Showing papers in "Journal of Applied Polymer Science in 1992"
TL;DR: In this paper, the polymerization of N-vinyl carbazole with NO2 and SO2 in dichloroethane has been studied and the kinetics of polymerization were followed gravimetrically.
Abstract: The polymerization of N-vinylcarbazole initiated with NO2 and SO2 in dichloroethane has been studied. The kinetics of polymerization were followed gravimetrically. The Polymerization is fast with NO2 but a relatively slow rate was obtained with SO2. The polymerization with these gases appears to be initiated by a charge transfer mechanism.
425 citations
TL;DR: In this paper, it has been found that carbon dioxide remarkably accelerates the absorption of many low molecular weight additives into a number of glassy polymers, due to the high diffusivity, solubility, and plasticizing action of compressed CO2 in polymers.
Abstract: It has been found that carbon dioxide remarkably accelerates the absorption of many low molecular weight additives into a number of glassy polymers. This effect is due to the high diffusivity, solubility, and plasticizing action of compressed CO2 in polymers. The transport of CO2 and the effects of CO2 pressure on the transport of other low molecular weight compounds in polymers have been studied by a simple gravimetric method: Polymer film samples were contacted in a pressure vessel with compressed CO2, or with CO2 plus various organic liquids or solids, and the sample weight was followed with a fast-response electronic balance during subsequent desorption at atmospheric pressure. Upon release of the pressure, absorbed CO2 rapidly diffuses from the polymer, while the other compounds desorb much more slowly. The amount of additive absorbed can be determined from the plateau weight of the sample after most of the CO2 has escaped. Extensive kinetic and equilibrium data are reported for the model system poly(vinyl chloride)/dimethyl phthalate/CO2, and a number of other examples of CO2-assisted additive absorption are given. This “infusion” process, in effect, amounts to the partitioning of the additive between the CO2- and polymer-rich phases; consequently, the relative solubility of the additive in CO2 and in the polymer is a major factor governing the amount of additive absorbed. Data reported here illustrate the generality and potentially broad applicability of CO2-assisted polymer impregnation.
232 citations
TL;DR: In this paper, the effects of particle size on the mechanical and impact properties of cured epoxy resins are studied, and a static flexural and tensile tests and an instrumented Charpy type impact test are carried out.
Abstract: Effects of particle size on the mechanical and impact properties of cured epoxy resins are studied. This resin was filled with spherical silica particles prepared by hydrolysis of silicon tetrachloride. Particles were sorted into five kinds of different mean sizes in the range from 6–42 μm. A static flexural and tensile tests and an instrumented Charpy type impact test were carried out. Flexural strength, tensile strength, and impact-absorbed energy increased with a decrease in the particle size. Fractured surfaces were observed using a scanning electron microscope to clarify the initiation point of fracture.
223 citations
TL;DR: In this article, a new carbon fiber was prepared from the lignin (steam-exploded Lignin), which was isolated from steamexploded birch wood (Betula platyphylla), and was modified to melt thermally on hydrogenolysis.
Abstract: A new carbon fiber was prepared from the lignin (steam-exploded lignin), which was isolated from steam-exploded birch wood (Betula platyphylla). The lignin was modified to melt thermally on hydrogenolysis. The chloroform soluble and carbon disulfide insoluble fraction (HL) of the reaction products was heated at 300–350°C for 30 min, giving a molten viscous material (HHL). The HHL had a softening point of 110°C and melted at over 145°C to form viscous liquid. When HHL was subjected to a spinning test, according to a conventional fusion spinning method at a speed over 100 m/min, a fine filament could be continuously formed through a pinhole (diameter: 0.3 mm). After the filaments were heated in air at 1–2°C/min up to 210°C, by which time the filament was converted to have an infusible property, the filaments were carbonized by heating from a room temperature to 1000°C at a heating rate of 5°C/min in a stream of nitrogen. The typical properties of the lignin based carbon fiber were as follows: Fiber diameter = 7.6 ± 2.7μ Elongation = 1.63 ± 0.29% Tensile strength = 660 ± 230 MPa; Modulus of elasticity = 40.7 ± 6.3 GPa. The chemical structure of the precursor was remarkably changed from that of the original lignin, indicating the elimination of aliphatic functional groups implied originally in the starting material.
