bluuebunny/crossref_metadata_2025 huggingface dataset:
Some aspects of autoignition delays and flammability limits of polyurethane based on diphenyl methane diisocyanate (MDI) and propoxylated trimethylol propane
Authors: Gaboriaud F. , Vantelon J. P. , Breillat C.
Published: April 2003

The main purpose of this work is a better understanding of the physicochemical phenomena involved during an unpiloted ignition. We intend to characterize the step corresponding to the degradation of the material, the production of combustible gases, and their combustion with the surrounding oxidizing gas, leading to the flame. The degradation gases which are essentially alkanes, alkenes, and aldehydes undergo oxidation by degenerate chain branching mechanism. The initiating chain propagates very quickly and creates intermediate species of increased stability which initiate new active centers leading to secondary chains. Then, ignition can occur after a relatively large induction period. We suggest that this period may be defined as the time to reach a critical rate of production of the intermediate species. A study of the active center distribution near the surface as a function of time and of the distance to the surface allows us to explain the experimental variation of ignition delays vs. oxidant pressure. The ignition limits of this polyurethane, i.e., temperature–pressure curves in air and in oxygen, have also been determined. It has been possible to correlate pressure and temperature and to specify the influence of nitrogen on the ignition process.
Reduction and hydroboration with borane and haloborane complexes of poly(propylene sulfide) grafted on crosslinked polystyrene
Authors: Domb Abraham , Avny Yair
Published: April 2003

Preparation of borane and haloborane complexes of poly(propylene sulfide) grafted on crosslinked polystyrene was investigated. Graft polymer–borane was prepared by reaction of graft polymer with B2H6 and BH3–THF. Graft polymer–haloborane was prepared by reaction with haloborane–tetrahydrofuran and by reaction of borane‐bound graft polymer with halogen. Graft polymers with high borane (2.44 mmol/g) and haloborane (163 mmol/g) content were reached. The use of these graft polymers as polymeric reagents for reduction of carbonyl compounds and hydroboration was investigated. Aldehydes, ketones, carboxylic acids, and esters were reduced in high yields to the corresponding alcohols by borane‐bound graft polymer. The graft polymer showed good chemoselectivity in competative reduction of cyclohexanone and other ketones and aldehydes, as well as in competative reduction of acetophenone and benzaldehyde. Reactivity of graft and homopolymer–borane was similar to that of borane–methyl sulfide. Hydroboration of alkenes with these graft polymers, followed by alkaline oxidation, led to the formation of the corresponding alcohols in high yields. Hydroboration was highly regioselective. Stability of the graft polymer–borane and recycling of that graft polymer were investigated. Cleavage of the poly(propylene sulfide) by the borane bound polymer took place to some extent. At 0°C no borane loss was found over a 5‐week period. When recycled, 85% of the original borane content could be regenerated at the end of the fourth cycle.
Control of free‐radical emulsion polymerization of methyl methacrylate by oxygen injection. II. Experimental study
Authors: Louie Brian M. , Franaszek Thomas , Pho Tina , Chiu Wen Yen , Soong David S.
Published: April 2003

Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order‐of‐magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate.
The chemistry of a polyamide–epichlorohydrin resin (hercosett 125) used to shrink‐resist wool
Authors: Guise G. B. , Smith G. C.
Published: April 2003

A polyamide–epichlorohydrin resin used to shrink‐resist wool [Hercosett 125 (Hercules Inc.)] was separated by ultrafiltration into fractions A, B, and C (in the approximate proportions 60, 40, and 2 by weight), which correspond to the three peaks in size exclusion chromatograms (SEC). Viscosity, spectra, and SEC results as well as results of experiments on the reaction of the parent polyamino–polyamide (PAA) with epichlorohydrin indicated that fraction A was high‐molecular‐weight crosslinked material whereas fraction B was essentially uncrosslinked. Fraction C was minor impurity, possibly a mixture containing a triazine, and it was also found in the PAA from which the original resin was prepared. High‐resolution proton NMR spectra of the Hercosett 125 indicated that chlorohydrin or epoxy groups were absent, and thus confirmed an earlier 13C‐NMR study that only azetidinium reactive groups were present. Two reactions are believed to occur in Hercosett 125 on storage: hydrolysis of azetidinium to dihydroxypropyl groups and hydrolysis of backbone amides. The small differences in the properties of wool treated with either A or B fractions, and those of wool treated with unfractionated Hercosett 125, were related to the extent of crosslinking before and after curing. As the extent of crosslinking increased, the amount of staining by an anionic dye decreased, and the shrink resistance improved slightly.
Investigation of the action of flame retardants in cellulose. I. Investigation of the flame retardant action of 2,2′‐oxybis(5,5‐dimethyl‐1,3,2‐dioxaphosphorinane‐2,2′‐disulfide) in cellulose
Authors: Choudhary Marjeet S. , Fink Johannes K. , Lederer Klaus
Published: April 2003

