Showing papers in "Polymer Engineering and Science in 1994"

Generation of microcellular polymeric foams using supercritical carbon dioxide. I: Effect of pressure and temperature on nucleation

Abstract: Supercritical carbon dioxide is known to swell and plasticize poly(methyl methacrylate), PMMA, dramatically. We have employed a pressure quench in a CO2-swollen PMMA sample to generate a microcellular core structure encased by a nonporous skin. Further, we have demonstrated that classical nucleation theory can be used to model the effects of saturation pressure, temperature, and time on the cell density of the porous materials, provided that the effects of the CO2-diluent on the surface tension of PMMA are adequately taken into account. This is because our system is in a homogeneous liquid state at our operating conditions because of the plasticization. Both model predictions and data indicate that cell density rises sharply at a saturation pressure of approximately 14 MPa (at 40°C), leveling out above 27 MPa. By contrast, the effect of temperature on cell density in the range 40°C to 80°C is minimal.

Generation of microcellular polymeric foams using supercritical carbon dioxide. II: Cell growth and skin formation

Abstract: We have generated microcellular polymeric foam structures using a pressure induced phase separation in concentrated mixtures of supercritical CO2 and poly(methyl methacrylate). The process typically generates a microcellular core structure encased by a nonporous skin, the thickness of which decreases with increasing saturation pressure. This trend can be described by a model for skin formation that is based on the diffusion rate of gas out of the sample. Significant density reductions on the order of 30 to 70% can be achieved by changing the pressure and temperature conditions in the foaming process. There are several ways in which the saturation pressure affects the average cell size, with the net effect that cell size decreases sharply with increasing pressure above 2000 psi, leveling out at higher pressures. Cell size increases with increasing temperature from 40°C to 70°C. A model for cell growth, based on a cell model of Aremanesh and Advani, modified to include the effect of CO2 on model parameters, reproduces these trends.

Long‐term properties of hot‐water polyolefin pipes—a review

Abstract: This is a review on the long-term behavior of polyolefin pipes used in hot-water environments. Included in the review is work done on pipes of crosslinked polyethylene, isotactic poly(butene-1), isotactic polypropylene and medium-density polyethylene, and in particular the extensive work performed at Studsvik, Sweden. A collective view of the changes in antioxidant concentration profiles and molecular /physical structure accompanying hot-water exposure is presented. Failure at high stress levels is preceded by gross deformation (Stage I failure), whereas at lower stresses fracture is brittle either without any signs of thermal oxidation (Stage II) or induced by a strong and spatially concentrated thermal oxidation (Stage III). It is shown that the Stage III lifetime can be divided into three phases, denoted Regimes A, B, and C. They involve internal precipitation of antioxidant from a supersaturated solution (Regale A), diffusion-controlled migration of antioxidant to the surrounding media (Regime B), and degradation of the polymer by thermal oxidation (Regime C). For hitherto reported cases the Regime B life constitutes 80% to 90% of the entire life. A presentation is also made of current lifetime extrapolation methods

Quiescent polymer crystallization: Modelling and measurements

Abstract: The problem of predicting nonisothermal crystallization kinetics based on isothermal data is considered, with reference to the difficulties involved, both experimental and theoretical. The kinetic model used is the differential form of the Nakamura equation which is an extension of the Avrami equation so as to apply to nonisothermal crystallization. Nonisothermal induction times are obtained from isothermal induction times according to the concept of induction time index. The theory of Hoffman Lauritzen is used to extrapolate the limited isothermal crystallization rate data. Good agreement between DSC (differential scanning calorimetry) nonisothermal crystallinity results and model predictions is obtained for our own data on poly(ethylene terephthalate) (PET) and some literature data on nylon-6, if the temperature lag between the sample and the DSC furnace is taken into account. The advantages of the present approach in process modeling are pointed out. Quenching experiments have also been performed in which PET slabs are allowed to cool and crystallize from the melt under quiescent conditions. The resulting crystallinity distributions in the thickness direction are measured and predicted by using kinetic parameter values obtained from isothermal DSC measurements alone.

