Mechanochemical deconstruction of lignocellulosic cell wall polymers with ball-milling

High-Energy Milling as a Pre-Treatment Alternative for Lignocellulosic Fibers Derived from Brewer's Spent Grain

The objective of this study was to evaluate how high-energy milling affects the structural, thermal, and morphological properties of brewer's spent grain fibers over time. The researchers determined the chemical composition of the samples using TAPPI techniques, particle size analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). The samples displayed distinct morphologies and particle sizes depending on the treatment duration. The sample treated for 120 min (T120) showed the smallest particle size (19.4 µm). FTIR spectra revealed that the mechanical treatment strongly disrupted the structure of hemicellulose. The thermal stability of the samples decreased because of the applied treatment. Mechanical milling also fully eliminated the crystalline structure of cellulose in the samples. These findings indicate that high-energy milling holds strong potential as a pre-treatment method for the valorization of lignocellulosic residues.

Lignocellulose-Derived Energy Materials and Chemicals: A Review on Synthesis Pathways and Machine Learning Applications

Lignocellulose biomass, Earth's most abundant renewable resource, is crucial for sustainable production of high-value chemicals and bioengineered materials, especially for energy storage. Efficient pretreatment is vital to boost lignocellulose conversion to bioenergy and biomaterials, cut costs, and broaden its energy-sector applications. Machine learning (ML) has become a key tool in this field, optimizing pretreatment processes, improving decision-making, and driving innovation in lignocellulose valorization for energy storage. This review explores main pretreatment strategies - physical, chemical, physicochemical, biological, and integrated methods - evaluating their pros and cons for energy storage. It also stresses ML's role in refining these processes, supported by case studies showing its effectiveness. The review examines challenges and opportunities of integrating ML into lignocellulose pretreatment for energy storage, underlining pretreatment's importance in unlocking lignocellulose's full potential. By blending process knowledge with advanced computational techniques, this work aims to spur progress toward a sustainable, circular bioeconomy, particularly in energy storage solutions.

On-site cellulase production by Trichoderma reesei RutC-30 to enhance the enzymatic saccharification of ball-milled corn stover

Cellulases are essential for the enzymatic saccharification of lignocellulose. They play a crucial role in breaking down the structure of lignocellulose to obtain fermentable sugars. In this study, we conducted on-site cellulase production by Trichoderma reesei RutC-30 through submerged fermentation. The effects of carbon source, nitrogen source, KH2PO4, and mineral elements on cellulase production were evaluated using the hydrolyzed total sugar concentration of ball-milled corn stover as an indicator. The optimal fermentation medium conditions for cellulase production were determined through orthogonal experimental design analysis. Additionally, by optimizing culture conditions, including inoculation, pH, and bottling volume, we achieved a total sugar concentration of 92.25 g/L. After the optimization, the FPA, CMCA, protein, and total sugar concentration increased by 75.49 %, 18.43 %, 89.71 %, and 17.83 %, respectively. Furthermore, corn stover pretreated by different methods was applied to induce cellulase production. Ball-milled and steam-exploded corn stover was identified as suitable incubation carbon sources with total sugar concentration up to 94.31 g/L. Our work exploits the cellulase induced by lignocellulose and then applies it to lignocellulose, enabling the customization and providing a reference for the production of cellulase with corn stover as an inducer.

Fermentation of Biomass and Residues from Brazilian Agriculture for 2G Bioethanol Production

Brazil is one of the world's leading producers of staple foods and bioethanol. Lignocellulosic residual sources have been proposed as a promising feedstock for 2G bioethanol and to reduce competition between food and fuels. This work aims to discuss residual biomass from Brazilian agriculture as lignocellulosic feedstock for 2G bioethanol production as bagasse, stalk, stem, and peels, using biorefining concepts to increase ethanol yields. Herein, we focused on biomass chemical characteristics, pretreatment, microorganisms, and optimization of process parameters that define ethanol yields for bench-scale fermentation. Although several techniques, such as carbon capture, linking enzymes to supports, and a consortium of microorganisms, emerge as future alternatives in bioethanol synthesis, these technologies entail necessary optimization efforts before commercial availability. Overcoming these challenges is essential to linking technological innovation to synthesizing environmentally friendly fuels and searching other biomass wastes for 2G bioethanol to increase the biofuel industry's potential. Thus, this work is the first to discuss underutilized lignocellulosic feedstock from other agrifoods beyond sugar cane or corn, such as babassu, tobacco, cassava, orange, cotton, soybean, potatoes, and rice. Residual biomasses combined with optimized pretreatment and mixed fermentation increase hydrolysis efficiency, fermentation, and purification. Therefore, more than a product with a high added value, bioethanol synthesis from Brazilian residual biomass prevents waste production.

