Ball-milled Cellulose Research Articles

Highly efficient hydrolysis of cellulose to sugars using supercritical CO2 as a green acid catalyst and solvent

Rapid depolymerization of cellulose into processable monomers (e.g., sugars) using solid acid catalysts is an important step for cost-effective biofuel and biochemical production, but has not yet been achieved due to the limited contact between solid cellulose and solid catalysts. Herein, the unique roles of supercritical CO2 (i.e., scCO2) as an in-situ acid catalyst and reaction solvent in achieving the ultra-fast full solid catalytic hydrolysis of cellulose are disclosed for the first time. When the ball-milling pretreated cellulose was hydrolyzed using oxidized carbon catalysts at 150 °C and 100–300 bar-CO2, the hydrolysis kinetics remarkably increased by 3× for conversion and 5× for glucose, resulting in ∼90% conversion and ∼85% total sugar selectivity at 20 min. The hydrolysis rate obtained with scCO2 here was higher than conventional ones with toxic and unrecyclable homogeneous catalysts (e.g., HCl) under harsh reaction conditions (i.e., 180–220 °C and pH of 1–2). A comprehensive reaction engineering study (e.g., temperature, CO2 pressure, stirring speed, catalyst acid properties) combined with the estimation of the solution pH by the CO2 phase equilibrium model and the in-situ and ex-situ monitoring of the phase behavior of the H2O/scCO2 solution were conducted to quantify the activity promotion by scCO2 and understand the acid-solvent roles of scCO2 toward the enhanced hydrolysis of cellulose. Specifically, the formation of the Pickering emulsions at the interface between scCO2 and water and their impact on the enhancement of the cellulose-carbon contact were proposed and verified in detail.

Preparation of hydrogels with self-reinforced mechanical properties using ball-milled microcrystalline cellulose and regenerated cellulose from deep eutectic solvent

Choline chloride–lactic acid deep eutectic solvent assisted by ball milling effectively dissolved microcrystalline cellulose. Regenerated cellulose was used to prepare novel cellulose hydrogel with self-reinforced mechanical properties.

Efficient one-pot conversion of cellulose to sorbitol over Ni-based carbon catalysts with embedment structure

The solid catalyst for one-pot hydrolysis hydrogenation of cellulose with remarkable activity and stability has aroused increasing attention. Herein, a highly active and stable Ni based bimetallic carbon catalyst with embedment structure was prepared by a facile one-pot thermal reduction method with assistant of ethylene glycol dispersant. The effects of the metal precursor, dispersant, and noble metal doping were systematically addressed. The bimetallic Ni-Ru@MC exhibited higher catalytic capability in sorbitol production from ball-milled cellulose with yield of 67.8 % at 200 °C within 3 h, in comparison with the traditional metal supported catalysts such as Ru/MC and Ni/MC. The various characterization techniques revealed that the superior catalytic performance of Ni-Ru@MC was associated with its mesoporous structure with large surface area, small metal nanoparticles embedded in carbon, and especially a reasonable match between mild acidity and improved hydrogenation activity of catalyst. Significantly, after five consecutive cycles, the catalyst still maintained the similar metal content and the catalytic ability to fresh catalyst, owing to its distinctive embedment structure and helpful Ru doping.

Characterization of a GH Family 43 β-Xylosidase Having a Novel Carbohydrate-binding Module from Paenibacillus xylaniclasticus Strain TW1.

