Study of sequential abiotic and biotic degradation of styrene butadiene rubber.

Styrene butadiene rubber is one of the main constituents of tire tread. During tire life, the tread material undergoes different stresses that impact its structure and chemical composition. Wear particles are then released into the environment as weathered material. To understand their fate, it is important to start with a better characterization of abiotic and biotic degradation of the elastomer material. A multi-disciplinary approach was implemented to study the photo- and thermo- degradation of non-vulcanized SBR films containing 15 w% styrene as well as their potential biodegradation by Rhodoccocus ruber and Gordonia polyisoprenivorans bacterial strains. Each ageing process leads to crosslinking reactions, much surface oxidation of the films and the production of hundreds of short chain compounds. These degradation products present a high level of unsaturation and oxidation and can be released into water to become potential substrates for microorganisms. Both strains were able to degrade from 0.2 to 1.2 % (% ThOD) of the aged SBR film after 30-day incubation while no biodegradation was observed on the pristine material. A 25-75 % decrease in the signal intensity of water extractable compounds was observed, suggesting that biomass production was linked to the consumption of low-molecular-weight degradation products. These results evidence the positive impact of abiotic degradation on the biodegradation process of styrene butadiene rubber.

Assessing biodegradation of roadway particles via complementary mass spectrometry and NMR analyses.

Roadway particles (RP) that can be collected with on-vehicle system, consist of a mixture of Tire and road wear particles (TRWP) with other traffic-derived particles (exhaust or non-exhaust) and/or biogenic compounds and represent a significant source of xenobiotics, susceptible to reach the different environmental compartments. The study of the RP fate is thus a major challenge to tackle in order to understand their degradation and impact. They offer a variety of carbon sources potentially usable by microorganisms, ranging from the tire-derived plasticizers, vulcanizing agents, protective agents and their transformation products, to other traffic, road and environmental-derived contaminants. A multi-analytical approach was implemented to characterize RP and study their biodegradation. Kinetics of RP extractions were monitored during 21 days in water, methanol, acetone and chloroform to identify leaching and extractable compounds and monitor the particle composition. The results confirmed that hundreds of readily leachable chemicals can be extracted from RP directly into water according to a dynamic process with time while additional poorly soluble compounds remain in the particles. Mass spectrometry (LC-HRMS and GC-MS) allowed us to propose 296 putative compounds using an extensive rubber database. The capacity of 6 bacterial strains, belonging to Rhodococcus, Pseudomonas and Streptomyces genera, to biodegrade RP was then evaluated over 14 days of incubation. The selected strains were able to grow on RP using various substrates. Elastomer monitoring by 1H NMR revealed a significant 12 % decrease of the extractable SBR fraction when the particles were incubated with Rhodococcus ruber. After incubation, the biodegradation of 171 compounds among leachable and extractable compounds was evaluated. Fatty acids and alkanes from rubber plasticizers and paraffin waxes were the most degraded putative compounds by the six strains tested, reaching 75 % of biodegradation for some of them.

Time-concentration profiles of tire particle additives and transformation products under natural and artificial aging.

Tire and road wear particles (TRWP) are polymer-based microparticles that are emitted into the environment during tire usage. Growing efforts are currently being made to quantify these emissions, characterize the leachates and assess their environmental impact. This study aimed to investigate the effect of aging on TRWP composition. Cryomilled tire tread particles (CMTTP) and TRWP were exposed for different durations to three aging conditions: accelerated thermal and photochemical aging and natural outdoor aging. Particles were then extracted with cyclohexane/ethanol. The time-concentration profiles of 23 additives and transformation products present in these extracts were determined by UHPLC-HRMS. Several chemicals, such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6-PPD) or 1,3-diphenylguanidine (DPG), decayed exponentially under all aging conditions, with half-lives of a few days under artificial photoaging versus dozens of days under pure thermal aging at 60 °C. The natural aging profiles lie between those 2 laboratory aging conditions. Other chemicals, such as 6PPD-quinone, presented bell-shaped concentration profiles within CMTTP when particles were exposed to UV light. 6PPD-quinone reached a maximal concentration within a month under natural aging. For TRWP, the initial load of 6PPD-quinone had already reached a maximum prior to the aging experiments and decreased exponentially under natural aging with a half-life below one month. Pure thermal aging induced a significantly slower decay of 6PPD-quinone within TRWP (half-life of half a year), emphasizing a greater stability and persistence in environmental compartments without light. This study highlighted that the more readily accessible CMTTP could be considered a reasonable proxy of TRWP to investigate the fate of chemicals within rubber particles, at least from a qualitative standpoint. Overall, the concentrations of 20 of the evaluated chemicals decreased by >50 % within 50 days under natural aging.

Detection of degradation products of chemical warfare agents by highly porous molecularly imprinted microspheres.

The multiplication of terrorist actions in the recent events is alarming and the detection of chemical warfare agents (CWAs) has become one of the highest research priorities in the fields of security and public health. The biomimetic properties of molecularly imprinted polymers (MIPs) render them attractive for molecular recognition as well as sensing purposes. The degradation products of easily hydrolysable organophosphorus nerve agents such as pinacolyl methylphosphonate (PMP), a hydrolysis by-product of soman, are often used as templates in MIP synthesis. In this study, we describe the first example of PMP-imprinted polymer microspheres synthesized by precipitation polymerization. This one-step process involves methacrylic acid (MAA) as the monomer and divinylbenzene (DVB) as the cross-linker, in a toluene/acetonitrile mixture. Subsequent morphological characterizations of the PMP-imprinted particles show that they have diameters between 1 and 10 mum (as opposed to 4-5 mum for the non-imprinted microspheres), surface areas of up to 680 m(2) g(-1) and high porosities with pore sizes smaller than 2 nm. The present investigation also evidences the imprinting effect via batch binding experiments and reports on the use of a novel fluorescence-based methodology, where 4-methylumbelliferone (4MU) is utilised as a sensing agent to determine the PMP concentration in solution.

Interactions between chloride and cement-paste materials.

The durability of cement-based materials with respect to exterior aggressions is one of the current priorities in civil engineering. Depending on their use, the cement-based materials can be exposed to different types of aggressive environments. For instance, damages to concrete structures in contact with a saline environment (sea water on bridges, deicing salts on roads, etc.) are of utmost importance. Upon exposure to saline water, Cl- ions penetrate into the structures and subsequently lead to reinforcement corrosion. Chloride attack is often combined with other aggressive influences such as temperature (e.g., freezing) or the ingress of other ions (e.g., sulfates in sea water). We therefore aim to explore the effect of sodium chloride (NaCl) on the structural chemistry of cement paste. Existing studies about reinforcement corrosion by chloride have focused on the penetration of Cl- ions and the comparison between "free" ions (water-soluble ions) and bound ones. However, little is known about the fixation mechanisms, the localization of Cl in the cement matrix and the structural interaction between Cl and the silicate and aluminate hydrate phases present in cement paste. We present here results of a multinuclear nuclear magnetic resonance study on the fixation of chloride in the hydration products and the characterization of new phases potentially appearing due to chloride ingress.