Showing papers in "Journal of Applied Polymer Science in 1974"
TL;DR: In this article, a graft polymer between maleic anhydride in polypropylene and terminal amino groups of nylon 6 was found to be formed by the formation of a certain graft polymer, which was confirmed by solvent extraction, estimation of the amino group and identification by differential scanning calorimetry.
Abstract: In the presence of maleic anhydride-grafted polypropylene, marked dispersibility of the polymer blend of isotactic polypropylene and nylon 6 was obtained. This appeared to be caused by the formation of a certain graft polymer between maleic anhydride in polypropylene and terminal amino groups of nylon 6. The same phenomenon was observed when polystyrene and nylon 6 were blended with styrene–methacrylic acid copolymer as the interpolymer. The existence of such a graft polymer was confirmed by solvent extraction, estimation of the amino group of nylon 6, and identification by differential scanning calorimetry. The physical properties, especially mechanical properties of nylon 6–polypropylene polymer blends, were remarkably improved with increase of maleic anhydride added to the polymer blend. On the other hand, the physical properties those of nylon 6–polystyrene polymer blends were very little improved even in the presence of good dispersibility.
447 citations
TL;DR: In this article, a semiquantitative model is proposed to explain the complex molecular orientation distribution, observed in injection moldings of amorphous polymers, incorporating flow and heat transfer mechanisms coupled with molecular theories.
Abstract: A semiquantitative model is proposed to explain the complex molecular orientation distribution, observed in injection moldings of amorphous polymers. The model incorporates flow and heat transfer mechanisms coupled with molecular theories. The orientation in the surface skin is related to steady elongational flow in the advancing front, whereas the orientation in the core is related to the shear flow, behind the front, between two solidyfying layers. Coupled with the elongational and shear-induced orientations, a molecular relaxation process takes place which is determined by the rate of heat transfer. The bead-and-spring macromolecular theory was used to calculate root mean end-to-end distances of macromolecules in the various flow fields, as well as the relaxation process.
324 citations
TL;DR: In this paper, a theoretical relationship has been developed which relates the ultimate strength of a composite containing spherical fillers to the size, volume fraction, and surface adhesion of the dispersed phase.
Abstract: A theoretical relationship has been developed which relates the ultimate strength of a composite containing spherical fillers to the size, volume fraction, and surface adhesion of the dispersed phase. The theoretical predictions are compared to experimental data using glass beads of known diameters in polyester resin matrix. Results were compared for the case of poor adhesion between the glass beads and the matrix and for the case of good adhesion. The derived relationships should be useful in helping to optimize the strength properties of particulate reinforced systems.
178 citations
TL;DR: In this paper, it was shown that polycaprolactone is degraded by the mold P. pullulans in the presence of other nutrients, and that degradation is directly proportional to the low molecular weight content in these short-term tests with a single species of mold.
Abstract: Polycaprolactone is degraded by the mold P. pullulans in the presence of other nutrients. The weight loss from solid polymer films covered by a nutrient agar gel on which colonies are growing is used to establish comparative rates of degradation. There is substantial loss (16 mg/cm2 surface area) from a whole polymer of low (2,000) molecular weight in three weeks at 30°C. A high (30,000) molecular weight whole polymer degrades about 0.15 as much in the same time period. A fraction in the same range (38,000) but with a narrower molecular weight distribution shows no significant loss. This indicates that whole polymers of high molecular weight may lose only a portion of their distribution by microbial degradation in short-term tests. This hypothesis is tested by making mixtures of high (61,000) molecular weight with low (2,000) molecular weight polymer. Degradation is directly proportional to the low molecular weight content in these short-term tests with a single species of mold. Other workers have shown previously that in long-term, soil-burial tests, even a high (40,000) molecular weight polycaprolactone is essentially completely degraded after one year.
166 citations
161 citations
TL;DR: In this paper, the authors determined the pore size of microporous polymer membranes based on the gas permeability of porous media, which is a simple and reliable means of estimating mean pore sizes of polysulfone membranes.
