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The influence of organically modified montmorillonate OMMT on the curing reversion of natural rubber NR and polychloroprene rubber CR blend has been demonstrated in this article. Characteristics of the NRCROMMT hybrid composite were undertaken by combining the cure kinetics, thermal stability, and the detection of phase morphology. Compared to the neat rubber blend, thermal gravity analysis has shown improved thermal stability results during degradation for the nanofiller filled ones. Differential scanning calorimetry study has offered cure kinetic results; among which blending with NR has lifted the cure activation temperature of CR low toward. Meanwhile, transmission electron microscopy has shown the intercalation and immobilization of OMMT in the CR phase formed a barrier to NR phase. In addition, to discover the reversion source, infrared spectroscopy has been applied to trace the oxygenic function units in the neat NR vulcanizate. All of the experimental results and related analysis has offered us the base to explain the improvement of the antireversion of the rubber blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [ABSTRACT FROM AUTHOR]

Rubber is the basis in the production of elastomeric materials which is transformed into the rubber-elastic state through the crosslinking procedure. A crosslinking agent is used for crosslinking - sulphur, as well as accelerators, activators and retarders if pre-crosslinking of rubber compound is to be prevented. Crosslinking occurs at higher temperatures. The type of used rubber determines the basic properties of the final rubber product: stability, ageing and flexibility at lower temperatures, strength and elasticity. In the work, the central composite test plan was used to study the mechanical properties of chloroprene rubber (CR) regarding different crosslinking parameters (time and temperature of crosslinking). [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an ultrasound-assisted headspace liquid-phase microextraction with in-drop derivatization was developed for the extraction and determination of hexanal and heptanal as the biomarkers in human blood. In the method, a polychloroprene rubber (PCR) tube was utilized as container to load extraction solvent (methyl cyanide) and derivatization reagent (2,4-dinitrophenylhydrazine, 2,4-DNPH). Volatile aldehydes were headspace extracted and simultaneously derivatized in the droplet, followed by LC-UV detection of the formed hydrazones. The stability of organic solvent and the sensitivity of the method enhanced greatly. Under the optimal conditions, good linearity was obtained in the concentration range of 0.01–10μmolL−1 (r >0.997) and the limits of detection (LOD) for hexanal and heptanal were 0.79 and 0.80nmolL−1, respectively. The recoveries in blood sample ranged from 75.2% to 101.1% with the inter- and intra-day precisions less than 9.8%. The method possesses the advantages such as simplicity, sensitivity, efficiency, low consumption of solvent, and little interference from sample matrix. It provides great potential for the investigation of volatile disease biomarkers (aldehydes) in complex biological samples. [Copyright &y& Elsevier]

The puncture and burst properties of short-fiber reinforced polychloroprene rubber under various conditions were investigated to yield the best mechanical properties. In addition to five types of interphase conditions, four types of fiber aspect ratios (AR: length of fiber/diameter of fiber) and three different fiber contents were studied for their roles in the puncture and burst properties of rubber products. Certain interphase conditions and higher fiber ARs were shown to provide higher puncture and burst stresses at a given fiber content. Since both testing methods measure biaxial properties of reinforced rubber, the relation between the two properties is studied. The discrepancy between regressed puncture and burst force is explained based upon the rubber stiffness due to reinforcing parameters and the stress concentration upon sharp edge. Overall, it was found that the interphase condition, fiber AR, and fiber content have an important effect upon puncture and burst properties. [ABSTRACT FROM AUTHOR]

Chloroprene rubber (CR)/organic modifier/sodium montmorillonite (NA-MMT) nanocomposites were prepared by melt intercalation. The morphology of the nanocomposites was studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM results showed that the silicate layers of the clay were dispersed in the CR matrix on the nano-scale by adding the organic modifier. X-ray diffraction also indicated that the silicate layers of clay were exfoliated. The mechanical and thermal properties of the nanocomposites could be therefore improved by adding clay and organic modifier, as the silicate layer of the clay was uniformly dispersed. Dynamic mechanical analysis was further performed to investigate the thermomechanical properties of CR-clay nanocomposites containing various amounts of clay. The glass-transition temperature of CR- clay nanocomposites increased with increasing amount of clay and organic modifier. [ABSTRACT FROM AUTHOR]

With the goal of elucidating the molecular and cellular mechanisms of chloroprene toxicity, we examined the potential DNA cross-linking of the bifunctional chloroprene metabolite, (1-chloroethenyl)oxirane (CEO). We used denaturing polyacrylamide gel electrophoresis to monitor the possible formation of interstrand cross-links by CEO within synthetic DNA duplexes. Our data suggest interstrand cross-linking at deoxyguanosine residues within 5′-GC and 5′-GGC sites, with the rate of cross-linking depending on pH (pH 5.0 > pH 6.0 > pH 7.0). A comparison of the cross-linking efficiencies of CEO and the structurally similar cross-linkers diepoxybutane (DEB) and epichlorohydrin (ECH) revealed that DEB > CEO ≥ ECH. Furthermore, we found that cytotoxicity correlates with cross-linking efficiency, supporting a role for interstrand cross-links in the genotoxicology of chloroprene. [ABSTRACT FROM AUTHOR]

The work consists in getting targeted, chemical modification of adhesive cold rejection based on chloroprene rubber having improved adhesion properties when bonding vulcanized rubber to each other and bonding them to metal. Also studied physical-mechanical, adhesive and mechanical properties of a mixture of chloroprene rubber with the resin. The influence of formulation-technological factors on the strength of the bond obtained by bonding adhesives developed composition and recommendations on the selection of process parameters bonding. Some new adhesive compositions based on chloroprene rubber stamp Skaypren G40-T, which can be widely used in the national economy, especially in the footwear and rubber industries. [ABSTRACT FROM AUTHOR]

2-Triethoxysilyl-substituted 1,3-butadiene has been prepared in 30-g quantities from chloroprene via a simple synthetic procedure. Silatrane- and catechol-substituted analogues of this main group element substituted diene were then prepared on a 10-g scale by ligand exchange and characterized by X-ray crystallography in addition to standard spectroscopic techniques. 2-Dimethylphenylsilyl-1,3-butadiene has also been prepared from chloroprene on an 8-g scale. Diels-Alder reactions of these dienes are reported as well as subsequent TBAF-assisted/Pd-catalyzed Hiyama cross-coupling reactions of those Diels-Alder adducts. Silicon-substituted cycloadducts and cross-coupled products were alto characterized by NMR spectroscopy and, in two cases, by X-ray crystallography. [ABSTRACT FROM AUTHOR]

