Effect of Moisture on the Orientation Birefringence of 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), and cellulose acetate propionate (CAP) exposed to three different humidities of environments. Hot-drawn CTA films show negative birefringence that decreases with increasing wavelength. On the other hand, CDA and CAP films show positive birefringence that increases with increasing wavelength, i.e., the so-called extraordinary wavelength dispersion of birefringence. Upon exposure to high humidity environment, the orientation birefringence of CDA and CAP decreases. The decrease is prominent for the samples containing a large amount of water. CTA, however, shows an increase in magnitude of its negative orientation birefringence with increasing moisture content. The results can be explained by the increase of the polarizability anisotropy perpendicular to the stretching direction in the cellulose esters. It is found from ATR-FTIR measurements that hydrogen bonds are formed between carbonyl groups of cellulose esters and water molecules. Considering that orientation birefringence of cellulose esters is determined mainly by ester groups, the formation of hydrogen bonds contributes to the polarizability anisotropy, thus affecting the orientation birefringence.

Strong orientation correlation and optical anisotropy in blend of cellulose ester and poly(ethylene 2,6‐naphthalate) oligomer

“…The films were immediately quenched by cold air blowing after stretching to avoid relaxation of molecular orientation. The stretched samples were kept in a humidic chamber (IG420, Yamato, Japan) at 25°C and 50%RH for 1 day in order to ignore the moisture effect on the optical properties as previously reported …”

Effect of aromatic additives with various alkyl groups on orientation birefringence of cellulose acetate propionate

“…The films were immediately quenched by cold air blowing after stretching to avoid relaxation of molecular orientation. The stretched samples were kept in a humidic chamber (IG420, Yamato, Japan) at 25°C and 50% RH for one day in order to ignore the moisture effect on the optical properties as previously reported . The birefringence of the drawn films was measured as a function of wavelength by using an optical birefringence analyzer (KOBRA‐WPR, Oji Scientific Instruments, Japan).…”

Miscible Transparent Polymethylmethacrylate/Cellulose Acetate Propionate Blend: Optical, Morphological, and Thermomechanical Properties

“…The transparency curve shows that there was a clear creep towards the visible region from 10% CAP down to 15% CAP concentration. This property has wide applications in different optical fields (Edgar et al 2001;Yamaguchi and Masuzawa 2007a;Manaf et al 2011). The PMMA/CAP blend samples started to become cloudy with increasing CAP concentration in PMMA.…”

“…It seems obvious from the absorbance curve that 10% CAP concentration in PMMA gave less absorbency in the UV region. This may be due to the nature of the chemical bonding between CAP and the PMMA backbone in the composition (Edgar et al 2001;Manaf et al 2011), while a high transparency of the sample of about 88.64% was maintained.…”