ABSTRACT PHOTO-OXIDATIVE DEGRADATION OF ABS COPOLYMER G&uuml / zel, Aylin M.S., Department of Polymer Science and Technology Supervisor: Prof. Dr. Teoman Tin&ccedil / er Co-Supervisor: Prof. Dr. Cevdet Kaynak September 2009, 55 pages Acrylonitrile-butadiene-styrene (ABS) polymer is one of the most popular copolymer having an elastomeric butadiene phase dispersed in rigid amorphous styrene and semi-crystalline acrylonitrile. Due to double bonds in the polybutadiene phase, ABS copolymers are very sensitive to photo-oxidative degradation. Photo-oxidation of butadiene rubber phase results in the formation of chromorphores and these chromorphores act as initiators in photo-oxidative degradation and after a while ABS starts yellowing. In this work, the relationship between the UV light and the yellowing of ABS samples was also investigated with respect to time. In this study, pure, light stabilized and commercial ABS samples were aged under UV light. As the UV light intensity increased from 800 to 2800 &amp / #61549 / W/cm2, yellowing of the samples were increased for pure ABS. This increase in yellowing of the samples was about 27 times higher compared to lower energy. In this study, UV stabilizers IRGANOX 1076 (sterically hindered phenolic antioxidant), IRGAFOS 168 (hydrolycally stable phosphite stabilizer) and TINUVIN P (hydroxyphenol benzotriazole) were used alone or in combination with each other. Pure ABS samples, commercial ABS samples and UV stabilized ABS samples were aged under the same UV light. UV aging degradation was followed by measuring the yellowness of the samples at certain time intervals. Yellowness of the samples was followed by using Coloreye XTH Spectrometer. Degradation in ABS, however, was followed by using FTIR with an increase in the peak area of carbonyl groups in the ABS matrix. Both color analysis and the FTIR analysis showed that combination of the IRGANOX 1076 and IRGAFOS 168 stabilizers gave the best stabilization. This revealed that combination of phenol and phosphate containing stabilizer is the most useful combination to prevent photo-oxidative degradation of ABS copolymer. Additionally, vegetable oil was applied to the surface of a new set of ABS samples and these samples were aged for 700 h. Yellowing tendency of these samples was compared with the yellowing tendency of ABS samples that are directly aged for 500 h. It was clearly observed that samples with oil smeared had more resistance to UV radiation with respect to others. This shows that oil acts protective layer to the UV light and oxygen and slow down the photo-oxidative degradation. Lastly some commercial ABS samples were compared to each other with respect to their yellowing tendency. Commercial ABS samples coded as K, L, A, B, C and D were aged under UV light at about 500 h. Sample A showed the best resistance against the yellowing among the other commercial ABS samples.

Le nettoyage laser Nd:YAG Q-switched (1064 nm) confère souvent aux surfaces nettoyées un aspect plus jaune que les autres techniques de nettoyage. Cet effet jaune peut conduire à l’obtention de contrastes de couleur inesthétiques si différentes techniques de nettoyage sont utilisées sur un même ensemble architectural, comme c’est le cas par exemple pour le portail des Valois de la basilique Saint-Denis près de Paris. Une des hypothèses émises pour expliquer le phénomène est que le jaunissement laser serait lié à la présence de résidus d’irradiation nanométriques formés par interaction du faisceau laser avec la salissure, en particulier les croûtes noires gypseuses communément observées sur les monuments en pierre. Dans le cadre de cette thèse, une méthodologie analytique multi-échelle allant jusqu’à l’échelle nanométrique a été développée pour observer et caractériser les composés néoformés responsables de la coloration jaune. Des éprouvettes de croûtes modèles à base d’hématite et de croûtes reconstituées à partir de croûte noire naturelle ont été élaborées. La croûte noire naturelle a été caractérisée pour déterminer