Pyrolysis experiments were performed in high vacuum and under reduced air pressure (100 Pa). The volatile products of pure cellulose and cellulose containing various amounts of flame retardant 2,2′‐oxybis (5,5‐dimethyl‐1,3,2‐dioxaphosphorinane‐2,2′‐disulfide), i.e., Sandoflam 5060 of Sandoz AG, were studied by means of gas chromatography in combination with mass spectroscopy. The volatile products were characterized with infrared spectroscopy. The studied revealed that the incorporation of the flame retardant enhanced the water release and shifted the onset of this reaction to lower temperature. On the basis of these findings an explanation for the mechanism of flame retardancy in generated cellulose fibers modified with this particular flame retardant is attempted. From experiments with different residual air pressure the influence of oxygen on the primary processes of the pyrolytic degradation of cellulose is being discussed.
Structure‐property relationships in thermoplastic elastomers III. Segmented polyacetal‐polyurethanes
Authors: Xu Baobei , Khanna D. N. , Lillya C. Peter , Chien James C. W.
Published: April 2003

Dihydroxy‐terminated polyacetals had been synthesized from aldehydes and glycols and used as soft segments to obtain segmented polyurethane block copolymers. For soft segment ≥ 1700Mn, the Tg ranges from–48 to −58°C and is insensitive to the structures of diisocyanate and chain extender. The Tg of PacPU with 1350 Mn polyacetals is raised to −38°C, and none was observed for shorter polyacetal chains. The copolymers can be synthesized to have a broad range of mechanical properties, such as modulus from 0.5 to 130 MPa, stress at break from 0.7 to 21 MPa, and elongation at break from 66 to 1300% through the variation of the constituents and composition. The rheologic properties are only slightly dependent on temperature for symmetrical diisocyanates but quite temperature sensitive with asymmetric diisocyanate copolymers. The polyacetals are selected to build in acid‐catalyzed thermal decomposition of the thermoplastic elastomers. The extreme acid sensitivity of the polyacetal block is buffered in the coplymers.
Graft copolymerization of methyl methacrylate (MMA) on hydrazine treated oxycellulose in limited aqueous system
Authors: Ghosh Premamoy , Dalal Jagadish Chandra
Published: April 2003

Graft copolymerization of methyl methacrylate (MMA) on oxycellulose modified with hydrazine treatment was studied in a limited aqueous system using K2S2O2 as the initiator. Hydrazine modified oxycellulose prepared from oxycellulose corresponding to low degrees of oxidation (copper nos. 2–6) produced the best grafting effects. Grafting parameters under different sets of conditions were studied and compared and the mechanism of graft copolymerization discussed.
Oxidative susceptibility of partially carboxymethylated cotton to gamma radiation
Authors: Hebeish A. , Zahran A. H. , El‐Naggar A. M. K.
Published: April 2003

Partially carboxymethylated cotton with a DS of about 0.05–0.15 retains its original fibrous nature and exhibits a number of potentially valuable properties, such as a crisp hand with a slightly starched feel, increased moisture regain, water absorbancy, water permeability, changed dyeing characteristics, increased resistance to soiling from aqueous dispersions, and greater ease of soil removal.5–8 Furthermore, detailed studies have been reported on the behavior of partially carboxymethylated cotton toward oxidation and hydrolysis,9 vinyl graft polymerization,10 transfer printing,11,12 cross‐linking,13 and thermal treatments.14
Preparation of high‐modulus and high‐strength poly(ethylene terephthalate) film by zone‐annealing method
Authors: Kunugi Toshio , Ichinose Chie , Suzuki Akihiro
Published: April 2003

The zone‐annealing method was attempted to prepare high‐modulus and high‐strength poly(ethylene terephthalate) (PET) film. The film having Young′s modulus of 14.5 × 1010 dyn/cm2 and a tensile strength of 86.9 kg/mm2 in the drawing direction was obtained. These values correspond to four times those of a biaxial‐stretched PET film available commercially. The dyanmic viscoelastic properties also were measured. The dynamic storage modulus was 15.4 × 1010 dyn/cm2 at room temperature, and a high value of 3.6 × 1010 dyn/cm2 even at 200°C. The latter value is slightly higher than the room temperature modulus of the commercially available film. From the intensity and temperature position of α‐dispersion E″ peak, it was suggested that the amorphous chains in the zone‐annealed film was densely packed in a highly oriented state. Furthermore, the crystallinity, orientation, especially double orientation, and molecular chain conformation of the films in the zone‐annealing process are discussed in the present paper.
Swelling properties of copolymeric hydrogels prepared by gamma irradiation
Authors: Huglin Malcolm B. , Zakaria Mat B.
Published: April 2003