Abstract: Compatibility via chemical coupling between electron-modified polytetrafluoroethylene (PTFE) powder and poly-2-chlorobutadiene rubber is accomplished by activation of the radiation-induced carboxylic groups on the PTFE surface by zinc oxide. This is achieved both prior to and during reactive blending of zinc oxide with chloroprene rubber. Spectroscopic analysis of the reaction products reveals an increase in characteristic chloroprene absorption (≈1660cm−1) due to the stretching of the Cicroscopic observations suggest that the PTFE dispersion is considerably improved, while the state of interphase between the PTFE particles and the chloroprene rubber indicates enhanced compatibility. The increase in the cross-link density determined by Mooney–Rivlin plots provides indirect evidence for the existence of chemical coupling. PTFE-based chloroprene composite exhibits a significant increase in modulus due to the strong reinforcement effect of the modified PTFE powder. Finally, we propose an explanation of the coupling mechanism based on the chemical activation of carboxylic groups in the PTFE powder in the presence of zinc oxide. [Copyright &y& Elsevier]

Roles of the two widely used chlorinated paraffins, namely Cereclor S45 and Cereclor 48, in properties of silica filled polychloroprene were investigated. The results reveal that chlorinated paraffin significantly improves the processability. The improvement is more pronounced for Cereclor S45 due to its lower viscosity. However, the addition of chlorinated paraffin has a negative effect on cure. Owing to the reduction of crosslink density and the plasticising effect of chlorinated paraffin, several mechanical properties are impaired, e.g. tensile strength, modulus, hardness, abrasion resistance as well as rebound resilience. However, the deterioration of both tensile strength and modulus is not pronounced at low loading of chlorinated paraffin (≤8·0 parts per hundred of rubber, phr). Although chlorinated paraffin has little influence on the relative tensile strength, the relative 100% modulus is affected to a greater extent due to the combination of post curing retardation and evaporation of chlorinated paraffin during thermal aging. [ABSTRACT FROM AUTHOR]

This article evaluates the quality and weight of evidence associated with epidemiologic studies of cancer among occupational cohorts exposed to chloroprene. The focus is on liver, lung, and lymphohematopoietic cancers, which had been increased in early studies. Literature searches identified eight morbidity/mortality studies covering seven chloroprene-exposed cohorts from six countries. These studies were summarized and their quality was assessed using the 10 criteria suggested by the U.S. Environmental Protection Agency. The limitations within this literature (primarily the early studies) included crude exposure assessment, incomplete follow-up, uncertain baseline rates, and uncontrolled confounding by factors such as smoking, drinking, and co-exposure to benzene and vinyl chloride. Four cohorts were studied by the same group of investigators, who reported no overall increased associations for any cancers. This four-cohort study was by far the most rigorous, having the most comprehensive exposure assessment and follow-up and the most detailed documentation. This study also contained the two largest cohorts, including an American cohort from Louisville, Kentucky, that ranked at or near the top for each of the 10 quality criteria. There was evidence of a strong healthy worker effect in the four-cohort study, which could have hidden small excess risks. Small increased risks were suggested by internal or company-specific analyses, but these were most likely caused by uncontrolled confounding and low baseline rates. Overall, the weight of evidence does not support any substantial link between chloroprene exposure and cancer, but inconsistencies and a lack of control for major confounders preclude drawing firmer conclusions. [ABSTRACT FROM AUTHOR]

Abstract: Blends of polychloroprene rubber (PCR) and ethylene propylene diene terpolymer rubber (EPDM) of different compositions were made and exposed to different gamma radiation doses. The radiation sensitivity and radiation vulcanization efficiency of blends was estimated by gel-content analysis, Charlesby-Pinner parameter determination and crosslinking density measurements. Gamma radiation induced crosslinking was most efficient for EPDM (p 0/q 0 ∼0.08), whereas it was the lowest for blends containing 40% PCR (p 0/q 0 ∼0.34). The vulcanized blends were characterized for solvent diffusion characteristics by following the swelling dynamics. Blends with higher PCR content showed anomalous swelling. The sorption and permeability of the solvent were not strictly in accordance with each other and the extent of variation in two parameters was found to be a function of blend composition. The ΔG values for solvent diffusion were in the range −2.97 to −9.58kJ/mol and indicated thermodynamically favorable sorption for all blends. These results were corroborated by dynamic swelling, experimental as well as simulated profiles and have been explained on the basis of correlation between crosslinking density, diffusion kinetics, thermodynamic parameters and polymer–polymer interaction parameter. [Copyright &y& Elsevier]

The article presents a study that investigated in-situ polymerized phenolic resin (PF) for reinforcement of chloroprene (CR) and ethylene-propylene rubber (EPDM) vulcanizates. It showed that the PF phase was effective in reinforcing the rubbers and that various properties could be enhanced depending on the morphologies of the formed PF phases. It attributed the improvements of the mechanical properties of the rubbers to their morphology, high flexibility and moderate stiffness among others.

The article explores the effect of dispersed organomodified montmorillonite (OMMT) on curing behaviors of natural rubber (NR)/chloroprene rubber blend. Sulfur was selected as the vulcanizing agent, and the research on vulcanization was performed through the rotor-Rheometer. Transmission electron microscopy demonstrated the dispersion of OMMT in the rubber blends and showed little OMMT migrated into the NR phase.

The article presents a study which predicted the recovery prediction of chloroprene rubber (CR) composite from deformation using the conventional compression set test and the circular deformation method to change a linear specimen into a circular one. The linear correlation for curve fitting was found to be very high and the instantaneous recovery was attained from the linear curve fitting equation. The instantaneous recovery at ambient temperature was predicted by the thermal aging results.

The study describes the solid state behaviour, and the thermal and structural features of four monosolvates of cinacalcet hydrochloride with acetic acid, chloroform, 1,4-dioxane, and tetrachloromethane, and summarises the transformation and production pathways of the seven crystal forms of this promising drug compound (calcimimetic). The solvates were identified and characterised by hot-stage microscopy, differential scanning calorimetry, thermogravimetric analysis, FT-infrared and Raman spectroscopy, powder diffractometry, and the structure of the acetic acid solvate was determined by single crystal X-ray diffraction. All solvates are unstable when removed from the mother liquor and desolvate to form II. To our knowledge, phase pure samples of this metastable but kinetically stable form are only obtainable viadesolvation of one of the solvates.Thermoanalytical data and a conformation and packing analysis of the acetic acid solvate and the polymorphs indicate that the desolvation is a destructive process forming an isotropic intermediate state with high molecular mobility. Therefore the desolvation process results in the kinetic form II, which is structurally less similar to the solvate than the thermodynamically stable form III°. The study demonstrates that in spite of strong structural similarities between a solvate and a polymorph we can obtain a polymorph with less structural resemblance to the solvent adduct if the structure collapses during the desolvation process. [ABSTRACT FROM AUTHOR]

