Browsing by Author "KRISHNAN, VK"

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    RADIATION GRAFTING OF HYDROPHILIC MONOMERS ON TO PLASTICIZED POLY(VINYL CHLORIDE) SHEETS
    (JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 1990) KRISHNAN, VK; JAYAKRISHNAN, A; FRANCIS, JD
    Medical-grade plasticized poly(vinyl chloride) (PVC) sheets were surface modified using gamma-radiation grafting of a combination of hydrophilic monomers based on 2-hydroxyethyl methacrylate (HEMA) and N-vinyl pyrrolidone (NVP). The modified surfaces were evaluated for their surface properties using contact angle measurements, phase-contrast photomicroscopy and scanning electron microscopy. Surface energy calculations of the modified surfaces indicated that the surfaces became highly hydrophilic when grafted with even a 1% (v/v) solution of HEMA-NVP combination in the presence of 0.005 M CuSO4. Migration of the plasticizer di(2-ethylhexyl phthalate) (DEHP) from the grafted sheets was examined in hydrocarbon solvents such as n-hexane, n-heptane and n-octane and in extractant media such as cotton seed oil and polyethylene glycol-400 (PEG-400). The migration from modified sheets was found to be < 4% of the migration from unmodified control sheets in hydrocarbon solvents at 30-degrees-C over a period of 5h. Accelerated leaching studies in cotton seed oil and PEG-400 demonstrated that virtually no plasticizer migrated out in the former over a period of 96h whereas the rate of migration in the latter medium showed only a mild reduction. The migration behaviour was Fickian in nature for grafted sheets. The method described may be useful as a simple, versatile technique for preventing plasticizer migration from plasticized PVC for medical applications.
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    RADIATION GRAFTING OF HYDROPHILIC MONOMERS ON TO PLASTICIZED POLY(VINYL CHLORIDE) SHEETS .2. MIGRATION BEHAVIOR OF THE PLASTICIZER FROM N-VINYL PYRROLIDONE GRAFTED SHEETS
    (BIOMATERIALS, 1991)
    The grafting of N-vinyl pyrrolidone, a hydrophilic monomer, on to flexible poly(vinyl chloride) sheets used in medical applications using ionizing radiation from a 60Co source was studied. The graft yield was found to increase linearly with monomer concentration and also with increasing radiation doses. The migration of the plasticizer di-(2-ethylhexyl)phthalate into a strong organic extractant such as n-hexane was studied at different time intervals for different grafted systems of poly(vinyl chloride) at 30-degrees-C. The results indicated a drastic reduction in the leaching of the plasticizer from grafted systems versus ungrafted controls. Incorporation of ethylene dimethacrylate cross-linker during grafting did not seem to affect the graft yield considerably but appeared to further reduce the plasticizer migration. Surface energy calculations of the grafted samples indicate that the surfaces are highly hydrophilic compared to ungrafted poly(vinyl chloride) and the polar and dispersion components tend to vary with increasing cross-linker concentration.
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    RADIATION GRAFTING OF HYDROPHILIC MONOMERS ONTO PLASTICIZED POLY(VINYL CHLORIDE) SHEETS .3. PHYSICAL AND MECHANICAL-PROPERTIES OF MIGRATION RESISTANT SHEETS
    (JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 1991) KRISHNAN, VK; JAYAKRISHNAN, A; FRANCIS, JD
    Medical grade poly(vinyl chloride) (PVC) sheets were surface modified by grafting a combination of 2-hydroxyethyl methacrylate (HEMA) and N-vinyl pyrrolidone (NVP) or NVP alone using gamma radiation in an effort to retard the migration of the plasticizer from the PVC matrix. Presence of cupric ions at a concentration of 0.005 M was found to be optimal in not only preventing the homopolymerization of the monomers but also producing the highest graft yield at all monomer concentrations used for grafting. The grafted PVC was characterized for its water absorption properties. Surface morphology of the grafted surface was examined using scanning electron microscopy (SEM). PVC sheets grafted on both sides as well as on one side were characterized for their physical and mechanical properties in order to assess their suitability in biomedical applications. While the tensile strength and percentage elongation values of PVC sheets grafted on both sides showed a downward trend with increasing graft yield, these properties were not drastically affected by surface modification on one side only at graft yields pertinent to prevent the migration of the plasticizer. Measurement of Shore A hardness and optical transparency of the migration resistant sheetings showed that such properties were not seriously affected by surface modification thus rendering them suitable for their intended applications.
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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.