Crosslinked xerogels in the form of rods have been prepared to > 99.9% conversion by the γ‐ray initiated copolymerization in vacuo ob n‐butyl acrylate (BA) with N‐vinyl‐2‐pyrrolidone (VP) in the presence and absence of a crosslinking agent. Thin (about 0.5 mm) disks were swollen in water at 21°C, the final equilibrium swelling being the true water content only for copolymers of high BA content. At low‐medium BA content, swelling was accompanied by the release of a small water‐soluble fraction, leading to a slightly reduced apparent value for the water content. True water contents could be obtained more rapidly by prior Soxhlet extraction with boiling water. For xerogels containing > about 75% VP by weight, the resultant hydrogels had water contents > about 80%. The influences of dose, dose rate copolymer composition, and concentration of crosslinker on the water content, sol fraction, and extension ratio were investigated. A high level of reproducibility in properties of the hydrogels was obtained by numerous replicate experiments. The feasibility of scaling up the preparation to produce long (60 cm) xerogel rods of uniform properties has been demonstrated. For these copolymers, swelling in several common organic solvents generally exceeds that in water.
Synthesis of N,N′‐bis [(dialkoxyphosphinyl) methyl]‐1,4‐benzenediamines and the corresponding polymers
Authors: Kallitsis J. K. , Tsolis A. K.
Published: April 2003

The title diamines were synthesized by condensation of 1,4‐phenylenediamine with paraformaldehyde and a suitable phosphorus acid triester. The N,N′‐dibenzoyl derivatives of the above compounds were also prepared. New flame‐retardant polyamides were synthesized under various experimental conditions by condensation of these diamines with terephthaloyl dichloride. The polyamides produced have low viscosities. Blends with polystyrene (PS) have been made and their flammabilities determined.
Semi‐ and fully interpenetrating polymer networks based on polyurethane‐polyacrylate systems. VIII. The influence of the degree of crosslinking of the second formed network on the morphology and properties of polyurethane polymethylacrylate interpenetrating polymer networks
Authors: Hourston D. J. , McCluskey J. A.
Published: April 2003

A series of polyurethane–polymethylacrylate sequential interpenetrating polymer networks containing 40% by weight of polyurethane were prepared in which the levels of crosslinking in the second formed network—polymethylacrylate—was systematically altered over a wide range. The polymethylacrylate networks and the interpenetrating polymer networks were investigated using dynamic mechanical analysis, sonic velocity measurements, and tensile testing. In addition, the interpenetrating polymer networkds were studied using transmission electron microscopy. The interpenetrating polymer networks showed high values of the Oberst damping factor. It was concluded that tightening the second formed network does not produce the dramatic effects associated with decreasing the average molecular weight between crosslinks of the first formed network.
Copolymers of ethylene with butene‐1 and long chain α‐olefins. II. Dodecene‐1 as long chain α‐olefin
Authors: Seppälä Jukka Veli , Oy Neste
Published: April 2003

Ethylene/dodecene‐1 and ethylene/butene‐1/dodecene‐1 copolymers were prepared and their polymerization reaction in heptane slurry was studied. The Ziegler–Natta catalyst was aluminium‐activated TiCl3, and the cocatalyst was triethylaluminium. The dodecene‐1 contents in the ethylene/dodecene‐1 copolymers were less than 3 wt %. The dodecene‐1 contents in terpolymers of ethylene, butene‐1, and dodecene‐1 ranged up to 10 wt %. The dependence of basic properties on composition of terpolymers was investigated.
Analytical and physical investigation of alkyd resin in the course of its preparation. I. Determination of composition of reaction mixture using volatile monocarboxylic acid for alkyd synthesis
Authors: Kaštánek Alois , Hájek Karel , Dufka Oldřich
Published: April 2003

The extent of esterification between isocaprylic acid, phthalic anhydride, glycerol, and pentaerythritol was followed by analysis of reaction mixture. Acid numbers, hydroxyl numbers, and saponification numbers of alkyd samples were determined at different stages of the reaction. A way of calculation of the losses of volatile monomer reactants from liquid reaction mixture was proposed. The amounts of condensed water experimentally measured during alkyd synthesis correspond to the amounts of water losses from the batch that were calculated.
Chemical modification of Kevlar fiber surfaces and of model diamides
Authors: Wu Yulong , Tesoro Guiliana C.
Published: April 2003

Organic reactions of aromatic diamides as models for PPTA fibers have been investigated to select reagents and conditions suitable for surface‐controlled heterogeneous reactions on Kevlar filaments and fabrics. Amine functional groups have been incorporated into fiber surfaces by bromination followed by ammonolysis and by nitration followed by reduction. Modification of filaments has been attained without impairment of fiber properties. Preliminary experiments have also shown that the presence of amino groups on Kevlar fabric can provide remarkably improved peel strength and apparent interlaminar shear strength in epoxy laminates, suggesting a significant role of covalent bonding in improving adhesion in aramidepoxy composites.
Selective transport of inorganic ions along CA membranes
Authors: Yellin N. , Ben‐Dor L. , Zelingher N.
Published: April 2003

Transport of inorganic ions along asymmetric cellulose acetate (CA) membrane from aqueous binary systems with a common ion: KCl–NaCl, Na2SO4–CuSO4, K2CrO4–KNO3, KCl–CaCl2, and NaCl–LiCl was studied. The transport proceeds via the support matrix of the membrane and can be measured by the growth of whiskers on its exposed surface and the change of composition of the solution. Differences in the growth rates resulted from differences in transport rates of the various ions. The selectivity of the membrane is attributed to the interaction support matrix–water–ion.
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 homopolyurethane elastomers by reaction with 4,&4prime;‐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 phaseseparated 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 strenghts in comparison with elastomers based on PB. These differences have been related to solfraction contents, the nature and distribution of molecular species present in the parent liquid rubbers and hence to polyol functionalities (f̄n). Analysis of the stress–strain data from the homopolyurethanes using the Mooney–Rivlin expression enabled the relationship between f̄n and elastomer structure to be quantified in terms of the molar mass (M̄c) of the polyurethane network chains forming the soft blocks.
Nitrogen–phosphorous antagonism in flame‐retardant cotton
Authors: Davies D. , Horrocks A. R.
Published: April 2003

