bluuebunny/crossref_metadata_2025 huggingface dataset:
Sizes of long branches in low density polyethylenes
Authors: Bugada Daniele C. , Rudin Alfred
Published: April 2003

13C‐NMR spectroscopy and size exclusion chromatography have been used to determine the mean length of long branches in a number of high pressure process low density polyethylenes (LDPEs). 13C‐NMR analyses count all branches longer than C5 as “long.” The polyethylenes studied all had 2–3 long branches per 1000 carbons. The mean branch length was of the order of 200–300 carbons in length. The size of long branches increases with increasing M̄n of the parent polyethylene, but the size of long branches relative to the overall macromolecular size decreases with increasing M̄n. The mean molecular weight of the long branches is some 5–20% of M̄n of the particular polymer and decreases as M̄n increases. Both autoclave and tubular reactor products were studied.
Glycerol contact angle measurements on exterior and interior surfaces of polyethylene rods: Difference between surface and bulk morphology
Authors: Gupta J. P. , Sefton M. V.
Published: April 2003

A difference between surface and bulk morphologies of extruded low density polyethylene (LDPE) has been observed through measurement of the contact angle of glycerol on both exterior and interior surfaces of the extrudate. The sessile drop contact angle on the exterior surface of LDPE rods prepared in a Brabender plasticorder increasea with increasing screw speed (40–180 rpm) and correspondingly increased die pressure at each extrusion temperature (110–130°C). On the other hand, the sessile drop contact angle on the interior surface of LDPE rod, exposed by grinding, decreased with increased screw speed. Qualitative trends were identical with exterior contact angle measured by the Wilhelmy plate method or with the interior surface exposed by fracture. Contact angle variations were interpreted in term of density or crystallinity to suggest that the bulk or interior crystallinity increased with increasing die pressure (even at constant screw speed), while the crystallinity of the exterior decreased with increasing screw speed (even at nearly constant die pressure). The difference between surface and bulk morphologies was consistent with that deduced from DICUP absorption kinetics and optical microscopy [J. Appl. Polym. Sci., 29, 2383 (1984)], although differences were noted in the effect of screw speed on surface morphology.
Surface modification of Egyptian delta titano magnetite ore and its effect on the aqueous polymerization of methyl methacrylate
Authors: Abd‐El‐Hakim A. A. , Badran A. S.
Published: April 2003

The surface modification of Egyptian delta titano magnetite ore (EDTMO) was carried out by adsorption of stearic acid molecules from benzene solution. The adsorption isotherm was found to be one‐step. The modification process affected the sedimentation properties of EDTMO in organic medium. It was found that the maximum stability of EDTMO in organic medium is concerned with monolayer surface formation. The modified EDTMO was found to catalyze the aqueous polymerization of methyl methacrylate and resulted in increasing the viscosity average molecular weights.
Recovery of uranium from sea water. IV. Influence of crosslinking reagent of the uranium adsorption of macroreticular chelating resin containing amidoxime groups
Authors: Egawa Hiroaki , Nakayama Morio , Nonaka Takamasa , Sugihara Eiichi
Published: April 2003

Macroreticular chelating resins (RNH) containing amidoxime groups with various degrees of crosslinking were synthesized by using various amounts of ethyleneglycol dimethacrylate (1G), dimethyleneglycol dimethacrylate (2G), triethyleneglycol dimethacrylate (3G), tetraethyleneglycol dimethacrylate (4G), and nanoethyleneglycol dimethacrylate (9G) as crosslinking reagent. The effect of crosslinking reagents on the pore structure, ion exchange capacity, swelling ratio, and adsorption ability for uranium of RNH was investigated. RNH (RNH–1G) prepared by using 1G were showed to have macroreticular structures by the measure of specific surface area. RNH–1G had the high adsorption ability and physical stability. Though RNH (RNH–4G) obtained by using 4G have little macroreticular structure (macropore), these resins showed the high adsorption ability for uranium by the treatment with 0.1 mol dm−3 NaOH at 30°C for 15 h (alkali treatment). These results suggest that the formation of not only the favorable macropore but also the micropore is important for the effective recovery of uranium in sea water, whereas RNH–4G was defined to be low physical and chemical stability. For the preparation of RNH which have effective pore structure for the recovery of uranium, chemical, and physical stability, the simultaneous use of divinylbenzene (DVB) and 1G or 4G as crosslinking reagent was examined (abbreviated as RNH–DVB–1G and RNH–DVB–4G). The specific surface area of RNH–DVB–1G increased with an increase of 1G used. These RNH–DVB–1G have been shown the high adsorption ability for uranium. On the other hand, the specific surface area and adsorption ability for uranium of RNH–DVB–4G decreased with an increase of 4G used. Repeated use did not cause the deterioration of both RNH–DVB–1G and RNH–DVB–4G. This result suggests that the simultaneous use of DVB and 1G or 4G contributed the improvement of chemical and physical stability. In particular, RNH–DVB–1G has the effective macropore and micropore for the recovery of uranium.
Application of chitosan to cobalt recovery: Evaluation by factorial design of experiments
Authors: Blazquez I. , Vicente F. , Gallo B. , Ortiz I. , Irabien A.
Published: April 2003

