Copper Doped Methylene Blue Sensitized Poly(vinyl alcohol)–Acrylamide Films for Stable Diffraction Efficiency

Copper doped methylene blue sensitized poly(vinyl alcohol) (MBPVA)–acrylamide films were fabricated to improve the storage life of recorded gratings. The films were fabricated using gravity settling method and the copper chloride concentration was optimized as 3:18 10 3 mol/l for a dye concentration of 6:2 10 4 mol/l. The gratings recorded on the optimized film constitution could be stored for months with stable diffraction efficiency (24%) without any chemical or thermal fixing techniques. The resolution of the material is found to be unaffected with the addition of copper chloride.

Studies on the Toughening of Epoxy Resins

This thesis aims to develop new toughened systems for epoxy resin via physical and chemical modifications. Initially the synthesis of DGEBA was carried out and the properties compared with that of the commercial sample. Subsequently the modifier resins to be employed were synthesized. The synthesized resin were characterized by spectroscopic method (FTIR and H NMR), epoxide equivalent and gel permeation chromatography. Chemical modification involves the incorporation of thermoset resins such a phenolics, epoxy novolacs, cardanol epoxides and unsaturated polyester into the epoxy resin by reactive belnding. The mechanical and thermal properties of the blends were studied. In the physical modification route, elastomers, maleated elastomers and functional elastomers were dispersed as micro-sized rubber phase into the continuous epoxy phase by a solution blending technique as against the conventional mechanical blending technique. The effect of matrix toughening on the properties of glass reinforced composites and the effect of fillers on the properties of commercial epoxy resin were also investigated. The blends were characterized by thermo gravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, scanning electron microscopy and mechanical property measurements. Among the thermoset blends, substantial toughening was observed in the case of epoxy phenolic novolacs especially epoxy para cresol novolac (ECN). In the case of elastomer blending , the toughest blends were obtained in the case of maleic anhydride grafted NBR. Among functional elastomers the best results were obtained with CTBN. Studies on filled and glass reinforced composites employing modified epoxy as matrix revealed an overall improvement in mechanical properties

Effect of curing temperature , fibre loading and bonding agent on the equilibrium swelling of isora-natural rubbercomposites

Isora fibre-reinforced natural rubber (NR) composites were cured at 80, 100, 120 and 150°C using a low temperature curing accelerator system. Composites were also prepared using a conventional accelerator system and cured at 150°C. The swelling behavior of these composites at varying fibre loadings was studied in toluene and hexane. Results show that the uptake of solvent and volume fraction of rubber due to swelling was lower for the low temperature cured vulcanizates which is an indication of the better fibre/rubber adhesion. The uptake of aromatic solvent was higher than that of aliphatic solvent, for all the composites. As the fibre content increased, the solvent uptake decreased, due to the superior solvent resistance of the fibre and good fibre-rubber interactions. The bonding agent improved the swelling resistance of the composites due to the strong interfacial adhesion. Due to the improved adhesion between the fibre and rubber, the ratio of the change in volume fraction of rubber due to swelling to the volume fraction of rubber in the dry sample (V,) was found to decrease in the presence of bonding agent. At a fixed fibre loading, the alkali treated fibre composite showed a lower percentage swelling than untreated one for both systems showing superior rubber-fibre interactions.

A Novel Accelerator Combination for the Low Temperature Curing of Silica-Filled NBR Compounds

Zinc salts of ethyl, isopropyl, and butyl xanthates were prepared in the laboratory. The effect of these xanthates in combination with zinc diethyldithiocarbamate (ZDC) on the vulcanization of silica-filled NBR compounds has been studied at different temperatures. The cure times of these compounds were compared with that of NBR compounds containing tetramethylthiuram disulphide/dibenzthiazyl disulphide. The rubber compounds with the xanthates and ZDC were cured at various temperatures from 60 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density, elongation at break, compression set, abrasion resistance, flex resistance, heat buildup, etc. were evaluated. The properties showed that zinc salt of xanthate/ZDC combination has a positive synergistic effect on the cure rate and mechanical properties of NBR compounds.