Phosphorous, as sodium dihydrogen phosphate, and nitrogen, in the form of a urea–for‐maldehyde condensate, were applied to cotton fabric. The flame‐retarding character of each treated fabric was assessed by determining the respective limiting oxygen index. Analysis of the results showed that at the lowest levels of applied phosphorous (P = 2%), the presence of nitrogen produced less than an additive combined flame‐retarding effect. At higher phosphorous levels, this deviation from additivity increased until at P > 6%, the presence of nitrogen antagonized the flame‐retarding effect of the phosphorous. These observations are discussed within the current ideas of nitrogen–phosphorous interaction in flame‐retardant systems, for cotton‐containing fabrics.
Carbon tetrachloride absorption in L‐O‐W‐density polyethylene pellets: Mathematical analysis of concentration profiles
Authors: Gupta J. P. , Sefton M. V.
Published: April 2003

Concentration profiles of carbon tetrachloride in low‐density polyethylene pellets were analyzed mathematically to estimate the concentration dependence of the diffusivity. Profiles were measured by electron microprobe analysis and energy dispersive x‐ray spectroscopy (EDAX) and found to be sharper than expected. However, the diffusion front position was proportional to \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt t $\end{document} rather than t as might have been expected if case II diffusion applied. The mathematical model assumed a constant diffusivity behind the diffusion front and zero diffusivity in advance of the front. The resulting moving boundary problem was solved by integral methods, yielding concentration profiles consistent with the essential features of the experimental profiles. The difference in shape between experimental and calculated profiles was attributed to the concentration dependence of the diffusivity, which was estimated by a curve‐fitting procedure. The resulting integral average diffusivity was 1.28 × 10−6cm2/s, four times that estimated assuming standard fickian absorption from the mass uptake curves. This difference was attributed to the inapplicability of the standard relationships to this system in which a discontinuous diffusivity concentration relationship was presumed to apply.
Morphological, structural, and interfacial changes produced in composites on the basis of polypropylene and surface‐treated sepiolite with organic acids II. Thermal properties
Authors: Acosta J. L. , Ojeda M. C. , Morales E. , Linares A.
Published: April 2003

Heat capacity and thermal expansion measurements in composites have been relatively little used as research procedures. In recent times, however, they are beginning to be increasingly utilized in morphological studies. This motivated the application of both techniques to composites on the basis of polypropylene and sepiolite that had been surface treated with linear organic acids. Assessment of our results allows for the interference that the incorporation of these sepiolites produces important structural changes in the polypropylene containing them. These changes can be explained by the complex interface (mesophase) theory.
The preparation and properties of vinyl cellulose
Authors: Träskman B. , Tammela V.
Published: April 2003

The vinylation of cellulose by acetylene under alkaline conditions was optimized with respect to both DS and DP. Shortening the reaction time reduced the harmful alkaline depolymerization of cellulose during the reaction and gave products with higher DP values. Thus cellulose, activated by KOH, was vinylated for 180 min at 431K and 5.5 MPa to yield 72.1% of a product with DS 1.46 and DPw 175. Results of vinyl cellulose analysis by new and old methods were in good agreement with each other. Trimethylsilylated vinyl cellulose was prepared for proton NMR and GPC measurements. It was found that vinyl cellulose slowly loses its vinyl groups when stored in light and air.
Sorption of carbon tetrachloride in low‐density polyethylene pellets
Authors: Gupta J. P. , Sefton Michael V.
Published: April 2003

Unsteady‐state conjugate sorption curves for carbon tetrachloride in low‐density polyethylene (LDPE) pellets at temperatures between 40 and 70°C suggested there was a maximum in the diffusivity‐concentration relationship at high values of concentration. The sorption curve at 70°C also displayed features characteristic of pseudofickian behavior, which was attributed to clustering of the penetrant at the high vapor acitivity corresponding to this temperature.
Polymerization of olefines through heterogeneous catalysis IV. Modeling of heat and mass transfer resistance in the polymer particle boundary layer
Authors: Floyd S. , Choi K. Y. , Taylor T. W. , Ray W. H.
Published: April 2003

Propylene and ethylene polymerization in liquid and gas media are described by a multigrain particle model. External boundary layer heat and mass transfer effects are investigated for various catalysts and operating conditions. For high‐activity catalysts used in slurry, external film mass transfer effects may be significant. For gas‐phase polymerization of propylene or ethylene, the model predicts significant particle overheating at short times, which may explain the particle sticking and agglomeration problems sometimes observed in industrial reactors.
Optical recording by a 823‐nm GaAlAs laser, based on stretched‐polymer birefringence relaxation
Authors: Murthy Parvathi S. , Klingensmith Kenneth A. , Michl Josef
Published: April 2003

