Process Optimization And Structure Study Of Microcrystalline Cellulose Prepared From Different Raw Materials

Microcrystalline cellulose(MCC)is a cellulose derivative which is purified and partially depolymerized by treating ?-cellulose in cellulose plant material,and is also a bio-based material has been widely used in medicine,food,cosmetics and other industries,and the application market is broad.Chinese medicine residue and distiller's grains are lignocellulosic biomass rich in cellulose polysaccharide,with a cellulose content of more than 22%,which has the potential to prepare microcrystalline cellulose.In this study,the traditional Chinese medicine slag and distiller's grains are used as raw materials,and the crude fiber is obtained by extraction with ethanol and then hydrolyzed by hydrochloric acid to obtain MCC product.The preparation parameters of microcrystalline cellulose were optimized by response surface methodology.The structural changes of cellulose in the preparation process were investigated by scanning electron microscopy,infrared spectroscopy,X-ray diffraction and thermogravimetric analysis.On this basis,the structural characterization and comparative analysis of MCC products prepared from different raw materials were carried out.The product was compared with the commercial MCC(Lowa?PH101)in terms of purity,degree of polymerization(DP),morphology,crystallinity,crystal structure and thermal properties.The main findings are as follows:The liquid-solid ratio was 26.9:1 mL/g,and the distiller's grains were pretreated with ethanol nitrate at a temperature of 72.3? for 105.3 minutes.The yield and purity of the crude fiber were the highest,33.00% and 83.97%,respectively.The optimum process for preparing MCC from hydrochloric acid hydrolysis of crude fiber was: 2 hours,temperature 72.3? and hydrochloric acid concentration 7.5%,liquid-solid ratio 20:1 mL/g.Under this condition,the MCC yield was 89.25%,the purity was 92.57%.The yield of MCC and DP were 29.45% and 276.39 respectively.The purity of the further bleached distiller's grains MCC rose to 93.31%,and the DP decreased to 255.86,which was close to the DP(244.69)of Lowa?PH101.Scanning electron microscopy analysis of the microscopic morphology showed that the distiller's grains MCC was irregularly granulated with a small amount of fiber fragments,and Lowa?PH101 was stacked in layers.Infrared spectroscopy analysis showed that the molecular structure of crude fiber and MCC did not change compared with the raw material of distiller's grains,and the molecular structure of cellulose was consistent with the infrared spectrum of Lowa?PH101.X-ray diffraction analysis showed that the MCC was type I cellulose structure,and the crystallinity was 67.49%,which was lower than that of Lowa?PH101(71.58%).Thermogravimetric analysis showed that the process of preparing MCC by ethanol pretreatment and acid hydrolysis gradually increased the stability of cellulose,while the stability of MCC after bleaching treatment decreased slightly.The liquid-solid ratio was 34:1 mL/g,and the temperature of the traditional Chinese medicine slag was pretreated by nitric acid ethanol at a temperature of 86.5? for 109 minutes.The highest yield and purity of the extracted crude fibers were 39.90% and 84.55%,respectively.Under the optimum conditions of temperature 71.5 ?,concentration of hydrochloric acid 6.9%,liquid-solid ratio 20:1 mL/g,hydrochloric acid hydrolyzed crude fibers for 1.5 h.The yield and purity of MCC from traditional Chinese medicine residue were 87.43% and 94.32%,respectively.The final yield of MCC was 34.88% and DP was 220.58,which was smaller than the DP of the Lowa?PH101(244.69).Scanning electron microscopy analysis of the microscopic morphology showed that the traditional Chinese medicine slag MCC had an irregular sheet-like structure,while the Lowa?PH101 was stacked in layers.Infrared spectroscopy analysis showed that the molecular structure did not change during the purification of traditional Chinese medicine slag,and it had the molecular structure characteristics of cellulose,which was consistent with the infrared spectrum of Lowa?PH101.X-ray diffraction analysis showed that the MCC of Chinese medicine residue was type I cellulose structure,and the crystallinity was 68.32%,which was lower than that of Lowa?PH101(71.58%).Thermogravimetric analysis showed that the thermal stability of traditional Chinese medicine slag MCC increased after pretreatment and acid hydrolysis to remove lignin,hemicellulose and other non-crystalline components,but lower than Lowa?PH101.This paper compares the structural characteristics of distiller's grains MCC,Chinese medicine residue MCC and Lowa?PH101.The three samples had different onlookers and had the molecular structure of cellulose I.The crystallinity was 67.49%,68.23% and 71.58,respectively.The initial weight loss temperatures of the three samples were 208.11?,299.05? and 319.76?,respectively.The corresponding temperatures with the fastest weight loss rate were 321.1?,330.55? and 354.98?,respectively.The thermal stability of the vinasse MCC was greater than that of the traditional Chinese medicine slag MCC,and the Lowa?PH101 was the worst.NMR showed that the crystal structure of traditional Chinese medicine residue MCC was the most complete,followed by Lowa?PH101,and the smallest MCC.The MCC products prepared by using the distiller's grains and Chinese medicinal slag respectively had different microstructures,and there were certain differences in crystallinity and thermal stability.This result laid a foundation for the investigation of the mechanism of preparation of MCC,the selection and optimization of preparation methods and their application.