Abstract: The effect of two chemically opposite type of nanofillers, namely montmorillonite (MMT) and layered double hydroxide (LDH), both in pristine and organically modified forms (OLDH and OMMT) on the mechanical properties and crystallization behavior of chloroprene rubber (CR) vulcanizates have been investigated. While the addition of very small amount of pristine clays shows a significant improvement of the physical properties of the CR based nanocomposites, the organic modification improves the reinforcing efficiency of MMT more than that of LDH. MMT is found to enhance the crystallization tendency of CR chains, whereas LDH has a role to resist it as observed from the dynamic mechanical analysis (DMA). The DMA results also show that the presence small amount of nanoclay enhances the storage modulus of CR based vulcanizates, which becomes more pronounced in case of organically modified clays, especially with OMMT. Finally, we report the ‘house of cards’ structure of exfoliated platelets of montmorillonite in the CR matrix which are produced by mechanical shear mixing. [Copyright &y& Elsevier]

Exposure of solutions of tetrabutylammonium chlorochromate in chloroform to UV or blue light causes decomposition of the chloroform and the buildup of HCl and peroxides in solution. The CrO3Cl−is converted during irradiation to CrO2Cl2, which forms a suspension in the chloroform, and then to CrOCl4−. CrO2Cl2does not by itself catalyze photodecomposition. The initial rate of HCl formation shows an apparently linear dependence on the incident light intensity and on the fraction of light absorbed by chlorochromate, but different values for the apparent quantum yield at 435 nm with high and low concentrations imply a nonlinear contribution to the rate. It is proposed that, at least initially, a cycle involving photoreduction of a Cr(vi) species and thermal reoxidation of Cr(v) by CCl3OOH produces radicals that initiate further decomposition. [ABSTRACT FROM AUTHOR]

Abstract: A bacterium (strain HL1) capable of growing with hexachlorobutadiene (HCBD) as sole carbon and energy sources was isolated from a mixture of soil contaminated with HCBD and activated sludge obtained from petrochemical plant wastewater treatment plant by using enrichment culture. Biochemical characteristics and phylogenetic analysis based on 16S rDNA sequence indicate that strain HL1 clearly belongs to Serratia marcescens sp. Resting cells of strain HL1 were found to remove HCBD from culture fluids with the concomitant release of chloride ion under aerobic conditions. The ranges of pH value and temperature for satisfactory growth of strain HL1 cells were from 7.0 to 8.0 and 25 to 30°C, respectively. Capability of resting cells to degrade HCBD was induced by HCBD in the culture fluids. HCBD (20mg/l) was removed from culture fluids by resting cells in 4 d without lag phase, but for 50mg/l and 80mg/l HCBD 7 days were needed with lag phase. Growth of strain HL1 cells was inhibited by HCBD at the concentration up to 160mg/l. First order kinetics could be fitted to the biodegradation of HCBD by HL1 cells after lag phase at initial concentrations of 20, 50, and 80mg/l. Strain HL1 also showed strong capacity to degrade chloroprene, trichloroethylene, tetrachloroethylene, and vinyl chloride at solely initial concentration of 50mg/l. Results could offer useful information for the application of strain HL1 in bioremediation or control of HCBD-polluted environment. [Copyright &y& Elsevier]

Abstract: Gaseous mixtures of HCl and vinylacetylene were permitted to react in Pyrex IR cells (NaCl windows). Gaseous 4-chloro-1,2-butadiene and 2-chloro-1,3-butadiene (chloroprene) were the major products. Kinetic data (FTIR) generated a rate expression in concert with surface catalysis. Computational studies involving surface associated water provide a view that accounts for the experimentally determined orders and a bifurcated pathway producing both products. The results are in accord with wall-adsorbed reactant(s) as well as previously reported computational studies on the reactants. [Copyright &y& Elsevier]

Polar ordering has been induced by pressure in solid chloroform (trichloromethane), CHCl 3, and bromoform (tribromomethane), CHBr 3, obtained by isochoric and isothermal freezing in a diamond anvil cell. Structures of these new polymorphs have been determined by single-crystal X-ray diffraction, CHCl 3at 0.62 and 0.75 GPa and CHBr 3at 0.20 and 0.35 GPa. Despite different centrosymmetric structures of all low-temperature phases of CHCl 3(space group Pbcn) and CHBr 3( P6 3/ m, P1̅, and P3̅), the high-pressure phases are isostructural in space group P6 3. The polar phase of CHBr 3is formed at 295 K, already at the freezing pressure of ∼0.1 GPa, while CHCl 3transforms from the Pbcnphase into the P6 3phase between 0.62 and 0.75 GPa. It has been demonstrated that the electrostatic contribution to halogen···halogen and H···halogen interactions in the CHCl 3and CHBr 3molecular crystals is favorable for the polar aggregation and that this effect intensifies with increasing pressure. [ABSTRACT FROM AUTHOR]

Abstract: Chloroprene rubber–polyaniline (PANI) coated nylon fiber composites containing PANI powder were prepared by mechanical mixing on a two-roll mill. PANI was synthesized by chemical polymerization of aniline in presence of hydrochloric acid. PANI coated nylon fiber was prepared by in situ polymerization of aniline on nylon fiber. The cure parameters cure kinetics, filler dispersion, mechanical properties, DC electrical conductivity and thermal degradation parameters of the composites were evaluated. Cure rate index and cure reaction constants indicated that the rate of cure reaction changes on filler addition. Filler addition at higher loadings led to agglomeration. The tensile strength and modulus values increased suggesting a reinforcement effect. The conductivity, thermal characteristics and thermal degradation kinetic parameters are also presented. [Copyright &y& Elsevier]

Zinc oxide nanoparticles were synthesised by a homogeneous precipitation and calcination method. Their dimensions were in the range of 30 - 50 nm. Their performance as curing agent for polychloroprene rubber was compared to that of rubber grade zinc oxide. The tensile strength was observed to increase by 30% and elongation at break by 10%, with the tensile modulus almost unaltered. The crosslink density was increased by 15% and the dynamic modulus at 25 °C was also 10% higher for the nanocomposites. The results from FTIR spectrometry and volume fraction of rubber in the swollen gel supported the fact that there was an increased interaction between the rubber and ZnO for the nanocomposites. [ABSTRACT FROM AUTHOR]

Abstract: The effect of light and FeCl3·6H2O on polychloroprene (PCP)/natural rubber (NR) blends in toluene solution were investigated to demonstrate the influence of each polymer on the degradation process. The contributions of total polymer concentration (C p), temperature (T) and polychromatic light exposure (L) on the degradation process were investigated through a 23 factorial design approach. Degradation kinetics was examined by solution viscosity time data. FTIR spectroscopy and TGA were used to characterize the degradation. The exposure of the PCP/NR blend solution containing FeCl3·6H2O to light induces degradation in the polymers. A decrease of up to 70% in solution efflux time at constant temperature and without aggregation or phase separation was observed. PCP degradation by-products amplify the degradation of NR, as evidenced by the decrease in the PCP/NR 1:99 (w/w) solution efflux time, which was larger than that of the pure NR solution. The film cast from the solution exposed to light was thermally less stable than the one which was cast without FeCl3·6H2O. [Copyright &y& Elsevier]

