Showing papers in "Journal of Applied Polymer Science in 1988"
TL;DR: In this article, the thickness of the matrix ligament is defined as the surface-to-surface interparticle distance between two neighboring rubber particles, and the ligament thickness is the single parameter determining whether a polymer/rubber blend will be tough or brittle.
Abstract: The thickness of matrix ligament is shown to be the single parameter determining whether a polymer/rubber blend will be tough or brittle. The matrix ligament is defined as the region of the matrix between two neighboring rubber particles. Specifically, the ligament thickness is the surface-to-surface interparticle distance. When the average ligament thickness is smaller than a critical value, a blend will be tough; when greater, it will be brittle. In other words, a sharp brittle–tough transition occurs at the critical ligament thickness. This critical parameter is independent of rubber volume fraction and particle size, and is characteristic of the matrix for a given mode, temperature and rate of deformation. What is important is the matrix ligament, not rubber particles. The single matrix parameter explains the effects of phase morphology, rubber volume fraction, particle size, particle-size polydispersity, and particle flocculation on toughness.
602 citations
TL;DR: In this paper, a new method to prepare polyanhydride microspheres via solvent removal was presented, which was used for the controlled release of insulin in treating diabetes mellitus.
Abstract: A new method to prepare polyanhydride microspheres, namely via solvent removal, is presented. Polyanhydrides composed of the following diacids were used: sebacic acid (SA), bis(p-carboxy-phenoxy) propane (CPP), and dodecanedioic acid (DD). Polymers were characterized by infrared (IR) spectroscopy, X-ray diffraction, viscosity, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Drug release was affected by polymer composition, physical properties of the microspheres, and type of drug. The potential for injectable microspheres (size range 1–300 μm) made of copolymer (CPP-SA 50:50), as biodegradable polymer carriers for the controlled release of insulin in treating diabetes mellitus, was assessed. Both 5% and 10% w/w insulin-loaded microspheres were prepared. The 10% loaded microspheres produced the best clinical response, demonstrating five days of urine glucose control and four days of serum glucose control in diabetic rats.
358 citations
TL;DR: In this article, a scaling law for the diffusion coefficient of spheroidal and ellipsoidal solutes in nonporous, equilibrium-swollen hydrogels was developed.
Abstract: A scaling law was developed for the diffusion coefficient of spheroidal and ellipsoidal solutes in nonporous, equilibrium-swollen hydrogels. The law relates the solute diffusion coefficient to the solute size, the gel mesh size, and the gel equilibrium volume degree of swelling. The law was verified by appropriate data of low and high molecular weight solute diffusion through hydrogels such as swollen networks of poly(vinyl alcohol), poly(2-hydroxyethyl methacrylate), cellulose, and others. An additional scaling law was developed which relates the rate of release of a small or large molecule from an equilibrium swollen hydrogel with time and with morphological characteristics of the polymeric network.
246 citations
TL;DR: In this article, the structure of skin layer in injection-molded polypropylen was studied by means of wide-angle X-ray diffraction, small-angle x-ray scattering, melting behavior, density, dynamic viscoelasticity, and tensile test.
Abstract: The structure of skin layer in injection-molded polypropylen which displayed a clear two-phase structure of skin and core has been studied by means of wide-angle x-ray diffraction, small-angle x-ray scattering, melting behavior, density, dynamic viscoelasticity, and tensile test. In skin layer, the c-axis and a*-axis were highly oriented to the machine direction (MD), and the plane of the lamellar structure of about 160 A in thickness was in normal to MD. The density was about 0.907 g/cm3, which was nearly the same as that of core layer. Although the majority of crystallites melted in the same temperature range as in that of the core layer, there was about 5.3% higher temperature melting structure (Tm = 182°C). The dynamic tensile modulus E′ in MD decreased more slowly with increasing temperature than that of the core layer and held high modulus in the range of ca. 30°C, just above the temperature at which E′ of the core layer suddenly dropped. E′ in MD was higher than that in TD in the temperature range below 33°C, which was slightly higher than the primary absorption temperature, and the order reversed above 33°C. The tensile yield stress in MD was 1.5 times higher than that of the core layer. The skin layer in MD ruptured just after yielding and did not show necking. The tensile yield stress in TD was about half of that in MD about 0.7 times that of the core layer. The necking stress in TD was about 0.6 times that of the core layer. In general, a polypropylene melt crystallizes under a high shear stress in injection molding. From these facts, it was concluded that the skin layer is composed of so-called “shishkebab”-like main skeleton structures, whose axis is parallel to MD, piled epitaxially with a*-axis-oriented imperfect lamellar substructure.
