Zuqiang Huang

A green and efficient technology for the degradation of cellulosic materials: structure changes and enhanced enzymatic hydrolysis of natural cellulose pretreated by synergistic interaction of mechanical activation and metal salt.

A new technology for the pretreatment of natural cellulose was developed, which combined mechanical activation (MA) and metal salt treatments in a stirring ball mill. Different valent metal nitrates were used to investigate the changes in degree of polymerization (DP) and crystallinity index (CrI) of cellulose after MA+metal salt (MAMS) pretreatment, and Al(NO3)3 showed better pretreatment effect than NaNO3 and Zn(NO3)2. The destruction of morphological structure of cellulose was mainly resulted from intense ball milling, and the comparative studies on the changes of DP and crystal structure of MA and MA+Al(NO3)3 pretreated cellulose samples showed a synergistic interaction of MA and Al(NO3)3 treatments with more effective changes of structural characteristics of MA+Al(NO3)3 pretreated cellulose and substantial increase of reducing sugar yield in enzymatic hydrolysis of cellulose. In addition, the results indicated that the presence of Al(NO3)3 had significant enhancement for the enzymatic hydrolysis of cellulose.

Green mechanical activation-assisted solid phase synthesis of cellulose esters using a co-reactant: effect of chain length of fatty acids on reaction efficiency and structure properties of products

Esterification is an important chemical modification for the preparation of natural cellulose-based materials. However, esterification of cellulose is commonly carried out in organic solvents, which reduces the economic and environmental feasibility of the synthetic technologies. Herein we report a novel technology for the production of cellulose esters, which combines mechanical activation (MA) and esterification in a stirring ball mill under solid phase conditions without the use of solvents. With the use of acetic anhydride as co-reactant and fatty acids as long chain esterifying agents, 1H and 13C NMR measurements confirmed that both acetyl and long chain fatty acyl groups were successfully grafted on cellulose by the technology of MA-assisted solid phase synthesis (MASPS). The factors which contributed to the successful preparation of cellulose esters were: the formation of highly reactive mixed acetic-long chain fatty acid anhydride, the generation of active hydroxyl groups in cellulose, the weakening of the steric effect of long chain fatty acids, and the improved contact between reagents and cellulose which were first induced by intense milling. It also showed that the reactivity of fatty acids and the degree of substitution (DS) of fatty acyls decreased with the increase in their chain length, and the long chain fatty acylium ions preferred to react with the more reactive hydroxyl group in the anhydro glucose unit of cellulose. Moreover, Fourier transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy analyses were used to measure the changes in chemical structure, crystal structure, and surface morphology of the cellulose before and after esterification by MASPS, respectively. The results indicate that this green, simple, and efficient technology is suitable for the direct production of cellulose esters with long chain substituents.

Structural changes and enhanced accessibility of natural cellulose pretreated by mechanical activation

A kind of natural cellulose, bleached pine pulp (BPP), was pretreated by mechanical activation (MA) using a self-designed stirring ball milling. The effect of MA pretreatment on the dissolving capacity and molecular chain structure of BPP were investigated by the determination of alkaline solubility (Sa) and degree of polymerization (DP). In addition, the changes in crystal structure of MA-pretreated BPP with different milling times were qualitatively and quantitatively measured by X-ray diffraction and Fourier transform infrared spectroscopy, and the morphology modification was observed by scanning electron microscopy. It was found that MA significantly increased the Sa and reduced the DP of BPP, contributing to the destruction of inter- and intramolecular hydrogen bonds and macromolecular chains in cellulose. The stable crystal structure of BPP was also remarkably damaged during MA processing, resulting in the variation of surface morphology, the increase of amorphous region ratio and hydrogen bond energy, and the decrease in crystallinity and crystalline size, which efficiently increased the accessibility of natural cellulose and would have positive effects on subsequent treatments. The crystalline form of natural cellulose was not changed by MA, and no new functional groups generated during milling.