High-performance material is typically used as bullet-resisting material. Although high-performance resists bullet penetration, it does not guarantee against non-penetrating damage. Design of a structure for reducing the non-penetrating damage would be useful. An elastic cushion structure has been used extensively for impact resistance. In this study, chloroprene rubber material was utilized to decay and transmit energy after being hit with a bullet. The cushion effect was examined based on the deformation of oil clay during a shooting test. The form of the elastic cushion structure and sequence of laminates were changed to determine the influence of these parameters on the cushion effect of a Kevlar laminated compound fabric. The reduction of non-penetrating damage and increase in safety use were achieved by designing a structure that reduced bullet impact. [ABSTRACT FROM AUTHOR]

The performance of protective gloves against metalworking fluids (MWFs) has rarely been studied because of the difficult chemical analysis associated with complex MWFs. In the present study, glove swelling was used as a screening parameter of glove compatibility after challenge of the outer surfaces of chloroprene, latex, nitrile, and vinyl disposable gloves by six MWF concentrates for 2 hours in an ASTM F-739-type permeation cell without collection medium. Swelling relative to original thickness was up to 39% for latex, 7.6% for chloroprene, and 3.5% for nitrile. Shrinking up to 9.3% occurred for vinyl. Chloroprene and latex did not swell significantly for the semisynthetic and synthetic MWFs. Vinyl, previously not tested, was a good candidate for MWFs other than the soluble oil type. Although nitrile was recommended by the National Institute for the Occupational Safety and Health (NIOSH) for all types of MWFs, its swelling after 2-hour challenge was significant with Student t-tests for the soluble oil, synthetic, and semisynthetic MWFs. Glove swelling can be used as a screening chemical degradation method for mixtures such as MWFs with difficult chemical analysis. Further studies need to be conducted on the relationship between permeation and glove swelling. [ABSTRACT FROM AUTHOR]

There has been a growing and widespread interest in the development of radar absorbing materials (RAM). Z-type hexaferrite is one of the most complex compounds in the family of hexaferrites that may be used in many applications. In this work, the citrate sol-gel process under an inert atmosphere was used to obtain the nanocrystalline Ba3Co0.9Cu1.1Fe24O41 powder to be used as RAM. Cu2+ ions were incorporated into the structure of Ba3Co2Fe24O41 and, consequently, low temperature sintering and good magnetic propertias were achieved. Composites of Ba3Co2Fe24O41 with polychloroprene (CR) were obtained for microwave absorption measurements by the transmission/reflection method, using a wavegnide medium for the S- band and X-Ku bands. The 80:20 nanocomposite of Ba3Co0.9Cu1.1 Fe24O41:CR with 3.0 ram thickness exhibited the best performance as a RAM for the X-band, with 99.50% microwave absorption at 9.5 GHz. [ABSTRACT FROM AUTHOR]

The aim was to investigate the permeation of a straight oil metalworking fluid (MWF) through four types of glove materials using the gravimetric method and the modified American Society for Testing and Materials (ASTM) F739-99a method with perfluorohexane and hexane as collection solvents. The residual masses on the collection side were determined after solvent evaporation for both MWF and blank (air) challenges. With perfluorohexane, the permeated MWF through gloves after 8h was around the lower quantifiable limit for nitrile, 0.7±0.2mg/cm2 for vinyl, 10.0±1.2mg/cm2 for chloroprene, and 33.0±0.7mg/cm2 for latex. Hexane increased the amounts and rates of MWF permeating all gloves 39–73 times, except for vinyl where extractable mass was so high that the residues for MWF challenges and for hexane blanks were indistinguishable. Hexane as a collection solvent also extracted more glove components than did perfluorohexane, and back-permeated gloves in much larger amounts. Perfluorohexane allows better estimates of the real permeation rates and breakthrough times than does hexane. Recommendations based on breakthrough times and permeation rates with hexane collection are thus too conservative, although the relative ranking of these four types of gloves was the same with either collection solvent. [Copyright &y& Elsevier]

Blends of 75/25 chloroprene rubber(CR)/natural rubber (NR) filled with various loadings of precipitated silica were prepared and their processability and mechanical properties as well as their resistance to thermal aging and oil were determined. The blend morphology was also studied using the atomic force microscopy technique. The results reveal that the mixing energy and the Mooney viscosity of the compound are increased continuously with increasing silica loading. It is also found that both scorch and optimum curing times are shortened while the total crosslink density is increased with increasing silica loading. The positive effect on cure could be explained by the chemical reaction between the allylic chlorine atom of CR and the silanol group on silica surface. The tensile strength, modulus, and hardness of the blend vulcanizate are noticeably improved while the compression set at elevated temperature is impaired with increasing silica loading. The results also reveal that both thermal aging resistance and oil resistance of the blend vulcanizates, as represented by the relative properties, are enhanced with the addition of silica. The resistance enhancement is believed to arise from the combination of the dilution effect, the increased crosslink density and also the reduction of NR dispersed phase size. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [ABSTRACT FROM AUTHOR]

The article studies the surface morphology of polychloroprene and piperylene-styrene copolymer (PSC) blend films using atomic force microscopy. The authors also investigated the dependence of the blend films surface roughness on PSC content with both fractal and correlation analyses. The Gaussian profiles for the height distribution upon blend composition were also studied by the authors.

Abstract: Thermal degradation experiments have been performed by thermogravimetry in order to study the kinetics of the decomposition of polychloroprene at different heating rates (5, 10 and 20°C/min) and different atmospheres (N2, N2:O2 9:1 and N2:O2 4:1). Some of the experiments were partially conducted in isothermal conditions in order to cover a wider range of operating conditions. Two different reaction models were proposed, one for pyrolysis and another one for combustion, which proved to simulate appropriately the experimental results at all the heating rates simultaneously. [Copyright &y& Elsevier]

2-Triethylsiloxy-substituted 1,3-butadiene has been prepared in gram quantities from chloroprene via a simple synthetic procedure. Silatrane and catechol-substituted analogues of this main group element substituted diene were prepared by ligand exchange and characterized by X-ray crystallography in addition to standard spectroscopic techniques. Diels−Alder reactions of these dienes are reported as well as subsequent TBAF assisted/Pd-catalyzed Hiyama cross-coupling reactions of those Diels−Alder adducts. [ABSTRACT FROM AUTHOR]