A natural polymer in a commercially available form (chitosan) has been tested using a factorial design of experiments for its application to cobalt recovery either in hydrometallurgy and in analytical separations. A simple mechanically stirred system has been used, evaluating the influence of the contact time, iron(II), cobalt (II), chitosan concentration, salinity, and pH in the separation. The pH value has a dramatic influence on the metal recovery from a negligible amount of metals at pH = 1.0 to a quantitative sorption at pH = 3.0. Linear relationships between sorbed metal and the variables have been determined at constant pH value and a quantitative evaluation of the metal recovery at different pH values can be performed using the maximum sorption capacity of the chitosan (a0) and the selectivity for both metals. The obtained results allow the evaluation of the recovery of metals using chitosan as solid phase.
Unsaturated polyesters. III. Kinetics of polyesterification of cinnamylsuccinic acid with ethylene glycol
Authors: Shaaban A. F. , Salem M. A. , Messiha N. N.
Published: April 2003

The polyesterification reactions of cinnamylsuccinic acid with ethylene glycol in both equimolar and nonequimolar ratios were investigated over the temperature range of 130–180°C in the absence and presence of p‐toluene–sulfonic acid as a catalyst. The kinetic equations were: −d[COOH]/dt = k1[COOH][OH]2 and −d[COOH]/dt = k2[COOH]2 for uncatalyzed and acid‐catalyzed polyesterification reactions, respectively. The apparent rate constants for uncatalyzed and acid‐catalyzed reactions were evaluated by using the method of least squares for various values of initial molar ratios between [OH] and [COOH]. Also, the activation parameters were calculated.
Polymers from renewable sources. III. Hydroxy‐terminated myrcene polymers
Authors: Cawse J. L. , Stanford J. L. , Still R. H.
Published: April 2003

A range of hydroxy‐terminated polymyrcenes has been prepared using hydrogen peroxide initiated polymerization of pyrolysate grade, β‐myrcene in n‐butanol solution at 100°C. An oligomeric fraction, containing a large proportion of dimeric material formed via the Diels‐Alder reaction, always accompanies the major polymeric fraction. Procedures are described for the removal of this oligomeric material. Polyols so prepared and purified had number average molecular weights (Mn) between 4000 and 2000 g mol−1 at low and high initiator concentrations, respectively, with corresponding number average functionalities (fn) between 1.3 and 2.3 and polydispersities (Mw/Mn) of ∼ 1.3. The microstructure of the polyols was investigated using NMR spectroscopy from which the main mode of propagation during polymerization of myrcene was deduced to be 1,4 addition across the conjugated double bonds. Glass transition temperatures of the polymyrcenes measured by differential scanning calorimetry were in the range −50–−60°C.
Polymers from renewable sources. IV. Polyurethane elastomers based on myrcene polyols
Authors: Cawse J. L. , Stanford J. L. , Still R. H.
Published: April 2003

Two hydroxy‐functionalized liquid rubbers, one a commercially available polybutadiene (PB) and the other a specially synthesized polymyrcene (PM), have been converted into homopoly‐urethane elastomers by reaction with 4,4′‐diphenylmethane diisocyanate (MDI). Additionally, PB and PM, each in admixture with various amounts of 1,4‐butane diol, were reacted with MDI to yield two series of segmented copolyurethanes having different hard‐block contents (0–30% w/w). The physical properties of these elastomers have been compared by stress‐strain, thermal, and dynamic mechanical analyses, and by swelling experiments. The two series of segmented copolyurethanes have similar morphologies being almost completely phase‐separated and variations in physical properties have been empirically related to hard block contents. The PM‐based elastomers exhibited higher Tg values, ultimate elongations, and larger swelling ratios, but were softer and possessed lower tensile strengths in comparison with elastomers based on PB. These differences have been related to sol‐fraction contents, the nature and distribution of molecular species present in the parent liquid rubbers and hence to polyol functionalities (fn). Analysis of the stress‐strain data from the homopolyurethanes using the Mooney‐Rivlin expression enabled the relationship between fn and elastomer structure to be quantified in terms of the molar mass (Mc) of the polyurethane network chains forming the soft blocks.
Evidence of pyrene formation in butadiene–styrene‐based rubber subjected to UV irradiation
Authors: Abu‐Zeid M. E. , Amer M. F. , Ollis W. D.
Published: April 2003

A strong pyrene emission was observed when certain block, alternate, and random butadiene–styrene‐based rubber films were subjected to intense UV irradiation in vacuum. Weak or no pyrene emission was obtained from the same films when they are irradiated in the presence of O2. A mechanistic scheme leading to pyrene formation in these samples is given together with qualitative explanation of the dependence of pyrene formation on sample composition.
Specific refractive index increments of ethylene–vinyl acetate copolymers in trichlorobenzene solutions at 145°C
Authors: Bugada D. C. , Gagnon R. , Rudin A.
Published: April 2003

Specific refractive index increments of ethylene/vinyl acetate copolymers have been masured in trichlorobenzene at 145°C. A relationship between these values and copolymer composition has been determined for use in light scattering measurements of weight‐average molecular weights of these materials. The data are also required for analysis of molecular weight distributions by size exclusion chromatography with light scattering detection.
Algorithm for computation of molecular weight distribution and its moments in reversible step‐growth polymerization in batch reactors
Authors: Kumar Anil
Published: April 2003

