Aimin 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.

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.

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.