bluuebunny/crossref_metadata_2025_split huggingface dataset:
Engineering plastics from lignin. III. Structure property relationships in solution cast polyurethane films
Authors: Saraf Vasudev P. , Glasser Wolfgang G. 
Published: April 2003

AbstractLignin‐based polyurethane films were synthesized by solution casting from hydroxypropyl lignin derivatives and either an aliphatic or an aromatic isocyanate. Two lignins, kraft and steam explosion lignin, and two diisocyanates, hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI), were chosen for the study. It was found necessary to use stoichiometric excess diisocyanate in the synthesis of the thermosetting polyurethanes. This part of the series addresses the effect of synthesis variables on film properties. The study examines the effect of lignin type, of diisocyanate type, and of composition in terms of NCO to OH stoichiometry on thermal and mechanical properties. Stoichiometric NCO‐excess was found to cause a more significant increase in the glass transition temperature of TDI‐based films than of films made with HDI. The films swelled less with increasing NCO/OH ratio. Use of aliphatic diisocyanate (HDI) resulted in films with lower moduli as compared to aromatic diisocyanate (TDI). Kraft‐lignin‐based polyurethanes had slightly inferior strength characteristics (Young's modulus and tensile strength) in comparison with those derived from steam explosion lignin. Variation in the NCO/OH stoichiometry had no noticeable effect on modulus or tensile strength, but did significantly influence glass transition temperature, swelling, and strain at break. It is observed that the properties of these thermosetting polyurethanes are very sensitive to their composition. The study illustrates that materials of satisfactory performance characteristics can be engineered by proper selection of synthesis variables and modification of network architecture.
Effects of catalyst on the electrical properties of silicone rubber
Authors: Yokoyama T. , Kinjo N. , Mukai J. 
Published: April 2003

AbstractElectrical properties, such as dissipation factor and electric conductivity, were studied for silicone rubber sheets. The specimens were prepared by the reaction of α,ω‐dihydroxypolysiloxane with ethoxysilane, using dibutyltin dilaurate as a catalyst, at a relative humidity of about 100% at various temperatures and for various reaction times. It was found that the electrical properties were a function of the vulcanizing conditions; i.e., the further the vulcanization proceeded, the higher the dissipation factor and the electric conductivity. A reaction describing deterioration in electrical properties was then considered. Infrared spectroscopic studies on dibutyltin dilaurate showed that the dibutyltin dilaurates were partly hydrolyzed to lauric acid and dibutyltin dihydroxide. It was concluded that electrical property deteriorations, which were caused by changes in the vulcanizing conditions, were due to dibutyltin dilaurate hydrolysis. However, since the decomposed products were finally oxidized at elevated temperatures in an oxygen atmosphere, with a subsequent change to electrically inactive compounds, the initial electrical properties were recovered.
Transformation of liquid to amorphous solid: The time to vitrify for styrene polymerization
Authors: Aronhime M. T. , Gillham J. K. 
Published: April 2003

AbstractA model is presented for the calculation of the time to vitrify vs. temperature for isothermal polymerization by the chain growth mechanism. The model is based on the glass transition temperature (Tg) rising from its initial value to the reaction temperature. The relationships between Tg and the volume fraction of polymer and monomer, the volume fraction of polymer and the extent of reaction, and the extent of reaction and time are also required. In a plot of temperature vs. time the vitrification curve is generally S‐shaped; the time passes through a maximum just above the glass transition temperature. The model applies to linear polymerization in which monomer and high molecular weight polymer are the dominant species, i.e., to chain reactions. In this communication the model is applied to the bulk polymerization of styrene by the free radical mechanism.
Radiant flash pyrolysis of biomass using a xenon flashtube
Authors: Hopkins Mark Willard , Antal Michael Jerry , Kay Jack G. 
Published: April 2003

AbstractBiomass materials, including lignin, redwood, corn cob, Calotropis Procera, Leucaena wood, Kraft paper, newsprint, cow manure, D‐glucose, and D‐cellobiose, were pyrolyzed in vacuum by the visible radiant flux emitted from a Xenon flashtube. The flux density exceeded 8 kW/cm2 during the 1 ms flash. Sirup yields were low (avg 25%), while the gas yield was high (avg 32%). The gaseous products were composed primarily of CO and CO2. The high relative yields of CO establish the existence of a high temperature fragmentation pathway active during the flash pyrolysis of all biomass materials.
A relaxation model for property changes during the cure reaction of filled and unfilled silicone elastomers
Authors: Hsich H. S.‐Y. , Yanyo L. C. , Ambrose R. J. 
Published: April 2003