The differential equations governing the molecular weight distribution (MWD) in step‐growth polymerization are coupled and nonlinear and a large number of them must be solved simultaneously to keep the truncation error low. In this work, these equations have been decoupled so that they can be solved sequentially. The solution of these is independent of the truncation error and there is considerable saving of computation time. To demonstrate the efficiency of the algorithm, the formation of polyethylene terephthalate (PET) in batch reactors with ethylene glycol evaporating has been analyzed. The feed to the reactor is taken as polymer with its oligomers present according to the Flory's distribution. The effect of pressure and temperature of the reactor on the progress of polymerization has been modelled and evaluated. The amount of ethylene glycol distilled, the concentrations of the first five oligomers Q1 to Q5, the number average chain length, and the polydispersity index of the polymer have been determined. It is shown that the reduced pressure and increased temperature reduce the concentration of the condensation product in the reaction mass, thus pushing the polymerization in the forward direction. Lastly the CPU time on Dec 1090 using this algorithm is only 0.40 s compared to about 10 min for similar computations using other existing methods.
Rheological parameters of polyolefin suspensions
Authors: Suuronen M. , Seppälä J. , Laine J. , Elovainio E.
Published: April 2003

Effects of rheological parameters of polyolefin suspension were studied to better understand stirred tank polymerization reactors and their engineering principles. Experimental results have been fitted into a quadratic model. Consistency index and behavior index have been determined as functions of solids concentration, temperature, and particle size.
Studies on tri‐n‐butyltin methacrylate (TBTM). IV. Antifouling compositions based on copolymers of tri‐n‐butyltin methacrylate and methyl methacrylate
Authors: Deb P. C. , Chakraborty B. C. , Samui A. B. , Sankholkar S. C.
Published: April 2003

Based on reactivity ratios reported earlier, a number of copolymers of methyl methacrylate and tri‐n‐butyltin methacrylate has been prepared. Release of tri‐n‐butyltin oxide into seawater from the copolymer films has been determined at 30°C as a function of time. The copolymers behave in a typical manner—an initial increase in leaching rate followed by a steady state which is reached after about 60 days. Pigmented copolymer films behave in a similar manner, even though the overall leaching rate is slightly lower. Release rate data are also presented for a typical antifouling paint formulation.
13C‐NMR determination of the tacticity of polyepichlorohydrin
Authors: Cheng H. N. , Smith D. A.
Published: April 2003

The microstructure of polyepichlorohydrin was directly studied by high‐field 13C‐NMR. Spectral features were found that correspond to different tacticities. By using curve deconvolution techniques, the different tacticities were assigned and quantified.
Processing and properties of poly(p‐phenylene benzobisthiazole)/nylon fibers
Authors: Wickliffe Susan M. , Malone Michael F. , Farris Richard J.
Published: April 2003

Composite fibers of poly(p‐phenylene benzobisthiazole) (PBT) with nylons were spun from dilute acid solutions. The effects of wet‐stretching, heat treatment time, tension, and temperature on the tensile properties are reported. Nylon 6,6 and nylon 6 at several molecular weights were studied. Moduli of 40 GPa and tensile strengths of 375 MPa were achieved for 30/70 PBT/nylon composites. Heat treatment of the nylon/PBT fibers at 160–225°C for 12–19 h increased the tensile modulus by 20–50% and the tensile strength by a smaller amount. At the same time, the intrinsic viscosity of the nylons increased as much as 100%, indicating the solid‐state polymerization of the nylon. The largest tensile modulus attained is less than half the theoretical value predicted by a linear “rule of mixtures” as might be expected for an oriented molecular composite. Although differential scanning calorimetry shows a melting transition at temperatures 5–10°C higher than the pure nylons, the composite does not flow at temperatures above this transition. Sulfuric acid dissolves most of the nylon, but does not destroy the mechanical integrity of the fibers; differential scanning calorimetry indicates that the remaining fiber contains little or no nylon. The results are consistent with a microstructure consisting of a microfibrillar network of PBT, surrounded by a separate nylon phase.
A comparative study of the response of cottons to zinc chloride and sodium hydroxide
Authors: Iyer P. Bhama , Sreenivasan S. , Patel G. S. , Iyer K. R. Krishna , Patil N. B.
Published: April 2003

Different varieties of cotton drawn from various botanical species were subjected to swelling and stretching in 64.5% (w/w) aqueous zinc chloride at 32° ± 1°C for different intervals ranging from 10 to 50 min. Swelling was almost complete in 30 min. Samples stretched to original length after this interval showed tremendous improvement in orientation and strength both at zero and 3 mm gauge lengths. In several cases, the improvement was higher than that obtained with similar treatment in sodium hydroxide of mercerizing concentration at room temperature. Swelling in zinc chloride was found to be independent of the variety of cotton as evidenced by the 50% X‐ray angle for the stretched fibers, which was about 9° for all the six cottons included in this study.
Water‐ethanol separation by pervaporation through plasma graft polymerized membranes
Authors: Hirotsu Toshihiro
Published: April 2003

Water‐ethanol permselective membranes were prepared through plasma graft polymerization of acrylic acid, methacrylic acid, and acrylamide onto porous polypropylene film. In these membranes, the functions of permseparation and mechanical properties are shared respectively to the graft polymer layer and the substrate film. Higher permselectivity of water is achieved with the ionization of the acrylic acid and the methacrylic acid‐grafted membranes. Permselectivity is dependent on the degree of grafting, and it is necessary to fill the pores of substrate film with graft polymers. Permseparation of water was investigated with respect to the feed ethanol concentration and also to the temperature dependence.
The effect of moisture on the dielectric behavior of poly(vinyl acetate)–natural rubber blend
Authors: Chuu Michael S. , Meyers Raymond R.
Published: April 2003