Abstract: Pore sizes of microporous polymer membranes were determined by the calculation based on the gas permeability of porous media. The gas permeability coefficient K (given by J = K Δp/l, where J is the steady-state gas flux, Δp is the pressure, difference, and l = the thickness of a membrane) for porous membrane can be given generally by
where K0 is the Knudsen permeability coefficient, η is the viscosity of the permeant gas, B0 is the geometric factor of a membrane, and Δp is the mean pressure of the gas on both sides of a membrane. From gas permeability measurements which yield the pressure dependence of gas permeability coefficient (expressed as above equation), the mean pore size of the porous membrane can be estimated as
where M is the molecular weight of the permeant gas. The validity of this method was examined with various Millipore filters of which nominal pore sizes are known. It was confirmed that the method provided a simple and reliable means of estimating mean pore size of microporous membranes. The method was applied to investigate the influence of factors involved in preparation of microporous polysulfone membranes by coagulation procedure. It was found that the mean pore size of porous polysulfone membrane increases with (1) increasing with casting thickness, (2) increasing temperature of coagulation bath, and (3) decreasing concentration of polymer in casting solution (DMF as solvent). Water flux and water flux decline due to compaction are also examined as a faction of pore size, porosity, and the thickness of membranes.
158 citations
TL;DR: In this paper, the development of crystallinity in polyethylene is controlled by a balance between increased crystallization kinetics caused by the stress in the fiber and a tendency for increased supercooling with change in any spinning variable that increases cooling rates.
Abstract: Apparatus has been developed for studying the development of crystallinity and orientation during the melt spinning of synthetic fibers. Tension in the fiber and temperature, diameter, and x-ray diffraction patterns are measured as a function of distance from the spinneret for a running monofilament. Measurements are presented for linear polyethylene over a range of spinning variables together with other investigations carried out on the final as-spun fibers. These data indicate that the development of crystallinity in polyethylene is controlled by a balance between increased crystallization kinetics caused by the stress in the fiber and a tendency for increased supercooling with change in any spinning variable that increases cooling rates in the fiber. The type of crystalline orientation observed, its development during the spinning process, and the changes observed with changes in spinning conditions suggest a model for the as-spun fiber structure in which varying amounts of row nucleation and twisting of lamellar, folded-chain crystal overgrowths occur depending on the spinning conditions. As-spun fiber birefringence was shown to depend primarily on the crystalline orientation. Mechanical properties correlated well with c-axis crystalline orientation function and spinline stress.
133 citations
TL;DR: In this article, an experimental study of the influence of carbon black loading, particle size and structure on the extrusion characteristics of polybutadiene and butadiene-styrene copolymer synthetic rubber is described.
Abstract: An experimental study of the influence of carbon black loading, particle size, and structure on the extrusion characteristics of polybutadiene and butadiene–styrene copolymer synthetic rubber is described. The development of extrudate distortion and its mechanisms are considered. The viscosity and die swell have been related to black loading, particle size, and structure. Generally, it is found that black surface area and structure acts to increase viscosity and decrease elastic memory. This situation is analyzed in terms of the theory of nonlinear viscoelasticity. Two mechanistic theories are described which may explain this behavior. One theory is based on the continuum mechanics analysis of suspensions of particles in viscoelastic media. The rheological behavior of the black compounds is explained in terms of the increased severity of deformation in the polymer matrix surrounding the particle agglomerates. The second theory is based on the view of an entanglement network containing black particles. Polymer chains may be adsorbed onto the surface giving rise to increased entanglement densities.
121 citations
TL;DR: In this paper, the idea that filled polymers, length fraction, area fraction, and volume fraction of filler are different appears to have gained wide acceptance, except for special directions in ordered arrangements, is demonstrated.
Abstract: The idea that, with filled polymers, length fraction, area fraction, and volume fraction of filler are different appears to have gained wide acceptance. The fallacy of this, except for special directions in ordered arrangements, is demonstrated. This misunderstanding has led to widespread misinterpretation of experimental results in this field.
105 citations
TL;DR: In this article, a thermal degradation of low-density polyethylene, free from additives, were heated at temperatures between 284° and 355°C under high-purity nitrogen.
