Preparation And Application Of Acetylated Corn-stalk Microfibrillated Cellulose

Cornstalk is a main agricultural waste in China, which is rich in cellulose but its utilization rate is low. Cellulose, especially microcrystalline cellulose(MCC) and nano-fibers show a wide application foreground in improving compounding materials, for their biodegradablility, high strength and high reactivity. In this paper, micrnized cellulose with different size was prepared from cornstalk with acidolysis-mechanico combined process to compare the efficiency of different mechanical processes. Then acetylated microcrystalline cellulose(AMCC) and acetylated microfibrillated cellulose(AMFC) with different degrees of substitution(DS) were prepared to study the affect of morphological feature and super molecular structure of cellulose on modification. Besides, the influence of nanoparticle addition on the mechanical of starch-base composite films was investigated. The main research contents and results were as follows:Firstly, cornstalk was used as raw material to prepare microcrystalline cellulose(MCC) and the effect on the degree of polymerization(DP) and yield of MCC with different acid reaction conditions were studied. The optimal conditions for MCC preparation were optimized by single factor analysis and the results were as follows: sulfuric acid concentration was 8%(w/w), and cornstalk was hydrolyzed at 85°C for 60 min. Under this condition, the DP of MCC was 292 with cellulose content of 92.6%, the yield and crystallinity reached 76.48% and 74.5% respectively. Cornstalk-MCC showed rod-like structure and remained natural cellulose-I structure, which was consistent with commercial cotton MCC. The thermal degradation performance was studied by thermal-gravimetric analysis(TGA). Compared with cornstalk cellulose, MCC showed higher thermal stability and the maximum degradation temperature increased by 30°C~40°C.Secondly, cornstalk MCC was exposed to different mechanical process to get micronized MCC, including ball-milling, shearing and high pressure homogeneous. Multiple modern analytical techniques, including scanning electron microscope(SEM), fourier-transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD) and TGA were used to investigate the structure and thermal stability of the samples so as to choose the effective ultra-micronization model. It turned out that with prolonged treatment time the particle diameter decreased, but when it reached a certain size, it no longer reduce. Ball milling seemed to have little effect on size decrease, When MCC was sheared at 7000 r/min for 0.5 h, it diameter was 19.9 μm. MFC could be obtained by homogeneous at 60 MPa for 30 times. Atomic force microscope(AFM) measurement was carried out to get a more precise characterization of MFC, which showed filaments winding structure with an average size of 24 nm. High-pressure homogenization process had no effect on the functional groups and crystalline structure of MCC, and the result MFC interwined into an ever stable three dimensional network structure, thus showed higher thermal stability. Overall, high-pressure homogeneous was an effective method to get micronized cellulose.Thirdly, the effect of the nature of MCC on modification was studied. By adjusting the ratio of cellulose to acetic anhydride was 4:1, 2:1, 4:3, 1:1, 1:2(g:mL), glacial acetic acid as medium, acetylated MCC(AMCC) and acetylated MFC(AMFC) with different DS could be collected. The results showed that when the reagent went deep into the samples, the compact structure of MFC could go against it. Acetylized modification might influence the properties of MCC and promote the micronization process. Thus it was a good way to get AMFC with different DS values by exposing AMCC to homogenization process. Under this condition, AMFC showed nano-order web-like network structure with diameter distribution of 10~24 nm. At DS 0.35 and 0.57, AMFC were also well dispersed in acetone.Finally, starch-based composite membranes were prepared by addition of mechanical treated MCC and AMFC. The performance of the composites was comprehensively evaluated. Both the shape and surface polarity of the filler could greatly influence the film properties. MCC and its derivatives had a good improvement function to the TS and water-resistance of all composite films. Web-like network structure of MFC was more conductive to strength, appropriate acetylated modification could improve the dispersion of additives in starch and the integrative performance had been greatly improved. At DS 0.35, AMFC/starch film showed best property with tension strength(TS) 15.87 MPa and its storage modulus at 30°C was 1288 MPa, increased by 124% and 243% respectively. In addition, the glass transition temperature increased by 30°C and water absorption decreased by 44.7%. The comprehensive performance of the composite membrane was improved obviously.