquid, generate a pressure gradient, and provide a discharge pressure at the end of the pump. Equations are given for drag flow rate, pressure backflow rate, and flow rate through the nip zone. It is shown how the analysis of single screw pumps can be modified for twin-screw pumps. In the second regime channels are partly full, which is the case with extraction equipment. Equations show how the degree of fill in the equipment changes with flow rate, speed, and dimensions.
109 citations
TL;DR: In this article, an experimental study of steady shear and elongational flow properties of polypropylene melts of varying molecular weight and distribution is reported. But the results of this study were limited to a series of polyethylene melts.
Abstract: An 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 developed.
108 citations
TL;DR: In this article, the effect of fiber concentration, fiber length, and temperature on the shear viscosity and die swell of several short glass fiber-filled thermoplastics has been determined.
Abstract: The effect of fiber concentration, fiber length, and temperature on the shear viscosity and die swell of several short glass fiber-filled thermoplastics has been determined. In addition, a study of the injection molding behavior of these materials has been performed. At low shear rates, viscosity increases appreciably with both fiber length and fiber concentration, but at high shear rates the effect is much less pronounced. A qualitative explanation is proposed for these effects in terms of the fiber orientation studies reported in Part I of this paper (1). The die swell is an important parameter in determining the method of mold filling of these materials, and depends strongly on fiber length.
TL;DR: In this article, a simple adhesion analysis is presented which explains well the weakness at the weld line expected for incompatible blends, adding an ethylene-propylene polymer with residual ethylene crystallinity was found to be a more effective "compatibilizer" for blends deficient in toughness than a related copolymer with less crystallinity.
Abstract: Blends of polypropylene (PP) and low density polyethylene (LDPE) were prepared by both batch mixing followed by compression molding and extruder compounding followed by injection molding. Compression molded PP-LDPE blends were found to have very poor toughness, whereas extruded blends, injection molded without weld lines, were quite tough. Injection molded blend specimens with weld lines were found to be weaker and failed at very low elongations at break. A simple adhesion analysis is presented which explains well the weakness at the weld line expected for incompatible blends. Addition of an ethylene-propylene polymer with residual ethylene crystallinity was found to be a more effective “compatibilizer” for blends deficient in toughness than a related copolymer with less crystallinity. This effect is attributed to the more block-like character of the former which permits it to play more nearly the interfacial role required of the ideal blend compatibilizing agent.
TL;DR: In this paper, cold compaction molding and sintering of ultra high molecular weight polyethylene (UHMWPE) has been examined as a function of particle size, sinting time and temperature, and cooling rate.
Abstract: Cold Compaction Molding and Sintering of Ultra High Molecular Weight Polyethylene (UHMWPE) has been examined as a function of particle size, sintering time and temperature, and cooling rate. Properties nearly equivalent to those obtained by compression molding can be obtained from samples with a fibrous particle morphology, sintered just above the melting point, with further improvement possible by control of particle size and addition of fine particles of normal molecular weight linear polyethylene. UHMWPE with a nodular particle morphology sintered poorly.
TL;DR: In this paper, a model of the thermoset injection molding process in simple rectangular or semi-circular cavities is presented, and the results obtained in conjunction with the characterization of an epoxy system are illustrated.
Abstract: The thermo-mechanical history of thermosetting compounds in injection molding cavities influences the ultimate properties of molded articles and affects both moldability and the productivity of the process. Mathematical modeling is an attractive approach for obtaining information regarding the thermo-mechanical history of the compound in the cavity. In order to obtain useful mathematical models of the thermoset injection molding process, it is necessary to have information regarding the kinetics and heats of reaction during cure; the rheological, thermal, and PVT properties of the thermosetting compound; and the variation of these properties with operating variables and the degree of cure. The paper outlines a model of the thermoset injection molding process in simple rectangular or semi-circular cavities. Methods are described for the experimental determination of the various physical and chemical properties of thermosets, which are required for modeling purposes. The results obtained in conjunction with the characterization of an epoxy system are illustrated. Finally, the paper demonstrates the results of mathematical modeling of the injection molding process for a commercial epoxy molding compound in a semi-circular cavity, and shows that reasonable agreement is obtained between model predictions and experimental data.
