@article { ISI:000225747800012, title = {Studies on characterization of nano CaCO3 prepared by the in situ deposition technique and its application in PP-nano CaCO3 composites}, journal = {Journal of Polymer Science Part B: Polymer Physics}, volume = {43}, number = {1}, year = {2005}, month = {JAN}, pages = {107-113}, publisher = {JOHN WILEY \& SONS INC}, type = {Article}, address = {111 RIVER ST, HOBOKEN, NJ 07030 USA}, abstract = {

The elegant approach of in situ deposition technique was used for the synthesis of nano CaCO3 the nanosize of particles was confirmed by the X-ray diffraction (XRD) technique. Differential scanning calorimetry (DSC) was used for determination of the enthalpy. The nano CaCO3 polypropylene (PP) composites were prepared by taking 2 and 10 wt \% of different nanosizes (21-39 nm) of CaCO3. Conversion of the alpha phase to beta was observed in the case of 2 wt \% of a 30-nm sized amount of CaCO3 in a PP composite. The decrement in DeltaH and percent. crystallinity, as well as the increment in melt temperature were recorded for 6 wt \% nano CaCO3 with a decrease in nanosize from 39 to 21 nm. The increment in tensile strength with an increase in the amount of nano CaCO3 was observed, and the tower particle size shoved Greater improvement. The improvement in thermal and mechanical properties is because of the formation of a greater number of small spherulites uniformly present in the PP matrix. (C) 2004 Wiley Periodicals, Inc.

}, keywords = {Crystallization, DSC, mechanical and thermal properties, nano CaCO3, polypropylene, XRD}, issn = {0887-6266}, doi = {10.1002/polb.20296}, author = {Mishra, Satyendra and Sonawane, S. H. and Singh, R. P.} } @article { ISI:000245141300028, title = {Synthesis and characterization of hindered amine light stabilizers based on end functionalization of polypropylene}, journal = {Journal of Applied Polymer Science}, volume = {104}, number = {3}, year = {2007}, month = {MAY}, pages = {1596-1602}, publisher = {JOHN WILEY \& SONS INC}, type = {Article}, address = {111 RIVER ST, HOBOKEN, NJ 07030 USA}, abstract = {

A polymeric hindered amine light stabilizer (HALS), where HALS moiety was attached at the terminal end of the polypropylene chain via end-functionalized vinylidine PP through simple organic reactions, was synthesized. It comprises the synthesis of vinylidine-terminated polypropylene by using Cp2ZrCl2/MAO as catalyst system and epoxidation of vinylidene polypropylene. The final product was synthesized by carrying out the reaction between epoxy end functionalized polypropylene and 4-amino-2,2,6,6-tetrametyl piperidine. The final product was characterized by using H-1 NMR, C-13 NMR, and FT-IR spectra. Functionality was calculated by using vapor phase osmometry and H-1 NMR. The solubility and diffusion coefficient of the product were calculated and also its stabilization performance was checked. (c) 2007 Wiley Periodicals, Inc.

}, keywords = {end functionalization, functionalization of polymers, polymeric HALS, polypropylene, vinylidine and photostabilization}, issn = {0021-8995}, doi = {10.1002/app.25745}, author = {Reddy, K. Raghunatha and Kumar, Bijendra and Rana, Sravendra and Tevtia, Amit K. and Singh, R. P.} } @article { ISI:000263212700021, title = {Effect of gamma-dose rate on crystallinity and morphological changes of gamma-sterilized biomedical polypropylene}, journal = {Polymer Degradation and Stability}, volume = {94}, number = {2}, year = {2009}, month = {FEB}, pages = {272-277}, publisher = {ELSEVIER SCI LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {

The present work is aimed to study the changes in crystallinity and morphology of biomedical polyolefins after gamma-sterilization. The isotactic polypropylene (iPP) films were sterilized by gamma-radiation and the changes were characterized by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and atomic force microscopy (AFM) techniques. The effect of dose rate on crystallinity changes also was focused. It was found that crystallinity and morphology significantly changed with gamma-irradiation. There was an increase in crystallinity Lip to 10 kGy accompanied with decrease in viscosity and mechanical properties. The changes in crystallinity mainly depend on gamma-irradiation dose and dose rate. The rise in crystallinity was attributed to chain scission and forming new perfect lamellae. However, the reduction was accompanied by occurrence of gamma- and beta-phases and crosslinking. Possible explanations for transitions in phases are also discussed based on our results. (C) 2008 Elsevier Ltd. All rights reserved.

}, keywords = {Crystallinity, Dose rate, Gamma radiation, mechanical properties, Morphology, polypropylene}, issn = {0141-3910}, doi = {10.1016/j.polymdegradstab.2008.10.027}, author = {Alariqi, Sameh A. S. and Kumar, A. Pratheep and Rao, B. S. M. and Singh, R. P.} } @article { ISI:000286469900005, title = {Gamma-initiated oxidation of isotactic polypropylene: effect of gamma-dose rate on durability}, journal = {Arabian Journal for Science and Engineering}, volume = {36}, number = {1}, year = {2011}, month = {JAN}, pages = {29-38}, publisher = {SPRINGER HEIDELBERG}, address = {TIERGARTENSTRASSE 17, D-69121 HEIDELBERG, GERMANY}, abstract = {

The effect of gamma-irradiation dose rate on the chemical, molecular, and mechanical properties of isotactic polypropylene (iPP) films was investigated using three different Co-60 sources with dose rates of 600, 660, and 780 Gy h(-1). Fourier transform infrared spectroscopy coupled with chemical derivatization with NO and SF4, and measurements of the elongation at break, toughness, and molecular weight were used to describe the effects of gamma-dose rate on iPP. It was found that the formation of oxidation products depended significantly on the dose rate. However, the kinetic accumulation of ketones were more sensitive to the dose rate of gamma source. Degradation induced by gamma-radiation depends on the dose rate-the degradation of mechanical properties was more significant at a low dose rate than at a high dose rate. It was found that the lower the dose rate, the higher the degree of oxidation in terms of the formation of gamma-products. The mechanism of gamma-degradation is discussed based on the correlation between the changes in chemical and physical properties upon exposure to gamma-radiation.

}, keywords = {Chemical and physical properties, Dose rate, gamma-irradiation, polypropylene}, issn = {1319-8025}, doi = {10.1007/s13369-010-0006-8}, author = {Alariqi, Sameh A. S. and Singh, R. P. and Rao, B. S. M.} }