226 citations
TL;DR: In this article, the degradative conversion of 14C present in low density polyethylene (LDPE) film to respiratory 14CO2 during a 10-year aerated cultivation with soil is presented.
Abstract: Data relating to the degradative conversion of 14C present in low density polyethylene (LDPE) film to respiratory 14CO2 during a 10-year aerated cultivation with soil are presented. The degradation was performed with two sets of LDPE samples, one without additive (PE) and the other containing UV sensitizer (NDPE). Samples were exposed to UV irradiation for 0, 7, 26, and 42 days. The degradation is characterized by three stages: (I) a constant degradation rate, (II) a parabolic decline in the rate of degradation, and (III) a subsequent final increase in the rate of degradation. The first step (I) is probably dependent on the environment. The material changes rapidly until some kind of equilibrium with the environment has been achieved. CO2 is evolved, oxygen uptake is rapid, and a rapid change in mechanical properties is also observed. The second step (II) is characterized by low oxygen uptake, a low evolution of CO2 and slow changes in the mechanical properties, crystallinity, and molecular weight. The changes in mechanical properties are not necessarily synchronous with the decrease in molecular weight. Step III, finally, is a rapid deterioration of the structure. The degradation rate increases again, and all the mechanical properties are more or less lost due to the final collapse of the structure. For an inert material such as PE, 10 years is a short time, so that only small indications of step III and a coming mineralization point can be observed. The changes are more evident for NDPE. The use of degradable materials, for example polypropiolactone, however, means that it is possible during a 2-year period to study all three stages. An understanding of the mechanisms in each step will give a better base for lifetime predictions.
179 citations
TL;DR: In this article, a new class of high performance engineering resins, poly(aryl ether ketone)s, has emerged with a property balance not offered by existing polymeric materials.
Abstract: A new class of high performance engineering resins, poly(aryl ether ketone)s, has emerged with a property balance not offered by existing polymeric materials Blends of poly(aryl ether ketone)s with other polymers have not been described in the open literature, although several patents have revealed interesting and important properties of certain blend combinations Ultem polyetherimide has been found to be miscible over the entire composition range and as a consequence is a very effective heat distortion temperature builder, particularly if the poly(aryl ether ketone) is allowed to crystallize Crystallization kinetics and mechanical properties were studied as a function of blend composition and poly(aryl ether ketone) melting point The blends exhibited a maximum in toughness at intermediate compositions along with an accompanying maximum in poly(aryl ether ketone) crystallinity The chemical resistance of the polyetherimide is significantly improved with the addition of a poly(aryl ether ketone) In organic chemicals, the improvement was expected when tensile stress was plotted vs log time to rupture However, in aqueous bases, the resistance of the blends was much greater than anticipated This property profile suggests that these blends will be useful as thermoplastic composite matrix resins
132 citations
TL;DR: In this paper, the kinetics of polyesterification of the glycolyzed PET waste with adipic acid was reported, and the reaction conditions were nonisothermal, comparable to the industrial process scheme consisting of two isothermal regions at 170° and 200°C.
