Negin Ghahrani; Noradin Nazarnezhad; Omid Ramezani; Ghasem Asadpour
Abstract
Regeneration of cellulose by direct solvent dissolution essentially involves the pretreatment of cellulose with a solvent for swelling the cellulose chains and weakening the cellulose molecules bonds. Aqueous solutions based on sodium hydroxide (NaOH) are low cost, non-volatile, non-toxic, environmentally ...
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Regeneration of cellulose by direct solvent dissolution essentially involves the pretreatment of cellulose with a solvent for swelling the cellulose chains and weakening the cellulose molecules bonds. Aqueous solutions based on sodium hydroxide (NaOH) are low cost, non-volatile, non-toxic, environmentally friendly cellulosic solvent with fast dissolution power at low temperatures. The mechanism of cellulose dissolution in this solvent is not yet fully understood because there are parameters such as temperature, crystallization and degree of cellulose polymerization that affect the solubility of cellulose in the NaOH / urea system. Therefore, this study investigated the effect of kappa factor changes in chlorine dioxide bleaching on the dissolution of OCC recycled pulp on chemical compounds (lignin and hemicellulose) and the degree of polymerization. The results showed that with further reduction of lignin, the dissolution of pulp decreases and this reduction in dissolution is more severe in lignin levels below 3% (reduction from 44% to about 37% dissolution). It seems that during the bleaching process and part of lignin and hemicellulose removal, a part of cellulose with low degree of polymerization is also removed and the average polymerization of the remaining cellulose increases which is more resistant to the phenomenon of pulp dissolution. With increasing kappa factor (to 0.2 and 0.3), there was no significant change in dissolution and hemicellulose. In general, it seems that lignin and the degree of polymerization are not only the effective factors in OCC pulp dissolving and hemicellulose content also can be effective.
Negin Ghahrani; Noraldin Nazrneghad; Omid Ramezani; Ghasem Asadpour
Abstract
One of the common applications of cellulose is dissolving pulp producing that requires high purity. Different cellulose sources are used to produce dissolving pulp. Due to Deforestation and lack of agricultural land and problems with cultivation, the use of wood and non-wood sources of cellulose is declining. ...
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One of the common applications of cellulose is dissolving pulp producing that requires high purity. Different cellulose sources are used to produce dissolving pulp. Due to Deforestation and lack of agricultural land and problems with cultivation, the use of wood and non-wood sources of cellulose is declining. Another source of cellulose is recycled pulp. Chlorine dioxide acts as a completely selective bleaching. Increasing kappa factors is very effective in removing lignin levels. In this research, dissolving pulp from recycled fibers is obtained during soda cooking and bleaching with chlorine dioxide. Then, the effect of changes in kappa factor of the second stage of chlorination on chemical composition (holocellulose and lignin), structural properties (degree of polymerization, alpha-cellulose and degree of brightness) and accessibility (water retention value) are investigated. The results showed that the degradation of holocellulose levels was not severe and did not cause cellulose damage and decreased alpha-cellulose levels as well as the degree of polymerization. The removal of lignin as a hydrophobic component and the presence of hemicellulose as a hydrophilic component increase accessibility (water retention) and decrease brightness degree.
