bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of recovery methods and conditions on the yield, solubility, molecular weight, and creep compliance of regenerated chitosan
Authors: Chen Rong Huei , Liu Chang Shu 
Published: August 2002

AbstractThe objective of this study is to explore the effect of using different recovery methods and conditions on the yield, solubility, molecular weight, and creep compliance of the regenerated chitosan. The results show that yields obtained by dialysis were higher than those using recovery medium of alkali solutions, organic solvents, or alkali–alcohol–water mixtures. For those chitosans employing alkali solutions as the recovery medium, the higher the alkali concentration used, the higher the yields obtained, although the total quantity of alkali in the solution were the same. Solubilities of regenerated chitosans were similar and independent at the methods of using alkali solution, organic solvent or alkali–alcohol–water mixture or at different concentrations of alkali solution. The molecular weight of regenerated chitosan decreased from 2.37 × 107 to 1.68 × 107 Da proportionally with the concentration of the alkali solution of the recovery medium from 1N to 8N. Creep compliance of regenerated chitosan gel obtained from 65% degree of deacetylation (DD) chitosan was lower than that of either 72 or 89% DD chitosan gel. Of the same DD chitosan, compliance of regenerated chitosan gels obtained by using a higher concentration of alkali solution was lower than that of a lower concentration ones. Hydrogels regenerated from different DD chitosans and/or different recovery mediums have different structure and tactile properties. Therefore, they can be used as wound dressings suited to different applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 193–202, 2002; DOI 10.1002/app.10296
Thermal degradation studies of different polar polyethylene copolymers
Authors: Jäger K.‐M. , Dammert R. C. , Sultan B.‐Å. 
Published: August 2002

AbstractThe thermal degradation of different polar polyethylene copolymers, ethylene/methylacrylate (EMA), ethylene/ethylacrylate (EEA), ethylene/butylacrylate (EBA), ethylene/methylmethacrylate (EMMA), and ethylene/hydroxyethylmethacrylate (EHEMA), was studied by using thermogravimetric analysis (TGA), infrared analysis (FTIR), and size exclusion chromatography (SEC). Weight loss measurements of the different copolymers were performed at 333°C by using a nitrogen atmosphere in a TGA instrument. The samples thus aged were then characterized with the help of FTIR and SEC. Degradation reactions, such as ester pyrolysis, chain scission, and gelation, were investigated. EBA, EEA, and EHEMA undergo ester pyrolysis, which is affected by the structure of the ester moiety. EHEMA reacts additionally by transesterification and thus forms crosslinks. EMA and EMMA do not react by ester pyrolysis. It is concluded that the reaction products formed during ester pyrolysis support chain scission, and therefore, these reactions are observed more for EBA and EEA than for EMA and EMMA. Finally, the rate of chain scission is higher for EMMA than for EMA. This is explained as being due to an initiation of chain scission at the α—C—C bond, in which formed radicals are stabilized by the additional methyl group in EMMA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1465–1473, 2002; DOI 10.1002/app.10510
Thermally stimulated creep (TSCr) study of viscoelastic behavior and physical aging of a polymeric matrix composite for spacecraft structures
Authors: Issoupov V. , Demont Ph. , Lacabanne C. , Startsev O. V. , Viel V. , Dinguirard M. 
Published: August 2002

AbstractThermally Stimulated Creep (TSCr) mechanical spectroscopy has been used to analyze molecular movements in KMU‐4lcarbon/epoxy composite material around the glass transition temperature. This technique is powerful to characterize the microstructure and micromechanical properties of the epoxy matrix and their evolution upon thermal aging. Three cooperative submodes have been distinguished by resolving the fine structure of the material complex α‐retardation mode. The elementary processes constituting this mode possess activation enthalpies and preexponential factors that strongly depend on the thermal history of the sample. The activation parameters of the composite are subject to perceptible evolution due to postcuring degradation. The α‐mode associated complex spectrum shifts towards higher temperatures by 27°C as a consequence of a series of quenching in the temperature range 260 to 0°C; the material shows a rise in the fragility and a deterioration in the crack‐growth resistance qualities. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 342–350, 2002
Polyether‐amide segmented copolymers based on ethylene terephthalamide units of uniform length
Authors: Bouma Krista , Wester Geertje A. , Gaymans Reinoud J. 
Published: August 2002

