bluuebunny/crossref_metadata_2025 huggingface dataset:
Bulk functionalization of ethylene–propylene copolymers. III. Structural and superreticular order investigations
Authors: Greco Roberto , Musto Pellegrino , Riva Fernando , Maglio Giovanni
Published: April 2003

An ethylene‐propylene copolymer (EPR) has been functionalized with dibutyl maleate (DBM) by means of a radical‐initiated bulk process. Different degrees of grafting have been obtained by varying the overall composition of the reaction mixture as well as the processing procedures. The influence of the grafting degree on the structural and superreticular (or “long range”) order has been investigated by differential scanning calorimetry (DSC), Fourier transform infrared analysis (FTIR), and wide (WAXS) and small angle X‐ray scattering (SAXS) techniques. The functionalization leads to a decrease of the “residual crystallinity” present in the parent copolymer. Linear relationships between the grafting degree and the crystallinity degree Xc evaluated by both DSC and WAXS have been obtained. The results of the structural investigations, in agreement with previously reported ones, suggest that the grafting preferentially occurs onto the longer or more perfect methylene sequences. SAXS investigations showed that the significant degree of structuration, i.e., crystalline and paracrystalline order, present in the parent elastomer, gradually disappears by increasing the degree of grafting.
Graft copolymerization of acrylonitrile onto acetylated jute fibers
Authors: Mohanty Amar K. , Patnaik S. , Singh B. C. , Misra M.
Published: April 2003

Graft copolymerization of acrylonitrile (AN) onto acetylated chemically modified jute was carried out in the temperature range 40–60°C using V5+‐cyclohexanone redox initiator system. The effects of temperature, time, concentrations of metal ion (V5+), monomer (AN), cyclohexanone, some inorganic salts, and organic solvents on percent grafting have been studied. IR spectra of acetylated chemically modified jute and grafted jute have been taken, and their characteristic bands have been identified. Grafting has improved the thermal stability and also the lightfastness rating of jute fibers dyed with basic dyes.
Studies in the graft copolymerization of vinyl monomers on cellulosic materials
Authors: Okieimen F. E. , Idehen K. I.
Published: April 2003

Graft copolymerization of acrylonitrile, methyl methacrylate, and vinyl acetate on bleached holocellulose initiated by ceric ions in aqueous medium was studied at 29°C. The extent of graft copolymer formation was poly(methyl methacrylate) > polyacrylonitrile > poly(vinyl acetate), indicating the influence of polarity of monomer on graft copolymerization. It was found that, although the molecular weights of the grafted polyacrylonitrile copolymer were lower than the values obtained for poly(methyl methacrylate), the latter was less frequently incorporated on the cellulosic backbone polymer than the polyacrylonitrile grafts. The marked reductions in graft level associated with thiolation of the cellulosic material suggest that hydrogen abstraction reactions from carbon atom carrying hydroxyl groups may not be important in graft copolymer formation.
Adhesion between aluminum and copolymers of ethylene and vinyltrimethoxysilane
Authors: Ulrén L. , Hjertberg T.
Published: April 2003

The adhension between aluminum and poly(ethylene‐co‐vinyltrimethoxysilane) (EVS) and poly(ethylene‐co‐butylacrylate‐co‐vinyltrimethoxysilane) (EVSBA), respectively, have been studied. For comparison an ordinary low density polyethylene (LDPE), a poly(ethylene‐co‐butylacrylate) (EBA), and an ionomer regarded as a bonding polymer were studied as well. The peel strength of laminates obtained by pressing were measured by a T‐peel test. The structure of the fracture surfaces were investigated by reflection‐IR, ESCA, and SEM. The peel strength of the LDPE and the EBA samples were 100 and 700 N/m, respectively. Although the amount of vinylsilane was low, about 0.2–0.3 mol %, its presence had a pronounced influence on the adhesion: 1800 and 3000 N/m for EVS and EVSBA, respectively. This is even higher than the value observed for the ionomer, 1560 N/m. Although there was a marked difference in surface topology, the SEM and ESCA analysis showed that the fracture was cohesive for both EVS and EVSBA. Immersion in water at 85°C increased the peel strength even more, especially in the case of EVSBA (up to 9000 N/m), in contrast to what is normally observed with aluminum polyethylene laminates. The results suggest that strong and nonhydrolyzable bonds, e.g., covalent bonds, have been formed across the polymer‐metal interface for the ethylene copolymers containing vinylsilane.
Effect of extension rate on the stress–strain characteristics of grafted casein film
Authors: Somanathan N. , Arumugam V. , Naresh M. D. , Sanjeevi R.
Published: April 2003

Casein was grafted with a binary mixture of acrylonitrile and n‐butyl methacrylate. The mechanical properties of the grafted casein films were studied at various extension rates. The fractured surfaces were analyzed using scanning electron microscopy. With the increase in extension rate, the strain at yield increases to a maximum value and then decreases to a limiting value. The stress at yield and the energy at break steadily increase with the increase in the rate of extension.
Polyisobutylene‐based urethane foams. II. Synthesis and properties of novel polyisobutylene‐based flexible polyurethane foams
Authors: Ako Masayuki , Kennedy Joseph P.
Published: April 2003