The large strain compression, tension, and simple shear of polycarbonate

Abstract: Polymeric materials subjected to large strains undergo an evolution in molecular orientation. The developing orientation and corresponding strengthening are highly dependent on the state of strain. In this paper, we examine and compare the very different stress-strain results of polycarbonate produced from four types of mechanical testing: uniaxial compression, plane strain compression, uniaxial tension, and simple shear. These tests produce different states of orientation within the material and, in the case of simple shear, the principle axes of orientation rotate during the deformation. The ability of the recent constitutive model of Anuda and Boyce (1992) to predict the observed behavior is evaluated. The model has been incorporated into a finite element code in order to properly simulate the material behavior during the inhomogeneous deformations of tension (cold drawing) and simple shear. The material properties of the model are obtained from the uniaxial compression test and the model is then found to be truly predictive of the other states of deformation demonstrating its fully three dimensional capability. The disadvantages of the tensile and simple shear tests for obtaining the data needed to accurately quantify the large strain material behavior of polymers are shown and discussed.

Rubber toughening of poly(lactide) by blending and block copolymerization

Abstract: Copolymers of L-lactide with 15 or more mole % D-lactide are amorphous, noncrystallizable hydrolytically degradable materials. These glassy materials are brittle in tension and bending. To make these materials suitable for use as load-bearing devices in biomedical applications, toughness has to be enhanced. This is effectively accomplished by introducing a separate degradable rubber phase in the amorphous matrix. Several approaches have been explored: solution blending and coprecipitation of trimethylene carbonate and epsilon-caprolactone rubbers and poly(lactide), preparation of ABA triblock copolymers and blending of ABA block copolymers with the amorphous poly(lactide) matrix. In all cases very tough materials could be prepared. These materials are easily processable by compression molding at relatively low temperatures.

The heterogeneous nucleation of microcellular foams assisted by the survival of microvoids in polymers containing low glass transition particles. Part I: Mathematical modeling and numerical simulation

Abstract: The existing models based on classical nucleation theory are not able to explain satisfactorily the nucleation phenomenon of microcellular foams in thermoplastics. Here, we extend the analysis of Kweeder (24), who developed a new model that considers the presence of microvoids, resulting from the thermal processing history of the polymer, as potential nucleation sites. The nucleation model “concentrates” on the stresses and thus void formations in the rubber particles. Since these are pre-existing microvoids, bubble nucleation depends on the survival of these voids to grow rather than the formation of a new phase as modeled by classical nucleation theory. The population of viable microvoids with a sufficiently large radius to survive and overcome surface and elastic forces has been modeled to yield the cell density. A log-normal distribution, which relates to the rubber particle size, has been used to model the distribution of microvoids in the polymer composite material. The model depends on various process parameters such as saturation pressure, foaming temperature, concentration of nucleating agents, solubility of the blowing agent in the polymer, and the modulus. High impact polystyrene (HIPS) was added to polystyrene to obtain polymers with different concentrations of rubber gel particles, the nucleating agent, and used here for this study.

On the pressure dependency of the viscosity of molten polymers

Abstract: A slit viscometer to measure the viscosity of polymer melts under processing conditions is described. Along the slit a pressure drop is generated by applying a pressure at both the entrance and the exit. In this way the pressure in the center can be controlled independently of the shear rate. The pressure gradient in the slit is measured by means of three pressure transducers which are mounted in the region of fully developed flow. Results of pressure-dependent viscosity measurements on polystyrene, polyacrylonitrile-butadiene-styrene, and polypropylene are presented in a shear rate range of five decades. The flow curves obtained at different pressures and temperatures can be shifted onto a master curve. The shear thinning behavior of the three materials is adequately described with the generalized Cross-Carreau equation, while the zero shear viscosity is modeled with a generalized Arrhenius-W.L.F. relationship, incorporating a pressure dependency. Alternatively, it is possible to describe the zero shear viscosity in terms of the free volume fraction and the temperature.