Synthesis and properties of novel superabsorbent hydrogels with mechanically activated sugarcane bagasse and acrylic acid

The aim of this study was to develop a sugarcane bagasse (SCB)-based biodegradable superabsorbent hydrogels (SAH) with a good swelling. To this end, SCB was firstly mechanically activated by home-made high efficiency stirring mill to enhance its reactivity by breaking the lignin seal and decreasing crystallinity of cellulose in SCB. Then, the SAH were synthesized by graft copolymerization of acrylic acid (AA) onto SCB with different mechanical activation times (tM) by using ammonium persulfate/sodium sulfite redox pair as an initiator in the presence of a crosslinker (N,N′-methylenebisacrylamide, MBAAm). The effect of tM on the equilibrium swelling capacity (Qeq), swelling kinetics of the SAH in deionized water, as well as the influences of pH, electrolytic media, and temperature on Qeq were studied. In addition, the products were characterized by scanning electron microscopy and differential scanning calorimetry. The results showed that mechanical activation promoted the graft copolymerization and thereby altered the Qeq of the SAH. The swelling process of the SAH exhibited anomalous swelling behavior and first-order dynamics, and the Qeq of the SAH was pH, salt, and temperature dependent.

A green technology for the synthesis of cellulose succinate for efficient adsorption of Cd(II) and Pb(II) ions

Cellulose succinate, which was used for efficient adsorption of heavy metals, was directly prepared by mechanical activation (MA)-assisted solid-phase synthesis in a stirring ball mill with bagasse pulp and succinic acid as materials without the use of organic co-reagents and solvents. FTIR, XRD, SEM, and specific surface area analysis were used to characterize the structural characteristics of cellulose succinate. Furthermore, the effects of different degrees of esterification of modified cellulose on the adsorption of Cd2+ and Pb2+ were investigated. A surface charge characteristic was used to prove the effect of pH on the adsorption ability of cellulose succinate. It was found that the adsorption kinetics of Cd2+ and Pb2+ onto cellulose succinate fitted well with the pseudo-second-order model. The adsorption of Cd2+ and Pb2+ onto cellulose succinate was well described by the monolayer adsorption of the Langmuir isotherm model rather than the multilayer adsorption of the Freundlich isotherm model. The E values for the adsorption of Cd2+ and Pb2+ by cellulose succinate calculated by the Dubinin–Radushkevich equation were all in the range of 8–16 kJ mol−1, suggesting that the adsorption process mainly proceeded by ion exchange. The MA-assisted solid-phase synthesis method can produce efficient and environmental-friendly adsorbents.

Effect of mechanical activation on structure changes and reactivity in further chemical modification of lignin

Lignin was treated by mechanical activation (MA) in a customized stirring ball mill, and the structure and reactivity in further esterification were studied. The chemical structure and morphology of MA-treated lignin and the esterified products were analyzed by chemical analysis combined with UV/vis spectrometer, FTIR,NMR, SEM and particle size analyzer. The results showed that MA contributed to the increase of aliphatic hydroxyl, phenolic hydroxyl, carbonyl and carboxyl groups but the decrease of methoxyl groups. Moreover, MA led to the decrease of particle size and the increase of specific surface area and roughness of surface in lignin. The reactivity of lignin was enhanced significantly for the increase of hydroxyl content and the improvement of mass transfer in chemical reaction caused by the changes of molecular structure and morphological structure. The process of MA is green and simple, and is an effective method for enhancing the reactivity of lignin.

Photoluminescent carbon dots derived from sugarcane molasses: synthesis, properties, and applications

Carbon dots (C-dots) were prepared through a simple, environmentally friendly hydrothermal method, with the use of sugarcane molasses derived from industrial waste as the carbon source. The C-dots were characterized via X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), and UV-vis absorption spectroscopy, as well as fluorescence spectroscopy. The C-dots exhibited a spherical shape with a diameter of around 1.9 nm, and emitted blue photoluminescence with a quantum yield of approximately 5.8%. The effects of pH, sodium chloride (NaCl), amino acids and metal ions on the photoluminescence were further investigated. Not only was the biocompatibility of the C-dots assessed in vitro and in vivo, but also their bioimaging ability was observed in MCF-7 cells. The effect of C-dots on secondary structure of bovine serum albumin (BSA) was investigated. Additionally, it was found that the fluorescence intensity of the C-dots decreased after addition of Fe3+ or sunset yellow. Furthermore, the underlying mechanism of fluorescence quenching was proposed in the C-dots/sunset yellow system.