AbstractSegmented copolymers were synthesized using the crystallizable bisesterdiamide segment (N,N′‐bis(p‐carbomethoxybenzoyl)ethanediamine) T2T‐dimethyl (a one‐and‐a‐half repeating unit of nylon 2,T) and poly(tetramethyleneoxide) segments. Poly(tetramethyleneoxide) (PTMO) is amorphous and has a low Tg. The segment length was varied from 650 to 2800 g/mol by extending PTMO650 using dimethyl isophthalate. The polymers were synthesized in the melt, and test samples were prepared by injection molding. The melting behavior, as well as the torsion modulus spectrum as a function of temperature, were studied using DSC and DMA, respectively. The T2T‐PTMO polymers were found to have sharp glass (Tg) and flow transitions (Tfl), and the modulus at the rubbery plateau appeared to be virtually temperature independent. The Tg value was found to be independent of the diamide concentration, thus indicating that the T2T segments were fully crystallized. The Tfl was found to decrease with increasing soft segment length; this was ascribed to a “solvent” effect of the amorphous phase of the crystalline T2T units. The difference between the melting and crystallization temperatures was found to be low, thus suggesting that on cooling, there is a high rate of crystallization. When ethanediol was added as a T2T segment extender, amide‐ester‐amide segments were introduced. These amide‐ester‐amide segments form a separate lamellar phase with a much higher melting temperature (>300°C). It was found that the crystallization rate of the T2T units was enhanced by the presence of the amide‐ester‐amide segments, indicating that upon cooling, the crystallized amide‐ester‐amide segments form the nucleation sites for the nonextended T2T segments. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1173–1180, 2001
Effect of talc/MMA in situ polymerization on mechanical properties of PVC‐matrix composites
Authors: Xie X. L. , Li B. G. , Pan Z. R. , Li R. K. Y. , Tjong S. C. 
Published: August 2002

AbstractIn this study, polymethyl methacrylate (PMMA)‐coated talc was produced by the in situ polymerization of methyl methacrylate on the talc surface. The polymerization reaction was performed by both batch and semicontinuous emulsion processes. The polymerization kinetics, particle size and distribution, grafting efficiency, and coated‐talc morphology were systematically investigated. It was found that the talc particles have no effect on the polymerization of PMMA. The PMMA produced was found to cover the talc surface well. However, only a small amount can be grafted onto the talc. The size distribution of talc particles treated by semicontinuous emulsion polymerization is more uniform than by batch polymerization. The treated talc was subsequently used as filler in a poly(vinyl chloride) (PVC) matrix, and mechanical properties of the PMMA‐coated‐talc/PVC composites were studied. Morphological structure of PVC‐matrix composites revealed that the PMMA coating on talc improved the dispersion of talc in the PVC matrix and enhanced the interfacial adhesion between the talc and PVC. The mechanical properties of the composites, especially the impact strength, were found to be improved. There appears to be a critical covering thickness of PMMA on the talc surface for optimum toughening. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2105–2112, 2001
Composite materials prepared from waste textile fiber
Authors: Bateman Stuart A. , Wu Dong Yang 
Published: August 2002

AbstractComposite materials were prepared utilizing whole carpet and LDPE. The addition of compatibilizers during processing was shown to provide an improvement in the mechanical performance of such materials. It is believed that the addition of a reactive compatibilizer to the system increases both the compatibility between components of the composite material and interfacial interactions, through chemical reactions between functional groups on the compatibilizer and the surface of the carpet fibers under the processing conditions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3178–3185, 2001
Preirradiation grafting polymerization of DMAEMA onto cotton cellulose fabrics
Authors: Jun Lu , Min Yi , Jiuqiang Li , Hongfei Ha 
Published: August 2002