Abstract: The kinetics of polyesterification of the glycolyzed PET waste with adipic acid is reported. Glycolysis of PET waste was carried out with ethylene glycol at three different ratios of PET waste to glycol. The glycolyzed products could be readily polyesterified by reacting with adipic acid, to give polyester polyols with low acid number. Kinetics of polyesterification of the glycolyzed product made from 62.5% ethylene glycol (EG) and 37.5% waste were investigated further at different hydroxyl to carboxyl ratios. Reaction conditions were nonisothermal, comparable to the industrial process scheme consisting of two isothermal regions at 170° and 200°C. The kinetic results of the polyesterification of glycolyzed PET waste are compared to the polyesterification of pure diols, namely ethylene glycol and bis(hydroxyethyl) terephthalate (BHET) with adipic acid. The reactions follow second-order kinetics at 170°C and the rate of polyesterification of the mixed diol system from PET waste lies intermediate between those of the pure diols, namely, EG and BHET. Ethylene glycol exhibited the highest reactivity. At 200°C the kinetic plots of the mixed diols from PET waste were nonlinear, and thus the reaction may not follow second-order kinetics. The nonlinearity is explained in terms of the different reactivities of the different diol species in the reaction mixture. The polyester polyols, when cured with polymeric 4,4′ diphenyl methane diisocyanates, gave polyurethane rigid foams and elastomers.
119 citations
TL;DR: In this paper, a polyacrylonitrile (PAN) fiber pretreated with potassium permanganate has been shown to reduce the activation energy of cyclization and the oxidation time, and also improved the properties of the resultant carbon fibers.
Abstract: Polyacrylonitrile (PAN) fibers pretreated with potassium permanganate have reduced the activation energy of cyclization and the oxidation time, and also improved the properties of the resultant carbon fibers. The activation energy of cyclization is reduced to 24 ± 1 kcal/mol from 30 ± 3 kcal/mol and the tensile strength of the carbon fibers increases by about 20−40%. The method of measuring the “aromatization index” (AI) value is modified and is recommended in checking the oxidation process. All fully stabilized PAN fibers have almost the same AI value. However, the oxidation time is decreases by 30 min when oxidation temperature is raised by 10°C.
109 citations
TL;DR: A series of four TDI-polypropylene oxide (PO) water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110 as mentioned in this paper.
Abstract: A series of four TDI–polypropylene oxide (PO) water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of both the foams and plaques was investigated using dynamic mechanical spectroscopy (DMS), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM), swelling, wide angle X-ray scattering (WAXS), and small angle X-ray scattering (SAXS). A high degree of microphase separation occurs in these foams, and its degree is nearly independent of water (hard segment) content. In the foam with the lowest water content the morphology possesses many similarities to that of typical linear segmented urethane elastomers. Small hard segment domains are present with a correlation distance of about 7.0 nm. When the water content is increased a binodal distribution of hard segment material appears. There are the small hard segment domains typical of segmented urethane elastomers as well as larger “hard aggregates” greater than 100 nm in size. The larger domains are thought to be aggregates of rich polyurea that develop by precipitation during the foaming reaction. WAXS patterns of the foams suggest urea and possibly hard segment ordering that may be of a paracrystalline nature but certainly lacking in true 3-dimensional crystallinity.
102 citations
TL;DR: In this article, the authors introduced a new fundamental approach to the modeling of diffusion-controlled free-radical polymerization reactions, where the termination and propagation rate constants are expressed in terms of both a purely reaction-limited term and a diffusion-limited one.
Abstract: The present paper introduces a new fundamental approach to the modeling of diffusion-controlled free-radical polymerization reactions. Our analysis follows the original work of Chiu, Carratt, and Soong (CCS), according to which the termination and propagation rate constants are expressed in terms of both a purely reaction-limited term and a diffusion-limited one. The contribution of the latter term to the apparent rate constants is described in terms of the polymer and monomer effective diffusion coefficients and an effective reaction radius. It is shown that all parameters appearing in the original CCS model can be calculated from first principles using available data on the physical and transport properties of a particular monomer–polymer binary system. The generalized free volume theory of Vrentas and Duda and the theory of excess chain end mobility are invoked for the calculation of the effective diffusion coefficients and the reaction radius, respectively. The approach followed in this study is general and needs only the specification of one unknown parameter with a clear physical meaning. All other parameters can be readily calculated from available data. The ability of the new model to predict molecular weight developments and monomer conversion in diffusion-controlled reactions is demonstrated by application of the proposed model equations to the bulk polymerization of MMA.
99 citations
TL;DR: In this paper, Fourier transform infrared (FTIR) spectroscopy has been used as a modern analytical tool to elucidate the structure of urea-formaldehyde (UF) resins.