Novel polyisobutylene‐based flexible polyurethane foams (PIB–PUF) have been prepared manually by the prepolymer method using three‐arm star hydroxyl‐terminated polyisobutylenes (PIB–triols) and toluene diisocyanate (TDI). Solvent extraction and IR spectroscopy of PIB–PUFs indicated essentially complete crosslinking. Conventional polyether‐based polyrethane foams (PE–PUFs) and polybutadiene‐based polyurethane foams (PBD–PUFs) have also been prepared by the same method and select physical‐mechanical properties of all these urethane foams, such as tensile strength, elongation, resilience, water permeability, hot air stability, and hydrolytic stability, have been examined and compared. Although the density of PIB–PUF is lower than that of PE–PUF, its tensile strength is superior to the latter. Elongation of PIB–PUF is almost the same as those of the other foams. The PIB–PUF exhibits low resilience which indicates good damping properties. Due to the hydrophobicity of the soft segment, PIB–PUF exhibits very low water permeability. The hydrolytic and hot air stability of PIB–PUFs are outstanding. Attempts have been made to determine gas permeabilities; however, due to the open‐cell nature of the foams, these studies could not be completed. The new PIB‐based urethane foams combine excellent thermal, environmental, barrier, and mechanical properties, unmatched by conventional PUFs.
The heterogeneous character of the dilute acid hydrolysis of crystalline cellulose
Authors: Wood Barry F. , Conner Anthony H. , Hill Charles G.
Published: April 2003

The end‐attack model proposed by Sharples [Trans. Faraday Soc., 53, 1003 (1957)] for the dilute acid hydrolysis of crystalline cellulose was tested using the results from the size‐exclusion chromatographic analysis of samples of crystalline cellulose I and cellulose II hydrolyzed in 6.1N HCl at 107°C. The differential number distribution of the molecular weight of hydrolyzed cellulose was found to be approximately exponential, a result which is consistent with the end‐attack model. Differences in the rates of hydrolysis of cellulosic materials appear to arise from differences in both the degree of polymerization and the microstructure of hydrolyzed cellulose. Evidence is also presented which suggests that the recrystallization upon hydrolysis results in part from the lateral accretion of chains which are cleaved during the hydrolysis of amorphous regions in the cellulose microfibrils.
Matrix relaxations in rubber‐toughened thermoplastics
Authors: Starkweather Howard W.
Published: April 2003

In several systems involving a rubber dispersed in a higher modulus polymer, we have found that both the storage modulus are temperatures below the major softening process and the maximum value of the loss modulus are proportional to the square of the volume fraction of the matrix. This agrees with a relationship for foams derived theoretically by Termonia using a finite‐difference approach. Similar relationships have been found for the glass transition in polymethyl methacrylate and for crystalline relaxations in polyethylene, polyoxymethylene, and polytetrafluoroethylene which involve large decreases in modulus.
Effect of diluents and/or fortifier on the glass fiber–epoxy composites
Authors: Thakkar Jatin , Patel Ravji , Patel Ranjan , Patel Vithal
Published: April 2003

The glass fiber‐epoxy composites were fabricated with the E‐type glass cloth and diglycidyl ether of bisphenol A (DGEBA) using 12% diethylenetriamine (DETA) as catalyst on the basis of DGEBA. The properties were modified by incorporating diluents such as epoxidized 2,2,6,6‐tetramethylolcyclohexanol (ETMC) and 1,4‐butandioldiglycidyl ether (BDDE) with/without 20 parts per 100 g of a condensation product of phenyglycidylether and 4‐hydroxyacetanilide (PGEHA) employed as fortifier. The characterization of these epoxy laminates includes resistance to chemical reagents, dynamic mechanical analysis, and mechanical properties like flexural strength, impact strength, and hardness. The dielectrical properties such as breakdown strength, dielectric constant (ε′), dielectric loss (ε″), and loss tangent (tan δ) were estimated.
Thermotropic mesomorphic polyesters. I. Copolyesters of terephthalic acid, hydroquinone, and flexible diols
Authors: Ghadage Ramesh S. , Ponrathnam Surendra , Nadkarni Vikas M.
Published: April 2003

A new series of copolyesters has been synthesized by low‐temperature solution polycondensation of terephthaloyl dichloride hydroquinone and flexible diols such as 1,2‐propane diol, 1,4‐butanediol, diethylene glycol, (cis) 1,4‐cyclohexanediol and (cis + trans) 1,4‐bis(hydroxymethyl) cyclohexane. The copolyesters are all insoluble and display thermotropic mesophases at relatively lower transitions than other commercially important systems. The transition temperatures, the crystallinity, and thermal characterization are reported.
Propylene polymerization in a semibatch slurry reactor over supported TiCl4/MgCl2/ethyl benzoate/triethyl aluminum catalyst. I. Catalytic behavior
Authors: Dumas Constantine , Hsu Cheng C.
Published: April 2003

High activity TiCl4/MgCl2/ethyl benzoate (EB)/triethyl aluminum (TEA) catalysts for the polymerization of propylene were synthesized and characterized for particle size distribution and crystallinity. Polymerization was carried out in a semibatch, constant pressure slurry reactor. A correction for interfacial mass transfer was found to be necessary to relate the monomer feed rate to the instantaneous rate of polymerization. Without such a correction serious misinterpretation of rate data could result. Optimum productivity was observed with respect to the Al/Ti ratio. Similar behavior was observed with polymerization temperature. Isotacticity increased with polymerization tamperature and decreased with Al/Ti ratio. The addition of a small amount of 2,2,6,6‐tetramethylpiperidine increased the percentage of isotactic polypropylene to 98% without significantly affecting productivity.
Electron beam effects on polymers. III. Mechanical and thermal properties of electron beam‐irradiated poly(phenylene sulfide)
Authors: El‐Naggar A. M. , Kim H. C. , López L. C. , Wilkes G. L.
Published: April 2003

