Study On The Modification Of Jute Fibers Based On Steam-explosion Pretreatment And The Assistance Of ScCO₂

Plant fiber is the most abundant renewable resource in nature,with rich source,low cost,biodegradable,good compatibility and low density.However,most of them are used as fuel or naturally consumed except for a small part of the fiber used in papermaking,textile and chemical fiber,and the utilization rate is low.To make high value-added application of plant fiber,preparation of environmentally friendly composite materials through chemical modification is an important research and development direction.However,due to the high degree of crystallinity and the large number of hydrogen bonds of plant cellulose,and a complex aggregate structure of plant fiber,plant fiber have low reactivity and accessibility.Esterification and graft copolymerization are methods for the functionalization of plant fiber,but these methods usually require large amounts of organic solvents,polluted environment,high cost,and most of the modifications will lose the excellent performance of the plant fiber themselves.In this paper,a method for graft copolymerization/esterification of jute fiber based on steam explosion pretreatment and the assistance of scCO₂ was proposed.In this paper,the continuous screw extrusion steam explosion?CSESE?equipment independently designed and developed by our research group was used to pretreat the jute fiber,and the effect of CSESE pretreatment on subsequent chemical modification was investigated.The results showed that the size of JSE?jute fiber pretreated by CSESE?decreased from 70-100?m to 20-30?m,the specific surface area was increased significantly,and the availability and activity of the reaction were significantly improved.And the CSESE-pretreated plant fiber had high utilization rate and was environmentally friendly,efficient and suitable for industrial production.Jute fiber was modified by CSESE pretreatment and radical graft copolymerization,followed by hydrolysis of NaOH to prepare J-g-P?AM-co-AANa?.The results showed that the synthetic process parameters had an important influence on the grafting percentage?GP?and grafting efficiency?GE?of JSE graft copolymer?JAM?.The optimized process conditions:reaction temperature is 35°C,reaction time is 4 h,initiator concentration is 0.02 mol/L and AM/JSE ratio is 5,GP and GE are 234%and 46.8%,respectively.The-CONH₂ and-COO^-groups are introduced into the molecular structure of J-g-P?AM-co-AANa?,the adsorption capacity for Cd²⁺is as high as 344.8 mg/g.The adsorption of Cd²⁺on J-g-P?AM-co-AANa?followed the pseudo-second-order kinetic model and the rate control step is chemical adsorption,the Cd²⁺adsorption isotherm data fitted the Freundlich model and the adsorption process is multi-layer adsorption.After four adsorption and desorption cycles,J-g-P?AM-co-AANa?can still effectively remove Cd²⁺from the aqueous solution.Jute fiber short-chain fatty acid ester?P-JAA-sc?was prepared by the combination of CSESE pretreatment and scCO₂-assisted esterification,the effect of synthetic process parameters on the weight gain percentage?WG%?,structure and properties of P-JAA-sc was investigated.Jute fiber,filter paper?FP?and JSE were used as raw materials for comparison.The results showed that the optimized process conditions of P-JAA-sc were 100°C,3 h,10MPa.The WG%and degree of substitution were as high as 43.2%and 1.623 respectively.Compared with jute and FP,the esterification product of P-JAA-sc has the highest WG%.Compared with raw materials,the crystallinity and thermal stability of all corresponding esterification products reduced.And the medium used for the reaction is environmentally friendly,easy to remove,and low energy consumption.To further study the synthetic process and properties of jute fiber fatty acid esters,based on the short-chain esterification,a one-step esterification method combining CSESE pretreatment and scCO₂-assisted was used to prepare jute fiber long-chain fatty acid esters?P-JL-sc?and the effects of synthetic process parameters on the WG%of esterification products were studied.The results showed that the crystalline area of JSE was partially destroyed and participated in the esterification reaction.Under the same conditions,the WG%of esterification products of jute and JSE in the scCO₂ were 93.5%and 110.7%,respectively.The optimizated synthesis conditions of P-JL-sc was 100°C,14 MPa and 4 h.The WG%,degree of substitution and contact angle were as high as 123.5%,1.10,and 118.1°,respectively.The side chain alkyl groups of P-JL-sc was crystallized,and the crystal peak position was 2?=19.86°.The plasticization properties of P-JL-sc was significantly improved,the tensile properties was 5.37MPa.The oil absorption ratio was significantly improved,up to17.01g/g.In order to further investigate the preparation process and properties of jute fiber long-chain fatty acid esters,based on CSESE pretreatment and one-step esterification method,a two-step method combining formic acid and scCO₂-assisted esterification was used to prepare jute fiber long-chain fatty acid ester?FA-JL?,and compared with the above one-step method.The results showed that the optimum synthesis conditions were 45°C,90 min and 14MPa,the WG%and the substitution degree of FA-JL were 97.5%and 0.87,respectively.Compared with the one-step method,the reaction time of FA-JL significantly shortened,the reaction temperature significantly reduced,the WG%and degree of substitution slightly reduced,and the thermal stability of the products increased.