AbstractA generalized kinetic model of cure, which is described by a distribution relaxation function, is used to predict physical and mechanical properties of silicone elastomers during isothermal and nonisothermal cure reactions. The model can also predict the effect of filler and cure behavior of filled elastomers. The structural relaxation times of the molecular state of uncured and cured elastomers is also discussed.
Microstructure of biaxially drawn ultrahigh molecular weight polyethylene
Authors: Kaito Akira , Nakayama Kazuo , Kanetsuna Hisaaki 
Published: April 2003

AbstractThe microstructure of ultrahigh molecular weight polyethylene (UHMW‐PE) sheets biaxially drawn in the molten state was investigated by means of wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering (SAXS), differential scanning calorimetry (DSC), and electron microscopy. The crystallographic c‐axis tended to be oriented in the sheet plane by the biaxial drawing in the molten state. The microstructure of the biaxially drawn UHMW‐PE was shown to depend upon molecular weight of UHMW‐PE. The biaxially drawn sheet of higher molecular weight (Mv = 2,700,000) showed a fibrous structure, while the lower molecular weight sample (Mv 700,000) had a lamellar structure. The result of DSC measurements suggested that a small number of nucleating extended chain crystals was produced by biaxial melt drawing of the UHMW‐PE sheet with higher molecular weight.
Development of a new composite material from waste polymers, natural fiber, and mineral fillers
Authors: Ramirez Amando Padilla , Solis Antonio Sánchez 
Published: April 2003

AbstractThis work describes a panel made from waste polyethylene, henequen fibers, and mineral fillers. The physical and mechanical properties of the product were determined and compared with the properties of commercial panels. The new material has good mechanical properties and high environmental resistance. Its thermal insulating capacity is about 10 times better than that of asbestos–cement panels. The adhesion grade between fibers and polymer was investigated.
Hydrolysis of cotton fibers by cellulase enzyme
Authors: Paralikar K. M. , Bhatawdekar S. P. 
Published: April 2003

AbstractCotton cellulose has been subjected to continuous and repeated enzymatic hydrolysis for different periods. It has been observed that the length of hydrocellulose particles obtained on repeated enzyme action is reduced to about 300–500 Å as compared to 900–3000 Å obtained on prolonged enzyme treatment. Corresponding changes in moisture regain, crystallinity of the hydrolysates, and weight loss brought out by the hydrolysis are also discussed.
Size exclusion chromatography of polyelectrolytes in dimethylformamide
Authors: Scheuing D. R. 
Published: April 2003

AbstractA study of the size exclusion chromatographic behavior of styrene–methacrylic acid and epoxyacrylic polymers has been made. These polymers exhibit strong “ion‐exclusion” effects in DMF, similar to that found for water‐soluble polyelectrolytes such as sodium polystyrene sulfonate. The addition of lithium bromide, at a concentration of 0.1M, overcomes ion exclusion on a set of silicabased, “deactivated” duPont SEC columns. Calibration of both the duPont columns and a set of styrene–divinyl benzene based columns (μ‐Styragel) is complicated by absorption of polystyrene standards in DMF and DMF/salt mobile phases. The absorption of monomeric solutes on the duPont columns in DMF/salt mobile phases is different from that of their corresponding polymers.
Dielectric properties of cellulose acylates
Authors: Morooka Toshiro , Norimoto Misato , Yamada Tadashi , Shiraishi Nobuo 
Published: April 2003