les composés susceptibles de réagir au faisceau laser et donc de contribuer au jaunissement. Des oxydes de fer (hématite, magnétite, maghémite) et des cendres volantes silico-alumineuses issues de la combustion du charbon ont ainsi pu être mis en évidence. La nature chimique et structurale des produits de l’irradiation laser des éprouvettes a ensuite été examinée à l’aide d’un panel de techniques incluant entre autres la microscopie électronique à transmission (MET) couplée à la diffraction électronique et aux spectroscopies de rayons X par dispersion d’énergie (EDX) et de perte d’énergie des électrons (EELS). Des nanostructures cristallisées sous forme de nano-sphères et de nano-résidus ont ainsi pu être observées. La caractérisation de la composition chimique à l’échelle nanométrique a permis de révéler la présence de fer dans toutes les nanostructures. Une étude approfondie de la couleur a en outre permis de relier les propriétés colorimétriques du processus de jaunissement à la nature des nano-composés néoformés par irradiation laser. D’autre part, le portail des Valois de la basilique Saint-Denis a été le sujet d’une étude de cas qui est venue complémenter la recherche tout en ancrant l’étude dans la réalité du monde de la conservation des monuments historiques. Enfin des essais de remédiation ont démontré les potentialités de l’utilisation d’un rayonnement UV pour atténuer ou ne pas produire de jaunissement. In fine, ce travail a permis de démontrer que le phénomène de jaunissement laser observé à l’échelle macroscopique est intimement lié à des transformations de matière à l‘échelle nanométrique, induites par l’interaction du rayonnement laser avec les oxydes de fer et les cendres volantes présents dans les encrassements. / Nd:YAG Q-Switched laser cleaning of soiled stone at 1064 nm can sometimes result in yellower appearances than other conventional cleaning techniques. This yellowing effect can lead to unsightly colour contrasts if different cleaning techniques are used on the same architectural complex, as is the case for the Valois Portal of the Saint-Denis basilica near Paris. One argument made to explain the phenomenon is that the laser yellowing is linked to the creation of nano-sized irradiation residues through the laser beam interaction with soiling matter such as black gypseous crusts. In this study, a multi-scale analytical method extending to the nanoscale has been used to observe and characterize the neo-formed compounds accountable for the yellow discoloration. Samples of model crusts containing hematite and reconstituted crusts prepared with natural black crust have been synthetized. The natural black crust has been characterized in order to identify the compounds that may react under the laser beam and thus contribute to the yellowing effect. Iron oxides (hematite, magnetite and maghemite) and aluminosilicate fly-ashes originating from coal combustion have been discovered. The chemical and structural nature of irradiation products has then been investigated by several techniques including in particular transmission electron microscopy (TEM) coupled with electronic diffraction and energy-dispersive X-ray (EDX) and electron energy-loss (EELS) spectroscopies. Iron containing nanostructures crystallized in the form of nano-spheres and nano-residues have been evidenced and characterized. By studying thoroughly the colour, the colorimetric properties of the yellowing process have been linked to the nature of the neo-formed compounds. Furthermore a case study on the Valois Portal has completed the research while setting it within the reality of the conservation world. Finally experiments with UV light have shown the promising potentiality of this tool as a remedy to the yellowing effect. In summary, this study has demonstrated that the yellowing phenomenon observed at the macroscale is intimately linked to matter transformations occurring at the nanoscale, induced by the interaction between the laser beam and the iron oxides and fly-ashes found in black crusts.