Mechanochemical Tailoring of Lignin Structure: Influence of Different Particle Sizes in the Organosolv Process

The autocatalyzed ethanolic organosolv process is gaining increasing attention for the sulfur-free isolation of lignin, which is subsequently used as a renewable substitute for various fossil-based applications. For the first time, the mechanochemical influence of seven different particle sizes of two different biomasses on the respective organosolv lignin structure is examined. Wine pruning (Pinot Noir) and wine pomace (Accent) are used for organosolv process with particle sizes ranging from 2.0-1.6 mm to less than 0.25 mm. As particle size decreases, the weight-average molecular weight increases, while the total phenol content decreases significantly. Additionally, the distribution of the lignin-typical monolignols and relevant substructures, as determined by two-dimensional heteronuclear nuclear magnetic resonance spectra single quantum coherence (HSQC), is observed. The degree of grinding of the biomass has a clear chemical-structural influence on the isolated HG and HGS organosolv lignins. Therefore, it is crucial to understand this influence to apply organosolv lignins in a targeted manner. In the future, particle size specifications in the context of the organosolv process should be expressed in terms of distribution densities rather than in terms of a smaller than specification.

Characterization of bamboo shoots dietary fiber modified by ball milling and its role in altering the physicochemical properties of shrimp surimi

A simple but robust strategy of ball milling (20 Hz, 30 Hz for 30 s, 60 s, 120 s, 180 s) was utilized to modify bamboo shoots fiber (BSDF) in shrimp surimi. The water holding capacity, swelling capacity, and oil binding capacity of 30 Hz-60 s milled BSDF exhibited the highest values of 5.61 g/g, 3.13 mL/g, and 6.93 g/g, significantly higher (P < 0.05) than untreated one (3.65 g/g, 2.03 mL/g, 4.57 g/g). Ball-milled BSDF exhibited a small-sized structure with the relative crystallinity decreased from 40.44 % (control) to 11.12 % (30 Hz-180 s). The myosin thermal stability, gelation properties of surimi were significantly enhanced by incorporating 20 Hz-120 s and 30 Hz-60 s BSDF via promoting protein unfolding, covalent hydrophobic interactions, and hydrogen bonding. A matrix-reinforcing and water entrapping effect was observed, exhibiting reinforced networks with down-sized water tunnels. However, BSDF modified at 180 s contributed to over-aggregated networks with fractures and enlarged gaps. Appropriate ball-milled BSDF (20 Hz-120 s, and 30 Hz-60 s) resulted in a significant decrease in α-helix (P < 0.05), accompanied by an increase of β-sheets and β-turn. This work could bring some insights into the applications of modified BSDF and its roles in the gelation of surimi-based food.

Extraction of super high-yield lignin-carbohydrate complexes from rice straw without compromising cellulose hydrolysis

Lignin-carbohydrate complexes (LCC) that exhibit both structural advantages of lignin and carbohydrates are promising amphiphilic biopolymers, but the extraction is challenged by its liable chemical bond cleavage between lignin and carbohydrates. This work proposed a facile chemical route to integrating the production of water-insoluble (WIS LCC) and water-soluble LCC (WS LCC) into the emerging deep eutectic solvent (DES) biorefinery at mild conditions. The tailored mechanochemical fractionation process of ball milling assisted aqueous alkaline DES could extract 24.2 % LCC in total, with the co-production of a highly hydrolysable cellulose fraction (98.7 % glucose conversion). The resulting LCC exhibited considerably high contents of β-O-4, phenyl glycoside, and ferulic acid linkage bonds. When 100 g starting straw was subjected to this technique route, 9.1 g WIS LCC, 15.1 g WS LCC and 45.5 g glucose were cascaded produced. It was proposed that the selective disruption of hydrogen bonding entangled network and the quasi-state dissolution of the whole biomass allowed the subsequent cascade fractionation of WIS LCC, WS LCC and highly hydrolysable cellulose through solution property adjustment. This work showed a promising approach for LCC production with high yield without compromising cellulose conversion potential, which has been challenging in the current lignocellulose biorefinery.