AbstractThirteen kinds of cellulose acylates from the acetate to stearate were prepared by trifluoro acetic anhydride–fatty acid esterification, and their dielectric constant and loss were measured over wide temperature and frequency ranges. Two types of relaxation process (αd and βd) were recognized for all the acylates and an additional relaxation process (γd) was detected for the acylates with side chain length longer than that of the butyrate. These αd to γd processes were attributed to the micro‐Brownian motion of the main chain (αd), the motion of oxycarbonyl group of the side chain (βd) and the motion initiated by minimum three methylene groups in addition to the oxycarbonyl group (γd), respectively. In the transition map for the βd process, inflection points were observed, and the temperature at the inflection point could be regarded as a freezing point of the micro‐Brownian motion of the acyl side chain. In the temperature region above the inflection point, plots in transition map for all the acylates were found to be on the same straight line.
Design of polymer membrane with permselectivity for water–ethanol mixture. II. Preparation of crosslinked poly(methyl acrylate) membrane with diethylene triamine and its permselectivity
Authors: Itoh Toshiaki , Toya Hideki , Ishihara Kazuhiko , Shinohara Isao 
Published: April 2003

AbstractIn order to permeate water from a water–ethanol mixture by pervaporation on the basis of the difference in solubility between two components toward a polymer membrane, polymer membrane having polar group, poly(methyl acrylate) (PMA) membrane crosslinked with diethylene triamine (DETA) was prepared. The permselectivity of the membrane was investigated with attention to the feed composition of water–ethanol mixture and the effect of introduction of DETA into the membrane. It is found that water was permeated through PMA–DETA crosslinked membrane preferentially in all ranges of feed composition, the highest permselectivity being observed at 25% ethanol aqueous solution. Moreover, the pervaporation rate of water was found to depend on the ratio of DETA introduction into the membrane. When the ratio of introduction into the membrane was 0.144, water was permeated through the membrane from 25% ethanol aqueous solution at a rate of 1.26 × 10−1 g m/m2 h. These results can be explained by high diffusivity of the membrane due to the low glass transition temperature of PMA and permeation of water through polar DETA moiety in the membrane.
Correlation of solubility in polydimethylsiloxane and polyisobutylene systems
Authors: Tseng Hsiao‐Show , Lloyd Douglas R. , Ward T. C. 
Published: April 2003

AbstractSolubility data of organic probes in polydimethylsiloxane (PDMS) and polyisobutylene (PIB) obtained by inverse gas chromatography (IGC) were collected from the literature and analyzed. Applying the principle of corresponding states, empirical correlations were derived and presented for the estimation of solubilities of nonpolar and slightly polar probe molecules in these polymers. Estimation of other thermodynamic properties, such as activity coefficient of the solute, Henry's law constant, Flory–Huggins interaction parameter, and heat of solution through the use of these correlation equations, was demonstrated.
Mercerization of cellulose. II. Alkali–cellulose intermediates and a possible mercerization mechanism
Authors: Okano T. , Sarko A. 
Published: April 2003

AbstractContinued study of the five crystalline Na–celluloses, previously shown to occur as intermediates during the mercerization of cellulose and exhibiting two types of crystallographic fiber repeats, further indicates that they fall into three classes based on their unit cells and NaOH contents. In one class are Na–celluloses I and III, both containing up to 34% NaOH; in the second class are Na–celluloses IIA and IIB, marked by ca.15 Å fiber repeat and containing up to 65% NaOH; and in the third class is Na–cellulose IV which is likely to be a hydrated form of cellulose II. Na–cellulose I was found to be the common first alkali–cellulose structure produced in the NaOH treatment of both cellulose I and cellulose II. Further study of this conversion step suggested a mercerization mechanism in which the alkali begins the conversion of cellulose to Na–cellulose I in the amorphous parts of the fiber. The conversion of the parallel‐chain cellulose I structure to an antiparallel one is likely to occur already in this first step.
No2–initiated polymerization of acrylamide in dimethylsulfoxide
Authors: Mishra Mahendra Kumar , Bhadani Suraj N. 
Published: April 2003

AbstractNO2‐initiated polymerization of acrylamide in dimethylsulfoxide was carried out. The dependence of monomer, initiator concentrations, and temperature on polymer yield and initial rate of polymerization was studied. The overall activation energy of polymerization was calculated to be about 15 kcal mol−1. The copolymerization of acrylamide with methyl methacrylate was also studied. The kinetic mechanism of polymerization was proposed.
Percolation conductivity in Nafion membranes
Authors: Wódzki Romuald , Narębska Anna , Nioch Wojciech Kwaś 
Published: April 2003

