Study On Design And Synthesis Of Cellulose Acetate Ester Based On Synchrotron Radiation And The Application In Optical Compensation Film

With the rapid development of new display technologies,liquid crystal displays（LCD）have become an important window for information interaction in the society today.Polarizer is the core component of LCD,which consists of polarizing film,supporting film and compensation film.The role of the compensation film is to correct the phase difference generated by the liquid crystal layer at different viewing angles,reduce light leakage,extend the viewing angle,and promote image quality such as contrast and chromaticity,which is the key optical film affecting display performance.In LCD,many different types of compensation films are usually laminated together to achieve the effect of optical compensation,but this approach will lead to a thick LCD,which is not suitable for its development trend of thinness and lightness.It is a very important and challenging idea to achieve the effect of laminating multiple layers of traditional compensation films with one single specialized compensation film.Cellulose acetate（CA）has high transparency and great mechanical strength and is mainly used as a support film and optical compensation film.The birefringence properties of common CA optical films cannot meet the requirements of compensation films,which need to be realized by the physical blending of raw materials or chemical modification.However,physical blending has a limited ability to modulate the optical properties of CA films,and chemical modification is expected to be a better choice.Yet,there is a lack of systematic studies on the effects of chemical modification of raw materials on the structure and properties of CA films,and the effects of the modification methods of raw materials and the substituent structure on the structure and properties of CA optical films are unclear.In this thesis,CA was used as raw material to design and synthesize cellulose acetate with different substituents by using irradiation grafting and chemical grafting modification methods,prepared into optical films by solution casting method,and then made into compensation films by hot stretching.Using synchrotron wide angle X-ray scattering（WAXS）,Fourier polarization infrared（FTIR）and phase difference instrumentation,the relationship between substitution group type,substitution degree,stretching temperature and stretching ratio on the structure and optical properties of CA-based compensation films was systematically investigated.Different types of raw material modification methods and preparation process conditions of compensation films are mastered,and the effects of different graft modification methods on the structure and properties of compensation films are compared.This will provide a theoretical basis and guidance for the development of high-performance optical compensation films.The specific research work and research results of this thesis are as follows:（1）For IPS（In-Plane Switching）mode LCD（IPS-LCD）,benzoylated cellulose acetate（BCA）optical films with different degrees of substitution(DS_Bz)were designed and prepared by combining theoretical calculation and chemical modification.The optical properties and orientation structures of the BCA films before and after stretching were investigated by WAXS and polarized FTIR.The orientation behavior of the benzoyl group during the stretching process and the effects on optical birefringence and wavelength dispersion properties were analyzed.The results show that by regulating the degree of substitution and orientation behavior of the benzoyl group,the optical compensated film with zero birefringence can be obtained when the DS_Bz reaches 0.511 and is not affected by the stretching conditions.This work constructs a correspondence between the substitution groups and the birefringence and wavelength dispersion properties in CA-based optical compensation films,which provides new theoretical guidance for the design and preparation of zero-birefringence optical compensation films and polarizer protection films for IPS-LCD.（2）For VA（Vertical Alignment）mode LCD（VA-LCD）,propionyl groups with weak wavelength-dependent positive birefringence were selected,and propionylated cellulose acetate（PCA）films with different degrees of substitution(DS_Pr)were designed and prepared by chemical modification.The effects of propionyl substitution degree,stretching temperature and stretching ratio on the molecular chain orientation and optical properties of PCA films were systematically investigated using synchrotron WAXS and polarized FTIR.It was found that compared with acetyl groups,propionyl groups exhibit normal wavelength dispersion and larger positive birefringence values at the C-2 and C-3 sites,while they exhibit extraordinary wavelength dispersion and smaller negative birefringence values at the C-6 site.When the DSPr is 0.537,the PCA film has large in-plane and out-plane birefringence and both exhibit very weak wavelength dispersion,which meets the requirement of VA-LCD compensation film.This work constructs the relationship of propionyl substitution degree-stretching process conditions-optical properties,which can provide ideas and theoretical guidance for the design and preparation of optical compensation films for VA-LCD.（3）Using the irradiation grafting method to graft benzophenone（BP）onto CA,CA-g-BP films were prepared by solution casting method.The effects of the degree of BP grafting and stretching ratio on the molecular chain orientation and birefringence properties of CA-g-BP films were systematically investigated using WAXS and polarized FTIR.The results show that BP grafting on the CA main chain contributes to positive birefringence and has very little effect on in-plane birefringence wavelength dispersion.With the increase of the stretching ratio,the in-plane birefringence of CA-g-BP films gradually increased,but the in-plane birefringence wavelength dispersion was almost unaffected.Compared with the conventional physical blending method,the chemical modification can significantly improve the orientation birefringence properties without affecting the orientation birefringence wavelength dispersion.When introducing a large volume of side groups for substitution,the orientation of the substituents during the stretching process is more affected by their spatial site resistance,and thus their birefringence contribution is more affected by the spatial hindrance than that of the substitution sites.This promotes our understanding of the effect of large spatial hindrance substituents on the birefringence properties of optical films and will provide theoretical support for the selection of substituents for cellulose acetate optical compensation films.（4）Using the chemical modification method of electron beam irradiation（EB）,polystyrene（PS）was grafted onto CA,and CA-g-PS films with different grafting ratios were prepared.The effects of grafting degree and stretching ratio on the birefringence and wavelength dispersion of CA-g-PS films were systematically investigated by using a high-temperature stretching device combined with WAXS,polarization FTIR and dynamic mechanical analysis（DMA）.It was found that the in-plane birefringence of CA-g-PS films gradually increased with the increase of stretching ratio,and the corresponding wavelength dependence also gradually increased.The in-plane birefringence of CA-g-PS films gradually increased with the increase of the PS grafting ratio at the same stretching ratio.Grafting PS side chains on CA,the former segment of PS side chains tend to be oriented perpendicular to the CA main chain during stretching,contributing positive birefringence to CA-g-PS films;the latter segment of PS side chains tends to be oriented parallel to the CA main chain,and the birefringence contributed by the latter segment of PS side chains is weakly influenced by the benzene ring alignment.This work promotes our understanding of the effect of polymer-based substituents on the birefringence properties of CA optical films,and provides reference and theoretical guidance for the design and preparation of cellulose acetate optical compensation films with polymer-based substituents.