OPTICAL PROPERTIES OF CELLULOSE ESTERS AND THEIR BLENDS
Authors: Masayuki Yamaguchi
Abstract: As increasing the global attention to environment, intensive research has been carried out for biomass-based plastics. Cellulose-derivative, as one of the biomass-based plastics, is also studied to replace from glassy petroleum polymers. Further, the excellent transparency and heat resistant property of cellulose esters, such as cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB), encourage the study on the optical anisotropy especially for the application of liquid crystal display (LCD). In this chapter, the optical properties of thermoplastic cellulose esters such as CAP and CAB are mentioned in detail. It is found that propionyl and butyryl contents in CAP or CAB affect the orientation and photoelastic birefringences to a great extent. In general, propionyl and butyryl groups provide positive orientation birefringence whereas acetyl group gives negative one. Therefore, cellulose triacetate (CTA) shows negative orientation birefringence. On the contrary, CAB and CAP provide positive one and the magnitude increases with the butyryl group content. Further, the birefringence is strongly affected by the addition of plasticizers. The plasticizer having a large solubility parameter, which shows good miscibility with cellulose esters, enhances the orientation and photoelastic birefringences, whereas the plasticizer with a small solubility parameter decreases it. Moreover, blending poly(epichlorohydrin) (PECH), poly(vinyl acetate) (PVAc), or poly(metyl methacrylate) (PMMA) decreases the orientation birefringence without losing the transparency, because PECH, PVAc, and PMMA show negative orientation birefringence. These experimental results will be basic information on the material design for optical films employed in LCD.