Extraordinary Wavelength Dispersion of Orientation Birefringence for Cellulose Esters

Abstract

Orientation birefringence and its wavelength dispersion are studied for hot-drawn films of cellulose esters such as cellulose triacetate (CTA), cellulose diacetate (CDA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB). The orientation birefringence of the cellulose esters is not proportional to the orientation function, indicating that the stress-optical law is not applicable for the cellulose esters. Furthermore, CTA shows negative birefringence, and the magnitude of the absolute value decreases with increasing the wavelength. On the contrary, CAP, CAB, and CDA show positive orientation birefringence that increases with the wavelength. The extraordinary wavelength dispersion of the orientation birefringence for CAP, CAB, and CDA is attributed to the difference in polarizability anisotropy of ester groups. Furthermore, the wavelength dependence of the orientation birefringence for CAP is dependent on the draw ratio and draw temperature, demonstrating that the contribution of polarizability anisotropy from each ester group to the orientation birefringence varies with the draw ratio and temperature. Moreover, the molecular weight and film-processing method also affect the orientation birefringence.

Effect of Moisture on the Orientation Birefringence of Cellulose Esters

“…CTA shows negative birefringence that decreases with increasing wavelength, i.e., ordinary dispersion which is a typical behavior for most polymers [5,6]. As demonstrated in our previous papers [8,9], the orientation birefringence in cellulose esters is determined by polarizability anisotropy and orientation of the side groups, e.g., acetyl, propionyl and hydroxyl groups. The result in Figure 2 indicates that the acetyl group in stretched cellulose esters contributes to negative birefringence with ordinary dispersion.…”

“…Consequently, it leads to a broad distribution of relaxation time as demonstrated in Figure 1. On the other hand, both CDA and CAP are not affected by crystallites as they are fully amorphous [8,12]. The sharp drop in the ' E of CAP corresponds to the narrow peak of ' ' E , around 144 °C.…”

“…Yamaguchi et al [8,9] have studied the orientation birefringence and the wavelength dispersion of various types of cellulose esters such as cellulose triacetate (CTA), cellulose diacetate (CDA), cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB), all drawn at a temperature above their respective glass transition temperature. It is found that CTA shows negative birefringence, in which the magnitude decreases with increasing wavelength.…”

Orientation birefringence of cross-linked rubber containing low-mass compound

“…[4][5][6][7][8] Furthermore, even plasticizer molecules are found to orient to the stretching direction by the alignment of polymer chains. [9][10][11][12][13][14] Therefore, LMCs having large intrinsic birefringence are added into an optical polymeric film in the industry, which becomes a key technology to control the birefringence and its wavelength dispersion. [9][10][11][12][13][14] However, the orientation relaxation of LMC molecules has not been clarified.…”

“…[9][10][11][12][13][14] Therefore, LMCs having large intrinsic birefringence are added into an optical polymeric film in the industry, which becomes a key technology to control the birefringence and its wavelength dispersion. [9][10][11][12][13][14] However, the orientation relaxation of LMC molecules has not been clarified. Since it is expected that LMC molecules could relax the orientation prior to the polymer chains, this should be clarified to establish the material design of an optical anisotropic film.…”