@article { ISI:000239688400001, title = {Preparation and performance evaluation of EPDM nanocomposites under accelerated weathering}, journal = {Journal of Thermoplastic Composite Materials}, volume = {19}, number = {5}, year = {2006}, month = {SEP}, pages = {461-474}, publisher = {SAGE PUBLICATIONS LTD}, type = {Article}, address = {1 OLIVERS YARD, 55 CITY ROAD, LONDON EC1Y 1SP, ENGLAND}, abstract = {

The degradability of ethylene propylene diene monomer (EPDM) nanocomposites, prepared from organically modified montmorillonite (CMMT), is studied under accelerated UV irradiation (lambda \>= 290 nm) for different time intervals. The development of functional groups during degradation is monitored by FT-IR spectroscopy whereas, surface changes are studied by scanning electron microscopy (SEM). The effect of clay modifier and clay concentration on the degradability are studied. The degradation of neat polymer and composites taking place traditionally and an increase in carbonyl and hydroxyl groups are observed with irradiation time. Neat EPDM is found to be less degradable than nanocomposites. Degradation products, as seen by FT-IR in nanocomposites are found to be the same as in neat polymer but are generated at a faster rate. According to the experimental results, one can define that both ammonium ion and neat montmorillonite (MMT) accelerate the photo-oxidation of EPDM.

}, keywords = {carbonyl index, Degradation, EPDM, layered silicates, Nanocomposites, photooxidation}, issn = {0892-7057}, doi = {10.1177/0892705706062204}, author = {Rana, Sravendra and Tevtia, Amit K. and Kumar, Bijendra and Singh, R. P.} } @article { ISI:000239536200026, title = {Stabilization of gamma-sterilized biomedical polyolefins by synergistic mixtures of oligomeric stabilizers}, journal = {Polymer Degradation and Stability}, volume = {91}, number = {10}, year = {2006}, month = {OCT}, pages = {2451-2464}, publisher = {ELSEVIER SCI LTD}, type = {Article}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {

The stabilization of polyolefins against gamma-sterilization has been studied with single or binary additive system. The present attempt is to utilize synergistic mixtures of stabilizers which are approved for food contact applications. Ethylene-propylene (EP) copolymer has been melt-mixed with hindered amine stabilizers (HAS), phenolic antioxidants and organo-phosphites (hydroperoxide decomposer). Samples were sterilized with different doses of gamma-radiation. Stabilization was characterized in terms of changes in the functional groups (oxidation products), tensile properties, yellowing and surface morphology by FTIR spectroscopy, Instron, colorimetry (reflectance) and scanning electron microscopy (SEM), respectively. Results were discussed by comparing the stabilizing efficiency of mixtures with and without phenol system. Among phenol containing systems, where we mostly observe discoloration due to the oxidation of hindered phenol and the combination of secondary HAS, tertiary HAS, organo-phosphite and hindered phenol exhibited improved stabilization efficiency than single or binary additive systems. The mixture of secondary HAS and tertiary HAS, has shown antagonistic effect of stabilization whereas their combination with organo-phosphite has exhibited synergistic effect of stabilization even at higher doses of gamma-sterilization. The effects have been explained through the interaction between the stabilizers. (c) 2006 Elsevier Ltd. All rights reserved.

}, keywords = {Antioxidants, discoloration, ethylene-propylene copolymer, gamma-sterilization, stabilization, tensile properties}, issn = {0141-3910}, doi = {10.1016/j.polymdegradstab.2006.03.010}, author = {Alariqi, Sameh A. S. and Kumar, A. Pratheep and Rao, B. S. M. and Tevtia, Amit K. 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:000319275700021, title = {Copolymerization of ethylene with unsaturated alcohols and methylmethacrylate using a silylated alpha-diimine nickel catalyst: molecular modeling and photodegradation studies}, journal = {Journal of Applied Polymer Science}, volume = {129}, number = {4}, year = {2013}, month = {AUG}, pages = {1820-1832}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

In this article, the experimental results obtained in the copolymerization of ethylene with polar monomers using a silylated -diimine nickel catalyst are described and compared with those obtained with a non-silylate similar one. The results show that the introduction of a siliyl group in the para-position of the imine moiety turns the catalyst less sensitive toward polar functionalities. However, the reactivity observed in copolymerization reactions was found to be reduced both the global polymerization and incorporation rates. Molecular modeling calculation allowed us to understand both the preferred insertion mode and the intermediate product structures for E/MMA copolymerization. Photodegradation studies showed that the presence of polar groups in the copolymers increases their rate of oxidation and turn them more easily degradable. The stabilization performed by Tinuvin 770 showed that for long-exposure times, it is not very effective regardless it is only mixed or grafted to the copolymer. (c) 2012 Wiley Periodicals, Inc.

}, keywords = {ageing, copolymers, Degradation, grafting}, issn = {0021-8995}, doi = {10.1002/app.38889}, author = {Matos, Ines and Fernandes, Susete N. and Liu, Hua-Rong and Tevtia, Amit K. and Singh, R. P. and Manda, Lemos and Lemos, Francisco and Marques, Maria M.} }