• R Bajpai

      Articles written in Bulletin of Materials Science

    • Surface modification on PMMA : PVDF polyblend: hardening under chemical environment

      R Bajpai V Mishra Pragyesh Agrawal S C Datt

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      The influence of chemical environment on polymers include the surface alteration as well as other deep modifications in surface layers. The surface hardening, as an effect of organic liquids on poly(methyl methacrylate): poly(vinylidene fluoride) (PMMA: PVDF), which is one of the few known miscible blends, has been detected using microhardness testing. Organic liquids like acetone, toluene, xylene and benzene were introduced on the surface of blend specimens for different durations. Vickers microhardness (𝐻v) was measured for treated and untreated specimens. The study reveals both hardening and plasticization of specimens at different exposure times. The degree of surface hardening is maximum under acetone treatment. All the specimens exhibit surface hardening at an exposure time of 1 h with all the four liquids. This feature is prominent with longer exposures for specimens with increasing content of PVDF. However, the degree of hardening decreases with the time of exposure in the respective environments. In general, acetone and toluene impart surface hardening, whereas, xylene and benzene soften the specimen. PMMA: PVDF (83 : 17) blend exhibits surface hardening under all the four treatments when compared with the respective untreated specimens.

    • Development of hardened PVF : PMMA polyblend: effect of gamma and electron irradiation

      R Bajpai N B Dhagat R Katare Pragyesh Agrawal S C Datt

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      Specimens of poly(vinyl formal) (PVF) : poly(methyl methacrylate) (PMMA) polyblends with different weight percentage ratios were subjected to gamma irradiation (1 to 50 Mrad) and electron irradiation (1 to 20 Mrad). The effect of irradiation on the strength of the blend specimens was studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. Significant changes were observed in the Vickers microhardness number, $H_v$. The $H_v$ values of gamma irradiated specimens are found to be higher than the unirradiated specimens indicating an occurrence of radiational crosslinking. The maximum value of $H_v$ is obtained at the gamma radiation dose of 15 Mrad. In case of electron irradiation the radiational crosslinking is found to take place for the blend specimens having lower wt% content of PMMA (0 and 1 wt%) in PVF matrix. On the other hand degradation of polymeric system is observed for the blends having PMMA content more than 1 wt%. The maximum value of $H_v$ is obtained for all the blend specimens at the electron irradiation dose of 8 Mrad. The degree of crosslinking in polyblends due to gamma irradiation is found to be more than electron irradiation. The scissioning mechanism is found to predominate in the polyblend system in case of electron irradiation.

    • Photoplastic effect in polycarbonate using microhardness measurements

      R Bajpai Sandhya Sharma V K Vastal B P Chandra

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      Vickers microhardness indentation technique has been employed to detect the photoplastic effect in the transparent polycarbonate specimens in darkness and under mercury illumination. For low applied loads, the hardening of specimens under illumination confirms the positive photoplastic effect that causes illumination-induced increase of crosslinking (in polymer). For high applied loads the positive photoplastic effect decreases as the level of microhardness decreases.

    • Morphological, thermal and annealed microhardness characterization of gelatin based interpenetrating networks of polyacrylonitrile: A hard biopolymer

      Sangita Rajvaidya R Bajpai A K Bajpai

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      The present paper reports the preparation of full IPNs of gelatin and polyacrylonitrile. Various compositions of gluteraldehyde crosslinked gelatin and N,N′-methylene-bis-acrylamide crosslinked PAN were characterized by SEM and DSC techniques. The IPNs were also thermally pretreated by the annealing process. The effects of annealing temperature on the microhardness of IPNs were studied using the Vickers method. SEM indicates the homogeneous morphological features for IPN. The role of gelatin, AN and crosslinker on the developed hard biopolymer has been described with the help of DSC thermograms and microhardness measurements of annealed specimens and good correlation is observed.

    • Transient charging and discharging current study in pure PVF and PVF/PVDF fluoro polyblends for application in microelectronics

      A K Gupta R Bajpai J M Keller

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      The transient current were analysed by considering the effect of variation of forming time, temperature, field and composition of blend specimens. Measurements indicated that transient charging and discharging currents exhibited thermally activated character but did not show mirror image behaviour at different temperatures and field values. The log 𝐼–log 𝑡 plots were found to follow the Curie–Von Schweidler law with the value of decay constant `𝑛’ lying in the range of 0.029–2.9456. These observed characteristics also indicated that the transient charging in PVF:PVDF fluoro polyblends occur partly due to orientation of dipoles but predominantly due to trapped space charges and hopping of charge carriers amongst localized states. The modification in transient behaviour on blending PVDF with PVF have been explained on the basis of plasticization effect which increases free volume and molecular mobility and 𝑇g modification in the trap structure.

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      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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