Degradation of unstabilized medium-density polyethylene pipes in hot-water applications

Abstract: Pipes of an unstabilized medium-density polyethylene have been pressure tested with internal stagnant water and moderately circulating air as the external medium at temperatures ranging from 70 to 105°C and changes in molecular structure and crystallinity have been studied. The stage III (fracture induced by thermal oxidation) life of the unstabilized polyethylene pipes was less than 12% of the life of the corresponding stabilized polyethylene pipes. Infrared spectroscopy and size exclusion chromatography showed an earlier and more extensive increase in the quantities of oxidation end-products and a more pronounced decrease in molar mass of the outer-wall-material than of the inner-wall-material of the pipe. Mass crystallinity, measured by differential scanning calorimetry, increased on an average by a quantity corresponding to 45 methylene groups per chain scission event. The life of the unstabilized pipe was divided into an induction period during which no detectable thermal oxidation occurred and a subsequent polymer degradation period. The induction period exhibited an Arrhenius-temperature-dependence with an activation energy of 75 kJ mol−1.

Investigation of processing-structure-properties relationships in polyethylene blown films

Abstract: Molecular orientation imparted during film fabrication is known to have a major effect on mechanical and thermal properties of both glassy and semicrystalline polymers. A three-variable Box-Behnken designed experiment was used to study the effects of die gap, die land length, and blowup ratio (BUR) on key linear low density polyethylene (LLDPE) blown film properties at constant final film thickness. In addition, differences in molecular orientation in the films were studied using optical birefringence and shrinkage methods. Measured key film properties were correlated to processing conditions and to measured molecular orientation. Die land length had no significant effect on film structure and properties. All LLDPE films exhibited about 70 to 80% shrinkage in the machine direction (MD) but expanded in the cross direction (CD). Most films exhibited negative in-plane birefringence. MD Elmendorf tear was found to be inversely related to drawdown ratio and MD shrinkage, suggesting that MD tear is dependent primarily on amorphous chain extension and hence, amorphous segments orientation for LLDPE blown films. Dart impact strength of the films was shown to be related to MD shrinkage and to the induced surface roughness due to varying die gap. In a separate study, blown films of three high pressure LDPEs were fabricated under nearly identical conditions. No correlation was found between birefringence and shrinkage data on the LDPE blown films.

The heterogeneous nucleation of microcellular foams assisted by the survival of microvoids in polymers containing low glass transition particles. Part II: Experimental results and discussion

Abstract: The experimental data obtained for the nucleation of microcellular foams are compared with the theoretical model developed in the first part of this paper Polystyrene (PS) with rubber particles as nucleation sites is used as an exploratory system Nitrogen is used as a physical blowing agent to nucleate the bubbles The influence of process variables, such as saturation pressure, foaming temperature, and concentration and size of rubber particles, is discussed Results indicate that all these variables play important roles during the nucleation process A nucleation mechanism based on the survival of microvoids against the resisting surface and elastic forces has been modeled to obtain the cell nucleation density Increase in saturation pressure increase the cell density to a critical pressure Beyond this critical pressure, there is no increase in bubble number, indicating that all microvoids are activated The effect of temperature is more complex than the effect of pressure Increase in concentration of the rubber particles increase the nucleation cell density In general, the experimental data are well described by the nucleation model presented in Part I

A model for the unfoamed skin on microcellular foams

Abstract: In microcellular plastics, an unfoamed skin that is integral with the foamed core can be created by allowing the nucleating gas to diffuse from the surfaces of a gas saturated specimen prior to foaming. In this paper, a semi-empirical model is proposed that predicts the skin thickness variation in microcellular foams as a function of gas desorption time. The model shows good agreement with experimental results on the polycarbonate–carbon dioxide system.

Effects of component addition protocol on the reactive compatibilization of HDPE/PET blends

Abstract: Polyethylene terephtyalate (PET) and high-density polyethylene (HDPE) constitute a major portion of the thermoplastic materials currently being used in the packaging industry. Blends of HDPE/PET can be compatibilized by utilizing ester groups or terminal carboxyl and hydroxyl groups present in PET. An ethyleneglycidyl methacrylate copolymer (EGMA) was found to be very effective in compatibilizing this blend by forming a compatibilizer in-situ. The in-situ formation of the compatibilizer and its distribution could be affected by different sequences and modes of component addition. To determine the best protocol of component addition for such a reactive compatibilization process, different sequences and modes of component addition were tried out in an intensive batch mixer and in a twin-screw extruder. All these experiments resulted in blends with vastly different dispersion of the minor phase and mechanical properties. In general, sequences where the reactive polymer was grouped with the nonpolar component of the blend initially resulted in the best compatibilization.