Abstract: Samples of low-density polyethylene, free from additives, were heated at temperatures between 284° and 355°C under high-purity nitrogen. Changes in molecular weight distribution (MWD), molecular weight averages, and degree of long-chain branching (LCB) were followed by gel chromatography (GPC) and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry (DSC). At 284° and 315°C, the MWD's were shifted toward higher molecular weights and the Mw values increased. At 333° and 355°C, the MWD's shift toward lower molecular weight, but the high molecular weight, tail is largely retained. Mw decreases slowly at 333°C. At 355°C, Mw undergoes a rapid initial drop which levels off. Mw/Mn and the degree of LCB increase with heating time and temperature. Olefinic unsaturation increases. The vinyl groups show a larger relative increase than do the trans-vinylene and vinylidene groups. At 355°C, the peak of the unimodal DSC thermogram is shifted to ∼3°C higher temperature. A lower melting peak then develops, and after 72 and 90 min the two peaks are about equal in size. The density increases from 0.922 g/cm3 to 0.930 g/cm3 for samples heated at 355°C, and the weight loss was 1.5% after 90 min. A reaction scheme for the thermal degradation of polyethylene is discussed. Initiation is suggested to be accomplished by scission of allylic CC bonds. Propagation proceeds by both intra- and intermolecular hydrogen abstraction, followed by β-scission. Termination can occur by both combination and disproportionation. Combination reactions are suggested to account for the observed formation of LCB and high molecular weight material. Due to changes in the degree of LCB during the degradation, viscometry alone will not give a proper measure of the changes in molecular weight.
104 citations
TL;DR: In this paper, a study was made of the effect of carboxylic monomers on the surfactant-free emulsion polymerization of styrene and styrene-butadiene.
Abstract: A study was made of the effect of carboxylic monomers on the surfactant-free emulsion polymerization of styrene and styrene–butadiene. Acid monomers, such as acrylic acid, methacrylic acid, and itaconic acid, were shown to play a critical role in particle formation and particle stabilization in such systems. In the emulsion polymerization of styrene, methacrylic acid forms particles more efficiently than acrylic acid. This difference is attributed to the more hydrophobic nature of the methacrylic monomer which allows it to diffuse more rapidly to the particle surface where it acts to prevent agglomeration. The ability of carboxyl groups to orient at the particle–water interface was studied by acid–base and soap titrations of carboxylated styrene–butadiene latices. The polymerization of itaconic acid onto the particle surface of a styrene–butadiene latex produces a surface carboxyl density much higher than is obtainable with classically adsorbed surfactants. This result is used to explain the greater stability of carboxylated versus noncarboxylated emulsion polymers. During the polymerization of styrene–butadiene latices, carboxyl groups dervied from methacrylic acid are shown to be buried more deeply into the particle as compared to carboxyls derived from the more hydrophilic acrylic acid which orient more at the particle–water interface.
TL;DR: The concept of flammability is fundamentally related to the potential thermal energy available per unit of volume of material emerged from attempts to correlate the effect of composition variables on the flammable of neoprene vulcanizates as measured by the oxygen index (O.I.) test as mentioned in this paper.
Abstract: The concept that flammability is fundamentally related to the potential thermal energy available per unit of volume of material emerged from attempts to correlate the effect of composition variables on the flammability of neoprene vulcanizates as measured by the oxygen index (O.I.) test. The origins of this test clearly show that it is a highly specific measure of flammability—the tendency of a composition to continue to burn once ignited—and that it is thermodynamically related to the heat of combustion of materials. This relationship is developed to a linear correlation which includes a wide variety of synthetic and natural materials and permits reasonable prediction of O.I. values from elemental analysis. Polymeric materials containing carbon and oxygen in atom ratios of less than 6 to 1 are more flammable than predicted. The effect of atmospheric temperature on O.I. can be predicted in relation to the O.I. value at normal temperature. This effect is shown to be independent of the composition of the material being tested. These two correlations permit the construction of a simple general map of flammability against which experimental data can be compared and judgments made with respect to the significant variables involved. There appears to be a significant relation between O.I. data, as viewed from these correlations, and the data of other flammability tests.
TL;DR: In this article, an experimental study was carried out to investigate the viscoelastic behavior of calcium carbonate-filled polypropylene melts, using the Han slit rheometer.
Abstract: An experimental study was carried out to investigate the viscoelastic behavior of calcium carbonate-filled polypropylene melts, using the Han slit rheometer. In the analysis of the experimental data, the pressure gradient was used to determine the wall shear stress, and the exit pressure to determine the elasticity of the filled polymers. The study shows that the materials studied follow a power law in viscous behavior over the range of shear rates investigated and that the viscosity increases and elasticity decreases as filler concentration is increased. Also investigated was the effect of temperature on the viscoelastic properties of filled polypropylene melts.