TL;DR: In this article, a theory is presented which assumes that large scale mixing is always adequate, provided the mixer operates in turbulent flow, and argues that the scale of segregation of the final mixture should depend on the size of the smallest eddies of the turbulent motion.
Abstract: The performance of confined impinging jet mixers, commonly used in reaction injection molding, was investigated. A theory is presented which assumes that large scale mixing is always adequate, provided the mixer operates in turbulent flow, and argues that the scale of segregation of the final mixture should depend on the size of the smallest eddies of the turbulent motion. The theory predicts that a length scale describing the quality of the mixture will decrease like the nozzle Reynolds number to the −3/4 power. Flow visualization experiments were used to find the point of transition to turbulent mixing flow. This transition occurs at a nozzle Reynolds number of 140 for directly opposed nozzles and at higher Reynolds numbers for nozzles angled downstream. Other geometric factors have little influence on the transition point. Quantitative mixing experiments using model fluids support the theory. Momentum ratio is shown to have no effect on mixing quality.
TL;DR: In this article, the impingement mixing is the unique feature of the reaction injection molding (RIM) process, but mixheads are largely designed by trial and error.
Abstract: Impingement mixing is the unique feature of the reaction injection molding (RIM) process but mixheads are largely designed by trial and error To visualize the impingement process we have taken high speed photographs To characterize mixing quality we have followed adiabatic temperature rise of mixtures, varying Reynolds number, mixhead geometry and the reaction rate These results are examined in terms of a simplified model which includes both fluid mechanical and polymerization aspects of the problem
TL;DR: The isothermal flow of a Newtonian liquid in a co-rotating twin screw extruder having screw elements with three tips has been analyzed when the effect of the intermeshing zone on flow can be neglected.
Abstract: The isothermal flow of a Newtonian liquid in a co-rotating twin screw extruder having screw elements with three tips has been analyzed when the effect of the intermeshing zone on flow can be neglected. It was found that values for four dimensionless parameters must be specified in order to obtain a unique relationship between the dimensionless axial pressure gradient and the dimensionless volumetric flow rate. These parameters included the number of screw tips, the helix angle, the ratio of the clearance to the screw radius, and the ratio of the distance between screw centers-to the screw radius Values for the dimensionless throughput and pressure gradient were computed for a range of helix angles at fixed values for all other dimensionless parameters. Shape factors were also computed and it was found that the shape-factor for pressure How is substantially less than that for drag flow. Asymptotic values for both these factors at large values of the channel width (large helix angles) were found to be less than unity.
TL;DR: This article showed that weld strength is strongly affected by hot plate temperature, heating time and melt flow during welding, and that excessive heating or melt flow produces strong transverse orientation, but in different ways, which can be distinguished by fracture mechanics tests.
Abstract: Welded joints were made under a range of conditions in polypropylene, glass fiber reinforced polypropylene and poly (methylmethacrylate) bars. Melt flow in the weld was investigated by microscopy and by contact microradiography, and weld strengths were measured by tensile tests. The fracture toughness of the weld zone was determined by tests on double edge notched specimens. The study shows that weld strength is strongly affected by hot plate temperature, heating time and melt flow during welding. Insufficient heating or melt flow results in incomplete bonding. Excessive melt flow produces strong transverse orientation. Both reduce strength, but in different ways, which can be distinguished by fracture mechanics tests.
TL;DR: In this paper, the residual stresses in injection molded bars of polypropylene have been examined using a stress relaxation method and by the layer removal technique, and a positive value for the internal stress parameter was obtained with newly molded specimens and was found to be retained by specimens stored at liquid nitrogen temperature.