216 citations
TL;DR: In this article, a detailed model describing particle growth in olefin copolymerization systems is presented, which considers monomer sorption, mass transfer and changing porosity within the growing particle, as well as heat and mass transfer across the external film of the particle.
Abstract: The development of a detailed model describing particle growth in olefin copolymerization systems is presented. The Multigrain Model considers in detail monomer sorption, mass transfer, and changing porosity within the growing particle, as well as heat and mass transfer across the external film of the particle. The model predicts catalyst performance, including polymerization rates and particle morphology, in different reactor media without parameter adjustment. Internal void fractions are calculated through an examination of the relative growth rates within the growing particle. The model is used to examine the effects of mass transfer limitations, prepolymerization, and nonuniform metal distribution on the particle growth process. Model predictions of morphology show the same trends as observed experimentally.
198 citations
TL;DR: In this article, a blend membrane consisting of polyvinyl alcohol (PVA) and chitosan was prepared from a solvent-casting technique and characterized for their intermolecular interactions using infrared and X-ray diffraction methods.
Abstract: Blend membrane consisting of poly(vinyl alcohol) (PVA) and chitosan was prepared from a solvent-casting technique and characterized for their intermolecular interactions using infrared and X-ray diffraction methods. Cross-linking the blend with glutaraldehyde produces a membrane with lower crystallinity and a smaller swelling degree, but having improved thermostability and mechanical properties. The present blend membrane shows a pH-dependent swelling characteristic and will be discussed in detail. © 1992 John Wiley & Sons, Inc.
186 citations
TL;DR: In this paper, the influence of stoichiometric imbalance on the thermoelastic properties of an epoxy-amine resin was investigated and it was shown that the modulus and glass transition temperature are significantly affected by relatively small variations in stoichiometry.
Abstract: Sizings and/or surface treatments are commonly employed to enhance the interaction of fiber reinforcements in polymer matrix composites. These modifications can induce physical and chemical interactions that cause local stoichiometric imbalances to occur that can affect the properties of the polymer matrix in the vicinity of the fiber surface. This work reports the results of an experimental study of the influence of stoichiometric imbalance on the thermoelastic properties of an epoxy–amine resin. It is shown that the modulus and glass transition temperature are significantly affected by relatively small variations in stoichiometry. These results suggest that a fiber-induced interphase region in thermosetting composites can exhibit material properties that are significantly different from those of the bulk resin. © 1992 John Wiley & Sons, Inc.
174 citations
TL;DR: In this article, the crystal structure of cotton was found on methylamine treatment followed by chloroform and pyridine washing and acetylation in the never-dried state (MeCP product).
Abstract: Both sodium hydroxide solution of mercerizing strength and anhydrous methylamine are suitable pretreatments for enhancing the reactivity of cotton cellulose. Favorable results are achieved by maintaining the fiber material in the never-dried state after the swelling treatment. Extraction by organic solvents is to be preferred over water-washing in order to remove the swelling agent. When cotton is swollen with either aqueous sodium hydroxide or anhydrous methylamine and then washed and dried, its crystallinity, as determined by X-ray diffraction is not lowered as much as it is if it is acetylated to an acetyl content of about 9% before drying. The greatest modifications of the crystal structure of cotton were found on methylamine treatment followed by chloroform and pyridine washing and acetylation in the never-dried state (MeCP product), as well as by alcoholic mercerization followed by ethanol and pyridine washing and acetylation in the never-dried state (AMEP). As determined by moisture regains, no significant differences are apparent between the accessibility of samples of low acetyl content (ca. 9%) prepared by either the AMEP or by the MeCP treatment. The DTA curves of methylamine-treated cotton with an acetyl content close to that of commercial diacetate and the commercial product are dissimilar. It can be concluded from the DTA curve of the deacetylated product prepared from this MeCP sample that it has a highly disordered structure. The tensile properties of the acetylated products of low acetyl content are considerably improved if acetylation is preceded by mercerization with subsequent solvent exchange, and less so if it is preceded by methylamine followed by solvent exchange. Incorporation of acetyl groups significantly enhances the breaking strength and extensibility of mercerized solvent-washed materials.
172 citations
TL;DR: A series of pH-sensitive hydrogels that exhibit volume phase transition phenomena have been synthesized in aqueous solution and characterized with respect to their dynamic swelling behaviors as mentioned in this paper.
