Branching of hemicelluloses through an azetidinium salt ring-opening reaction

Gram-Scale Domino Synthesis in Batch and Flow Mode of Azetidinium Salts

Azetidinium salts are important motifs in organic synthesis but are difficult to obtain due to extremely long synthetic protocols. Herein, a rapid continuous-flow process for the on-demand synthesis of azetidinium salts is described. In particular, the nucleophilic addition of secondary amines and the subsequent intramolecular N-cyclization have been investigated in batch and continuous-flow modes, exploring the effects of solvent type, temperature, reaction time, and amine substituent on the synthesis of azetidinium salts. This has enabled us to quickly identify optimal reaction conditions and obtain microkinetic parameters, verifying that the use of a flow reactor leads to a reduction of the activation energy for the epichlorohydrin aminolysis due to the better control of mass and heat transfer during reaction. This confirms the key role of continuous-flow technologies to affect the kinetics of a reaction and make synthetic protocols ultrarapid and more efficient.

TEMPO/NaClO2/NaOCl oxidation of arabinoxylans

TEMPO-oxidation of neutral polysaccharides has been used to obtain polyuronides displaying improved functional properties. Although arabinoxylans (AX) from different sources may yield polyuronides with diverse properties due to their variable arabinose (Araf) substitution patterns, information of the TEMPO-oxidation of AX on its structure remains scarce. We oxidized AX using various TEMPO:NaClO₂:NaOCl ratios. A TEMPO:NaClO₂:NaOCl ratio of 1.0:2.6:0.4 per mol of Ara gave an oxidized-AX with high molecular weight, minimal effect on xylose appearance, and comprising charged side chains. Although NMR analyses unveiled arabinuronic acid (AraAf) as the only oxidation product in the oxidized-AX, accurate AraA quantification is still challenging. Linkage analysis showed that > 75 % of the β-(1→4)-xylan backbone remained single-substituted at position O-3 of Xyl similarly to native AX. TEMPO-oxidation of AX can be considered a promising approach to obtain arabinuronoxylans with a substitution pattern resembling its parental AX.

Enhancement of Mechanical and Barrier Property of Hemicellulose Film via Crosslinking with Sodium Trimetaphosphate

Hemicellulose is a kind of biopolymer with abundant resources and excellent biodegradability. Owing to its large number of polar hydroxyls, hemicellulose has a good barrier performance to nonpolar oxygen, making this biopolymer promising as food packaging material. Hydrophilic hydroxyls also make the polymer prone to water absorption, resulting in less satisfied strength especially under humid conditions. Thus, preparation of hemicellulose film with enhanced oxygen and water vapor barrier ability, as well as mechanical strength is still sought after. Herein, sodium trimetaphosphate (STMP) was used as esterification agent to form a crosslinked structure with hemicellulose through esterification reaction to render improved barrier performance by reducing the distance between molecular chains. The thus modified hemicellulose film achieved an oxygen permeability and water vapor permeability of 3.72 cm3 × μm × m-2 × d-1 × kPa-1 and 2.85 × 10-10 × g × m-1 × s-1 × Pa-1, respectively, at the lowest esterification agent addition of 10%. The crosslinked structure also brought good mechanical and thermal properties, with the tensile strength reaching 30 MPa, which is 118% higher than that of the hemicellulose film. Preliminary test of its application in apple preservation showed that the barrier film obtained can effectively slow down the oxidation and dehydration of apples, showing the prospect of application in the field of food packaging.

Barrier Film of Etherified Hemicellulose from Single-Step Synthesis

Hemicellulose with good biodegradability and low oxygen permeability shows great potential in food packaging. However, its strong hydrophilicity leads to its poor moisture resistance, which hinders its wider application. In this paper, a near-hydrophobic hemicellulose was obtained by using single-step synthesis from poplar powder via etherification modification with epoxy chloropropane. This proposed approach has the advantage of avoiding the destruction of hemicellulose structure by secondary alkali-hydrolysis, which was what usually occurred in traditional etherification procedures. The feasibility of using epoxy chloropropane as an alkylation reagent to etherify hemicellulose was confirmed, and the reaction mechanism was elucidated. Contact angle test, thermogravimetric analysis, oxygen transmittance test, and infrared spectrum analysis showed that the barrier property and thermal stability of etherified hemicellulose films have been significantly improved. At an epoxy chloropropane/wood powder ratio (volume/weight) of 2/3 (mL/g), the epoxy hemicellulose films contained the most epoxy groups and displayed the best performance, i.e., tensile strength of 14.6 MPa, surface contact angle of 71.7° and oxygen transmission coefficient of 1.9 (cm3·µm)/(m2·d·kPa), showing great promise as barrier film in food-packaging.

Hemicellulose-Based Film: Potential Green Films for Food Packaging

Globally increasing environmental awareness and the possibility of increasing price and dwindling supply of traditional petroleum-based plastics have led to a breadth of research currently addressing environmentally friendly bioplastics as an alternative solution. In this context, hemicellulose, as the second richest polysaccharide, has attracted extensive attention due to its combination of such advantages as abundance, biodegradability, and renewability. Herein, in this review, the latest research progress in development of hemicellulose film with regard to application in the field of food packaging is presented with particular emphasis on various physical and chemical modification approaches aimed at performance improvement, primarily for enhancement of mechanical, barrier properties, and hydrophobicity that are essential to food packing materials. The development highlights of hemicellulose film substrate are outlined and research prospects in the field are described.

Reutilization of discarded biomass for preparing functional polymer materials

Biomass is abundant and recyclable on the earth, which has been assigned numerous roles to human beings. However, over the past decades, accompanying with the rapid expansion of man-made materials, such as alloy, plastic, synthetic rubber and fiber, a great number of natural materials had been neglected and abandoned, such as straw, which cause a waste of resource and environmental pollution. In this review, based on introducing sources of discarded biomass, the main composition and polymer chains in discarded biomass materials, the traditional treatment and novel approach for reutilization of discarded biomass were summarized. The discarded biomass mainly come from plant wastes generated in the process of agriculture and forestry production and manufacturing processes, animal wastes generated in the process of animal husbandry and fishery production as well as the residual wastes produced in the process of food processing and rural living garbage. Compared with the traditional treatment including burning, landfill, feeding and fertilizer, the novel approach for reutilization of discarded biomass principally allotted to energy, ecology and polymer materials. The prepared functional materials covered in composite materials, biopolymer based adsorbent and flocculant, carrier materials, energy materials, smart polymer materials for medical and other intelligent polymer materials, which can effectively serve the environmental management and human life, such as wastewater treatment, catalyst, new energy, tissue engineering, drug controlled release, and coating. To sum up, the renewable and biodegradable discarded biomass resources play a vital role in the sustainable development of human society, as well as will be put more emphases in the future.