Showing papers in "Journal of Applied Polymer Science in 2000"
TL;DR: In this paper, the ultrastructure and morphology of potato (Solanum tuberosum L.) tuber cells were investigated by optical, scanning, and transmission electron microscopies, and composite materials were processed from this potato cellulose microfibril suspension, gelatinized potato starch as a matrix and glycerol as a plasticizer.
Abstract: The ultrastructure and morphology of potato (Solanum tuberosum L.) tuber cells were investigated by optical, scanning, and transmission electron microscopies. After removal of starch granules, pectins and hemicelluloses were solubilized under alkaline conditions. The alkaline insoluble residue consisted mainly of primary cell wall cellulose, which can be disintegrated under shearing to produce a homogenized microfibril suspension, as reported in a previous work.40 Composite materials were processed from this potato cellulose microfibril suspension, gelatinized potato starch as a matrix and glycerol as a plasticizer. After blending and casting, films were obtained by water evaporation. The mechanical properties and water absorption behavior of the resulting films were investigated, and differences were observed depending on the glycerol, cellulose microfibrils, and relative humidity content. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2080–2092, 2000
499 citations
TL;DR: In this paper, a series of polyurethanes from polyols derived from soybean, corn, safflower, sunflower, peanut, olive, canola, and castor oil were prepared, and their thermal stability in air and nitrogen assessed by thermogravimetric analysis, FTIR, and GC/MS.
Abstract: A series of polyurethanes from polyols derived from soybean, corn, safflower, sunflower, peanut, olive, canola, and castor oil were prepared, and their thermal stability in air and nitrogen assessed by thermogravimetric analysis, FTIR, and GC/MS. Oil-based polyurethanes generally had better initial thermal stability (below 10% weight loss) in air than the polypropylene oxide-based polyurethane, while the latter was more stable in nitrogen at the initial stage of degradation. If weight loss at a higher conversion is taken as the criterion of stability, then oil polyurethanes have better thermal stability both in air and in nitrogen. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1723–1734, 2000
378 citations
TL;DR: In this article, the effect of formulation variables on foam properties was studied by altering the types and amounts of catalyst, surfactant, water, crosslinker, blowing agent, and isocyanate, respectively.
Abstract: Both HCFC- and pentane-blown rigid polyurethane foams have been prepared from polyols derived from soybean oil. The effect of formulation variables on foam properties was studied by altering the types and amounts of catalyst, surfactant, water, crosslinker, blowing agent, and isocyanate, respectively. While compressive strength of the soy foams is optimal at 2 pph of surfactant B-8404, it increases with increasing the amount of water, glycerin, and isocyanate. It also increases linearly with foam density. These foams were found to have comparable mechanical and thermoinsulating properties to foams of petrochemical origin. A comparison in the thermal and thermo-oxidative behaviors of soy- and PPO-based foams revealed that the former is more stable toward both thermal degradation and thermal oxidation. The lack of ether linkages in the soy-based rather than in PPO-based polyols is thought to be the origin of improved thermal and thermo-oxidative stabilities of soy-based foams. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 467–473, 2000
363 citations
TL;DR: The recent advances in the studies of the toughening methods and theories of polypropylene (PP)-elastomer blends are reviewed in the present article as mentioned in this paper, and the major theories interpreting the toughness mechanisms of the blends are: multiple crazing, damage competition theory, shear-yielding theory, microvoids, and cavitation theories.
Abstract: The recent advances in the studies of the toughening methods and theories of polypropylene (PP)–elastomer blends are reviewed in the present article. Inclusions are key to toughening PP; they can play the role of agent-induced crazing, cause shear yielding of the matrix around them, and end the propagation of cracks. The major theories interpreting the toughening mechanisms of the blends are: multiple crazing, damage competition theory, shear-yielding theory, microvoids, and cavitation theories. The factors affecting the toughening effect are relatively complicated. Therefore, these theories have been verified only in some cases when they have been applied in relevant conditions. To achieve the objective of better toughening, it is important to improve the uniform distribution of dispersed-phase particle size and suitable filler size, as well as improving the dispersion of the inclusions formed in the matrix; in addition the matrix materials or fillers must be functional with suitable modifier in order to enhance the interfacial adhesion or to improve the interfacial morphological structure between the filler and matrix. However, the exact toughening mechanisms for PP–rubber blends have to be studied further because of complications resulting from the crystallinity of the matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 409–417, 2000
325 citations
TL;DR: In this paper, a control series with the same concentrations of micron-size silica filler was prepared with different concentrations of nanofiller, giving composites with the polyurethane that were transparent at all concentrations.
