Study On The Bio-enzyme Treatment To Improve The Performance Of Reconstituted Tobacco Sheet And Its Mechanism

Under the background of strict carbon reduction policies and serious shortage of fiber resources,papermaking reconstructed tobacco sheets(RTS)have received widespread attention as a product of resource utilization of tobacco wastes.It has the advantage of high control performance,and can improve the quality of RTS by regulating the coating solution and RTS.In order to improve the running performance and physical properties of the paper machine during the paper-making process of RTS,wood pulp fibers(softwood pulp and hardwood pulp,etc.)will be added to the pulp.However,the addition of wood pulp will affect the smoking quality of RTS.In order to improve the smoking taste of RTS,there are two ways to reduce the damage of wood pulp to the smoking quality of RTS.One way is to prepare RTS pulp by co-refining the mixed soaking wood pulp,tobacco leaf scraps and tobacco stem pulp.Another way is to replace part of the wood pulp with tobacco-based cellulose nanofibril(TCNF).This topic mainly focuses on the papermaking RTS raw materials prepared from tobacco stem and tobacco leaf scraps,which include extract,pulp and TCNF.The main research contents and results are as follows:(1)The tobacco extract is prepared by ultrasound-assisted enzymatic hydrolysis process using tobacco leaf scraps as raw material.The extraction rate and aroma component content of the tobacco extract was mainly investigated.After ultrasound-assisted enzymatic hydrolysis,the total aroma components content in tobacco extracts was increased by 5.0times compared with that in aqueous extracts,and the total extraction yield was increased by51.57%.Moreover,other compositions in tobacco extracts,including total sugar,nicotine,lignin,total phenols,formic acid and acetic acid were also increased.The concentrate prepared by this method has good total oxidation resistance and reducing ability,which is helpful to reduce the harm of smoking.Therefore,ultrasound-assisted enzymatic hydrolysis can be considered as a method to obtain high-quality tobacco extraction,which can provide a new method for improving the aroma and quality of RTS.(2)Tobacco stem pulp was prepared by enzymatic pretreatment and PFI refining.Then,the prepared tobacco stem pulp,tobacco leaf scraps and bleached softwood pulp was as raw material to produce the co-refined pulp(CRs pulp).The fiber morphology,physical strength and thermal cracking performance of CRs pulp and sieve fraction were mainly studied.Co-refining process is a method of refining with several kinds of raw materials.It can simplify the stock preparation process,reduce energy consumption and improve properties of pulp.Compared with the separated refining pulp(SRs pulp),the sieve fractionation of CRs pulp fiber was significantly changed and the pulp uniformity was better,among which the short fiber content was increased by 34.34%,and the long fiber and fine fiber content decreased by 11.43%and 42.88%,respectively.Therefore,CRs pulp has a lower beating degree and a higher drainage speed.Compared with SRs sheets,CRs sheets has more cellulose intra-molecular hydrogen bonding force,which can indicate it has a more uniform surface and better strength performance.In the thermal cracking products of CRs sheet,the content of nicotine in CRs sheets was reduced by 97.01%and the contents of 5-methylfurfural,2(5H)-furanone,furanol and 5-hydroxymethylfurfural were increased by 2.56%,13.04%,20.16%and 25.27%,respectively.Therefore,co-refining process can be used to protect the fiber and improve physical properties of the RTS sheets.It further can be used to reduce the nicotine content in the RTS.(3)TCNFs with different properties was prepared by cellulase,ferulic acid esterase/cellulase and TEMPO oxidation pretreatment combined with PFI milling and high-pressure homogenization treatment.The tobacco stem pulp was as raw materials.The influence of biological enzymes on hydrolysis efficiency and high-pressure homogenization effect was mainly explored.Then,the effect of different properties TCNF instead of part of wood pulp to prepare RTS on the physical properties of RTS was studied.It can be found that ferulic acid esterase(FAE)can increase the accessibility of the cell wall by hydrolyzing the ester bonds between ferulic acid and polysaccharides,which can increase the accessibility of polysaccharides for cellulase.The pulp pretreated by FAE and cellulase has a reduction in fiber length,fiber width,DP and hydrogen bonding,which can facilitate subsequent PFI refining and high-pressure homogenization treatment for TCNF preparation.The obtained TCNF by FAE/cellulase U0 pretreatment displays a uniform particle size(diameter,41.6 nm),a desirable morphology,high stability and well-dispersed colloids.Then,the prepared TCNF(0.5 wt%)was further utilized in the RTS preparation to reduce the proportion of wood pulp(7 wt%,from 25wt%to 18wt%).The tensile index(15.383 N·m/g)and bursting index(0.692k Pa·m~2/g)of RTS with 0.5 wt%TCNF are similar to those of the control group(RTS-25/0)and bursting index(0.694 k Pa·m~2/g).(4)In order to improve the performance of TCNF,using tobacco stem pulp and softwood pulp as raw materials,tobacco and softwood based cellulose nanofiber(TSCNF)was prepared by FAE/cellulase pretreatment combined with mechanical process(PFI milling and high-pressure homogenization treatment).The influence of mixed preparation on energy consumption and the main performance of TSCNF were mainly studied.It is found that mixed preparation process can save the total energy consumption(refining and homogenization energy consumption)in the preparation process of TSCNF.When the softwood pulp content was 50%,the total energy consumption was the lowest,which was27.05 k W·h/kg.Compared with CNF obtained from tobacco stem pulp and softwood pulp,the total energy consumption was decreased by 58.20%and 48.51%,respectively.The TSCNF prepared by mixed pulp,including 50%softwood pulp and 50%tobacco stem pulp,combines the advantages of SCNF and TCNF.Thus,it has a uniform particle size,good morphology and good colloidal stability.It can improve the strength of RTS,and its tensile index and bursting index were 18.08 N·m/g and 0.728 k Pa·m~2/g,respectively.(5)TSCNF was used to prepare a thermal conductive composite material for heat not burning.The thermal conductivity,thermal stability and mechanical properties of this composite were studied.It was found that the addition of silver nanowire(Ag NWs)and boron nitride nanosheet(BNNS)fillers and the increase of TCNF content were beneficial to improve the thermal conductivity and thermal stability of the composites.When the TCNF content of TSCNF was 50%,the in-plane and through-plane thermal conductivity of the composites were 33.667 W/(m·K)and 0.275 W/(m·K),respectively.It shows that the existence of filler and lignin particles greatly enriches the heat conduction channels of the composites,thereby improving the thermal conductivity of the composites.Moreover,the heat dissipation performance of TSCNF/BNNS/Ag NWs(TBA)composites was also better.At this time,the tensile strength and elongation at break of the composite were 64.32 MPa and 3.036%,respectively.In this paper,ultrasound-assisted enzymatic hydrolysis method was used to improve the extraction rate and the content of aroma component in the tobacco extract.The mixed pulp was used to protect the tobacco leaf scraps fiber effectively,improve the uniformity of the mixed pulp and the strength of RTS base paper,and clarify the strengthening mechanism.TCNF and TSCNF were prepared by enzyme-mechanical method to improve the properties of RTS base paper.The obtained TSCNF were applied to heat conduction composites.The results can promote the performance of RTS and strengthen the resource utilization of tobacco wastes.