Paenibacillus xylaniclasticus strain TW1, a gram-positive facultative anaerobic bacterium, was isolated as a xylanolytic microorganism from the wastes of a pineapple processing factory. A gene encoding one of its xylanolytic enzymes, a β-xylosidase, was cloned and sequenced. Sequence analysis revealed that this β-xylosidase, named PxXyl43A, was composed of a glycoside hydrolase (GH) family 43 subfamily 12 catalytic module and an unknown function module (UM). The full-length PxXyl43A (PxXyl43A) was heterologously expressed in Escherichia coli and purified. Recombinant PxXyl43A exhibited hydrolysis activity against both p-nitrophenyl-β-D-xylopyranoside (pNPX) and p-nitrophenyl-α-L-arabinofuranoside at specific activities of 250 and 310 mU/mg, respectively. The optimal reaction pH and temperature for pNPX hydrolysis were 7.1 and 54 ˚C, respectively. At pH 7.0 and 54 ˚C, the Km and kcat for pNPX were 1.2 mM and 2.8 ± 0.15 s-1, respectively. It was also discovered that the recombinant unknown function module of PxXyl43A (PxXyl43A-UM) could bind to insoluble xylans like birchwood xylan and oat spelt xylan, whereas it did not bind to cellulosic substrates such as ball-milled cellulose, carboxymethyl cellulose or lichenan. The PxXyl43A-UM's binding constant value Ka for oat spelt xylan was 2.0 × 10-5 M-1. These results suggest that PxXyl43A possesses a novel carbohydrate-binding module, named as CBM91, specific for xylan-containing polysaccharides.

Efficient Shaping of Cellulose Nanocrystals Based on Allomorphic Modification: Understanding the Correlation between Morphology and Allomorphs.

Cellulose nanocrystals (CNC) are green, safe, and renewable nanomaterials with a variety of excellent performances but their morphologies are notoriously difficult to control as this is unfavorable to the diversification of the end products. Allomorphic conversion plays an important role in diversifying the morphology of CNC. However, this further complicates the prediction, design, and control of the geometric dimensions of CNC. Herein, allomorphically modified cellulose (mercerized cellulose, ethylenediamine (EDA)-treated cellulose, and ball-milled cellulose) is designed and used as the starting material for CNC isolation. Subsequently, the morphological evolution of cellulose particles during acid hydrolysis is traced by scanning electron microscopy observations. A mechanism that facilitates further understanding of CNC shaping during sulfuric acid hydrolysis is proposed. According to the CNC shaping mechanism, precise prediction, design, and efficient control of the morphology of CNC (needle-like, ribbon-like, ellipsoid, and spherical) can be realized. CNC with various morphologies are favorable for their applications, such as templating synthesis of porous materials and Pickering emulsion dispersion.

Solid waste and graphite derived solar steam generator for highly-efficient and cost-effective water purification

Utilizing the clean and renewable solar energy to generate steam for wastewater purification or seawater desalination is a promising solution to the worldwide scarcity of fresh water. Herein, we report a highly-efficient, eco-friendly and cost-effective solar steam generator based on ball-milling graphite and cellulose fiber from waste paper. Ball-milling graphite/cellulose fiber composite aerogels are facilely developed via a freeze casting-drying method, endowing a featured vertically aligned porous structure. The fabrication of composite aerogels and the construction of evaporation systems take full advantages of recycled materials, contributing to the low cost and solid waste reclamation. High porosity, strong solar absorption, hydrophilicity and low thermal conductivity of the composite aerogels collectively contribute to a splendid solar evaporation rate of water as high as 1.61 kg m−2 h−1, with photothermal efficiency of ~90% under one sun illumination (1 kW m−2). Quantitative studies reveal the effects of ball-milling graphite/cellulose fiber ratio, ball-milling graphite concentration and thickness of composite aerogels on the solar evaporation rates, suggesting the optimal design of composite aerogels. Furthermore, the cycling stability and the capability for seawater desalination as well as polluted water purification manifest the potential of the composite aerogels to purify diverse water. Outdoor tests show 8–13 L of fresh water could be produced daily by 1 m2 of composite aerogel.

Tuning of polyurethane foam mechanical and thermal properties using ball-milled cellulose

Cystalline-Cc and ultra-milled Amorphous-Ca cellulose were used as reactive filler to tune the performances of composite polyurethane-cellulose-foams, PUC. The effect of Cc and Ca on chemo-physical and mechanical properties of PUC was analysed through FTIR, morphological analysis, thermal conductivity and compression measurements. FTIR results show that, both Cc and Ca react with isocyanate through the OH functional groups contributing to the formation of a tough cellulose-polyurethane network. Morphological observations show that the addition of both Cc and Ca induces a decrease of average cell-size compared to the pristine-PU, thus confirming that they act as nucleating agent. In addition, the better dispersion of the Ca in the polyol, with respect to Cc induces, a finer cell leading to a reduction of the thermal conductivity around 33 % (for the composite loaded with 20 %wt-Ca) with respect to pristine-PU. Finally, the addition of Ca highly reactive modifies the mechanical behaviour from rigid-brittle to semi-rigid.