Abstract: Nanocomposites with different concentrations of nanofiller were prepared by adding nanosilica filler to the single-phase polyurethane matrix. A control series was prepared with the same concentrations of micron-size silica. The nanosilica filler was amorphous, giving composites with the polyurethane that were transparent at all concentrations. The nanocomposites displayed higher strength and elongation at break but lower density, modulus, and hardness than the corresponding micron-size silica-filled polyurethanes. Although the nanosilica showed a stronger interaction with the matrix, there were no dramatic differences in the dielectric behavior between the two series of composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 133–151, 2000
324 citations
TL;DR: In this paper, a polypropylene-clay hybrid (PPCH) was prepared by melt blending maleic anhydride modified PP and organophilic clay, and the tensile modulus of the PPCH with 5 wt % clay was 1.9 times higher than that of the matrix resin at 25°C.
Abstract: Polypropylene–clay hybrids (PPCHs) were prepared by melt blending maleic anhydride modified PP and organophilic clay. In these PPCHs the silicate layers of the clay were exfoliated and dispersed to the monolayers. The hybridization of the clay in PP was achieved with modified PP with a small amount of maleic anhydride groups. The tensile modulus of the PPCH with 5 wt % clay was 1.9 times higher than that of the matrix resin at 25°C. The dynamic storage moduli (E′) of the PPCHs were also higher than those of the modified PP. The E′ was 2.5 times higher than that of the matrix resin at 60°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1918–1922, 2000
304 citations
TL;DR: In this paper, the main structure of the dispersion of clay in the SBR was a layer bundle whose thickness was 4-10 nm and its aggregation formed by several or many layer bundles.
Abstract: Based on the character of a clay that could be separated into many 1-nm thickness monolayers, clay styrene-butadiene rubber (SBR) nanocomposites were acquired by mixing the SBR latex with a clay/water dispersion and coagulating the mixture. The structure of the dispersion of clay in the SBR was studied through TEM. The mechanical properties of clay/SBR nanocomposites with different filling amounts of clay were studied. The results showed that the main structure of the dispersion of clay in the SBR was a layer bundle whose thickness was 4–10 nm and its aggregation formed by several or many layer bundles. Compared with the other filler, some mechanical properties of clay/SBR nanocomposites exceeded those of carbon black/SBR composites and they were higher than those of clay/SBR composites produced by directly mixing clay with SBR through regular rubber processing means. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1873–1878, 2000
276 citations
TL;DR: In this paper, a milder sulfonation process was used to produce ion exchange poly-mers from a commercial polysulfone (PSU), which are potential substitutes for perfluorosulfonic acid membranes used now in polymer electrolyte fuel cells.
Abstract: A new, milder sulfonation process was used to produce ion-exchange poly- mers from a commercial polysulfone (PSU). Membranes obtained from the sulfonated polysulfone are potential substitutes for perfluorosulfonic acid membranes used now in polymer electrolyte fuel cells. Sulfonation levels from 20 to 50% were easily achieved by varying the content of the sulfonating agent and the reaction time. Ion-exchange capacities from 0.5 to 1.2 mmol SO3H/g polymer were found via elemental analysis and titration. Proton conductivities between 10 26 and 10 22 Sc m 21 were measured at room temperature. An increase in intrinsic viscosity with increasing sulfonation degree confirms that the sulfonation process helps to preserve the polymer chain from degra- dation. Thermal analysis of the sulfonated polysulfone (SPSU) samples reveals higher glass transition temperatures and lower decomposition temperatures with respect to the unsulfonated sample (PSU). Amorphous structures for both PSU and SPSU mem- branes were detected by X-ray diffraction analysis and differential scanning calorime- try. Preliminary tests in fuel cells have shown encouraging results in terms of cell performance. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1250 -1257, 2000
274 citations
TL;DR: In this paper, the effects of crystallinity (xc) on the hydrolysis of high molecular weight poly(L-lactide) (PLLA) films in a phosphate-buffered solution at 37°C was investigated by gel permeation chromatography, tensile testing, differential scanning calorimetry, scanning electron microscopy, and polarizing optical microscopy.