AbstractThe grafting yield of N,N′‐dimethylaminoethyl methacrylate (DMAEMA) on cotton cellulose fabric increased with grafting time, absorbed dose, and concentration of the monomer in the aqueous solution, but decreased with grafting temperature. The dose rate had a small effect on the grafting yield. The optimal grafting yields of DMAEMA on cotton cellulose were rather low, approximately 50% compared with N‐isopropylacrylamide (NIPAAm), although both monomers could be synthesized to be thermally reversible hydrogels. The relationship between the grafting yield and the grafting temperature indicated that the trapped radicals located in the interphases between crystalline and amorphous regions of irradiated samples were the main active species inducing the grafting reaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3578–3581, 2001
Interpenetrating polymer networks based on poly(acrylic acid) and gelatin. I: Swelling and thermal behavior
Authors: Burugapalli Krishna , Bhatia Dhiraj , Koul Veena , Choudhary Veena 
Published: August 2002

AbstractThis article describes the synthesis of full and semi‐interpenetrating polymer networks (IPNs) based on poly(acrylic acid) and gelatin as polymers 1 and 2, which were crosslinked sequentially using N,N′‐methylene bisacrylamide (BAm) and glutaraldehyde, respectively. Various samples were prepared by taking varying amounts of acrylic acid and gelatin in the initial feed. Sequential IPNs were prepared by first polymerizing and crosslinking acrylic acid in the presence of gelatin using redox initiators (ammonium persulphate and sodium metabisulphite) and BAm as a crosslinking agent. Gelatin present in the firm gels was then crosslinked using 4% glutaraldehyde. Characterization of these gels was done by measuring their swelling behavior as a function of pH, temperature, and time. Percent swelling increased with increasing amounts of acrylic acid. The swelling ratio was also determined in the pH range of 1 to 12. Acid/alkali or buffers were used for maintaining pH. A significant increase in the percent swelling was observed when pH of distilled water was above 10. On the other hand, in the case of buffer, the swelling ratio increased with increasing the pH, and a maxima was observed at pH 8.4. A further increase in pH resulted in a decrease in the swelling ratio. Thermal and morphological characterization was done using thermogravimetric analyzer and scanning electron microscopy, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 217–227, 2001
Bulk and solution copolymerization of methyl methacrylate and vinyl acetate
Authors: Scorah M. J. , Hua H. , Dubé M. A. 
Published: August 2002

AbstractA series of batch, bulk and solution (in toluene) copolymerizations of methyl methacrylate and vinyl acetate was performed under various reaction conditions to high monomer conversions. In addition, low conversion bulk experiments were performed to estimate monomer reactivity ratios using the error in variables model method, based on terminal model (Mayo–Lewis) kinetics. A combination of the low and high conversion data with data from a previous study yielded reactivity ratio (r) estimates of 27.465 and 0.0102 for rMMA and rVAc, respectively, using the integrated copolymer composition (Meyer–Lowry) equation. In the high conversion experiments the effects of various factors on the reaction rate, cumulative copolymer composition, number‐ and weight‐average molecular weights, and molecular weight distribution were studied. The factors included the monomer feed composition, initiator concentration, temperature, solvent concentration, and the addition of n‐dodecyl mercaptan chain transfer agent. These factors were examined in light of the wide difference in the monomer reactivity ratios. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1238–1255, 2001
Properties and morphology of poly(ethylene terephthalate) and high‐density polyethylene blends
Authors: Guerrero Carlos , Lozano Tomás , González Virgilio , Arroyo Eliud 
Published: August 2002

AbstractBlends of poly(ethylene terephthalate) (PET) and high‐density polyethylene (HDPE) with and without a compatibilizing agent were studied. Both materials are widely used in the soft drink bottle industry. The compatibilizing agent was a copolymer of ethylene and methacrylic acid partially neutralized with zinc (Surlyn). The olefinic segment of Surlyn is compatible with HDPE, whereas the Surlyn carboxylic acid groups is affine with the PET carbonyl groups. The effectiveness of the compatibilizing agent was evaluated using different techniques, such as infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy, and mechanical properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1382–1390, 2001
Improved polyimide/metal adhesion by chemical modification approaches
Authors: Ranucci Elisabetta , Sandgren Åsa , Andronova Natalia , Albertsson Ann‐Christine 
Published: August 2002