Dynamic dielectric analysis was used to analyze the miscibility of poly(vinyl acetate) and natural rubber and the effect of moisture on the dielectric properties of the polymer blend. Two separate dielectric relaxations were observed within the temperature range studied. The high‐temperature relaxation was a result of the glass transition of poly(vinyl acetate), whereas the low‐temperature relaxation was attributed to that of natural rubber. The peak temperatures of ε″ of the high‐temperature relaxation decreased with increasing aging time, while the magnitudes of the ε″ peaks increased with increasing days of aging. The peak temperatures of ε″ of the low‐temperature relaxation stayed constant, while the magnitudes of the ε″ peaks increased with increasing days of aging. This indicates that both polymers are responsible for the sorption of moisture; however, water is an effective plasticizer only for poly(vinyl acetate). Anomalous increases in the magnitudes of ε″, especially in the low frequency sides, of the Argand diagrams were explained by Maxwell–Wagner–Sillar (MWS) polarization at component interfaces. The oscillator strength, relaxation time, and the two distribution parameters, A and B, calculated from the skewed circular are equation, were affected with days of aging.
On‐line studies of structure development during melt spinning of poly(butylene terephthalate)
Authors: Chen Shida , Yu Weiyan , Spruiell J. E.
Published: April 2003

An on‐line study of structure development during poly(butylene terephthalate) melt spinning was carried out. Two polymers with different molecular weights (intrinsic viscosities of 0.75 and 1.0 dL/g) were used. The range of take‐up velocities studied was 1500 to 4500 m/min. On‐line measurements included diameter, temperature, birefringence, and tension. The phenomenon of diameter thinning (necking) was observed for both polymers at take‐up velocities of 3500 and 4500 m/min with a mass throughput of 4 g/min. At a constant mass throughput, the distance from the spinneret at which the necking occurred varied with take‐up velocity and molecular weight of the polymer. Increasing the take‐up velocity at constant mass throughput caused an increase in cooling rate and a slight increase in the rate at which the temperature decreased with distance from teh spinneret. A small but detectable change in the rate of temperature decrease was observed at a position near or just beyond the formation of the neck. It is suggested that this effect is due to the increased heat transfer caused by the rapid increase in filament velocity and increased surface to volume ration in the neck. Increased take‐up velocity also caused necking to occur at higher temperature, as did an increase of polymer molecular weight. Birefringence increased with distance from the spinneret and indicated substantial molecular orientation was developed in the filament prior to the necking zone. A sharp increase of birefringence in the necking zone was observed for take‐up velocities of 3500 and 4500 m/min. A discussion of the mechanism of neck formation is presented, and it was concluded that necking is intimately associated with stress‐induced crystallization in PBT. An increase of spinline stress resulting from either an increase of take‐up velocity or an increase of molecular weight can cause stress‐induced crystallization and, hence, necking to occur nearer the spinneret and at higher temperature. For a given polymer this leads to filaments with higher levels of crystallinity, crystalline orientation, and crystalline perfection (greater crystal size). These changes in morphology result in changes in the filament mechanical properties. The effect of molecular weight change on the structure and properties is complicated by the fact that the development of crystallinity seems to be affected by the molecular weight independent of the spinline stress.
The study on die swell, fiber length distribution, and crystallinity of PP composite through extrusion
Authors: Chiu Wen‐Yen , Shyu Goang‐Ding
Published: April 2003

Die swell of PP and glass fiber reinforced PP (GFRPP) through an extruder was investigated. It was observed that the die swell decreased as (1) the temperature increased, (2) the fiber content increased, and (3) the screw speed was lowered. Fiber length distribution in GFRPP was measured. The average fiber length would increase as (1) the fiber content decreased, (2) the temperature increased, and (3) the screw speed was around 25 rpm. The crystallinity of extrudate was measured by DSC and found to be independent of the screw speed and the fiber content.
New aspects in cationization of lignocellulose materials. VI. Modification of steam‐exploded aspen wood chips with quarternary ammonium groups
Authors: Šimkovic Ivan , Ebringerová Anna , Antal Miroslav , Micko Michael M.
Published: April 2003

Holocellulose prepared from steam‐exploded aspen wood was gradually fractionated with 2.5% NH4OH, 4.5% NaOH, and 17.5% NaOH, respectively. Some residual polysaccharides were extracted from the material in this way, but their yield was only about 5%. Trimethylammonium‐2‐hydroxypropyl (TMAHP)‐derivatives, exploded aspen wood (EXAW), were prepared by the reaction with 3‐chlor‐2‐hydroxypropyl trimethylammoniumchloride (CHMAC) in alkaline medium. The quantity of water and alkali extracted TMAHP–polysaccharides (yield 2.6%) was lower than the yields from modified healthy beech and aspen, as well as rotten aspen. On the other hand, we can obtain more modified cellulose‐rich and lignin‐rich material than from previously mentioned species. The steam‐explosion process is suitable for increasing the accessibility of cellulose component in lignocellulose material for chemical modification.
Synthesis and characterization of poly(vinyl carbazole) complexes with copper(II) chloride in THF solution
Authors: Katime Issa A. , Ochoa Jose R. , Nido Carlos Sieiro Del
Published: April 2003