A ∼5‐μm‐thick stretched sheet of a vinyl chloride–vinyldene chloride copolymer containing a suitable polymethine dye providing an optical density of 1–2 at 823 nm has been used to record ∼3μm‐diameter relaxed spots, produced with pulses of 250 μs or longer from a 5‐mW GaAlAs laser operating at 823 nm. The spots have been observed under polarizing microscope. It is proposed that this demonstrates a principle that could be used for recording and retrieval of information by a laser beam, using a stretched polymer as the storage medium.
Utilizing zero crossover points in the near infrared reflectance analysis of industrial polymers
Authors: Weyer Lois G.
Published: April 2003

Near infrared reflectance methods were developed for the analysis of polymer pellets and films. Second derivative spectra were used to minimize the effects of scattering and to enhance spectral features. Zero crossover points, places in the derivative spectra where there is negligible response to concentration changes, were employed to minimize interferences at the measuring wavelengths. Two examples illustrate the utility of this technique for industrial quality assurance analyses. The examples include the measurement of three hydrocarbon polymers, directly in transparent pellets, and the determination of 0.1% MEK in an acrylic film. Precision and accuracy were found to be at least equal to that of other methods, and time savings were considerable.
Prediction of thermoset viscosity using a thermomechanical analyzer
Authors: Tong Ho‐Ming , Appleby‐Hougham Gareth
Published: April 2003

A thermomechanical analyzer (TMA) in the parallel‐plate configuration was employed to study the viscosity behavior of an unfilled, FR‐4 type epoxy resin by monitoring its thickness change with time under a constant compressive force at various temperatures. With a dual‐Arrhenius reheology model, we were able to predict viscosities under nonisothermal conditions of high heating rate from more easily obtained isothermal viscosity data. Due to its simplicity and speed, this technique is well suited for investigating resin viscosity behavior during composite lamination in a manufacturing environment.
Reaction engineering aspects of suspension polymerization
Authors: Mikos Antonios G. , Takoudis Christos G. , Peppas Nikolaos A.
Published: April 2003

Suspension polymerization is used for the production of polymer particles with diameter in the range of 50–750 μm. The particle size distribution of the particles produced in batch‐suspension polymerization is calculated using a population balance model. Power laws are derived for the average particle size and the standard deviation of the distribution. It is found that both quantities scale to the stable droplet mass of the initial dispersion of the organic phase into the aqueous one, which is a function of the agitation rate and the surface tension.
Kinetics of gelatinization of cornstarch adhesive
Authors: Inoue M. , Lepoutre P.
Published: April 2003

In the manufacture of corrugated board, thermal gelatinization of raw starch granules in the adhesive is essential for bonding setting. Kinetic studies of gelatinization of cornstarch adhesive under conditions simulating those at the corrugator revealed that the rate of advance of the gelatinization front in the starch film was linear with square root of time. A quasiactivation energy of 35.5 kJ/mol was found. The gelatinization process, above the gel point, was controlled by the rate of diffusion of water into the starch granules.
Modeling of melamine formaldehyde polymerization. II. Development of a simpler model
Authors: Gupta Santosh K.
Published: April 2003

The kinetic modeling of melamine–formaldehyde polymerization presents a relatively formidable mathematical challenge because of the simultaneous presence of several types of deviations from Flory's equal reactivity hypothesis. A molecule of melamine has six reactive amide hydrogens, which can react with the CH2OH groups of formaldehyde in solution. The reactivity of the secondary hydrogens on the melamine is about 61% of that of the primary hydrogens (induced asymmetry). There is a shielding effect present, i. e., the reactivity of the hydrogens near the outside of a multiringed polymer molecule is higher than that of the hydrogens inside the coiled molecules. Two bound CH2OH groups on the polymer molecules can self‐condense to give methylene linkages, the reactivity depending upon the location of the two groups. And, to confound modeling effort still further, all these reactions are reversible. An earlier attempt at molding this system considered the reactions between 36 “basic” species. This model was far too detailed and failed to acount for the reverse reactions. In the present study, a simpler model has been proposed which involves fewer “basic” species. An improved model for intramolecular reactions is also developed. Several important characteristics of the polymerization have been obtained as a function of time. Results from this model have been compared with those obtained from the earlier model, and also compared with the short‐time experimental results. The present model can be extended to account for the reverse reactions quite easily.
Compatibility studies of polystyrene–polybutadiene blends by thermal analysis
Authors: Kim Woo‐Nyon , Burns Charles M.
Published: April 2003