An aggregated understanding of the influence of aqueous ammonia pretreatment on the physical deconstruction of cell walls in sugar beet pulp

The underlying interplay between physicochemical property and enzymatic hydrolysis of cellulose still remains unclear. The impacts of matrix glycan composition of sugar beet pulp (SBP) on physical structure and saccharification efficiency were emphasized. The results showed that aqueous ammonia (AA) pretreatment could remove the non-cellulosic polysaccharides and destroy the linkage between the pectin and lignin. The cellulose supramolecule was changed significantly after AA pretreatment, in terms of the decline in hardness, gumminess, springiness, thickness and degree of polymerization. Furthermore, vascular cell was exposed and degraded. The highest reducing sugar yield of 355.06 mg/g was obtained from the pretreated SBP (80 °C) with enzyme loading of 30 U/g, which was 1.01 times higher than that of the untreated SBP. This research also supported the idea that recognizing and precisely removing the primary epitopes in cell walls might be an ideal strategy to accomplish the improved enzymatic hydrolysis through mild pretreatment.

3D Filaments Based on Polyhydroxy Butyrate-Micronized Bacterial Cellulose for Tissue Engineering Applications

In this work, scaffolds based on poly(hydroxybutyrate) (PHB) and micronized bacterial cellulose (BC) were produced through 3D printing. Filaments for the printing were obtained by varying the percentage of micronized BC (0.25, 0.50, 1.00, and 2.00%) inserted in relation to the PHB matrix. Despite the varying concentrations of BC, the biocomposite filaments predominantly contained PHB functional groups, as Fourier transform infrared spectroscopy (FTIR) demonstrated. Thermogravimetric analyses (i.e., TG and DTG) of the filaments showed that the peak temperature (Tpeak) of PHB degradation decreased as the concentration of BC increased, with the lowest being 248 °C, referring to the biocomposite filament PHB/2.0% BC, which has the highest concentration of BC. Although there was a variation in the thermal behavior of the filaments, it was not significant enough to make printing impossible, considering that the PHB melting temperature was 170 °C. Biological assays indicated the non-cytotoxicity of scaffolds and the provision of cell anchorage sites. The results obtained in this research open up new paths for the application of this innovation in tissue engineering.

Recent advances on physical technologies for the pretreatment of food waste and lignocellulosic residues

The complete deployment of a bio-based economy is essential to meet the United Nations' Sustainable Development Goals from the 2030 Agenda. In this context, food waste and lignocellulosic residues are considered low-cost feedstocks for obtaining industrially attractive products through biological processes. The effective conversion of these raw materials is, however, still challenging, since they are recalcitrant to bioprocessing and must be first treated to alter their physicochemical properties and ease the accessibility to their structural components. Among the full pallet of pretreatments, physical methods are recognised to have a high potential to transform food waste and lignocellulosic residues. This review provides a critical discussion about the recent advances on milling, extrusion, ultrasound, and microwave pretreatments. Their mechanisms and modes of application are analysed and the main drawbacks and limitations for their use at an industrial scale are discussed.

Effects of Ambient Temperature and Humidity on Natural Deposition Characteristics of Airborne Biomass Particles

In the production process of biomass energy with crop straw as the raw material, the indoor dust environment created by smashed plant fiber can affect the health of workers and lead to the risk of fire and explosions. The physical properties of biomass vary with the ambient air conditions, resulting in different deposition processes for airborne biomass particles. In this study, the deposition of biomass particles in different environments in an experimental chamber was examined by independently controlling the internal temperature and relative humidity. The results show that in the ambient temperature range of 20~40 °C and at a relative humidity of 25~65%, the water absorption rates of the biomass particles were 15.4~24.7%. The deposition rates of the airborne biomass particles with different sizes were 0.9~2.9 h^-1, which positively correlated with the particle sizes in the same ambient conditions. The increase in ambient temperature and relative humidity promoted the deposition of biomass particles with diameters over 0.5 μm. For the particles with diameters below 0.5 μm, the deposition rates were nonlinearly related to the ambient temperature and relative humidity and were greater at lower temperatures. The significance levels of the factors influencing the particle deposition were particle size > ambient temperature > ambient relative humidity. For the biomass particles below 0.5 μm, the influence of the relative humidity on the deposition was much weaker than that of the temperature.

