Preparation And Properties Of Nanocrystalline Cellulose/Graphene-based Composite Films

Nanocellulose can be prepared by separating from wood and other fiber raw materials,and is biocompatible,renewable and biodegradable.As a new type of green nanomaterial with great research value,the preparation of high value-added products based on nanocellulose is one of the solutions to the serious consumption of non-renewable energy and environmental pollution,but the characteristics of nanocellulose itself limit it,making it difficult to directly apply it to electricity,heat,magnetism and other fields.Nanocellulose-based composites can be prepared by introducing a medium to give them new functional properties.In this paper,nanocellulose（NCC）and graphene oxide（GO）with stable dispersion were prepared,and a nanocellulose/graphene composite film with conductivity and heat dissipation was prepared by vacuum filtration,which solved the limitations of nanocellulose in practical applications,and by adding polyethylene glycol and hydroxypropyl guar gum,nanocellulose/reduced graphene oxide/polyethylene glycol composite film and nanocellulose/reduced graphene oxide/hydroxypropyl guar gum composite film were prepared,which enhanced the flexibility and water resistance of the composite film,respectively,and improved the application value of the composite film as a flexible conductive film and a heat dissipation film in the field of high-performance composite materials.In this study,SEM,FTIR,XRD,TG,a four-probe resistivity tester,and a laser thermal conductivity meter were used to characterize and analyze the samples.The main research content is as follows.（1）Four ratios of NCC:GO=87.5:12.5 wt.%,75:25 wt.%,62.5:37.5 wt.%and 50:50 wt.%of nanocellulose and graphene were prepared into composite films by a simple vacuum filtration method,and the formation of intermolecular hydrogen bonds promoted the uniform insertion of nanocellulose between graphene sheet layers and slowed down the stacking of graphene.The total thermal weight loss of the nanocellulose/graphene composite film（58.67%）was significantly reduced compared with that of NCC（67.12%）,indicating that the addition of reduced graphene oxide（rGO）improved the thermal stability of the composite film.The conductivity and thermal diffusivity of the nanocellulose/graphene composite film increased with the increase of rGO content in the composite film,and the conductivity and thermal diffusivity of the composite film were the largest at the highest rGO content（50 wt.%）,which were 5.67 S/m and 5.028 cm²/s,respectively.The tensile strength of the NCC/rGO composite film was 18.97 MPa and the toughness was 71.86 KJm^-3 when the rGO content was 50 wt.%.this nanocellulose/graphene composite film with uniform and dense layer structure,good thermal stability,good conductivity and thermal performance,improving the development and utilization of nanocellulose in the field of high-performance composites.（2）To solve the problem that traditional conductive materials such as metals,glass and ceramics cannot be applied to flexible electronic devices due to their high rigidity and difficulty in degradation,polyethylene glycol（PEG）was added to the nanocellulose/graphene composite film to enhance its mechanical properties.Preparation of NCC/rGO/PEG composite films with PEG content of 25 wt.%,42.5 wt.%,55.5 wt.%,and 65.6 wt.%respectively by mixing nanocrystalline cellulose,graphene and polyethylene glycol.The addition of PEG significantly improved the thermal stability of the composite film,and the temperature at the maximum thermal weight loss rate shifted to the high temperature region with a minimum total thermal weight loss rate of 49%,which was 9.67%less than that of the NCC/rGO composite film.The resistivity of the composite film gradually decreased with the increase of rGO content,and the conductivity value of the composite film could still reach 0.33 S/m at the rGO addition due to9.8 wt.%.The addition of PEG also enhanced the mechanical strength of the composite film,and the tensile strength of the composite film with a thickness of only 22μm（65.6 wt.%PEG content）was 30.56 MPa,which was 1.83%of that of the control（NCC/rGO film）,and the toughness was 727.18 KJm^-3,which was 2.32 times that of the control group.This green,thermally stable and mechanically excellent flexible conductive film has greater potential for application in flexible electronic devices.（3）To meet the specific working requirements of the material in different environments and to improve the application of the composite film in practice,hydroxypropyl guar gum（HPG）was added to the nanocellulose/graphene composite film to enhance its resistance to water and water vapor.Nanocrystalline cellulose/reduced graphene oxide/hydroxypropyl guar gum composite films with HPG contents of 0,12.5 wt.%,25 wt.%,37.5 wt.%and 50 wt.%were prepared by mixing nanocrystalline cellulose,graphene oxide and hydroxypropyl guar gum.The three components were connected by hydrogen bonding,which not only effectively slowed down the agglomeration of graphene,but also promoted the homogeneous mixing of the three components.The addition of HPG significantly improved the water resistance of the composite membrane,and the minimum water vapor transmission rate of NCC/rGO/HPG composite membrane was 3.79×10^-3 g·m/（m²·24h·MPa）,the minimum saturated water absorption rate is6.62%,the maximum water contact angle is 61.29°,and the heat diffusion rate of the composite film is 4.42 cm²/s.The rGO/PEG film with the highest HPG content（50 wt.%）had the best mechanical properties with a tensile strength of 43.29 MPa and a toughness of 694.07 KJm^-3.This green environmental protection Heat dissipation film water repellency significantly improved.It has potential applications for electronic devices with high humidity in the working environment or with high requirements for water resistance.