bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on process variables for natural fiber composites—effect of polyesteramide polyol as interfacial agent
Authors: Pal S. K. , Mukhopadhyay D. , Sanyal S. K. , Mukherjea R. N. 
Published: April 2003

AbstractA systematic study of the process variables for polyester composites based on different natural fibers like jute, sisal, ramie, and pineapple has been made with a view to determine the most suitable processing conditions for such composites. Effect of polyesteramide polyol (PEAP) as interfacial agent in such composites has also been discussed. Fracture modes of jute/polyester (JP) composite sample having different fiber volume fractions have been examined by scanning electron microscope (SEM). Fracture surfaces of untreated and PEAP‐treated JP composite samples have been examined in SEM, both before and after 72 h immersion in boiling water, to study the nature of interfacial bonding on fiber treatment with PEAP. A qualitative improvement in bonding in case of PEAP‐treated JP composites is evident from SEM photomicrographs. This is also supported by physicomechanical properties of the composite samples.
Solution properties of poly(thiocarbonates)
Authors: Gargallo Ligia , Soto Elia , Tagle Luis H. , Radić Deodato 
Published: April 2003

AbstractPoly(thiocarbonates) with alkyl side chains have been prepared, and the solution properties of these polymers were studied in different solvents. Comparison with other poly(thiocarbonate) analogues and poly(carbonates) shows that the conformational parameter (Kθ) and rigidity factor increase as the volume of the side chain increases. The effect of the side‐chain structure on the solution properties is analyzed.
Grafting of acrylamide onto guar gum using KMNO4/oxalic acid redox system
Authors: Bajpai U. D. N. , Rai Sandeep 
Published: April 2003

AbstractThe grafting of acrylamide onto guar gum in aqueous medium initiated by KMnO4/oxalic acid redox system has been studied gravimetrically at the temperature 35 ± 0.2°C. The effect of redox components, acrylamide concentration and quantity of guar gum has been studied in terms of percentage and efficiency of grafting. A plausible mechanism of grafting and a suitable rate expression has been suggested. The rate of grafting was found to increase with increase in temperature and concentrations of redox components and acrylamide, but, at high concentration of guar gum, the rate was found to decrease.
Modeling of asymmetric membrane formation. II. The effects of surface boundary conditions
Authors: Yilmaz L. , McHugh A. J. 
Published: April 2003

AbstractAn analysis is carried out to evaluate the effects of alternate surface boundary conditions on the predictions of our previously developed (Part I) pseudobinary diffusion model for membrane formation by the phase inversion process. Attention is addressed to a comparison of concentration profiles in the quenched film for a constant flux interface (CF) condition and a mass transfer rate (MT) interface condition. A numerical algorithm is developed to handle the MT condition based on an explicit, finite difference marching method. Comparison of concentration profiles with those obtained earlier for the CF boundary condition show that since results for both cases are very similar, either condition can be used in concentration profile calculations. Changes in bath conditions will mainly affect membrane formation through the changed solvent/nonsolvent flux ratio during quenching.
Study on rough‐surface biaxially oriented polypropylene film. I. Formation of β‐form crystals in sheet cast with T‐die extruder
Authors: Fujiyama Mitsuyoshi , Kawamura Yoshimasa , Wakino Tetsuo , Okamoto Tomomi 
Published: April 2003

AbstractSheets were cast by extruding polypropylenes (PP) which contained γ‐quinacridone, a β‐crystal nucleator, at levels of 0–10 ppm using a 30 mm ϕ extruder with a T‐die at extrusion temperatures of 200–260°C and chill roll temperatures of 30–90°C. The influences of raw resin characteristics such as γ‐quinacridone content and MFI of the base PP and casting conditions such as extrusion temperature and chill roll temperature on the amount of β‐crystals formed in the sheet were studied. The amount of the β‐crystals formed was larger as the γ‐quinacridone content was higher and the extrusion temperature was lower and almost independent of the chill roll temperature. As for the influence of MFI of the base PP, the amount of the β‐crystals formed was maximum at MFI ≑ 8 dg/min.
Effects of film history on gas transport in a fluorinated aromatic polyimide
Authors: Moe M. , Koros W. J. , Hoehn H. H. , Husk G. R. 
Published: April 2003

