Qualitative Effect of the Polymerization Rate on the Nanoparticle Dispersion in Poly(methyl methacrylate)/Silica Nanocomposite Films

In this study, we investigate the effect of the polymerization rate, mainly mediated by the initiator concentration, on the nanoparticle dispersion in the nanocomposite films formed by poly(methyl methacrylate) (PMMA) and [3-(methacryloyloxy)propyl]trimethoxysilane-modified silica nanoparticles (M-SiO2) via free radical polymerization of the precursory solution, that is, 15.5 wt % M-SiO2 nanoparticles dispersed in the methyl methacrylate (MMA) monomer, in which the tethered silanes at the particle surface bearing the reactive vinyl groups were capable of polymerizing with the MMA monomer. At slower polymerization, the nanoparticles self-organized to form a large-length scale network structure with the mass fractal of average dimension of 2.7; contrarily, the nanoparticles exhibited better dispersion when the polymerization proceeded at a faster rate. According to the scenario of perturbed polymerization kinetics in the presence of nanoparticles, we propose a possible mechanism through which the MMA monomers at a lower polymerization rate may constitute longer “multiple grafted PMMA chains” along particle surfaces by an optimal balance between the polymerization of the monomer and the grafting reaction of the monomer onto the particle surface, forming the M-SiO2-rich clusters by interparticle bridging; the multiple grafting reaction also occurred in between any two neighboring M-SiO2 nanoparticles situated respectively at the two adjoining clusters to induce the intercluster bridging, thereby leading to a hierarchical fractal network. However, both the polymerization and the grafting reaction of MMA monomers at a higher polymerization rate formed the shorter free and grafted PMMA chains, providing steric stabilization to retain better dispersity of nanoparticles

A research challenge vision regarding management of agricultural waste in a circular bio-based economy

International audienceAgricultural waste is a huge pool of untapped biomass resources that may even represent economic and environmental burdens. They can be converted into bioenergy and bio-based products by cascading conversion processes, within circular economy, and should be considered residual resources. Major challenges are discussed from a transdisciplinary perspective, focused on Europe situation. Environmental and economic consequences of agricultural residue management chains are difficult to assess due to their complexity, seasonality and regionality. Designing multi-criteria decision support tools, applicable at an early-stage of research, is discussed. Improvement of Anaerobic Digestion (AD), one of the most mature conversion technologies, is discussed from a technological point of view and waste feedstock geographical and seasonal variations. Using agricultural residual resources for producing high-value chemicals is a considerable challenge analysed here, taking into account innovative eco-efficient and cost-effective cascading conversion processes (bio-refinery concept). Moreover, the promotion of agricultural residues-based business is discussed through industrial ecology, to promote synergy, on a local basis, between different agricultural and industrial value chains. Finally, to facilitate a holistic approach and optimise materials and knowledge flows management, the connection of stakeholders is discussed to promote cross-sectorial collaboration and resource exchange at appropriate geographic scales