Hikaru Shimada

Development of microporous structure and its application to optical film for cellulose triacetate containing diisodecyl adipate

Phase separation in plasticized cellulose triacetate (CTA) films is investigated to produce a microporous film that can be used in optical devices. Hot-stretched CTA films containing diisodecyl adipate (DIDA) show negative orientation birefringence similar to the hot-stretched pure CTA. After extracting DIDA from the stretched films by immersion into an organic solvent, however, the films exhibit positive birefringence. Moreover, the magnitude of the birefringence increases with the wavelength, known as extraordinary dispersion, which is an essential property in the preparation of an ideal quarter-wave plate. Numerous ellipsoidal pores with micro-scale were detected in the film after the immersion, indicating that DIDA were segregated and formed ellipsoidal domains in the CTA matrix during annealing and stretching. These results indicate that extraordinary wavelength dispersion is given by the combinations of orientation birefringence from CTA and form birefringence from micropores. Furthermore, it was found that annealing time and stretching condition affect the phase separation as well as the shape and size of pores.

Effect of acetylation site on orientation birefringence of cellulose triacetate

The effect of a substitution site on orientation birefringence for cellulose triacetate (CTA) was investigated by the addition of xylan ester. Since CTA has three substitution sites (C-2, C-3, and C-6) while xylan ester has two substitution sites (C-2 and C-3), the change of birefringence by xylan acetate (XylAc) is attributed to the contribution of the C-6 acetyl group. Dynamic mechanical analysis and thermal measurements showed a single glass transition peak, indicating that XylAc is miscible with CTA at any compositions. The orientation birefringence (Δn) of CTA/XylAc films stretched beyond the glass transition temperature increased with increasing the XylAc content. The result for the stretched film suggested that the contribution of acetyl group in the C-2 and C-3 sites to Δn is positive while that in the C-6 is negative. The negative sign for the C-6 site is in agreement with the result simulated by using the molecular dynamics method. In addition, Δn of CTA films containing xylan propionate (or butyrate) indicated that the propionyl and butyryl groups in the C-2 and C-3 sites show positive birefringence similar to the acetyl group.

Zero birefringence films of pullulan ester derivatives

High-performance films with almost zero-birefringence and zero-wavelength dispersion were succeeded to prepare from pullulan esters derivatives (PLEs) without any additives. Optical transmittance analysis, birefringence measurement of PLE cast film and hot stretched films, and infrared dichroism analysis were conducted to characterize optical properties of PLE films comparing with cellulose triacetate which is commercially used as low-birefringence in optical devices. The aims of this study, characterization of optical properties of pullulan esters, can develop a deep understanding of the fundamental knowing and applicability of polysaccharides. Accordingly, authors believe this paper will open the gate for researches in the application of polysaccharides.

Effect of acetyl substitution on the optical anisotropy of cellulose acetate films

The effect of acetyl substitution on the optical properties of cellulose acetate (CA) was investigated in the present study, because a strong demand for advanced retardation films increases greatly these days. The hot-stretched films with high acetyl substitution had negative orientation birefringence, whereas those with low acetyl substitution had positive orientation birefringence with extraordinary wavelength dispersion. It should be noted that orientation birefringence hardly relaxed even after cessation of hot-stretching. The slow relaxation of crystal orientation was responsible for the anomalous optical anisotropy, as confirmed by two-dimensional X-ray diffraction. Moreover, the slow relaxation of orientation birefringence would greatly benefit the preparation of CA optical retardation films by hot-stretching, because it would simplify the precise control of retardation. The stress-optical coefficient in the glassy state was also evaluated, and was found to decrease with the degree of acetyl substitution. This is an attractive property for optical film applications.Graphical Abstract