Isolation, Oxidation, and Application of Crystalline-Pristine Cellulose: Natural Products That Could End Plastic...

ConspectusGiven this special issue's efforts to highlight the research emanating from HBCUs (Historically Black Colleges and Universities) and the trials and tribulations associated with their research, the authors have presented work associated with the characterization and application of cellulosic materials as renewable products. Despite challenges, the research completed in this laboratory at Tuskegee, a HBCU, hinges upon the many investigations of cellulose as a carbon-neutral, biorenewable material that can potentially replace environmentally unfriendly and hazardous petroleum-based polymers. Although cellulose is one of the most promising candidates, overcoming the challenge of its incompatibility (i.e., lack of good dispersion, interfacial adhesion, etc.) with most hydrophobic polymers due to its hydrophilic nature is critical to usage in plastic products across industries. Chemical isolations via acid hydrolysis and surface functionalities have emerged as new approaches to modulate the surface chemistry of cellulose to improve its compatibility and physical performance within the polymer composites. Recently, we have explored the influence of (1) acid hydrolysis and (2) chemical modifications via surface oxidation to ketones and aldehydes on the resulting macrostructural arrangements and thermal performance and (3) the application of crystalline cellulose as reinforcement agents in ABS (acrylonitrile-butadiene-styrene) composites.XRD structural characterizations of crystalline cellulose isolated from wheat straw under dissimilar acid hydrolysis conditions showed induced alterations in the native cellulose polymorph (CI). Mixing of the native polymorph (CI) with CIII was observed and found to be more prominent under sulfuric acid isolation conditions which is one of the more commonly used methods of chemical isolation. Thermal evaluations using TGA confirmed that the introduction of the mixed polymorphs changed the thermal behavior of the isolated crystalline cellulose. Further, FTIR analysis and Tollens testing of chemically oxidized crystalline cellulose via the Albright-Goldman reaction revealed the transformation of surface OH groups to ketones and aldehydes, respectively. We observed similar macrostructural disruption behavior to that of acid hydrolysis processing (i.e., mixing of polymorphs) for oxidation of crystalline cellulose, which had no negative impacts on the thermal stability of the cellulosic structure. The application of acid-hydrolyzed pristine cellulose (PC) as reinforcement agents in ABS composites showed increased thermal-mechanical performance as revealed by TGA and thermal mechanical analysis (TMA). As the ratio of crystalline cellulose increased, the thermal stability of the ABS composite increased, and at extremely high ratios, increased dimensional stability (i.e., low coefficient of thermal expansion (CTE) value) was observed, expanding the application of ABS plastic products.