Preparation And Application Of Nanometer Cellulose Whiskers Based On Supercritical Carbon Dioxide/Ethanol Pretreatment

Microcrystalline cellulose?MCC?is an excellent new type of Nano-scale functional material with diameter of less than 100 nm and length of 300 nm 3000 nm,because of its large specific surface area,biocompatibility and biodegradability Therefore,it is widely used in food,Nano-paper,aerogel,composite materials,papermaking,medicine and other fields.Since cellulose,lignin and hemicellulose are closely cross-linked to form a "natural anti-degradation barrier" in the supramolecular structure of natural fiber and the cellulose supramolecular structure has an ordered crystalline structure,it is difficult to prepare Nano cellulose whiskers directly through mechanical refining achieve.In this dissertation,the subcritical CO₂ / ethanol pretreatment system was used to catalyze the disassembly of the superfamily structure of natural fiber materials.The structure change of MCC under CO₂ and acid catalysis was studied in subcritical ethanol environment.The effects of pretreatment Environmental conditions were discussed to get the best MCC pretreatment process conditions in the supercritical carbon dioxide pretreatment,the solid yield was higher,the amorphous region is also effectively removed,the use of FTIR analysis of changes in the characteristics of cellulose chemical structure.The morphology of cellulose supramolecular structure was characterized by SEM.The change of crystallinity of cellulose was analyzed by X-ray diffraction.The TG was used to reflect the change of thermal stability.The experimental results show that the catalyst and temperature have the greatest impact on the pretreatment.The MCC has the highest crystallinity at 135 ? and 30 min after being pretreated by supercritical carbon dioxide.The pretreatment effect is too short when the temperature is too low and the temperature is too high,Lower yield,crystallinity also declined,are not conducive to pretreatment.Scanning electron microscopy showed that the particle size of MCC decreased significantly after pretreatment,the specific surface area increased,and the chemical structure remained unchanged,the crystallinity increased,and the thermal stability improved.On the basis of this,the preparation of a polyvinyl alcohol film is advantageous.The Nano-crystallite whisker?Nano cellulose whiskers,NCWS?was used in polyethylene membrane.In the preparation of polyethylene film,the NCWS is enhanced and the strength of polyethylene film is improved effectively.In this experiment,the effect of different content of microcrystalline cellulose?MCC?on the properties of polyvinyl alcohol?PVA?thin films was studied by adding NCWS solids with different contents?0%,2%,6%?,and the method of determining the color and.The influence of optical properties,mechanical properties and surface microscopic morphology.Results with the increase of NCWs content,the transmittance and elongation of PVA films decreased significantly,compared with pure PVA films,the tensile strength of PVA film with NCWs mass fraction of 6% was increased,the elongation of rupture increased insignificantly,and when the NCWs mass fraction was 6%,a small number of large particles can be observed in the local area of thin film surface and transverse truncated surface.In conclusion,the addition of NCWs improves the mechanical properties and hydrophobicity of PVA films,and can improve the properties of PVA film effectively.