Modeling of the Dynamics of Water and R‐11 blown polyurethane foam formation

Abstract: Polyurethane foam formation involves both polymerization and expansion processes. The dynamics of the water and R-11 blown foams depend on the rates of chemical and physical blowing processes, along with the rate of viscosity increase of the reacting mixture. Experiments were carried out to study the dynamics of free rising, water and R-11 blown rigid polyurethane foams. The density and temperature change during the foam formation were monitored. A theoretical model was developed to predict the density and temperature variation with time. In the model, the physical blowing agent (R-11) evaporation process is assumed to be heat generation–controlled and the carbon dioxide generation process to be controlled by the rate of the water-isocyanate reaction. The kinetic parameters of the reactions of isocyanate with polyol and water were obtained separately and were asssumed to be independent of each other. The water-isocyanate reaction appears to follow first-order kinetics with respect to concentration of water. The theoretical predictions of the model show good agreement with the experimental data for density variation with time. The model predictions for temperature rise also match experimental data, except at the later stages of foaming when it is found to be slower than the experimental measurements. However, this deviation does not affect the dynamics of density change since it occurs after the completion of the expansion process.

Interfacial tension in polymer melts. I: An improved pendant drop apparatus

Abstract: An apparatus is described to measure interfacial tension for molten polymer pairs. The apparatus is based on the pendant drop method. A CCD color video camera captures the image of a pendant drop profile, which is analyzed on-line using a microcomputer. These almost continuous measurements permit the detection of possible changes in the behavior of the melt that might affect the interfacial tension through thermal degradation. A special syringe to inject the pendant drop has been designed in order to avoid problems such as the capillary effect of the tube of the syringe and the necking and detachment of the pendant drop. The accuracy of the apparatus was verified using water/n-hexane and water/n-octane. Experimental results for polypropylene/polystyrene (PP/PS) are presented. The interfacial tension between the polymer pair decreases as temperature increases and as molecular weight decreases. Interfacial tension is estimated from the drop shape when the drop is at mechanical equilibrium. For polymer systems, mechanical equilibrium normally takes from 1 to 10 h to occur. However, transient values of interfacial tension (apparent interfacial tension values obtained before mechanical equilibrium is reached) may be used to estimate the interfacial tension at equilibrium by extrapolation, thus reducing the required experimental time.

Rheological properties of structured fluids

Abstract: The kinetic theory proposed by Soong and Liu for describing the rheological properties of structured fluids has been extended to predict shear-thinning, shear-thickening, thixotropy, and antithixotropy in different ranges of shear rates. Viscoelastic properties, as given by the Gordon-Schowalter Maxwell model, with a non-constant modulus, have also been considered. The theoretical predictions are compared with the predictions of a model used by Ait-Kadi, et al. (1988), for a hydrolyzed polyacrylamide solution containing 20 g/1 of NaCl. the predictions and experimental data for the viscosity and primary normal stress coefficient are in reasonably good agreement. The stress growth functions have also been calculated and have been found to be consistent with experimental observations.

Thermoplastic starch blends with a poly(ethylene-co-vinyl alcohol) : processability and physical properties

Abstract: We investigated the effect of poly(ethylene-co-vinyl alcohol) (EVOH) concentration on the processability and physical properties of thermoplastic starch plasticized with glycerine and water. Waxy maize starch (Amioca), native corn starch (Melogel), and a treated high amylose corn starch (Hylon VII) were employed to explore the effect of starch type on blend properties. All the starches exhibited similar changes in properties with increasing EVOH content. The minimum injection pressure required for filling a standard test specimen (a measure of processability) decreased with increasing EVOH concentration and provided an indication of improved processability. Blends with high amylose corn exhibited higher injection pressures than the corresponding waxy maize or native corn starch blends. The ductility of all the thermoplastic starches was significantly increased upon the addition of EVOH. The waxy maize blends were stiffer and the high amylose corn blends exhibited higher elongation at low EVOH concentrations, but all the starch/EVOH blends exhibited similar physical properties when the EVOH concentration was ≥ 50 wt%. An investigation of physical properties of this blend series after long term aging from 10% to 90% relative humidity is in progress. Future studies include rheology, electron microscopy, and thermal analysis to more fully elucidate phase behavior in these binary blends.

