| Large amounts of waste from preparation nano-cellulose with traditional acid hydrolysis have bad impact on the environmental and reaction apparatus.Preparation of nano-cellulose with mechanical method without adding chemicalagents,this approach has little pollution on the environmental.However,hydrogen bonding of plant fiber and complex multi-layer wall structure between microfibril make mechanical preparation of nano-cellulose consume high energy.Besides,the nano-cellulose have large variability.It is not conducive to industrial production.So pretreatment methods combined with conventional mechanical method for preparing nano-cellulose is necessary.Compared with strong acid and alkali pretreatment,enzymatic pretreatment is a gentle process with low energy consumption..This pretreatment is in line with the requirements of safety and environmental protection.In this study,nano cellulose fibrils were prepared through mechanical grinding process after pretreatment with different enzymatic reaction parameters.Scanning electron microscopy(SEM),Transmission electron microscopy(TEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),Thermal gravimetric analysis(TGA)and high rotational rheometer were used to characterizatied the morphology and property of nano cellulose fibrils.At the same time,according to the morphology of eucalyptus pulp fiber with enzymatic hydrolysis and the effect of enzyme on the morphology of nano cellulose fibrils could analyze the mechanism of enzyme pretreatment process.What's more,the preparation and the properties of PVA films that modified by nano cellulose fibrils were discussed.The main conclusions are as follows:?Compared nano cellulose fibrils were extracted from enzymatically treated pulp and untreated pulp prepared by grinding.The diameter of nano cellulose fibrils prepared by grinding after enzymolysis one hour is 87 nm.Eucalyptus pulp without enzyme hydrolysis were grinded two hour could prepared nano cellulose fibrils with the diameter was higher than 500 nm.Enzymatic pretreatment process could reduce grinding time and energy consumption effectively.?With the extension of enzyme dosage or the increasing of enzyme hydrolysis time,the crystallinity of the enzymatic hydrolysis pulp and the yield of the nano cellulose fibrils increased,but the diameter of nano cellulose fibrils decreased.The enzyme pretreatment condition was: temperature 50?,pH 4.8,time of enzyme treatment 6h,enzyme dosage 60ECU/g.The average diameter of the nano cellulose fibrils produced by this pretreatment was 57 nm,the yield was 50.67%,the crystallinity was 67.52%.The nano cellulose fibrils still maintained the natural structure of cellulose.?By studying the change of eucalyptus pulp fiber morphology during the enzyme pretreatment process and grinding process,we found that the surface of fiber became wrinkled after enzyme effect on the fiber surface.As the concentration of cellulase enzyme,a part of cellulose molecular chain had been decomposed,cellulose molecular chain was cut off.The surface of enzymatic hydrolysis pulp fiber wrinkled seriously in the initial time.Sub-wire broom phenomenon was evident,but fiber diameter did not changed significantly.With the extension of the milling time,the fiber diamete reduced,fiber strand gradually opened.At last,the final uniform cellulose fiber were separated.Enzyme treatment may loosed cellulose,reduced grinding time and energy consumption.?The tensile strength of PVA films adding nano cellulose fibrils was higher than those with no nano-cellulose inside.But the tensile breaking elongation declined.When the nano cellulose fibrils content of 1%,the tensile strength of the composite film was 56.15 MPa,increased by about 91% than that of pure PVA film.The tensile breaking elongation was35.36%,reduced by about 40% than that of pure PVA rigidity of modified films increased,while the plasticity reduced.After adding the nano cellulose fibrils,the maximum decomposition temperature and thermal stability of composite film both improved. |
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