The effect of electron beam (EB) irradiation on the mechanical and thermal properties of initially amorphous and semicrystalline poly(phenylene sulfide) (PPS) films has been investigated. Irradiations were carried out either in a nitrogen or air atmosphere. Subsequent mechanical testing carried out at 23°C suggested that oxidative degradation occurs in air for high radiation dosages. However, modulus and tensile strength were not greatly affected by irradiation level. Moreover, it was found that elongation by yielding no longer occurs at doses higher than 1000 Mrad for initially amorphous materials and above 500 Mrad for the initially semicrystalline materials. Differential scanning calorimetry (DSC) measurements utilized to determine crystallinity and melting behavior suggest the likely occurrence of some crosslinking with high irradiation levels. Scanning electron microscopy (SEM) of the irradiated PPS surface suggest the possible occurrence of gas evolution—at least for high dosage levels.
Thermal stability and degradation studies of polyester resins
Authors: Bansal Raj K. , Mittal Jagjiwan , Singh Prakash
Published: April 2003

Thermal behavior and degradation mechanisms of three polyester resins, namely bisphenol A based, isophthalic acid based, and general purpose were studied. These resins were cured with styrene in the presence of benzoyl peroxide (BPO) and methyl ethyl ketone peroxide (MEKP) as initiators. The cured resins were studied by thermogravimetric analysis and mass spectrometry. From the thermogravimetric data it was observed that the cured bisphenol‐A‐based polyester resin was thermally more stable than the cured isophthalic acid‐based and general purpose polyester resins. It was also observed that polyester resins cured with MEKP are thermally more stable than benzoyl peroxide‐cured products. Thermogravimetric analysis data shows that there are two first‐order degradation reactions during thermal degradation in nitrogen atmosphere. The first degradation step involves the scission of cross‐links/weak links with the liberation of free linear chains. The second step involves a random scission of the free linear chains into smaller fragments. The framentation patterns of the polyester resins were identified by mass spectrometery. Possible mechanisms for the degradation of the cured polyesters accounting for the experimental observations are discussed.
Graft copolymerization of acrylonitrile onto jute fibers (studies on Ce(IV)‐hippuric acid redox system)
Authors: Patnaik S. , Sarangi S. , Mohanty A. K. , Singh B. C.
Published: April 2003

Graft copolymerization of acrylonitrile (AN) onto chemically modified bleached jute fibers was studied using Ce(IV)‐hippuric acid redox initiator system. The effects of time, temperature, concentration of monomer (AN), metal ion (Ce4+), hippuric acid, sulfuric acid, and amount of jute fiber on graft yield have been studied. The effects of some organic solvents and inorganic salts on graft yield have also been studied. Infrared spectra of chemically modified bleached jute and grafted jute have been taken and their characteristic bands have been identified. More than 90% graft yield could be achieved with the present system.
FTIR study on structural transformation of keratin films induced by stretching
Authors: Koga Joichi , Kawaguchi Kiyohiko , Nishio Etsuo , Joko Kyohei , Ikuta Nobuo , Abe Ikuo , Hirashima Tsuneaki
Published: April 2003

Fourier transform infrared spectroscopy (FTIR) was employed to explore the structural transformation by stretching of the film composed of a keratin derivative. The derivative was prepared by S‐carboxymethylation of the low‐sulfur keratin of wool. The cast film was stretched to different ratios in ethanol/water (7:3 v/v). The amide infrared absorption bands of the derivative were changed by stretching the film. Curve analysis was undertaken to estimate the contribution of each peptide conformation to the amide II band at each stretching. The analysis shows that the stretching mainly causes the structural transformation from random coil to β‐structure. Moreover, a transient state arises in the course of the transformation. In such a state, the part of random coil increases while that of β‐structure decreases. The infrared dichroism of the film also supports the existence of the transient state. On curve analysis, only the α‐structure was found to reverse the dichroism of the amide II band in the transient state. This result suggests that the crystalline phase of α‐structure is rearranged. Such rearrangement results in inhibition of the transformation from random coil to β‐structure.
Diffusion mechanism of direct dyes into a cellulose membrane: The structural effect of direct dyes on the adsorption rate
Authors: Maekawa Masako , Udaka Masako , Sasaki Mika , Tujii Yasuko , Yoshida Hiroyuki , Kataoka Takeshi , Nango Mamoru
Published: April 2003

The transport of three typical direct dyes, C.I. Direct Yellow 12, C.I. Direct Red 2, and C. I. Direct Blue 15, into a cellulose membrane has been studied at 55°C. Sodium chloride was used as a stimulator for dyeing. The effects of the concentration of the stimulator on the adsorption isotherms, the adsorption rate, and the concentration profiles in the membrane were tested. The experimental adsorption rates of three dyes were quite different. The diffusion mechanism of the dyes into a cellulose membrane was analyzed on the basis of the parallel transport equation of surface and pore diffusion as developed in our previous paper. The experimental uptake curves showed good agreement with the theoretical curves for surface diffusion control. Experimental concentration profiles also agreed reasonably well with the theoretical lines for surface diffusion control rather than pore diffusion control. The surface diffusivities of three dyes were quite different and nearly independent of the adsorbed phase concentration of the dye.
Multiphase materials with lignin. IV. Blends of hydroxypropyl cellulose with lignin
Authors: Rials Timothy G. , Glasser Wolfgang G.
Published: April 2003