AbstractTo increase their adhesion to silver, polyimide (PI) surfaces were modified by sulfonation reactions by means of different experimental procedures. The results of these modification reactions were analyzed in terms of the variation of the surface chemical composition examined by X‐ray photoelectron spectroscopy. Long‐time reactions were also followed by monitoring the increase in weight of the PI films. Changes in the total surface free energy were evaluated by contact angle measurements with the sessil drop method. The influence of the modification reactions on silver/PI adhesion was estimated by means of a 180° peeling test according to ASTM standards. Finally, the effect of chemical modification on film roughness was investigated by means of atomic force microscopy. The results obtained showed that a net improvement, that is, over the maximum rate according to the reference ASTM test, was attained via both the gaseous SO3 and concentrated H2SO4 procedures, with the latter procedure more effective in the presence of silver sulfate as a catalyst. However, the former was judged more convenient because of the low amount of reagents used and the simplicity of cleaning operations. Interestingly, optimum adhesion levels were attained after only very low contact times with all sulfonating agents, that is, after about 30 s. These results were compared with the effects on PI/silver adhesion of traditional etching procedures with KOH aqueous solutions at different temperatures. In this case, good adhesion was observed only after longer reaction times, that is, on the order of 1–2 min in the case of 1M KOH and 1 h in the case of 0.1M KOH. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1971–1985, 2001
Water‐soluble esters of biosynthetic poly(γ‐glutamic acid)
Authors: Pérez–Camero Graciela , Vázquez Blanca , Muñoz–Guerra Sebastián 
Published: August 2002

AbstractWater‐soluble poly(γ‐glutamic acid) (PGGA) esters were prepared by transesterification of poly(α‐methyl‐γ‐glutamate) with mono‐, di‐, and triethylene glycols with one hydroxyl end group blocked as methyl ether. Only the monoglycol appeared to be crystalline with melting at 160°C, and glass‐transition temperatures were found to increase from 10 to 60°C with the length of the oxyethylene side chain. All these poly(γ‐glutamate)s are stable up to temperatures near 250°C. Moisture sorption, surface wettability, and hydrodegradability were evaluated as a function of time. It was found that in overall sensitivity to water increased with the glycol chain length but the behavior at short contact times was critically affected by conformational factors. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2027–2036, 2001
Structure and reaction mechanism for the monoacid diol polyester from caprolactone and 2,2′‐bis(hydroxymethyl)propionic acid: NMR and melting‐point evidence
Authors: Simms J. A. , McCord E. F. 
Published: August 2002

AbstractThe product distribution in the synthesis of acidic hydroxypolyesters from a 6/1 mol ratio of caprolactone and 2,2′‐bis(hydroxymethyl)propionic acid (DMPA) changes with reaction time and temperature. 13C‐nuclear magnetic resonance (NMR) signals were identified that are specific for all the possible substitution products around the quaternary carbon in the DMPA. This allows quantitative determination of the six different species that are present. NMR studies showed that over one‐half of the product is substituted on only one of the DMPA hydroxyls. The residual DMPA concentration increases at times and temperatures higher than those required to just complete caprolactone conversion because of equilibration of the kinetic product. All process conditions produced polyesters with two melting points. This suggests that the monosubstituted and disubstituted families of oligomers which are present are not completely miscible with one another. Polyester melting points increase as reaction time and temperature increase. This indicates that the degree of polymerization of the polycaprolactone arms increases as the severity of the preparative condition increases. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2217–2226, 2001
Reexamination of the miscibility of stereoregular poly(methyl methacrylate) with poly(vinyl phenol)
Authors: Hsu Wen‐Ping 
Published: August 2002

