Influence of chitosan protonation degree in nanofibrillated cellulose/chitosan composite films and their morphological, mechanical, and surface properties

Composite films of nanofibrillated cellulose (NFC) and chitosan (CS) were prepared by spray deposition method, and the influence of polymers ratio and protonation degree (α) of chitosan was evaluated. Films were characterized using morphological, mechanical, and surface techniques. Higher NFC content increased Young's modulus of film composites and reduced air permeability, while higher CS content increased water contact angle. Variations in the degree of protonation of chitosan from non-protonated (α = 0) to fully protonated (α = 1) in the NFC/CS composite film with a fixed composition allowed to modulate surface, mechanical, and structural properties, such as water contact angle (31.3-109.2°), Young's modulus (1.7-5.3 GPa), elongation at break (3.1-1.2 %), oxygen transmission rate (9.0-5.5 cm3/m2day) and air permeability (2074-426 s). Highly protonated chitosan composite films showed similar contact angles to pure chitosan films, while low protonated chitosan composite films presented contact angles similar to pure NFC films, suggesting a possible coating effect of NFC by CS through electrostatic interactions, evidenced by microscopy and spectroscopy analysis. By mixing both polymers and adjusting composition and protonation degree it was possible to enhance their properties, making pH adjustment a useful tool for NFC/CS composite films formation.

Xylan extraction from hardwoods by alkaline pretreatment for xylooligosaccharide production: A detailed fractionation analysis

In the last decades, the production of value-added products from lignocellulosic biomass (LCB) has gained relevance. Xylans, which are the main hemicellulose compounds in LCB, may be extracted by alkaline pretreatment and employed for xylooligosaccharide (XOS) production. However, xylan extraction currently works as a black box due to the lack of characterization of the involved streams. Therefore, the appropriate operational conditions often remain unclear, especially in hardwoods. In this study, alkaline/thermal pretreatments at different operational conditions were evaluated for xylan extractions from Chilean Nothofagus species sawdust, determining the chemical compositions of the fractions at each step of the process. Results indicated that increasing alkali concentration (NaOH) leads to a higher xylan extraction, but also to high salt production during the acid neutralization step, decreasing xylan's purity and therefore XOS production. In this context, decreasing NaOH concentration and neutralizing it by membrane filtration, allow extracting xylans (62.5 %) of higher-purity (77 %).

Upcycling agro-industrial blueberry waste into platform chemicals and structured materials for application in marine environments

Blueberry pruning waste (BPw), sourced as residues from agroforestry operations in Chile, was used to produce added-value products, including platform chemicals and materials. BPw fractionation was implemented using biobased solvents (γ-valerolactone, GVL) and pyrolysis (500 °C), yielding solid fractions that are rich in phenols and antioxidants. The liquid fraction was found to be enriched in sugars, acids, and amides. Alongside, filaments and 3D-printed meshes were produced via wet spinning and Direct-Ink-Writing (DIW), respectively. For the latter purpose, BPw was dissolved in an ionic liquid, 1-ethyl-3-methylimidazolium acetate ([emim][OAc]), and regenerated into lignocellulose filaments with highly aligned nanofibrils (wide-angle X-ray scattering) that simultaneously showed extensibility (wet strain as high as 39%). BPw-derived lignocellulose filaments showed a tenacity (up to 2.3 cN dtex^-1) that is comparable to that of rayon fibers and showed low light reflectance (R _ES factor <3%). Meanwhile, DIW of the respective gels led to meshes with up to 60% wet stretchability. The LCF and meshes were demonstrated to have reliable performance in marine environments. As a demonstration, we show the prospects of replacing plastic cords and other materials used to restore coral reefs on the coast of Mexico.

Effects on Lignin Redistribution in Eucalyptus globulus Fibres Pre-Treated by Steam Explosion: A Microscale Study to Cellulose Accessibility

The objective of this study was to investigate structural changes and lignin redistribution in Eucalyptus globulus pre-treated by steam explosion under different degrees of severity (S₀), in order to evaluate their effect on cellulose accessibility by enzymatic hydrolysis. Approximately 87.7% to 98.5% of original glucans were retained in the pre-treated material. Glucose yields after the enzymatic hydrolysis of pre-treated material improved from 19.4% to 85.1% when S₀ was increased from 8.53 to 10.42. One of the main reasons for the increase in glucose yield was the redistribution of lignin as micro-particles were deposited on the surface and interior of the fibre cell wall. This information was confirmed by laser scanning confocal fluorescence and FT-IR imaging; these microscopic techniques show changes in the physical and chemical characteristics of pre-treated fibres. In addition, the results allowed the construction of an explanatory model for microscale understanding of the enzymatic accessibility mechanism in the pre-treated lignocellulose.

Condensed lignin structures and re-localization achieved at high severities in autohydrolysis of Eucalyptus globulus wood and their relationship with cellulose accessibility

Eucalyptus globulus wood was subjected to autohydrolysis pretreatment at different severity factors. The pretreated materials were enzymatically saccharified at a substrate load of 10% (w/v) using a cellulase enzyme complex. Around 82-95% of original glucans were retained in the pretreated material, and the enzymatic hydrolysis yields ranged from 58% to 90%. The chemical and structural changes in the pretreated materials were investigated by microscopic (SEM, LSCM) and spectroscopic (2D-HSQC NMR and FT-IR) techniques. 2D-NMR results showed a reduction in the amounts of β-O-4 aryl-ether linkages and suggested the presence of newly condensed structures of lignin in the biomass pretreated at the more severe conditions. Furthermore, the microscopic analysis showed that lignin migrates out of the cell wall and re-deposits in certain regions of the fibers at the more severe conditions to form droplet-like structures and expose the cellulose surface. These changes improved the glucose yield up to 69%, on dry wood basis.

Cationic hemicellulose-based hydrogels for arsenic and chromium removal from aqueous solutions

In this work the synthesis of hemicellulose-based hydrogels and their application for the removal of arsenic and chromium ions is described. In a first step O-acetyl galactoglucomannan (GGM) was subjected to a transesterification applying glycidyl methacrylate (GMA) for the synthesis of novel GGM macromonomers. Two distinguished and purified GGM fractions with molar mass of 7.1 and 28 kDa were used as starting materials. The resulting GGM macromonomers (GGM-MA) contained well-defined amounts of methacrylate groups as determined by (1)H NMR spectroscopy. Selected GGM-MA derivatives were consecutively applied as a crosslinker in the synthesis of tailored hydrogels using [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MeDMA) as monomer. The swelling rate of the hydrogels was determined and the coherence between the swelling rate and the hydrogel composition was examined. The morphology of the GGM-based hydrogels was analysed by SEM and the hydrogels revealed a high surface area and were assessed in respect to their ability to remove arsenate and chromate ions from aqueous solutions. The presented bio-based hydrogels are of high interest especially for the mining industries as a sustainable material for the treatment of their highly contaminated wastewaters.