Molecular Orientation and Optical Anisotropy in Drawn Films of Miscible Blends Composed of Cellulose Acetate and Poly(N-vinylpyrrolidone-co-methyl methacrylate)

Abstract

Poly(N-vinylpyrrolidone) (PVP) is miscible with cellulose acetate (CA) with a degree of acetyl substitution (DS) of less than ca. 2.75, and a random copolymer of N-vinylpyrrolidone (VP) and methyl methacrylate (MMA) can also form completely miscible blends with CA, when the VP fraction in the copolymer is >30 mol % and the DS of CA is ≤2.5. The molecular orientation and optical anisotropy induced by uniaxial deformation of the miscible blends of the VP-containing vinyl polymers [P(VP-co-MMA)s] with CA were characterized by a fluorescence polarization method and birefringence quantification, respectively. Film samples of more than 10 pairs of CA/P(VP-co-MMA) were cast from mixed polymer solutions in N,N-dimethylformamide containing a slight amount of a stilbene derivative as a fluorescent probe, to assume different blend compositions for each individual polymer pair. Through analysis of polarized fluorescence intensity, it was found that all the drawn films gave a positive orientation function, but the orientation development became suppressed with increasing content of the vinyl polymer component. In comparison between different CA/PVP series, the drawn blends comprising a CA of comparatively lower DS and a PVP of higher molecular weight indicated a higher degree of orientation at any stage of elongation. The molecular orientation in CA/VP−MMA copolymer blends was affected by the DS of CA in a similar manner to that in the CA/PVP series, but the VP:MMA ratio in the copolymer was less effective. The optical birefringence of the drawn films, when compared at a given draw ratio for a series of blends, decreased drastically with an increase in the vinyl polymer content and changed from positive to negative values at a certain blend composition. This optical behavior is interpretable in terms of an effect of birefringence compensation due to the positive and negative contributions of oriented CA and vinyl polymer, respectively, to the overall birefringence. The critical binary composition where the blend remains a birefringence-free material shifted to the CA-rich composition side with increasing DS of the CA used as well as with increasing VP fraction in the P(VP-co-MMA) component. At vinyl polymer-rich compositions, the negative birefringence observed for the drawn blends was even greater in absolute value than that of the drawn, unblended vinyl polymer, suggesting that the two constituent polymers can orient cooperatively as a result of their high miscibility.

Molecular orientation and optical anisotropy in drawn films of cellulose diacetate-graft-PLLA: comparative investigation with poly(vinyl acetate-co-vinyl alcohol)-graft-PLLA

“…4a and b, the film of unmodified CDA showed a high level of molecular orientation upon stretching, so as to make a just fit of the \cos 2 x[ vs. percent elongation plot to the theoretical curve of the affine deformation; however, the film specimen was prone to break at an earlier stage of elongation (e = *50%). The capability of CDA to assume such a high orientational action may be attributed not only to its semi-rigid carbohydrate backbone, but also partly to the intermolecular interaction via hydrogen-bonding between the residual hydroxyl groups (Ohno and Nishio 2007). A high degree of molecular orientation was also observed for PVOH homopolymer capable of forming a well-developed hydrogen-bonding network in the film material.…”

“…For intimately mixed multicomponent polymer systems such as random copolymers (Tagaya et al 2006) and compatible polymer blends (Hahn and Wendorff 1985;Nishio et al 1990Nishio et al , 1994Ohno and Nishio 2007;Yamaguchi and Masuzawa 2007), a noteworthy effect may be found in the optical properties of their oriented materials. That is, by adequately combining two ingredients that have opposite polarizability, the strain-induced birefringence can be voluntarily controlled, and, in a special case, the original optical isotropy is maintained regardless of the polymer chain orientation.…”

Insight into miscibility behaviour of cellulose ester blends with N-vinyl pyrrolidone copolymers in terms of viscometric interaction parameters

“…For improvement in physical properties of CEs toward their further applications, the designing of high-functional multicomponent materials based on the cellulosics via graft copolymerization or polymer blending is a significant approach (Edgar et al 2001;Nishio 2006;Yamaguchi 2010;Sugimura et al 2015). In the field of optical materials such as regulator or modulator of polarized light in modern displays, great attention of researchers has been focused on the delicate control of orientation birefringence and its wavelength dependence for CE-based films (Ohno and Nishio 2007a;Yamaguchi 2010;Yamaguchi et al 2012;Yamanaka et al 2013;Sugimura et al 2013b;Hayakawa and Ueda 2015;Sugimura et al 2015). Especially, miscible polymer blending is practically useful to manipulate the physical properties and functions of CEs readily at the lowest cost possible.…”

Effect of Moisture on the Orientation Birefringence of Cellulose Esters

“…Orientation birefringence of miscible blends of two-component polymers with mutually opposite sign of birefringence, e.g., cellulose acetate (CA) and Poly(N-vinylpyrrolidone-co-methyl methacrylate) (P(VP-co-MMA)) random copolymer, was studied by Ohno and Nishio [10]. It was reported that the birefringence of the blend decreases with decreasing CA fraction and eventually changes from positive to negative at a certain combination.…”