TL;DR: In this article, the authors used Pervaporation and osmotic distillation techniques to achieve separation of the benzene-cyclohexane mixtures, and found that the flux of the permeate increases sharply with increasing temperature, concentration of benzene in the feed solution, and fraction of polyphosphonate in the membrane.
Abstract: Membranes prepared from polymeric alloys of polyphosphonates and acetyl cellulose are highly permeable to benzene and the cyclohexene, but practically impermeable to the aliphatic hydrocarbons cyclohexane and decalin. Pervaporation and osmotic distillation techniques were used in order to achieve separation of the benzene–cyclohexane mixtures. The flux of the permeate increases sharply with increasing temperature, concentration of benzene in the feed solution, and fraction of polyphosphonate in the membrane. The increase of permeate flux is accompanied by a slight decrease of the separation factors. The permeation characteristics of the membranes were compared with those predicted from the results of sorption experiments. The agreement between the observed and the predicted fluxes and separation factors indicates that the permeation mechanism can be described in terms of molecular diffusion. The high selectivity of the membranes makes possible the development of a novel “osmotic distillation” technique. Such a technique, which combines osmotic permeation of organic liquids with conventional distillation, may be advantageous in the separations of azeotropic mixtures.
TL;DR: In this article, the rate constants and activation energies of four homologous aliphatic bismaleimides were determined, and an almost linear correlation between the activation energy and the number of methylene groups in the sequence between the maleimide residues was found.
Abstract: Bismaleimides polymerize at elevated temperatures, forming highly crosslinked, high temperature-resistant polymers. From the decrease of the ν(HC) band at 3100 cm−1, rate constants and activation energies of the polymerization of four homologous aliphatic bismaleimides were determined. Up to a 20–30% conversion, the polymerization is pseudofirst order. An almost linear correlation between the activation energy and the number of methylene groups in the sequence between the maleimide residues was found.
TL;DR: In this paper, the effect of some factors including temperature, pressure, film thickness, and grafting ratio on the fractionation of binary liquid mixtures has been investigated by pervaporation through poly(tetrafluoroethylene) films grafted with N-vinylpyrrolidone or 4vinylpolypyridine.
Abstract: The effect of some factors including temperature, pressure, film thickness, and grafting ratio on the fractionation of binary liquid mixtures has been investigated by pervaporation through poly(tetrafluoroethylene) films grafted with N-vinylpyrrolidone or 4-vinylpyridine The purpose was to estimate the best conditions in which the pervaporation process must be carried out It was concluded that the pervaporation rate is increased at roughly constant selectivity when the temperature of the liquid charge is higher or when the downstream vapor pressure or the film thickness are decreased A pressure higher than 1 atmosphere above the liquid does not increase the rate When the grafting ratio is increased, the rate shows a maximum, and for particular conditions, the selectivity becomes much higher
TL;DR: In this paper, the solubility and diffusion coefficient of two antioxidants in polyethylene have been determined by using a thermogravimetric technique, which relies directly on the ability of the additives to suppress oxidation reaction.
Abstract: As an aid in assessing the ability of antioxidant additives to persist in polymers and thus remain effective in protecting against oxidation, the solubility and diffusion coefficient of two antioxidants in branched polyethylene have been determined in this work. A method was developed for this purpose by which the diffusion coefficient and solubility could be determined simultaneously. The method consists of analyzing the concentration profile across a stack of polyethylene sheets through which the antioxidant was allowed to diffuse. The concentration of antioxidants in polyethylene was determined by a thermogravimetric technique which relies directly on the ability of the additives to suppress oxidation reaction. The diffusion coefficients determined showed excellent agreement with values in the literature which were obtained by a radiotracer method. The solubility of the antioxidants in three normal hydrocarbon solvents of varying molecular sizes was also determined by a conventional technique at various temperatures and found to correlate well with their solubility in polyethylene determined by the diffusion method. In particular, the dependence of the solubility on the size of solvent molecules and on temperature agrees well with an equation derived on the basis of the regular solution theory of liquid mixtures.
TL;DR: The stability of melt spinning has been studied theoretically by solving for transients the perturbed form of the simultaneous partial differential equations of Melt Spinning introduced by the author in a previous study.