Abstract: The effects of crystallinity (xc) on the hydrolysis of high molecular weight poly(L-lactide) (PLLA) films in a phosphate-buffered solution at 37°C was investigated by gel permeation chromatography, tensile testing, differential scanning calorimetry, scanning electron microscopy, and polarizing optical microscopy. The change in molecular weight distribution and surface morphology of the PLLA films after hydrolysis revealed that the hydrolysis of PLLA film in a phosphate-buffered solution proceeded homogeneously along the film cross section, mainly via the bulk-erosion mechanism. The induction period until the start of the decrease in mass remaining and the tensile strength became longer with a decrease in the initial xc of the PLLA films. The rate of molecular weight reduction was higher as the initial xc of the PLLA films increased when hydrolysis was carried out up to 24 months. Melting and glass transition temperatures of the PLLA films increased in the first 12 months of hydrolysis, while they decreased in another 24 months, irrespective of the initial xc. The xc value of the PLLA films increased monotonously by hydrolysis. The lamella disorientation in PLLA spherulites after hydrolysis implied that the hydrolysis of PLLA chains occurred predominantly in the amorphous region between the crystalline regions in the spherulites. The area of a specific molecular weight in GPC spectra at 36 months increased with increase in the initial xc of the PLLA film, suggesting that the specific peak should be due to the component of one fold in the crystalline region. The reason for enhanced hydrolysis of PLLA films having higher initial crystallinities was discussed in terms of tie chains and terminal groups of PLLA. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1452–1464, 2000
261 citations
TL;DR: In this paper, the effect of fiber treatment by chemical modification of the fibers (acetylation) or the use of silane or titanate coupling agents on the mechanical properties of coir or oil palm reinforced polyester composites was investigated.
Abstract: The use of plant fibers as a reinforcement in polyester matrices requires the issue of compatibility between the two phases to be addressed. Because plant fibers present hydrophilic surfaces and polyesters are generally hydrophobic, poor fiber–matrix dispersion and wetting of the fibers by the matrix may result. As a consequence, the mechanical properties of the composite are severely reduced. This study considers the effect of fiber treatment by chemical modification of the fibers (acetylation) or the use of silane or titanate coupling agents on the mechanical properties of coir or oil palm reinforced polyester composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1685–1697, 2000
255 citations
TL;DR: In this article, the elastic modulus (E), yield strength, tensile breaking strength, and shear modulus were derived from diameter measurements performed by scanning electron microscopy.
Abstract: Mechanical tests were performed on single brins of Bombyx mori silkworm silk, to obtain values of elastic modulus (E), yield strength, tensile breaking strength, and shear modulus (G). Specimen cross-sectional areas, needed to convert tensile loads into stresses, were derived from diameter measurements performed by scanning electron microscopy. Results are compared with existing literature values for partially degummed silkworm baves. The tensile modulus (16 ± 1 GPa) and yield strength (230 ± 10 MPa) of B. mori brin are significantly higher than the literature values reported for bave. The difference is attributed principally to the presence of sericin in bave, contributing to sample cross-section but adding little to the fiber's ability to resist tensile deformation. The two brins in bave are found to contribute equally and independently to the tensile load-bearing ability of the material. Measurements performed with a torsional pendulum can be combined with tensile load-extension data to obtain a value of E/ that is not sensitive to sample cross-sectional dimensions or, therefore, to the presence of sericin. The value of E measured for brin can be used together with this result to obtain G = 3.0 ± 0.8 GPa and E/G = 5.3 ± 0.3 for brin. The latter value indicates a mechanical, and therefore microstructural, anisotropy comparable to that of nylon. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1270–1277, 2000
TL;DR: Rubber-clay nanocomposites were prepared by two different methods and characterized with TEM and XRD as discussed by the authors, which showed that the clay layer could be uniformly dispersed in the rubber matrix on the nanometer level.
Abstract: Rubber–clay nanocomposites were prepared by two different methods and characterized with TEM and XRD. The TEM showed clay had been dispersed to one or several layers. The XRD showed that the basal spacing in the clay was increased. It was evident that some macromolecules intercalated to the clay layer galleries. The clay layer could be uniformly dispersed in the rubber matrix on the nanometer level. The mechanical tests showed that the nanocomposites had good mechanical properties. Some properties exceeded those of rubber reinforced with carbon black, so the clay layers could be used as an important reinforcing agent as the carbon black was. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1879–1883, 2000
TL;DR: In this paper, a combination of chemical and mechanical methods was used for the extraction of bamboo fibers and the fiber population from both the techniques were characterized, and the fibers obtained from CMT and RMT were used to make unidirectional composites of polyester.
