Browsing by Author "PAL, SN"

Now showing 1 - 6 of 6
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    CURING OF VISIBLE LIGHT-ACTIVATED DENTAL RESTORATIVE COMPOSITES
    (BULLETIN OF MATERIALS SCIENCE, 1991) PAL, SN; VOWLES, R; WILLIAMS, DF
    FTIR spectroscopy and microhardness measurements were employed to follow the degree of curing of visible light activated dental composites. The observed dependence of curing on grade and shade of the materials, exposure time and depth from the light exposed surface have been discussed. Immediately after curing, it was found that direct correlation of microhardness values with that of double bond conversion estimated by FTIR technique could not be established.
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    EVALUATION OF DGEBA
    (JOURNAL OF APPLIED POLYMER SCIENCE, 1991) TAMARESELVY, K; SHEELA, MS; KALLIYANAKRISHNAN, V; PAL, SN
    Analytical studies using chemical, spectral, and chromatographic methods have been carried out for four commerical diglycidyl ether of bisphenol A (DGEBA) resins (AER, EER, DER, and NER) in order to evaluate the essential parameters of DGEBA for synthesizing 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)]phenyl propane (BIS-GMA), an important precursor for dental composites. Parameters such as epoxy equivalent weight, hydroxyl value, and hydrolyzable chlorine content have been estimated. The role of these parameters in determining the final purity of BIS-GMA has also been discussed.
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    GAS-PERMEABILITY STUDIES ON POLY(VINYL CHLORIDE) BASED POLYMER BLENDS INTENDED FOR MEDICAL APPLICATIONS
    (JOURNAL OF APPLIED POLYMER SCIENCE, 1992) PAL, SN; RAMANI, AV; SUBRAMANIAN, N
    Plasticized PVC finds applications in a wide range of medical products. However, plasticizer leaching, known to take place from these conventional materials, is not desirable. A number of approaches to overcome this problem are mentioned in the literature. We suggest pursuing the polyblend approach. Plasticized PVC containing different amounts of plasticizer, binary polyblends of plasticized PVC (PPVC) with acrylonitrile-butadiene rubber (NBR1), and compounded graft polymer of vinyl chloride and ethylene-vinyl acetate copolymer (EVAPVC), and ternary blends of PPVC, NBR1, and EVAPVC, were formulated. In this article, we report our results of studies on water vapor, O2, CO2, and N2 permeabilities. Increased plasticization for PVC was found to increase permeability for water vapor, O2, CO2, and N2. Rise in temperature increased the permeability for water vapor and the change became faster as the materials crossed the region of T(g). A simple model suggested for permeability worked satisfactorily. The binary and ternary blends, based on PPVC, had lower O2, CO2, and N2 permeability. This improvement in property is of great practical significance and interest and the results indicate that PVC-based polyblends can be investigated further for potential applications in medicine.
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    STUDIES ON POLY(VINYLCHLORIDE)-BASED POLYMER BLENDS INTENDED FOR MEDICAL APPLICATIONS .2. MECHANICAL-PROPERTIES
    (POLYMER ENGINEERING AND SCIENCE, 1992) PAL, SN; RAMANI, AV; SUBRAMANIAN, N
    Binary polyblends of plasticized poly(vinylchloride) (PPVC1) with acrylonitrile-butadiene rubber (NBR1), compounded graft polymer of vinyl chloride and ethylene-vinyl acetate copolymer (EVAPVC) and ternary blends of PPVC1, NBR1, and EVAPVC were formulated to study mechanical proper-ties. For the "pure" components, elongation at break was found to be in the order PPVC1 < EVAPVC < NBR1. Addition of both EVAPVC and NBR1 resulted in improvement of ultimate elongation and tensile energy to break. PPVC1-NBR1 binary blends exhibited synergistic behavior for both ultimate tensile stress and elongation at break, indicating the presence of appreciable specific interactions between the polymers. About 30% replacement of PPVC1 by NBR1 or EVAPVC resulted in marginal fall in modulus and significant improvement in elongation at break. EVAPVC or blends containing EVAPVC had a tendency to creep. A simple generalized equation suggested for various mechanical properties works satisfactorily. The results obtained have practical implications and indicate that PVC-based polyblends can be investigated further for potential applications in medicine.
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    STUDIES ON THE EFFECTS OF GAMMA-IRRADIATION ON NONTOXIC PVC FORMULATIONS
    (JOURNAL OF APPLIED POLYMER SCIENCE, 1987) SAXENA, A; KALLIYANAKRISHNAN, V; PAL, SN
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    STUDIES ON THE SYNTHESIS OF A METHACRYLATE-BASED DENTAL RESTORATIVE RESIN
    (JOURNAL OF APPLIED POLYMER SCIENCE, 1991) SHEELA, MS; SELVY, KT; KRISHNAN, VK; PAL, SN
    The synthesis of bisphenol A-glycidyl methacrylate (BIS-GMA), the resin component in most dental composite restorative materials, catalyzed by different tertiary amine accelerators such as N,N'-dimethyl-p-toluidine (DMPT), N,N'-dimethylamino phenethyl alcohol (DMAPEA'), and N,N'-dimethylamino ethyl methacrylate (DMAEMA) is reported in this work. The effect of varying concentrations of accelerators and the reaction conditions of the synthesis as a function of time is studied in detail. The kinetics of the reaction between epoxide and carboxyl group during the formation of BIS-GMA is monitored using infrared (IR) and chemical techniques. The reaction is found to follow first-order and zero-order kinetics with respect to epoxide and acid, respectively. The degree of epoxide and acid conversion has been calculated as a function of time. The percentages of various isomers, formed under different reaction conditions have been reported. Characterization procedures for BIS-GMA have been developed.