Content: Providing peculiar enhanced features to leather items is a factor of primary importance for the marketing of high-end articles; although the tanning production is oriented to satisfy a wide market range, it is mainly in the 'high end' and 'premium luxury' categories that the quality properties of the material are more expressed, indeed, and where the main current challenges have been focalized, in terms of technological innovation, sustainability and product quality. The light-coloured leathers belongs to the category of materials designed especially for the luxury market. For this type of articles, the uniformity of the colour and the agreeableness of the overall surface appearance are crucial requirements for the most of international fashion and luxury brands. One of the most common and undesirable defects of this type of article is the alteration of the color, with particular reference to the effects of yellowing of the surface of the material. There are several causes able to contribute to this type of defects, due to the complexity of the matrix and to the variability of traditional or innovative production processes used: from the fragility, photosensitivity and thermo-sensitivity of the finishing polymers, to the chemical instability of some finishing pigments, further than the presence of photosensitive additives, the migration of skin components or assembly components of the articles (fats, fillers, plasticizers, glues, etc.), up to the indirect contribution of environmental and thermo-climatic factors able to affect negatively the performance of the material. SSIP, which has always been involved in research and consulting activities for the leather industry with regards to defect monitoring, through this work, would offer an overview of all the main tools for advanced diagnostics (with particular reference to Scanning Electronic Microscopy and to chromatographic and spectroscopic methods) aimed to the identification of the causes of yellowing, beside to explore innovative solutions for the development of strategies for the resolution and / or minimization of the problem of yellowing. The technical solutions will include innovative tanning processes, innovative finishing methods, and leather surface treatments carried out in order to provide a sensible attenuation of surface absorption of IR (infrared) and UV (ultraviolet)-visible radiation. Take-Away: Advanced Diagnostics and innovative solutions for leather yellowing

Brightness reversion, also known as yellowing, is a well-known phenomenon which means that the brightness of paper products decreases during ageing. The name of this phenomenon is based on that paper products usually change in color towards yellow during ageing. Yellowing is considered to occur due to a mixture of chemical and physical factors, which makes it a complex problem for the pulp & paper industry. The majority of the literature and research conducted with respect towards yellowing claims that light and heat is the two main factors that contributes the most to a brightness reversion, depending on the type of pulp and process that is utilized. Smurfit Kappa in Piteå is a manufacturer of the paper grade Kraftliner and has during some occasions noted unstable brightness. Based on previous work at Smurfit Kappa, it is known that the finished liners produced from bleached pulp in a completely chlorine-free process is very sensitive to heat, especially for longer periods of time during storage. It has also been documented that the storage temperature for paper products is of great importance, especially the cooling rate of the paper-rolls from production, which could take around two weeks to reach the ambient temperature. This thesis work, alongside with a literature study as a basis will examining the effect of pH towards yellowing during thermal exposure. Through a factorial experiment it was initially found that the yellowing is favored by higher temperatures in conjunction with lower pH values. In order to obtain a brightness reversion of a paper product within a reasonable timeframe an accelerated aging method was used according to the ISO standard 5630-1. Throughout this thesis is the brightness reversion expressed in the so-called b* value, which indicates the color change from blue to yellow. Further experiments, including ageing methods with moisture, also concluded that an acidic pH results in a more severe yellowing. It was also observed that the pH was decreasing during experiments of pulp storage, this most likely to the chemical phenomena known as acidic hydrolysis. The b*-value seemed to be favorable of the decreased pH, thus could the pulp be stored at pH around 8 instead of 9-10 in order to suppress potential yellowing reactions.  