Interfacial tension in polymer melts. Part II: Effects of temperature and molecular weight on interfacial tension

Abstract: Interfacial tension is one of the most important parameters that govern the morphology of polymer blends and the quality of adhesion between polymers. However, few data are available on interfacial tension due to experimental difficulties. A pendant drop apparatus was used for the determination of the interfacial tension for the polymer pair polypropylene/polystyrene (PP/PS). The effects of temperature and molecular weight were evaluated. The range of temperatures used was from 178 o to 250 o C, and the range of molecular weights used was from 1590 to 400,000. The interfacial tension decreased linearly with increasing temperature. With only one exception, higher molecular weight systems showed weaker dependence of interfacial tension on temperature than lower molecular weight systems. Also, polydisperse systems showed a stronger dependency on temperature than the monodisperse systems. The value of the interfacial tension, which increases with molecular weight, appears to level off at molecular weights above the entanglement chain length. For the polymer pair PP/PS, the dependency of the interfacial tension on the number average molecular weight appears to follow the well-known semi-empirical (-2/3) power rule over most of the range of molecular weights. Comparable correlations were obtained with values of the power between -1/2 and -1.0

Kinetic parameters estimation for cure reaction of epoxy based vinyl ester resin

Abstract: A new graphical estimation technique is proposed for the determination of the kinetic parameters describing an autocatalytic reaction. A differential scanning calorimeter was used to monitor the reaction kinetics of an epoxy-based vinyl ester resin. The method utilizes information from a zero initial reaction rate, conversation at vitrification, the ratio of reaction rate constants under different isothermal conditions, and characteristics of the phenomenological kinetic model with assumptions being made about the overall reaction order. By fitting data to the integrated reaction rate equation with adjustments for the isothermal conditions, the kinetic parameters are estimated without using a linear or nonlinear regression method. Different kinetic parameters can be estimated from data before and after the gel point which was obtained from the relationship between the glass transition temperature and the degree of cure.

Functionalized elastomeric compatibilizer in PA 6/PP blends and binary interactions between compatibilizer and polymer

Abstract: Superior impact properties were obtained when maleic anhydride grafted styrene ethylene/butylene styrene block copolymer (SEBS-g-MAH) was used as a compatibilizer in blends of polyamide 6 (PA 6) and isotactic polypropylene (PP), where polyamide was the majority phase and polypropylene the minority phase The optimum impact properties were achieved when the weight relation PA:PP was 80:20 and 10 wt% SEBS-g-MAH was added The blend morphology was systematically investigated Transmission electron microscopy (TEM) indicated that the compatibilizer forms a cellular structure in the PA phase in addition to acting as an interfacial agent between the two polymer phases In this cellular-like morphology the compatibilizer appears to form the continuous phase, while polyamide and polypropylene form separate dispersions In microscopy, PA appeared as a fine dispersion and PP as a coarse dispersion The mechanical properties indicated that in fact PA, too, is continuous, and the blend can be interpreted as possessing a modified semi-interpenetrating network (IPN) structure with separate secondary dispersion of PP The coarser PP dispersion plays an essential role in impact modification Binary blends of the compatibilizer and one blend component were also investigated separately The same cellular structure was observed in the binary PA/SEBS-g-MAH blends, and SEBS-g-MAH again appeared to form the continuous phase when the elastomer concentration was at least 10 to 20 wt% By contrast, in PP/SEBS-g-MAH only conventional dispersion of elastomeric SEBS-g-MAH was observed up to 40 wt% elastomer Impact strength was improved and the elastic modulus was lowered in both PA/SEBS-g-MAH and PP/SEBS-g-MAH blends when the elastomer content was increased The changes in modulus indicate that the semi-IPN-like structure is formed in the binary PA/SEBS-g-MAH blends as well as in the ternary structure

