... References 1. George, G. Α.; Celina, M. Homogeneous and heterogeneous oxidation of polypropyl... more ... References 1. George, G. Α.; Celina, M. Homogeneous and heterogeneous oxidation of polypropylene. Handbook of Polymer Degradation (2nd Edn) S.Halim, Ed.; Marcel Dekker, New York, 2000; p. 277. ... 4. Goss, BGS; Barry, MD; Birtwhistle, D.; George, GA Polym. Degrad. ...
... The positive value of q and a relatively high value of K GT indicate that strong interactions... more ... The positive value of q and a relatively high value of K GT indicate that strong interactions (ElMiloudi et al., 2009) exist between OH groups of lignin and the carbonyl groups of PHB for the blends containing up to 40 wt% lignin. [Fig. 5], [Fig. 6] and [Fig. ...
Page 1. Prognostic Tools for Lifetime Prediction of Aircraft Coatings: Paint Degradation John M C... more Page 1. Prognostic Tools for Lifetime Prediction of Aircraft Coatings: Paint Degradation John M Colwell 1,a , Javaid H Khan 2,b , Geoffrey Will 2,c , Kathryn E Fairfull-Smith 3,d , Steven E Bottle 3,e , Graeme A George 1,f and Antony Trueman 4,g ...
Degradation of polypropylene (PP) during melt processing was studied using a novel profluorescenc... more Degradation of polypropylene (PP) during melt processing was studied using a novel profluorescence technique. The profluorescent nitroxide probe, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was added to PP during melt processing to act as a sensor for carbon-centred radicals. Trapping of carbon-centred radicals, formed during degradation of PP, led to an increase in fluorescence emission from TMDBIO adducts. Through analysis of viscosity changes during
ABSTRACT This paper describes recent developments in the use of chemiluminescence (CL) and proflu... more ABSTRACT This paper describes recent developments in the use of chemiluminescence (CL) and profluorescent nitroxides (PFNs) in probing the “induction period” of polymer oxidation. CL measures the instantaneous rate of reaction of hydroperoxides responsible for initiating degradation and the spreading of oxidation, while PFNs can be used to measure the concentration of alkyl radicals produced in oxidation events and thus provide an integrating sensor for the extent of cumulative damage. The PFN additive acts as an oxidation retarder by competing with oxygen to scavenge the alkyl radicals that generate chain carrying peroxy radicals and so mirrors the performance of hindered amine stabilisers (HAS) in one part of their stabilisation cycle. Using the example of polypropylene (PP) and cis-polyisoprene (PIP) as substrates which can rapidly spread oxidative damage, the factors controlling the reaction of PFNs can be determined from CL and fluorescence as well as infra-red (IR) spectroscopy through the detection of oxidation products as measured by the carbonyl index. Matrix effects on the reactivity are demonstrated using a polyethylene-norbornene copolymer (TOPAS) as carrier for both PIP and the PFN and it is seen that the PFN is a radical scavenger only above Tg of the carrier. When PIP alone is oxidized, the PFN is an integrating sensor for free radical production under ambient conditions for up to twelve months while also stabilizing the polymer. Critically, it is thus able to determine the underlying rate of radical production in the oxidation induction period.
ABSTRACT The profluorescent nitroxide, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO... more ABSTRACT The profluorescent nitroxide, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was investigated as a probe for the radical-mediated degradation of stabilised polypropylene. TMDBIO has been previously shown to be a sensitive probe for free-radical degradation during the thermo-oxidation of unstabilised polypropylene. Here we report on the effect that adding hindered phenol or phosphite stabilisers to polypropylene has on the free-radical sensing ability of TMDBIO during thermo-oxidation. In addition, novel dual-functional, hindered phenol containing profluorescent nitroxides, 5-[2-(4-hydroxy-3,5-di-tert-butylphenyl)ethenyl]-1,1,3,3-tetramethylisoindolin-2-yloxyl (HSTMIO) and its derivatives were investigated as probes for the radical-mediated degradation of polypropylene. These dual-functional probes were shown to be efficient stabilisers for polypropylene during thermo-oxidation at 150 °C in oxygen and sensors of thermo-oxidation during its early stages, in the so-called “induction period”.