Abstract: Fourier transform infrared (FTIR) spectroscopy has been used as a modern analytical tool to elucidate the structure of urea—formaldehyde (UF) resins. Several low molecular weight condensation products of urea and formaldehyde were synthesized and characterized. Structural differences were observed for prepolymers prepared in alkaline and acidic media. Plausible mechanistic routes are proposed to explain the prepolymer structural differences prepared in different experimental conditions. The structural elucidation of the UF resins is considerably increased and improved by using absorbance magnification to further enhance the observed signals.
TL;DR: In this article, the effects of increasing sample size on the polymer retention volumes were examined and it was found that modest increases in load resulted in shifts toward higher retention volumes and broadening of the sample peaks without a major loss of peak symmetry.
Abstract: There are two subtechniques of field-flow fractionation (FFF), thermal FFF and flow FFF, that have been successfully employed for polymer fractionation and characterization. These techniques are primarily analytical in nature, yielding accurate polymer characteristics from small sample loads (∼ 10 μg or less, depending on detection sensitivity). In this study the effects of increasing sample size are examined. Modest increases in load are found to result in shifts toward higher retention volumes. These modest loads also result in some broadening of the sample peaks without a major loss of peak symmetry. Excessive loading, by contrast, appears to give rise both to skewed peaks and to new artifact peaks at higher levels of retention. These observations are discussed in terms of the concentration dependence of various properties (viscosity, diffusivity, thermal diffusivity) which influence polymer transport through the FFF channel. The results are used to indicate upper limits to suitable sample concentrations.
TL;DR: In this article, the dispersive and polar components of the surface energy were calculated from the measured contact angles using both the geometric and the harmonic mean methods, and it was found that these components are similar for untreated cellulose and glass fibers, and that they both have a high polar component corresponding to a hydrophilic surface.
Abstract: Average advancing and receding contact angles made against cotton and glass fibers by a set of probe liquids are determined using the Wilhelmy technique. The dispersive and polar components of the surface energy are calculated from the measured contact angles using both the geometric and the harmonic mean methods. It is found that these components are similar for untreated cellulose and glass fibers, and that they both have a high polar component, corresponding to a hydrophilic surface. Changes in surface energy caused by treatment of the cellulose fiber surfaces with melamine, polyethyleneimine (PEI), and a silane coupling agent are reported. It is found in particular that polyethyleneimine treatment of cellulose significantly reduces the polar component of its surface energy. While treatment of glass fibers with a silane coupling agent reduces the polar component and increases the dispersive component of the surface energy it shows little effect on the surface energy of cellulose.
TL;DR: In this paper, the Sanchez-Lacombe equation of state was used to model the sorption of high-pressure gases into solid, amorphous polymers and molten polymers.
Abstract: The Sanchez-Lacombe equation of state was used to model the sorption of high-pressure gases into solid, amorphous polymers and molten polymers. Only one adjustable parameter per binary pair, δ12, was used in the mixing rules to correct the deviation of the characteristic pressure of the mixture, P12*, from the geometric mean. The values of δ12 which gave the best fit of the available literature data for the carbon dioxide–polymethyl methacrylate, carbon dioxide–silicone rubber, ethylene–low density polyethylene, methane–polyisobutylene, methane–low-density and high-density polyethylene, and methane–polystyrene systems ranged from −0.019 to 0.136. In all cases, the calculated sorption isotherms were in reasonably good agreement with the experimental data. The resultant swelling of polymethyl methacrylate and silicone rubber was also well represented by the Sanchez-Lacombe equation of state. Because the Sanchez-Lacombe theory is based on lattice-fluid theory, the sorption calculations are limited to polymers which are noncrystalline, not cross-linked or slightly crosslinked, above their glass transition temperature, or above their melting temperature. The sorption data for the amorphous polymers considered in this study were either at temperatures above the glass transition temperature of the polymer or were at sufficiently high pressures that the temperature was above the effective glass transition temperature as predicted from a theoretical relation presented by Chow.
TL;DR: In this paper, ionically crosslinked polyacrylic acid (PAA) and Nylon 6 membranes were used for the pervaporation separation of acetic acid-water mixtures.
