Effect of delignification on thermal degradation reactivities of hemicellulose and cellulose in wood cell walls

Abstract

The thermal degradation reactivities of cellulose and hemicellulose are substantially different in Japanese cedar (Cryptomeria japonica, a softwood) and Japanese beech (Fagus crenata, a hardwood). Uronic acid and its salts act as acid and base catalysts, respectively, and their specific placement in the cell walls has been considered a factor that influences degradation reactivity. In this study, the role of lignin in degradation reactivity was investigated using holocellulose prepared from cedar and beech woods. The thermal degradation reactivities of cellulose and hemicellulose in holocellulose were evaluated according to the recovery of hydrolyzable sugars from heat-treated samples and compared with those of wood samples. Results show that the reactivities of xylan and glucomannan in both woods became similar to those of the corresponding isolated samples when lignin was removed. By contrast, the cellulose in both woods became more reactive when lignin was removed, and the degradation could be separated into two modes depending on the reactivity. These results were analyzed in terms of the effect of lignin on the matrix of cell walls and the interaction between the matrix and surface molecules of cellulose microfibrils. Differential thermogravimetric curves of the holocellulose samples were obtained and explained in terms of the degradation of hemicellulose and cellulose. The reported findings will provide insights into the research fields of wood pyrolysis and cell wall ultrastructures.

Innovative ionic liquid pretreatment followed by wet disk milling treatment provides enhanced properties of sugar palm nano-fibrillated cellulose

“…The first weight loss of SPF, which occurs largely between 25 and 150 C, has been associated with the vaporization of volatile substances (water) within the samples [ 107 ]. Following that, in the second stage, significant weight losses were seen for all samples throughout the 200–360 °C range, consistent with cellulose and hemicellulose decomposition [ 108 ]. Nevertheless, different chemical components of untreated SPF, like hemicellulose, lignin, and cellulose, break down at different temperatures, leading to a degradation process with multiple stages.…”

From Natural Woods to High Density Materials: An Ecofriendly Approach

“…The densification process is a physical and not a chemical process [8][9][10][11]. During this step, the delignified sample is subjected to an external pressure in a tangential direction to the sample.…”

“…All currently known delignification processes involve the use of strong bases (such as NaOH) capable of hydrolyzing the ethereal bridges constituting the lignin structure, among the reagents that are mostly used in the delignification phases we can find Na 2 SO 3 , H 2 O 2 , and choline chloride. Delignification processes using Na 2 SO 3 and H 2 O 2 require the use of strong bases, such as NaOH, at high concentrations [8][9][10][11]. The removal of the lignin fraction can be carried out applying various conditions such as: using selective oxidizing agents [9], or reagents that can break ether groups to form fragments of lignin with polar groups which can increase their solubility [11], and, lastly, employing high temperatures, strong bases, and compounds able to make the reaction environment as nonpolar as possible to increase the amount of removed lignin [10].…”

“…Regardless of the technique used in the delignification phase to obtain densified woods, it is necessary to subject the material to physical treatments, e.g., applying pressures, to obtain the approach of the cellulose chains and the formation of new interactions. After the physical treatments, the chains of cellulose can form hydrogen bonds with neighboring chains, increasing the mechanical properties of the material [8][9][10][11]. After densification process, the woody materials can be called "densified wood" and their mechanical performances can be the same or superior compared to different metal alloy [8].…”

“…After the physical treatments, the chains of cellulose can form hydrogen bonds with neighboring chains, increasing the mechanical properties of the material [8][9][10][11]. After densification process, the woody materials can be called "densified wood" and their mechanical performances can be the same or superior compared to different metal alloy [8].…”