Dégradation d'un polymère

Résumé

vignette|Délaminage d'une peinture automobile. La plupart des polymères organiques (et des matériaux correspondants) sont, de par leur structure caténaire, considérés comme des composés « vivants », car sensibles à leur environnement et sujets au vieillissement. La dégradation d'un polymère est le changement, généralement non désiré, de ses propriétés physiques et mécaniques, causé par des facteurs environnementaux plus ou moins agressifs : attaque d'un produit chimique tel un acide concentré, dioxygène (oxydation), chaleur, radiation (photolyse), eau (hydrolyse), contrainte Ensemble, ces facteurs agissent souvent en synergie. La dégradation peut rendre le matériau inutilisable. Présentation Les réactions de dégradation font partie, avec les réactions fonctionnelles classiques (celles des molécules ordinaires : additions, substitutions…) et les réactions de réticulation (ou de pontage, telles la vulcanisation), des trois grandes catégories de réactions chimiques des polymèr

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https://fr.wikipedia.org/wiki/D%C3%A9gradation_d'un_polym%C3%A8re

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La photodégradation des polymères, appelée parfois photo-oxydation des polymères ou plus simplement photo-oxydation, est une détérioration moléculaire de ce dernier due à son exposition à des rayonnem

Polymer stabilizers (British: polymer stabilisers) are chemical additives which may be added to polymeric materials, such as plastics and rubbers, to inhibit or retard their degradation. Common polym

vignette|Les matières plastiques font désormais partie de notre quotidien. Structure typique d'une formule : matière plastique = polymère(s) brut(s) (résine(s) de base) + charges + plastifian

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Chlorinated ethenes solvents (CEs) are one of the most common contaminants identified in groundwater ecosystems. Long used as a degreaser in industry, perchloroethene (PCE) and trichloroethene (TCE) are particularly persistent in the environment as recalcitrant to oxic degradation, and classified as unhealthy and dangerous for the environment. Under anaerobic conditions, CEs can be degraded naturally in the environment by organohalide respiring bacteria (OHRB) through dehalogenase enzymes reducing them into ethene, a non-hazardous end product. However, toxicity of the intermediate daughter compounds of the degradation (TCE, DCE and VC) is higher than PCE. As this natural attenuation is a slow process, intermediate compounds accumulate in the environment and biostimulation is often used to enhance the complete degradation of CEs. Substrates are added to the contaminated aquifer and used by fermentative bacteria releasing by-product such as H2 that is essential for the dehalorespiration of CEs. Biostimulation has been studied in a PCE contaminated-aquifer located in Jablunkov (Czech Republic). Cheese whey (CW) has been injected into the groundwater in November 2012 and June 2013. The objective of the current project is to evaluate the efficiency of the CW applications by analysing microbiologic and physico-chemical parameters describing the aquifer at six sampling dates from September 2012 to December 2013 within six wells allocated over the aquifer. Global bacterial community structures were analysed in laboratory using Polymerase Chain Reaction (PCR) and T-RFLP (Terminal Restriction Fragment Length Polymorphism). OHRB were analysed as well by specific PCR targeting 16S rRNA and dehalogenase genes of bacteria known to degrade completely the CEs. Then, contaminants and ethene concentrations as well as others Terminal Electron Acceptors implicated in the respiratory processes (Terminal Electron Accepting Processes – TEAPs) were measured to give information about the redox conditions within the aquifer. Finally, others hydrogeological parameters such as pH and temperature were measured. All data were analysed using Multiple Factor Analysis (MFA) in the R software. Interpretations provided a global model indicating the characteristics and functioning of the aquifer. The successive CW applied on-site have a gradual impact on the environmental conditions and on the structures of bacterial communities. After the two CW applications, the aquifer has partly changed to conditions favourable for complete dechlorination. It was the case for three wells over six. Two CW injections have been necessary to allow the production of ethene for two wells whereas only one was needed for the other one. Biostimulation were efficient but not sufficient to completely degrade the CEs on the whole aquifer. In one well, the accumulation of DCE were more important than the production of ethene. In two other wells, ethene was not produced but the statistical analysis showed that they tend toward complete dechlorination conditions. New CW applications would be necessary to completely remediate this aquifer.