Polymer blends of hydroxypropyl cellulose (HPC) and organosolv lignin (OSL) were prepared by mixing in solutions of both pyridine and dioxane, and casting as films, and by mixing in the melt followed by extrusion. All preparations exhibited partial miscibility as evidenced by a single Tg up to a composition of 40 wt % lignin above which phase separation was detected. Dioxane‐cast and injection‐molded blends were distinguished from the pyridine‐cast materials by a positive Tg deviation from additivity, an approximation which adequately described the latter. This positive deviation in Tg is attributed to the formation of a liquid‐crystal mesophase with a resultant reduction of amorphous HPC available for interaction with the lignin component. This explanation is supported by a rapid rise in modulus (∼150%) and tensile strength with very low lignin content, and by an associated sharp decline in ultimate elongation. The development of morphological features, as observed by scanning electron microscopy provide further substantiation of this hypothesis.
Properties of networks obtained by internal plasticization of epoxy resin with aromatic and aliphatic glycidyl compounds
Authors: Misaki Toshikazu , Hirohata Takeshi , Yoshii Minoru , Hamasaki Takehiko
Published: April 2003

In order to improve the fracture properties of p, p′‐diaminodiphenylmethane‐cured epoxy resin, various kinds of aromatic and aliphatic glycidyl compounds were investigated as a modifier at an amount of 30 wt %. Several compounds promoted the fracture toughness. In any glycidyl compounds, however, heat resistance was decreased by the modification. The dynamic mechanical properties of the modified epoxy resins were measured. The crosslinking density ρ was calculated from the theory of rubber elasticity, and the mechanical properties of the resins were discussed in regard to the crosslinking density. Tensile strength was scarcely affected by the crosslinking density. Elongation at break and Izod impact strength increased remarkably with decrease in crosslinking density. The fracture toughness KIc‐ increased with decrease in crosslinking density except at small ρ.
Effect of K‐value on the tensile yield properties of poly(vinyl chloride)
Authors: Havriliak S. , Shortridge T. J.
Published: April 2003

Tensile measurements were made on milled compression molded test specimens of PVC of different K values from strain rates of 0.0001–0.1 s−1 and temperatures of −40 to 25°C. The dependence of yield stress on temperature and strain rate was treated in terms of the Ree–Eyring model as proposed by Roetling for poly(methyl methacrylate) and Bauwens‐Crowet et al. for poly(vinyl chloride). The data reduction was achieved using sophisticated and unbiased statistical techniques that not only provided parameter estimates but their confidence intervals. The yield stress parameters for the alpha and beta processes were found to be independent of K value and within experimental error the same as those reported by Bauwens‐Crowet et al. The activation energy for the beta process from these yield stress studies (15.1 ± 0.3 kcal) is within experimental error the same as that determined from viscoelastic measurements (14.1 ± 1.2 kcal) reported by the authors. This observation supports the contention that beta process in the viscoelastic and yield stress measurements are closely related mechanisms.
Engineering plastics from lignin. XVII. Effect of molecular weight on polyurethane film properties
Authors: Kelley Stephen S. , Ward Thomas C. , Rials Timothy G. , Glasser Wolfgang G.
Published: April 2003

A series of five fractions with number average molecular weights (M̄n) between 1500 and 10,000 daltons were isolated from a Kraft hydroxypropyl lignin (HPL). From 1H‐NMR and UV analysis the chemical properties of the HPLs were found to vary slightly with molecular weight. The hydroxyl content decreased while the glass transition temperature (Tg) increased as the HPL molecular weight increased. The Fox‐Flory equation adequately described the M̄n vs. Tg relationship. The HPL fractions were used as polyols for the preparation of solvent‐cast polyurethane networks (PU) in film form. The Tg of the PUs increased from 40° to 120°C as the M̄n of the polyol rose from 1500 to 10,000 daltons. The molecular weight between crosslinks (M̄c) of the networks was determined by swelling. An observed decrease in M̄c with an increase in M̄n was related to the functionality of the system. The strength properties of films prepared from fractionated HPLs were superior to those prepared from nonfractionated HPLs.
Molecular weight distribution of cellulose as its tricarbanilate by high performance size exclusion chromatography
Authors: Evans Robert , Wearne Ross H. , Wallis Adrian F. A.
Published: April 2003

Cellulose tricarbanilates (CTCs) were prepared from a range of cellulose samples (cotton linters, wood pulps, Avicel, amorphous cellulose, and cellulose II) for molecular weight distribution (MWD) studies by high performance size exclusion chromatography (HPSEC). The HPSEC columns were calibrated using CTC standards with the aid of a microcomputer. CTCs were prepared by reaction of cellulose samples with phenylisocyanate in pyridine at 80°C. For some samples, e.g., cellulose II, activation with liquid ammonia and pyridine was necessary prior to reaction in pyridine. All samples tested were also derivatised in dimethylsulfoxide at 70°C, although for high molecular weight (MW) cellulose samples some MW reduction occurred in this solvent. Conditions were determined for optimum precipitation of CTCs in aqueous methanol without coprecipitation of low MW impurities.
Molecular weight distribution in continuous stirred tank vinyl acetate emulsion polymerization
Authors: Lee Chan H. , Mallinson Richard G.
Published: April 2003