Alcoholysis kinetics and mechanism studies of ethyl levulinate production from ball milled corn stover

Alcoholysis of ball-milled biomass over catalysts with Brønsted and Lewis acid sites provides an efficient and sustainable scheme to produce versatile biobased chemicals under mild conditions; however, optimizing the process parameters is challenged by the complexity of reaction pathways and the multiplicity of ball milling and combination catalyst gains. To address these challenges, we present kinetic analysis of ethyl levulinate (EL) production from ball-milled corn stover catalyzed by Brønsted (B) acidic ionic liquid [Bmim-SO3H][HSO4] (SO3H-IL) and Lewis (L) acidic Al2(SO4)3. Product analysis shows that cellulosic substrates can form EL either through the intermediate ethyl-d-glycopyranoside (EDGP) or levoglucosenone (LGO), with the former leading the alcoholysis reaction. Kinetics results reveal that ball milling accelerates the reaction rate by promoting the formation of EDGP and LGO from cellulose. Pure SO3H-IL gives high selectivity towards EDGP from ball-milled corn stover and promotes the LGO production, whereas addition of Al2(SO4)3 substantially facilitates their further conversion to EL. Our findings contribute to the rational design of efficient catalytic strategies for sustainable and profitable biorefinery.

Mechanical pretreatment of lignocellulosic biomass toward enzymatic/fermentative valorization

Lignocellulosic biomass (LCB) has the potential to replace fossil fuels, thanks to the concept of biorefinery. This material is formed mainly by cellulose, lignin, and hemicellulose. To maximize the valorization potential of this material, LCB needs to be pretreated. Milling is always performed before any other treatments. It does not produce chemical change and improves the efficiency of the upcoming processes.

Additionally, it makes LCB easier to handle and increases bulk density and transfer phenomena of the next pretreatment step. However, this treatment is energy consuming, so it needs to be optimized. Several mills can be used, and the equipment selection depends on the characteristics of the material, the final size required, and the operational regime: continuous or batch. Among them, ball, knife, and hammer mills are the most used at the laboratory scale, especially before enzymatic or fermentative treatments. The continuous operational regime (knife and hammer mill) allows us to work with high volumes of raw material and can continuously reduce particle size, unlike the batch operating regime (ball mill).

This review recollects the information about the application of these machines, the effect on particle size, and subsequent treatments. On the one hand, ball milling reduced particle size the most; on the other hand, hammer and knife milling consumed less energy. Furthermore, the latter reached a small final particle size (units of millimeters) suitable for valorization.

Simultaneous bio-reduction of nitrate and Cr(VI) by mechanical milling activated corn straw

Abundant lignocellulose waste is an ideal energy source for environmental bioremediation, but its recalcitrance to bioavailability makes this a challenging prospect. We hypothesized that the disruption of straw's recalcitrant structure by mechanochemical ball milling would enhance its availability for the simultaneous bioreduction of nitrate and Cr(VI). The results showed that the ball-milling process increased the quantity of water-soluble organic matter released from corn straw and changed the composition of organic matter by strongly disrupting its lignocellulose structure. The increase in ball-milling time increased the specific surface area of the straw and favored the adhesion of microorganisms on the straw surface, which enhanced the bioavailability of the energy in the straw. Substantially increased removal of NO₃^--N (206.47 ± 0.67 mg/g) and Cr(VI) (37.62 ± 0.09 mg/g) was achieved by using straw that was ball milled for 240 min, which validated that ball milling can improve the utilization efficiency of straw by microorganisms. Cellular and molecular biological analyses showed that ball-milled straw increased microbial energy metabolism and cellular activity related to the electron transport chain. This work offers a potential way to achieve the win-win goal of utilizing agricultural wastes and remediating environmental pollution.

Effect of Ball-Milling Pretreatment of Cellulose on Its Photoreforming for H2 Production

Photoreforming of cellulose is a promising route for sustainable H₂ production. Herein, ball-milling (BM, with varied treatment times of 0.5-24 h) was employed to pretreat microcrystalline cellulose (MCC) to improve its activity in photoreforming over a Pt/TiO₂ catalyst. It was found that BM treatment reduced the particle size, crystallinity index (CrI), and degree of polymerization (DP) of MCC significantly, as well as produced amorphous celluloses (with >2 h treatment time). Amorphous cellulose water-induced recrystallization to cellulose II (as evidenced by X-ray diffraction (XRD) and solid-state NMR analysis) was observed in aqueous media. Findings of the work showed that the BM treatment was a simple and effective pretreatment strategy to improve photoreforming of MCC for H₂ production, mainly due to the decreased particle size and, specifically in aqueous media, the formation of the cellulose II phase from the recrystallization of amorphous cellulose, the extent of which correlates well with the activity in photoreforming.