AbstractThe effects of film formation procedures on transport properties are reported for a rigid‐chained, fluorinated, aromatic polyimide. Residual dimethylacetamide (DMAC) solvent present in films formed under certain casting protocols produces complexities in the permeation behavior of helium and carbon dioxide. Specifically, helium permeabilities are lower, while those of carbon dioxide are higher, in a film containing 8 wt% residual DMAC than in an annealed film containing < 1 wt% DMAC. Significant differences in transport properties are also observed between films prepared using two different casting techniques. These differences appear to be due to differences in organization of chain segments within films. The results of this study emphasize the considerable care needed in formation and postformation processing of these materials to ensure optimum flux/selectivity properties in such applications.
Water sorption kinetics in poly(aryl ether ether ketone)
Authors: Mensitieri G. , Apicella A. , Kenny J. M. , Nicolais L. 
Published: April 2003

AbstractThe kinetics of diffusion of water from different activity vapors and liquid phase have been investigated in glassy amorphous poly(aryl ether ether ketcne) (PEEK) films at the temperature of 60°C and in glassy semicrystalline PEEK sheets at different temperatures, respectively. In the case of the amorphous PEEK films (250 μm thick) the data at low activity levels were interpreted by means of a purely Fickian mechanism. At higher activity levels the material has shown the presence of a relaxation process; in this case the data have been interpreted using a model proposed by Berens and Hopfenberg. Equilibrium sorption isotherm is also reported. Liquid water sorption in semicrystalline (30%) PEEK sheets (2 mm thick) has been determined to follow the classical Fickian mechanism. The water uptake values obtained for both amorphous and semicrystalline PEEK, confirm the good moisture and liquid water resistance of this kind of high performance thermoplastic polymer.
Structural changes and molecular motion of polyacrylonitrile fibers during pyrolysis
Authors: Ko Tse‐Hao , Lin Chung‐Hua , Ting Hsing‐Yie 
Published: April 2003

AbstractThe stabilization process of polyacrylonitrile (PAN) fiber is necessary to develop high‐performance carbon fiber. This work is concerned with studies of the activation energy of PAN fibers during the stabilization process. A wide‐angle X‐ray diffractometer combined with a fiber specimen holder for heating was used to measure the activation energy of crystal transition Ec. Ec is almost the same as the activation energy of the cyclization reaction E which is measured by a differential thermal analysis (DTA). The variation of crystal size in PAN fiber and a model of the ladder polymer in stabilized fiber transformed from acrylontrile (AN) units of PAN fiber are discussed also. The crystal size of PAN fiber increases when the thermal treatment temperature is raised. When exposed to temperatures above the crystal degradation temperature Td, the molecular rods of PAN fiber are destroyed completely, and ladder polymer is formed in the ordered phase of the original PAN fiber. The transformation of ladder polymer is initiated in the disordered phase, and then at the boundaries of the ordered phase.
A methodology for characterizing reactive coatings: Time–temperature–transformation (TTT) analysis of the competition between cure, evaporation, and thermal degradation for an epoxy‐phenolic system
Authors: Gan S. , Gillham J. K. , Prime R. B. 
Published: April 2003

AbstractA methodology, in terms of a macroscopic isothermal time–temperature–transformation (TTT) diagram, is presented for characterizing the changes that occur isothermally in a reactive thermosetting system in which evaporation, cure, and thermal degradation occur. Iso‐weight loss contours show the progress of the loss of volatile material (mostly solvent). The gelation contour corresponds to the macroscopic viscosity rising to a definite level. The vitrification contour corresponds to the glass transition temperature (Tg) rising to the temperature of cure (Tcure). Iso‐Tg contours show the progress of cure in terms of the easily measured Tg (rather than chemical conversion). The iso‐Tg contours also show the influence of thermal degradation competing with cure. Degradation is responsible for difficulties in assigning the glass transition temperature of the fully cured material (i.e., Tg∞).
High strength and high toughness aromatic polyamide fiber. I. Preparation and properties of block poly(p‐phenylene and 4,4′‐diphenyl ether terephthalamide) fiber
Authors: Goto Tomoko , Maeda Matsuo , Hibi Sadao 
Published: April 2003

