Enzymolysis Preparation Of Spherical Nanocellulose And Its Application In Flexible Transparent Conductive Film

Cellulose is the most abundant renewable resource on the earth.As one of its most important derivatives,nanocellulose has a series of advantages such as high specific surface area,high mechanical properties and good thermal stability.At present,acid hydrolysis,oxidation and mechanical homogenization are mainly used to prepare cellulose nanocrystals（CNCs）and cellulose nanofibers（CNF）at home and abroad.But these methods have the disadvantages of high pollution or high energy consumption.Due to its advantages of environmental protection,mild reaction conditions and specificity,more and more attention has been paid to the preparation of nanocellulose by enzymatic hydrolysis.Manufacturing flexible transparent conductive films is one of the important applications of nanocellulose.With the rapid development of modern science and technology,the iterative updating of electronic products has accelerated,and the life cycle has continued to shorten,resulting in a series of problems such as energy consumption and environmental pollution.Biodegradable electronic devices and components are one of the most potential solutions to this problem.Biodegradable flexible transparent nanocellulose membrane is a membrane material with excellent performance,which can be used for electronic device substrates and flexible electronic display screens.Spherical CNCs（SCNCs）with a diameter of about 30 nm were prepared by hydrolyzing eucalyptus pulp with a composite enzyme with a total enzyme activity of 300μ/m L for 4 hours.Through the flocculation of dilute acid with p H 2 and multiple washings,and quantitative analysis of impurity content by ion chromatography and Coomassie Brilliant Blue G-250,SCNCs with a purity of about 99.99%were finally obtained.The analysis shows that the pure SCNCs still retain the natural cellulose structure,but the crystallinity is reduced;the thermal stability is better,and the fastest decomposition temperature(T_max)is 329.5℃,which can be up to about 95℃higher than that obtained by other methods.SCNCs and strip-shaped CNCs（RCNCs）were added as reinforcing agents to the polyvinyl alcohol（PVA）solution respectively.PVA/CNCs flexible transparent films with different contents were prepared by solution casting,and their enhancement effects were compared.The two morphology CNCs have good dispersion performance in PVA and have little effect on the transparency of the composite films,of which the lowest is 89.32%（PVA/RCNCs-6.0）.The analysis showed that with the increase of the content of CNCs,the crystallinity of the composite film showed a trend of decreasing first and then increasing and then decreasing again.The maximum crystallinity was 46.67%（PVA/RCNCs-4.0）.In terms of thermal stability,the addition of RCNCs has a small effect on the thermal stability of the composite membrane,while the addition of SCNCs increases by 50-90°C.In terms of mechanical properties,the mechanical properties of the composite membrane of RCNCs are higher than that of SCNCs.When 1.0%RCNCs were added,the tensile stress and Young’s modulus of the composite membrane were 64.28±0.65 MPa and 659.83±41.37 MPa,respectively,which were increased by 100.62%and 120.97%relative to pure PVA.Nano-silver wire（AgNW）was prepared by hydrothermal method and spin-coated onto PVA/CNCs composite film to prepare flexible transparent conductive film.After hydrolysis for 3 hours,pure AgNW with an aspect ratio of about 500 was prepared.The transparency and conductivity of the PVA/CNCs/AgNW composite film are adjusted by controlling the number of spin-coating AgNW.When spin-coated four times,the square resistance can reach12.9Ω/?,and the transparency is still 72.65%.After 5 scratch tests,the square resistance of the composite film is 22.1Ω/□,which has good adhesion to AgNW.