Preparation Of Cellulose Nanofibrils From Okara Pretreated By Deep Eutectic Solvent

As the non-renewable petroleum resources in the nature are increasingly depleted,the current high-value development and utilization of biologically sustainable resources is imminent.Natural cellulose is the most abundant,sustainable and widely distributed biological resource in nature.It mainly exists in various types of animals and plants and colonies.Cellulose Nanofibrils(CNFs)are a kind of natural cellulose with nano-level characteristics and good mechanical strength,and have broad application prospects.In long-term research,people have focused on the research on the preparation of CNF from wood fiber resources and its performance,but there is less systematic research on the preparation of CNF from agricultural waste.Agricultural waste has a wide range of sources and low cost,but its fiber composition and structure are very different from wood fiber raw materials.Therefore,how to get a clean,green and efficient preparation technology and its reaction mechanism from the raw material structure is not only beneficial to agriculture the high-value utilization of waste reduces environmental pollution,and also broadens the thinking for the development of CNF technology.In this paper,the agricultural waste okara are taken as the research object.Deep eutectic solvents(DES)are used to pre-process the raw materials,and light mechanical dissociation is used to prepare CNF.First,five different DES systems were synthesized.The effects of the five DES systems on the extraction yield of okara cellulose,cellulose ultrastructure,cellulose crystallinity,and chemical structure were explored.Mechanism,determine the appropriate DES pretreatment system.Secondly,the effects of different mechanical treatment methods on the preparation of okara CNF were explored.By comparing the conventional high-pressure homogenization treatment,the regulation of the CNF scale of okara by high-speed stirring,ultrasonic treatment and high-speed stirring-ultrasonic treatment was explored,and an energy-saving light mechanical treatment method was derived,which revealed that DES pretreatment can reduce the mechanical dissociation strength Mechanism.Thirdly,the effects of DES pretreatment on CNF yield,crystallinity,surface morphology and chemical structure,and a light-transmitting,surface morphology and mechanical properties of the film CNF such as acid,alkali and enzyme okara pre-processing.The control technology for preparing CNF with different properties was obtained.Finally,the effects of DES reuse times on the pretreatment effect of the system and the effect of okara CNF on the properties of PVA/CNF composite film materials were explored.The main research methods,content and results are as follows:(1)Through choline chloride-oxalic acid(ChCl-O),choline chloride-citric acid(ChCl-C),sulfamic acid-urea(Sula-U),choline chloride-glycerin(ChCl-G)and choline chloride-urea(ChCl-U)five DES systems were synthesized.The pretreatment effect of DES system on okara was studied.By comparing the extraction yield,fiber morphological characterization,crystallization index,and composition of okara fiber of the five types of DES system,these five types of DES have a dissolving effect on cellulose,but ChCl-O on cellulose the separation effect is the best,which can effectively remove the fat and protein in the raw materials.The comprehensive cellulose content is 95.81%,and the?-cellulose is as high as 92.6%.According to Design-Expert software analysis and experimental data and FTIR and SEM analysis,the best DES pretreatment technology is ChCl-O system.Among them:when the concentration of oxalic acid,reaction time and reaction temperature are 48%,45 min and 100?,respectively CNF yield was 26.64%.The dissolution mechanism of ChCl-O DES system on okara cellulose was clarified,which provided a theoretical basis for further experimental progress.(2)The effects of mechanical dissociation on the size regulation of CNF preparation of okara cellulose were studied through different weak mechanical dissociations such as high-pressure homogenization,sonication,high-speed stirring,and high-speed stirring-sonication.With the help of SEM spectrum and Nano Measurer analysis software,the parameters of CNF size distribution prepared by different mechanical treatments were established.The CNF with an average diameter of 27 nm can be prepared by the weak mechanical dissociation method of high-speed stirring,and its size and morphology are better than that of high-pressure homogenization and ultrasonic treatment.The obtained CNF has stable and uniform dimensions,and reveals that DES pretreatment can reduce mechanical dissolution.Mechanism of off-strength it provides a new idea for the low energy consumption and simple and fast preparation of nano-cellulose.(3)The effects of different acid,alkali and enzyme pre-treatments on the properties of okara produced by DES treatment were studied.The results show that:DES-H2O,DES-NaOH,P-DES,and F-DES,the four different early treatments,have higher crystallinity and stronger mechanical strength for the okara CNF prepared after the later DES treatment.The CNF prepared by DES-H2O treatment with high-speed agitation has the best effect,which is more conducive to the later use of okara CNF.The water resistance after F-DES and P-DES treatment is better;and D-S-1,D-S-3 and Na-S-DES treated film had higher light transmittance,which were 98.63%,98.21%and 94.31%,respectively.(4)The effects of DES solvent recycling times on recovery efficiency and extraction yield of okara cellulose were studied.The DES solvent can be used directly after 3 times of recycling,and the recovery rate is greater than 93%.At this time,the cellulose extraction yield is 24.03%.After 5 cycles,the recovery rate is reduced to 87%.The effects of processing temperature on the properties of PVA/CNF composite films were studied.At a high temperature of 160?,the crystallinity of PVA/CNF films is the highest,reaching 70.64%,and the transmittance of PVA/CNF films is 98.45%.