Surprisingly from the results depicted in Fig. 4, percentage ofregenerated cellulose in the pulps reduced in the order of pretreatmenttemperatures 120 ◦C > 100 ◦C > 80 ◦C. Higher temperature issupposed to accelerate the dissolution as well as degradationprocess and therefore decrease the amount of regenerated cellulose.The temperature profile of regenerated cellulose above wascompared to the temperature profile of remaining lignin in thepulps (Fig. 2) and it was found that the poorer the delignificationefficiency, the greater the amount of cellulose that can be regeneratedespecially when short retention time was employed. Thus asshown in Fig. 4, 120 ◦C gave the highest cellulose recovery becausethe barrier caused by condensed lignin which might cross-linkwith hemicellulose that is embedded with cellulose has inhibitedthe dissolution process [8]. With limited dissolution, cellulose isnot lost through either degradation or regeneration process, thushigher percentage of cellulose can be retained in the pulps. Forpretreatment under this condition, some of the cellulose will beswollen while some will be solubilized but cellulose chain migrationis restricted by the presence of more lignin and hemicellulosearound it [42]. Cellulose was recrystallined in the same positionduring regeneration process and thus the composition and structureof cellulose only change marginally, resulting only in slightcellulose loss and only slight decrease in its crystallinity which willbe further discussed in following section. As mentioned previously,condensed lignin unit was found to gradually decompose and dissolveinto ionic liquid as retention time is prolonged. Similarly,cellulose in the pulps was seen to reduce with higher retentiontime. This is due to the disappearance oflignin barrier that persistedat lower retention time and thus improving cellulose dissolutionefficiency with higher retention time, causing greater amount ofcellulose to be degraded and lose during regeneration process.
đang được dịch, vui lòng đợi..