Abstract: Few investigations have been carried out with bamboo fibers despite its high strength, biodegradability, and low cost. The overall objective of this work was to investigate fiber extraction from bamboo and the use of these bamboo fibers as reinforcement in polymeric composites. A combination of chemical and mechanical methods was used for the extraction of bamboo fibers. Conventional methods of compression molding technique (CMT) and roller mill technique (RMT) were explored for the mechanical separation. Fiber population from both the techniques were characterized. Mechanical properties of the fibers also were evaluated. Bamboo fibers obtained from CMT and RMT were used to make unidirectional composites of polyester. High values of tensile strength were observed in all the composites. The predominant mode of failure for the composite was shown to be the cracking of the fiber–matrix interface. Quantitative results from this study will be useful for further and more accurate design of bamboo reinforced composite materials. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 83–92, 2000
TL;DR: In this paper, the authors investigated the effect of the degree of substitution (DS) on the crosslinking of carboxymethylcellulose (CMC) hydrogels.
Abstract: Radiation crosslinking of carboxymethylcellulose (CMC) with a degree of substitution (DS) from 0.7 to 2.2 was the subject of the current investigation. CMC was irradiated in solid-state and aqueous solutions at various irradiation doses. The DS and the concentration of the aqueous solution had a remarkable affect on the crosslinking of CMC. Irradiation of CMC, even with a high DS, 2.2 in solid state, and a low DS, 0.7 in 10% aqueous solution, resulted in degradation. However, it was found that irradiation of CMC with a relatively high DS, 1.32, led to crosslinking in a 5% aqueous solution, and 20% CMC gave the highest gel fraction. CMC with a DS of 2.2 induced higher crosslinking than that with a DS of 1.32 at lower doses with the same concentration. Hence, it was apparent that a high DS and a high concentration in an aqueous solution were favorable for high crosslinking of CMC. It is assumed that; high radiation crosslinking of CMC was induced by the increased mobility of its molecules in water and by the formation of CMC radicals from the abstraction of H atoms from macromolecules in the intermediate products of water radiolysis. A preliminary biodegradation study confirmed that crosslinked CMC hydrogel can be digested by a cellulase enzyme. (C) 2000 John Wiley & Sons, Inc.
TL;DR: A series of degradable polyurethanes of variable soft segment chemistry and content were synthesized and characterized in this paper, where an amino acid-based diester chain extender was used to confer degradability and both polycaprolactone diol and polyethylene oxide (PEO) were used as soft segments.
Abstract: A series of degradable polyurethanes of variable soft segment chemistry and content were synthesized and characterized. An amino acid-based diester chain extender was used to confer degradability and both polycaprolactone diol (PCL) and polyethylene oxide (PEO) were used as soft segments. In addition, the diisocyanate component was a potentially nontoxic diisocyanate (2,6-diisocyanato methyl caproate, LDI). The physicochemical properties of these unique series of polyurethanes were investigated. It was found that the PEO containing polyurethanes were generally weak, tacky amorphous materials. In contrast, the PCL polyurethanes were relatively strong, elastomeric materials which ranged from completely amorphous to semicrystalline as noted by differential scanning calorimetry. The PCL containing polyurethanes exhibited increasing tensile strength, modulus, and ultimate strain with increasing PCL molecular weight because of increasing phase separation and increasing soft segment crystallinity. Fourier transform infrared analysis showed significant hard segment urea and urethane hydrogen bonding which increased with hard segment content, although interphase bonding is believed to be significant for the PCL polyurethanes. Surface characterization carried out by contact angle analysis and X-ray photoelectron spectroscopy indicated soft segment surface enrichment for all of the polyurethanes. The PEO-based polymers were very hydrophilic whereas the PCL-based polymers displayed significantly higher contact angles, indicating greater surface hydrophobicity. The observed diversity in material properties suggests that these polyurethanes may be useful for a wide range of applications. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1522–1534, 2000
TL;DR: The graft copolymer and blend were characterized by Fourier transform-infrared, thermogravimetric analysis, X-ray diffraction measurements, and solubility test as discussed by the authors.
Abstract: Thermo- and pH-sensitive polymers were prepared by graft polymerization or blending of chitosan and poly(N-isopropylacrylamide) (PNIPAAm) The graft copolymer and blend were characterized by Fourier transform-infrared, thermogravimetric analysis, X-ray diffraction measurements, and solubility test The maximum grafting (%) of chitosan-g-(N-isopropylacrylamide) (NIPAAm) was obtained at the 05 M NIPAAm monomer concentration, 2 × 10−3M of ceric ammonium nitrate initiator and 2 h of reaction time at 25°C The percentage of grafting (%) and the efficiency of grafting (%) gradually increased with the concentration of NIPAAm up to 05 M, and then decreased at above 05 M NIPAAm concentration due to the increase in the homopolymerization of NIPAAm Both crosslinked chitosan-g-NIPAAm and chitosan/PNIPAAm blend reached an equilibrium state within 30 min The equilibrium water content of all IPN samples dropped sharply at pH > 6 and temperature > 30°C In the buffer solutions of various pH and temperature, the chitosan/PNIPAAm blend IPN has a somewhat higher swelling than that of the chitosan-g-NIPAAm IPN © 2000 John Wiley & Sons, Inc J Appl Polym Sci 78: 1381–1391, 2000
TL;DR: In this paper, contact angle measurements, FTIR-ATR, AFM, and XPS were used to study the surface structure and dynamics of PET surfaces, showing that the surface acquired oxygen containing polar functional groups such as -C=O, -OH, and -OOH.