Emulsion polymerization typically produces polymers of high molecular weight with broad distributions of molecular size. Many models have been proposed that use either a Flory type distribution, resulting in a polydispersity of two, or a distribution function to represent the breadth of the distribution. In this work, a model for the distribution of molecular weights is derived as a approximation from a detailed molecular weight model that was previously developed. The model is found to approximate the distribution of molecular weights well for several emulsifier concentrations is continuous stirred tank emulsion polymerization of vinyl acetate. An analysis is also conducted of the transformation of gel permeation chromatography data to weight and number fractional distributions of the molecular sizes.
Pervaporation separation of water/ethanol mixtures through polysaccharide membranes. II. The permselectivity of chitosan membrane
Authors: Mochizuki Akira , Sato Yoshio , Ogawara Hisashi , Yamashita Shuzo
Published: April 2003

The separation of water/alcohol mixtures through chitosan membrane was investigated. The degree of the deacetylation of chitosan did not affect the selectivity of the membrane in the separation of the water/ethanol mixture. The selectivity of the chitosan membrane was affected by the specific salts such as CoSO4, ZnSO4, and MnSO4 and it increased when the salts were present in the feed mixture or the membrane was pretreated with the salt solution. This behavior would be explained by the contraction of the “holes” produced by the thermal motion of polymer chains and this contraction would be correlated with the conformation change of chitosan molecule due to the formation of complexes with metal ions.
The structure of organosilicon plasma‐polymerized coatings on metal substrates
Authors: Coopes I. H. , Griesser H. J.
Published: April 2003

The structure of coatings formed by the low pressure plasma‐polymerization of hexamethyldisiloxane has been studied by FTIR and XPS techniques. The coatings were performed in two pressure regions: 0.63–0.88 and 0.36–0.44 torr. At both pressures much of the structure of the monomer appeared to be maintained. Coatings deposited at the higher pressure showed the expected increase in abstraction of methyl groups and formation of Si  O  Si crosslinks with increasing discharge power. The lower pressure coatings showed a markedly more diverse pattern of peaks associated with Si  O bonds. The spectra of the moncmer, hexamethyldisiloxane, and of a highly crosslinked silicone resin were examined in order to clarify the way in which FTIR spectra varied during the polymerization and crosslinking processes. The different structures observed emphasize a considerable potential for tailoring structure by varying deposition conditions.
Water sorption in polyamide–imide films and its effect on dielectric loss
Authors: Tchangai T. , Segui Y. , Doukkali K.
Published: April 2003

Water sorption and diffusion has been measured in polyamide–imide over a range of temperature and relative humidities. The results are compared to those obtained on Kapton and discussed in terms of chemical differences between these two materials. Changes in dielectric loss during hydrothermal aging under 85°C and 85% RH have been measured. These changes are correlated to the water sorption kinetics.
Preparation and properties of soluble and colorless fluorine‐containing photoreactive polyimide precursors
Authors: Omote Toshihiko , Yamaoka Tsuguo , Koseki Kenichi
Published: April 2003

Photoreactive polyimide precursors, which are readily soluble in common organic solvents and optically transparent at light of 365 nm wavelength (i‐line), similar to aliphatic polyimide precursors, were obtained by polycondensation of biphenyltetracarboxylic dianhydride (BPDA) and fluorine‐containing diamine compounds. In particular, the polyimide precursor prepared from 2,2 bis(3‐amino‐4‐methylphenyl) hexatluoropropane showed high solubility in common organic solvents and complete transparence at i‐line wavelength. A 3 μm thick film of the polyimide precursor on a silicon wafer was exposed and developed, and offered high resolution (0.5μm line) patterns with an aspect ratio of 6.0. This polymide precursor swells very little in the developing solvent, resulting in the high resolution. Conversion of polyamic acid to polyimide at several curing temperatures was observed by infrared spectrophotometer and thermogravimetry.
Branched and linear polyethyleneimine supports for resins with retention properties for copper and uranium. VII
Authors: Rivas B. L. , Maturana H. A. , Catalán R. E. , Perich I. M.
Published: April 2003

Weak and strong basic resins were synthesized by crosslinking with 1,7‐dibromoheptane and 1,12‐dibromododecane and subsequent N‐methylation reaction of branched and linear polyethyleneimine. All the resins are insoluble in water. It was found that the N‐methylated resins showed the highest retention ability for uranium. The resins do not retain significatively iron (> 10%), and only two of them retain copper above 80% at optimum pH. Elution assays with sulphuric acid, sodium carbonate, and thermal stability were also carried out.
Plasma‐induced polymerization
Authors: Epaillard F. , Brosse J. C. , Legeay G.
Published: April 2003

Low vapor tension polymerized acrylates as thin films when they are subjected to a cold plasma. The plasma‐induced polymerization is described in terms of direct or indirect energy transfer from the plasma to the monomer. The indirect transfer is related to the absorption of UV‐visible radiations by the monomer. The radiations are emitted from excited species of the plasma. Direct transfers correspond to the reactive species collision (radicals, ions metastable species) with a molecule of monomer. The polymerization is a result of these two kinds of transfers. Direct transfers lead to competitive reactions (addition, terminations and degradation, etc.) and acrylate polymerization is mostly induced by the UV‐visible radiations.
Influence of cations and borate on the alkaline extraction of xylan and glucomannan from pine pulps
Authors: Scott Ralph W.
Published: April 2003