Low Temperature Curing of NBR for Property Improvement

Zinc salts of ethyl, isopropyl, and butyl xanthates are prepared in the laboratory, and the effect of these xanthates with zinc diethyl dithiocarbamate (ZDC) on the vulcanization of HAF-filled nitrile butadiene rubber (NBR) compounds has been studied at different temperatures. The cure times of these compounds have been compared with that of NBR compounds containing TMTD/MBTS. The rubber compounds with the three xanthate accelerators and ZDC are cured at various temperatures from 60 to 150°C. The sheets are molded and properties such as tensile strength, tear strength, cross-link density, elongation at break, compression set, abrasion resistance, flex resistance, etc. have been evaluated. The properties show that zinc salt of the xanthate/ZDC accelerator system has a positive synergistic effect on the cure rate and mechanical properties of NBR compounds.

Studies on Xanthate/Dithiocarbamate Accelerator Combination in NR/BR Blends

Zinc butyl xanthate [Zn(bxt)2] was prepared in the laboratory . The effect of this xanthate with zinc diethyl dithiocarbamate (ZDC) on the vulcanization of natural rubber ( NR), polybutadiene rubber (BR), and NR/BR blend has been studied at different temperatures. The amounts of Zn (bxt)2 and ZDC in the compounds were optimized by varying the amount of ZDC from 0 . 75 to 1.5 phr and Zn (bxt)2 from 0 . 75 to 1 .5 phr. The cure characteristics were also studied . HAF filled NR, BR, and NR / BR blend compounds were cured at different temperatures from 60 to 150 C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density and elongation at break, compression set, abrasion resistance, etc. were evaluated. The results show that the mechanical properties of 80NR/20BR blends are closer to that of NR vulcanizates, properties of 60NR/40BR blends are closer to BR vulcanizates, while the 70NR/30BR blends show an intermediate property.

Synergism of Xanthate/Dithiocarbamate Accelerator in Carbon Black Filled NR Compounds

Zinc salts of ethyl, isopropyl and butyl xanthates were prepared in the laboratory. The effect of these xanthates with zinc diethyldithiocarbamate (ZDC) on the vulcanization of HAF filled NR compound has been studied at different temperatures. The rubber compounds with the three xanthate accelerators and ZDC were cured at various temperatures from 60°C to 150°C. The sheets were moulded and properties such as tensile strength , tear strength , cross-link density, elongation -at-break, compression set, heat build up, abrasion resistance, flex resistance , etc. were evaluated . The properties showed that zinc xanthate/ZDC accelerator combination has a positive synergistic effect on the mechanical properties of NR compounds. The curing of HAF filled NR compound containing zinc xanthate /ZDC is slightly slower than the curing of the corresponding gum compounds . It is observed that, by gradually increasing the amount of the accelerator, the cure time of black filled NR compound can be made equal to that of the gum compou

EPDM/CIIR Blends : Effect of EPDM Grade on Mechanical Properties

Blends of chlorobutyl rubber (CIIR) with two grades of ethylene-propylene diene monomer rubber (EPDM) were prepared and the effect of blend ratio on the cure characteristics, hot air ageing resistance, steam ageing resistance, and mechanical properties were evaluated. The blend of CIIR with EPDM grade 301 T showed additive behavior and the blend with the other grade of EPDM (NDR 4640) showed synergistic behavior.