Abstract: The stability of melt spinning has been studied theoretically by solving for transients the perturbed form of the simultaneous partial differential equations of melt spinning introduced by the author in a previous study. Computed stability limits summarized in the form of maps in the (t*—St) plane with the cooling air speed serving as the third parameter showed that the thread must be in a molten state at the take-up before an instability can develop and that the cooling of the thread by air plays a predominant role in stabilizing the melt spinning. Here, t* is air temperature and St is the Stanton number. Draw resonances were observed experimentally in a water-quenched melt spinning of PET fiber and in the casting of PP film. Experimental results agreed well with theoretical simulations with respect to oscillation periods and stability. Draw resonance observed by Bergonzoni et al. was closely simulated by means of the present theories.
TL;DR: In this paper, the reversible part of the fracture mechanics (F-M) fracture energy γc is redefined in terms of current theory for surface energetics (S-E) interactions at regular interfaces.
Abstract: The reversible part of the fracture mechanics (F-M) fracture energy γc is redefined in terms of current theory for surface energetics (S-E) interactions at regular interfaces. These new failure criteria are applied to the definition of surface energy criteria for spontaneous interfacial failure, where γc = 0, produced by selected conditions of liquid-phase immersion. For cases where γc > 0, the total fracture energy W = γc + Wp, where the irreversible plastic work of surface formation Wp ≈ W ≫ γc. A qualitative relation between γc1/2 ∝ Wp is observed for the case of steady-state crack propagation in peeling. For adsorption bonds, the theory provides a new method of mapping the surface energy effects of the immersion phase upon the Griffith fracture energy γc. Essential factors which determine water sensitivity of interfacial bonds are incorporated into the analysis and experimentally verified.
TL;DR: In this paper, the thermogravimetric measurements combined with mass-spectrometric analysis were used to analyze the thermal behavior of polystyrene polymers with pendent phosphonate groups in the presence of etheral solvents.
Abstract: Soluble chloromethylated polystyrene and its copolymers with vinylidene chloride as well as poly(phenyl oxides) brominated in the side chains and in the ring were synthesized and characterized in detail by NMR. The halogenated polymers were phosphonylated with alkyl phosphites. Uncrosslinked polymers with pendent phosphonate groups were prepared in the presence of etheral solvents, which solvate the ionic intermediates of the Arbuzov reaction. These polyphosphonates are highly hygroscopic and are soluble in a variety of solvents. Their Tg's are in the range of 50–175°C. Their thermal behavior was analyzed on the basis of thermogravimetric measurements combined with mass-spectrometric analysis. Poly(styrene phosphonate) seems to be the most stable, and its thermal decomposition starts at ∼330°C. The polymeric phosphonates are compatible with an unusually large number of polymeric systems and seem to form “true” polymeric alloys with acetylcellulose.
TL;DR: In this article, the second dimension was used to improve the agreement between the calculated solubility and that measured using a ternary solution technique, which proved most useful for predicting the effect of small structural modifications.
Abstract: The two-dimensional solubility parameter approach has been applied to the prediction of solubility of one polymer in another. The solubility parameters of a number of polymers have been calculated and the second dimension shown to improve the agreement between the calculated solubility and that measured using a ternary solution technique. The method proved most useful for predicting the effect of small structural modifications on solubility, and several examples of changing solubility, monitored by calculations and measurements, are given. Structural modifications included copolymer ratio variations and substitutions to affect polymer density or reduce polarity of functional groups. The effects of temperature and molecular weight on solubility are discussed in terms of regular solution theory, which could not account for the decrease in solubilities with increased temperature observed for several polymer–polymer systems.
TL;DR: In this article, the effects of variations of casting solution temperature and solvent evaporation period were also briefly studied, and the results offer definitive physicochemical criteria in terms on solution structure-evaporation rate concept for developing useful cellulose acetate ultrafiltration membranes.
