Radiation degradation of microcrystalline cellulose in solid status

On the Mechanism of the Ionizing Radiation-Induced Degradation and Recycling of Cellulose

The use of ionizing radiation offers a boundless range of applications for polymer scientists, from inducing crosslinking and/or degradation to grafting a wide variety of monomers onto polymeric chains. This review in particular aims to introduce the field of ionizing radiation as it relates to the degradation and recycling of cellulose and its derivatives. The review discusses the main mechanisms of the radiolytic sessions of the cellulose molecules in the presence and absence of water. During the radiolysis of cellulose, in the absence of water, the primary and secondary electrons from the electron beam, and the photoelectric, Compton effect electrons from gamma radiolysis attack the glycosidic bonds (C-O-C) on the backbone of the cellulose chains. This radiation-induced session results in the formation of alkoxyl radicals and C-centered radicals. In the presence of water, the radiolytically produced hydroxyl radicals (●OH) will abstract hydrogen atoms, leading to the formation of C-centered radicals, which undergo various reactions leading to the backbone session of the cellulose. Based on the structures of the radiolytically produced free radicals in presence and absence of water, covalent grafting of vinyl monomers on the cellulose backbone is inconceivable.

Radiation-Induced Structural Changes of Miscanthus Biomass

Efficient pretreatment is a prerequisite for lignocellulosic biomass biorefinery due to the structure of lignocellulose. This study is a first-time investigation into the structural changes of Miscanthus biomass treated with 60Co γ-ray irradiation in different doses up to 1200 kGy. The structural properties of the treated sample have been systematically characterized by FTIR, thermogravimetric analysis (TGA), XRD, gel permeation chromatography (GPC), a laser particle size analyzer, SEM, an atomic force microscope (AFM), and NMR. The results show that irradiation treatment can partially destroy the intra- or inter-molecular hydrogen bonds of biomass. Irradiation treatment can also reduce particle size, narrow the distribution range, as well as increase the specific surface area of biomasses. Noticeably, the TGA stability of the treated biomass decreases with increasing absorbed doses. To respond to these structural changes, the treated biomass can be easily hydrolyzed by cellulases with a high yield of reducing sugars (557.58 mg/g biomass), much higher than that of the untreated sample. We conclude that irradiation treatment can damage biomass structure, a promising strategy for biomass biorefinery in the future.

Study on enzymatic hydrolysis efficiency and physicochemical properties of cellulose and lignocellulose after pretreatment with electron beam irradiation

In lignocellulosic biomass biotransformation technology, pretreatment is the most important step to increase the conversion efficiency and reduce cost. The electron beam irradiation (EBI) pretreatment method was discussed in this study. First, the effects of a 0-1200 kGy irradiation dose on saccharification efficiency of lignocellulose biomass (birch) and analytically pure cellulose were studied. Then, the pretreated samples were tested for composition, X-ray diffraction, degree of polymerization, and Fourier transform infrared spectroscopy. Finally, the mechanism of the EBI pretreatment was analyzed from the aspects of lignin content, cellulose crystallinity, cellulose polymerization degree, and cellulose molecular structure. The results show that the EBI pretreatment can significantly improve the efficiency of enzymatic hydrolysis by degrading the lignin in lignocellulose, reducing the crystallinity and polymerization degree of cellulose, and destroying the cellulose molecules. It also obtained that the pretreatment of cellulose and lignocellulose with irradiation has a different trend in enzymatic hydrolysis efficiency with irradiation dose. This indicates that there is a difference in irradiation effects between pure cellulose and lignocellulose. And a possible degradation pathway of cellulose was proposed. This study has important guide for the application and development of EBI pretreatment methods.

Physico-chemical oxidative cleavage strategy facilitates the degradation of recalcitrant crystalline cellulose by cellulases hydrolysis

BACKGROUND

Efficient enzymatic conversion of recalcitrant crystalline cellulose is critical for enabling cost-effective industrial conversion of cellulosic biomass to biofuels and chemicals. Fully understanding enzyme digestion mechanism is paving a new way to design efficient process for biomass conversion. Accordingly, a continuing drive is inspiring to discover new routes to promote crystalline cellulose disruption.

RESULTS

Herein, a physico-chemical oxidative cleavage strategy of irradiation oxidation/post-reduction (IOPR) was employed to treat crystalline cellulose I to cleave glycosidic bonds association with some new oxidized and reduced chain ends, thus boosting downstream degradation by cellulases from Trichoderma reesei. The hydrolysis performance of treated crystalline cellulose was conducted with either T. reesei Cel7A (TrCel7A) alone, or a cellulase enzyme mixture (90% Celluclast 1.5 L, 10% β-glucosidase). 81.6 and/or 97% of conversion efficiency have been reached for 24-h and 48-h cellulase hydrolysis, respectively. The high efficient conversion of crystalline cellulose after IOPR is mainly attributed to generating some new chain ends, which are identified by MAIDI-TOF-MS and HPLC. Furthermore, the nanoscale architectures of crystalline cellulose before and after IOPR are systematically investigated by XRD, EPR, ATR- FTIR, GPC, and XPS techniques. Together with TEM images, the results reveal a fascinating digestion mechanism of "peel-off" and "cavity-formation" paradigms toward degrading crystalline cellulose by cellulase mixtures after IOPR treatment.

CONCLUSIONS

This encouraging results show that the proposed IOPR approach will become a potential competitive alternative to current biomass pretreatment. It opens a new avenue toward the implementation of pretreatment and the design of enzyme cocktails in lignocellulosic biorefinery.