AbstractHigh strength and high toughness organic fibers can be prepared by molecular design of a suitable block copolymer with mixed segment of rigid and flexible molecular chains. In this paper, the synthesis of fiber forming high molecular weight block copolymer of poly(p‐phenylene terephtalamide) (PPTA) and poly(4,4′‐diphenyl ether terephthalamide) (DPETA) was studied by the low temperature solution polycondensation method. The high molecular weight block copolymer could be obtained in the mixed solution of 1,3‐dimethyl1‐2‐imidazolidone (DMI) and N,N′‐dimethyl acetamide (DMAc) in the presence of triethylamine. The copolymer structures were characterized by elemental analysis and IR spectra. The thermal stability of the block copolymer was better than that of PPTA homopolymer and the ordered copolymer. The wet spinning of the block copolymer was performed using the reaction solution as the spinning dope. The maximum tensile strength and elongation were observed for the filament containing 50% PPTA. The block copolymer had high strength and high Yound's modulus but had a low elongation compared with the ordered copolymer.
Modeling of chemorheology of thermoset cure by modified WLF equation
Authors: Mijovic Jovan , Lee Chee Hung 
Published: April 2003

AbstractAn analysis of chemorheology of cure of a formulation composed of diglycidyl ether of bisphenol‐A (DGEBA) type epoxy resin and a mixture of aromatic amines was performed. A series of kinetic and rheological tests were run, and the experimentally obtained results were checked against the proposed model. A modified form of the classical Williams–Landel–Ferry (WLF) equation was used to model the chemorheology of the formulation. To arrive at the appropriate form of the modified WLF equation, expressions were developed for (i) the cure kinetics, (ii) the glass transition temperature as a function of the degree of cure, and (iii) the changes in parameters C1 and C2 as a function of temperature. By using these correlations in conjunction with the WLF equation, good agreement between predicted and experimental findings was observed.
Effects of silane coupling agents on mica‐filled styrene‐butadiene rubber
Authors: Debnath Shankar , De Sadhan K. , Khastgir Dipak 
Published: April 2003

AbstractThe effects of silane coupling agents on styrene‐butadiene rubber (SBR)‐mica composites have been studied with special reference to the technical properties and polymer‐filler interaction. Silane‐treated mica improves polymer‐filler interaction, which subsequently enhances the tensile and other technically important mechanical properties. Failure surfaces of tensile, tear, and wear specimens have been examined under scanning electron microscope (SEM) and the fractographs have been correlated with the strength and failure mode of the composites.
Melt rheological properties of polypropylene–wood flour composites
Authors: Maiti S. N. , Hassan M. R. 
Published: April 2003

AbstractThis article presents study of melt rheological properties of composites of polypropylene (i‐PP) filled with wood flour (WF), at filler concentrations of 3–20 wt%. Results illustrate the effects of (i) filler concentration and (ii) shear stress or shear rates on melt viscosity and melt elasticity properties of the composites. Incorporation of WF intoi‐PP results in an increase of its melt viscosity and a decrease of melt elasticity such as die swell and first normal stress differences; these properties, however, depend on filler concentration. Processing temperature of the filledi‐PP increases as compared to the nonfilled polymer.
Chiroptical filters from aqueous (hydroxypropyl) cellulose liquid crystals
Authors: Charlet Gérard , Gray Derek 
Published: April 2003

AbstractAn experimental procedure has been designed for the preparation of aqueous mesophases of (hydroxypropyl)cellulose (HPC) exhibiting a stable low turbidity Sandwich chiroptical filters have been made from these right‐handed cholesteric liquid crystals confined between two parallel glass plates. Their optical properties, studied with new circular polarizers prepared from oriented polyethylene films, depend on the mesophase thickness. Thin filters (liquid crystal thickness ≤ 200 μm) reflect selectively up to 36% of normal incident light (i.e., 72% of the right‐handed circularly polarized component) in a very narrow wavelength band (bandwidth ≤ 10 nm). An increase of the reflected intensity is observed at higher sample thickness, although it is accompanied by an increasing loss of selectivity of the filter toward circularly polarized light. However, a range of thickness exists where both selectivity and reflectivity are close to their optimum values. The availability, low cost, and UV resistance of (hydroxypropyl)cellulose make HPC–water liquid crystals attractive for optical applications.
Photolithography of polytetrafluoroethylene for adhesion
Authors: Rye R. R. , Martinez R. J. 
Published: April 2003