Spin coating of very thin polymer films

Abstract: Very thin films of natural rubber, polystyrene, and poly(methylmethacrylate) have been spun-cast on silicon wafers from dilute solutions of toluene and cyclohexane. Layers were uniform across the wafers, ranging from 0.5 to 170 nm, as measured by ellipsometry. Their average thickness e increased with solution concentration and decreased with rotational rate ω. Changing the volume of the solution pipetted onto the wafers did not affect the final thickness, whereas changing the solvent did. The previously reported empirical relation for much thicker films, e ∞ ω -1/2 , held over the range investigated here

Modeling of the dynamics of R‐11 blown polyurethane foam formation

Abstract: The dynamics of R-11 blown polyurethane foam formation depend on the rates of viscosity increase of the reacting mixture and R-11 evaporation, and both are controlled by the polymerization process. Detailed experiments were carried out to study the dynamics of foaming and the measurements made included the cream and rise times, the density change of the expanding foam with time, and the temperature rise during reaction. Dynamic temperature measurements at different points in the foaming mixture were also made to study the spatial variation of the temperature in the foam. The experimental results showed the rate of foaming, the final density, and the maximum temperature decreased with increasing R-11 concentration. The heat losses from the foam were also found to be significant towards the later stages of foaming when density was low. Theoretical models were developed to predict the temperature and density change with time and spatial variation of temperature in the foam due to heat losses, by considering the foaming dynamics to be either heat generation controlled or heat and mass transfer controlled. In the former, the foam was assumed to be a pseudohomogeneous phase and the approach was similar to that of Rojas, et al. (5). New features accounted for in the model were dilution of the reactant concentration due to the presence of liquid blowing agent and heat loss from the foam due to radiation. While excellent agreement between theoretical predictions and experimental results was obtained for temperature variation with time at different locations in the foam, the model gave a much sharper reduction in density with time as compared to the experimental data. In the second model, the rate of foaming was assumed to be controlled by the rate of heat and mass transfer to a single bubble in the foam. Assuming a film model for heat and mass transfer, the theoretical predictions for both temperature and density were found to be in very good agreement with experimental data.

Simulation of non‐isothermal flow in modular co‐rotating twin screw extrusion

Abstract: Non-isothermal flow is simulated in the screw and kneading disc elements in a modular co-rotating twin screw extruder. Methods of calculating mean temperature rises for individual elements are discussed and results are presented. The implications of non-isothermal operation for scale-up is discussed. A method is then described for making calculations in a modular co-rotating machine, that contains many different elements. Example calculations are given showing the tendency of larger machines to buildup greater temperatures when viscous heating is included.

Quantitative model relating electrical resistance, strain, and time for carbon black loaded silicone rubber

Abstract: A quantitative model has been developed relating electrical resistance with strain and time for carbon black filled silicone rubber compounds. The model is based on concepts and methods used in the field of viscoelasticity. Relaxation experiments are performed in order to evaluate material parameters. With these, resistance-strain-history relations, under other loading conditions may be predicted.

Construction of fast-response heating elements for injection molding applications

Abstract: A new type of heating element was developed capable of changing the mold surface temperature by about 70 K in 0.2 s, thus enabling reduction of frozen-in orientation and stresses in injection molded products without undue increase in cycle time. The heater, which consists of two insulation layers with a resistance layer in between, is discussed in this paper. The thickness of this insulation layer proves to be the most important design parameter. Too thick an insulation layer increases the cooling time too much, whereas with a thin layer the surface temperatures will stay too low. Temperature measurements at the heater surface and in the mold wall are reported and demonstrate the extreme fast response characteristics.

