1,720,958 research outputs found
Alternative approach for polystyrene biodegradation by selected bacteria
No full textPlastics pose a growing concern towards the environment. Mitigating actions are required as most of them do not report significant biodegradation. Biodegradable plastics are proposed as alternatives. Unfortunately, it remains difficult to compete with traditional petroleum-based polymers. Besides technical and economic obstacles, intrinsic biodegradability also shows some negative effects. For applications like food packages, biodegradable polymers are single-use items. Recycling of Biodegradable polymers is difficult and it contaminates current recycling stream. Reuse and recycling of plastics saves a lot of resources and associated greenhouse gas (GHG) emissions. These savings will be reduced by increased use of biodegradable plastics. It seems a catch 22: traditional petroleum-based plastics are not biodegradable and accumulate in nature, but their biodegradable alternatives exhibit other adverse effects on the environment by increased use of resources and GHG emissions. An alternative approach could be to search for specific microorganisms capable of degrading current petroleum-based plastics. While a practical method to apply them is not available yet, a first requirement is to search for useful microorganisms. This knowledge can contribute to the development of alternative biotechnological solutions for the environmental threats posed by plastics. In this study the extraction and enrichment of polystyrene (PS) consuming bacteria is reported. After 2 enrichment cycles, five bacteria were identified using PS as their sole carbon source. In a subsequent mass loss experiment over 5 months period on PS film material, a small loss (0.5 wt.%) was detected. These results confirm bacterial degradation of PS. As biodegradation rates are relatively small, more research is required to make it applicable for plastic waste remediation
Alternative approach for polystyrene biodegradation by selected bacteria
No full textPlastics pose a growing concern towards the environment. Mitigating actions are required as most of them do not report significant biodegradation. Biodegradable plastics are proposed as alternatives. Unfortunately, it remains difficult to compete with traditional petroleum-based polymers. Besides technical and economic obstacles, intrinsic biodegradability also shows some negative effects. For applications like food packages, biodegradable polymers are single-use items. Recycling of Biodegradable polymers is difficult and it contaminates current recycling stream. Reuse and recycling of plastics saves a lot of resources and associated greenhouse gas (GHG) emissions. These savings will be reduced by increased use of biodegradable plastics. It seems a catch 22: traditional petroleum-based plastics are not biodegradable and accumulate in nature, but their biodegradable alternatives exhibit other adverse effects on the environment by increased use of resources and GHG emissions. An alternative approach could be to search for specific microorganisms capable of degrading current petroleum-based plastics. While a practical method to apply them is not available yet, a first requirement is to search for useful microorganisms. This knowledge can contribute to the development of alternative biotechnological solutions for the environmental threats posed by plastics. In this study the extraction and enrichment of polystyrene (PS) consuming bacteria is reported. After 2 enrichment cycles, five bacteria were identified using PS as their sole carbon source. In a subsequent mass loss experiment over 5 months period on PS film material, a small loss (0.5 wt.%) was detected. These results confirm bacterial degradation of PS. As biodegradation rates are relatively small, more research is required to make it applicable for plastic waste remediation
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