Hydrolysis of cellulose and woody biomass over sustainable weak-acid carbon catalysts from alkaline lignin

Low-cost and sustainable weak-acid carbon catalysts were prepared from alkaline lignin (AL) by pyrolysis of AL followed by an acid solution treatment process, and applied for the hydrolysis of cellulose and woody biomass for the production of monomeric sugars such as glucose and xylose, which are important for production of industrial platform chemicals. The effect of pyrolysis temperature on the acidity of the final carbon catalyst was investigated. It is found that the AL-derived carbon catalysts at the pyrolysis temperature of 450 °C (denoted as AL-Py-450) exhibited the highest activity in the hydrolysis of ball-milled cellulose with a cellulose conversion of 70.8% and a glucose yield of 46.3% in a neat water reaction system. Furthermore, with the addition of 0.012 wt% hydrochloric acid (HCl) in the above reaction system, the cellulose conversion was increased to 96.1% with a glucose yield of 69.8%. In the same reaction conditions, the AL-Py-450 carbon catalyst also exhibited good catalytic activity for the hydrolysis of lignocellulosic biomass, i.e., Japanese cedar wood, with yields of glucose and xylose of 47.1% and 40.3%, respectively. Therefore, this study could provide a new perspective to utilize the wasted alkaline lignin as a source for the preparation of sustainable weak-acid carbon catalysts for the hydrolysis of cellulose and lignocellulosic biomass.

Coupled Pretreatment with Liquid Nitrogen and Ball Milling for Enhanced Cellulose Hydrolysis in Water.

A key problem in the conversion of cellulose into chemicals and fuels is the low product yield from cellulose due to its robust structure. In this work, for the first time, cellulose was pretreated with coupling of liquid nitrogen and ball milling (LN–BM) for cellulose hydrolysis. After the LN–BM treatment, the glucose yield from cellulose by HCl in water increased by almost 2 times and yield of formic acid catalyzed by H2SO4–NaVO3 was more than 3-fold that obtained from untreated cellulose. The yields were also much higher than that from the individually ball-milled cellulose. The structure variation of cellulose indicated that reduction of both crystallinity index and molecular weight contributed to improving the conversion efficiency, but the former was the dominant factor. The combination of liquid nitrogen and ball milling developed in this work is an effective and environment-friendly approach for cellulose pretreatment.

Hydrolysis of mechanically pre-treated cellulose catalyzed by solid acid SO42−-TiO2 in water–ethanol solvent

Abstract An efficient catalyst SO42−-TiO2 (ST) from industrial metatitanic acid has been successfully prepared to catalyze hydrolysis of ball-milling cellulose. The results show that the highest catalytic efficiency is obtained for ST calcined at 450 °C (ST-450) with the yield of 21.8% glucose, 13.0% 5-HMF and 4.2% furfural at 200 °C for 30 min. The ball milling of cellulose and solid acid catalyst significantly enhances the cellulose hydrolysis. The high Lewis to Bronsted acid sites ratio for ST-450 induced by bidentate ligands between SO42− and TiO2 benefits high organics yield, and high total acid sites contribute to the high cellulose conversion. The large pore volume of 0.29 cm3·g−1 and appropriate pore size of 7.35 nm of ST-450 also contribute to the high performance. High reaction temperature over 200 °C exhibits negative effect on glucose and 5-HMF yield due to undesired side reactions, while furfural product is stable in the reaction system. The bidentate ligands between SO42− and TiO2 are considered as active acid sites for cellulose hydrolysis in water–ethanol solvents.