AbstractIrradiation of polytetrafluoroethylene (PTFE) with Mg(Kα) X‐rays is shown to protect the surface against the chemical etching steps used to prepare PTFE for adhesion. Preirradiated etched samples of PTFE have adhesion strengths to epoxies of less than 3% of that for nonirradiated etched samples. The major portion of this decrease in adhesion strength occurs for X‐ray exposures of less than 10 min and failure in every case occurs in PTFE and not in the bonded transition region. XPS measurements (20 Å sampling depth) show little difference in F content between irradiated and nonirradiated samples, but thermal desorption shows increasing short chain fluorocarbon desorption with irradiation time. These results are consistent with previous studies showing that irradiation produces free radicals that lead to branching and/or crosslinking, and a surface rich in low molecular weight fluorocarbons. The crosslinked surface is resistant to deep (10,000 Å) chemical attack and rich in short chain fluorocarbons; both effects are expected to lead to weak adhesive bonding.
Properties of gels obtained by freezing/thawing of poly(vinyl alcohol)/water/dimethyl sulfoxide solutions
Authors: Yamaura Kazuo , Itoh Masayasu , Tanigami Tetsuya , Matsuzawa Shuji 
Published: April 2003

AbstractMelting points of poly(vinyl alcohol) (PVA) gels obtained by repeated freezing/thawing cycles of the solutions in mixed solvents of water and dimethyl sulfoxide (DMSO) were measured. PVA solutions in 1–30 and 90 vol % DMSO froze at −40°C. The melting point of a gel increased with an increase in freezing/thawing cycles for all the solutions frozen and with an increase in freezing time in 10–30 vol % DMSO. The solutions in 1–5 vol % DMSO gelled even at very low polymer concentration of 1.0 g/dL by repeated freezing/thawing. The melting point of all the gels with a 5% polymer concentration reached ca. 73°C after 14 freezing/thawing cycles except for the gels in 90 vol % DMSO. However, the melting point of the gels with the same polymer concentration prepared at −40°C using an unfrozen mixed solvent in 60 vol % DMSO was ca. 77°C and the largest. The maximum apparent enthalpy of fusion of the gels prepared by repeated freezing/thawing was ca. 40 kcal/mol. The gels in 90 vol % DMSO were transparent independent of cycles where as those in 1–80 vol % DMSO were opaque. The degree of opaqueness increased with decreasing DMSO content.
Comparative study of various methods for thermal degradation of poly[3‐dimethyl(methacryloyloxyethyl) ammonium propanesulfonate]
Authors: Lee Wen‐Fu 
Published: April 2003

AbstractThe comparative study of thermal degradation for poly[3‐dimethyl(methacryloyloxyethyl)ammonium propanesulfonate] [poly(DMAPS)] was studied by various methods under different conditions. The reaction order, the activation energy, and the preexponential factor were evaluated from thermal gravimetric curves. The activation energy and the preexponential factor increase with increasing heating rate in a nitrogen atmosphere and decrease with increasing heating rate in air. The activation energy is higher in an air atmosphere at lower heating rates (5, 10, 20°C/min), for any of the methods used.
Thermogravimetric analysis of cellulose: Effect of the molecular weight on thermal decomposition
Authors: Calahorra M. E. , Cortázar M. , Eguiazábal J. I. , Guzmán G. M. 
Published: April 2003

AbstractCellulose fractions of different molecular weights were subjected to dynamic thermogravimetric analysis in a nitrogen atmosphere. From the experimental data, activation energies and reaction orders were obtained following the Freeman–Carroll and Broido methods. The thermal stabilities of the samples were estimated taking into account the values of Ti, Tmax, and Ea. The results show that thermal stability increases as the molecular weight increases. It was also found that the cellulose pyrolisis process cannot be described as having a single value of Ea over the entire pyrolisis range. The dependence of Ea. The dependence of Ea on molecular weight is also discussed.
A study on the mechanism of the curing of LARC–TPI high temperature adhesive
Authors: Chang Shu‐Ying , Huang Samuel J. , Johnson Julian F. 
Published: April 2003

