Angelini, Stefania (2017) Exploitation of Lignocellulosic Biowastes in the Production of Bio-Composites. [Tesi di dottorato]

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This Ph.D. thesis deals with the exploitation of lignocellulosic industrial biowastes as potential reinforcing agents and flame retardants in sustainable polymer matrices, with the aim of obtaining bio-composites with improved properties and reduced production costs. The work is based on two main activities, the first one involved a lignocellulosic biowaste (LC) from a second generation bioethanol production process, while lignosulfonates (LS) from pulp and paper industry were used in the second one. In the first activity, LC was submitted to a thorough morphological, chemical and thermal characterization. Afterwards, it was used as a filler in a biodegradable microbial polymer, poly(3-hydroxybutyrate) (PHB). Blends and compression-moulded bio-composites were prepared. Their rheological, thermal, mechanical properties were studied, along with the biodegradation rate in soil. In order to identify which of the LC components was responsible for the effects recorded on PHB properties, the biomass was further processed and fractionated to isolate its lignin and polysaccharide constituents. Acid-insoluble lignin (IL) and holocellulose (HC), along with polar and apolar extractive-free solid residues (W, TE) were obtained from the parent LC and used as fillers in PHB in order to prepare bio-based blends and composites. The rheological, thermal, mechanical and crystallization properties of the resulting materials were investigated. This study showed that the use of LC and particularly of IL and HC derivatives, produced a remarkable improvement of PHB processability and crystallization. Such outcomes were relevant in the perspective of replacing oil-based composites with bio-based materials to be exploited in agriculture or packaging. In the second activity, waste lignosulfonates from pulping process were purified through dialysis in order to remove most of sugar contaminants. Plain and dialysed lignosulfonates were characterized through morphological, chemical and thermal analysis, then used as additives in the production of wood-flour based particleboards (WFP). Their potential fire retardant effect was investigated, and compared to reference WFP containing different amounts of a commercial flame retardant, namely ammonium polyphosphate. The flame retardancy, thermal stability and mechanical performance of the obtained WFP were studied, in order to investigate the effect of lignosulfonates along with their potential synergistic role with ammonium polyphosphate. This activity provided proof of evidence of the possibility to reduce the amount of commercial expensive and toxic flame retardants by partially replacing them with cheap and sustainable lignocellulosic-based biowastes for applications in construction field.

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