Herein are reported the synthesis of a conjugate of chitosan with L-leucine, the preparation of n... more Herein are reported the synthesis of a conjugate of chitosan with L-leucine, the preparation of nanoparticles from both chitosan and the conjugate for use in pulmonary drug delivery, and the in vitro evaluation of toxicity and inflammatory effects of both the polymers and their nanoparticles on the bronchial epithelial cell line, BEAS-2B. The nanoparticles, successfully prepared both from chitosan and the conjugate, had a diameter in the range of 10-30 nm. The polymers and their nanoparticles were tested for their effects on cell viability by MTT assay, on trans-epithelial permeability by using sodium fluorescein as a fluid phase marker, and on IL-8 secretion by ELISA. The conjugate nanoparticles had a low overall toxicity (IC50 = 2 mg/mL following 48 h exposure; no induction of IL-8 release at 0.5 mg/mL concentration), suggesting that they may be safe for pulmonary drug delivery applications.
ABSTRACT The oxidation of linear low density polyethylene (LLDPE) films containing the combinatio... more ABSTRACT The oxidation of linear low density polyethylene (LLDPE) films containing the combination of prooxidants titanium (IV) dioxide (TiO2) with either cobalt (II) stearate (CoSt) or iron (II) stearate (FeSt) have been evaluated under accelerated photo- and thermo-oxidative conditions as well as on outdoor weathering. LLDPE containing only surface-compatibilised nano-TiO2 rapidly photo-whitens and embrittles at a low apparent extent of oxidation (as measured by carbonyl index) due to formation of microscopic voids of w150 nm. When CoSt was also included in the film, antagonism occurred shown by embrittlement times longer by w90%, higher carbonyl index and absence of film whitening. In contrast, films containing TiO2/FeSt whitened during photo-oxidation and exhibited lower antagonism with only 44% longer times to embrittlement and lower carbonyl index. Antagonism between pro-oxidants was not observed under dark thermo-oxidative conditions. X-ray Fluorescence Microspectroscopy elemental maps revealed that the TiO2 nanoparticles were spatially correlated with iron and cobalt metal ions allowing scavenging of electrons and holes through cycling of the redox states of the metal without producing radical species to initiate polymer oxidation. It is suggested that the antagonism differences between TiO2/CoSt and TiO2/FeSt pro-oxidants is related to the respective reduction potentials of Co3þ/2þ and Fe3þ/2þ and their effect on the UV conduction and valence band edges of the TiO2 particle. In these ways the photochemistry of TiO2 is suppressed and the photo-oxidative lifetime is governed by the chemistry of the transition metal pro-oxidant. Crown Copyright
... References 1. George, G. Α.; Celina, M. Homogeneous and heterogeneous oxidation of polypropyl... more ... References 1. George, G. Α.; Celina, M. Homogeneous and heterogeneous oxidation of polypropylene. Handbook of Polymer Degradation (2nd Edn) S.Halim, Ed.; Marcel Dekker, New York, 2000; p. 277. ... 4. Goss, BGS; Barry, MD; Birtwhistle, D.; George, GA Polym. Degrad. ...
... The positive value of q and a relatively high value of K GT indicate that strong interactions... more ... The positive value of q and a relatively high value of K GT indicate that strong interactions (ElMiloudi et al., 2009) exist between OH groups of lignin and the carbonyl groups of PHB for the blends containing up to 40 wt% lignin. [Fig. 5], [Fig. 6] and [Fig. ...
Page 1. Prognostic Tools for Lifetime Prediction of Aircraft Coatings: Paint Degradation John M C... more Page 1. Prognostic Tools for Lifetime Prediction of Aircraft Coatings: Paint Degradation John M Colwell 1,a , Javaid H Khan 2,b , Geoffrey Will 2,c , Kathryn E Fairfull-Smith 3,d , Steven E Bottle 3,e , Graeme A George 1,f and Antony Trueman 4,g ...
Degradation of polypropylene (PP) during melt processing was studied using a novel profluorescenc... more Degradation of polypropylene (PP) during melt processing was studied using a novel profluorescence technique. The profluorescent nitroxide probe, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was added to PP during melt processing to act as a sensor for carbon-centred radicals. Trapping of carbon-centred radicals, formed during degradation of PP, led to an increase in fluorescence emission from TMDBIO adducts. Through analysis of viscosity changes during
ABSTRACT This paper describes recent developments in the use of chemiluminescence (CL) and proflu... more ABSTRACT This paper describes recent developments in the use of chemiluminescence (CL) and profluorescent nitroxides (PFNs) in probing the “induction period” of polymer oxidation. CL measures the instantaneous rate of reaction of hydroperoxides responsible for initiating degradation and the spreading of oxidation, while PFNs can be used to measure the concentration of alkyl radicals produced in oxidation events and thus provide an integrating sensor for the extent of cumulative damage. The PFN additive acts as an oxidation retarder by competing with oxygen to scavenge the alkyl radicals that generate chain carrying peroxy radicals and so mirrors the performance of hindered amine stabilisers (HAS) in one part of their stabilisation cycle. Using the example of polypropylene (PP) and cis-polyisoprene (PIP) as substrates which can rapidly spread oxidative damage, the factors controlling the reaction of PFNs can be determined from CL and fluorescence as well as infra-red (IR) spectroscopy through the detection of oxidation products as measured by the carbonyl index. Matrix effects on the reactivity are demonstrated using a polyethylene-norbornene copolymer (TOPAS) as carrier for both PIP and the PFN and it is seen that the PFN is a radical scavenger only above Tg of the carrier. When PIP alone is oxidized, the PFN is an integrating sensor for free radical production under ambient conditions for up to twelve months while also stabilizing the polymer. Critically, it is thus able to determine the underlying rate of radical production in the oxidation induction period.