Abstract: Plasma treatment of PET films was carried out under argon, followed by exposure to an oxygen atmosphere. The films underwent considerable changes in surface composition and morphology, as demonstrated by contact angle measurements, FTIR-ATR, AFM, and XPS. It was found that the surface acquired oxygen containing polar functional groups such as -C=O, -OH, and -OOH, which increased in number as the plasma treatment time increased. During storage, the treated films underwent significant surface reorganization, and both the time and temperature contributed to the increase in the contact angle. As revealed by AFM measurements, these changes were accompanied by an increase in roughness in the form of ridges. The ridges were observed to grow in height with increasing treatment time, although their spacing showed little evolution. A correlation among the observations obtained from various techniques was established, giving a comprehensive picture of the structure and dynamics of plasma-treated PET surfaces. (C) 2000 John Wiley & Sons, Inc.
TL;DR: In this paper, the effect of fiber surface pretreatment on the interfacial strength and mechanical properties of wood fiber/polypropylene (WF/PP) composites is investigated. And the results demonstrate that fiber surface conditions significantly influence the fiber-matrix interfacial bond, which, in turn, determines the mechanical properties.
Abstract: The effect of fiber surface pretreatment on the interfacial strength and mechanical properties of wood fiber/polypropylene (WF/PP) composites are investigated. The results demonstrate that fiber surface conditions significantly influence the fiber–matrix interfacial bond, which, in turn, determines the mechanical properties of the composites. The WF/PP composite containing fibers pretreated with an acid–silane aqueous solution exhibits the highest tensile properties among the materials studied. This observation is a direct result of the strong interfacial bond caused by the acid/water condition used in the fiber pretreatment. Evidence from coupling chemistry, rheological and electron microscopic studies support the above conclusion. When SEBS-g-MA copolymer is used, a synergistic toughening effect between the wood fiber and the copolymer is observed. The V-notch Charpy impact strength of the WF/PP/SEBS-g-MA composite is substantially higher than that of the WF/PP composite. The synergistic toughening mechanisms are discussed with respect to the interfacial bond strength, fiber-matrix debonding, and matrix plastic deformation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1000–1010, 2000
TL;DR: In this paper, the authors combine the principles of time-temperature superposition, time-cross-link den-sity superposition and the rubbery elasticity of networks to accurately model the evolution of the viscoelastic properties during cure using limited experimental data.
Abstract: The cure kinetics for a commercial epoxy have been established and theinfluence of the degree of cure on the glass transition determined. Time-temperatureand time-conversion superposition principles have been built into a model that success-fully predicts the development of the viscoelastic properties of the epoxy during iso-thermal cure from gelation to after vitrification. © 2000 John Wiley & Sons, Inc.* J ApplPolym Sci 76: 495–508, 2000 Key words: cure; epoxy; thermoset; viscoelastic properties; shear modulus INTRODUCTION Understanding the cure of thermosetting materi-als is important to their application in the auto-motive, aerospace, and electronics industries. Theisothermal time-temperature-transformation (TTT)cure diagram of Gillham 1,2 has provided an intel-lectual framework for understanding the behav-ior of these systems during cure, particularly theeffects of gelation and vitrification on the curekinetics and properties. Although the kinetics ofthe cure reaction(s) in cross-linking systems arevery well-described, quantitative descriptions ofthe evolution of mechanical properties duringcure are not well developed. Here we propose amethodology that combines the principles of time-temperature superposition, time-cross-link den-sity superposition, and the rubbery elasticity ofnetworks to accurately model the evolution of theviscoelastic properties during cure using limitedexperimental data. Such modeling may be ex-pected to facilitate optimization of cure proce-dures in thermosetting systems, particularly forthe reduction of residual stresses in, for example,composite materials.The well-known principle of time-temperaturesuperposition is based on the hypothesis that themechanical response at short times (or high fre-quencies) is analogous to the response at low tem-peratures, and vice versa. The general validity ofthe concept is supported by the ability to satisfac-torily reduce creep or stress relaxation data toform master curves.