CreA-independent carbon catabolite repression of cellulase genes by trimeric G-protein and protein kinase A in Aspergillus nidulans.

Cellulase production in filamentous fungi is repressed by various carbon sources. In our preliminary survey in Aspergillus nidulans, degree of de-repression differed depending on carbon sources in a mutant of creA, encoding the transcriptional repressor for carbon catabolite repression (CCR). To further understand mechanisms of CCR of cellulase production, we compared the effects of creA deletion with deletion of protein kinase A (pkaA) and G (ganB) genes, which constitute a nutrient sensing and signaling pathway. In plate culture with carboxymethyl cellulose and D-glucose, deletion of pkaA and ganB, but not creA, led to significant de-repression of cellulase production. In submerged culture with cellobiose and D-glucose or 2-deoxyglucose, both creA or pkaA single deletion led to partial de-repression of cellulase genes with the highest level by their double deletion, while ganB deletion caused de-repression comparable to that of the creA/pkaA double deletion. With ball-milled cellulose and D-glucose, partial de-repression was detected by deletion of creA but not of pkaA or ganB. The creA/pkaA or creA/ganB double deletion led to earlier expression than the creA deletion. Furthermore, the effect of each deletion with D-xylose or L-arabinose as the repressing carbon source was significantly different from that with D-glucose, D-fructose, and D-mannose. Consequently, this study revealed that PkaA and GanB participate in CreA-independent CCR and that contribution of CreA, PkaA, and GanB in CCR differs depending on the inducers, repressing carbon sources, and culture conditions (plate or submerged). Further study of CreA-independent mechanisms is needed to fully understand CCR in filamentous fungi.

An aggregated understanding of cellulase adsorption and hydrolysis for ball-milled cellulose

This study evaluated the effects of physicochemical properties of a series of ball-milled cellulose on cellulase adsorption and glucose yield. The relationship between cellulase adsorption and initial hydrolysis rate was also discussed. We found that hydrophobicity and surface charge are the key factors affecting cellulase adsorption on ball-milled cellulose. The results demonstrated that glucose yield had a positive correlation with specific surface area, while showed a negative correlation with particle size, degree of polymerization and crystallinity. Among these properties, specific surface area and crystallinity are the key factors affecting glucose yield. As ball milling progressed, cellulose showed lower enzyme adsorption capacity/amount of bound enzyme during initial stage of hydrolysis, but had higher initial hydrolysis rate. The enhanced rate is attributed to the fact that the amorphous region produced by ball milling reduces the free energy required for decrystallization thus increases the catalytic efficiency of the bound enzyme.

Enhanced hydrolysis of mechanically pretreated cellulose in water/CO2 system

The aim of this work was to study promotion of ball milling and CO2 assistance on cellulose hydrolysis kinetics in water medium. Kinetic behaviors were analyzed based on first-order and shrinking core models. The results showed that cellulose hydrolysis is enhanced by ball milling and CO2 assistance. Ball milling reduced crystallinity and particle size of cellulose, resulting in high cellulose conversion, while hydrolysis promoted by CO2 assistance was weaker. Double-layer hydrolysis was observed for ball-milled cellulose, and rate constant in active layer is higher. Based on double-layer shrinking core model (DL-SCM), activation energy of cellulose conversion decreased from 73.6 to 39.8 kJ/mol when ball milling and CO2 assistance were applied. Hydrolysis active layer was about 0.9 μm, representing activated thickness of ball-milled cellulose. Hydrolysis promotion by crystallinity and particle size reduction was distinguished via DL-SCM, and crystal evolution possesses greater improvement than particle size decrease on hydrolysis of ball-milled cellulose.

Facile Fabrication of 100% Bio-based and Degradable Ternary Cellulose/PHBV/PLA Composites.