Tribological properties of nano cellulose fatty acid esters as ecofriendly and effective lubricant additives

Three cellulose esters, cellulose acetate-butyrate, cellulose acetate-octanoate, and cellulose acetate-laurate, were synthesized by both conventional co-reactant reaction (CCR) and mechanical activation-assisted co-reactant reaction (MACR) methods, and the corresponding nano-cellulose esters were prepared by high pressure homogenization to comparatively investigate their tribological properties as lubricant additives in liquid paraffin base oil. MACR method was more effective than CCR method for preparing long chain cellulose esters, and the MACR-prepared cellulose esters were more easily homogenized to smaller nanoparticles. Tribological testing indicated that anti-wear and load-carrying properties of the lubricants were significantly enhanced with nano-cellulose esters as additives compared to those of pure liquid paraffin, especially the MACR-prepared long chain cellulose esters. The wear scar diameter on worn surface of the steel balls reduced with the increase in degree of substitution (DS) and chain length of long chain substituents and the decrease in size dimension of nano-cellulose esters. The polar ester carbonyl groups, unesterified hydroxyl groups, and long hydrocarbon alkyl chains in nano-cellulose esters could lead to the formation of a film layer in the steel/steel contact surfaces for protecting the metals from friction and wear, which gave the lubricants with good anti-wear and load-carrying properties. The nano-cellulose esters with high DS and long chain substituents prepared by MACR technology as ecofriendly additives exhibited better lubricating ability.Graphical abstractNano-cellulose esters with high DS of long chain substituents prepared by mechanical activation-assisted co-reactant reaction technology used as ecofriendly lubricant additives in base oil showed good anti-wear and load-carrying properties, ascribing to the formation of a film layer in the steel/steel contact surfaces for protecting the metals from friction and wear.

Esterification mechanism of lignin with different catalysts based on lignin model compounds by mechanical activation-assisted solid-phase synthesis

In order to learn about the esterification mechanism of lignin by mechanical activation-assisted solid-phase synthesis (MASPS) technology, lignin model compounds, p-hydroxy benzaldehyde (H), vanillin and vanillyl alcohol (G), and syringaldehyde (S), were used in the reaction with acetic anhydride, with 4-dimethyl amino pyridine (DMAP), sodium acetate, and sulfuric acid as catalysts. FTIR, NMR, and UV/vis analyses of the products showed that all of the catalysts could enhance the esterification. Both the phenolic hydroxyl and aliphatic hydroxyl participated in the esterification and the reactivity of the basic structural units of lignin had a descending order of H, G, and S. Oxidations could happen in the presence of unsaturated groups such as aldehyde in the lignin model compounds. The catalytic mechanism of the three kinds of catalyst was different, and the catalytic activity had a descending order of DMAP, sodium acetate, and sulfuric acid. The reactivity of phenolic hydroxyl was higher than that of aliphatic hydroxyl with DAMP as the catalyst, but the reactivity of aliphatic hydroxyl was higher than that of phenolic hydroxyl with sodium acetate or sulfuric acid as the catalyst. With sulfuric acid as the catalyst, some side reactions took place and resulted in the ring cleavage or cross-linking of the benzene ring. Consistency verification indicated that the use of lignin model compounds for studying the esterification mechanism of lignin was reasonable and feasible.

Esterification of bagasse cellulose with metal salts as efficient catalyst in mechanical activation-assisted solid phase reaction system

The present study focused on investigating the catalytic mechanism of metal salts (sodium hypophosphite, sodium bisulfate and ammonium ferric sulfate) for esterification of bagasse cellulose carried out by mechanical activation-assisted solid phase reaction in a stirring ball mill. FTIR analysis of the products confirmed that these metal salts could catalyze the esterification of cellulose. XRD, SEM, FTIR, and 31P-NMR analyses of different samples indicated a synergistic effect between metal salt and ball milling, and the presence of metal salts enhanced the destruction on crystal structure of cellulose by mechanical force. The catalytic mechanism of three metal salts was difference: sodium bisulfate and ammonium ferric sulfate belonged to the catalytic mechanism of protonic acid and Lewis acid, respectively, while the catalytic mechanism of sodium hypophosphite was considered as that it could react with maleic acid to form active intermediates under ball milling.