Several polymer‐metal complexes were prepared by reacting poly(vinyl carbazole) (PNVC) with copper(II) chloride, CuCl2.2H2O, in refluxing tetrahydrofurane (THF) for mole ratios of CuCl2.2H2O to monomeric unit (Cu:PNVC ratio) ranging between 0.086 and 4.98. Complexes were characterized by infrared (IR) and elemental analysis. Thermal behavior of complexes was studied by differential thermal analysis (DTA). It appears that THF behaves as a specific solvent for complexation of PNVC with copper(II) chloride.
Determination of the structure and composition of clinically important polyurethanes by mass spectrometric techniques
Authors: Richards Joseph M. , McClennen William H. , Meuzelaar Henk L. C. , Shockcor John P. , Lattimer Robert P.
Published: April 2003

Curie‐point pyrolysis mass spectrometry (Py‐MS) and direct probe pyrolysis high resolution mass spectrometry (Py‐HRMS) were used to identify the components and additives used in the synthesis and compounding of Biomer, Lycra Spandex, Tecoflex, and Pellethane. Two types of Biomer were identified (P and Q, our notation) which are composed of poly(tetramethylene glycol) (PTMG) capped with 4,4′‐methylenebis(phenylisocyanate) (MDI) and chain‐extended with ethylenediamine (EDA). Both forms contain 4,4′‐butylidene‐bis‐(6‐t‐butyl‐m‐cresol) antioxidant, and Biomer Q also contains an additive which appears to be a quaternary ammonium chloride salt. Lycra Spandex was found to be identical to Biomer Q, with the exception that a low molecular weight polydimethylsiloxane oil is also present. This silicone oil can be removed by solvent extraction. Tecoflex (type SG80A) is composed of PTMG capped with 4,4′‐diisocyanatodicyclohexylmethane and extended with 1,4‐butanediol (BD). An industrial grade and a medical grade of Pellethane were analyzed. Both were composed of PTMG capped with MDI and extended with 1,4‐butanediol. the industrial grade also contains an antioxidant, possibly butylated diphenylamine.
Characterization of cured polysulfide polymers by thermal degradation: Pyrolysis‐GC and thermogravimetric studies
Authors: Radhakrishnan T. S. , Rao M. Rama
Published: April 2003

Polymers prepared by curing thiol‐terminated liquid polysulfide polymer [HS(RS2)nRSH, R = CH2CH2OCH2OCH2CH2] with p‐quinonedioxime, PbO2, and MnO2 were studied by pyrolysis‐GC and thermogravimetry. Characteristic differences were observed in the composition of the pyrolyzates under flash pyrolysis at 420 and 470°C. The concentration of the cyclic monomer, 1,3‐dioxa‐6,7‐dithionane, in the pyrolyzates was found to vary considerably from polymer to polymer. The change in mechanism with the extent of degradation and the corresponding overall activation energies were evaluated by thermogravimetry. The pyrolysis‐GC and thermogravimetric data were shown to provide partial characterization of the substrates. Mn appears to be in a coordinated complex in the MnO2‐cured polymer.
Polysulfone‐bonded polyvinylpyridinium membranes
Authors: Montoneri E. , Orlandoni A. M. , Modica G. , Maffi S. , Pappalardo G. C.
Published: April 2003

Polydivinylbenzene‐4‐vinyl‐N‐methylpyridinium iodide (MeVP+‐DVBI−) membranes are obtained by solvent evaporation from dispersions of copolymer powder in polysulfone dichloroethane solutions. The membranes' macroporosity increases from 2.5 to 46.4% and the pore size distribution concentrates in the 103–105 Å range upon varying the concentration of polypyridinium polymer from 0 to 67% w/w. Similarly, the specific conductivity increases from 10−11 to 10−4 ohm−1 cm−1 and the mechanical strength decreases from 500 to 8.8 kg/cm2. The ion selectivity is maximum at 40–50% MeVP+‐DVBI− and lower above or below this concentration range. The properties are discussed in relation to the membrane chemical and physical parameters.
Plasma‐polymerized membranes and gas permeability III
Authors: Sakata Jiro , Hirai Masana , Yamamoto Minoru
Published: April 2003

Plasma‐polymerized films of hexamethyldisiloxane were deposited onto various porous substrates having different pore sizes, and the gas permeability of these composite membranes was studied. In each membrane, permselectivity between oxygen and nitrogen was found, but the oxygen permeation rate was different with each substance tested. The minimum thickness of the plasma‐polymerized film needed to plug all pores and show permselectivity is about five times the pore radius of the porous substrate. The maximum oxygen permeation rates of the permselective composite membranes are approximately proportional to the effective areas for the gas permeation and inversely proportional to the pore sizes. The composite membranes show high oxygen permeation rates in cases using porous glass hollow fibers which have small pore sizes and large surface porosity as porous substrates. In cases using polysulfone hollow fibers which have high permselectivity, the composite membranes show much higher permeability ratios of oxygen‐to‐nitrogen than do those of the porous glass hollow fibers.
Photosensitive resins containing p‐dimethylaminobenzylidene derivatives and diphenyliodonium salt as photoinitiators
Authors: Ichimura K. , Kameyama A. , Hayashi K.
Published: April 2003