Abstract: A series of pH-sensitive hydrogels that exhibit volume phase transition phenomena have been synthesized in aqueous solution and characterized with respect to their dynamic swelling behaviors. Positively charged hydrogels were prepared by copolymerizing varying ratios of N-isopropylacrylamide and NN′-dimethylaminopropylmethacrylamide. The hydrogels based on a temperature-sensitive hydrogel demonstrate a large change of equilibrium swelling in response to small variations of pH and/or temperature. These hydrogels exhibit different lower critical solution temperature (LCST) ranges depending on the environmental pH values. Below their LCST, they exhibit small and broad pH sensitivities normally observed in most hydrophilic polyelectrolyte gels, but above their LCST, they exhibit sharp pH dependent phase transition behaviors. The pH-dependent phase transition is strongly affected by temperature, while the temperature-dependent transition is, in turn, largely influenced by the pH. As the temperature is raised, the transitional degree of gel swelling change becomes sharper and larger, and the phase transition pH value shifts to a lower pH. It was also found that swelling is faster than deswelling for these cationic hydrogels, which suggests the existence of a water diffusion barrier during the deswelling. The swelling kinetics of initially dry and glassy gels were strongly dependent on both the pH value and temperature.
170 citations
TL;DR: In this article, the rate of adsorption of mercuric ions on chitosan can be interpreted in terms of intraparticle diffusion as the rate-limiting step.
Abstract: The adsorption of mercuric ions by chitosan was investigated. The study of the adsorption kinetics shows that the rate of adsorption of mercuric ions on chitosan can be interpreted in terms of intraparticle diffusion as the rate-limiting step. The experimental data of adsorption equilibrium from mercuric chloride solutions correlate well with the Langmuir isotherm equation, although at high-solute concentrations, a multilayer type of adsorption with the subsequent increase in the uptake is observed. Column experiment confirms the ability of chitosan for the removal of mercuric ions from solutions in the absence of a high concentration of chlorides.
165 citations
TL;DR: In this article, the bending of polyvinyl alcohol hydrogel mixed with poly(sodium acrylate) chains, PVA-PAA gel, under the influence of dc electric fields was studied.
Abstract: Bending of poly(vinyl alcohol) hydrogel mixed with poly(sodium acrylate) chains, PVA–PAA gel, under the influence of dc electric fields was studied. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixture of PVA and polyacrylic acid aqueous solutions. The PVA–PAA gel was a hydrogel with the PAA chains, which were entangled with the PVA polymer network and were fixed in the gel. The PVA–PAA gel bent toward the negative electrode in electrolyte solutions under dc electric fields as did the polyelectrolyte gel with negatively charged polyions. The PVA gel, free of PAA, was insensitive to dc electric fields. The deflection of the bending and the bending speed were influenced by the filed intensity, the concentration of the polyion in the gel, and the thickness of the gel. The bending of the PVA–PAA gel was qualitatively explained by a bending theory of polyelectrolyte gel, based upon the change of the osmotic pressure due to the ion concentration difference between the inside and the outside of the gel.
TL;DR: The functional dependence of the diffusion coefficient of vitamin B-12 on the equilibrium swelling ratio of the material in water has been investigated in this article, showing that the functional dependence is consistent with the pore type transport mechanism for vitamin b-12 in these membranes.
Abstract: The permeability and diffusion results using the time lag technique suggest that the diffusion coefficient D of vitamin B-12 for both crosslinked and blended chitosan membranes depends solely upon the equilibrium swelling ratio Q of the material in water. The functional dependence of D on Q was obtained from the data. The partition coefficients calculated for vitamin B-12 in all membranes studied were nearly constant. The results are shown to be consistent with the pore type transport mechanism for vitamin B-12 in these membranes.
TL;DR: In this paper, the effects of sodium alginate on the physical properties of fibroin membranes, such as rupture elongation, rupture strength, water absorption, and thermal properties, were investigated.