Deformation and entanglement in semicrystalline polymers

Abstract: Transmission electron microscopy and optical studies of thin films of isotactic polystyrene (iPS) and polyoxymethylene (POM) provide evidence for a distinction between crazing mechanisms in semicrystalline polymers above and below Tg. In the latter temperature regime, deformation in iPS and POM crystallized at high supercooling has been discussed in terms of existing models for crazing in amorphous glassy polymers, based on entanglement ideas. Above Tg, where the difference in mechanical behavior of the amorphous and crystalline regions becomes marked, the fibrillar nature of local deformation appears to be a consequence of the inhomogeneity of the undeformed polymer.

Start-up pressure transients in a capillary rheometer

Abstract: The “rise time” required to achieve a steady pressure reading in a capillary rheometer operated at constant piston speed can be very long, up to several hours under certain circumstances. This phenomenon can pose a serious problem in the measurement of melt viscosity, and it would be useful to be able to estimate the rise time in the planning of experiments. Based on experiments involving several types of polyethylene, we found that the rise time increases with L/D and the amount of polymer initially in the reservoir and decreases with diameter and piston speed. When the rise time is short, melt viscoelasticity contributes to the rise time, but when it is long, melt compressibility is the dominant factor. A model was developed for the latter case, and this was found to give an accurate prediction of the rise time, given the viscosity and compressibility. The model can also be used to determine the power-law parameters from the start-up pressure trace, P(t), for a single experiment. Alternatively, if the viscosity is known, the compressibility can be inferred from a single pressure trace.

J-R curve calculation with the normalization method for toughened polymers

Abstract: The method of normalization is used to develop the J-R curve fracture toughness characterization for polymeric materials. This method can develop J-R curves directly from load vs. displacement records without a need for an on-line crack monitoring system. It was used previously to develop J-R curves for metallic materials and is applied here for the first time to polymer materials. Single edge notched bend specimens of rubber toughened nylon 6/6 and rubber toughened amorphous nylon are used in this study. The J-R curves from the method of normalization are compared with the results obtained from the multiple specimen method of ASTM Standard E813. The results show that the method of normalization gives reasonable J-R curves; both methods show agreement over the early J-R curve region. In addition the JIc values are determined for each method and compared. Based on this work it is suggested that the method of normalization could be used as a general test method to develop J-R curves for polymeric materials.

Acrylic acid containing copolymers as reactive compatibilitzers for toughening nylon 6

Abstract: Nylon 6 has been toughened by rubber particles that were dispersed within the matrix via additives that physically interact with the elastomer phase but chemically react with the polyamide phase. To disperse a core-shell impact modifier having a poly(methyl methacrylate) or PMMA shell, most of the work presented is based on the use of a styrene/acrylic acid copolymer containing 8 wt% acrylic acid, SAA8. SAA8 is miscible with PMMA and should located in the PMMA grafted chains of the impact modifier while chemically reacting with the nylon 6 matrix; hence, it should aid in both the dispersal and strenghtening the modifier-matrix interface. Microscopy and mechnical properties confirm that SAA8 does function in this way but less effectively than styrene/maleic anhydride copolymers, which are also miscible with PMMA but evidently react more effectively with the polyamides. The use of ethylene/acrylic acid copolymer for dispersal of the coreshell impact modifier and a styrene/ethylene-butene/styrene block copolymer in nylon 6 was also briefly considered. Low-temperature toughness of the blends proved to be a much more critical test of the effectiveness of such additives than room temperature impact strenght.

Curing of acrylated epoxy resin based on bisphenol‐S

Abstract: The acrylated diglycidyl ether of bisphenol-S was prepared by reacting diglycidyl ether of bisphenol-S (DGEBS) with acrylic acid using dimethyl benzylamine as a catalyst. The acrylated epoxy resin thus obtained was characterized by IR, 13C-NMR, and DSC. The curing reaction of the acrylated epoxy resin with dicumyl peroxide was investigated by differential scanning calorimetry at three different heating rates. The overall curing kinetics were found to be approximately second order, independent of the scan rate. The TGA was used to investigate the thermal decomposition of acrylated epoxy resin and to determine the kinetic parameters such as activation energy, preexponential factor, and reaction order. Such information can be used for quick estimation of polymer lifetimes.