A series of p‐dimethylaminobenzylidene derivatives was able to sensitize the photodecomposition of diphenyliodonium salt to afford highly photosensitive negative‐type resins. When a polymer‐bearing methacryloylated group in the side chain was sensitized with a combination of the p‐dimethylaminobenzylidene compounds and the iodonium salt, the polymer demonstrated high sensitivity even to 488 nm light emitted from an Argon laser. The same photoinitiator systems were applicable to insolubilize poly(glycidyl methacrylate) through cationic photopolymerization. The storage stability of these types of photoinitiators depends on the structure of the benzylidene compounds; decreasing the basicity of the amino group enhanced the thermal stability.
Effect of high energy radiation on the stress–relaxation of ultra‐high molecular weight linear polyethylene
Authors: Bhateja S. K. , Andrews E. H.
Published: April 2003

Stress–relaxation behavior was studied in ultra‐high and normal molecular weight linear polyethylenes (UHMWPE and NMWPE) as a function of radiation dose over the range 0–128 Mrad. Irradiation up to 16 Mrad raises the crystallinity in both types of PE, as demonstrated previously,1 and thus increases the initial modulus. Also, the initial modulus of NMWPE is higher than that of UHMWPE because the former has a higher crystallinity. Consequently, the initial stress at a constant imposed strain of 1% varies greatly between the two materials. To eliminate the effect of this initial difference on relaxed stress, the stress–relaxation data were normalized with respect to the initial stress and plotted as the fraction, retained stress after time t/initial stress. The normalized plots show no significant difference between NMWPE and UHMWPE in their stress–relaxation behavior. For both materials stress retention improves progressively with increasing radiation dose, the percentage improvement being greatest at long times (50% at 50 h and 64 Mrad, compared with 6% at 10−2 h). These results are interpreted to indicate that radiation crosslinking in the amorphous phase is independent of molecular weight and preferentially retards those molecular motions responsible for short relaxation times. The motions in question could involve molecular flow in the amorphous phase or “pull out” of tie molecules from the crystalline lamellae.
Relationship between the mechanical relaxations in the α zone and the calorimetric transitions in low density polyethylene
Authors: Ribes‐Greus Amparo , Diaz‐Calleja Ricardo
Published: April 2003

The α‐relaxation spectra of LDPE, irradiated and unirradiated, has been compared with their calorimetric thermograms. There exists a correlation between the two mechanical relaxations that appear in the α zone and the two fusion peaks observed in the calorimetric thermograms, confirming that the parameter that governs the temperature of the relaxations αI and αII is the most probable crystallite thickness, whereas the height of the α‐relaxation zone, as measured by means of tan δmax, depends on the total crystalline content of the sample.
Aggregation of basic dyes induced by anionic polyelectrolytes
Authors: Neumann Miguel G. , Hioka Noboru
Published: April 2003

The aggregation of basic dyes in aqueous solution in the presence of polyelectrolytes has been studied to determine the nature of the interaction between the dye molecules and the polymer sites. The aggregation induced by carboxymethylcellulose with isolated anionic sites cannot be explained assuming interaction between dye molecules bound to neighbouring sites. Maximum aggregation for various dyes on that polyelectrolyte has been found around P/D = 0.3 whereas for PSS that value is found around 1. Dimerization constants calculated for these systems are in good agreement with the values expected from dimerization in aqueous solutions. A new model is proposed to explain these results.
Photoacoustic monitoring of adhesive curing
Authors: Torres‐Filho A. , Perondi L. F. , Miranda L. C. M.
Published: April 2003

The crosslinking reaction of an epoxy‐based resin has been monitored by observing the time evolution of the thermal diffusivity of the mixture, using photoacoustic spectroscopy. The results are interpreted in terms of the expected thermal properties of liquids, polymers and solids, and a comparison with the reported viscosity behavior in similar systems is also made. The potential of the technique for following the curing process is discussed.
Effect of methylene chloride sorption on the mechanical properties of poly(aryl‐ether‐ether‐ketone) (PEEK)
Authors: Pao Peter S. , Grayson Michael A. , Wolf Clarence J.
Published: April 2003

The effect of sorbed methylene chloride on the tensile strength and fatigue crack growth (FCG) resistance of PEEK were determined. PEEK sorbs up to 23 wt% methylene chloride; the transport process is essentially Case II, that is, the methylene chloride advances as a sharp front. Sorbed methylene chloride significantly reduces the tensile strength of neat PEEK and the strength reduction is linearly proportional to the amount of solvent sorbed. FCG rates in neat PEEK are increased by the methylene chloride sorption. At saturation, the FCG rates are two orders of magnitude higher than in dry PEEK. Methylene chloride plasticizes the resin, thereby reducing its glass transition temperature (Tg), tensile strength, and FCG resistance.
Preparation of aldehydocelluloses from completely allylated methylcellulose, allylated ethylcellulose, and tri‐O‐allylcellulose by ozonization
Authors: Kondo Tetsuo , Ishizu Atsushi , Nakano Junzo
Published: April 2003