Southern pine pulp fibers were extracted with Na, K, and Li hydroxides at several concentrations from 0.5 to 4.0 m (molal). The amounts of extracted xylan and glucomannan increased with the swelling of the cellulose structure up to 2.0–2.5 m. The addition of H3BO3 to alkaline solutions produced the B(OH) anion, which had less swelling power than OH−. It was not effective for removal of xylan except for some very accessible xylan of holocellulose. Removal of xylan from chemical pulps depended upon OH− in molar excess over H3BO3. In the same extractions, glucomannan removal was enhanced by B(OH) alone and further increased by additional OH−. The formation of anions (carboxylate in xylan and borate complex of glucomannan) appeared to be important for the release of polymer from within the cellulose structure. Some glucomannan was more accessible in oxygen pulp than in holocellulose. The resorbed xylan of kraft pulp was less accessible than the xylans of either holocellulose or oxygen pulp.
Bending‐beam study of water sorption by thin poly(methyl methacrylate) films
Authors: Tong H. M. , Saenger K. L.
Published: April 2003

A bending‐beam technique has been employed to study the effects of film thickness (7–55 μm) and rate of cooling during film preparation (∼ 6°C/h to a dry ice quench) on sorption characteristics of water by poly(methyl methacrylate) films coated on thin fused quartz beams (˜ 84 μm thick). In each experiment, the curvature of a polymer coated beam exposed to liquid water was monitored as a function of time by a low power laser pointer. With the use of a transport model which considers the sorption process as the linear superposition of contributions from Fickian diffusion and a first‐order polymer molecular relaxation process, the beam curvature data were analyzed to determine the governing transport kinetics and associated transport parameters such as water diffusion coefficient and relaxation rate constant. From curvature analysis for thin films (7–13 μm in thickness), it was found that water diffusion proceeds at early times in a Fickian‐like manner with a diffusion constant of 2–4 × 10−9 cm2/s. At later times, significant relaxation contributions lead to non‐Fickian diffusion behavior, an effect that is more pronounced as the film thickness or sample cooling rate decreases. In addition, sorption of water was found to reduce the film stress (initially tensile at ˜ 108 dyn/cm2) at a rate that increases with sample cooling rate. The high initial film stress not present in free‐standing films may account for the relatively higher diffusion coefficient (∼ 2 × 10−8 cm2/s) found here for very thick (55 μm) PMMA coatings. Because the bending‐beam technique uses coated samples, it is especially well suited for studying penetrant transport into polymer coatings.
The effect of γ radiation on the physical structure and mechanical properties of ultrahigh molecular weight polyethylene
Authors: Birkinshaw C. , Buggy M. , Daly S. , O'neill M.
Published: April 2003

Ultrahigh molecular weight polyethylene has been irradiated using a cobalt 60 source to give received dose between zeor and 50 Mrad. Irradiacted specimens were subjected to tensile characterization, dynamic mechanical analysis, and differential scanning calorimetry. Changes in tensile and dynamic mechnaical properties following irradiation arise from both molecular rearrangement and from increased crystallinity following scissionof long interlamella tie chains. The effects of post‐irradiation aging on mechanical properties are associated with increasing crystallinity resulting from decomposition of metastable groups formed in the amorphous region during irradiation. Irradiated materials have been subject to sinusoidal stressing between 0.275 and 0.55 of yield stress for 100,000 cycies, and changes in mechnaical and physical properties measured. Increased resistance to creep during stressing was observed with the irradiated materials, behavior which is consistent with previsouly observed changes in crystallinity and crosslink density. Overall property changes measured following stressing were small compared with those induced by the initial irradiation.
Magnetic filed effect on sensitized photocrosslinking reaction of azidomethylated polytsyrene
Authors: Morita Hiroshi , Uchino Noriaki , Nakamura Yasuhiro , Yamaoka Tsuguo
Published: April 2003

Characteriscs curves for the lithographic sensitivity of poly(styrene‐co‐vinylblenzyl azide) (AZMA) with such sensitizer as 2,4‐diisopentvlthioxanthone (DITX), 2‐chlorothioxanthone (CTX), and Michier's ketone wer emeasured in the basence and in the presence of a magnetic filed. By the application of a magnetic field, the get fraction increases, and efficiency of photocrosslink formation increases by ≈ 45% (at 0.1 T) for AZMA/DITX and by ≈ 20% (at 0.5 T) for AZMS/CTX. Senstization mechanism was investigated by measuring UV, IR, and FT‐IR spectra, and AZMS is found to be sensitized effectively by DITX and CTX through the triplet energy transfer, and to produce the triplet nitrene as an intermediate. The magnetic field effect on photocrosslink formation of AZMS/sensitizer systems is interpreted in term of the radical pair model of intermediate species which is formed by hydrogen abstraction of the nitrene from the sensitizer.
HPLC determination of the pore distribution and chromatographic properties of cellulosic textile materials
Authors: Grünwald Michael , Burtscher Eduard , Bobleter Ortwin
Published: April 2003

HPLC columns packed with cellulosic textile materials as stationary phase were examined with respect to their chromatographic parameters. The interaction of the stationary phase with water‐soluble substances (mainly textile chemicals) was also studied. The size‐exclusion effects of the porous material were measured for molecules with MW 20−2 × 106, thus giving further information concerning structural changes during the pretreatment of textile materials. Electrostatic and sorptive interactions were detected simultaneously, but found to exert a minor influence. Using a recently developed mathematical model, the pore volume distribution of swollen celluose could be determined from the size‐exclusion data without the introduction of empirical factors. The applied HPLC method of characterizing cellulosic materials offers an alternative to the previously utilized static and chromatographic methods, especially for studies on pretreated textile materials.
Molecular size and solvation of low molecular weight poly(ethylene oxide) and phenol–formaldehyde resols in different solvents
Authors: Riedl Bernard , Vohl M.‐J. , Calvé Louis
Published: April 2003