In order to examine the behavior of incompatible blends of polystyrene and polybutadiene, the glass transition temperature, the melting point, and the specific heat increment at the glass transition temperature for atactic polystyrene (a‐PS), isotactic polystyrene (i‐PS), polybutadiene (PBD), and blends of a‐PS/PBD and i‐PS/PBD were determined by use of a differential scanning calorimeter. Blends were prepared by solution casting, freeze‐drying, and milling. Weight fractions of polystyrene in the blends ranged from 0.95 to 0.05. The glass transition temperature of polystyrene changed with weight fraction in the blends, and with blending preparation methods; the glass transition temperature of polybutadiene remained essentially unchanged. The specific heat increment at the glass transition temperature of PBD decreases linearly with increasing proportions of PS in the PS/PBD blend for the broad and narrow molecular weight distribution polybutadience polymers, whereas the specific heat increment for PS did not decrease with increasing proportions of PBD in the PS/PBD blend. These results suggest that the polybutadiene dissolves more in the polystyrene phase than does the polystyrene in the polybutadiene phase.
Intrinsic birefringence of amorphous poly(bisphenol‐A carbonate)
Authors: Wu Maan‐Shii S.
Published: April 2003

The birefringence of uniaxially oriented poly(bisphenol‐A carbonate) (PC) samples stretched over a wide range of temperatures has been measured accurately with a combination of the compensator and the wedge methods. The Hermans' orientation function of anisotropic PC was calculated from the measured dichroic ratio of the infrared absorption band at 1364 cm‐1. Measurements using differential scanning calorimetry, X‐ray diffraction, or infrared spectroscopy indicated no stress‐induced crystallinity in stretched amorphous PC. At each state having a defined molecular orientation, samples stretched below the glass transition temperature (Tg) always exhibited excess birefringence and slightly higher density. This phenomenon is attributed to bond distortion during stretching, a result of the suppression of large‐scale segmental motions of polymer chains below the Tg. The birefringence of samples stretched above the Tg arises exclusively from the orientation effect as a result of greater chain mobility. These measured birefringence values are proportional to Hermans' orientation functions, yielding a linear relationship which allows precise determination of the intrinsic birefringence of amorphous PC as 0.192 ± 0.006.
Exposure of cross‐linked epoxy resins to the space environment
Authors: Garton A. , McLean P. D. , Wiebe W. , Densley R. J.
Published: April 2003

Two specimens of cross‐linked epoxy resins were attached to the Remote Manipulator Arm (“Canadarm”) of the space shuttle and exposed to the space environment (about 225 km altitude) experienced on the 41‐G shuttle mission. Portions of the specimens which had been coated with 10 nm of inconel, then gold, were relatively unaffected by space exposure, while the uncoated areas were eroded to a depth of about 5 μm. The eroded surfaces had a porous texture, consisting of tunnel‐like features extending a further 10 μm below the surface, with a hole density of 3 × 106 holes/mm2. Surface infrared (IR) spectroscopy showed that the first 1–2 μm of porous surface material was little affected chemically by the erosion process, indicating that any chemical erosion must have occurred progressively in a very thin surface layer, which then volatilized away, exposing fresh surface for attack. As a qualitative laboratory simulation, specimens of the same plastics were exposed to low‐pressure air and oxygen plasmas. Somewhat similar surface damage was observed, with no IR‐detectable change in surface chemistry. The criteria for selection of a satisfactory laboratory simulation of the space environment, and the factors responsible for the directionality of the erosion processes are discussed.
Tensile failure of γ‐ray irradiated blends of high‐density polyethylene and natural rubber
Authors: Akhtar Sania , De Prajna P. , De Sadhan K.
Published: April 2003

The effect of 60Co γ‐radiation on the tensile properties of thermoplastic elastomer blends of natural rubber (NR) and high‐density polyethylene (HDPE) has been investigated. The samples were irradiated to absorbed doses ranging from 0.1 to 100 Mrad in air at room temperature (25°C) at a dose rate of 0.21 Mrad/hr. The effect of blend ratio and addition of carbon black (N 330) dicumyl peroxide (DCP) on the radiation resistance of the blends has also been studied. High energy radiation at a high dose rate was found to cause extensive crosslinking in the bulk, which in effect, caused a minima in the ultimate tensile strength in the range of 10–25 Mrad and a continuous decline in the elongation at break in all the blends. Chain scission, on the other hand, was restricted to the surface under the above‐mentioned experimental conditions. This contention was substantiated by the results of irradiation of the samples in a nitrogen environment. Scanning electron microscopy (SEM) studies on the tensile fracture surface morphology of the blends have also been undertaken in order to gain insight to the mechanism of failure.
Transport of direct dye into cellulose membrane
Authors: Yoshida Hiroyuki , Kataoka Takeshi , Nango Mamoru , Ohta Shozo , Kuroki Nobuhiko , Maekawa Masako
Published: April 2003

The dyeing process for a cellulose membrane–direct dye system is analyzed based on a parallel transport mechanism of surface and pore diffusion with Freundlich isotherm. Numerical solutions were obtained in order to clarify how the surface and pore diffusion resistances affect the uptake curve. The numerical solutions were also compared with an analytical solution for surface diffusion control to establish the range where the analytical solution can be considered as an acceptable approximation. The uptake curves in the cellulose membrane‐chromophore (C.I. Direct Yellow 12) system in the presence of inorganic electrolyte were measured. The rate of adsorption and the maximum amount of adsorption increased with an increase in the concentration of those electrolytes. The rate of adsorption was approximately controlled by the surface diffusion rather than by pore diffusion. The surface diffusivities of the dye were little affected by either the concentration and or nature of the electrolyte.
Sorption and transport of inert gases in PVF2/PMMA blends
Authors: Chiou J. S. , Paul D. R.
Published: April 2003