In order to prepare aldehydocelluloses which are more stable than periodate‐oxidized cellulose, completely allylated methylcellulose, allylated ethylcellulose, and tri‐O‐allylcellulose were subjected to ozonization followed by reduction with dimethylsulfide. The aldehydocelluloses thus prepared without any degradation showed the presence of many free aldehyde groups by IR and 13C‐NMR spectrometries, as well as the presence of hydroxyl groups which were produced by deallylation. The degree of substitution (DS) by aldehyde group was 0.6 for the products from both completely allylated methylcellulose and tri‐O‐allylcellulose, and 0.02 for that from allylated ethylcellulose.
ESR study and copolymer analysis of acrylamide‐methacrylamide solid solutions
Authors: Ramelow Ulku , Baysal Bahattin M.
Published: April 2003

When acrylamide‐methacrylamide mixed crystals are irradiated by ultraviolet (UV) rays, a copolymeric sample is obtained containing both monomeric constituents. For identification and quantitative analysis of these copolymers, a modified form of UV spectroscopy was used. The greatest advantage of UV spectroscopy for copolymer analysis lies in its rapid application. A comparison of the spectrum of the unknown compositions with spectra of known systems by using a calibration curve and the shifts in absorption maxima in different concentrations are valuable aids in establishing the composition. Electron spin resonance (ESR) provides a correlation between the obtained copolymer composition and the shape of the signal of the responsible radical. ESR spectra obtained for UV‐irradiated acrylamide‐methacrylamide mixed crystals reveal that during polymerization both radicals are present. As methacrylamide percentage increases in the mixture, the signal becomes similar to the 9‐line spectrum of pure methacrylamide. When there is 90% methacrylamide present in the original mixture, a 5‐line signal is observed, with even‐numbered peaks in the methacrylamide signal appearing now as shoulders. When the methacrylamide percentage is about 16%, a characteristic 3‐line signal of acrylamide is dominant. As the methacrylamide percentage increases in the original mixture of the copolymers, ESR signals indicate a decrease in the rate constant values for second‐order decay at 60°C. The stability of the formed radicals was studied by admitting oxygen to the copolymeric samples as well as to the homopolymeric systems. Since the peroxidic radicals are more active in the hydrogen abstraction process, they decay more rapidly than the macro radical itself by a bimolecular termination reaction. As the methacrylamide percentage increases in the copolymeric mixtures, the peroxide radical formation becomes more difficult. This indicates that polymethacrylamide brings more stability in copolymerization reactions with acrylamide. The polymerization rate of both monomers and their mixed crystals were enhanced by adding chlorine gas before irradiation. Chlorine acts as an agent for slowing down the radical decay as well as accelerating the radical initiation reactions.
Studies on the reaction of bis(diisopropyl) thiophosphoryl disulfide with silica in the vulcanization of NR
Authors: Mandal Swapan Kumar , Datta Rabindra Nath , Das Prasanta Kumar , Basu Dipak Kumar
Published: April 2003

The reaction between bis(diisopropyl) thiophosphoryl disulfide (DIPDIS) and silica has been investigated. The study reveals that DIPDIS can be used as a coupling agent for silica. The chemical bond between the silanol groups of silica and DIPDIS has been established through the isolation and characterization of isopropyl alcohol that is eliminated from the reaction. The chemical nature of the bond is also supported by the IR analysis of the reaction products of silica and DIPDIS obtained both in the presence and absence of rubber. From the exploratory studies it is indicated that DIPDIS can also react with NR even during mixing of ingredients. When used with 2‐mercaptobenzothiazole (MBT) or N‐oxydiethylene‐2‐benzothiazole sulfenamide (OBTS) in the presence of silica, DIPDIS exhibits notable activation of cure and enhances the torque, modulus, tensile strength, and the scorch safety.
Stress relaxation and the domain structure of thermoplastic elastomer
Authors: Hsiue Ging‐Ho , Chen Der‐Jang , Liew Yeong‐Kang
Published: April 2003

The relationship between the stress relaxation phenomena and domain structure of thermoplastic elastomer (TPE) was studied. Two representative thermoplastic elastomers: styrenebutadiene‐styrene block copolymer (SBS) and 1,2‐syndiotactic polybutadiene (1,2‐PB), representing the amorphous glassy domain and crystalline domain, respectively, were tested in different atmospheres and temperatures. Results show that the structure of the domain has a significant effect on the stress relaxation curve. It is found that the way the glassy domain is formed determines the failure of the domain and hence the stress relaxation rate. In the case of crystalline domain, the history of heat treatment determines the crystal structure and, in turn, the stress relaxation rate.
Reactive extrusion of polypropylene I: Controlled degradation
Authors: Suwanda D. , Lew R. , Balke S. T.
Published: April 2003

Polypropylene was degraded by injection of a free‐radical initiator during extrusion. Molecular weight distribution, molecular weight averages, and melt flow index were measured to see the effect of initiator concentration (0.00 to 0.04 wt%), temperature (200 and 220°C), and screw rpm (31 and 44). Initiator concentration was the most significant variable. In all cases, increased initiator concentration degraded the high molecular weight tail of the polypropylene and narrowed the molecular weight distribution. Melt flow index varied linearly with initiator concentration beyond 0.01 wt% initiator. Reaction temperature had no effect on the measured properties of the extrudate. This was attributed to the minimum residence time in the extruder being sufficient for all degradation reactions to be completed. It also implied that the same reactions occurred at both temperatures. Increased screw rpm slightly increased molecular weight. No interaction among initiator concentration, temperature, and screw rpm was observed.
Modeling reverse osmosis separations with strong solute‐membrane affinity at different temperatures using the finely porous model
Authors: Connell P. J. , Dickson J. M.
Published: April 2003