AbstractThis article deals with the method of determination of a threshold volume fraction of the conductive phase within perfluorosulfonic acid ionomer Nafion. Experiments have been performed with the commercial Nafion‐120 and Nafion‐427 membranes equilibrated with concentrated sodium chloride and sodium hydroxide solutions at 353 K. It has been stated that the insulator‐to‐conductor transition in membranes occurs at the critical volume fraction of the conductive phase (Vc) equal to 0.1. The same Vc has been estimated for a geometrical cluster‐network model. Lower than the theoretical Vc for a classical dense‐packed‐hard‐sphere model (Vc = 0.15), the volume fraction for the membranes is caused mainly by channels connecting the ionic clusters. The critical exponent t has been calculated for both membranes and found to be equal to 1.6 for Nafion‐120 and 1.5 for Nafion‐427. Both these constants correspond to those theoretically predicted for 3D systems. The ratios of sodium ion mobility in the internal membrane solution to its mobility in the equilibrating NaCl or NaOH solutions (u+/u+) are below unity, and they are dependent on the nature and concentration of the electrolyte.
Tensile properties of carbon fibers from acrylic fibers stabilized under isothermal conditions
Authors: Takaku A. , Hashimoto T. , Miyoshi T. 
Published: April 2003

AbstractA series of carbon fibers were prepared from the acrylic fibers thermally stabilized in air under various temperature–time conditions, and the relation between the extent of stabilization and the tensile properties of carbon fibers was investigated. The density of stabilized fibers was adopted as a measure of the extent of stabilization. The tensile modulus of carbon fibers changed dependently on stabilization temperature. However, the variation of the tensile modulus of carbon fibers with the density of stabilized fibers was small if stabilization temperature was constant. In the relation between the tensile strength of carbon fibers and the density of stabilized fibers, a feature depending on stabilization temperature was not evident, and the tensile strength of carbon fibers showed a maximum in the density range from about 1.34 to 1.39 g/cm3 of stabilized fibers.
The tensile behavior of polycarbonate and polycarbonate–glass bead composites
Authors: Dekkers M. E. J. , Heikens D. 
Published: April 2003

AbstractThe tensile behavior at 20°C of unfilled polycarbonate and polycarbonate–glass bead composites (90/10 vol %) has been investigated by tensile testing with simultaneous volume change measurements. Both the effect of the bead size and the degree of interfacial adhesion on the tensile behavior of the composites has been studied. A simple model has been applied to obtain quantitative information on the separate contributions of several possible deformation mechanisms to the total deformation. For unfilled polycarbonate and the polycarbonate–glass bead composites with excellent interfacial adhesion, shear deformation is found to be the only significant non‐Hookean deformation mechanism. By means of strain recovery experiments it is shown that the shear deformation is highly elastic in character. For the composites with poor interfacial adhesion, besides shear deformation also dewetting cavitation contributes to the non‐Hookean deformation. The differences in tensile behavior between the composites with excellent and poor interfacial adhesion are explained by the different mechanisms for shear band formation at excellently and poorly adhering glass beads.
Active transport and selective transport of alkali metal ions through polyelectrolyte complex membranes consisting of the three materials [2‐(diethylamino)ethyl]dextran hydrochloride, sodium carboxymethyldextran, and sulfate of poly(vinyl alcohol)
Authors: Kikuchi Yasuo , Kubota Naoji 
Published: April 2003

AbstractActive and selective transport of alkali metal ions through the polyelectrolyte complex membranes consisting of [2‐(diethylamino)ethyl]dextran hydrochloride, sodium carboxymethyldextran, and sulfate of poly(vinyl alcohol) have been investigated for the first time. The transport behavior was much affected by the hydrogen ion concentration. The driving force for the active transport of alkali metal ions was considered to be the hydrogen ion concentration. It was suggested that both the appropriate changes of chemical and physical properties of polyelectrolyte complex membrane and the affinity of the carrier fixed to the membrane for alkali metal ions controlled the active transport and selectivity through the membranes.
Mechanical, thermal, and electric properties of polyurethaneimide elastomers
Authors: Masiulanis Bogumiła , Zielin̂ski Ryszard 
Published: April 2003