Furthermore, it was found that cooling of the paper resulted in a decrease of the b* value, it is however unclear what causes this phenomenon but a theory could be that chromophoric groups are being deactivated/activated due to the temperature changes and hence making the phenomena reversible. / Eftergulning är ett välkänt fenomen som innebär att ljusheten hos pappersprodukter minskar när dessa åldras. Namnet på detta fenomen grundar sig i att pappersprodukter vanligtvis skiftar i färg mot det gula hållet. Detta anses bero på en blandning av kemiska och fysikaliska faktorer, vilket därmed gör det till ett komplext problem som berör massa & pappersindustrin. Majoriteten av litteraturen och den forskning som utförts inom området gällande eftergulning visar att de två faktorerna ljus och värme påverkar förändringen av ljusheten i högst omfattning, beroende på vilken typ av massa och process som pappret är producerat av. Smurfit Kappa i Piteå är en tillverkare av papperstypen Kraftliner och har under olika perioder noterat ostabila ljushetsvärden på grund av eftergulningen. Frida Sandin konstaterade genom sitt examensarbete hos Smurfit Kappa under 2008 att massan som bleks i en helt klorfri process är extra känslig mot värme, speciellt under längre tidsperioder. Sandin konstaterade även att lagringstemperaturen för pappersprodukter har stor betydelse, speciellt gällande avsvalningsförloppet i de nytillverkade pappersrullarna under papperstillverkning vilka kunde ta ungefär två veckor på sig att nå omgivningens temperatur. Detta arbete fortsätter på Sandins tidigare studier, samt med en litteraturstudie som grund, genom att undersöka pH:s påverkan på papper i samband med varierande temperaturer mer noggrant. Genom ett inledande faktorförsök konstaterades det att eftergulningen gynnas av högre temperaturer i samband med lägre pH värden. För att kunna få en eftergulning på en pappersprodukt inom en rimlig tid så användes en accelererad åldringsmetod, i detta arbete användes främst en metod med en temperatur på 105 °C enligt ISO standarden 5630–1. Eftergulningen inom detta arbete uttrycks i det så kallade b*-värdet vilket indikerar en färgskiftning mellan blått och gult. Ytterligare försök, bland annat i kombination med fukt, konstaterade vidare att ett surt pH starkt missgynnar stabiliteten på eftergulningen för pappersprodukter. Det observerades också att pH-värdet sjönk under experiment där pappersmassa lagrades, detta skedde mest troligt på grund av det kemiska fenomenet som kallas sur hydrolys. b*-värdet tycktes däremot vara gynnsamt av det sänkta pH-värdet. Förslagsvis så borde massan lagras vid pH runt 8 istället för 9–10 för att reducera potentiella eftergulnings-reaktioner. Det konstaterades också att kylning av papperet resulterar i en sänkning av b*-värdet, det är dock oklart vad som får detta att ske men en teori är att det är kromofora grupper som aktiveras/inaktiveras.

Um dos grandes desafios da citricultura brasileira, como grande produtora de lima ácida \'Tahiti\', tem sido a conservação do fruto in natura com destino à exportação. A prevenção da mudança na coloração de verde para amarelo durante o armazenamento constitui o foco de grandes esforços na área de pesquisas em pós-colheita. O presente trabalho teve como objetivo: (1) avaliar a aplicação de concentrações de etileno visando determinar a concentração mínima necessária para ativar a mudança da cor na casca dos frutos; (2) avaliar o tratamento térmico por imersão em água quente, visando utilizá-lo como alternativa para retardar o amarelecimento. No capítulo 1 foram realizados dois experimentos, sendo avaliados 4 tratamentos no experimento 1: 0 μL L-1, 3 μL L-1 , 6 μL L-1 e 12 μL L-1 de etileno, armazenados por 18 dias a 22 ± 2 °C e 85 ± 5% de umidade relativa (UR), utilizando frutos beneficiados, mas não tratados com ácido giberélico (GA). Se observou baixa perda de massa fresca e uma aceleração no desverdecimento a partir do dia 10 nos tratamentos de 3, 6 e 12 μL L-1 de etileno. No experimento 2 foram avaliados seis tratamentos: 0, 1, 2, 3, 6 e 12 μL L-1 de etileno, armazenados por 21 dias a 25 ± 2 °C e 85 ± 5% de UR. Foram utilizados frutos beneficiados, e