Abstract: The effects of sodium alginate on the physical properties of fibroin membranes, such as rupture elongation, rupture strength, water absorption, and thermal properties, were investigated. The experimental results showed the β-form crystal and β-form molecular conformation increased due to the increase of intermolecular hydrogen bonds, such as CO---HN and CO---HO. The kind of intermolecular interaction and β-form molecular conformation of polymer blends were clarified by 13C–NMR and infrared spectroscopy. The increase in β-form crystal was examined by X-ray analysis. Further, membranes were characterized by thermogravimetric analysis (TGA) and by determining their water contents and tensile properties.
TL;DR: In this article, the properties of composites of bacteria-produced polyesters reinforced with wood cellulose were investigated, showing that cellulose fibers improved the strength and stiffness of the polyhydroxybutyrate (PHB), but the samples were very brittle.
Abstract: This paper presents an investigation of the properties of composites of bacteria-produced polyesters reinforced with wood cellulose. Although cellulose fibers improved the strength and stiffness of the polyhydroxybutyrate (PHB), the samples were very brittle. The impact strength and elongation at break of these composites were significantly improved when PHB copolymers with increased amounts of hydroxyvalerate (HV) were used as the matrix. Dynamic mechanical properties of PHB copolymers of varying compositions and of cellulose-filled composites were investigated. The introduction of cellulose resulted in a decreased loss factor owing to restrictions of the chain mobility in the amorphous phase. An improvement was observed in the dynamic modulus, which was seen to be greatest at elevated temperatures. An excellent dispersibility of cellulose fibers was achieved in the PHB matrix as compared with such synthetic matrices as polystyrene or polypropylene. The degree of dispersibility was strongly affected by processing conditions. The defibrillation observed on extracted fibers suggests a possible hydrolysis of cellulose by crotonic acid formed in situ as a result of the thermal decomposition of the PHB matrix.
TL;DR: In this article, cycloaliphatic epoxides with aryl sulfonium salts as photoinitiators and polypropylene glycols of variable length as flexibilizers were investigated with respect to the network-forming reactions and the morphology of the resulting polymers.
Abstract: Cationic UV-polymerized resins, based on cycloaliphatic epoxides with aryl sulfonium salts as photoinitiators and polypropylene glycols of variable length as flexibilizers, have been investigated with respect to the network-forming reactions and the morphology of the resulting polymers. The combination of UV-curing and thermal postcure makes the chemical process complex and dependent on many variables, such as photoinitiator, exposure time, reaction temperature, and polyol components. Structure and curing of the epoxide were investigated by 13C CPMAS NMR. Morphology and domain sizes were studied by spin diffusion experiments using the novel “dipolar filter” technique for selective magnetization of mobile components.
TL;DR: The morphology of bioerodible polyanhydride microspheres produced by spray drying is described in this article, where a variety of homo-and copolymers were studied and characterized using X-ray powder diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM).
Abstract: The morphology of bioerodible polyanhydride microspheres produced by spray drying is described. Microspheres prepared from a variety of homo- and copolymers were studied and characterized using X-ray powder diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Crystalline polymers, such as poly(sebacic anhydride) (P(SA)) and poly(fumaric acid) (P(FA)), yielded microspheres with a crenelated and porous surface, as judged by SEM. Polymers, with lower crystallinity, such as copolymers of carboxyphenoxypropane and sebacic acid P(CPP-SA), yielded microspheres with a smooth external surface. Polymer crystallinity decreased after spray drying, for both blank and drug loaded microspheres.
TL;DR: In this article, the tensile properties of isotactic polypropylene filled with particulate kaolin fillers were evaluated in the composition range 0-60 wt % kaolin. And the authors attributed the restriction on the molecular mobility of the polymer imposed by kaolin particles.
Abstract: Tensile properties of isotactic polypropylene filled with particulate kaolin fillers were evaluated in the composition range 0–60 wt % kaolin. Tensile modulus increased with filler concentration while breaking elongation and tensile strength decreased. The modulus increase was attributed to the restriction on the molecular mobility of the polymer imposed by kaolin particles. The decrease in elongation was also an effect of this restriction coupled with interference to stress transfer by the filler particles. Generation of discontinuity in the composite structure through formation of stress concentration points accounted for the tensile strength decrease. Morphology studies by SEM also indicated the introduction of stress concentration points by the presence of bare and nonadherent kaolin particles and their agglomerates with sharp edges in these composites.