Mechanochemical Transformations of Biomass into Functional Materials

Biomass is one of the promising alternatives to petroleum-derived materials and plays a major role in our fight against climate change by providing renewable sources of chemicals and materials. Owing to its chemical and structural complexity, the transformation of biomass into value-added products requires a profound understanding of its composition at different scales and innovative methods such as combining physical and chemical processes. In this context, the use of mechanochemistry in biomass valorization is currently growing owing to its potentials as an efficient, sustainable, and environmentally friendly approach. This review highlights the latest advances in the transformation of biomass (i. e., chitin, cellulose, hemicellulose, lignin, and starch) to functional materials using mechanochemical-assisted methods. We focused here on the methodology of biomass processing, influencing factors, and resulting properties with an emphasis on achieving functional materials rather than breaking down the biopolymer chains into smaller molecules. Opportunities and limitations associated this methodology were discussed accordingly for future directions.

Structure-property-degradability relationships of varisized lignocellulosic biomass induced by ball milling on enzymatic hydrolysis and alcoholysis

Background

Valorization of lignocellulosic biomass to obtain clean fuels and high-value chemicals is attractive and essential for sustainable energy and chemical production, but the complex structure of biomass is recalcitrant to catalytic processing. This recalcitrance can be overcome by pretreating biomass into deconstructable components, which involves altering the structural complexities and physicochemical properties. However, the impact of these alterations on biomass deconstruction varies considerably, depending on the pretreatment and subsequent conversion type. Here, we systematically describe the changes in structure and properties of corn stover after ball milling as well as their influence on the following enzymatic saccharification and acid-catalyzed alcoholysis, with the aim of elucidating the relationships between structures, properties and deconstructable potential of lignocellulosic biomass.

Results

Ball milling causes dramatic structural changes, since the resistant plant cell walls are destroyed with size reduction to a cellular scale, leading to the increase in surface area and reducing ends, and decrease in crystallinity and thermal stability. As a result, ball-milled corn stover is more susceptible to enzymatic saccharification to fermentable sugars and provides more industrially viable processing approaches, as it is effective at high solids loading and minor enzyme loading, without any other pretreatment. Acid-catalyzed alcoholysis of corn stover to biofuels, on the other hand, is also enhanced by ball milling, but additional processing parameters should be tailored to the needs of efficient conversion. Further, a detailed examination of process variables coupled with a kinetic study indicates that acid-catalyzed alcoholysis is limited by the process variables rather than by the substrate parameters, whereas ball milling facilitates this reaction to some extent, especially under mild conditions, by lowering the activation energy of corn stover decomposition.

Conclusions

The efficient catalytic conversion of biomass is closely related to its structure and properties, an understanding of which offers prospects for the rational improvement of methods aimed at more economic commercial biorefineries.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02133-x.

Effect of combined wet alkaline mechanical pretreatment on enzymatic hydrolysis of corn stover and its mechanism

BACKGROUND

To further optimize the mechanochemical pretreatment process, a combined wet alkaline mechanical pretreatment of corn stover was proposed with a short time and less chemical consumption at room temperature.

RESULTS

The combined alkaline mechanical pretreatment significantly enhanced enzymatic hydrolysis resulting a highest glucose yield (Y_G) of 91.9% with 3% NaOH and ball milling (BM) for 10 min. At this optimal condition, 44.4% lignin was removed and major portion of cellulose was retained (86.6%). The prehydrolysate contained by-products such as monosaccharides, oligosaccharides, acetic acid, and lignin but no furfural and 5-HMF. The alkaline concentration showed a significant impact on glucose yield, while the BM time was less important. Quantitative correlation analysis showed that Y_G (%) = 0.68 × BM time (min) + 19.27 × NaOH concentration (%) + 13.71 (R² = 0.85), Y_G = 6.35 × glucan content - 231.84 (R² = 0.84), and Y_G =  - 14.22 × lignin content + 282.70 (R² = 0.87).

CONCLUSION

The combined wet alkaline mechanical pretreatment at room temperature had a boosting effect on the yield of enzymatic hydrolysis with short treatment time and less chemical consumption. The impact of the physical and chemical properties of corn stover pretreated with different BM times and/or different NaOH concentrations on the subsequent enzymatic hydrolysis was investigated, which would be beneficial to illustrate the effective mechanism of the mechanochemical pretreatment method.

Mechanochemical effects on the structural properties of wheat starch during vibration ball milling of wheat endosperm

Pure wheat endosperm was fully ground in a vibratory ball mill and structural changes in wheat starch were measured to assess the effect of mechanochemical action during the grinding process. Vibratory ball milling changed the endosperm granule size to ~30 μm (D50). There was a significant increase in damaged starch content, and this was positively correlated with the grinding time. The relative crystallinity of starch decreased by 5% after milling 105 min, and the short-range order decreased. The damaged structure of amylopectin starch decreased with milling time, as detected macroscopically by the peak viscosity and final viscosity of milling samples. Overall, the in vitro digestion results showed that mechanical modification caused irregular defects inside wheat starch crystals, increased the sensitivity of wheat starch to enzymes, enhanced the hydrolysis rate three-fold, and increased the maximum starch hydrolysis by 50%. Mechanochemistry effects was used to analyze the quality changes in wheat milling.