Abstract: The residual stresses in injection molded bars of polypropylene have been examined using a stress relaxation method and by the layer removal technique. A positive value for the internal stress parameter was obtained with newly molded specimens and was found to be retained by specimens stored at liquid nitrogen temperature. The stress relaxation parameter reduced to zero both for specimens aged at room temperature and also for those aged at −40°C. Nevertheless the relaxation behavior of specimens aged at all three temperatures was quite distinct. The layer removal technique showed that the stresses near to the surface were compressive and those in the interior tensile, in apparent contradiction to the interpretation of Kubat and Rigdahl for the meaning of a positive internal stress parameter. A marked reduction in stress levels on aging at room temperature was confirmed, however. The relevance of the relaxation spectrum of polypropylene to these observations is discussed.
TL;DR: In this paper, high pressure CO2 sorption data in polycarbonate (PC) were reported as a function of temperature and thermal history, and the bulk physical structural changes produced by annealing at 125 and 135°C were monitored by density and thermal property changes.
Abstract: High pressure CO2 sorption data in polycarbonate (PC) are reported as a function of temperature and thermal history. The bulk physical structural changes produced by annealing at 125 and 135°C were monitored by density and thermal property changes. The sorption data are analyzed by the dual sorption model which assumes the sorption isotherm to consist of Henry's law and Langmuir sorption terms; The Langmuir capacity term C of PC can be grossly correlated with the reported volumetric parameters of the polymer. This excess volume interpretation of C has found support in the good correlation between C and the corresponding enthalpy relaxation from parallel Differential Thermal Analysis of the samples. Density measurements provide gross evidence of the free volume interpretation of C. The experimental uncertainties in the data compromise a more critical test of the relationship between C and the density of annealed samples.
TL;DR: In this article, the authors applied linear elastic fracture mechanics (LEFM) to polypropylene, a homopolymer and two copolymers, with a view to characterizing their brittle behavior at slow rates (0.5 cm/min) in terms of a fracture toughness, KIc.
Abstract: The concepts of Linear Elastic Fracture Mechanics (LEFM) are applied to polypropylene, a homopolymer and two copolymers, with a view to characterizing their brittle behavior at slow rates (0.5 cm/min) in terms of a fracture toughness, KIc. The effect of thickness, notch sharpness, and the mode of loading on KIc have been investigated in order to determine the plane strain toughness values, KcI for the materials. The two types of material are compared in terms of their toughness values over a range of temperatures between +30 and −160°C. Evidently, the small amounts of ethylene added to the copolymers show plasticizing effects, suppressing the yield stress and the ductile-brittle transition temperature. In addition, the copolymers exhibit a ductile-brittle region between −100 and −45°C where notch strengthening is apparent in the tension mode and a slow crack growth region between −45 and −30°C where slow growth precedes unstable fracture. The homopolymer, however, shows no clear evidence of such intermediate regions, except for slight amounts of slow growth above 0°C, and becomes ductile around 30°C.
TL;DR: In this article, turbulent drag reduction measurements were used to augment the usual analytical techniques of viscosity and gel permeation chromatography to evaluate the effects of polystyrene degradation, and the degradation causes a shift in the distribution to lower molecular weights with little change in the shape.
Abstract: The flow-assisted degradation behavior of polystyrene was studied as a function of solvent, polymer concentration, molecular weight, and molecular weight distribution. To obtain data at concentrations as low as 100 parts per million by weight, turbulent drag reduction measurements were used to augment the usual analytical techniques of viscosity and gel permeation chromatography. Turbulent flow measurements were found to be a valuable technique for evaluating the effects of degradation: the drag reduction onset point provides information about the largest molecules in the sample while the flow rate dependence is related to the shape of the top part of the molecular weight distribution. For the polymers and flow conditions studied, the degradation causes a shift in the distribution to lower molecular weights with little change in the shape. This suggests a complex mechanism where the probability of bond scission is not random but varies along the polymer backbone.
TL;DR: In this article, the effect of viscosity ratio for melts of the components on the processes of fiber formation in extrudates and on the rheological properties of the molten blend has been tested.
