Anika Salanti

Structural characterization and antioxidant activity evaluation of lignins from rice husk.

In recent years, lignin and extractives from herbaceous plants and crops are receiving increasing attention for their renewability and large annual biomass stock. It is worth noting that only a few studies deal with the chemical characterization of rice husk, a side product of one of the most important crops with regard to human nutrition. Thus, in this study lignin from rice husk was isolated and characterized. Two different extraction procedures were optimized and tested: acidolysis and alkaline enzymatic (AE). The different lignins isolated were fully characterized by means of gravimetric, chromatographic (GPC), and spectroscopic (31P NMR, 2D-HSQC-NMR) analyses with the aim to compare yields, sample purity, and chemical properties, recognized as key parameters for future development. Notwithstanding the extraction procedure, the results highlighted that rice husk lignin is mainly formed by guaiacyl and p-hydroxyphenyl units. The acidolytic approach showed an appreciable lignin recovery and high purity, whereas the AE lignin sample was found to be rich in residual polysaccharides and oxidized functionalities. Moreover, different rice husk extracts, along with acidolysis lignin and AE lignin specimens, were assayed for their antioxidant activity by means of a DPPH radical scavenging test.

Chromatographic Detection of Lignin–Carbohydrate Complexes in Annual Plants by Derivatization in Ionic Liquid

The opportunity for detecting the presence and the amount of lignin-carbohydrate complexes (LCCs) in renewable feedstocks is a major issue for the complete utilization of biomass. Indeed, LCCs are known to shield cellulose from enzymatic hydrolysis, reducing the efficiency of the digestion processes needed for the production of biobased products. This study is focused on the chromatographic characterization of lignocellulose from agricultural residues (rice husk, wheat straw) and herbaceous energy crops ( Arundo donax , Miscanthus sinesis ) and their fractionation products (hemicellulose, cellulose, and lignin). Exploiting alternative chemical derivatizations on the aforementioned samples, it was possible to discern the connectivity among the various lignocellulosic components. The complete acetylation and benzoylation of the milled native substrates in ionic liquid media, and the systematic comparison between their GPC-UV chromatograms collected at different wavelengths has revealed itself as a straightforward technique in the detection of LCCs. This novel approach proved an extensive connectivity between the lignin and the hemicellulosic for all the analyzed specimens, whereas the cellulosic fraction was conceived as a substantially unbound moiety, accounting for the sample composition at higher molecular weights. Moreover, the collected lignin fractions were extensively characterized by means of (31)P NMR and 2D-HSQC techniques.

Oxidation of isoeugenol by salen complexes with bulky substituents.

The catalytic properties of bulky water-soluble salen complexes in the oxidation of isoeugenol (2-methoxy-4-(1-propenyl) phenol) have been investigated in aqueous ethanol solutions in order to obtain a mixture of polymeric compounds through dehydrogenative polymerization. The average molecular weight of dehydrogenated polymers (DHPs) was monitored by GPC and correlated to reaction conditions such as time, concentration of substrate, concentration of catalyst, type of oxidation agent, etc. The DHP synthesized by adopting the best reaction conditions was characterized by different analytical techniques (GPC, 13C-NMR, 31P-NMR and LC-MS) to elucidate its structure. The lignin-like polymer resulting from isoeugenol radical coupling possesses valuable biological activity and finds applications in a variety of fields, such as packaging industry and cultural heritage conservation.

Chemical modifications of lignin for the preparation of macromers containing cyclic carbonates

An epoxidized lignin derivative was prepared directly inserting epichlorohydrin on the phenolic functionalities. The epoxidized lignin was then converted to cyclic carbonates through the coupling reaction of CO2 with the oxirane rings. Imidazolium based ionic liquids, acting as both solvents and catalysts, were successfully employed in the carbonation reaction. Moreover, the ionic liquid was reused up to three times without significant loss in activity. Finally, an exhaustive spectroscopic characterization was carried out on the epoxidized and carbonated lignins by quantitative 31P and 13C NMR analyses.

Influence of acidic and alkaline aqueous regeneration on enzymatic digestibility of the cellulose fraction recovered from [amim]Cl-treated rice husk.

The recalcitrance of lignocelluloses toward enzymatic hydrolysis necessitates pretreatments. Ionic liquid pretreatment with 1-allyl-3-methylimidazolium chloride ([amin]Cl) was applied to risk husk and cellulose-containing fractions were recovered from the ionic liquid solutions by acidic, alkaline, and alkaline-acidic regeneration respectively. Enzymatic hydrolysis of the recovered materials was carried out and results demonstrated that: (i) acidic regeneration was not substantial to ensure enhanced enzymatic digestibility; (ii) alkaline regeneration increased the enzymatic hydrolysis; (iii) alkaline-acidic regeneration led to an almost complete hydrolysis of the carbohydrate fraction. The obtained results were rationalized by means of chromatographic analyses of soluble fractions collected after the different regeneration processes: the removal of hemicellulose, which increased going from the acidic to the alkaline-acidic regeneration, seemed to play a crucial role in enhancing the rice husk saccharification.

Synthesis and characterization of lignin–silicone hybrid polymers as possible consolidants for decayed wood

The consolidation of samples of waterlogged wood was attempted using allylated lignin as cross-linker and compatibilizer in the silicone oil conservative treatment. During the curing of the composite, allylated lignin was reacted with a poly(dimethylsiloxane) hydride terminated on both the ends of the silicone chain through a hydrosilylation reaction in the presence of the Karstedt’s catalyst. Three lignin–silicone hybrids were prepared using different allyl/hydride group ratios. Preliminary wood consolidation was thus accomplished treating pieces of wood with lignin–silicone hybrids prepared in situ with silicone and allylated lignin in different concentrations in the presence of the Karstedt’s catalyst. IR and SEM-EDX analysis proved that the growth of the silicone–lignin polymer was easier within the external layers. In addition, water uptake tests and contact angle measurements were performed on consolidated wood samples to evaluate the extent of hydrophobicity.

Sphingoid esters from the molecular distillation of squid oil: A preliminary bioactivity determination.

A mixture of sphingoid esters was isolated (1.4% w/w) from the molecular distillation of crude squid visceral oil. A preliminary investigation on the bioactivity profile and toxic potential of this residue was carried out by in vitro experiments. No cytotoxicity and a moderate lipase inhibition activity were highlighted.

Utilization of cyclocarbonated lignin as a bio-based cross-linker for the preparation of poly(hydroxy urethane)s

In this work, cyclocarbonated modified lignin, the most abundant reservoir of aromatic moieties in nature, was used as a green bio-based cross-linker on polyhydroxy urethane formulations. As a preliminary study, a complete 13C NMR characterization of the aminolysis products of cyclocarbonated lignin with 1,12-diaminododecane was provided. The best reaction conditions found for the aminolysis reaction were applied for the preparation of thermoset resins. Cyclocarbonated lignin was then reacted with 1,12-diaminododecane, acting as a chain extender, in the presence of poly(ethylene glycol) bis cyclic carbonate, a soft segment used to tune the resin properties. Different (total cyclocarbonates)/(total amines) equivalent ratios and diverse poly(ethylene glycol)/lignin stoichiometry were tested. The evolution in time of the molecular weight distribution of a selected composition was followed by gel permeation chromatography until the solubility in THF was appreciable. Moreover, some significant resin samples were subjected to DSC analysis to evaluate favourable changes in the glass transition temperature and compared to blank experiments that did not include lignin in the composition.