Preparation Of Nanocellulose Aerogel And Its Application In Cigarette Filter

Due to the advantages of high specific surface area,low density,high porosity and regeneration,nanocellulose aerogels have shown broad application prospects in the fields of filtration,adsorption,thermal insulation and biomedicine,etc.The preparation and high value-added applications of nanocellulose aerogels are the research hotspots at home and abroad.In this thesis,bleached softwood pulp is used as raw material,and two technical routes of enzyme pretreatment-ball milling-homogenization and ultrafine grinding are used to prepare nanocellulose?CNF-B and CNF-G?.The physical and chemical properties of the nanocellulose prepared by the two methods were systematically analyzed and compared.Pure nanocellulose aerogel was prepared by directional freeze-drying of nanocellulose suspension,and the effects of nanocellulose morphology,structure and the concentration of nanocellulose on the microstructure and mechanical properties of aerogels were studied.Finally,composite aerogels?CSGs?were prepared by blending nanocellulose suspension with nanosilica?Si O₂?particles and then directional freeze-drying.The effect of the amount of nanosilica particles added on the physical and chemical properties of CSGs was explored.At the same time,CG and CSGs were applied to cigarette filters respectively,and the adsorption of CG and CSGs on the harmful components of smoke was discussed.The CG and CSGs prepared by directional freeze-drying have a regular sheet structure,which is beneficial to the flow of cigarette smoke and reduces the smoking resistance.This research provides new ideas for the high-value utilization of nanocellulose.?1?First,nanocellulose CNF-B was prepared by enzyme pretreatment-ball milling-homogenization,and the changes of physical and chemical properties such as fiber morphology,degree of polymerization,crystallinity and surface structure during the treatment process were analyzed.The results show that the fiber length,diameter,degree of polymerization and crystallinity show a downward trend with the increase of ball milling time.After the high-pressure homogenization treatment of the ball milled fiber,the fiber length is further shortened and the size becomes more uniform.Then,the nanocellulose CNF-G was prepared by ultrafine grinding,and the effects of the grinding disc gap and numbers of grinding passes on the fiber morphology,degree of polymerization,crystallinity and surface structure were analyzed.The results show that the CNF-G has a large aspect ratio and is highly entangled.With the reduction of the grinding disc gap and the increasing number of passes through mechanical grinding equipment,the fiber length,diameter,degree of polymerization and crystallinity gradually decrease,but the crystalline structure and surface structure of the fiber are not affected seriously.?2?Using the prepared CNF-B and CNF-G as raw materials,the effect of nanocellulose suspension concentration on the microstructure and mechanical properties of aerogel was studied.Because the CNF-B fibers are short and non-twisted,they cannot form a three-dimensional network structure,leading to the collapse of the prepared aerogel.The CNF-G has high aspect ratio and entangled,so the structure of the prepared aerogel is relatively regular.When the concentration of CNF-G suspension increased from 0.2%to1.0%,the prepared aerogel gradually became dense.The aerogel density increased from 2.22mg/cm³ to 10.10 mg/cm³,and the porosity decreased from 99.86%to 99.37%.The pore diameter of aerogel becomes smaller as the concentration of nanocellulose suspension increases,but its compression performance gradually increases.When the compressive strain is 80%,the compressive stress in the parallel to the ice crystal direction?perpendicular direction?is 0.51?69.82 k Pa.Pure nanocellulose aerogel was prepared by directional freeze-drying,the resulting aerogel exhibits anisotropy.The strength in the perpendicular direction is higher,and the compression recovery properties in the perpendicular to the ice crystal direction?axial direction?is better.The prepared pure nanocellulose aerogel?CG?were used to completely replace commercial cigarette filters and their adsorption effects on cigarette smoke were investigated.The results of the smoking experiment show that CG can significantly reduce the total particulate matter?TPM?,tar,nicotine and CO.?3?In order to further improve the adsorption effect of nanocellulose aerogel on cigarette smoke,CNF-G and nanosilica particles were blended in different proportions,directional pre-freezing with liquid nitrogen and then freeze-dried to prepare composite aerogel CSGs.The effect of the amount of Si O₂ added on the microstructure,mechanical properties,chemical structure and thermal stability of aerogel was studied.The results show that the addition of Si O₂ particles did not destroy the three-dimensional structure of the aerogel.When the amount of Si O₂ added increased from 0 to 80%,the CSGs aerogel gradually became dense.The aerogel density increased from 6.45 mg/cm³to 11.34 mg/cm³,and the porosity decreased from 99.44%to 99.59%.With the increase of the amount of Si O₂,the compression performance of CSGs gradually increased.When the amount of Si O₂ was 80%,the compression performance was slightly decreased due to the large amount of Si O₂deposited on the aerogel surface.When the compressive strain is 80%,the compressive stress in the perpendicular direction is 17.85?56.8 k Pa;the compressive strength in the axial direction is low,but the compression recovery properties is better than the perpendicular direction.X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared spectroscopy?FTIR?,X-ray diffraction?XRD?and X-ray energy spectroscopy?EDS?confirmed that Si O₂is physically deposited on the surface of the three-dimensional network structure formed by nanocellulose in CSGs,and there is no change in chemical structure.The addition of Si O₂will improve the thermal stability of CSGs.The prepared composite aerogel CSGs were used to completely replace commercial cigarette filters and their adsorption effects on cigarette smoke were investigated.The results of the smoking experiment show that CSGs can significantly reduce the TPM,tar,nicotine and CO,and with the increase of Si O₂ addition,the release of TPM,tar and nicotine gradually decreased.Compared with commercial cigarettes,the reduction rates of TPM,tar,nicotine and CO emissions were 30.6%?90.25%,35.1%?92.08%,49.32%?95.02%,9.37%?22.59%.This indicates that the effect of compound aerogel CSGs on retaining harmful components of smoke is very obviously,and It can be used as a choice of cigarette filter material.