Abstract: Blends of polyoxymethylene (POM) with a copolymer of ethylene and vinyl acetate (CEVAc) have been studied. The effect of viscosity ratio for melts of the components on the processes of fiber formation in extrudates and on the rheological properties of the molten blend has been tested. The viscosity ratio of the fiber-forming POM and the matrix varied in the range 0.35-27.7. POM ultrathin fibers of unlimited length can be formed in the CEVAc only at a viscosity ratio close to unity. For ratios much greater than unity, the extrudate is found to contain short fibers and a finely dispersed powder or no fibers at all. If the viscosity of the POM melt is lower than that of the matrix, films are formed in addition to fibers. The second factor that governs fiber formation is the extrusion shear stress. An optimum shear stress exists at which the amount of ultrathin fibers is a maximum.
TL;DR: In this paper, the authors analyzed the performance of H2O in glassy polyacrylonitrile (PAN) for a range of relative vapor pressures at temperatures from 20C to 50C.
Abstract: : Sorption data for H2O in glassy polyacrylonitrile (PAN) are presented for a range of relative vapor pressures at temperatures from 20C to 50C. Simple dual mode sorption, involving 'hole-filling' and molecular solution appears to dominate the low activity region of sorption. Based on the clustering analysis suggested by Zimm and Lundberg, pronounced clustering of penetrant appears to occur above a relative pressure of 0.6. The form of the effective concentration-dependent diffusion coefficient for H2O in PAN, determined by analysis of steady state permeation data, suggests that water in the microvoids and clusters has a lower mobility than the molecularly dissolved water in the polymer matrix. Time lag measurements at high upstream realtive water vapor pressures suggest that the transient state permeation has a non-Fickian character due to relaxations which occur slowly to accommodate the clustering process. (Author)
TL;DR: In this paper, the authors studied the reactions of the treated surfaces with a free-radical compound, diphenyl picryl hydrazyl (DPPH), focusing mainly on the rate effects.
Abstract: Polymeric films, chiefly polyethylenes, were subjected to corona-discharge treatment in a continuous treater at commercial rates in a program covering wide ranges of the main processing factors. Electron-spin-resonance measurements on freshly treated films found no free radicals. We studied the reactions of the treated surfaces with a free-radical compound, diphenyl picryl hydrazyl (DPPH), focusing mainly on the rate effects. The evidence indicates that corona treatment produces fairly stable peroxide structures of the forms RO/sub 2/R and RO/sub 3/R on polyethylene surfaces. RO/sub 3/R reacts rapidly with DPPH alone, while RO/sub 2/R undergoes a slower reaction after addition of the catalyst, triethylene diamine. DPPH is capable of detecting as few as 10/sup 13/ peroxide groups per square centimeter. Activation energies were 12 kcal/mole for the uncatalyzed reaction and 16 kcal/mole for the amine-catalyzed reaction. As with the physical effects reported earlier, the production of peroxides is most strongly dependent on the energy delivered to the film during treatment. This energy is proportional to the quotient of corona current and web speed, I/S. Regression analysis showed that air-gap thickness, relative humidity, and number of electrodes used also were significant factors, while dielectric thickness and corona frequence were not. We found that ..gamma../submore » S//sup P/, the polar component of surface energy of the treated film, which is nearly zero for untreated polyethylenes, is exponentially related to the concentrations of both RO/sub 2/R and RO/sub 2/R with a correlation coefficient for 92 specimens tested of 0.88.We believe this is the first strong evidence linking treatment factors, at commercial levels of treatment, to chemistry of the treated surface and linking both of those to changes in physical behavior of the surface.« less
TL;DR: In this article, two pilot studies using White Carneau pigeons on high cholesterol diets have demonstrated substantial reduction in arterial plaque accumulations when the birds were periodically injected with dilute aqueous solutions of a drag reducing polymer (Separan AP-30) so as to maintain circulating blood concentrations of approximately 60 ppm.
Abstract: Results from two pilot studies using White Carneau pigeons on high cholesterol diets have demonstrated substantial reduction in arterial plaque accumulations when the birds were periodically injected with dilute aqueous solutions of a drag reducing polymer (Separan AP-30) so as to maintain circulating blood concentrations of approximately 60 ppm. Initiation of arterial plaque formation may be fluid-mechanically motivated such that regions subjected to fluid turbulence, rapidly developing boundary layers, and alternate separation and reattachment, arc; the most prone lo attack. Viscoelastic fluid response, as seen in drag reducing media, is known to alter such phenomena. Comparative documentation of plaque deposition in experimental as well as control birds shows significant differences in both the aortas and coronary arteries, at optical magnifications from 20 to 15000X.