TL;DR: In this article, the morphology of CB fillers in polyurethane matrix and the resulting conductivity of the composites were investigated, and it was found that CB filler exist in the forms of aggregates.
Abstract: The polyurethane composites with conducting carbon black (CB) were prepared by a solution-precipitation process, which was followed by melt compression molding. The polyurethane used has good shape memory effect. The morphology of CB fillers in polyurethane matrix and the resulting conductivity of the composites were investigated. It has been found that CB fillers exist in the forms of aggregates. The percolation threshold is achieved at the CB concentration of 20 wt %. The presence of CB fillers decreases the degree of crystallinity of polycaprolactone (PCL) soft segments of the polyurethane. However, the composites still have enough soft-segment crystals of polyurethane to fulfil the necessary condition for the shape memory properties. Dynamic mechanical data show that CB is an effective filler for the reinforcement of the polyurethane matrix, but does not deteriorate the stable physical cross-link structure of the polyurethane, which is necessary to store the elastic energy in the service process of the shape memory materials. Addition of CB reinforcement in the polyurethane has influenced the strain recovery properties, especially for those samples with CB concentrations above the percolation threshold. The response temperature of the shape memory effect Tr has not been affected too much. Strain fixation Sf, which expresses the ability of the specimens to fix their strain, has been improved in the presence of the CB fillers. The final recovery rates Rf and strain recovery speeds Vr of the shape memory measurements, however, have decreased evidently. It is expectedly ascribed to the increased bulk viscosity as well as the impeding effect of the inter-connective structure of CB fillers in the polymer matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 68–77, 2000
TL;DR: In this article, composites that incorporate a conductive filler into an EO elastomer matrix were evaluated for DC electrical and mechanical properties, and it was found that the composite with high structure carbon black exhibited a combination of properties not generally achievable with this type of filler.
Abstract: Composites that incorporate a conductive filler into an ethylene- octene (EO) elastomer matrix were evaluated for DC electrical and mechanical properties. Comparing three types of fillers (carbon fiber, low structure carbon black, and high structure carbon black), it was found that the composite with high structure carbon black exhibited a combination of properties not generally achievable with this type of filler in an elastomeric matrix. A decrease in resistivity at low strains is unusual and has only been reported previously in a few instances. Reversibility in the resistivity upon cyclic deformation is a particularly unusual feature of EO with high structure carbon black. The mechanical and electrical performance of the high structure carbon black composites at high strains was also impressive. Mechanical reinforcement in accordance with the Guth model attested to good particle-matrix adhesion. The EO matrix also produced composites that retained the inherent high elongation of the unfilled elastomer even with the maximum amount of filler (30% by volume). The EO matrix with other conducting fillers did not exhibit the exceptional properties of EO with high structure carbon black. Composites with carbon fiber and low structure carbon black did not maintain good mechanical properties, generally exhibited an increase in resistivity with strain, and exhibited irreversible changes in both mechan- ical and electrical properties after extension to even low strains. An explanation of the unusual properties of EO with high structure carbon black required unique features of both filler and the matrix. The proposed model incorporates the multifunctional phys- ical crosslinks of the EO matrix and dynamic filler-matrix bonds. © 2000 John Wiley &
TL;DR: In this article, the surface energies of polypropylene (PP), polystyrene (PS), and on plates of a liquid crystalline polymer (LCP) were measured at 20°C.
Abstract: In the present work, contact angles formed by drops of diethylene glycol, ethylene glycol, formamide, diiodomethane, water, and mercury on a film of polypropylene (PP), on plates of polystyrene (PS), and on plates of a liquid crystalline polymer (LCP) were measured at 20°C. Then the surface energies of those polymers were evaluated using the following three different methods: harmonic mean equation and geometric mean equation, using the values of the different pairs of contact angles obtained here; and Neumann's equation, using the different values of contact angles obtained here. It was shown that the values of surface energy generated by these three methods depend on the choice of liquids used for contact angle measurements, except when a pair of any liquid with diiodomethane was used. Most likely, this is due to the difference of polarity between diiodomethane and the other liquids at the temperature of 20°C. The critical surface tensions of those polymers were also evaluated at room temperature according to the methods of Zisman and Saito using the values of contact angles obtained here. The values of critical surface tension for each polymer obtained according to the method of Zisman and Saito corroborated the results of surface energy found using the geometric mean and Neumann's equations. The values of surface energy of polystyrene obtained at 20°C were also used to evaluate the surface tension of the same material at higher temperatures and compared to the experimental values obtained with a pendant drop apparatus. The calculated values of surface tension corroborated the experimental ones only if the pair of liquids used to evaluate the surface energy of the polymers at room temperature contained diiodomethane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1831–1845, 2000
TL;DR: In this paper, the influence of the initiator content, bath temperature, isopropanol content, initial monomer concentration, and crosslinker content (Cc) on water absorbency was investigated.
