1,720,979 research outputs found
Synthesis of biodegradable styrene copolymers
No full textPolystyrene (PS), a versatile polymer with many applications (e.g. packaging) representing about 10% of the total annual polymer consumption, shows practically no biodegradability. In this study a styrene (ST) based copolymer is synthesized and examined regarding its ability to degrade in a composting test. As second monomer, to introduce biodegradable ester groups, 5,6-benzo-2-metylene-dioxepane (BMDO) has been used in radical copolymerization reactions performed in inert and stirred 10 ml
Schlenck bottles. The composition of the copolymers was measured by NMR.Their molecular weight (Mw) was done by GPC. Biodegradation was validated with a 4 months test in an aerated bioreactor by monitoring the CO2 production. In a typical copolymerization reaction 25 mol % of BMDO and 0,05 mol% dicumylperoxide (DCP) was added to styrene. Reaction was done during 24 hours at 120°C. The resulting copolymers contained 12
mol% ester groups and had a Mw of 115 000 g/mol. Copolymer reaction parameters are estimated at rBMDO = 0,52 and rST= 7,55. Time and temperature are indicated as important reaction parameters. Other parameters to be investigated are monomer concentrations, initiator and solvent. To validate the potential for biodegradation, 2 low Mw (23340 and 31060 g/mol) BMDO-ST copolymer with respectively 5,7 and 14,2 mol% BMDO were subjected to a 4 month composting resulting in a loss in weight of 21 and 27% respectively. This study showed a potential way to make polystyrene susceptible to biodegradation. In the follow-up study a comprehensive parameter study will be needed to obtain high
Mw copolymers with sufficient ester groups incorporated to achieve biodegradation. The higher Mw material will be used to validate the material properties
Synthesis of biodegradable styrene copolymers
No full textPolystyrene (PS), a versatile polymer with many applications (e.g. packaging) representing about 10% of the total annual polymer consumption, shows practically no biodegradability. In this study a styrene (ST) based copolymer is synthesized and examined regarding its ability to degrade in a composting test. As second monomer, to introduce biodegradable ester groups, 5,6-benzo-2-metylene-dioxepane (BMDO) has been used in radical copolymerization reactions performed in inert and stirred 10 ml
Schlenck bottles. The composition of the copolymers was measured by NMR.Their molecular weight (Mw) was done by GPC. Biodegradation was validated with a 4 months test in an aerated bioreactor by monitoring the CO2 production. In a typical copolymerization reaction 25 mol % of BMDO and 0,05 mol% dicumylperoxide (DCP) was added to styrene. Reaction was done during 24 hours at 120°C. The resulting copolymers contained 12
mol% ester groups and had a Mw of 115 000 g/mol. Copolymer reaction parameters are estimated at rBMDO = 0,52 and rST= 7,55. Time and temperature are indicated as important reaction parameters. Other parameters to be investigated are monomer concentrations, initiator and solvent. To validate the potential for biodegradation, 2 low Mw (23340 and 31060 g/mol) BMDO-ST copolymer with respectively 5,7 and 14,2 mol% BMDO were subjected to a 4 month composting resulting in a loss in weight of 21 and 27% respectively. This study showed a potential way to make polystyrene susceptible to biodegradation. In the follow-up study a comprehensive parameter study will be needed to obtain high
Mw copolymers with sufficient ester groups incorporated to achieve biodegradation. The higher Mw material will be used to validate the material properties
Lightweight wooden packaging : chemical migration between wood and food
No full textLes emballages alimentaires existent depuis la nuit des temps, depuis que l'homme transporte des aliments solides ou liquides. Comme tous les matériaux destinés à entrer au contact des aliments, le bois peut être une source de contaminations chimiques et/ou biologiques, il est donc soumis au règlement (CE) 1935/2004 du parlement européen. Cependant en France, la réglementation spécifique « bois » date de novembre 1945. Elle définit les espèces autorisées pour le contact alimentaire. Il existe également une note d'information « bois » de l'agence sanitaires française « DGCCRF » qui détaillent quelques phénomènes de migration entre le bois et l'aliment mais elles sont très peu développées. L'objectif de cette thèse est d'étudier les différents facteurs qui influencent la migration des composés organiques du bois après un contact alimentaire afin de développer une méthodologie d'analyse simple applicable par les industriels de l'emballage. A l'échelle locale, ce projet innovant apporte une réponse auprès des autorités sanitaires françaises et auprès de la filière française emballages bois et palettes. Et fournira des éléments nécessaires pour la mise à jour de la fiche « matériau bois n°2012-93 » et permettront aux industries agroalimentaires d'avoir à disposition une méthode d'analyse de référence.Food packaging has existed for millennia; ever since man wished to transport solid or liquid foods that were gathered previously. As in the case most materials, wood could be a source of contamination by chemical or biological products. To date, there are no studies available that assess the migration potential of wood components in to food. Food in contact with materials, like wood, is subject to the European Regulation (EC) 1935/2004. In contrast to other materials, there is no specific directive for wooden food contact packaging. In France, the only specific regulation concerning "wood" dates from November 1945 and is very underdeveloped. This thesis aims to study various factors that influence the migration of organic compounds from wood to food when in direct or indirect contact with one another. The final outcome will be a simple methodology that can be applied to industrial packaging. At the national level, this innovative project is in response to the needs of both the French health authorities and the French wood packaging industry. And provide the information necessary to update the information contained in "wood material No. 2012-93” which will, in turn, give the food industry an analytical method and a point of reference
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