Abstract: The film-casting solution consisted of a mixture of cellulose acetate, acetone, and aqueous magnesium perchlorate [Mg(ClO4)2:H2O = 1:8.5], designated as polymer P, solvent S, and nonsolvent N, respectively. Using the composition P:S:N = 17: 69.2: 13.8 as reference, films were obtained from 19 different casting solutions in which the weight ratios S/P, N/S, and N/P were varied in different directions. The casting solution temperature was 0°C, and solvent evaporation period during film formation was minimum in most cases. The effects of variations of casting solution temperature and solvent evaporation period were also briefly studied. Reverse osmosis experiments with resulting membranes were carried out at 100 psig using 200 ppm NaCl–H2O as the feed solution. Decrease in S/P, increase in N/S, and increase in N/P in the casting solution, decrease in temperature of the casting solution, and increase in solvent evaporation period tend to increase the size of pores on the surface of resulting membranes in the ascast condition. Increase in S/P in the casting solution, and increase in the temperature of the casting solution tend to increase the effective number of pores on the membrane surface. These results offer definitive physicochemical criteria in terms on solution structure–evaporation rate concept for developing useful cellulose acetate ultrafiltration membranes.
TL;DR: In this paper, a new phenomenological observation regarding the stress crazing of glassy polystyrene was reported, which was interpreted in the light of knowledge from the literature and provided a better understanding of the crazing process.
Abstract: This paper reports a new phenomenological observation regarding the stress crazing of glassy polystyrene. It was found that the applied stress to initiate a craze, often called the critical crazing stress, is independent of molecular weight. Further, the gross structure of the craze does depend on molecular weight, and other phenomenological aspects previously reported have been reaffirmed. These observations are interpreted in the light of knowledge from the literature and provide a better understanding of the crazing process.
TL;DR: In this paper, the effect of specific functional group modification of wool on the binding of a number of metal ions (individually) from aqueous solutions was studied, and the metal ion uptake profiles for the different modified keratin polymers showed that a degree of specificity of binding is imparted by the various modifications in terms of changes in capacities or rates of metal ion uptakes.
Abstract: The effect of specific functional group modification of wool on the binding of a number of metal ions (individually) from aqueous solutions was studied. The metal ion uptake profiles for the different modified keratin polymers show that a degree of specificity of binding is imparted by the various modifications in terms of changes in capacities or rates of metal ion uptakes. The changes of uptake depend on both the particular ion and the particular protein modification involved. The results show the potential usefulness of the keratin derivatives for removal of toxic and industrial metal ions from water and contribute to interpretation of metal ions interactions with native wool and proteins in general. Treatments of woven wool with aqueous solutions of certain metal salts impart flame and insect resistance to the fabric.
TL;DR: The solubility of benzene in polymeric alloys (P/A) consisting of polyphosphonates (PPN) and acetyl cellulose (AC) is nearly two orders of magnitude larger than that of cyclohexane as mentioned in this paper.
Abstract: The solubility of benzene in the polymeric alloys (P/A) consisting of polyphosphonates (PPN) and acetyl cellulose (AC) is nearly two orders of magnitude larger than that of cyclohexane. The preferential absorption of benzene by P/A membranes is also maintained upon its dilution with cyclohexane, though the solubility of the latter in the P/A membranes is affected by their swelling with benzene. Absolute values of solubilities increase exponentially with increase in the weight fraction of PPN in P/A membranes. They are also affected by the thermal and solvent “history” of a membrane. For the sorption of benzene by a P/A-50 membrane
The diffusion coefficients of benzene in the solvent-swollen membranes are strongly concentration dependent and increase exponentially up to ∼10−6 cm2/sec with the increase in the volume fraction of benzene. Values of D0 are of the order of 10−11 to 10−10 cm2/sec. Sorption experiments indicate a pronounced time dependence of the diffusion coefficients. Self-diffusion experiments conducted with 14C-labeled benzene revealed that values of D* derived from the steady-state permeation measurements are in certain membranes much larger than those derived from the “time-lag.” It was observed that the discrepancies between the two sets of values depend strongly upon the thermal “history” of the membranes and vanish when the membranes are swollen to a high degree at elevated temperatures. The above phenomenon is discussed in terms of differences in the membrane structure; a model is proposed. The apparent energy of activation of diffusion of benzene at 10–40°C in the swollen P/A-50 membrane EBD 14.4 kcal/mole was derived from the temperature dependence of the self-diffusion coefficients. For the same temperature range at C(B) → 0, EB = 8.3 kcal/mole was derived from the final slopes of the desorption curves. The small difference between the energies of activation in a swollen and in an unswollen system is due to the fact that at room temperature it remains below Tg even upon extensive swelling with benzene.