Several solvent systems are presently used to characterize the molecular weight of phenol–for‐maldehyde resins. However, results reported in the literature for different molecular weights may not be representative of true molecular weight, but rather may be distorted by aggregation and solvation. In this report an effort to clarify this situation was conducted, first by using a suitable calibration with poly(ethylene glycol) and then using this polymer as a molecular size standard to determine the size of phenol–formaldehyde oligomers in solution. In the calculation of the molecular sizes of phenol–formaldehyde resols, proper accounting of the variation of the Mark–Houwink parameters with molecular weight for low degrees of polymerization must be made for poly(ethylene glycol). The Mark–Houwink constants for poly(ethylene glycol) are very similar in presence or absence of salts, and are considered to be unaffected by solution ionic strength. It is not the case for phenol–formaldehyde, whose apparent molecular size varies with the nature of the solvent. The actual molecular weight and molecular dimension distribution are discussed for different type A resols used as adhesives in the wood composite industry.
The role of porosity in polyethylenimine adsorption onto cellulosic fibers
Authors: Alince B.
Published: April 2003

The total adsorption of a given polyethylenimine on pulp fibers, the porosity of which was altered by different drying conditions, was determined and compared with the available internal surface of the fibers. Since polymer adsorption takes place in an aqueous environment, the pore volume and the internal surface of pores as a function of their size were determined from a first benzene desorption isotherm, measured on fibers in which water was replaced by benzene to preserve their swollen structure. The total adsorption of a given polyethylenimine was found to be in a direct relation to the internal surface available in pores larger than a certain size, regardless of the total porosity. Consequently, it is concluded that the adsorption capacity is determined by the accessible surface.
Blends of nylon 6 with a polyethylene functionalized by photooxidation
Authors: Curto D. , Valenza A. , La Mantia F. P.
Published: April 2003

An easy and cheap method to prepare functionalized polyethylene is reported in which polyethylene is photooxidized and then melt‐blended with nylon. Structural, rheological, and mechanical modifications indicate that carbonyl, formed during photooxidation, and amine groups react giving rise to copolymers which stabilize the blends. Photooxidized polyethylene from waste could be very effective in preparing polyethylene/polyamide blends with improved properties. This new approach improves over current methods in which compatibilization of polyolefines and polyamides is mostly performed by reacting functionalized polyolefines with polyamides in molten state. The functionalization is achieved by chemical modification of the polyolefines chains. This step could be very expensive.
Competition between cure and thermal degradation in a high Tg epoxy system: Effect of time and temperature of isothermal cure on the glass transition temperature
Authors: Pang K. P. , Gillham J. K.
Published: April 2003

The isothermal cure of a diglycidyl ether of bisphenol A with a tetrafunctional aromatic diamine has been studied in an attempt to achieve full cure (maximum glass transition temperature, Tg∞, ca. 170°C). Since high temperatures of cure are necessary for high Tg∞ systems (because of low reaction rates after vitrification), cure and thermal degradation reactions often compete. In this work Tg is used as a direct measure of conversion. An approach leading to a series of iso‐Tg contours in a temperature vs. time transformation (TTT) diagram, which can be used to design time‐temperature cure paths leading to particular values of Tg, is discussed.
Molecular structure, melting behavior, and crystallinity of 1‐octene‐based very low density polyethylenes (VLDPEs) as studied by fractionation and heat capacity measurements with DSC
Authors: Mathot V. B. F. , Pijpers M. F. J.
Published: April 2003

Heat capacity measurements with DSC on 1‐octene‐based very low density polyethylenes (VLDPEs), with densities from 888 to 907 kg/m3, show crystallization between 120 and −60°C and melting between −60 and 130°C. Under the assumption that hardly any octene groups are present in the crystal lattice, the experimental heat capacity values were compared with reference values for purely amorphous and purely crystalline linear polyethylene on the basis of a two‐phase model. The enthalpy‐based weight crystallinity data as a function of temperature show that the crystallinities at −60°C are about 40% higher than those at room temperature, which vary from 25 to 40% and are in good agreement with volume‐based weight crystallinities. The crystallization and melting curves show several peaks. Fractionations by the crystallization/dissolution method and the direct extraction method show that this is due to intermolecular heterogeneity of comonomer incorporation and that VLDPE is a reactor blend of molecules ranging from the uncrystallizable and poorly crystallizable type to the HDPE type.
Electroinitiated polymerization of commercial divinylbenzene in acetonitrile medium
Authors: Mahata Prafulla Kumar , Nayak Bimbadhar
Published: April 2003

The electroinitiated polymerization of commerical divinylbenzene (DVB) containing p‐ and m‐DVB and p‐ and m‐ethylvinylbenzene (EVB) and traces of diethylbenzene has been studied in acetonitrile medium with an added electrolyte, namely, tetrabutylammonium fluoroborate (TBAFB). A white partially crosslinked polymer is formed only after the passage of an electrical current. The dependence of yields on parameters such as current strength, temperature, time of electrolysis, and stirring of the reaction mixture has been determined. A detailed IR analysis of the polymeric product has been made and the linear polymeric product is identified as poly(p‐DVB‐co‐m‐DVB‐co‐p‐EVB‐co‐m‐EVB). The electropolymer is thermally stable up to 645 K as found by its DTA, TG, and DTG studies and possesses partial crystallinity as indicated by the X‐ray diffraction experiments. Experiments conducted with a split cell indicated the formation of the polymer in the anode compartment; hence the polymerization mechanism appears to be cationic in nature.
Internal stress of epoxy resin modified with acrylic polymers produced by in situ UV radiation polymerization
Authors: Nakamura Yoshinobu , Yamaguchi Miho , Kitayama Akiko , Iko Kazuo , Okubo Masayoshi , Matsumoto Tsunetaka
Published: April 2003