tratados com ácido giberélico (GA). Os resultados mostraram pouco desverdecimento segundo análise no colorímetro, sendo esse resultado mais perceptível na análise por nota de cor para concentrações de 3 μL L-1 de etileno e baixa perda de massa fresca. O beneficiamento com GA e cera pode ter afetado a ação do etileno. No Capítulo 2 foi conduzido um experimento utilizando frutos colhidos diretamente do campo e avaliado o tratamento térmico por imersão em água quente e posterior armazenamento em presença ou ausência de 3 μL L-1 de etileno. Foram estabelecidos 6 tratamentos: controle sem etileno, controle + 3 μL L-1 de etileno, 3 minutos a 50 ± 2 °C sem etileno, 3 minutos a 50 ± 2 °C + 3 μL L-1 de etileno, 5 minutos a 50 ± 2 °C sem etileno, e 5 minutos a 50 ± 2 °C + 3 μL L-1 de etileno. Os frutos foram armazenados por 30 dias a 25 ± 2 °C e 90 ± 5% UR. Foi observado que o tratamento hidrotérmico por 5 minutos a 50 ± 2 °C ajudou na manutenção da cor verde na casca dos frutos, também houve redução significativa na taxa respiratória e na perda de massa fresca dos frutos. Esses resultados sugerem que o tratamento térmico auxilia na manutenção da qualidade de frutos de lima ácida \'Tahiti\', uma vez que tem efeito no retardo de processos envolvidos no amadurecimento e senescencia. / One of the great challenges of the Brazilian citrus industry, as a major producer of \'Tahiti\' acid lime, has been the conservation of the fruit in natura with destiny to export. Preventing the change in color from green to yellow during storage is the focus of great efforts in post-harvest research. The objective of the present work was: (1) to evaluate the application of ethylene concentrations in order to determine the minimum concentration necessary to activate the color change in the fruit peels; (2) to evaluate the heat treatment by immersion in hot water, in order to use it as an alternative to delay the yellowing. In Chapter 1, two experiments were carried out and four treatments were evaluated in experiment 1: 0 μL L-1, 3 μL L-1, 6 μL L-1 and 12 μL L-1 of ethylene, stored for 18 days at 22 ± 2 ° C and 85 ± 5% of relative humidity (RH), using fruits benefited, but not treated with gibberellic acid (GA). It was observed low fresh mass loss and an acceleration in de-greening from day 10 in the treatments of 3, 6 and 12 μL L-1 of ethylene. In the experiment 2, six treatments were evaluated: 0, 1, 2, 3, 6 and 12 μL L-1 of ethylene, stored for 21 days at 25 ± 2 ° C and 85 ± 5% RH. The fruit was benefited and treated with gibberellic acid (GA). The results showed little de-greening according to the colorimeter analysis, being this result more noticeable in the analysis by color rating for concentrations of 3 μL L-1 of ethylene and low fresh mass loss. Processing with GA and wax may have affected the action of ethylene. In Chapter 2 an experiment was conducted using fruits harvested directly from the field and the heat treatment was evaluated by immersion in hot water and subsequent storage in the presence or absence of 3 μL L-1 of ethylene. Six treatments were performed: control without ethylene, control + 3 μL L-1 ethylene, 3 minutes at 50 ± 2 ° C without ethylene, 3 minutes at 50 ± 2 ° C + 3 μL L-1 ethylene, 5 minutes at 50 ± 2 ° C without ethylene, and 5 minutes at 50 ± 2 ° C + 3 μL L-1 ethylene. The fruits were stored for 30 days at 25 ± 2 ° C and 90 ± 5% RH. It was observed that the hydrothermal treatment for 5 minutes at 50 ± 2 ° C helped to maintain the green color in the fruits peel, also there was a significant reduction in the respiratory rate and the loss of fresh fruit mass. These results suggest that the hydrothermal treatment helps to maintain the quality of \'Tahiti\' acid lime fruits, since it has an effect on the delay of processes involved in ripening and senescence