Abstract: Beta-chloroprene (C4H5Cl, chloroprene, 2-chloro-1,3-butadiene, CASRN 126-99-8) is a volatile, flammable liquid monomer utilized primarily in the manufacture of neoprene (polychloroprene) elastomer used in belts, hoses, gloves, wire coatings, and tubing. Absorption into the body occurs primarily via the respiratory system and may occur via the gastrointestinal tract or the skin. Once absorbed, chloroprene is widely distributed as evidenced by effects in several target organs including nose and lung, liver, and skin. Chloroprene metabolism is believed to include cytochrome P450 oxidation to a monoepoxide, hydrolysis by epoxide hydrolases, and glutathione conjugation. Similar to 1,3-butadiene, the epoxide is considered to be the toxic moiety, and species differences in metabolic capacity may influence the severity of effects as well as what tissues are affected. EPA has not previously developed an assessment of chloroprene''s potential for human health effects. Existing human epidemiological studies offer little data on noncancer effects, and the associations of exposure with increased cancer (liver and lung) mortality reported are inconclusive. Recent epidemiological studies (submitted for publication) could offer information that may impact chloroprene''s health assessment. Multiple-site tumors have been reported in rats and mice exposed to chloroprene by inhalation; nevertheless, there are marked differences in strain sensitivities (i.e., tumors in F344 rats versus no tumors in Wistar rats). Recently developed physiologically based toxicokinetic models may allow for the resolution of species and tissue differences and sensitivities as well as exposure—dose–response relationships relevant to humans. (This presentation does not necessarily reflect EPA policy.) [Copyright &y& Elsevier]

Abstract: Mathematical models are increasingly being used to simulate events in the exposure-response continuum, and to support quantitative predictions of risks to human health. Physiologically based pharmacokinetic (PBPK) models address that portion of the continuum from an external chemical exposure to an internal dose at a target site. Essential data needed to develop a PBPK model include values of key physiological parameters (e.g., tissue volumes, blood flow rates) and chemical specific parameters (rate of chemical absorption, distribution, metabolism, and elimination) for the species of interest. PBPK models are commonly used to: (1) predict concentrations of an internal dose over time at a target site following external exposure via different routes and/or durations; (2) predict human internal concentration at a target site based on animal data by accounting for toxicokinetic and physiological differences; and (3) estimate variability in the internal dose within a human population resulting from differences in individual pharmacokinetics. Himmelstein et al. [M.W. Himmelstein, S.C. Carpenter, P.M. Hinderliter, Kinetic modeling of beta-chloroprene metabolism. I. In vitro rates in liver and lung tissue fractions from mice, rats, hamsters, and humans, Toxicol. Sci. 79 (1) (2004) 18–27; M.W. Himmelstein, S.C. Carpenter, M.V. Evans, P.M. Hinderliter, E.M. Kenyon, Kinetic modeling of beta-chloroprene metabolism. II. The application of physiologically based modeling for cancer dose response analysis, Toxicol. Sci. 79 (1) (2004) 28–37] developed a PBPK model for chloroprene (2-chloro-1,3-butadiene; CD) that simulates chloroprene disposition in rats, mice, hamsters, or humans following an inhalation exposure. Values for the CD-PBPK model metabolic parameters were obtained from in vitro studies, and model simulations compared to data from in vivo gas uptake studies in rats, hamsters, and mice. The model estimate for total amount of metabolite in lung correlated better with rodent tumor incidence than did the external dose. Based on this PBPK model analytical approach, Himmelstein et al. [M.W. Himmelstein, S.C. Carpenter, M.V. Evans, P.M. Hinderliter, E.M. Kenyon, Kinetic modeling of beta-chloroprene metabolism. II. The application of physiologically based modeling for cancer dose response analysis, Toxicol. Sci. 79 (1) (2004) 28–37; M.W. Himmelstein, R. Leonard, R. Valentine, Kinetic modeling of β-chloroprene metabolism: default and physiologically-based modeling approaches for cancer dose response, in: IISRP Symposium on Evaluation of Butadiene & Chloroprene Health Effects, September 21, 2005, TBD—reference in this proceedings issue of Chemical–Biological Interactions] propose that observed species differences in the lung tumor dose–response result from differences in CD metabolic rates. The CD-PBPK model has not yet been submitted to EPA for use in developing the IRIS assessment for chloroprene, but is sufficiently developed to be considered. The process that EPA uses to evaluate PBPK models is discussed, as well as potential applications for the CD-PBPK model in an IRIS assessment. [Copyright &y& Elsevier]

Abstract: Chloroprene (2-chloro-1,3-butadiene, 1) is oxidised by cytochrome P450 enzymes in mammalian liver microsomes to several metabolites, some of which are reactive towards DNA and are mutagenic. Much less of the metabolite (1-chloroethenyl)oxirane (2a/2b) was formed by human liver microsomes compared with microsomes from Sprague-Dawley rats and B6C3F1 mice. Epoxide (2a/2b) was a substrate for mammalian microsomal epoxide hydrolases, which showed preferential hydrolysis of the (S)-enantiomer (2b). The metabolite 2-chloro-2-ethenyloxirane (3a/3b) was rapidly hydrolysed to 1-hydroxybut-3-en-2-one (4) and in competing processes rearranged to 1-chlorobut-3-en-2-one (5) and 2-chlorobut-3-en-1-al (6). The latter compound isomerised to (Z)-2-chlorobut-2-en-1-al (7). In microsomal preparations from human, rat and mouse liver, compounds 4, 5 and 7 were conjugated by glutathione both in the absence and presence of glutathione transferases. There was no evidence for the formation of a chloroprene diepoxide metabolite in any of the microsomal systems. The major adducts from the reaction of (1-chloroethenyl)oxirane (2a/2b) with calf thymus DNA were identified as N7-(3-chloro-2-hydroxy-3-buten-1-yl)-guanine (20) and N3-(3-chloro-2-hydroxy-3-buten-1-yl)-2′-deoxyuridine (23), with the latter being derived by alkylation at N-3 of 2′-deoxycytidine, followed by deamination. Adducts in DNA were identified by comparison with those derived from individual deoxyribonucleosides. The metabolite (Z)-2-chlorobut-2-en-1-al (7) formed principally two adducts with 2′-deoxyadenosine which were identified as a pair of diastereoisomers of 3-(2′-deoxy-β-d-ribofuranosyl)-7-(1-hydroxyethyl)-3H-imidazo[2,1-i]purine (25). The chlorine atom of chloroprene thus leads to different intoxication and detoxication profiles compared with those for butadiene and isoprene. The results infer that in vivo oxidations of chloroprene catalysed by cytochrome P450 are more important in rodents, whereas hydrolytic processes catalysed by epoxide hydrolases are more pronounced in humans. The reactivity of chloroprene metabolites towards DNA is important for the toxicology of chloroprene, especially when detoxication is incomplete. [Copyright &y& Elsevier]

