REINFORCED PLASTICS AND BIOPLASTICS USING ADDED VALUE ADDITIVES EXTRACTED FROM LIGNOCELLULOSIC AGRO-WASTE FEEDSTOCKS

This PhD thesis dealt with the extraction of cellulose and cellulose nanocrystals (CNCs) from three different lignocellulosic agro-waste feedstocks, that is, corncob, giant cane cut-up and garlic stalk through a customized and standardized chemical procedure. In particular, for giant cane cut-up original biomass, a process optimization was performed aimed both to reduce the impact of the usage of organic solvents and to make the extractive conditions more ‘environmental-friendly’ in both cellulose and CNCs extractions. Moreover, the extracted cellulose and CNCs from giant cane cut-up were subsequently compared with bacterial cellulose (BC) and bacterial CNCs (BCNCs), produced by acetic acid bacteria, which represent the pure counterparts. Therefore, a comparison between the structural features of both the extracted plant-based cellulose and BC by means of 13C Cross-Polarization Magic Angle Spinning Nuclear Magnetic Resonance (13C CP MAS NMR), Fourier Transform Infrared Spectroscopy (FT-IR) and by optical microscopy analyses, was performed. As same, the top-down approaches of the agro-waste-derived cellulose in the production of cellulose nanocrystals, involved the use of both chemical and enzymatic methods. Nowadays, cellulose nanocrystals are one of the most promising alternatives to synthetic fillers, while representing an important field of investigation within numerous research groups due to its attractive properties such as high crystallinity, purity, non-toxicity, dimensional and origin. The most commonly employed method for the extraction of CNCs, is represented by the chemical hydrolysis (by means of concentrated acids solution, such as HCl, H2SO4 and HF), but enzymatic hydrolysis by using e.g. cellulase and endoglucanase, represents today a sustainable and more environmental-friendly approach than chemical procedures. As for giant cane-derived cellulose, a characterization of the extracted CNCs was performed, as well as a detailed comparison with the bacterial counterpart, mainly in terms of size distribution, morphology and yield of the extraction process. Moreover, because the enzymatic hydrolysis is time-consuming, in order to investigate the possibility to introduce a ‘booster’ during the enzymatic process, an expansin-like cerato-platanin (CP) protein as a pre-treatment for the enzymatic hydrolysis of BC was used. Up to now, the pre-treatment was performed only on cellulose from bacterial origin (which represents the pure counterpart) but, according to the literature, the testing of CP protein on giant cane cut-up-derived cellulose will represent an upcoming priority. CNCs were used as organic nanofiller to form a bionanocomposite coating deposited on plastics (polyethylene terephthalate – PET and biaxially oriented polypropylene – BOPP) and bioplastics (polylactic acid – PLA and starch-based compound – Mater-Bi) intended for food packaging applications, where the main biopolymer phase is represented by both polysaccharides and proteins (i.e., chitosan, pullulan and gelatin). The final coated packaging films exhibited enhanced oxygen barrier, surface and optical properties, which can expand the use of plastics and bioplastics for food packaging applications. Due to the pronounced difference in size distribution and morphological features between giant-cane derived CNCs and BCNCs, both the characterization and the overall performance evaluation of a cellulose nanocrystals/pullulan-based nanocomposite coating on PET, were discussed.