TL;DR: In this paper, X-ray diffraction and Raman analyses were performed on cellulose-chitosan blend films and the results indicated the presence of interactions between cellulose, chitosans, and water molecules in the films.
Abstract: Interactions between cellulose and chitosan molecules in cellulose–chitosan blend films, prepared using trifluoroacetic acid as a cosolvent for the two polysaccharides, were studied by X-ray diffraction and Raman analyses and by measurements of mechanical properties of the blend films. Crystallinity of cellulose in the blend films decreased with an increase in chitosan content. The blend films had tensile strengths of 45–100 MPa and Young's moduli of 2–7.5 GPa in dry states. These values had the maximum around 30% chitosan content in the blend films. These results suggested the presence of interactions between cellulose, chitosan, and water molecules in the films. However, Raman analysis suggested that cellulose and chitosan molecules in the blend films seemed to have the same secondary structures as those in 100% cellulose and 100% chitosan films, respectively. Thus, these results indicate the presence of interactions in the interfacial region between small domains of cellulose and chitosan. The presence of chitosan molecules may lead to decrease in the domain size of cellulose, and to increase in the interfacial region between cellulose and chitosan domains.
TL;DR: In this paper, surface degradation of implanted poly (ether urethane) s was studied quantitatively with a micro-ATR-FTIR technique, and substantial degradation was observed particularly in the soft segment at the α-carbon adjacent to the ether linkage.
Abstract: Surface degradation of implanted poly (ether urethane) s was studied quantitatively with a micro-ATR-FTIR technique. Substantial degradation was observed particularly in the soft segment at the α-carbon adjacent to the ether linkage. The degradation caused changes in the concentration profiles of the soft-segment groups in the depth direction, and the affected depth was up to 10 microns after implantation for 10 weeks. Inhibition of degradation by antioxidants indicated the oxidative nature of degradation. An in vivo poly (ether urethane) degradation mechanism was proposed
TL;DR: In this article, the chemical structures of cellulose and chitosan dissolved in trifluoroacetic acid (TFA) were studied by 13C-NMR and IR spectroscopy.
Abstract: Chemical structures of cellulose and chitosan dissolved in trifluoroacetic acid (TFA) and those of cellulose and chitosan films cast from their TFA solutions were studied by 13C-NMR and infrared (IR) spectroscopy. Cellulose is trifluoroacetylated selectively at the C6–hydroxyl groups in the TFA solution, and chitosan is dissolved in TFA by forming amine salts with TFA at the C2–amine groups. IR analyses of cellulose films cast from its TFA–acetic acid solutions showed that partly trifluoroacetylated cellulose in the solution state turns to partly acetylated cellulose in the solid state during evaporation of the solvents in air by the ester interchange. Chitosan films cast from its TFA–acetic acid solutions still have the amine salts with TFA. These acetyl groups in cellulose films and TFA in chitosan films are removable by soaking the films in 1N NaOH at room temperature for 1 day.
TL;DR: In this article, a series of different modified chitosan membranes were prepared by blending with polyvinylpyrrolidone (PVP), and the physical, thermal, and mechanical properties were evaluated in terms of the amorphous and hydrophilic nature of PVP.
Abstract: Chitin was isolated from prawn shells, and chitosan was prepared from it. The degree of N-deacetylation and the molecular weight were determined using IR spectroscopy and viscometry, respectively. A series of different modified chitosan membranes were prepared by blending with polyvinylpyrrolidone (PVP). These membranes were characterized by various techniques, including differential scanning calorimetry (DSC), wide-angle X-ray diffractometry (WAXD), and tensile testing. The physical, thermal, and mechanical properties were evaluated, and the change in these properties upon the addition of PVP into the blends has been discussed in terms of the amorphous and hydrophilic nature of PVP. Hydrophilicity of the blends increases due to the presence of PVP in the chitosan substrate. This helps in breaking the hydrogen bonds in between chitosan molecules and causes the blends to swell in three dimensions.
TL;DR: In this article, the structure-property relationships of a polyester-type thermotropic liquid crystalline polymer (LCP) with polyethylene terephthalate (PET), polypropylene (PP), and polyphenylene sulfide (PPS) were investigated.