Abstract: Chloroprene (2-chloro-1,3-butadiene, CAS 126-99-8, CP) is a colorless volatile liquid used in manufacture of polychloroprene, a synthetic rubber polymer. National Toxicology Program inhalation studies of CP in rats and mice gave clear evidence of carcinogenic activity. CP is metabolized by CYP2E1 to electrophilic epoxides, including R- and S-(1-chloroethenyl)oxirane (CEO), which form adducts with nucleic acids and other nucleophiles including glutathione and hemoglobin. As detection of these epoxide metabolites in vivo is technically challenging, measurements of CEO-Hb adducts may provide biomarkers of exposure to bioactivated metabolites of CP. The present studies involved exposure of C57BL/6 mouse erythrocytes (RBC) in vitro to pure enantiomers of CEO. Headspace analysis of CEO using Cyclodex-B capillary GC/MS with selected ion monitoring enabled separation, specific detection, and quantification of CEO enantiomers as reactions proceeded in vitro with RBC. These analyses indicated that R-CEO was much more persistent when incubated in vitro with RBC, while S-CEO disappeared rapidly. After periods of exposure of RBC to various concentrations of R- or S-CEO, erythrocytes were lysed and globin isolated. Covalent adducts, formed by reaction of CEO with N-terminal valine in Hb, were analyzed following Edman cleavage and trimethylsilylation. SIM-GC/MS analyses using a 5%-phenyl-dimethylsiloxane capillary column enabled quantification of CEO-Hb adducts. These analyses produced two chromatographic peaks of CEO-valine adduct derivatives, which were tentatively identified from mass spectra, reaction, and abundance data to be 1-(3-chloro-2-trimethylsilyloxybut-3-en-1-yl)-5-isopropyl-3-phenyl-2-thiohydantoin and 1-[2-chloro-1-(trimethylsilyloxymethyl)prop-2-en-1-yl]-5-isopropyl-3-phenyl-2-thiohydantoin. Analyses quantified significantly greater levels of adducts formed from R-CEO than from S-CEO. Studies involving pretreatment of RBC with glutathione-depleting diethyl maleate diminished the selective detoxification of S-CEO, and suggest enantiomeric selectivity of mouse glutathione-S-transferase as a mechanism of differential detoxification of CEO enantiomers. These results indicate more rapid detoxification of S-CEO by mouse RBC in vitro, while R-CEO may persist to react with cellular nucleophiles. [Copyright &y& Elsevier]

Abstract: As part of an historical cohort study to investigate the mortality experience of industrial workers exposed to chloroprene (CD) and other substances, including vinyl chloride monomer (VC), we analyzed mortality from all cancers combined, respiratory system (RSC) and liver cancer in relation to CD and VC exposures. Subjects were 12,430 workers ever employed at one of two U.S. sites (Louisville, KY (n =5507) and Pontchartrain, LA (n =1357)) or two European sites (Maydown, Northern Ireland (n =4849) and Grenoble, France (n =717)). Historical exposures for individual workers were estimated quantitatively for CD and VC. For sites L, M, P and G, respectively, average intensity of CD exposures (median value of exposed workers in ppm) were 5.23, 0.16, 0.028 and 0.149 and median cumulative exposures (ppmyears) were 18.35, 0.084, 0.133 and 1.01. For sites L and M, respectively, average intensity of VC exposures (median value of exposed workers in ppm) was 1.54 and 0.03 and median cumulative exposures (ppmyears) were 1.54 and 0.094. We performed relative risk (RR) regression modeling to investigate the dependence of the internal cohort rates for all cancers combined, RSC and liver cancer on combinations of the categorical CD or VC exposure measures with adjustment for potential confounding factors. We categorized exposure measures into approximate quartiles based on the distribution of deaths from all cancers combined. We also considered 5- and 15-year lagged exposure measures and adjusted some RR models for worker pay type (white/blue collar) as a rough surrogate for lifetime smoking history. All modeling was site-specific to account for exposure heterogeneity. We also computed exposure category-specific standardized mortality ratios (SMRs) to assess absolute mortality rates. With the exception of a one statistically significant association with duration of exposure to CD and all cancers combined in plant M, we observed no evidence of a positive association with all cancers, RSC or liver cancer and exposure to CD and/or VC using both the unlagged and lagged exposure measures: duration, average intensity or cumulative exposure to CD or VC; time since first CD or VC exposure; and duration of CD exposure or time since first CD exposure in presence or absence of VC exposure. We observed elevated and statistically significantly elevated RRs for some analysis subgroups, but these were due to inordinately low death rates in the baseline categories. With the possible exception of all cancer mortality in plant G, our additional adjustment of RRs for pay type revealed no evidence of positive confounding by smoking. We conclude that exposures to CD or VC at the levels encountered in the four study sites do not elevate mortality risks from all cancers, RSC or liver cancer. This conclusion is corroborated by our analysis of general mortality patterns among the CD cohort reported in our companion paper [G. Marsh, A. Youk, J. Buchanich, M. Cunningham, N. Esmen, T. Hall, M. Phillips, Mortality patterns among industrial workers exposed to chloroprene and other substances. I. General mortality patterns, Chem.-Biol. Interact., submitted for publication]. [Copyright &y& Elsevier]

Abstract: The DuPont Company has maintained a mortality registry for all active and pensioned U.S. employees since 1957. Standardized mortality ratios (SMRs) for each plant site in the U.S. can be calculated based on the comparison with the entire U.S. DuPont population or with a regional subset of DuPont employees. We compared the SMRs derived from a large, international cohort mortality study of chloroprene workers (IISRP study) with those derived from the entire DuPont Registry and appropriate subpopulations of the registry for two U.S. neoprene plants—Louisville (Kentucky) and Pontchartrain (Louisiana). SMRs from the IISRP study for the Louisville cohort based on national rates for all causes of death, all cancers, respiratory cancer, and liver cancer are higher than those based on local mortality rates. Both the national and local comparisons (several counties surrounding each plant) for all-cancer SMRs are lower than 1.0, the local comparison being statistically significantly reduced. In contrast, the SMRs based on the total U.S. DuPont worker mortality rates for all causes of death (1.13), all cancers (1.11), and respiratory cancers (1.37) are statistically significantly increased. The SMR for liver cancer (1.27), although elevated, is not statistically significant. SMRs based on DuPont Region 1 were closer to 1.0, and the SMR for all cancers was no longer significant. Stratification of the Louisville subcohort of males using the same cumulative exposure categories used in the IISRP study yielded SMRs calculated against DuPont Region 1 that were generally higher than those calculated against U.S. and local rates. Only the third exposure category showed SMRs statistically significantly above 1.0 for all cancers and for cancer of bronchus, trachea, and lung. However, there does not appear to be an exposure–response trend. The SMRs from the IISRP study for the Pontchartrain cohort based on national rates are higher than those based on local rates for all causes of death, but all are less than 1.0. The all-cause SMRs for both local and national comparisons are significantly reduced. There were no deaths from liver cancers observed in this cohort. Comparisons of the Pontchartrain cohort against the total U.S. DuPont worker mortality rates resulted in higher SMRs for all causes of death (0.98), all cancers (1.03), and respiratory cancer (1.08), but none were statistically significant. SMRs based on DuPont Region 2 showed very little change from those based on the total registry. The use of reference rates based on regional workers in the same large company produces SMRs lower than those based on the entire company population (regional socio-cultural effects) but higher than those based on geographically closer local general populations (healthy worker effect). The healthy worker effect is seen in cancer mortality rates as well as in other chronic diseases. [Copyright &y& Elsevier]