2014

Chargement

The photo-Fenton process is a promising emerging technology for the treatment of contaminated water streams. It is based on the generation of reactive oxygen species that are capable of destroying recalcitrant contaminants otherwise unaffected by conventional municipal wastewater treatment method. Among its innate advantages are that it can be catalyzed naturally by solar radiation and the main reagents required are iron and hydrogen peroxide, both abundant and relatively cheap. There are however some important limitations. The process functions best at acidic pH, is negatively affected by some inorganic ions present in natural water and the water requires pH neutralization and iron recuperation following the treatment. These limitations inhibit the application of the process at larger-scale. This work is an attempt to develop new strategies for enhancing the photo-Fenton process for making it a more attractive option for the treatment of municipal or industrial wastewaters. Two main pathways are investigated, the use of ultrasound and the use of iron-complexing agents. Ultrasonic processes have been shown to improve degradation kinetics when applied in combination with photo-Fenton, while at the same time are not as negatively affected by some of the inorganic ions present in water. Iron-complexing agents can maintain iron soluble at a wider operational pH and can also improve process efficiency via pathways discussed at length in the text. Chapter 2 is focused on the application of ultrasound in combination with photo-Fenton for two very distinct applications: 1) A pilot-scale ultrasound/photo-Fenton system was set-up and evaluated for the treatment of three different contaminants with distinct physicochemical properties and at different concentrations. Synergy was evaluated in terms of degradation kinetics and H2O2 consumption efficiency. 2) Ultrasound was applied alone and in combination with photo-Fenton for the treatment of the iodinated contrast agent Iohexol. These agents are injected in patients during radiographic procedures and excreted via urine. This provided an opportunity to examine if ultrasound could improve their treatment in such a complex aquatic medium. Treatment options both in urine (at the source) and in the context of municipal wastewater are discussed. Chapter 3 is focused on the use of EDDS as an iron-complexing agent for degrading contaminants at near neutral pH across a concentration range usually found in different wastewaters (from ÎŒg L-1 to mg L-1 ). EDDS was used both for the treatment of microcontaminants (ÎŒg L-1) in municipal wastewater treatment plant effluents as well as for highly contaminated ( several mg L-1) water. The importance of several factors and operational conditions is discussed. Chapter 4 discusses the possibility of exploiting natural iron-complexing agents (mainly phenolic/polyphenolic compounds) that can be found in some types of wastewater (e.g from natural products processing industries). The concept of reusing polyphenol-rich wastewater in small quantities as an alternative to artificial complexing agents is introduced. As a case study, water containing highly concentrated cork bark extracts (Cork Boiling Wastewater) has been added in natural water spiked with one or several contaminants. Its capacity to maintain Fe3+ soluble at near-neutral pH as well as the effect on Fenton/photo-Fenton degradation were observed.

EPFL2016

Chargement

Study of loading and delivery of drugs from various hydrogel matrices for orthopaedic applications

Tamsine Wills

Nowadays, there are still several unmet medical needs in the field of orthopaedic and trauma surgery leading to the incentive of finding alternative and innovative clinical therapeutics for the treatment of bone regeneration. For example, the entrapment of osteoinductive growth factors in a polymeric matrix with subsequent gradual release and local delivery to the site of trauma. This new technology inspired the activities relating to my project in which I investigated the potential use of synthetic hydrogels for the sustained in situ release of bioactives. The tasks relating to my project were divided into two main experiments; release assays and bioactivity assays. During the release assays, the in vitro release of three osteoinductive growth factors from five different synthetic hydrogels was investigated. The goal was to characterise the release of the protein drugs from the different polymers, selected on the basis of their swelling and degradation behaviour. The quantification of the released bioactives was assessed by performing an enzyme-linked immunosorbent assay (ELISA), for which different parameters were optimised. As a result, release profiles of the different protein drugs from the different hydrogel formulations were obtained. Then, it was investigated if the growth factors were still biologically active or if incubation in synthetic matrices influenced their properties. This was assessed by performing bioassays during which the alkaline phosphatase (ALP) activity of a mouse myoblast cell line (C2C12 cells) was evaluated. Indeed, ALP is a marker of osteoblastic activity which indicates increased levels of osteogenesis, implying biological activity of the tested osteoinductive bioactives. These results gave a good representation of the effect of the synthetic hydrogels and their incubation in release buffer on the bioactivity of the incorporated protein drugs

2009

Chargement

2014

EPFL2016

Study of loading and delivery of drugs from various hydrogel matrices for orthopaedic applications

Tamsine Wills

2009