Abstract: Membranes consisting of ionically crosslinked polyacrylic acid (PAA) and Nylon 6 were prepared and tested for the pervaporation separation of acetic acid-water mixtures. The polyacrylic acid (PAA) membranes were crosslinked in aluminum nitrate aqueous solution while the polyacrylic acid (PAA)-Nylon 6 blends were cast from homogeneous PAA-Nylon 6 mixtures to appropriate thicknesses and then crosslinked in aqueous aluminum nitrate solutions. Optimum pervaporation results were obtained from blends of Nylon 6 and PAA in the weight ratio of 60–75 wt% Nylon 6 and 25–40 wt% PAA which have separation factors (water/acetic acid) of over 60 and flux rates higher than 100 g/m2 h at 15°C for the separation of acetic acid-water mixtures. The flux rates and separation factors could be altered by changing the blend composition of the membrane. The effects of the feed composition on the separation factors were investigated.
TL;DR: In this article, the effects of ultraviolet radiation from a medium pressure mercury vapor lamp and sunlight were found to be almost equally effective in bringing about the depolymerization and hydroxylation of natural rubber.
Abstract: Photochemical degradation of natural rubber yielded hydroxyl-terminated liquid natural rubber (HTNR) when carried out in solution in presence of H2O2. Ultraviolet radiation from a medium pressure mercury vapor lamp and sunlight were found to be almost equally effective in bringing about the depolymerization and hydroxylation of natural rubber. The variations in the composition of the reagents and exposure time on the extent of depolymerization was conducted, and a suitable procedure for the large scale preparation of HTNR was described. A probable mechanism leading to the formation of HTNR as well as the side products is discussed based on the analytical data.
TL;DR: In this paper, the authors used differential scanning calorimetry (DSC) to study the crystallization kinetics and thermal characteristics of poly(aryl-ether-ether−ether-ketone) (PEEK) samples heated under a variety of conditions.
Abstract: Differential scanning calorimetry (DSC) has been used to study the crystallization kinetics and thermal characteristics of poly(aryl-ether–ether-ketone) (PEEK) samples heated under a variety of conditions. Samples were heated in nitrogen and air at temperatures between 380 and 420°C for times up to 120 min. The results indicate that as the holding time and temperature of the melt increased, the amount of recrystallizable material decreased, especially when heated in air. Isothermal crystallization kinetics confirmed the presence of a two-stage crystal nucleation and growth process with Avrami exponents of the order of about 2.4 and 1.5 for the first and second processes, respectively. Analysis of the primary crystallization process using the Avrami equation revealed that PEEK samples heated above the melt temperature in air crystallized at a much slower rate than samples heated in nitrogen.
TL;DR: In this paper, the effect of free radical initiator injection during extrusion of polypropylene was investigated and it was shown that increased initiator concentration degraded the high molecular weight tail of the polyethylene and narrowed the molecular weight distribution.
Abstract: Polypropylene was degraded by injection of a free-radical initiator during extrusion. Molecular weight distribution, molecular weight averages, and melt flow index were measured to see the effect of initiator concentration (0.00 to 0.04 wt%), temperature (200 and 220°C), and screw rpm (31 and 44). Initiator concentration was the most significant variable. In all cases, increased initiator concentration degraded the high molecular weight tail of the polypropylene and narrowed the molecular weight distribution. Melt flow index varied linearly with initiator concentration beyond 0.01 wt% initiator. Reaction temperature had no effect on the measured properties of the extrudate. This was attributed to the minimum residence time in the extruder being sufficient for all degradation reactions to be completed. It also implied that the same reactions occurred at both temperatures. Increased screw rpm slightly increased molecular weight. No interaction among initiator concentration, temperature, and screw rpm was observed.
TL;DR: In this paper, the authors analyzed the dynamic viscoelastic properties of binary blends of nearly monodisperse polybutadienes, polystyrenes, and poly(methyl methacrylate)s.