TL;DR: In this article, the authors investigated the effect of temperature variations of the phenomenological model parameters of Fickian and Henry's law on carbon dioxide sorption and transport in poly(ethylene terephthalate) and poly(acrylonitrile) polymers.
Abstract: At temperatures at least 30°C above the glass transition (Tg) the sorption and transport of carbon dioxide in poly(ethylene terephthalate) (PET) can be described conveniently using Henry's law and Fick's law with a constant diffusion coefficient. Below Tg Fick's law with a concentration- dependent diffusion coefficient, coupled with a sorption isotherm which is concave toward the pressure axis adequately describes the observed sorption and transport data. Physical interpretations of the quantitative deviations from Henry's law and the form of the concentration dependence of the diffusion coefficient is provided by a model which hypothesizes dual modes of sorption and separate non zero mobilities of two populations of sorbed species in local equilibrium. The implications of the observed temperature variations of the phenomenological model parameters are discussed. Dilatometric parameters for PET, polycarbonate, and poly(acrylonitrile) (PAN) are shown to correlate well with a simple. relationship developed to explain the existence of the “extra” mode of sorption responsible for deviations from Henry's law for CO in glassy polymers. In the temperature range from Tg to + 20°C, deviations from Fickian behavior are also apparent. These effects are consistent with a transition in the nature of the polymer from an elastic solid below Tg to a viscous liquid above Tg In the narrow temperature range slightly above T the time scale for chain rearrangements apparently approaches that for the diffusion process. The polymer's viscoelastic response to the probing molecule, therefore, causes deviations from the classical time lag predictions. These deviations disappear 30°C above Tg.
TL;DR: In this article, a tie chain length distribution model was used to quantitatively interpret the IR data, and the observed long lifetimes of highly stressed chains suggest a reappraisal of existing fracture theories.
Abstract: Infrared (IR) spectroscopy was used to study molecular deformation processes in polymers as a function of stress, strain, time and temperature. Stress-induced frequency shifts were found to depend on temperature and morphology. Deformation of viscoelastic polypropylene was examined in terms of time dependent molecular stress distributions, orientation changes, conformational variations, and chain fracture. A tie chain length distribution model was used to quantitatively interpret the IR data. Molecular deformation processes of creep and stress relaxation were found to be opposite in nature, Observed long lifetimes of highly stressed chains suggest a reappraisal of existing fracture theories.
IBM1
TL;DR: A critical angle illumination microscopy technique was used to study the in situ dissolution dynamics of polystyrene, poly (α-methylstyrene) and the two tactic forms of poly (methyl methacrylate), (PMMA), in several solvents as discussed by the authors.
Abstract: A critical angle illumination microscopy technique was used to study the in situ dissolution dynamics of polystyrene, poly (α-methylstyrene) and the two tactic forms of poly (methyl methacrylate), (PMMA), in several solvents. The dissolution characteristics; of polymers were found to be greatly influenced by several factors: type of polymer, processing condition of the sample, type of solvent, and tacticity, Polystyrene was found to exhibit extensive swelling in several solvents while atactic PMMA exhibited extensive cracking on dissolution. Isotactic PMMA, which has a glass temperature of about 70°C lower than the atactic PMMA, showed swelling behavior similar to atactic polystyrene, while the α-methylstyrene showed the cracking phenomena exhibited by atactic PMMA.
TL;DR: In this article, an approach based on polymerization kinetics and the corresponding solution rheology and phase diagrams is proposed for predicting rheological changes during ionic, condensation, and free-radical polymerization.
Abstract: Parameters are developed for predicting rheological changes during ionic, condensation, and free-radical polymerization. Polymerization is viewed as changes in molecular weight and concentration for polymer solutions. Polymerization data in the laboratory and in tubular reactors are shown to be consistent with the proposed rheokinetic theory. This approach is based on polymerization kinetics and the corresponding solution rheology and phase diagrams.