Recycling of NR Based Cured Latex Material Reclaimed with 2,2'-Dibenzamidodiphenyldisulphide in a TruckTire Tread Compound

It is observed that reclamation of natural rubber latex based rubber using 2,2'-dibenzamidodiphenvldisulphide as reclaiming agent is an optional methodology for recycling of waste latex rubber (WLR). For progressive replacement of virgin natural rubber by the reclaim, two alternatives curing system were investigated: adjustment or reduction of the curing system with increasing reclaim content, to compensate for the extra amount of curatives brought along by the reclaim. For fixed curing system, as if the reclaim were equivalent to virgin NR. The cure behavior, final crosslink density and distribution, mechanical properties, and dynamic viscoelastic properties of the blends with reclaimed WLR are measured and compared with the virgin compound. The morphology of the blends, sulfur migration, and final distribution are analyzed.The mechanical and dynamic viscoelastic properties deteriorate for both curing systems, but to a lesser extent for fixed curing system compared to adjusted curing system. With the fixed cure system, many properties like tensile strength and compression set do still deteriorate, but tan 6 and Mrrr„/Murxr, representative for the rolling resistance of tires are improved. On the other hand, with the adjusted cure system both mechanical and dynamic properties still deteriorate.

Effect of Diphenyldisulfides with Different Substituents on the Reclamation of NR Based Latex Products

The latex industry has expanded over the years to meet the world demands for gloves, condoms, latex thread etc. Because of the strict specifications for the products and the unstable nature of the latex, as high as 15%, of the final latex products are rejected. Since waste latex rubber (WLR) represents a source of high quality rubber hydrocarbon, it is a potential candidate for generating reclaimed rubber of superior quality. Two types of WLR with different amounts of polysulfidic bridges are used in these experiments, which are reclaimed with variation of the concentration of the reclaiming agents, the reclamation temperature and time, Di phenyldisultide, 2-aminophenyldisulfide and 2,2'-dibenzamidodiphenyldisulfide (DBADPDS) are used as reclaiming agents, and the effect of diphenyldisulfides (DPDS) with different substituents, on the reclamation efficiency of WLR is investigated. A kinetic study of the reclamation reaction with the three reclaiming agents is done. The reaction rates and activation energies are calculated and compared with literature values. The comparative study of the three different reclaiming agents shows that (DBADPDS) is able to break the crosslinks at temperature levels 20'C below the temperature levels normally used with DPDS. Another advantage of this reclaiming agent is the reduced smell during the reclamation process and of the final reclaims, one of the most important shortcomings of other disulfides used for this purpose.

Blends of Polychloroprene and Polyvinylchloride

Blends of polychloroprene rubber and plasticized polyvinylchloride have been prepared in various compositions and their properties evaluated. The properties of the blends show that they can be used to replace polychloroprene in many applications

Study of the Effect of Polyethylene Glycols and Glycerol in Filled Natural RubberLatex Vulcanizates

The mechanical properties of filled natural rubber latex vulcanizates were found to be improved by the addition of polyethylene glycols of different molecular weight and glycerol. There is a slight reduction in the optimum cure times of the compounds containing PEG/Glycerol. The morphology study shows that the filler distribution is more uniform in the compounds containing PEG/Glycerol.

Improved Mechanical Properties of NR/EPDM and NR/Butyl Blends by Precuring EPDM and Butyl

Ethylene-propylene-diene rubber (EPDM) and isobutylene-isoprene rubber (IIR) were compounded, precured to a low degree, and then were blended with natural rubber (NR). The compounding ingredients for NR were then added and the final curing was done. NR/ EPDM and NR/IIR blends, prepared using this method, were found to possess much improved mechanical properties as compared to their conventional counterparts. The optimum precuring crosslink density that has to be given to the EPDM and IIR phases has been determined.

Utilisation of IIR Tube Reclaim for Developing NR/IIR Blends

Butyl (IIR) tube reclaim (RR) was mixed with carbon black filled natural rubber (NR) compounds at various percentages. The blend containing a low percentage of RR was found to show improved ageing resistance and improved processability with out much reduction in the mechanical properties.

Polymer-Solvent Interaction Parameter for NR/SBR and NR/BR Blends

Polymer-solvent interaction parameters for the blends of natural rubber (NR) with styrene-butadiene rubber (SBR) and polybutadiene rubber ( BR) are calculated using the Flory-Rehner equation by equating the network density of the vulcanizates in two solvents.