ABSTRACT The profluorescent nitroxide, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO... more ABSTRACT The profluorescent nitroxide, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was investigated as a probe for the radical-mediated degradation of stabilised polypropylene. TMDBIO has been previously shown to be a sensitive probe for free-radical degradation during the thermo-oxidation of unstabilised polypropylene. Here we report on the effect that adding hindered phenol or phosphite stabilisers to polypropylene has on the free-radical sensing ability of TMDBIO during thermo-oxidation. In addition, novel dual-functional, hindered phenol containing profluorescent nitroxides, 5-[2-(4-hydroxy-3,5-di-tert-butylphenyl)ethenyl]-1,1,3,3-tetramethylisoindolin-2-yloxyl (HSTMIO) and its derivatives were investigated as probes for the radical-mediated degradation of polypropylene. These dual-functional probes were shown to be efficient stabilisers for polypropylene during thermo-oxidation at 150 °C in oxygen and sensors of thermo-oxidation during its early stages, in the so-called “induction period”.
Herein are reported the synthesis of a conjugate of chitosan with L-leucine, the preparation of n... more Herein are reported the synthesis of a conjugate of chitosan with L-leucine, the preparation of nanoparticles from both chitosan and the conjugate for use in pulmonary drug delivery, and the in vitro evaluation of toxicity and inflammatory effects of both the polymers and their nanoparticles on the bronchial epithelial cell line, BEAS-2B. The nanoparticles, successfully prepared both from chitosan and the conjugate, had a diameter in the range of 10-30 nm. The polymers and their nanoparticles were tested for their effects on cell viability by MTT assay, on trans-epithelial permeability by using sodium fluorescein as a fluid phase marker, and on IL-8 secretion by ELISA. The conjugate nanoparticles had a low overall toxicity (IC50 = 2 mg/mL following 48 h exposure; no induction of IL-8 release at 0.5 mg/mL concentration), suggesting that they may be safe for pulmonary drug delivery applications.
ABSTRACT The oxidation of linear low density polyethylene (LLDPE) films containing the combinatio... more ABSTRACT The oxidation of linear low density polyethylene (LLDPE) films containing the combination of prooxidants titanium (IV) dioxide (TiO2) with either cobalt (II) stearate (CoSt) or iron (II) stearate (FeSt) have been evaluated under accelerated photo- and thermo-oxidative conditions as well as on outdoor weathering. LLDPE containing only surface-compatibilised nano-TiO2 rapidly photo-whitens and embrittles at a low apparent extent of oxidation (as measured by carbonyl index) due to formation of microscopic voids of w150 nm. When CoSt was also included in the film, antagonism occurred shown by embrittlement times longer by w90%, higher carbonyl index and absence of film whitening. In contrast, films containing TiO2/FeSt whitened during photo-oxidation and exhibited lower antagonism with only 44% longer times to embrittlement and lower carbonyl index. Antagonism between pro-oxidants was not observed under dark thermo-oxidative conditions. X-ray Fluorescence Microspectroscopy elemental maps revealed that the TiO2 nanoparticles were spatially correlated with iron and cobalt metal ions allowing scavenging of electrons and holes through cycling of the redox states of the metal without producing radical species to initiate polymer oxidation. It is suggested that the antagonism differences between TiO2/CoSt and TiO2/FeSt pro-oxidants is related to the respective reduction potentials of Co3þ/2þ and Fe3þ/2þ and their effect on the UV conduction and valence band edges of the TiO2 particle. In these ways the photochemistry of TiO2 is suppressed and the photo-oxidative lifetime is governed by the chemistry of the transition metal pro-oxidant. Crown Copyright
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