Abstract: Polyacrylate superabsorbents were prepared by in situ aqueous solution polymerization in a polyethylene bag, which was submerged in a water bath. The influence of the initiator content, bath temperature, isopropanol content, initial monomer concentration, and crosslinker content (Cc) on water absorbency (Q) were investigated. The temperature change of the monomer mixture during polymerization was also analyzed. Increase of the chain ends in networks resulting from decrease of the molecular weight in free-radical polymerization causes an increase of the water absorbency of superabsorbents and also reduces the crosslinking efficiency. The results are in conformity with the classical network theory. An empirical relation of Q = 2.45 Cc−0.600 was obtained and the validity of Flory's swelling equation was confirmed indirectly. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 808–814, 2000
TL;DR: The precursors of polysiloxanes bearing quaternary ammonium salts (QAS) showed bactericidal activity against bacteria such as Escherichia coli and Aeromonas hydrophila as mentioned in this paper.
Abstract: Polysiloxanes with 3-(alkyldimethylammonio)propyl pendant groups were synthesized by quaternization of n-octyldimethylamine or n-dodecyldimethylamine with linear polysiloxanes containing 3-chloropropyl groups and/or 3-bromopropyl groups attached to silicon atoms. The precursor polysiloxanes, poly[(3-chloropropyl)methylsiloxane] homopolymer and various copolymers containing (3-halogenopropyl)methylsiloxane and dimethylsiloxane units, were obtained by equilibrium cationic polymerization of linear and cyclic siloxanes with (3-halogenopropyl)methylsiloxane units. The polysiloxanes bearing quaternary ammonium salts (QAS) showed bactericidal activity against bacteria such as Escherichia coli and Aeromonas hydrophila when incorporated in a polysiloxane network. The activity was retained after 66 days of immersion in water. The QAS-containing polysiloxanes are also active in aqueous solution. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1005–1012, 2000
TL;DR: In this paper, the flame-retardant properties of the phosphorus/silicon-containing epoxy were studied and the phosphorus-silicon synergistic effect on LOI enhancement and increasing flame retardancy of the epoxy materials were demonstrated.
Abstract: Epoxy resins containing phosphorus and/or silicon are prepared from phosphorus/silicon-containing epoxides and diamine curing agents. The flame-retardant properties of the phosphorus/silicon-containing epoxy were studied. Furthermore, the phosphorus–silicon synergistic effect on LOI enhancement and increasing flame retardancy of the epoxy materials were demonstrated. While under flame, phosphorus provides the tendency of char formation, and silicon provides the enhancement on thermal stability of the char, to show their individual benefit on flame retardancy. Introducing both phosphorus and silicon together in the epoxy resin composition brings the success of combining these two factors in a flame retardation mechanism. An LOI enhancement from 26 to 36 is observed for epoxy resins containing both phosphorus and silicon. Moreover, the synergistic effect of phosphorus–silicon on fire resistance can be further leveled up by using siloxane reagents to replace silanes. Epoxy resins with a composition of phosphorus epoxides and siloxane diamines exhibit a high LOI value of 41, to demonstrate the high synergistic efficiency of phosphorus and silicon on flame retardation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1–7, 2000
TL;DR: In this article, the cure kinetics of four epoxy/amine systems including commercial RTM6 and F934 resins have been investigated under both isothermal and dynamic curing conditions.
Abstract: The cure kinetics of four epoxy/amine systems including commercial RTM6 and F934 resins have been investigated under both isothermal and dynamic curing conditions. Differential Scanning Calorimetry (DSC) was the thermoanalytical technique used to determine the cure kinetics of these resin systems. The complexity of the cure reactions, illustrated by the results, was attributed to the variety of chemical reactions between the epoxy and the amine groups. Various cure kinetics models were implemented in order to achieve an accurate description and simulation of the cure profiles obtained from the DSC measurements in the chemically controlled region. These varied from simple nth order kinetic models to complicated combinations of nth order and autocatalytic kinetic schemes. The mathematical techniques used to evaluate the parameters of the kinetic models varied from simple linear regression to non-linear regression and peak analysis. The resulting fits were in a good agreement with the experimental results for all the resin systems and for all the experimental conditions used. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1419–1431, 2000
TL;DR: In this article, the influence of side-chain fluorination on the performance of a series of acrylic-based copolymers as protective coating materials for stones has been carried out by comparing them with unfluorinated polymeric analogues.
