Studies On The Preparation And Application Of Nanocellulose Extracted From Mulberry Branch

China is a traditional and big country of sericulture,which is rich in mulberry resources.Mulberry branch is the most productive resource in sericulture production.According to statistics,about 65% of the annual dry matter of mulberry field is mulberry branch produced by cutting in early spring and summer every year.At present,most of the mulberry branches produced every year will be abandoned,except for a small part of them are used in the traditional Chinese medicine and edible fungus.The abandoned mulberry branch has a serious impact on the ecological environment.As a result,the environmental friendly development and utilization of mulberry branch resources has been highly valued.According to the research reported,mulberry branch contains 51.88% of cellulose,which is an important raw material source for the development of cellulose.In this study,the waste mulberry branches in mulberry garden were used as raw materials,choline chloride-1,4-butanediol method,nitric acid-ethanol method and sodium hydroxide-sodium chlorite method were used to extract cellulose from mulberry branches and Van Soest method was used to determine the content of cellulose.Finally,we wanted to explore the best way to extract cellulose from mulberry branch.Nanocellulose(NCC)was prepared from mulberry branch cellulose by sulfuric acid hydrolysis,and the differences of micromorphology,crystallinity and thermal stability between cellulose and nanocellulose were compared.NCC was used to disperse graphene(RGO)evenly,and then added to polyvinyl alcohol(PVA).The NCC-RGO/PVA composite membrane was prepared by overcasting method,and the effect of the addition of NCC-RGO on the properties of the composite membrane was studied.The specific research results are as follows: 1.Separation of cellulose from mulberry branchThe cellulose was extracted from mulberry branch by choline chloride-1,4-butanediol,sodium hydroxide-sodium chlorite and nitric acid-ethanol methods.The optimum extraction conditions and the highest cellulose content of the three methods were obtained through the direct observation of orthogonal test.When the mulberry branch was treated by choline chloride-1,4-butanediol for 5 hours at 90°C and solid-liquid ratio of 1:25(g/m L),the cellulose content was the highest(43.74%).The optimum conditions of sodium hydroxide-sodium chlorite method was as follows: temperature,90°C;time,3 h;solid-liquid ratio,1:20(g/m L).Under these conditions,the content of cellulose was 70.16%.The optimum conditions of nitric acid-ethanol method was as follows: temperature,90°C;time,1.5 h;solid-liquid ratio,1:20(g/m L).Under these conditions,the cellulose content was 86.59%.Scanning electron microscopy(SEM)analysis showed that the apparent morphology of mulberry branches treated by three methods changed significantly,and most of lignin and hemicellulose were removed.The results of Fourier transform infrared spectroscope(FT-IR)and thermogravimetric(TG)analysis showed that the cellulose content in the samples was increased after treated by three methods.Among them,nitric acid-ethanol method increased the most,which was 56.58%;sodium hydroxide-sodium chlorite method increased 40.15%;while choline chloride-1,4-butanediol method increased relatively less,which was 13.73%.X-ray diffraction(XRD)analysis showed that the crystalline type of the extracted cellulose did not change,and the crystallinity was significantly improved compared with the untreated sample.The crystallinity of the cellulose extracted by nitric acid-ethanol method was 39.08% higher than that of the untreated sample.In a word,nitric acid-ethanol method is the best way to extract cellulose from mulberry branches.2.Preparation of nanocellulose from mulberry branch celluloseUsing mulberry branch cellulose as raw material,nanocellulose was prepared by acidolysis method.The best condition of acidolysis was obtained by single factor test: time of 50 minutes,temperature of 45°C and solid to liquid ratio of 1:20(g/m L).The results of FT-IR analysis showed that the structure of mulberry branch nanocellulose was unchanged,which indicated that its dispersibility in water was mainly due to its nanometer size.XRD results showed that the crystallinity of mulberry branch nanocellulose was 4.35% higher than that of cellulose.In addition,TG analysis shows that compared with mulberry branch cellulose,the thermal stability of nanocellulose was significantly improved,and when the mass loss of both was 10%,the pyrolysis temperature of nanocellulose was 56.18°C higher than that of cellulose.As a result,mulberry branch nanocellulose can be better used in the fields of dispersant and packaging film.3.Preparation of NCC/RGO/PVA composite filmNCC-RGO/PVA composite films were prepared by plate casting in order to make full use of mulberry branch nanocellulose.A certain proportion of nanocellulose can make graphene uniformly and stably disperse in water.Based on the test results and considering the economic benefits,we choosed 5:1 NCC-RGO as additive and PVA as matrix to prepare 0.5%,1.0% and 2.0% NCC-RGO/PVA composite films,and studied the influences of NCC-RGO on the properties of composite films.The results of XRD showed that the crystallinity of the composite film with NCC-RGO increased,but the increase was not significant.At the same time,the results of tensile test and TG test showed that a certain proportion of NCC-RGO can improve the tensile strength,tensile modulus and thermal stability of PVA composite film.In addition,it was found that 0.5% and 1.0% NCC-RGO could effectively reduce the water absorption of PVA composite film,but when the addition amount increased to 2.0%,the water absorption would increase.All in all,the addition of NCC-RGO can improve some properties of PVA film,but the amount of NCC-RGO has a certain requirement,which needed to be further explored.