Abstract: We conducted an historical cohort study to investigate the mortality experience of industrial workers potentially exposed to chloroprene (CD) and other substances, including vinyl chloride (VC), with emphasis on cancer mortality, including respiratory system (RSC) and liver. In 1999, the International Agency for Research on Cancer (IARC) classified CD as a possible carcinogen (Group 2B); VC was classified in 1987 as a known human carcinogen (Group 1). Subjects were 12,430 workers ever employed at one of two U.S. industrial sites (Louisville, KY (n =5507) and Pontchartrain, LA (n =1357)) or two European sites (Maydown, Northern Ireland (n =4849) and Grenoble, France (n =717)), with earliest CD production dates ranging from 1942 (L) to 1969 (P). Two sites (L and M) synthesized CD with the acetylene process that produced VC exposures. We determined vital status through 2000 for 95% of subjects and cause of death for 95% of the deaths. Historical exposures for individual workers were estimated quantitatively for CD and VC. Workers ever exposed to CD ranged from 92.3% (M) to 100% (G); to VC from 5.5% (M) to 22.7% (L). We computed standardized mortality ratios (SMRs) (using national and regional standard populations) in relation to selected demographic, work history and exposure factors. We used worker pay type (white or blue collar) as a rough surrogate for lifetime smoking history. For the combined cohort, SMRs (95% CIs) for all causes combined, all cancers combined, RSC and liver cancer were, respectively, 0.72 (0.69–0.74), 0.73 (0.68–0.78), 0.75 (0.67–0.84) and 0.72 (0.43–1.13). Site-specific (L, M, P and G, respectively) SMRs were: for all cancers combined: 0.75 (0.69–0.80), 0.68 (0.56–0.80), 0.68 (0.47–0.95) and 0.59 (0.36–0.91); for RSC: 0.75 (0.66–0.85), 0.79 (0.58–1.05), 0.62 (0.32–1.09) and 0.85 (0.41–1.56); for liver cancer: 0.90 (0.53–1.44) (17 deaths), 0.24 (0.01–1.34) (1 death), 0.0 (0–2.39) (no deaths) and 0.56 (0.01–3.12) (1 death). Among all workers ever exposed to CD, SMRs were: for all cancers combined: 0.71 (0.66–0.76); for RSC: 0.75 (0.67–0.84); for liver cancer: 0.71 (0.42–1.14). We also observed no increased mortality risks among cohort subgroups defined by race, gender, worker pay type, worker service type (short/long term), time period, year of hire, age at hire, duration of employment, the time since first employment, and CD or VC exposure status (never/ever exposed). In summary, our study has many strengths and is the most definitive study of the human carcinogenic potential of exposure to CD conducted to date. We conclude that persons exposed to chloroprene or vinyl chloride at the levels encountered in the four study sites did not have elevated risks of mortality from any of the causes of death examined, including all cancers combined and lung and liver cancer, the cancer sites of a priori interest. This conclusion is corroborated by our detailed analyses of mortality in relation to qualitative and quantitative exposures to CD and VC at each of the four study sites, reported in our companion paper (Marsh et al., submitted for publication). [Copyright &y& Elsevier]

Abstract: As part of an historical cohort study to investigate the mortality experience of industrial workers exposed to chloroprene (β-CD) and other substances, all available industrial hygiene exposure monitoring data were collected and summarized. From discussions with on-site industrial hygiene personnel, it was apparent that these data were not collected for epidemiological purposes and, therefore, their use in characterization of exposures was problematic as the data mostly pertained to samples collected to investigate the performance of specific tasks. These data were, however, informative for validating the exposure modeling process used to estimate historical exposures. The data summarized below clearly indicate that exposures to β-CD were lowered across the time period of this study. Typically, the exposures recorded were less than the occupational exposure limits of the periods in which the exposures were recorded. Additionally, exposure measurements recorded in the recent past do not represent the exposure actually experienced by the worker as a strict personal protective equipment use program has been in place for the facilities studied since the mid-1980s. [Copyright &y& Elsevier]

Abstract: In a four-facility occupational epidemiology study of chloroprene monomer and polymer production workers, the chloroprene (CD) and vinyl chloride monomer (VCM) exposures were modeled for plant specific job title classes. In two facilities an acetylene-based process was used and in the other two plants only a butadiene-based process was used in the monomer synthesis. In the Acetylene process VCM was an undesirable by-product to be removed. In the newer butadiene-based process, VCM was not involved and the exposures to CD were considerably lower than they were in the earlier years. One of the limiting factors was the operator rotation within a number of job titles. This rotation and inability to differentiate between job titles subsumed in job classifications recorded in the work histories required an exposure classification scheme based on an order of magnitude separation of exposure classes. In the four facilities with considerable variation in the mix of the production methods, the CD exposures were remarkably similar in both calculated and measured values. The reductions in exposures were much more dependent upon the improvement of the production methods, rather than deliberate exposure control for occupational hygiene considerations. This is reasonable since the exposures were generally lower than the coeval exposure limits and/or guidelines. The estimated exposures were less than 100ppm in the pre-1960 era and less than 10ppm in the 1960–1980 era, less than 1ppm 1980–1990 era and less than 0.5ppm thereafter. The exposures were categorized in four classes for VCM and six classes for CD. The characteristic class exposure values were used to cumulate individual exposures over time with a quantification of the potential range for exposures that are reasonably certain to ascribe correct ranking to job classes. [Copyright &y& Elsevier]

Abstract: 1,3-Butadiene and chloroprene are multisite carcinogens in B6C3F1 mice with the strongest tumor response being the induction of lung neoplasms in females. Incidence of brain tumors in mice exposed to 1,3-butadiene was equivocal. This article reviews the efforts of our laboratory and others to uncover the mechanisms of butadiene and chloroprene induced lung and brain tumor responses in the B6C3F1 mouse. The formation of lung tumors by these chemicals involved mutations in the K-ras cancer gene and loss of heterozygosity in the region of K-ras on distal chromosome 6, while alterations in p53 and p16 were implicated in brain tumorigenesis. [Copyright &y& Elsevier]

