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Previous research into the friction behaviour of elastomers has typically focused on the effects of velocity, contact pressure, counter surface and lubrication on the coefficient of friction. O-ring type elastomer seals are common in many different industries. Friction plays a critical role during the setting and in service of these components. An experimental O-ring friction testing rig has been developed that can measure the effects of sliding speed and hydrostatic pressure on elastomer friction. Finite element analysis (FEA) packages can adopt fixed friction coefficients or ones that are pressure dependent. For the latter case, the dependence of the frictional behaviour is typically obtained from the instantaneous stress response at any given pressure and then related to the normal force response. The friction rig described in this paper uses industry standard dimensions for the O-ring gland, the pre-compression levels, extrusion gap size and pressure rating. The coefficient of friction is derived by dividing the measured friction force by the normal force, which was determined using an FEA modelling approach, as it could not be measured directly. Finally, a relationship between the frictional velocity and surface roughness is obtained in order to provide a frequency dependent Coefficient of Friction (CoF) that is easily translatable between surfaces.

The electrospinning technique combined with the electrospraying process provides a straightforward and versatile approach for the fabrication of novel nanofibrous biocomposite scaffolds with structural, mechanical, and biological properties potentially suitable for bone tissue regeneration. In this comparative investigation, three types of poly(3-hydroxybutyrate) (PHB)-based scaffolds were engineered: (i) PHB mats by electrospinning of a PHB solution, (ii) mats of PHB/hydroxyapatite nanoparticle (nHA) blends by electrospinning of a mixed solution containing PHB and nHAs, and (iii) mats constituted of PHB nanofibers and nHAs by simultaneous electrospinning of a PHB solution and electrospraying of a nHA dispersion. Scaffolds based on PHB/nHA blends displayed improved mechanical properties compared to those of neat PHB mats, due to the incorporation of nHAs within the fibers. The electrospinning/electrospraying approach afforded biocomposite scaffolds with lower mechanical properties, due to their higher porosity, but they displayed slightly better biological properties. In the latter case, the bioceramic, i.e. nHAs, largely covered the fiber surface, thus allowing for a direct exposure to cells. The 21 day-monitoring through the use of MTS assays and SEM analyses demonstrated that human mesenchymal stromal cells (hMSCs) remained viable on PHB/nHA biocomposite scaffolds and proliferated continuously until reaching confluence.

Straightforward and versatile routes to functionalize the surface of poly(3-hydroxyalkanoate) (PHA) electrospun fibers for improving cell compatibility are reported under relatively mild conditions. The modification of nanofibrous PHAs is implemented through two different methodologies to introduce epoxy groups on the fiber surface: (1) preliminary chemical conversion of double bonds of unsaturated PHAs into epoxy groups, followed by electrospinning of epoxy-functionalized PHAs blended with nonfunctionalized PHAs, (2) electrospinning of nonfunctionalized PHAs, followed by glycidyl methacrylate grafting polymerization under UV irradiation. The latter approach offers the advantage to generate a higher density of epoxy groups on the fiber surface. The successful modification is confirmed by ATR-FTIR, Raman spectroscopy, and TGA measurements. Further, epoxy groups are chemically modified via the attachment of a peptide sequence such as Arg-Gly-Asp (RGD), to obtain biomimetic scaffolds. Human mesenchymal stromal cells exhibit a better adhesion on the latter scaffolds than that on nonfunctionalized PHA mats. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 816–824

Ring-opening polymerization of D,L-lactide is critically reevaluated under both microwave dielectric heating and conventional conduction/convection heating in order to probe the nonexistence of “nonthermal” microwave effects. All experiments are conducted in toluene by resorting to a fiber-optic sensor that allows for accurate internal reaction temperature measurements. For a given temperature, the results obtained either with a “temperature control” microwave heating mode or with a “power control” procedure can well be reproduced through conventional thermal heating. Microwave irradiation does not induce any alteration of the polymerization kinetics or “livingness”, clearly demonstrating the absence of any specific “nonthermal” effect in the microwave-assisted process.

The degradation of poly(3-hydroxyalkanoate)s (PHAs) could be performed in a rapid, inexpensive and straightforward way via microwave irradiation with good potential for further scale-up. One such degradation was compared to that induced by conventional heating at 190 °C. The experimental results showed that PHA oligomers with varying molar masses, characterized by a terminal crotonic double bond and a carboxyl group on the other chain end, could be effectively obtained from native PHAs in the bulk by both degradation approaches. The kinetics of PHA oligomer production was monitored by size exclusion chromatography and 1 H NMR. The influence of temperature as well as microwave irradiation time and power was investigated, and the optimal conditions of degradation are described. It turned out that this treatment was much more efficient than a conventional thermally-induced degradation, as oligomers with similar molar masses were formed with an about 100 times faster rate corresponding to very short irradiation times (maximum 15 min). Two microwave-assisted procedures could be advantageously used: an irradiation with constant temperature was appropriate to afford PHA oligomers with molar masses lower than 1000 g.mol −1 and high yields, while irradiation under constant power was more convenient to provide oligoesters with higher molar masses.