Abstract: Literature data for the dynamic viscoelastic properties of binary blends of nearly monodisperse polybutadienes, polystyrenes, and poly(methyl methacrylate)s was analyzed using logarithmic plots of dynamic storage modulus G′ versus loss modulus G″, based on a recent theoretical study by Han and John.28 It has been found that for binary blends of monodisperse polymers with molecular weights M much greater than the entanglement molecular weight Me, the value of G′ in log G′ − log G″ plots becomes independent of molecular weight, increases sharply as small amounts of a high-molecular-weight component are added to a low-molecular-weight component, and passes through a maximum G′max at a critical blend composition (ϕ2)max, and that G′max becomes larger and (ϕ2)max becomes smaller as the ratio of component molecular weights increases. However, as the molecular weight distribution of the constituent components becomes broader, the effect of blend composition on G′ in log G′ − log G″ plots becomes less pronounced. This observation has enabled us to explain why log G′ − log G″ plots of binary blends of commercial polymers, namely, blends of two low-density polyethylenes, blends of poly(ϵ-caprolactone) and poly(styrene-co-acrylonitrile), and blends of poly(methyl methacrylate) and poly(vinylidene fluoride), all having broad molecular weight distributions, give rise to values of G′ between those of the constituent components. When one of the constituent components has molecular weight smaller than Me, while the other has molecular weight larger, and as small amounts of the high-molecular-weight component are added to the low-molecular-weight component, log G′ − log G″ plots of binary blends give rise to values of G′ larger than those of the constituent components at low values of G″, but approaches the value of G′ for the low-molecular-weight component as the value of G″ is increased. However as the amount of the high-molecular-weight component is increased above a certain critical composition, binary blends give rise to values of G′ close to that of the high-molecular-weight component at all values of G″. The experimentally observed dependence of G′ on blend composition in log G′ − log G″ plots is favorably compared to the theoretical prediction of a blending law proposed by Montfort and co-workers.14,15
TL;DR: In this paper, a polypyrrole-PMMA composite film was prepared with the chemical oxidative polymerization by spreading the water-insoluble solvent solution of pyrrole and PMMA mixture on the surface of the aqueous solution containing K2S2O8, the oxidizing agent.
Abstract: Polypyrrole–PMMA composite films have been prepared with the chemical oxidative polymerization by spreading the water-insoluble solvent solution of pyrrole and PMMA mixture on the surface of the aqueous solution containing K2S2O8, the oxidizing agent. The conductivity of the films increases rapidly, passes through a plateau, and then decreases gradually as the reaction time increases. The conductivity of the oxidized side of the film is higher by over 1 order of magnitude than that of the evaporated side. It is due to the fact that the former is rich in polypyrrole while the latter is rich in PMMA. The thickness of the films can be controlled by adjusting the PMMA concentration. However, the lower limit of the film thickness is practically in submicron order. The relationship between the transmittance and the logarithm of the conductivity of the films gives a straight line with a gradient, ca. −8. The conductivity of the films is stable on silicagels in a desiccator over 2000 h at 25°C. The conductivity of the film is, however, very sensitive to the moisture in atmosphere and gives rise to decrease with humidity.
TL;DR: In this paper, the authors compared the behavior of polypropylene fire retarded with different additive systems and proposed new measurements with the oxygen index apparatus, which give parameters related to ease of ignition, behavior on forced burning, and thermal insulating characteristics of char developed on burning the material.
Abstract: The oxygen index test is a fundamental tool in basic research on polymer combustion and on mechanisms of fire retardance. Although the oxygen index should provide an evaluation of intrinsic flammability of polymeric materials, its response may depend on geometry of the specimen. This is shown by comparing the behavior of polypropylene fire retarded with different additive systems. The implication of such in mechanistic studies is discussed. Furthermore, new measurements are proposed to be carried out with the oxygen index apparatus, which give parameters related to ease of ignition, behavior on forced burning, and thermal insulating characteristics of char developed on burning the material.
TL;DR: In this article, a polytheylene composite was prepared and tested, consisting of a high-density polyethylene (HDPE) matrix and uniaxial gel-spun high-modulus PE fiber.
