Fundamental Studies On Bioconversion Of Lignocellulosic Biomass

Lignocellulosic biomass, as the most abundant renewable resource on Earth, has great potential for biofuels and biomaterials production. Pretreatment as a key step for biofuels conversion can break lignin seal and expose cellulose and hemicellulose for enzymatic action. Green liquor, acidic bisulfite and sulfite-formaldehyde pretreatments were comparatively investigated to understand their effects on the chemical composition and enzymatic digestibility of poplar. Lignin can be efficiently removed with more than 90% cellulose remained for all pretreatments, but significant hemicellulose degradation was followed for acidic bisulfite pretreatment. The maximum total sugar enzymatic digestibility for green liquor, acidic bisulfite and sulfite-formaldehyde pretreated poplar were 90.2%, 63.6% and 80.3%, respectively. Green liquor pretreatment, as an effective method for improving enzymatic digestibility, was applied to pretreat four different plant species, namely masson pine, poplar, moso bamboo, and miscanthus for investigating its effect on the chemical composition and enzymatic hydrolysis of different lignocellulosic materials. The results indicated that herbaceous materials exhibited better delignification selectivity in green liquor pretreatment than woody materials according to the order: miscanthus > moso bamboo > poplar > masson pine. The effect of green liquor pretreatment on the enzymatic sugar yield was rather different depending on the varieties of lignocellulosic materials. Higher lignin removal with less polysaccharide degradation during green liquor pretreatment improved the enzymatic sugar yield.Presence of lignin in lignocellulosic biomass is correlated with its enzymatic digestibility. Hydrophilic sulfonated lignin and hydrophobic kraft lignin were introduced into the enzymatic IV hydrolysis process to investigate their effects on enzymatic digestibility of different pretreated lignocellulose. The influence of lignin addition on the enzymatic digestibility varied with both introduced lignin type and pretreated substrates. Slight enhancement of enzymatic digestibility was observed for all substrates by adding kraft lignin. The addition of sulfonated lignin could effectively improve the enzymatic digestibility of green liquor and acidic bisulfite pretreated materials, but has little effect on sulfite-formaldehyde pretreated samples. The enzymatic digestibility of green liquor pretreated masson pine increased from 42% without lignin addition to 75% with 0.3 g/g-substrate sulfonated lignin addition.Cellulose nanofibrils(CNFs) has attached considerable interest because of its low thermal expansion, high aspect ratio, good mechanical and optical properties which may find many applications in nanocomposites, paper making, coating additives, security papers, food packaging, and gas barriers. Energy consumption is a major concern for mechanical CNFs production. Enzymatic pretreatment is able to facilitate nanofibrillation by reducing energy input. Endoglucanase pretreatment and post-treatment combined with mechanical fibrillation were investigated for CNFs production. The endoglucanase pretreatment can reduce mechanical energy input by at least 30% when compared with using fibers without enzymatic treatment to produce similar quality CNFs in terms of fibril length, diameter, and optical transparency. TEM imaging indicated that hyperthermostable endoglucanase Ph-GH5 pretreatment produced longer and entangled CNFs than commercial endoglucanase FR with similar diameter. Physical and mechanical properties of CNF films from endoglucanase pretreatment and microfluidization were characterized. Highest specific modulus of CNF films was obtained from FR pretreatment, reaching 56 MNm/kg, approximately 271% of the CNF films from untreated bleached Eucalyptus pulp(BEP) at 40 passes through the microfluidizer. CNF film from Ph-GH5(1 mg/g) at 40 passes provided the highest specific maximum tensile strength at 120 k Nm/kg. Endoglucanase post-treatment could improve the nanosize uniformity of cellulose nanofibrils from Super Mass Colloider fibrillation efficiently. All GH5 endoglucanase post-treated cellulose nanofibrils had a diameter distribution between 3 nm and 19 nm with 70–89% cellulose nanofibrils between 5 nm and 9 nm. The GH5 endoglucanase(Fn-GH5) with no activity on crystalline cellulose was the most aggressive of the GH5 s in reducing the DP of cellulose nanofibrils. This suggests that hydrolysis of the amorphous regions of fibrils is the dominant enzymatic factor contributing to fibril length and morphology.