Nanocellulose based biodegradable polymers

There are numerous examples where animals or plants synthesize extracellular high-performance skeletal biocomposites consisting of a matrix reinforced by fibrous biopolymers. Cellulose, the world's most abundant natural, renewable, biodegradable polymer, is a classical example of these reinforcing elements, which occur as whisker-like microfibrils that are biosynthesized and deposited in a continuous fashion. In many cases, this mode of biogenesis leads to crystalline microfibrils that are almost defect-free, with the consequence of axial physical properties approaching those of perfect crystals. This quite "primitive" polymer can be used to create high performance nanocomposites presenting outstanding properties. This reinforcing capability results from the intrinsic chemical nature of cellulose and from its hierarchical structure. Aqueous suspensions of cellulose crystallites can be prepared by acid hydrolysis of cellulose. The object of this treatment is to dissolve away regions of low lateral order so that the water-insoluble, highly crystalline residue may be converted into a stable suspension by subsequent vigorous mechanical shearing action. During the past decade, many works have been devoted to mimic biocomposites by blending cellulose whiskers from different sources with polymer matrixes.

Cellulose nanofibers were extracted from the agricultural residues, wheat straw and soy hulls, by a chemi-mechanical technique to examine their potential for use as reinforcement fibers in biocomposite applications. The structure of the cellulose nanofibers was investigated by transmission electron microscopy. The wheat straw nanofibers were determined to have diameters in the range of 10-80 nm and lengths of a few thousand nanometers. By comparison, the soy hull nanofibers had diameter 20-120 nm and shorter lengths than the wheat straw nanofibers. Chemical characterization of the wheat straw nanofibers confirmed that the cellulose content was increased from 43% to 84% by an applied alkali and acid treatment. FT-IR spectroscopic analysis of both fibers demonstrated that this chemical treatment also led to partial removal of hemicelluloses and lignin from the structure of the fibers. PXRD results revealed that this resulted in improved crystallinity of the fibers. After mechanical treatments of cryocrushing, disintegration and defibrillation, the thermal properties of the nanofibers were studied by the TGA technique and found to increase dramatically. The degradation temperature of both nanofiber types reached beyond 290 degrees C. This value is reasonably promising for the use of these nanofibers in reinforced-polymer manufacturing.