Preparation And Characterization Of Modified Tea Microcrystalline Cellulose Materials And Its Application

In this study,tea cellulose was extracted and separated from tea residue and was then converted into tea microcrystalline cellulose?TMCC?via acid hydrolysis method.TMCC was carboxylated-modified in TEMPO/NaClO/NaClO₂ system as the TEMPO-oxids of microcrystalline cellulose?OMCC?and nanocrystalline cellulose?ONCC?.OMCC was then prepared into regenerated cellulose hydrogels in ionic liquid.The crystal structure,chemical properties and thermodynamic properties of OMCC,ONCC and OMCC-hydrogel were characterized by a series of detection methods including ¹³C-NMR,XRD,FT-IR,TGA/DSC.The specific results are concluded as follows:?1?Microcrystalline cellulose?MCC?was prepared from tea residue via acid hydrolysis method.Single factor tests and orthogonal experiments were performed to research the effects of time,temperature,hydrochloric acid concentration and solid-to-liquid ratio on the yield,degree of polymerization?DP?and crystallinity of the MCC.The results showed that the optimal conditions for MCC preparation were hydrolysis at 95°C for 90 min,at HCl concentration of 8%?w/w?and 1:16 of solid-to-liquid ratio?g/m L?.Under the optimal conditions,the yield of MCC reached about 54.34%.The DP of the MCC product was detected 128 and crystallinity was 67.77%with crystallite sizes of 3.98 nm.FT-IR analysis confirmed that chemical structure of the cellulosic fragments was not influenced by the acid hydrolysis.?2?OMCC and ONCC were successfully isolated from TMCC via a TEMPO-oxidation.The results showed that OMCC and ONCC prepared at 7.3 mmol/g and 9.7 mmol/g NaClO respectively had high yield and carboxyl content.OMCC-hydrogels were prepared by mixing TMCC and OMCC in ionic liquid of BMImCl.The results showed that Gel-3 prepared at ratio of 1%TMCC:3%OMCC exhibited the optimal texture behaviors and higher carboxyl content.A series of detection methods were used to characterize these three products.The results revealed that TEMPO-oxidation can selectively oxidize the primary hydroxyl groups of C6 in the cellulose to carboxyl groups but no affected the secondary hydroxyl groups of C2and C3.During the dissolution and regeneration of OMCC in ionic liquids,the crystalline status was changed from cellulose I to cellulose II with a slightly decreasing of crystallinity.And there was no derivatization reaction occurred during this period.Although the thermal stability of OMCC,ONCC and OMCC-hydrogels was slightly declined comparing to TMCC,the second stage onset degradation temperature was still maintained above 200°C,which means that these three products could be used as a heat-resistant composite materials and adsorption materials.?3?Using OMCC-hydrogel as the adsorbent to remove methylene blue from aqueous solution in the experiments,the influences of hydrogel dosage,solution p H value,adsorption time,methylene blue concentration and temperature on adsorption capacity of methylene blue were investigated.The results showed that,when the hydrogel dosage was 0.01 g,the initial mass concentration of methylene blue was 100 mg/L,the pH value was 7,the temperature was 30°C,the maximum adsorption capacity and rate of methylene blue could reach 171.83mg/g and 90.21%respectively.The adsorption kinetics fitted pseudo-second order kinetics equation and the adsorption process followed Langmuir isotherm model.The theoretical saturated absorption amount of OMCC-hydrogel was 238.10 mg/g at 30°C.The results showed that the OMCC-hydrogel had a good adsorption capacity attributed to the introduction of carboxylate functionalities and it can be applied as a new type of adsorbent to the treatment of dye wastewater.