Forecasting of reducing sugar yield from corncob after ultrafine grinding pretreatment based on GM(1,N) method and evaluation of biohydrogen production potential

Pretreatment of biomass helps to enhance reducing sugar yield from biomass during enzyme hydrolysis tests. Ultrafine grinding was applied to pretreat corncob. The effect of affecting factors including milling time, initial particle size and ball to power weight on the reducing sugar yield from corncob was investigated firstly. And then, an GM(1,N) model was constructed to model the ultrafine grinding pretreatment system predicting the reducing sugar yield from corncob based on experimental data, the results demonstrate GM(1,N) could predict the reducing sugar yield accurately and effectively without depending on the number of samples. The initial particle size was the most critical influential factor affecting reducing sugar yield according to the driving coefficient. The cumulative hydrogen yield was significantly affected by ultrafine grinding pretreatment, the hydrogen yield of pretreated corncob was 153.60 ± 5.8 mL/g total solids, which was higher than that of untreated corncob (113.20 ± 3.2 mL/g total solids).

Efficient saccharification of wheat straw pretreated by solid particle-assisted ball milling with waste washing liquor recycling

Wheat straw was pretreated using ball milling (BM) promoted by solid particles (NaOH, NaCl, citric acid). NaOH showed the best synergistic interaction effect, due to the breakage of β-1,4-glycosidic bonds among cellulose molecules by the alkali solid particles induced by BM. NaOH-BM pretreatment decreased the straw crystallinity from 46% to 21.4% and its average particle size from 398.3 to 50.6 μm in 1 h. After 4 h milling, the reducing-end concentration of cellulose increased by 3.8 times from 12.5 to 60.2 μM, with glucose yield increased by 2.1 times from 26.6% to 82.4% for 72 h enzymatic hydrolysis at cellulase loading of 15 FPU/g dry substrate. The pretreatment washing liquor was recycled for the re-treatment of partially pretreated biomass at 121 °C for 30 min, resulting in 99.4% glucose yield by enzymatic hydrolysis. BM assisted with alkali particles was an effective approach for improving biomass enzymatic saccharification.

Rheology of enzyme liquefied corn stover slurries: The effect of solids concentration on yielding and flow behavior

The measurement of yield stress and shear thinning flow behavior of slurries formed from unpretreated corn stover at solids loadings of 100-300 g/L provides a key metric for the ability to move, pump, and mix this lignocellulosic slurry, particularly since corn stover slurries represent a major potential feedstock for biorefineries. This study compared static yield stress values and flow hysteresis of corn stover slurries of 100, 150, 200, 250, and 300 g/L, after these slurries were formed by adding pellets to a cellulase enzyme solution (Celluclast 1.5 L) in a fed-batch manner. A rotational rheometer was used to quantitate relative yield stress and its dependence on processing history at insoluble solids concentrations of 4%-21% (wt/vol). Key findings confirmed previous observations that yield stress increases with solids loadings and reaches ~3000 Pa at 25% (wt/vol) solids concentration compared to ~200 Pa after enzyme liquefaction. While optimization of slurry forming (i.e., liquefaction) conditions remains to be done, metrics for quantifying liquefaction extent are needed. The method for obtaining comparative metrics is demonstrated here and shows that the yield stress, shear thinning and shear thickening flow behaviors of enzyme liquefied corn stover slurries can be analyzed using a wide-gap rheometry setup with relative measuring geometries to mimic the conditions that may exist in a mixing vessel of a bioreactor while applying controlled and precise levels of strain.

Systematic comparison for effects of different scale mechanical-NaOH coupling treatments on lignocellulosic components, micromorphology and cellulose crystal structure of wheat straw

In order to compare the effect of different mechanical-chemical coupling treatment on wheat straw and provide guidance for the subsequent preparation of cellulose nanomaterials, this paper systematically explored the impact of different scale mechanical fragmentation coupling various NaOH concentration treatment on the lignocellulosic components, micromorphology and cellulose crystal structure of wheat straw. The results showed that the relationship between hemicellulose and lignin removal with NaOH concentration can be expressed as exponential function Y = a_i(1-exp(-b_iX)), and micro-nano-scale ball-milling coupling NaOH treatment can facilitate the removal of hemicellulose and lignin. Micromorphology analysis found that wet ball milling coupling NaOH one-step treatment can disintegrate cellulose fiber into crosslinked network structure of cellulose microfibrils. XRD results indicated that wet ball milling with NaOH solution was contributed to retaining cellulose crystal structure and conducive to cellulose crystalline transformation. In conclusion, wet ball milling coupling NaOH simultaneous treatment can be a promising pretreatment for cellulose nanomaterials preparation.