Abstract: Structure–property relationships were investigated for blends of a polyester-type thermotropic liquid crystalline polymer (LCP) with polyethylene terephthalate (PET), polypropylene (PP), and polyphenylene sulfide (PPS). The polymers were melt blended in a twin-screw extruder and the blends were extruded to strands of different draw ratios. Tensile properties of the blends were determined as a function of LCP content and draw ratio and compared with the results of morphological and rheological analyses. In general, the strength and stiffness of the matrix polymers were improved with increasing LCP content and draw ratio. At a draw ratio of 11, the blends of PET/30 wt % LCP exhibited a tensile strength about three times and an elastic modulus nearly four times that of pure PET. All blends exhibited a skin/core morphology with thin fibrils in the skin region. The formation and the sizes of the fibril-like LCP domains in the matrices were found to depend on LCP content and the viscosity ratio of the blend components.
TL;DR: In this article, macroporous particles with predesigned properties for use in size-exclusion high-performance liquid chromatography in both aqueous and organic mobile phase were studied.
Abstract: Monodisperse beads based on hydrolyzed macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) for use as size-exclusion HPLC packings were synthesized by the method of “activated” swelling of polystyrene seeds followed by a suspension polymerization of both methacrylates. Effects of the type and fraction of the swelling agent, inert porogenic solvent, and cross-linking monomer on the uniformity of the particles, extent of the specific surface area, pore volume, pore size, and pore-size distribution and chromatographic properties (size-exclusion limit and column effciency) have been investigated. Trends leading to the synthesis of macroporous particles with predesigned properties for use in size-exclusion high-performance liquid chromatography in both aqueous and organic mobile phase were studied. © 1992 John Wiley & Sons, Inc.
TL;DR: In this article, samples of a high-purity isotactic polypropylene (iPP) were quenched from the melt so as to monitor cooling history, and a continuous variation of morphology and crystal structure was obtained with cooling rate.
Abstract: SYNOPSIS Samples of a high-purity isotactic polypropylene (iPP) were quenched from the melt so as to monitor cooling history. A continuous variation of morphology and crystal structure was obtained with cooling rate. This is discussed in relation to sample thermal history evidencing that cooling history relevant to quenched samples is in the neighborhood of 90°C. In particular the samples are essentially mesomorphic when at this temperature cooling rates larger than 80°C/s were adopted, while below a few tens of °C/s only a monocline form is obtained. Densities of quenched samples were compared with predictions of an isokinetic extrapolation of Avrami model of polymer crystallization kinetics.
TL;DR: In this article, the mechanism of grafting and crosslinking of polyethylene and polypropylene copolymers has been discussed and the influence of the structure of the catalyst, its concentration, moisture concentration, temperature, and time on degree and rate of crosslinkings has been evaluated.
Abstract: Peroxide initiated graft copolymerization of vinyl trimethoxy silane (VTMO) and vinyl triethoxy silane (VTEO) onto polyethylene (PE) and ethylene propylene copolymer (EPR) was studied. The kinetics of grafting, studied by differential scanning calorimetry, are the same for all the systems and the activation energy for VTMO is 170 ± 4 KJ/mol. Activation energy for VTEO is 185 ± 5 KJ/mol. The VTMO and VTEO graft copolymers of PE and EPR were prepared by reactive processing in a Brabender extruder in the temperature range of 150–200°C. Moisture catalyzed crosslinking of the silane grafted copolymer was also studied. The influence of the structure of the catalyst, its concentration, moisture concentration, temperature, and time on degree and rate of crosslinking has been evaluated. Crosslinking reactions follow first order kinetics with respect to both catalyst and moisture concentration. Activation energy (Ea) of the crosslinking reaction has been determined as 65 KJ mol−1. The mechanism of grafting and crosslinking is discussed.
TL;DR: In this article, the influence of plasma parameters (treatment time, power) on the behavior of two model molecules in oxygen or argon plasmas was investigated, and the degradation rates, the formation and evolution of the degradation products were investigated.
