(721e) Role of Interfacial Adhesion in Rate-Dependent Deformation and Failure of Model Ring Opening Metathesis Polymer (ROMP) Filled Composites
Glassy polymers formed by ring opening metathesis polymerization (ROMP) such as poly(dicyclopentadiene) (PDCPD) have unique potential as structural and protective materials due to their combination of high glass transition temperature, remarkable toughness, and outstanding low-temperature performance. However, these polymers tend to be highly nonpolar and thus do not adhere well to glass, limiting their application in fiber reinforced composites (FRPCs), laminates, and structural adhesives. Commercial glass fibers feature proprietary sizing packages optimized for conventional resins, which are challenging to remove without compromising fiber roughness and mechanical integrity. Therefore we have systematically investigated rate-dependent deformation and failure mechanisms of model composites comprising ROMP polymers containing well-defined rigid particulate fillers, focusing on the effects of filler-matrix interfacial chemistry and adhesion. Monodisperse micron-sized silica spheres are modified with a library of organosilanes and characterized using surface spectroscopic and wettability measurements. Mechanical effects of filler surface treatments presenting high, moderate, and inert reactivity toward the polymer network formed during curing are evaluated using a combination of high rate impact testing and quasistatic tensile and fracture testing in controlled environmental conditions, combined with in-situ and post-mortem imaging of failure processes. Preliminary results suggest well-bonded, reactively functionalized fillers suppress void growth in highly ductile resins with low crosslink density, facilitating deformation by shear. This results in a 10-fold increase in ultimate elongation relative to the unfilled polymer, and a 5-fold increase relative to an equivalent formulation containing poorly bonded fillers. These results are in contrast to our previous work on semi-brittle poly(methyl methacrylate), in which well-bonded fillers severely restrict plastic deformation and degrade toughness. The results suggest a rich design space for optimizing impact energy dissipation of protective systems based on interfacial properties and matrix ductility.