Enzymatic conversion of pretreated lignocellulosic biomass: A review on influence of structural changes of lignin

The demands of energy sustainability drive efforts to bio-chemical conversion of biomass into biofuels through pretreatment, enzymatic hydrolysis, and microbial fermentation. Pretreatment leads to significant structural changes of the complex lignin polymer that affect yield and productivity of the enzymatic conversion of lignocellulosic biomass. Structural changes of lignin after pretreatment include functional groups, inter unit linkages and compositions. These changes influence non-productive adsorption of enzyme on lignin through hydrophobic interaction and electrostatic interaction as well as hydrogen bonding. This paper reviews the relationships between structural changes of lignin and enzymatic hydrolysis of pretreated lignocellulosic biomass. The formation of pseudo-lignin during dilute acid pretreatment is revealed, and their negative effect on enzymatic hydrolysis is discussed.

Revealing the structural characteristics of lignin macromolecules from perennial ryegrass during different integrated treatments

To reveal the structural characteristics and physicochemical properties of perennial ryegrass lignin, sequential alkali extractions or double ball-milling and enzymatic hydrolysis on the basis of ultrasonic and hydrothermal pretreatments were proposed in this study. Results revealed that sequential alkali extractions released 89.4% of original lignin from the ryegrass cell walls and 0.75-4.16% of associated carbohydrates as compared to the double ball-milling and enzymatic hydrolysis (96.0% and 18.39%). It was observed that the two types of lignin prepared were SGH-type and had different amounts of p-coumarates and ferulates, and primarily consisted of β-O-4' linkages combined with minor amounts of β-β' and β-5' linkages. Besides, alkali-soluble lignins exhibited relatively fewer β-O-4' linkages, higher S/G ratios and H-type units, and abundant phenolic OH groups as compared to the double enzymatic lignin. Overall, the deeper investigation of the lignin structure of ryegrass will provide useful information for the efficient utilization of lignin macromolecules in biorefineries.

Superfine pulverisation pretreatment to enhance crystallinity of cellulose from Lycium barbarum L. leaves

Superfine pulverisation (SFP) pretreatment of Lycium barbarum L. leaves was performed to obtain highly crystalline cellulose. Compared with other common pulverisation methods, SFP enhanced cellulosic crystallinity by 18.3 % and 8.4 %, with and without post-acid treatments, respectively. XRD and solid-state NMR analyses showed that SFP facilitated the exposure of amorphous substances (i.e., hemicellulose and lignin) to NaOH and H₂O₂. Large amounts of silicon (5.5 %) and aluminium (2.1 %) were found to incorporate into the crystalline regions of SFP-produced cellulose. Further FTIR and thermogravimetric analyses revealed that SFP-produced cellulose contained large amounts of hydroxyl groups, affecting the cellulosic crystallinity and thermal stability. These findings demonstrate the potential for SFP to serve as a green technology for production of highly crystalline and mineral-rich cellulose.

One-pot fractionation of corn stover with peracetic acid and maleic acid

Lignocellulose fractionation is a primary treatment to enhance cellulose accessibility and multi-component use. Herein, the development of a one-step fractionation is reported for cellulose enrichment from corn stover using a low concentration of peracetic acid combined with maleic acid (PAM). The effects of pretreatment parameters on the contents of cellulose, hemicellulose, and lignin were investigated. After cooking for 1 h at 130 °C with 1.5 wt% peracetic acid and 3 wt% maleic acid, 86.83% of corn stover cellulose remained in the solid residue while 88.21% of hemicellulose and 87.77% of lignin dissolved into the aqueous liquid. Hemicellulose was primarily hydrolyzed into xylose with 84.58% recovered during the PAM process. The cellulose-rich residue was enzymatically hydrolyzed with a glucose yield of 89.65%, which was two to three times that of untreated substrate. Generally, the proposed process offers a promising approach for efficient fractionation of lignocellulose under mild and environmental-friendly conditions.