Abstract: The 2005 International Symposium on the evaluation of butadiene and chloroprene health risks provided the opportunity to consider the past, present and future state of research issues for 1,3-butadiene. Considerable advancements have been made in our knowledge of exposure, metabolism, biomarkers of exposure and effect, and epidemiology. Despite this, uncertainties remain which will impact the human health risk assessment for current worker and environmental exposures. This paper reviews key aspects of recent studies and the role that biomarkers of internal dosimetry can play in addressing low to high exposure, gender, and cross-species differences in butadiene toxicity and metabolism. Considerable information is now available on the detection and quantification of protein adducts formed from the mono-, di- and dihydroxy-epoxide metabolites of butadiene. The diepoxide metabolite appears to play a key role in mutagenesis. Species differences in production of this critical metabolite are reflected by the diepoxybutane-specific hemoglobin adduct, pry-Val. To date, the pry-Val adduct has not been quantifiable in human blood samples from workers with cumulative occupational exposures up to 6.3ppm-weeks; whereas, the pry-Val was quantifiable in the blood of mice and rats with similar cumulative exposures. Levels in mice were much higher than in rats. Further improvements in analytical sensitivity for the pyr-Val adduct are on the horizon. Epidemiology studies are also described and ongoing efforts promise to help bridge our understanding of past and future risks. [Copyright &y& Elsevier]

Abstract: This paper provides information on 1,3-butadiene (BD) and chloroprene as atmospheric pollutants in Texas and reviews available emission estimates and monitoring data. Ambient BD concentrations in most areas of Texas are predominantly influenced by on-road and off-road vehicular emissions or biomass burning, since BD is a product of combustion. However, large industrial point sources of BD emissions in Texas locally influence ambient concentrations. Total industrial BD emissions to the atmosphere in Texas for 2003 were estimated at 695tonnes per year (TPY), approximately 70% of the total reported national industrial BD air emissions. Since 1998, there have not been any large industrial sources of chloroprene emissions in Texas, and total industrial chloroprene emissions for 2003 was estimated at only 0.09 TPY. Chloroprene was never detected at air monitoring sites. In 2003, the Texas Commission on Environmental Quality (TCEQ) monitored BD ambient air concentrations at 57 sites, some of which have been operational since 1992. These air monitors provide information on ambient BD concentrations in Texas and allow spatial and temporal trend evaluation. In 2003, annual average concentrations at monitoring sites in Texas ranged from less than the reporting limit of 0.01 to 3.2 parts per billion by volume (ppbv) with an overall average of 0.2ppbv. This overall average is reduced to 0.1ppbv if BD data from monitoring sites in Port Neches and Milby Park in Houston, which are located downwind of significant point sources of BD, are excluded. Ambient air monitoring has been conducted in Port Neches and in Milby Park in Houston since 1996 and 1999, respectively. At the Port Neches monitor, trend evaluation indicates that ambient concentrations of BD have declined since 1996 due to cooperative agreements with industries emitting BD. Annual average BD concentrations at the Port Neches monitor decreased from 8.3ppbv in 1996 to 1.3ppbv in 2003, giving an 8-year average of 3.8ppbv. Annual average BD concentrations at the Milby Park monitor varied between 2.1 and 4.4ppbv from 1999 through 2003, giving a 5-year average of 3.1ppbv. The results of cancer cluster studies based on Cancer Registry 1995–2001 incidence data and 1993–2002 mortality data conducted by the Texas Department of State Health Services for zip codes 77017/77012 (Houston) and 77651 (Port Neches) will be presented. [Copyright &y& Elsevier]

Abstract: These proceedings represent nearly all the platform and poster presentations given during the International Symposium on Evaluation of Butadiene and Chloroprene Health Risks, held in Charleston, South Carolina, USA, on September 20–22, 2005. The Symposium was attended by 78 participants representing private industry (37), academia (21), government (11), not-for-profit organizations (5), and consulting (4). The program followed the format of previous symposia on butadiene, chloroprene, and isoprene in London UK (2000) and butadiene and isoprene in Blaine, Washington USA (1995). This format enabled the exchange of significant new scientific results and discussion of future research needs. Isoprene was not evaluated during the 2005 Symposium because of lack of new data. For background information, the reader is referred to the proceedings of the London 2000 meeting for a thorough historical perspective and overview of scientific and regulatory issues concerning butadiene, chloroprene, and isoprene [Chem.-Biol. Interact. (2001) 135–136:1–7]. The Symposium consisted of seven sessions: (1) Introduction and Opening Remarks, (2) Butadiene/styrene-butadiene rubber (SBR)—Process Overview, Exposure and Health Effects/Human Studies; (3) Chloroprene—Process Overview, Exposure and Health Effects/Human Studies; (4) Mode of Action/Key Events; (5) Risk Assessment; (6) Poster Presentations; and (7) Panel Discussion and Future Directions. The Symposium concluded with a discussion by all participants of issues that arose throughout the course of the Symposium. The Proceedings of the Symposium published in this Special Issue are organized according to the Sessions outlined above. The purpose of this foreword is to summarize the presentations and their key findings and recommend future research directions for each chemical. [Copyright &y& Elsevier]

Abstract: The interaction between precipitated silica and chloroprene rubber (CR) was investigated using a nuclear magnetic resonance (NMR) technique. The results reveal that the silanol groups on silica surface could chemically react with CR. Crosslinking of CR is therefore possible in the presence of silica at high temperature. The effects of silica and ethylene thiourea (ETU) loadings on properties of the silica-filled CR were thereafter investigated. With increasing silica loading, the compound viscosity increases considerably due to the dilution effect. As silica could act as a curative for CR, increasing silica loading results in both faster cure rate and increased crosslink density. The optimum tensile strength is found at approximately 30phr of silica loading. The results also show that silica loading has little effect on most aging properties, except the relative modulus in which it increases rapidly with increasing silica loading due to the post curing effect. Similar to the effect of silica loading, the compound viscosity, cure rate and crosslink density are all increased with increasing ETU loading. The tensile strength is, on the other hand, slightly affected by ETU loading. Exception is found at high loading where the tensile strength drops noticeably. Interestingly, aging resistance of the vulcanizate is found to improve with the addition of ETU. Explanation is given by the hindrance capability of ETU to post curing. [Copyright &y& Elsevier]

Magnetically active elastomer materials were prepared by incorporating nickel powder in synthetic elastomeric matrices, polychloroprene and nitrile rubber. Cure characteristics, mechanical, electrical and magnetic properties were experimentally determined for different volume fractions of magnetoactive filler. The cure time decreases sharply for initial filler loading and the decrease is marginal for additional loading of filler. The tensile strength and modulus at 100% strain was found to increase with increase in the volume fraction of nickel due to reinforcement action. The magnetic impedance and a.c. conductivity are found to increase with increase in volume fraction of nickel as well as frequency. [ABSTRACT FROM AUTHOR]