Research Of Cellulose Nanofibers/Polycarbonate Composites For The Flexible OLED Display Substrate

By far,the most common flexible substrate material is high polymers,such as PET and PI.High polymer has good transparency.Its quality is light and it is easy to get.It is a kind of substrate materials that has a broad application prospect.The common defects of polymer such as high thermal expansion coefficient and poor water and oxygen resistance performance are the main factors that restrict its use as flexible substrate.Polycarbonate is a kind of engineering plastics that are widely used.It is colorless and transparent.Its glass transition temperature?Tg?is 150?or so.The linear expansion coefficient of polycarbonate is lower than most of the polymers.It is easy to get and have great potential applications in the field of flexible displays.The addition of cellulose nanofibers can improve the performance of polycarbonate and make it better for flexible substrate.The main work of this paper includes:1.Used TEMPO/Na Br/NaClO oxidation system to oxidize softwood pulp under alkaline condition,then obtained nanocellulose through homogenization treatment.Sodium carboxylate group on the TOCN could be converted into carboxylic acid group after acidification by 1M hydrochloric acid.With DMF as dispersion medium,pyridine as catalyst,acetic anhydride as esterification agent and acetylated modification was carried out on the TOCN-COOH.Use thermogravimetric analyzer?TGA?,Fourier transform infrared spectrometer?FT-IR?,X-ray diffraction analyzer?XRD?,atomic force microscope?AFM?and surface contact Angle meter to characterize A-TOCN-COOH films and TOCN-COOH films.Results showed that after 7h acetylation reaction,TOCN-COOH was acetylated successfully.The contact angle of the A-TOCN-COOH films increased from 46.3°to 66.9°.Hydrophobicity of the films was improved significantly.2.In order to prepare the composite films,we dispersed A-TOCN-COOH in chloroform and CH₂Cl₂ respectively for dispersion test,the test to the solvent exchange by ultrasonic dispersion and freeze drying by ultrasonic dispersing two ways.A-TOCN-COOH could not be dispersed in CH₂Cl₂ through the two ways.It could suspended in the CH₃Cl through solvent exchange,while only a tiny part of A-TOCN-COOH could dispersed in CH₃Cl by means of freeze drying with ultrasonic dispersion.Freeze drying with ultrasonic dispersion was not effective.3.A-TOCN-COOH was dispersed in chloroform,mixed with PC solution and A-TOCN-COOH/PC composite films,the content of A-TOCN-COOH were 0.5%,1%,2%,1%,5%,8%,the performance of the composite film is as follows:1)When A-TOCN-COOH content was 3%,composite membrane cross-section didn't see the obvious phenomenon of reunion,under the AFM surface roughness is around 4 nm.2)Composite film of light transmittance increased with the increase of A-TOCN-COOH content has A certain degree of decline.A-TOCN-COOH content increased from 0 to3%,the light transmittance decreased from 91.3%to 86.2%;When A-TOCN-COOH content was 8%,the light transmittance of composite film had minimum with the value of 73.1%.3)TGA curve showed that initial decomposition temperature of the composite film had maximum with the value of 350?,when A-TOCN-COOH content was 1%.4)When A-TOCN-COOH content was 3%,the glass transition temperature of composite films reached the maximum with the value of 171.1?,20.3?higher than that of pure PC.5)A-TOCN-COOH could lower the thermal expansion coefficient of composite membrane.When A-TOCN-COOH content was 8%,the CTE had a maximum with the value of 38 ppm/K.6)A-TOCN-COOH could improve the composite film yellowing resistance.The most significant effect of content was 3%,yellowing index was reduced by 0.25.7)The addition of A-TOCN-COOH could improve the mechanical properties of composite films.such as tensile strength and elastic modulus.8)When the amount of A-TOCN-COOH was 3%,the composite films showed good ability to suffer from chemicals and solvents.After soaking in Photoresist1813,Developer and acetone for one day,the shape of composite films remained unchanged.9)The addition of A-TOCN-COOH could reduce the oxygen permeability of composite films.When the content was 8%,it had the lowest oxygen permeability,The oxygen permeability was 401 cm³·um/m²·day·kPa.10)By modification,the surface roughness,light transmittance,glass transition temperature,thermal stability,yellowing resistance,solvent resistance,tensile strength,elastic modulus of composite film had basically met the requirements of OLED substrates.CTE and oxygen resistance ability still needed to be further improved.