Nano- and micron-sized cellulose crystals were prepared and utilized as reinforcements for polyurethane composites. The cellulose crystals obtained from microcrystalline cellulose (MCC) were incorporated into a polar organic solvent, dimethylformamide (DMF), and ultrasonicated to obtain a stable suspension. The suspension was an effective means for incorporating the cellulose crystals into the polyol-isocyanate mixture, utilized to produce polyurethane composite films. The use of DMF presents an interesting alternative for the use of cellulose crystals as reinforcement of a broad new range of polymers. Moreover, the rheology of the uncured liquid suspensions was investigated, and analysis of the results indicated the formation of a filler structure pervading the liquid suspension. Besides, films were prepared by casting and thermal curing of the stable suspensions. Thermomechanical and mechanical testing of the films were carried out to analyze the performance of the composites. The results indicated that a strong filler-matrix interaction was developed during curing as a result of a chemical reaction occurring between the crystals and the isocyanate component.

Two new single-component, highly cross-linked polymeric materials have been developed that are capable of undergoing repeated cycles of mending. On the basis of the thermally reversible Diels-Alder (r-DA) cycloaddition reaction, these materials are comprised of a dicyclopentadiene core which acts as both diene and dienophile in the r-DA reaction. Polymer specimens have been prepared from two monomeric units, monomers 400 and 401, and the thermal and mechanical properties of these materials have been studied via differential scanning calorimetry, dynamic mechanical analysis, and three-point bending, compression, and fracture tests. After fracture, these hard, colorless, transparent materials are capable of thermal mending at 120°C, effectively healing cracks formed in the specimen.