Abstract: A polytheylene composite was prepared and tested. It was consisted of a high-density polyethylene (HDPE) matrix and uniaxial gel-spun high-modulus PE fiber. Aided by the similarity between matrix and fiber, transcrystallization of HDPE melt on the PE fiber surface was generated. Nucleating agents were not employed. The transcrystalline growth of HDPE on the PE fiber surface was found to consist of an inner and an outer zone. The inner zone, 2–3 μm thick, is composed of HDPE crystals nucleated on the PE fiber surface. Photomicrographs showed a well-defined region of row-nucleated HDPE on the surface of PE fiber. This means the fibrils of HDPE were found to grow out from the PE fiber axis and HDPE crystallites are oriented in planes perpendicular to the PE fiber axis. The fiber in the composite induced the transcrystalline growth of HDPE on the PE fiber surface at higher temperature than on cooling the melt. For 36 wt% fiber, the increase was 2.5°C, also resulting in ∼ 10% more crystals. Crystallization of a composite with 50 wt% fiber at 124°C involved two steps: The first a fast transcrystallization of HDPE on the PE fiber surface followed by the bulk crystallization of the HDPE.
TL;DR: In this article, the authors examined the application of IR spectrometry to the determination of polypropylene (PP) stereoregularity, and the effect of instrument type on the calibration has been investigated for both dispersive and Fourier transform type infrared spectrometers.
Abstract: This study examines the application of infrared (IR) spectrometry to the determination of polypropylene (PP) stereoregularity. The use of the absorption bands at 998 cm−1 and 841 cm−1 as indices of isotacticity and bands at 1167 cm−1 and 973 cm−1 as internal references have been explored. Calibration curves relating various absorption ratios to isotacticity as measured by 13C nuclear magnetic resonance are reported. The ratios A998/A973 and A841/A973 are the most useful and provide linear correlations with isotacticity. The effect of instrument type on the calibration has been investigated for both dispersive and Fourier transform type IR spectrometers. For samples annealed at room temperature the average of measurements on the same set of PP films by five instruments provide the calibrations: A998/A973 = 1.08 ± 0.02 (mm)−0.15 ± 0.03; and A841/A973 = 0.84 ± 0.06 (mm)−0.04 ± 0.02. High temperature annealing increases the crystallinity of the samples and the corresponding value of the absorption ratio but is not necessary for obtaining reproducible calibration curves.
TL;DR: In this article, the effects of structure of bismaleimides and curing conditions on the thermal and mechanical properties of the cured resins such as initial decomposition temperature (Td), glass transition temperature, and flexural strength were studied.
Abstract: New bismaleimides containing ether bonds were prepared. The thermal properties of the bismaleimides were investigated by differential scanning calorimetry (DSC). The effects of structure of the bismaleimides and curing conditions on the thermal and mechanical properties of the cured resins such as initial decomposition temperature (Td), glass transition temperature (Tg), and flexural strength were studied. The introduction of ether bonds to bismaleimide resins decreased the brittleness of the resins without reductions in their heat-resistant properties.
TL;DR: In this paper, controlled reactions on the inner side, outer side, and both sides of the surfaces of polysulfone ultrafiltration hollow fibers with propane sultone and Friedel-Crafts catalysts were developed.
Abstract: Controlled reactions on the inner side, outer side, and both sides of the surfaces of polysulfone ultrafiltration hollow fibers with propane sultone and Friedel-Crafts catalysts were developed. EPMA measurements and MTR spectra for the chemically modified fibers suggested existence of CH2CH2CH2SO3− segments on the modified surfaces. The modified fibers were found to have smaller molecular weight cut-off than nonmodified fibers, and the fibers modified on the internal surfaces gave better rejection of polyethylene glycol 6000 than those modified on the external surfaces, although the fibers that reacted with solution of the propane sultone and SnCl4 at 70°C and 80°C showed negative rejection of the polyethylene gylcol. Absorption of polyethylene glycol on the modified fibers is estimated to be less than the nonmodified fibers from the flux ratios of aqueous polyethylene glycol solution to pure water. This effect is attributed to the heparinlike active group of modified segments.
TL;DR: Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were used to characterize the morphology of solvent cast hydroxypropyl cellulose (HPC) films.
