Research On Plant Fiber Plasticization Assisted By Steam Explosion

The main components of natural plant fiber are cellulose, hemicellulose and lignin. Thethree-dimensional network structure of lignin and highly crystallinity of cellulose cause thatthe melting temperature of the plant fiber is much higher than the thermal decompositiontemperature. So the plant fiber can not be processed by melt molding like plastic. Plant fibercontains a lot of free hydroxyl groups, which can be etherified and esterified with the addedreagents and make the intermolecular and intramolecular hydrogen bonding weakened, thusfunctional materials with thermal plasticization processing performance can be obtained.In this dissertation, the changes of the lignin and typha fiber which were modified bydifferent molecular weights polyethylene glycol（PEG） during the steam explosion werestudied, respectively. The infrared spectroscopy, thermogravimetric analysis, differentialscanning calorimetry and scanning electron microscope were employed to analyze the effectof the steam explosion and modifers on the structure units, thermal properties, morphology ofthe lignin and typha fiber. The different degree of etherification among different PEGmodified lignins and typha fibers were discussed, respectively. And the variation of thethermal performance of lignin and typha fiber after plasticizing modification were alsodiscussed. Lastly, the mechanical properties of composites prepared by the PEG modifiedtypha fiber were researched.The reactive group in the surface of lignin increased after steam explosion, meanwhile,the microstructure of lignin also changed a lot, with a large number of holes in the ligninsurface. The glass transition temperature of the lignin material was164.1℃, and the glasstransition phenomenon of lignin occured at about90℃after steam explosion. However, theglass transition phenomenon of the plasticized lignin appeared at about50℃. The PEG withlong-chain structure grafted onto the molecular chain of lignin can form the stericallyhindered, which made the interaction between the molecular chains of lignin weakened. Andthen the glass transition phenomenon of plasticized lignin occurred at low temperature. Thelignin plasticized by PEG2000at200℃with the aid of steam explosion can occur the glasstransition at41.5℃. The linkage among components in the typha fiber were weakened after steam explosion.In addition to the appearance of glass transition phenomenon in the range of120-150℃, thesteam exploded twice and four times fibers appeared another glass transition phenomenon inthe range of70-80℃, the glass transition temperatures were75.3and71.1℃, respectively.The typha fibers which were modified by20wt%PEG2000occured the glass transitionphenomenon at48℃. Compared with the hot pressed fiberboards of steam explosion fourtimes typha fibers, the flexural strength and modulus of the hot pressed fiberboards of thetypha fibers which were modified with20wt%PEG2000increased by39.4%and30.1%,respectively.