Quantitative and qualitative characterization of dual scale mechanical enhancement on cellulosic and crystalline-structural variation of NaOH treated wheat straw

In order to explore the effects of different mechanical fragmentation on cellulose separation and cellulose polymorphic transformation of wheat straw during alkali treatment, one coarse milled (CM) and two ball milled wheat straw samples (BM30 and BM120) were treated with different NaOH concentrations (1%-10%), and the lignocellulosic compositions and crystalline-structural various were quantitative and qualitative characterized. The quantitative equations between cellulose content and NaOH concentration of different mechanical treated samples were Y_CM = 69.8-35.1exp(-0.64X)), Y_BM30 = 71.3-35.1exp(-0.86X)) and Y_BM120 = 73.5-35.1exp(-1.82X)). The enhancement effect of cellulose separation with the increasing mechanical fragmentation intensity is mainly due to the increasing hemicellulose solubilization. X-ray diffraction results reveals that the NaOH concentration required for cellulose crystalline transformation of CM, BM30 and BM120 is 10%, 8% and 2%, respectively. In conclusion, mechanical fragmentation contributes to cellulose separation and cellulose crystalline transformation under lower NaOH concentration.

Ball milling pretreatment facilitating α-amylase hydrolysis for production of starch-based bio-latex with high performance

Starch based bio-latex has been widely researched in the coating paper area for the purpose of partial replacement of petroleum-based binders. In this paper, a green and facile ball milling pretreatment was proposed to modify the starch granules before α-amylase hydrolysis by breaking up their crystalline structure, thus improving the accessibility and susceptibility of amylase into starch structure. It was found that the improved hydrolysis process after 8 h ball milling can generate suitable degree of polymerization of polysaccharides or oligosaccharides, which further facilitated the following H₂O₂ oxidation and SHMP crosslinking processes. In addition, a mechanism was also demonstrated to illustrate the improvement induced by ball milling pretreatment. The prepared bio-latex with crosslinking-structure performed excellent adhesive properties when substituted 25 % of petroleum-based latex during paper coating application, which showed great potential in improving the economic, cost, and environment benefits of traditional production of coated paper.

An overview of biomass conversion: exploring new opportunities

Recycling biomass is indispensable these days not only because fossil energy sources are gradually depleted, but also because pollution of the environment, caused by the increasing use of energy, must be reduced. This article intends to overview the results of plant biomass processing methods that are currently in use. Our aim was also to review published methods that are not currently in use. It is intended to explore the possibilities of new methods and enzymes to be used in biomass recycling. The results of this overview are perplexing in almost every area. Advances have been made in the pre-treatment of biomass and in the diversity and applications of the enzymes utilized. Based on molecular modeling, very little progress has been made in the modification of existing enzymes for altered function and adaptation for the environmental conditions during the processing of biomass. There are hardly any publications in which molecular modeling techniques are used to improve enzyme function and to adapt enzymes to various environmental conditions. Our view is that using modern computational, biochemical, and biotechnological methods would enable the purposeful design of enzymes that are more efficient and suitable for biomass processing.

High-solids enzymatic hydrolysis of ball-milled corn stover with reduced slurry viscosity and improved sugar yields

BACKGROUND

High-solids enzymatic hydrolysis has attracted increasing attentions for the production of bioethanol from lignocellulosic biomass with its advantages of high product concentration, water saving, and low energy and capital costs. However, the increase of solids content would worsen the rheological properties, resulting in heat/mass transfer limitation and higher mixing energy. To address these issues, ball milling was applied to corn stover prior to enzymatic hydrolysis, and the rheological behaviors and digestibility of ball-milled corn stover under high-solids loading were investigated.

RESULTS

Ball milling significantly modified the physicochemical properties of corn stover. The apparent viscosity of slurries at 30% solid loading decreased by a factor of 500 after milling for 60 min, and the yield stress was less than 10 Pa. The dramatic decrease of viscosity and yield stress enabled the hydrolysis process to be conducted in shake flask, and remained good mixing. Meanwhile, the estimated energy consumption for mixing during saccharification decreased by 400-fold compared to the untreated one. The resultant hydrolysate using 10 FPU g^-1 solids was determined to contain 130.5 g L^-1 fermentable sugar, and no fermentation inhibitors were detected.

CONCLUSIONS

The proposed ball milling pretreatment improved rheological behavior and sugar yield of high-solids corn stover slurry. Ball milling enables high-solids slurry to maintain low viscosity and yield stress while obtaining a non-toxic high-concentration fermentable syrup, which is undoubtedly of great significance for inter-unit processing, mixing and downstream process. In addition, the energy input for ball milling could be balanced by the reduced mixing energy. Our study indicates ball milling a promising pretreatment process for industrial bioethanol production.