Cobalt-60 gamma-ray irradiation pretreatment and sludge protein for enhancing enzymatic saccharification of hybrid poplar sawdust

In order to improve the enzymatic saccharification of hybrid poplar sawdust, gamma irradiation pretreatment and enzymatic hydrolysis in the presence of sludge protein were investigated. The cellulose crystallinity index were significantly decreased after irradiation pretreatment, and adding sludge protein improved enzyme activity and increased the reducing sugar yield. The conditions of irradiation pretreatment and enzymatic hydrolysis in the presence of sludge protein were systematically examined. The maximum reducing sugar yield was 519mg/g under an irradiation dose of 300kGy, a sludge protein dosage of 2mg/mL, an enzymatic hydrolysis temperature of 45°C, an enzymatic hydrolysis time of 84h, and a 90FPU/g enzyme loading. This work indicated that the combined method of gamma irradiation pretreatment and enzymatic hydrolysis in the presence of sludge protein was a promising potential for the saccharification of hybrid poplar sawdust.

Profiling microbial lignocellulose degradation and utilization by emergent omics technologies

The use of plant materials to generate renewable biofuels and other high-value chemicals is the sustainable and preferable option, but will require considerable improvements to increase the rate and efficiency of lignocellulose depolymerization. This review highlights novel and emerging technologies that are being developed and deployed to characterize the process of lignocellulose degradation. The review will also illustrate how microbial communities deconstruct and metabolize lignocellulose by identifying the necessary genes and enzyme activities along with the reaction products. These technologies include multi-omic measurements, cell sorting and isolation, nuclear magnetic resonance spectroscopy (NMR), activity-based protein profiling, and direct measurement of enzyme activity. The recalcitrant nature of lignocellulose necessitates the need to characterize the methods microbes employ to deconstruct lignocellulose to inform new strategies on how to greatly improve biofuel conversion processes. New technologies are yielding important insights into microbial functions and strategies employed to degrade lignocellulose, providing a mechanistic blueprint in order to advance biofuel production.

Microalgal lipid production using the hydrolysates of rice straw pretreated with gamma irradiation and alkali solution

BACKGROUND

Lignocellulosic biomass has long been recognized as a potential sustainable source of sugars for biofuels. However, many physicochemical structural and compositional factors inhibit the enzymatic digestibility of the lignocellulosic biomass. In this study, efficient pretreatment method of rice straw (RS) was developed and the RS hydrolysate was applied in the cultivation of microalgae for lipid production.

RESULTS

Gamma ray irradiation (GRI) and alkali solution were used for the pretreatment, and saccharification was carried out with lignocellulolytic enzymes. When RS was pretreated by combined GRI and alkali method, the glucose and xylose saccharification yield after enzymatic hydrolysis increased up to 91.65 and 98.84 %, respectively. The enzymatic hydrolysate from the RS pretreated with the combined method was used to cultivate Chlorella protothecoides for lipid production. The maximum concentrations of biomass and fatty acid methyl ester of cells were 6.51 and 2.95 g/L, respectively. The lipid content of C. protothecoides from RS hydrolysate was comparable to that from glucose, and the lipid composition was similar between different carbon sources.

CONCLUSION

These results demonstrate that the combined pretreatment with gamma irradiation was highly effective in preparing hydrolysate, and the rice straw hydrolysate could be used as an alternative carbon source for microalgal lipid production for biofuel.

Comparison of γ-irradiation with other pretreatments followed with simultaneous saccharification and fermentation on bioconversion of microcrystalline cellulose for bioethanol production

The effect of γ-irradiation pretreatment was compared with other pretreatment methods including ionic liquids (ILs), 1% HCl, 1% H2SO4, acidic aqueous Ils (AA-ILs), on the bioconversion efficiency of microcrystalline cellulose (MCC) for bioethanol production. The efficiency of MCC pretreatment followed with simultaneous saccharification and fermentation (SSF) was firstly evaluated according to the variations of the irradiation-derived compounds and structure of MCC, as well as yeast growth curve and bioethanol yield. Results showed that the appropriate irradiation dose (891 kGy used in our work) could eliminate the negative effect of toxic irradiation-derived compounds on SSF for ethanol bioconversion with the yield value of 67%. Analyses of SEM, FT-IR, reducing sugar and bioethanol yield showed that the efficiency of pretreatment on MCC was ILs ≈ irradiation pretreatment > AA-ILs pretreatment > 1% HCl pretreatment > 1% H2SO4 pretreatment.

Insights into the effects of γ-irradiation on the microstructure, thermal stability and irradiation-derived degradation components of microcrystalline cellulose (MCC)

The microstructure, thermal stability and irradiated degradation components of microcrystalline cellulose were investigated under ⁶⁰Co γ-irradiation (0–1400 kGy).

Radiation-induced high-temperature conversion of cellulose

Thermal decomposition of cellulose can be upgraded by means of an electron-beam irradiation to produce valuable organic products via chain mechanisms. The samples being irradiated decompose effectively at temperatures below the threshold of pyrolysis inception. Cellulose decomposition resembles local “explosion” of the glucopyranose unit when fast elimination of carbon dioxide and water precede formation of residual carbonyl or carboxyl compounds. The dry distillation being performed during an irradiation gives a liquid condensate where furfural and its derivatives are dominant components. Excessively fast heating is adverse, as it results in a decrease of the yield of key organic products because pyrolysis predominates over the radiolytic-controlled decomposition of feedstock. Most likely, conversion of cellulose starts via radiolytic formation of macroradicals do not conform with each other, resulting in instability of the macroradical. As a consequence, glucosidic bond cleavage, elimination of light fragments (water, carbon oxides, formaldehyde, etc.) and formation of furfural take place.