Modifying bio-based degradable polymers such as polylactide (PLA) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) with non-degradable agents will compromise the 100% degradability of their resultant composites. This work developed a facile and solvent-free route in order to fabricate 100% bio-based and degradable ternary cellulose/PHBV/PLA composite materials. The effects of ball milling on the physicochemical properties of pulp cellulose fibers, and the ball-milled cellulose particles on the morphology and mechanical properties of PHBV/PLA blends, were investigated experimentally and statistically. The results showed that more ball-milling time resulted in a smaller particle size and lower crystallinity by way of mechanical disintegration. Filling PHBV/PLA blends with the ball-milled celluloses dramatically increased the stiffness at all of the levels of particle size and filling content, and improved their elongation at the break and fracture work at certain levels of particle size and filling content. It was also found that the high filling content of the ball-milled cellulose particles was detrimental to the mechanical properties for the resultant composite materials. The ternary cellulose/PHBV/PLA composite materials have some potential applications, such as in packaging materials and automobile inner decoration parts. Furthermore, filling content contributes more to the variations of their mechanical properties than particle size does. Statistical analysis combined with experimental tests provide a new pathway to quantitatively evaluate the effects of multiple variables on a specific property, and figure out the dominant one for the resultant composite materials.

Green Preparation of Cellulose Nanocrystal and Its Application

A green method was used to prepare cellulose nanocrystals (CNCs) with no use of harsh chemicals or organic solvents. This method was simple via ball milling cellulose with water followed by centrifugation. The diameter and length of the CNCs were 3–10 nm and 120–400 nm, separately, with a aspect ratio of 20–60. The yield was about 20%. The thermal stability of the CNCs was the same as that of raw cellulose owing to lacking of chemical modification. So it was superior to CNCs prepared by acid hydrolysis. Then poly(vinyl alcohol) (PVA)/CNC composite film was made by solution casting. The results showed that the tensile strength of the composite film was 79% increased from neat PVA film when adding 5% CNCs to the PVA matrix. In addition, the composite films possessed good transparency and thermal stability.

Catalysis performance comparison of a Brønsted acid H2SO4 and a Lewis acid Al2(SO4)3 in methyl levulinate production from biomass carbohydrates

An experimental investigation was conducted to understand the roles of the Brønsted acid H2SO4 and Lewis acid Al2(SO4)3 in methyl levulinate (ML) production from biomass carbohydrates, including glucose, fructose and cellulose. The product distributions with different catalysts revealed that the Lewis acid was responsible for the isomerization of methyl glucoside (MG), producing a significant amount of the subsequent product 5-methoxymethylfurfural (MMF), while the Brønsted acid facilitated the production of ML from MMF. Al2(SO4)3 was efficient for monosaccharide conversion but not for cellulose. Using ball-milled cellulose with Al2(SO4)3 resulted in a desired ML yield within a reasonable reaction time. The significant catalysis performances of two types of acids will guide the design of efficient catalytic processes for the selective conversion of biomass into levulinate esters.

Fracture Surface Morphology and Impact Strength of Cellulose/PLA Composites.

Polylactide (PLA)-based composite materials reinforced with ball-milled celluloses were manufactured by extrusion blending followed by injection molding. Their surface morphology from impact fracture were imaged with scanning electron microscopy (SEM) and investigated by calculating their fractal dimensions. Then, linear regression was used to explore the relationship between fractal dimension and impact strength of the resultant cellulose/PLA composite materials. The results show that filling the ball-milled celluloses into PLA can improve the impact toughness of PLA by a minimum of 38%. It was demonstrated that the fracture pattern of the cellulose/PLA composite materials is different from that of pristine PLA. For the resultant composite materials, the fractal dimension of the impact fractured surfaces increased with increasing filling content and decreasing particle size of the ball-milled cellulose particles. There were highly positive correlations between fractal dimension of the fractured surfaces and impact strength of the cellulose/PLA composites. However, the linearity between fractal dimension and impact strength were different for the different methods, due to their different R-squared values. The approach presented in this work will help to understand the structure–property relationships of composite materials from a new perspective.