A cured epoxy resin is modified with polybutyl acrylate (A) and polyethyl acrylate (B) produced by in situ ultraviolet radiation polymerizations of their corresponding monomers in the epoxy resin, respectively, to reduce the internal stress. In the A system, a heterogeneous structure with submicron domains was formed. In the B system, however, the B mixed well with the epoxy matrix. In both systems, the internal stress was decreased by the modification. The glass transition temperature of the epoxy matrix decreased in the B system more than in the A system. The A‐modified resin was superior to the B‐modified resin in reducing the internal stress without decreasing the thermal resistance of epoxy resin.
Mechanism of persulfate decomposition in aqueous solution at 50°C in the presence of vinyl acetate and nitrogen
Authors: Sarkar Swati , Adhikari Mukti Sadhan , Banerjee Monoranjan , Konar Ranajit Singha
Published: April 2003

The rate of the thermal decomposition of potassium persulfate has been studied in an unbuffered aqueous solution at 50°C in nitrogen atmosphere in the presence of vinyl acetate (VA) monomer (M). It has been found that the initial rate of persulfate decomposition may be written as

in the concentration range of persulfate (1.85 × 10−2–1.85 × 10−3 m/dm3) and VA (0.054–0.27 m/dm3). The pH of the aqueous solution of persulfate was found to decrease continuously at 50°C, but there was no measurable change of pH of the aqueous solution containing persulfate and VA at 50°C in the presence of nitrogen at the early stages of the reaction. VA, methyl acetate, and ethyl acetate have been found to undergo very slow hydrolysis in aqueous solution at 50°C. The partition coefficient (β) of the monomer between the polymer phase and the aqueous phase was found to be 21 ± 2 in the presence and absence of electrolytes (K2SO4, 10−4–10−3 m/dm3) by the bromometric estimation of the monomer present in the aqueous phase containing known amounts of monomer [1.80–2.20%, w/v] and freshly prepared polymer (0.3–0.5 g/100 mL). Above 10−2 (m/dm3) persulfate, the polymer obtained was found to be insoluble in common solvents, viz., acetone, benzene, etc. Highly purified sodium dodecyl sulfate (0.5–5.0 × 10−3 m/dm3) had no measurable effect on the rate of persulfate decomposition.
Radiation grafting of α,β,β‐trifluorostyrene onto poly(ethylene–tetrafluoroethylene) film by preirradiation method. III. Properties of anion‐exchange membrane obtained by chloromethylation and quaternization of the grafted film
Authors: Momose Takashi , Kitazumi Tomoko , Ishigaki Isao , Okamoto Jiro
Published: April 2003

A study was made of certain properties of the anion‐exchange membranes obtained by the preirradiation grafting of α,β,β‐trifluorostyrene (TFS) onto poly(ethylene–tetrafluoroethylene) (ETFE), followed by chloromethylation and quaternization of the grafted film. Swelling, water uptake, electric conductivity, and transport number of the membranes were measured as a function of ion‐exchange capacity. Thermal and chemical stability were also investigated. These properties were found to be mainly dependent on ion‐exchange capacity. The stable membrane properties were established due to a homogeneous ion‐exchange group distribution in the membrane, as confirmed by X‐ray microscopy analysis of the membrane cross sections. In addition, the membranes showed good electrochemical, thermal, and chemical properties, and were found to be acceptable for practical use as anion‐exchange membranes.
High‐strength poly(L‐lactide) fibers by a dry‐spinning/hot‐drawing process. II. Influence of the extrusion speed and winding speed on the dry‐spinning process
Authors: Postema A. R. , Luiten A. H. , Oostra H. , Pennings A. J.
Published: April 2003

This paper is concerned with the influences of the extrusion speed and the winding speed during dry spinning of 4 wt % solutions of poly(L‐lactide) (PLLA) in mixtures of chloroform and toluene, on the ultimate fiber tenacities after hot drawing. It was found that high‐strength PLLA fibers (1.5 GPa) can be produced at high spinning rates (> 180 m/min) if rupturing of the entanglement network and oriented crystallization during spinning is suppressed. This could be accomplished by avoiding spinline stretching and applying low elongational deformation rates in the spinneret during spinning.
Reversible crosslinking in epoxy resins. II. New approaches
Authors: Sastri V. R. , Tesoro G. C.
Published: April 2003

Epoxy resins of varying epoxy equivalent weight were crosslinked with 4,4*‐dithiodianiline (DTDA) at a 2/1 mole ratio. Resin of equivalent weight 190 (Epon 828) was cured with DTDA at mole ratios varying from 2/1 to 1.25/1. Properties of cured resins were evaluated and their reduction was investigated. Under the conditions used, reduction to the point of complete solubilization was possible providing crosslink density did not exceed a threshold value tentatively established as Mc = 400 −; 500. Recurring of reduced resins was accomplished by oxidation and by reaction of thiol groups with polyfunctional reagents, including bismaleimides and polyepoxides.