The reverse osmosis separation of toluene from water has been studied using an asymmetric cellulose acetate membrane at different temperatures, pressures, and feed concentrations. The finely porous transport model is used to describe the performance of the membrane as a function of the operating conditions. Based on experimental data, the transport parameters for the membrane are estimated. These parameters include the pore size of the membrane, the frictional parameter for the solute in the membrane pore, the relative porosity of the membrane surface, and the partition coefficients on the high and low pressure sides of the membrane. The influence of operating temperature on some of these parameters is presented and discussed. A modified form of the finely porous model which includes the effect of temperature is presented.
Investigation on the long‐term behavior of polyethylene and poly(vinyl chloride) under static load
Authors: Natov M. , Vassileva St. , Evtimova S.
Published: April 2003

The long‐term behavior of high density polyethylene (HDPE) and poly(vinyl chloride) (PVC) under static mechanical load is investigated. The long‐term behavior is determined as a function of stress and temperature. The applicability of the equation proposed by the authors which describes the dependence between the time‐dependent failure, stress, and temperature of the two polymers is examined. The equation, derived on theoretical considerations, represents a modification of the Arrhenius equation for the chemical reaction rate. It is found that there is a complete agreement between the experimentally determined long‐term behavior of PVC and HDPE and that calculated by the equation over the whole examined range of temperatures and stresses, with the exception of narrow intervals for HDPE where an intensive plastic deformation is developed.
Microstructural investigations of PBT/nylon 6,6 composites
Authors: Néhmé O. A. , Gabriel C. A. , Farris R. J. , Thomas E. L. , Malone M. F.
Published: April 2003

The microstructure of composites made from blends of poly(p‐phenylene benzobisthiazole) [PBT] and nylon 6,6 has been investigated with wide‐angle X‐ray diffraction, selected area electron diffraction, and small‐angle X‐ray scattering techniques. The composite samples investigated were spun in both fiber and film forms dilute solutions of methane sulfonic acid.

The structure of the composites was found to be a microfibrillar network of PBT in a matrix of partially crystalline nylon 6,6. The diameters of the PBT microfibrils were in the range of 30 to 70 Å.
The fibrillar structure of cellulosic man‐made fibers spun from different solvent systems
Authors: Lenz J. , Schurz J. , Wrentschur E.
Published: April 2003

The development of new methods of spinning cellulosic fibers requires a better understanding of their fibrillar structure in order to explain their special physical properties. By means of transmission electron microscopy (TEM), light microscopy (LM), small‐angle X‐ray scattering (SAXS), and wide‐angle X‐ray diffraction (WAXD) it is shown that six different kinds of regenerated cellulosic fibers consist of uniform elementary fibrils composed of cellulose‐II crystals. Systematic distinctions between these fiber types are found with regard to the aggregation of the elementary fibrils to nonswelling bundles or clusters. The clusters differ from each other in diameter, length, and frequency of occurrence.
Crystallization of cellulose
Authors: Paralikar K. M. , Aravindanath S.
Published: April 2003

Crystallization of cellulose from low DP acetylated hydrolyzed bagasse pulp has been studied. The morphology of the crystals obtained after crystallization at 50°C for different intervals of time (5, 20, and 40 days) revealed needle‐shaped, elongated, ribbonlike fibrous crystals. The electron diffraction pattern obtained on these crystals was typical of cellulose II lattice.
Low temperature exotherm in starch/water systems: A retrogradation marker
Authors: Kwak Yoon Tae , Winter William T.
Published: April 2003

DSC measurements at slow ( < 1.0°C min−1) heating speeds reveal a crystallization exotherm in the −4‐−6°C region for starch/water systems. The same exotherm is not observed for other polysaccharides such as guar and is sensitive to chemical modification of the starch sample. The DSC thermograms have been interpreted in terms of three different levels of water organization in the starch matrix.
Grafting of methyl methacrylate onto guar gum by hydrogen peroxide initiation
Authors: Raval Dipak K. , Patel Ranjan G. , Patel Vithal S.
Published: April 2003

Graft copolymerization of methyl methacrylate (MMA) onto guar gum (GG) in aqueous slurry has been carried out using hydrogen peroxide (H2O2) as initiator. The copolymers were characterized by infrared spectroscopy. The grafting parameters like percent grafting, grafting efficiency, percent add‐on, and the grafting frequency were determined, and the effect of reaction time, concentration of initiator, and [GG]/[MMA] ratios on the grafting parameters have been discussed. The decrease in % add‐on at increasing concentration of H2O2 indicated enhancement in the rate of homopolymerization of methyl methacrylate.
A method for calculating dynamic mechanical properties using fourier transforms of pulse deformation experiments
Authors: Vratsanos Menas S. , Farris Richard J.
Published: April 2003

A general method for determining the dynamic mechanical properties of a material is presented. It involves Fourier transforms of the stress and strain responses of a material subject to arbitrary deformation. As an example, uniaxial pulse‐strain deformations were used to calculate the dynamic properties of a cured epoxy. A comparison of the properties calculated from uniaxial sinusoidal deformations and those obtained by Fourier transform analysis of the uniaxial pulse‐strain indicate excellent agreement over a wide range in mechanical behavior. These results suggest that dynamic mechanical properties may be obtained when deformations other than that of a sine wave are used.