High hexitols selectivity in cellulose hydrolytic hydrogenation over platinum (Pt) vs. ruthenium (Ru) catalysts supported on micro/mesoporous carbon

The “one-pot” hydrolyltic hydrogenation of cellulose towards C2-C6 sugar alcohols has been recognized as one of the most promising biomass valorization routes for the production of high added-value chemicals. In this work, we studied the performance of Ru and Pt catalysts supported on micro/mesoporous activated carbon, in the hydrolytic hydrogenation of microcrystalline and ball-milled cellulose, in neat water, at 180°C and at relatively low hydrogen pressure of 2MPa. The impact of metal loading (1–5wt.%), metal reduction method (H2 at 350°C or NaBH4) and acidification (sulfonation) of the AC support on cellulose conversion and selectivity to the various products were systematically addressed. It was shown that Pt is significantly more selective towards hexitols (sorbitol and mannitol) compared to Ru, in glucose-rich reaction media, such as those offered by the easily hydrolyzed ball-milled cellulose. For example, the 5wt%Pt/AC-SO3H catalyst afforded hexitols yield of 69.5wt.% (at 96.1% conversion) compared to 10.9wt.% (at 95.2% wt.% conversion) obtained by the corresponding Ru catalyst, the latter being also selective towards glycerol and propane-1,2-diol (propylene glycol). A relatively moderate metal loading, such as in 3wt.%Ru/AC-SO3H, was more favorable for hexitols production (44.5wt.% yield, at 94.8wt.% conversion) with Ru catalysts. These results were also verified by glucose hydrogenation experiments that were conducted at the same experimental conditions. Both Pt and Ru exhibited relatively high glucose hydrogenation activity towards hexitols, versus retro-aldol reactions that lead directly to smaller C2–C4 compounds, while the difference in the final product yields between the two metals was attributed to the higher hexitols hydrogenolysis (CC cleavage) reactivity of Ru. HRTEM data showed the formation of metallic crystalline Pt and Ru nanoparticles (≤4nm, depending on loading) as well as of amorphous oxygen-rich M(O)xδ+ phases, which were also confirmed by the XPS data. The presence of these phases which may be a source of acidity, as well as the bacisity of the parent AC used in this study, were mainly responsible for inducing isomerization, retro-aldol and dehydration reactions leading eventually to increased glycerol and propylene glycol selectivity, as was observed for both low-metal catalysts, i.e. 1wt.% Pt or Ru/AC.

Highly Selective Conversion of Cellobiose and Cellulose to Hexitols by Ru-Based Homogeneous Catalyst under Acidic Conditions

The catalytic transformation of the most abundant cellulose to valuable platform chemicals is one of the significant issues to overcome the shortage of fossil fuels. Herein, we reported the first example of Ru-based homogeneous catalyst for the highly selective conversion of cellobiose and ball-milled cellulose to hexitols (including sorbitol, mannitol, and 1,4-sorbitan) under an acidic condition with the yield of 94.5% and 56.4%, respectively. The main features of this catalytic system were the high conversion efficiency of biomass, mild reaction condition (100 °C), and low catalyst loading, which was 1/20 of the related Ru/C heterogeneous catalyst. This work opened up a new avenue for the transformation of cellulose to hexitols under mild conditions.

Impact of Ball-Milling Pretreatment on Pyrolysis Behavior and Kinetics of Crystalline Cellulose

Effect of ball-milling pretreatment on pyrolysis characteristics of cellulose was studied by thermogravimetric analysis (TGA) at four different heating rates; 5, 10, 20, and 40 K/min. Variation in the thermal stability and activation energy of cellulose with ball-milling were calculated by TGA Kinetics using Kissinger, Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa and Starink model free methods. Results demonstrated that ball-milling reduced the thermal stability and activation energy of cellulose. The original and ball-milled cellulose were thoroughly characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, and Scanning electron microscopy. X-ray diffraction analysis revealed that ball-milling decreased the crystallinity of cellulose from 93 to 51 %. The results suggested that ball-milling pretreatment led to effective disruption of crystalline cellulose to amorphous cellulose. It is, therefore, concluded that the ball-milled cellulose can easily become a useful source of chemicals and energy than crystalline cellulose.