AbstractA study of the changes in a LARC–TPI adhesive during a three‐stage thermal curing process has been conducted. The multistage curing conditions followed commonly used industrial curing specifications. Using thermogravimetric analysis plus gas chromatography plus mass spectrometry, the gasses involved in the curing were identified. Water analysis was performed by two separate techniques and supplementary information gathered using Fourier transform infrared spectroscopy. These analytical studies permitted determination of the degree of cure at each stage and to determine whether any degradation is taking place under curing condition.
Functionalized polymers derived from the reaction of polymaleic anhydride with amines and alcohols
Authors: Tsiourvas D. , Paleos C. M. , Dais Photis 
Published: April 2003

AbstractIn the present study the application of polymaleic anhydride as a reactive polymer is illustrated in its reactions with didodecylamine, diphenylamine, and dodeecanol. These polymers consisting of lipophilic segments (originating from the long aliphatic chains) or of the mesomorphic diphenyl moiety coupled with the polar carboxylic or carboxylate group can in principle exhibit mesomorphism in the melt and aggregate in dispersion. Of these derivatives didodecyl derivative froms mesomorphic‐like structure in the melt, dodecanol monoester derivative dissolves freely in water whereas the sodium salts of the polymers disperse in water due to the presence of distinct polar and lipophilic moieties in their molecules.
The thermal stability of poly(aryl‐ether–ether‐ketone) as assessed by thermogravimetry
Authors: Day M. , Cooney J. D. , Wiles D. M. 
Published: April 2003

AbstractThe high temperature engineering thermoplastic poly(aryl‐ether–ether‐ketone) (PEEK) has been subjected to dynamic and isothermal thermogravimetry in both nitrogen and air. The dynamic data have been analyzed using both the Kissinger peak maximum technique and an isoconversional procedure developed by Flynn. These techniques gave apparent global activation energies of 223.5 and 235.7 kJ/mol, respectively, for the degradation of PEEK in nitrogen, in good agreement with the value of 219.7 determined from the isothermal experiments. The thermal stability of PEEK in air is substantially less than in nitrogen, and the decomposition mechanism is more complex. The global apparent activation energies for the weight loss in air were found to be 116.9 and 159.5 kJ/mol from dynamic slow heat rate data and isothermal data, respectively. The data obtained from fast heating rate experiments in air were found to be misleading, suggesting caution in the use of “commercial” software packages for lifetime estimates under these conditions, especially where oxidative processes may be occurring.
Selective permeation through hydrophobic–hydrophilic membranes
Authors: Park Jun Seo , Ruckenstein Eli 
Published: April 2003

AbstractHydrophobic–hydrophilic composite membranes, containing polystyrene as the dispersed phase and polyacrylamide as the continuous phase, have been prepared by the concentrated emulsion polymerization method. They are highly absorptive for methyl chloride, benzene, and toluene, but poorly absorptive for cyclohexane. The absorption from toluene–cyclohexane mixtures was found to increse with increasing temperature and toluene concentration and to decrease with increasing fraction of polyacrylamide in the composite. The absorption is controlled by diffusion. The permeation rate through the membrane, which was determined by the pervaporation method, exhibits similar trends with respect to temperature, concentration, and fraction of polyacrylamide as absorption does. Higher permeation was obtained by increasing the temperature and by increasing the toluene concentration or by decreasing the fraction of polyacrylamide. The selectivity which was in the range of 4–8 varies inversely with the permeation rate through the membrane which was in the range of 2 × 103−1.0 × 104 g/m2 h.
Molecular weight advancement of poly(ethylene ether carbonate) polyols
Authors: Harris Robert F. 
Published: April 2003

AbstractPoly(ethylene ether carbonate) polyols have been prepared from ethylene carbonate and monoethylene glycol (MEG) or diethylene glycol (DEG) using sodium stannate trihydrate as catalyst. When these polyols (catalyst removed) are heated to elevated temperatures (< 180°C) at reduced Pressures, volatile impurities are removed, as distillate, molecular weight builds in a controllable manner. This is thought to be a transesterification process in which OC(O)CH2CH2OCH2CH2OH end groups on one molecule react with carbonate moieties on a second molecule with loss of DEG. These advanced polyols form rapidly with high CO2 retention and relatively low polydispersity. This process has been characterized by size exclusion chromatography, quantitative capillary gas chromatography of the distillates, 13C‐NMR of the products, and alkaline hydrolysis of the products followed by quantification of the resultant glycols. The advanced polyols are largely alternating copolymers of DEG and CO2. They are valuable polyols for polyurethane fabrication.