Sorption and transport of several inert gases (He, Ar, N2, and CH4) in miscible blends of PMMA and PVF2 are reported as a function of pressure at 35°C. For each gas, the permeabilities are independent of pressure for all blend compositions. Sorption isotherms are linear for rubbery compositions (PVF2‐rich) and nonlinear for glassy compositions (PMMA‐rich) as expected. In contrast to CO2, these gases do not plasticize any of these materials. The data are analyzed using appropriate models for sorption and transport, and the parameters are correlated in terms of blend composition and molecular characteristics of the gases. Effects of crystallinity are discussed. Sorption behavior is compared with poly(methyl acrylate) and poly(vinyl acetate).
Short fiber formation during extrusion of polyethylene–sodium lignosulfonate blends
Authors: Albihn P. , Franzén B. , Kubát J. , Rigdahl M.
Published: April 2003

When extruding a blend of low density polyethylene (LDPE) and a technical grade of sodium lignosulfonate through a capillary it was observed that LDPE formed fibers in a matrix of the lignosulfonate. With short capillaries and low shear rates, short fibers of LDPE with lengths between 0.5 and 5 mm and with diameters in the range 2–20 μm can be produced. Since sodium lignosulphonate is water‐soluble, the LDPE fibers can easily be isolated. Such fibers can be used for synthetic wood pulp or in nonwoven types of applications.
Internal stress of epoxy resin modified with acrylic core‐shell particles prepared by seeded emulsion polymerization
Authors: Nakamura Yoshinobu , Tabata Haruo , Suzuki Hideto , Iko Kazuo , Okubo Masayoshi , Matsumoto Tsunetaka
Published: April 2003

In order to reduce the internal stress in a cured epoxy resin, the submicron polymer particles were dispersed therein prior to curing. For this purpose, four kinds of poly(butyl acrylate), poly(methyl methacrylate) core‐shell particles were prepared by seeded emulsion polymerization for methyl methacrylate with poly(butyl acrylate) seed particles having different particle diameter, and subsequently were powdered by drying at room temperature. It was observed by SEM that poly(butyl acrylate) particles as core were dispersed in the cured epoxy matrix. Poly(methyl methacrylate) as shell seems to dissolve in the matrix. The internal stress of cured epoxy resin decreased with the modification of the particles and the tendency was enhanced with a decreasing in the particle diameter.
Solid state polymerization of poly(ethylene terephthalate): Kinetic and property parameters
Authors: Jabarin S. A. , Lofgren E. A.
Published: April 2003

The kinetics of solid state polymerization of poly(ethylene terephthalate) (PET) have been investigated at a variety of conditions. Equations have been developed to describe the relationships of time, temperature, and final molecular weight for PET precursors prepared from specified catalyst and monomer systems. These studies show effects of: time and temperature of solid stating, moisture concentration, oxygen exposure, and nitrogen purge flow rate. Measurements of inherent viscosity, carboxyl end group concentration, melting point, residual acetaldehyde, and acetaldehyde generated during melting are used to monitor molecular weight, purity, and thermal stability of these solid stated resins.
High shear rheology and shear degradation of aqueous polymer solutions
Authors: Buchholz F. L. , Wilson L. R.
Published: April 2003

We have investigated the possibility of replacing hydraulic oils with aqueous polymer solutions having the same rheological properties. We measured the low and high shear rate viscosities of polymer solutions at several moderate concentrations and compared the results to the predictions of a molecular model. We found that viscosities measured at shear rates near 1 million reciprocal seconds are in good agreement with those calculated using the model of Mochimaru.6 Shear degradation studies were also conducted using higher molecular weight versions of some of the polymers. Exposure of these to very high shear rate caused a permanent decrease in viscosity and a corresponding change in the molecular weight and molecular weight distribution. Taken together, these results show that very low molecular weight polymers at moderate concentrations are necessary to formulate an aqueous hydraulic fluid with approximately Newtonian behavior at shear rates near 1 million reciprocal seconds, and without long‐term polymer degradation.
Water immersion of polysulfide sealants. II. An interpretation of the influence of curing systems on water resistance
Authors: Hanhela Peter J. , Huang Robert H. E. , Paul D. Brenton , Symes Theodore E. F.
Published: April 2003

