Optimization Processing Of Nanocellulose Whiskers And Study On Properties Of PLA/NCC Nanofibers

In this paper, nanocellulose whiskers(NCC) were prepared from microcrystalline cellulose(MCC) by sulfuric acid hydrolysis. In addition, the NCC hydrogel was obtained by ultrasonic dispersion, high-speed centrifugation and dialysision. Finally, the NCC was gained with the freeze drying of NCC hydrogel. The effects of sulfuric acid mass fraction, temperature and time on the yield of nanocellulose whiskers were optimized with response surface methodology. The mathematical model was established using the Design—Expert software. The effect of various factors and their interactions were analyzed as well. The results showed that quadratic model was the best model to describe the relationship between the yield of nanocellulose whiskers and the factors. The interactions between sulfuric acid concentration and temperature, sulfuric acid concentration and time, temperature and time were significant. Optimal technological condition: sulfuric acid concentration was 57%, reaction temperature was 58℃and reaction time was 141 min, the yield of nanocellulose whiskers would reach 70.89%. It was the highest value in this investigation. Furthermore, the results show the NCC was rod-like fibers, the diameter was about 10-20 nm, with the length was 50-100 nm. NCC belong to cellulose I whiskers form analyzed by TEM. The FTIR show NCC had the same functional groups with MCC.Nanofibers composite mats consisting of cellulose whiskers(NCC) and polylactic acid(PLA) were electrospinning from a kind of solvent mixture consisting of N, N-dimethylformamide(DMF)and chloroform(V:V=1:4) at room temperature. Adding a little of emulator Span80. The SEM images showed, when the content of NCC was under 5%, the average diameter of the electrospun fibers decreased with increased NCC-loading level. The fibers had the minimum average diameter of 61 nm,when NCC content up to 5%. Thermal properties of PLA and PLA modified with nanocellulose whiskers were deeply investigated by TG and DSC. In addition to the PLA/1wt.%NCC nanofibers, the thermal parameters index of the other nanofibers composites were higher than pure polylactic acid fiber. NCC demonstrated the role of nucleating agents in the PLA matrix. Mechanical properties testing pointed out, Tensile strength and modulus of nanofibers were effectively improved by the addition of NCC up to the 5wt.%. At the NCC content of 5wt.%, the maximum tensile stress and Young’s modulus of the nanofibers composite increased by 5 and 10 times than those of neat PLA nanofibers, respectively. However, with the mass fraction increasing of NCC, the elongation at break decreased. Water absorption test showed water absorption increased with increased NCC-loading level. Moreover, compared with neat PLA nanofibers, the nanofibers composite mats, especially at high NCC-loading levels, degraded more rapidly in phosphate-buffered saline(PBS)solution.