Um dos grandes desafios da citricultura brasileira, como grande produtora de lima ácida \'Tahiti\', tem sido a conservação do fruto in natura com destino à exportação. A prevenção da mudança na coloração de verde para amarelo durante o armazenamento constitui o foco de grandes esforços na área de pesquisas em pós-colheita. O presente trabalho teve como objetivo: (1) avaliar a aplicação de concentrações de etileno visando determinar a concentração mínima necessária para ativar a mudança da cor na casca dos frutos; (2) avaliar o tratamento térmico por imersão em água quente, visando utilizá-lo como alternativa para retardar o amarelecimento. No capítulo 1 foram realizados dois experimentos, sendo avaliados 4 tratamentos no experimento 1: 0 μL L-1, 3 μL L-1 , 6 μL L-1 e 12 μL L-1 de etileno, armazenados por 18 dias a 22 ± 2 °C e 85 ± 5% de umidade relativa (UR), utilizando frutos beneficiados, mas não tratados com ácido giberélico (GA). Se observou baixa perda de massa fresca e uma aceleração no desverdecimento a partir do dia 10 nos tratamentos de 3, 6 e 12 μL L-1 de etileno. No experimento 2 foram avaliados seis tratamentos: 0, 1, 2, 3, 6 e 12 μL L-1 de etileno, armazenados por 21 dias a 25 ± 2 °C e 85 ± 5% de UR. Foram utilizados frutos beneficiados, e tratados com ácido giberélico (GA). Os resultados mostraram pouco desverdecimento segundo análise no colorímetro, sendo esse resultado mais perceptível na análise por nota de cor para concentrações de 3 μL L-1 de etileno e baixa perda de massa fresca. O beneficiamento com GA e cera pode ter afetado a ação do etileno. No Capítulo 2 foi conduzido um experimento utilizando frutos colhidos diretamente do campo e avaliado o tratamento térmico por imersão em água quente e posterior armazenamento em presença ou ausência de 3 μL L-1 de etileno. Foram estabelecidos 6 tratamentos: controle sem etileno, controle + 3 μL L-1 de etileno, 3 minutos a 50 ± 2 °C sem etileno, 3 minutos a 50 ± 2 °C + 3 μL L-1 de etileno, 5 minutos a 50 ± 2 °C sem etileno, e 5 minutos a 50 ± 2 °C + 3 μL L-1 de etileno. Os frutos foram armazenados por 30 dias a 25 ± 2 °C e 90 ± 5% UR. Foi observado que o tratamento hidrotérmico por 5 minutos a 50 ± 2 °C ajudou na manutenção da cor verde na casca dos frutos, também houve redução significativa na taxa respiratória e na perda de massa fresca dos frutos. Esses resultados sugerem que o tratamento térmico auxilia na manutenção da qualidade de frutos de lima ácida \'Tahiti\', uma vez que tem efeito no retardo de processos envolvidos no amadurecimento e senescencia. / One of the great challenges of the Brazilian citrus industry, as a major producer of \'Tahiti\' acid lime, has been the conservation of the fruit in natura with destiny to export. Preventing the change in color from green to yellow during storage is the focus of great efforts in post-harvest research. The objective of the present work was: (1) to evaluate the application of ethylene concentrations in order to determine the minimum concentration necessary to activate the color change in the fruit peels; (2) to evaluate the heat treatment by immersion in hot water, in order to use it as an alternative to delay the yellowing. In Chapter 1, two experiments were carried out and four treatments were evaluated in experiment 1: 0 μL L-1, 3 μL L-1, 6 μL L-1 and 12 μL L-1 of ethylene, stored for 18 days at 22 ± 2 ° C and 85 ± 5% of relative humidity (RH), using fruits benefited, but not treated with gibberellic acid (GA). It was observed low fresh mass loss and an acceleration in de-greening from day 10 in the treatments of 3, 6 and 12 μL L-1 of ethylene. In the experiment 2, six treatments were evaluated: 0, 1, 2, 3, 6 and 12 μL L-1 of ethylene, stored for 21 days at 25 ± 2 ° C and 85 ± 5% RH. The fruit was benefited and treated with gibberellic acid (GA). The results showed little de-greening according to the colorimeter analysis, being this result more noticeable in the analysis by color rating for concentrations of 3 μL L-1 of ethylene and low fresh mass loss. Processing with GA and wax may have affected the action of ethylene. In Chapter 2 an experiment was conducted using fruits harvested directly from the field and the heat treatment was evaluated by immersion in hot water and subsequent storage in the presence or absence of 3 μL L-1 of ethylene. Six treatments were performed: control without ethylene, control + 3 μL L-1 ethylene, 3 minutes at 50 ± 2 ° C without ethylene, 3 minutes at 50 ± 2 ° C + 3 μL L-1 ethylene, 5 minutes at 50 ± 2 ° C without ethylene, and 5 minutes at 50 ± 2 ° C + 3 μL L-1 ethylene. The fruits were stored for 30 days at 25 ± 2 ° C and 90 ± 5% RH. It was observed that the hydrothermal treatment for 5 minutes at 50 ± 2 ° C helped to maintain the green color in the fruits peel, also there was a significant reduction in the respiratory rate and the loss of fresh fruit mass. These results suggest that the hydrothermal treatment helps to maintain the quality of \'Tahiti\' acid lime fruits, since it has an effect on the delay of processes involved in ripening and senescence

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