Dichromate cured polysulfide sealants have superior resistance to swelling in hot water than those cured with manganese dioxide and examinations to identify the reasons for this difference were undertaken. The commercial sealants PR‐1422, PR‐1750, and Pro‐Seal 899 were shown to contain similar types and loading of fillers. Crosslink densities were compared through a procedure involving an oscillating disc cure meter modified to accommodate mobile mixtures. No relationship between stability and crosslinking was observed. Formation of large voids in MnO2‐cured sealants after prolonged immersion at 70–90°C, suggests the formation of a water‐soluble acid which then reacts with the CaCO3 filler, and this was supported by pH measurements. The acid was shown to arise through autoxidation of formal groups in the polysulfide, and this process can be suppressed by radical scavengers (including ammonium dichromate). When PR‐1750 was examined under nitrogen or with carbon black as filler, a similar time–swell curve to that of PR‐1422 was produced. It was concluded that abnormal swell does not result simply from autoxidation: a filler capable of reacting with the acid must also be present.
Electrical conductivity of γ‐irradiated native and mercerized cotton celluloses
Authors: Moharram M. A. , Abou‐Sekkena M. M. , Hakeem Nagwa Abdel
Published: April 2003

In the present study the electrical conductivity (σ) of ball‐milled and NaOH‐treated cotton fibers were measured in vacuum. The induced electrical conductivity and the activation energy ΔE of γ‐irradiated samples were measured as a function of radiation doses and at various temperatures. It was found that γ‐irradiation of cotton fibers either decreases or increases its electrical conductivity. Thus, it was found that γ‐irradiation of cotton reduces the conductivity of the samples having particle sizes ranging from 0.07 to 0.11 mm and the magnitude of the reduction diminishes as the particle size increases. The results have also shown that, for any given concentration, γ‐irradiation of NaOH‐treated samples causes an increase of the measured electrical conductivity.
Heterogeneous styrene–divinylbenzene copolymers. Stability conditions of the porous structures
Authors: Okay Oğuz
Published: April 2003

The change in the porosity of styrene–divinylbenzene (S–DVB) copolymers during drying as a function of the quality of the diluent and of the divinylbenzene (DVB) concentration was investigated after drying the networks from water (maximum porosity) and from toluene (stable porosity). Two different diluents, namely toluene and cyclohexanol, were used in the polymerization system at a fixed volume fraction of the organic phase (0.50). The phase separation in toluene is accompanied by a slight deswelling of the network phase, whereas that in cyclohexanol leads to largely unswollen network phase. The stable porosity increases abruptly over a narrow range of the DVB concentration, i.e., between 40 and 50% DVB in toluene and between 15 and 25% DVE in cyclohexanol. The maximum porosity increases almost linearly with increasing DVB concentration up to a certain value, and then remains constant. The results indicate that the two main factors which determine the physical state of the swollen heterogeneous S–DVB copolymers, as well as the stability of the porous structures, are (1) the critical conversion at the incipient phase separation and (2) the degree of the inhomogeneity in crosslink distribution.
Manufacturing of polypropylene laminates and related structural reorganization in the crystalline phase
Authors: Guerra Gaetano , Rosa Claudio De , Petraccone Vittorio
Published: April 2003

The conditions for obtaining recrystallization in more ordered modifications are described for an uniaxially oriented sample of isotactic polypropylene, annealed with fixed ends. These recrystallization conditions are related to the conditions of a lamination process.
Modification of partially carboxymethylated cotton via crafting with acrylic acid and styrene using gamma radiation
Authors: Hebeish A. , Zahran A. H. , Rabie A. M. , El‐Naggar A. M. Kh.
Published: April 2003

Partially carboxymethylated cottons (PCMC) having 15.549, 27.409, and 46.834 meq COOH/100 g cellulose as well as untreated cotton and alkali‐treated cotton, which was prepared in an analogous manner to PCMC but, in the absence of monochloroacetic acid, were graft‐copolymerized with either acrylic acid or styrene using gamma radiation under different conditions. Moisture regain and dyeing properties of the copolymers so obtained were investigated. It was found that the graft yeld increases by increasing monomer concentration and radiation dose irrespective of the monomer or substrate used. Using water/methanol mixtures as polymerization media are advantageous for grafting of styrene onto the substrates in question. The graft yields of PCMCs are much lower than those of unmodified and alkali‐treated cottons when they were grafted with acrylic acid. In case of styrene on the other hand, the graft yields for PCMCs are higher than the corresponding yields obtained with the unmodified and alkali‐treated cottons. Poly(acrylic acid)–PCMC graft copolymers show much higher moisture regain than PCMCs particulary when the carboxylic groups of the graft were in the sodium form. The opposite holds true for polystyrene–PCMC graft copolymers which exhibit much lower moisture regain as compared with PCMCs. The color strength of PCMC dyed with direct or reactive dyes decreases significantly after being copolymerized with poly(acrylic acid) prior to dyeing. On the other hand, this copolymerization improves the affinity of PCMCs for the basic dye and brings about perceptible shade. Polystyrene–PCMC graft copolymers acquire higher color strength than the PCMC when dyed with direct, disperse, and basic dyes but lower color strength upon dyeing with the reactive dye. Also reported were the moisture regain and dyeability of unmodified and alkali‐treated cotton before and after copolymerization with acrylic acid or styrene for comparison.
Quick estimation of dilute polymer solution rheology and activation energy
Authors: Saini D. R. , Shenoy A. V.
Published: April 2003

A simple method for estimation of dilute polymer solution kinematic viscosity versus shear rate curve at temperature of interest and activation energy for viscous flow through the use of efflux time measurement is demonstrated.