Microwave (MW)-assisted ring-opening polymerization (ROP) provides a rapid and straightforward method for engineering a wide array of well-defined poly(3-hydroxyalkanoate)-b-poly(D,L-lactide) (PHA-b-PLA) diblock copolymers. On MW irradiation, the bulk ROP of D,L-lactide (LA) could be efficiently triggered by a series of monohydroxylated PHA-based macroinitiators previously produced via acid-catalyzed methanolysis of corresponding native PHAs, thus affording diblock copolyesters with tunable compositions. The dependence of LA polymerization on temperature, macroinitiator structure, irradiation time, and [LA]0/[PHA]0 molar ratio was carefully investigated. It turned out that initiator efficiency values close to 1 associated with conversions ranging from 50 to 85% were obtained only after 5 min at 115 °C. A kinetic investigation of the MW-assisted ROP of LA gave evidence of its “living”/controlled character under the experimental conditions selected. Structural analyses and thermal properties of biodegradable diblock copolyesters were also performed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

The nonlinear effect at small strains (Payne effect) has been investigated in the case of silica-filled styrene-butadiene rubber. The originality of this study lies in the careful preparation of samples in order to fix all parameters except one, that is, the modification of the silica surface by grafting silane (introduced at different concentrations) via reactive mixing. The organosilane can be either a coupling or a covering surface treatment with an octyl alkyl chain. A careful morphological investigation has been performed prior to mechanical characterization and silica dispersion was found to be the same whatever the type and the amount of silane. The increasing amount of covering agents was found to reduce the amplitude of the Payne effect. A similar decrease is observed for low coupling agent concentration. At higher concentrations, the evolution turns through an increase due to the contribution of the covalent bonds between the matrix and the silica acting as additional crosslinking. The discussion of the initial modulus was done in the frame of both the filler-filler and filler-polymer models. It is unfortunately not possible to distinguish both scenarios, because filler-filler and filler-matrix interactions are modified in the same manner by the grafting covering agent. On the other hand, the reversible decrease of the modulus versus strain (Payne effect) is interpreted in terms of debonding of the polymeric chains from the filler surface.

A straightforward and versatile method for immobilizing macromolecules and silver nanoparticles on the surface of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) electrospun fibers is developed with the objective of designing a new functional material having significant antibacterial activity. The approach relies on a two-step procedure: UV photografting of poly(methacrylic acid) (PMAA) on the surface of PHBHV fibers according to a "grafting from" method, and complexation of in situ photogenerated silver nanoparticles (Ag NPs) by carboxyl groups from tethered PMAA chains. The photografting process is conducted through a photoinduced free-radical process employing a ketone-based photoinitiator in aqueous medium. Under appropriate conditions, the photogenerated radicals abstract hydrogen atoms from the PHBHV backbone, thus initiating the UV-mediated photopolymerization of MAA from the PHBHV microfibrous surface. The photochemical mechanism of the ketone photolysis is entirely described by the electron spin resonance/spin-trapping technique, and the modified PHBHV microfibrous scaffold is extensively characterized by ATR-FTIR spectroscopy, water contact-angle measurements, and mercury intrusion porosimetry. In a second step, the in situ synthesis of Ag NPs within the microfibrous scaffold is implemented by photoreduction reaction in the presence of both a silver precursor and a photosensitizer. The photoinduced formation of Ag NPs is confirmed by UV spectrophotometry and XPS analysis. SEM and TEM experiments confirm the formation and dispersion of Ag NPs on the surface of the modified fibers. Finally, a primary investigation is conducted to support the antibacterial activity of the new functionalized biomaterial against Staphylococcus aureus and Escherichia coli.

The effect of different silica treatments on the vulcanization of silica filled Styrene Butadiene Rubber (SBR) is investigated. The concentration, the length and the functionality (coupling or non coupling) of the silane used for this treatment are the parameters studied. It is shown that the silane grafting, by covering the silica surface, modifies the adsorption and desorption on this surface of the accelerators used in the vulcanization system, which in turn modifies the crosslinking kinetic and therefore should influence the final crosslinking state of the matrix.

International audience; Original in situ measurements of volume variation and small angle light scattering (SALS) are performed on silica filled Styrene Butadiene Rubber (SBR) during tensile tests. The influence of the silica treatment on the mechanisms involved is explored with sample carefully characterised and with the same filler dispersion. Two different types of silane are used as treatment, an alkoxy silane (so called covering agent) and a coupling agent which enables covalent bonds between the silica and the polymer matrix. It is shown that the coupling agent delays void formation in the samples and leads at intermediary strain to the reorganisation of the filler structure while the covering agent eases the void formation which also occurs without silica surface treatment.

A straightforward and versatile method for immobilizing polysaccharides on the surface of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) electrospun fibers is developed with the objective of designing a new functional biomaterial having a significant effect on cell proliferation. The approach relies on a one-step procedure: UV grafting of a photosensitive dextran (AQ-Dext) on the surface of PHBHV fibers according to a "grafting onto" method, with the use of an anthraquinone derivative. The photografting is conducted through a photoinduced free radical process employing an anthraquinone-based photosensitizer in aqueous medium. Under appropriate conditions, AQ-Dext reacts with C-H σ-bonds of the polymer substrate (PHBHV) to produce a semianthraquinone radical according to an H-abstraction reaction. This radical recombines together with the alkylradical (R˙) formed at the surface of PHBHV fibers via the oxygen atom of the anthraquinone photolinker. The photochemical mechanism of the AQ-Dext photolysis is entirely described for the first time by an electron spin resonance technique and laser flash photolysis. The modified PHBHV microfibrous scaffolds are extensively characterized by water contact angle measurements, XPS analysis and atomic force microscopy, confirming the covalent grafting of dextran on PHBHV fibers. Finally, a primary investigation demonstrates that dextran modified PHBHV fibers are permissive for optimized cell colonization and proliferation. The cell morphologies are described by SEM micrographs, revealing a significant affinity and favorable interactions for adherence of human mesenchymal stem cells (hMSCs) on scaffolds provided by dextran chemical structure. Moreover, the proliferation rate of hMSCs increases on this new functionalized biomaterial associated with a higher extra-cellular matrix production after 5 days of culture in comparison with native PHBHV fibers.