TL;DR: In this paper, it was shown that high viscosity H-SPAN water mixtures consist of swollen, deformable gel particles closely packed in intimate contact, and that at high dilution or at high ionic strength conditions, the gel particles no longer are tightly packed, solvent is present in excess, the viscoity drops precipitously, and the thickening action effectively disappears.
Abstract: Hydrolyzed starch–polyacrylonitrile (H-SPAN) graft copolymers form highly viscoelastic mixtures with water, even at concentrations less than 1% by weight. In many ways these mixtures behave like ordinary polyelectrolyte solutions, but dilution experiments revealed that linear reduced viscosity–concentration plots could not be obtained even under ostensibly isoionic dilution conditions. This result, combined with a determination of gel content from centrifugation studies, led to the conclusion that high viscosity H-SPAN water mixtures consist of swollen, deformable gel particles closely packed in intimate contact. Under high dilution or at high ionic strength conditions, the gel particles no longer are tightly packed, solvent is present in excess, the viscosity drops precipitously, and the thickening action effectively disappears. For comparative purposes, a commercial thickening agent (Carbopol 941) was examined and found to act in the same way. All reduced viscosity-concentration curves obtained by dilution, either with salt solutions or water, can be shifted to a single normalized reduced viscosity plot. This shift is done by using as the concentration variable the quantity cQ, where c is the polyelectrolyte concentration and Q is the swelling which the gel particles undergo in an excess of solvent at the corresponding total ionic strength of the solution of concentration c.
TL;DR: In this paper, a study of the curing reactions of a cycloaliphatic epoxy resin/anhydride system by torsional braid analysis showed the existence of two critical isothermal temperatures - namely, the maximum glass transition temperature of the thermoset system and the glass transition ratio of the material at its gel point.
Abstract: A study of the curing reactions of a cycloaliphatic epoxy resin/anhydride system by torsional braid analysis showed the existence of two critical isothermal temperatures - namely, the maximum glass transition temperature of the thermoset system and the glass transition temperature of the material at its gel point. Two rheologically active kinetic transitions occur during isothermal cure which correspond to gelation and vitrification. Three types of isothermal behavior occur. Methods for determining the time to gel and the time to vitrify, and also the two above-mentioned critical isothermal temperatures, have been developed. The time to gel obeyed the Arrhenius relationship, whereas the time to vitrify passed through a minimum. Application of these results to thermosetting systems in general is discussed in terms of the influence of molecular structure on the values of the critical isothermal temperatures.
TL;DR: In this paper, two-component interpenetrating polymer networks (IPN) of the SIN type were prepared from three different polyurethanes and two epoxies, which showed significant improvement in thermal resistance, as measured by thermogravimetric analysis.
Abstract: Two-component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks) were prepared from three different polyurethanes and two epoxies. The linear prepolymers were combined in solution, together with crosslinking agents and catalysts, films cast, and subsequently chain extended and crosslinked in situ. Two of the IPN's showed significant improvement in thermal resistance, as measured by thermogravimetric analysis (TGA). All of the IPN's showed maxima in tensile strength significantly higher than the tensile strengths of the component networks at 25% polyurethane and minima at 75% polyurethane. The minima were explained by an initial dilution of the strong polyurethane hydrogen bonds by the epoxies, and the maxima, by an increase in crosslink density due to interpenetration.
TL;DR: In this article, the chemical structure and cure characteristics of a group of phenolic resole resins were studied by means of three major analytical techniques: Gel permeation chromatography, NMR and differential scanning calorimetry.
Abstract: The chemical structure and cure characteristics of a group of phenolic resole resins were studied by means of three major analytical techniques. In particular, the effects on structure and reactivity of formaldehyde/phenol ratio and the type of reaction catalyst used were studied. Gel permeation chromatography was used to determine resin molecular weight distributions, and NMR, to determine chemical structural features. In this connection a selective oxidation procedure, converting free methylol groups to adehydes, has allowed unambiguous determination of methylene ether bridge structures to be made from the NMR data. The F/P ratio in a resole largely determines the type of molecular structures which are formed. However, triethylamine as a catalysts tends to favor methylene ether bridge formation, whereas sodium hydroxide favors methylene bridges. The rate and direction of subsequent thermal cure of the resoles prepared is shown by differential scanning calorimetry to depend markedly on the type of catalyst present during the curing stage. The DSC curing curves are interpreted in the light of the structural information provided by NMR.