Abstract: Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were used to characterize the morphology of solvent cast hydroxypropyl cellulose (HPC) films. DSC results were indicative of a semicrystalline material with a melt at 220°C and a glass transition at 19°C (T1), although an additional event was suggested by a baseline inflection at about 80°C (T2). Corresponding relaxations were found by DMTA. A secondary relaxation at −55°C was attributed to the interaction between hydroxyl groups of the polymer and residual diluent. The tan δ peak at T2 was found to arise from an organized phase, presumably from a liquid-crystal mesophase formed while in solution. Crosslinking with a diisocyanate increased the peak temperature of the two primary relaxations, and resulted in a more clearly defined peak for the T2 transition. From this behavior it was concluded that both T1 and T2 are similar to glass transitions (Tg's) associated with an amorphous component and a more highly ordered phase (due to a residual liquid crystal superstructure) in the HPC bulk.
TL;DR: In this article, the compositional dependence of the glass transition temperature of amorphous polyamide blends containing hydrophobic and hydrophilic constituents has been adequately accounted for using an existing predictive expression derived from both a conformational entropy and a thermodynamic treatment of glass transition phenomenon.
Abstract: The moisture-induced plasticization of some amorphous polyamides in pure and blended form has been determined by calorimetric methods. The compositional dependence of the glass transition temperature of these polymer-diluent systems has been adequately accounted for using an existing predictive expression derived from both a conformational entropy and a thermodynamic treatment of the glass transition phenomenon. The success of this approach to account for the behavior of amorphous polyamide blends containing hydrophobic and hydrophilic constituents exemplifies the importance of compositional parameters in determining the overall response of morphologically complex hydrophilic polymers. The results add further credence to the simple plasticizing action of water in polar polymers irrespective of their chemical and physical constitution.
TL;DR: In this article, the effects of film formation procedures on transport properties are reported for a rigid-chained, fluorinated, aromatic polyimide, and significant differences in transport properties were also observed between films prepared using two different casting techniques.
Abstract: The effects of film formation procedures on transport properties are reported for a rigid-chained, fluorinated, aromatic polyimide. Residual dimethylacetamide (DMAC) solvent present in films formed under certain casting protocols produces complexities in the permeation behavior of helium and carbon dioxide. Specifically, helium permeabilities are lower, while those of carbon dioxide are higher, in a film containing 8 wt% residual DMAC than in an annealed film containing < 1 wt% DMAC. Significant differences in transport properties are also observed between films prepared using two different casting techniques. These differences appear to be due to differences in organization of chain segments within films. The results of this study emphasize the considerable care needed in formation and postformation processing of these materials to ensure optimum flux/selectivity properties in such applications.
TL;DR: In this paper, the influence of polymer structure on the orientational memory in the molten state has been studied by observing the crystallization behavior of the molten polymer through differential scanning calorimetry.
Abstract: The influence of polymer structure on the orientational memory in the molten state has been studied by observing the crystallization behavior of the molten polymer through differential scanning calorimetry. It is shown that polymers with strong intermolecular forces (e.g., H-bonding) retain the orientation memory even at temperatures above their equilibrium melting temperatures. The retained orientation memory of the polymer melt is shown to influence its recrystallization rate and the morphology.
TL;DR: In this article, a series of ionically crosslinked polyacrylic acid (PAA)-Nylon 6-blended membranes crosslinked to varying degrees in aluminum nitrate solution was used for pervaporation separation of ethanol-water mixtures.
Abstract: The pervaporation separation of ethanol–water mixtures was carried out through a series of ionically crosslinked polyacrylic acid (PAA)–Nylon 6-blended membranes crosslinked to varying degrees in aluminum nitrate solution. The polyacrylic acid (PAA)–Nylon 6 membranes were cast from homogeneous PAA–Nylon 6 mixtures to various thicknesses and then crosslinked. Optimum pervaporation results were obtained from crosslinked blends containing 75 wt% Nylon 6 and 25 wt% PAA. These membranes have separation factors (water/ethanol) of 35–40 at flux rates of 120–160 g/m2 h. The optimum crosslinking time was found to be approximately 35 h to yield membranes with the best separation and flux rates at 25 wt% PAA content.