AbstractLinear polyurethaneimide elastomers (PUI) were obtained from polyether‐ or polyester‐diols, diphenylmethane diisocyanate or bitolylene diisocyanate and pyromellitic acid dianhydride. It was found that these polymers have considerably better mechanical properties than typical linear polyurethanes (PU). The elastic modulus and stress at break increase with contents of the hard polyimide segments. The softening temperatures and thermal stability of the PUI at 500°C were higher than the ones of PU with similar hard segment contents. Electric properties of PUI were close to the ones of conventional PU. It was shown that cellular PUI had considerably lower dielectric constant. Tg's of the soft segments PUI were less than Tg's corresponding to PU. It is connected with greater phase separation of the hard imide segments from the soft polyether– or polyester–urethane matrix.
The conduction mechanism of polymer–filler particles
Authors: Miyauchi Shin'nosuke , Togashi Eiki 
Published: April 2003

AbstractIn this paper, the electrical properties and the conductive mechanism of polymer‐filler particles are discussed using polymer‐grafted carbon black. Resistors with resistivities in the range of ca. 10–108 Ω cm were made, and the resistance–temperature relationship was measured between 77 and 298° K. In this temperature range, the resistance decreased with an increase of temperature, suggesting that the electrical conduction is thermally activated. The resistance as a function of field strength was measured by a pulse method. The resistor was a resistivity of ca. 104 Ω cm showed field dependence, and the change of resistance was reversible. It was found that the resistance was independent of temperature at high field strength, and tunneling conduction is predominant. On the basis of these facts, theoretical equations were derived and compared with the experimental values.
Bonding in cotton fiber from formaldehyde‐free crosslinks
Authors: Frick J. G. 
Published: April 2003

AbstractCotton fabric was crosslinked with five agents, three of which were prepared form formaldehyde and two of which were formaldehyde‐free. The formaldehyde‐free agents produced less bonding between layers in the laminated microstructure of the cotton fiber. One agent, 4,5‐dihydroxy‐1,3‐dimethyl‐2‐imidazolidinone, gave no evidence of any interlayer bonding. All five agents gave the same relationship between wrinkle recovery angle and molar substitution on the cotton up to moderate recovery angles, but only agents based on formaldehyde gave higher wrinkle recovery angles with additional reaction. Intralayer crosslinking did not reduce absorptivity, as shown by moisture regain and dye receptivity, but did restrict swelling in cupriethylenediamine hydroxide to the same extent as combined interlayer and intralayer crosslinking. The decrease in extensibility of treated fabric with increasing wrinkle recovery angle was the same with all agents. These results indicate the regions of the fiber that are important for each of these properties.
Mechanical degradation of PVC films monitored by photoacoustic spectroscopy
Authors: Abu‐Zeid M. E. , Nofal E. E. , Tahseen L. A. , Abdul‐Rasoul F. A. 
Published: April 2003

AbstractPVC films were subjected to mechanical degradation at room and elevated temperatures and monitored by photoacoustic spectroscopy. Broken bonds in the main PVC chain result in the formation of “mechano‐radicals,” which in turn yield a zipper reaction and the formation of submicrocracks in the PVC samples. The mechanistic schemes based on the formation of the mechano‐radicals are introduced and are successfully supported by the experimental results.
The effect of cobalt complex addition on the cure and properties of an epoxy matrix resin
Authors: Stoakley D. M. , St. Clair A. K. 
Published: April 2003

AbstractThe effects of adding various cobalt complexes to a tetraglycidyl methylene dianiline‐based epoxy resin were determined. The addition of cobalt(III) acetylacetonate was found to alter the epoxy cure and improve the flexural strength and fracture toughness of the cured resin. These effects were not duplicated by the addition of various other cobalt complexes.
Surface modification of cellulose fibers III. Durability of cellulose–polyester composites under environmental aging
Authors: Zadorecki Pawel , Flodin Per 
Published: April 2003

AbstractThe effects of improved interfacial adhesion on the environmental aging behavior of cellulose–polyester composites were studied. The reduction in maximum water content of the composites upon immersion in water which occurs for surface‐treated fibers is explained by the restrictions from fiber/matrix network. Whitening of the specimens based on the untreated fibers, or on fibers treated but not covalently bonded to the matrix, was found to be due to the formation of debonding cracks. Such cracks were formed on drying the materials. When the fiber and the matrix are covalently bonded, the matrix follows the fiber during shrinking, and thus no cracks are formed.