Abstract: The influence of plasma parameters (treatment time, power) on the behavior of two model molecules in oxygen or argon plasmas was investigated. The degradation rates, the formation and evolution of the degradation products were investigated. The following conclusions are drawn: (1) degradation is higher in an oxygen plasma than in an argon plasma; (2) CO, H 2 O, CO 2 and H 2 are the main degradation products in an oxygen-rich plasma whereas H 2 is the most important in an argon-rich plasma (3) the degradation products are the same for both model molecules, but when the power increases, the formation of H 2 and H 2 O is favored in the case of C 36 H 74 , while for the ester, it is CO that is enhanced
TL;DR: In this paper, the reaction of maleic anhydride (MAH) with molten 2 MI poly(ethylene-co-butene-1) (LLDPE) at 160°C in the presence of peroxyesters (t 1/2 < 10 s) as catalysts resulted in the formation of a mixture of cross-linked and trichlorobenzene-soluble LLDPE-g-MAH.
Abstract: The reaction of maleic anhydride (MAH) with molten 2 MI poly(ethylene-co-butene-1) (LLDPE) at 160°C in the presence of peroxyesters (t1/2 < 10 s) as catalysts resulted in the formation of a mixture of cross-linked and trichlorobenzene-soluble LLDPE-g-MAH. The soluble fraction constituted more than 50% of the mixture and had an MI of 0.0 and an MAH content ranging from 0.3 to 1.8 wt %. The presence of tri(nonylphenyl) phosphite (TNPP) in the LLDPE–MAH–t-butyl peroctoate (tBPO) reaction at 160°C increased the MI of the soluble product to 0.7–2. The amount of soluble polymer increased at higher TNPP concentrations while its MAH content ranged from 0.05 to 0.54 wt %, with most contents in the 0.2–0.3 wt % range. The color development that usually occurs in polyolefin–MAH reactions was reduced by the presence of TNPP. However, the reaction of TNPP with the peroxide and from the thermal decomposition thereof reduced the availability of the excited species necessary for the appendage of MAH units onto the polyofin.
TL;DR: In this article, isothermal curing of a DGEBA epoxy resin with a hardener derived from phtalic anhydride was performed at temperatures T c between 30 and 130°C.
Abstract: Isothermal curing of a DGEBA epoxy resin with a hardener derived from phtalic anhydride was performed at temperatures T c between 30 and 130°C. The structural relaxation process was found to begin at higher curing times (t c ) when T c decreases because the vitrification of the systems starts later. Both the enthalpy recovery and the temperature of the endothermic peak increase with the annealing time, calculated as the difference between t c and the time in which vitrification occurs, and tend tohave a limiting value.
TL;DR: In this article, the effect of particle size on the mechanical properties of cured epoxy resins has been studied, where the particle size of the resin was sorted into six groups having different mean sizes ranging from 2-47 μm.
Abstract: Effect of particle size on the mechanical properties of cured epoxy resins has been studied. Resin was filled with angular-shaped silica particles prepared by crushing fused natural raw quartz. These particles were sorted into six groups having different mean sizes ranging from 2–47 μm. Flexural and compressive moduli of the cured epoxy resin slightly decreased with decrease in the particle size of the silica, whereas tensile modulus slightly increased. Flexural and tensile strengths increased with decrease in particle size. Fractured surfaces were observed using scanning electron microscopy to clarify the initiation point of fracture.
TL;DR: It is postulated that the total water content of membranes need not be the prime factor governing the permeability of solutes through water-swollen membranes, however, many other parameters govern the solute permeability, like the amount of solute dissolved in bound water and the status of water in the polymer matrix.
Abstract: A series of membranes are prepared by air drying thin films, which were composed of poly(vinyl alcohol) blended with chitosan [a (1 4)2-amino-2-deoxy-β-D-glucan] (PVA–Chit) in different ratios. The PVA-blended chitosan membranes showed improved strength properties and permeability functions for low-molecular-weight compounds. Nonthrombogenic PVA–Chit (4 : 6) membranes were derived by immobilizing bioactive molecules like PGE1 on heparin-modified membranes, via free radical mechanisms, by N2 plasma. This novel membrane demonstrated good permeability properties for small molecules and showed a dramatic reduction in platelet attachment. The prostaglandin E1-immobilized substrate also indicated an increase in albumin surface attachment and a reduction in fibrinogen binding. This may be one of the parameters for a reduced platelet-surface attachment, which may also improve the blood compatibility of the substrate. It is also postulated that the total water content of membranes need not be the prime factor governing the permeability of solutes through water-swollen membranes. However, many other parameters govern the solute permeability, like the amount of solutes dissolved in bound water and the status of water in the polymer matrix.