Cellulose nanoparticles: A route from renewable resources to biodegradable nanocomposites

With 1013 tons biosynthesized annually cellulose is the most abundant polymer on earth. In this thesis, preparation and characterization of nanocrystalline celluloses (NCC)s from agricultural waste, apple pomace, will be discussed. Nanocrystalline celluloses are particles with 3-20 nm lateral dimensions that may be intact, but dispersed, microfibrils or crystalline whiskers obtained by acid hydrolysis of the amorphous regions within those microfibrils. Such particles may be useful as reinforcing filler particles in composites since they have a relatively lower density than common fillers such as glass-fiber or clay. Cellulose is relatively insoluble and thermally stable to over 200°C. Purification and isolation involved chlorite bleaching and dispersion, while hydrolysis with sulfuric acid converts the nanofibers to nanocrystalline whiskers. White NCC powders were prepared and characterized by both High-Resolution and Cross-Polarization/Magic-Angle Spinning Nuclear Magnetic Resonance spectroscopy, as well as X-ray diffraction and thermogravimetric analysis. The crystallinity of NCC was 35% for particles with three nm transverse dimensions that correlates with the measured surface area, 575 m2/g. Surface silylation, maleation and phosphorylation of NCC proceeded without altering the NCC crystal structure. Modifications improved the both the dispersability in low-polarity solvents and filler-matrix interaction, as shown by work of adhesion measurements. The mechanical properties were improved by forming composites of surface modified NCC fillers with polycaprolactone (PCL), epoxidized (SBO-E) or acrylated (SBO-EA) soybean oils. PCL composites with either 0.5 or 3 wt% filler content show higher modulus than unfilled or 5% filled PCL. Filler aggregation occurred when filler content was more than 5 wt%. The storage moduli of PCL with silylated NCC (AAPSNCC) and SBO-EA with AAPSNCC were 3.5 and 11 times that of unfilled PCL, respectively. The biodegradation study of nanocomposites showed that NCC fillers accelerated degradation of PCL. Both crystallite and spherulite dimensions of PCL were smaller with filler. Evidence is presented for initiation of degradation at NCC suggesting that the microorganisms could metabolize the NCC more effectively than polymer matrix.; Keywords. Apple Pomace / Biodegradation / Nanocomposite / Nanocrystalline Cellulose / Polycaprolactone / Renewable / Soybean Oil / Surface Modification / Sustainable /...