Abstract: An investigation on the influence of side-chain fluorination on the performance of a series of acrylic-based copolymers as protective coating materials for stones has been carried out by comparing them with unfluorinated polymeric analogues. For this purpose, a series of copolymers of 1H,1H,2H,2H-perfluorodecyl methacrylate (XFDM) and 2,2,2 trifluoroethyl methacrylate (TFEM) with unfluorinated vinyl ether or acrylic comonomers have been synthesized, as well as their not fluorinated analogues, and applied to limestone and marble substrates. A silicone-type commercial product, widely employed in the protection of stones in buildings and other artifacts, has also been tested as a reference material. Their protection efficiencies were then comparatively evaluated in terms of surface properties, water permeability, and appearance. It is shown that the presence of fluorine always has, as expected, a positive influence on the protective action of the polymer, increasing the water repellency of the coated stone. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 962–977, 2000
TL;DR: In this paper, the blending of thermoplastic starch (TPS) with other biodegradable polyesters such as polyesteramide (BAK) could be an interesting way to produce new bioregradable starch-based materials.
Abstract: The blending of thermoplastic starch (TPS) with other biodegradable polyesters such as polyesteramide could be an interesting way to produce new biodegradable starch-based materials. Different mixes of wheat starch and polyesteramide (BAK) were melt blended by extrusion. After pelletization, granules were injection molded to produce test specimens. A range of blends was studied with glycerol (plasticizer)/starch content ratios varying from 0.14 to 0.54. BAK concentrations were up to 40 wt %, TPS remaining as the major phase in the blend. Various properties were examined with mechanical, thermomechanical (dynamic mechanical thermal analyzer) and thermal (differential scanning calorimetry) analysis. Hydrophobicity was determined with contact angle measurements. Thanks to the knowledge of the properties of each polymeric system, we analyzed the blends' behavior by varying each component concentration. The material aging was also studied. We showed that structural changes occurred during several weeks after injection. We noticed a certain compatibility between both polymeric systems. The addition of BAK to TPS matrix allowed us to overcome the weaknesses of pure thermoplastic starch: low mechanical properties, high moisture sensitivity, and high shrinkage in injection, even at 10 wt % BAK. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1117–1128, 2000
TL;DR: Submicron core-shell polymer particles, with molecularly imprinted shells, were prepared by a two-stage polymerization process as discussed by the authors, and were found to be 76 nm in diameter with a surface area of 82 m2 g−1.
Abstract: Submicron core-shell polymer particles, with molecularly imprinted shells, were prepared by a two-stage polymerization process. Particles of this type, prepared with a cholesterol-imprinted ethyleneglycol dimethacrylate shell and in the absence of porogen, were found to be 76 nm in diameter with a surface area of 82 m2 g−1. Cholesterol uptake from a 1 mM solution in isohexane was measured at both 10 and 30 mg mL−1, with the imprinted polymer showing considerable binding (up to 57%). Imprinted but not hydrolyzed and hydrolyzed nonimprinted polymers showed very low uptakes (≤4.5%) and a phenol-imprinted polymer showed reduced binding (36%) under the same conditions. Imprinted shells were also prepared over superparamagnetic polymer cores and over magnetite ferrocolloid alone. The cholesterol binding to magnetic particles was very similar to that of equivalent nonmagnetic materials. Magnetic particles could be sedimented in as little as 30 s in a magnetic field. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1851–1859, 2000
TL;DR: The pressure sensitive paint (PSP) properties of a fluoroacrylic polymer, FIB, with the luminophor platinum tetra(pentafluorophenyl)porphine (PtTFPP) are presented in this paper.
Abstract: The pressure sensitive paint (PSP) properties of a fluoroacrylic polymer, FIB, with the luminophor platinum tetra(pentafluorophenyl)porphine (PtTFPP) are presented. This paint forms a hard coating that displays Stern–Volmer plots with a high dynamic range (∼ 0.9) [defined as (Ivac − Iatm)/Ivac], good photostability, a response time of less than 1 s and a relatively low temperature dependence (∼ 0.6% per degree). The temperature dependence is low because FIB has a unusually low activation energy for the diffusion of oxygen. Pressure and temperature affect intensity independently making this PSP “ideal.” The basecoat affects the functionality of the PSP it underlies, and the optimal basecoat used to date also includes the FIB polymer. The synthesis of the FIB polymer is a copolymerization that occurs in one step with a peroxide initiator. Annealing the painted model above Tg = 70°C procures adhesion and ideality. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2795–2804, 2000