Modification of hemicelluloses with polycarboxylic acids

Abstract

Polycarboxylic acids (PCAs) aroused interest as crosslinking agents for natural polymers, such as cellulose, starch, chitosan, and hemicelluloses (HC), for improving their water resistance and imparting them new properties. Here, PCAs were studied for the crosslinking of HC films. HCs were isolated from gray alder (Alnus incana L.) wood as a water-soluble fraction by sawdust extraction with 7% potassium hydroxide. Citric acid (CA), maleic acid (MA), and butane tetracarboxylic acid (BTCA) served as crosslinking agents in the presence of sodium hypophosphite as a catalyst. The crosslinking reaction was followed by the analysis of free and esterified COOH groups in HC films. At temperatures below 100–110°C, the HC esterification process with BTCA proceeded very slowly. At 140°C, most of the acids’ COOH groups reacted with HC during 1–1.5 h. BTCA had a higher esterification activity than CA and MA. The obtained films retained their form on immersing in water and subsequent drying in the open air. The water retention value of films followed the reaction kinetics, that is, decreased with increasing reaction time. Water-resistant films were obtained with no <10–11% of BTCA and 20% of CA based on the weight of HC. The water vapor sorption capacity of the films after modification with 10% BTCA decreased approximately twice in the whole range of the relative humidity of air compared with the case of unmodified HC films.

Esterification of wood with citric acid: The catalytic effects of sodium hypophosphite (SHP)

“…Polycarboxylic acids -such as 1,2,3,4-butanetetracarboxylic acid (BTCA) and citric acid (CA) -have the potential to react with cell wall polymers (Bischof Vukusic et al 2006;Zoldners and Kiseleva 2013). BTCA is more efficient in cross-linking cellulosic materials than CA because of its higher COOH group content (Welch and Kottes-Andrews 1989;Morris et al 1995).…”

A Review of Water‐Resistant Hemicellulose‐Based Materials: Processing and Applications

“…Hemicellulose‐based films can have low oxygen transmittance and are biodegradable; this makes them useful barrier films for food products. Although hemicellulose‐based films are sensitive to water, the sensitivity can be overcome by esterification of the hemicellulose, such as acetylation . Hemicellulose AcGGM has been used in oxygen barrier films .…”

“…Modified hemicellulose, mainly hemicellulose acetate, films have been used for food packaging. These films have shown improved oxygen barrier capabilities compared with those of unmodified hemicellulose films …”

“…Although hemicellulose-based films are sensitivet ow ater,t he sensitivity can be overcome by esterification of the hemicellulose, such as acetylation. [74] Hemicellulose AcGGM has been used in oxygen barrierf ilms. [72] It has been shown that AcGGM is soluble in water ando rganic solvents.…”

“…These films have shown improved oxygen barrier capabilities compared with those of unmodified hemicellulose films. [74,120,121] To facilitatet he utilization of hemicellulose for coating applications,v arious sources of hemicelluloses need to be applied as coating materials and also different combinations with other coating agents shouldb et ested. From the reviewed data, it can be observed that hemicelluloses have been used in many applications, and further investigationsw ould benefit this developing area.…”