| A key challenge in sustainable materials research is to employ low-value municipal and agricultural waste and bio-based byproducts as fillers to produce green, commercially attractive polymer composites and nanocomposites. Examples of such waste or byproducts include rice husk ash (~90% silica and a major waste disposal issue), eggshell (mostly calcium carbonate), lignin (the only biomass source of aromatic functionality and a byproduct of the pulping process for making paper), and waste paper and cardboard (mostly cellulose). Relatively low-value, renewable, virgin, and bio-based materials such as soy flour (made from grinding roasted soybeans into a fine powder) and cellulose (the most abundant organic polymer on earth) also have the potential to be synergistic fillers in polymer composites and nanocomposites. However, poor dispersion of these hydrophilic fillers within a hydrophobic polymer matrix achieved via conventional melt processing has often led to minimum improvement or deterioration in mechanical properties of the composites.;My thesis research addresses the utility of each of these waste materials/byproducts as filler for polymers and demonstrates that effective filler dispersion can be achieved via solid-state shear pulverization (SSSP) without the necessity for surface modification or compatibilization. The composites thus produced exhibit major enhancements in thermal stability, mechanical properties, and crystallizability. This research also shows that incorporation of well-dispersed, natural antioxidant-rich agro-waste in polymers can effectively improve processing and recycling stability of polyolefins. Using the concept of specific energy in SSSP, this thesis further demonstrates how green polymer composites can be prepared in a cost effective and energy efficient manner. Thus, when appropriately processed with polyolefins, waste materials, byproducts, and virgin bio-based materials are excellent substitutes for synthetic fillers and antioxidants in the production of polymer composites with superior properties. In addition, SSSP was also employed to produce polyolefin/cellulose nanocrystal (CNC) composites with major increases in Young's modulus, including the highest modulus enhancement (69% relative to neat polymer) ever reported for polyolefin/CNC composites. Finally, a model study with nanosilica has shown that good dispersion of unmodified nanofiller in a metastable dispersed state results in more robust polymer nanocomposites than when modified nanofiller is used to compatibilize the polymer-nanofiller interface. |
