It has been demonstrated that radiation pretreatment can cause a significant breakdown of the stubborn cellulose structure, which will increase the accessibility of cellulose and enhance enzyme hydrolysis in bio-fuel processes. In this study, using microcrystalline cellulose (MCC) as a model substrate, the impacts of irradiation dose on the microstructure, thermal stability and irradiated-degradation components of cellulose under 60 Co g-irradiation (0-1400 kGy) was comprehensively investigated. FT-IR, EPR and NMR analyses show that irradiation destroys the glycosidic bond and inter-and intramolecular hydrogen bond of cellulose, resulting in the generation of reductive carbonyl groups and free radicals. SEM, XRD and GPC analyses confirm that irradiation can damage the crystalline microstructure and surface morphology of MCC, which reduces its degree of polymerization from 183 045 kDa to 4413 kDa. TGA and DGA curves indicate that the activated energy (E a ) and thermal stability of treated MCC decrease with the increasing irradiation dose. Ion chromatography (IC) analysis demonstrates that there exist fermentation sugars such as glucose (10.73 mg g À1 ), xylose (1.58 mg g À1 ), arabinose (0.46 mg g À1 ), fructose (4.31 mg g À1 ), and cellobiose (1.90 mg g À1 ) as well as low amounts of glucuronic acid (0.35 mg g À1 ) and galacturonic acid (1.46 mg g À1 ) in the irradiation-derived degradation components. Therefore, the findings in this study suggest that g-irradiation processing is an environment-friendly, promising and effective approach to treat lignocellulose biomass.
To elucidate the physicochemical properties and degradation mechanism of hemicellulose treated with irradiation doses (from 0 to 1200 kGy), a set of experiments on hemicellulose morphology, structure, molecular weight, free radicals, thermal stability, and irradiation mediated fractions was performed. Fourier transforms infrared spectroscopy and nuclear magnetic resonance analyses show that irradiation destroys the inter-and intra-molecular hydrogen bonds of hemicellulose leading to the generation of reductive carbonyl group. Scanning electron microscope, electron paramagnetic resonance and gel permeation chromatography measurements further confirm that the damage degree of hemicellulose structure and morphology surface in dependence on irradiation doses. Thermogravimetry/differential thermogravimetry analyses indicate that the activated energy and thermal stability of irradiated hemicellulose decrease with the increasing of absorbed dose. Irradiation mediated degradation compounds analyses by ion chromatography reveal that xylose (7.64 ± 0.92 mg g -1 ), and arabionose (3.58 ± 0.08 mg g -1 ) and cellubiose (0.27 ± 0.00 mg g -1 ) are observed at 1200 kGy. Amount of glucuronic acid (3.61 ± 0.02 mg g -1 ) and galacturonic acid (7.44 ± 0.38 mg g -1 ), which are respectively derived from glucose and galactose, are also obtained in the water soluble irradiation mediated degradation fraction. These data provide a basis support on a full utilization of hemicellulose after c-irradiation pretreatment.
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