Studies On Thermally Conductive Properties Of Nanocellulose/Carbon-based Materials Hybrid Films

Thermal conductive films are extensively applied in various merchant portable electronic with more condensedly packed integrated circuits.Light weight polymer composites are promising candidate to solve this problems.Carbon-based nanomaterials with high thermal conductivities and excellent mechanical properities are promising candidate as fillers to fabricate high thermal conductive polymer composites.Graphene and nanodiamond（ND）have attracted researches’interest due to their incredibly high thermal conductivities and mechanical properities.In order to improve the effect of fillers in the enhancement of thermal conductivies of polymer,creat the aligned thermal conductive pathways is the key issue to fabricate lateral thermal conductive polymer composites.Nanofibrillated cellulose（NFC）is chosen as matrix to prepare the required polymer composites.The defect of graphene have significant effect on improving the thermal conductivity of polymer.In this work,graphene with different defect densities,nanodiamond and low-defect graphene-nanodiamond were used as fillers to systematic study the effect of graphene defect on thermal conductivities of hybrid films,enhancement of thermal conductivity in hybrid films with low mass fraction of nanodiamond and the synergistic enhancing effect of composite filler on hybrid films.The main results are as shown below:1.Graphene with different defect densities were prepared in laboratory or available in the commercial.The defect densities（n_d）of GSs were monitored by various methods,and calculated by formulas.NFC/GSs hybrid films with graphene with different defect densities and NFC are fabricated via a vacuum-assisted self-assembly（VASA）progress.And the morphology,structure and properties of hybrid films are also characterized.The results indicate that the GSs align in NFC and form well-organized layered structure.Hybrid films show higher in-plane thermal conductivities and rising trend with the decrease of defect n_d.The hybrid films with low-defect GSs(n_d=0.15-0.27×10¹¹cm^-1)exhibit high in-plane thermal conductivity of 6.75 W·m^-1·K^-1,which is 501.6%higher than pure NFC film,and203.0%higher than hybrid films with high-defect GSs(n_d=1.06-1.88×10¹¹cm^-1).Hybrid films show higher tensile strength and flexibility and rising trend with the decrease of defect n_d.2.The hybrid films with controlled content of ND are fabricated by VASA technique.Different kinds of characterization methods are used to analysis the interface interaction,morphology,structure and properties of NFC/ND hybrid films.The results indicated that the layered stucture of NFC forms aligned thermal conductive pathways with ND.And the in-plane thermal conductivities of hybrid films increase with the increasing of ND content.The results indicated that the thermal conductivity of NFC/ND hybrid films at low ND content can be significantly enhanced.When the content was only 0.5 wt%the in-plane thermal conductivity of NFC/ND hybrid films were increased by 775.2%,the in-plane thermal conductivity was 9.82 W·m^-1·K^-1.CND-05 hybrid film has 66.35%transmittance at 550 nm wavelength,which exhibit excellent tensile strength and flexibility.3.GSs and ND was modified with PY-NH₂ as the filler to enhance the thermal conductivity of NFC via VASA technique.The interface interaction,morphology,structure and properties of f-G/ND/NFC hybrid films are characterized.And the effect of hybrid fillers on enhancing the thermal conductivity of polymer are also studied.The results of test indicated that the modification with PY-NH₂ shows significant improvement on enhancing the thermal conductivity of polymer,and the best ratio of GSs and ND is 7:3.The in-plane thermal conductivity of f-G/ND/NFC hybrid film is 14.35 W·m^-1·K^-1 with 10 wt%concent of hybrid filler,which is higher than that only with GSs and ND.