AbstractPreviously, isotactic, atactic, and syndiotactic poly(methyl methacrylates) (PMMAs) (designated as iPMMA, aPMMA, and sPMMA) were mixed with poly(vinyl phenol) (PVPh) separately in tetrahydrofuran (THF) to make three polymer blend systems. According to calorimetry data, iPMMA was found to be miscible with PVPh; however, partial miscibility or immiscibility was found between aPMMA (or sPMMA) and PVPh. According to the article by C. J. T. Landry and D. M. Teegarden, Macromolecules, 1991, 24, 4310, THF is the reason for causing aPMMA and PVPh to phase separate, but 2‐butanone instead produces miscible blends. Therefore, in this article these three polymer systems were investigated again using 2‐butanone as solvent. Films were prepared under specific conditions to minimize the effect of aggregation in PMMA. The formation of hydrogen bonding between PMMA and PVPh and the attendant changes in the aggregation of PMMA segments were determined in the solid states by means of FTIR. Based on the results of calorimetry, iPMMA and aPMMA were found to be miscible with PVPh. For iPMMA/PVPh blends, different degrees of hydrogen bonding were observed based on DSC data and FTIR spectra when compared to previous study. An elevation of the glass transition temperatures (Tgs) of aPMMA/PVPh blends above weight average was detected and the Tg values were fitted well by the Kwei equation. But partial miscibility was still found between sPMMA and PVPh on account of the observation of two Tgs in most compositions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1425–1431, 2002
A comparative study of gut‐associated lymphoid tissue in calf and chicken
Authors: Yasuda Masahiro , Tanaka Shogo , Arakawa Hiroshi , Taura Yasuho , Yokomizo Yuichi , Ekino Shigeo 
Published: August 2002

AbstractThe calf contains two types of Peyer's patches (PPs): jejunal and ileal. The ileal PP has been thought to be equivalent to the bursa of Fabricius (BF) as a central lymphoid organ. The morphologies of ileal and jejunal PPs in the calf were compared with those of the BF and the caecal tonsil (CT) in the chicken. Immunoglobulin G–positive (IgG+) cells appear in the follicles of them all and exhibited a dendritic appearance after birth. We investigated whether the IgG in these follicles was produced in situ. IgG‐producing cells were detected in the follicular medullas of the jejunal PP and the CT, but not in those of the ileal PP and the BF. CD4+ cells were distributed in the follicular medullas of the jejunal PP and the CT, but not in those of the ileal PP and the BF. The data suggest that Ig class switching occurs in both jejunal PP follicles and CT follicles, but does not occur in either the ileal PP follicles or the bursal follicles. Because CD4+ T cells would be prerequisite for Ig class switching in these follicles, IgG+ cells of the follicular medullas in the ileal PP and the BF would trap immune complexes from the gut lumen. The primary B‐cell repertoire might be selected by gut‐derived antigens in the ileal PP and the BF before seeding the periphery. Anat Rec 266:207–217, 2002. © 2002 Wiley‐Liss, Inc.
Reparative myogenesis in long‐term denervated skeletal muscles of adult rats results in a reduction of the satellite cell population
Authors: Dedkov Eduard I. , Kostrominova Tatiana Y. , Borisov Andrei B. , Carlson Bruce M. 
Published: August 2002

AbstractThis study, conducted on 25‐month denervated rat hindlimb muscles, was directed toward elucidating the basis for the poor regeneration that is observed in long‐term denervated muscles. Despite a ∼97.6% loss in mean cross‐sectional area of muscle fibers, the muscles retained their fascicular arrangement, with the fascicles containing ∼1.5 times more fibers than age‐matched control muscles. At least three distinct types of muscle fibers were observed: degenerating, persisting (original), and newly formed (regenerated) fibers. A majority of newly formed fibers did not appear to undergo complete maturation, and morphologically they resembled myotubes. Sites of former motor end‐plates remained identifiable in persisting muscle fibers. Nuclear death was seen in all types of muscle fibers, especially in degenerating fibers. Nevertheless, the severely atrophic skeletal muscles continued to express developmentally and functionally important proteins, such as MyoD, myogenin, adult and embryonic subunits of the nicotinic acetylcholine receptor, and neural‐cell adhesion molecule. Despite the prolonged period of denervation, slow and fast types of myosin were found in surviving muscle fibers. The number of satellite cells was significantly reduced in long‐term denervated muscles, as compared with age‐matched control muscles. In 25‐month denervated muscle, satellite cells were only attached to persisting muscle fibers, but were never seen on newly formed fibers. Our data suggest that the absence of satellite cells in a population of immature newly formed muscle fibers that has arisen as a result of continuous reparative myogenesis may be a crucial, although not necessarily the only, factor underlying the poor regenerative ability of long‐term denervated muscle. Anat Rec 263:139–154, 2001. © 2001 Wiley‐Liss, Inc.