Zero birefringence films of pullulan ester derivatives

Tuning 3D refractive indices via constrained uniaxial stretch in cellulose triacetate films plasticized with triethyl citrate

Tuning 3D refractive indices of polymers is urgently needed for optical films, but it is quite challenging. Here, we proposed a simple constrained uniaxial stretch method that successfully tuned the 3D refractive indices in cellulose triacetate (TAC) films plasticized with triethyl citrate (TEC). Our results suggest that, under constrained uniaxial stretch, the main chains and side groups prefer to orientate in the stretch direction and the constrained direction, respectively. Such a unique chain arrangement differentiates the refractive indices in three directions of the film. The branched small molecule TEC is also crucial for tuning refractive indices, which promotes chain activity and enhances the chain orientation under stretching, leading to a considerable change in refractive indices before samples fracture. The polymer film we fabricated possesses a direction-dependent optical performance, where the refractive index in the film thickness direction is between that of the stretch direction and constrained direction. This work provides a fundamental understanding on the chain structure and optical performance of polymer films. The constrained uniaxial stretch method, in general, should also be applicable to tuning other 3D physical properties through tuning the direction-dependent orientation of polymers.

Polysaccharide-based component and their relevance in edible film/coating: a review

Purpose

The purpose of this paper is to present an overview of functional properties of the polysaccharide-based component and their application in developing edible film and coating for the food processing sector.

Design/methodology/approach

In this review study, approximately 271 research and review articles focusing on studies related to polysaccharide-based components and their film-forming properties. This article also focused on the application of polysaccharide-based edible film in the food sector.

Findings

From the literature reviewed, polysaccharide components and components-based edible film/coating is the biodegradable and eco-friendly packaging of the materials and directly consumed by the consumer with food. It has been reported that the polysaccharide components have excellent properties such as being nontoxic, antioxidant, antimicrobial, antifungal and with good nutrients. The polysaccharide-based edible film has lipid and gas barrier properties with excellent transparency and mechanical strength. In various studies, researchers worked on the development of polysaccharide-based edible film and coating by incorporating plant based natural antioxidants. This was primarily done for obtaining improved physical and chemical properties of the edible film and coating. In future, the technology of developing polysaccharide-based edible film and coating could be used for extending the shelf life and preserving the quality of fruits and vegetables at a commercial level. There is more need to understand the role of edible packaging and sustainability in the food and environment sector.

Originality/value

Through this review paper, possible applications of polysaccharide-based components and their function property in the formation of the edible film and their effect on fruits, vegetables and other food products are discussed after detailed studies of literature from thesis and journal article.

DFT study of the influence of acetyl groups of cellulose acetate on its intrinsic birefringence and wavelength dependence

The effect of the acetyl groups of cellulose acetate (CA) on its intrinsic birefringence and its wavelength dependence was investigated using density functional theory (DFT). Seven types of CA repeating-unit models that differ in their degree of substitution (DS) and substitution sites were used in the calculations. The results suggested that the intrinsic birefringence (Δn°) and its wavelength dependence significantly depended on the conformations of the acetyl group at C6. Additionally, the intrinsic birefringence of CA films was estimated as the ensemble average of the calculated Δn° values of the conformers. The increase in the DS of CA led to a more negative intrinsic birefringence and a larger wavelength dependence. The computational results were in good qualitative agreement with the experimental results and suggested that conformational variety and/or its control would be important factors for the design of optical films containing CA.

Optical and mechanical properties of pullulan films studied by uniaxial stretching

Optical properties of pullulan films were examined before and after uniaxial stretching to obtain the specific molecular characteristics of pullulan. It was shown that the specific optical rotation for pullulan film was not affected by uniaxial stretching, being the same as that for pullulan in aqueous solution. Combined with the mechanical measurement, the stress-optical coefficient for pullulan was estimated as a material constant on the basis of the modified stress-optical rule. The birefringence was positive and increased with time during the stress relaxation of uniaxially-stretched pullulan film. A set of the stress-optical coefficients C_R=1.9×10^-9Pa^-1 and C_G=-4.6×10^-12Pa^-1 were obtained, where the subscripts R and G stand for the rubber and the glass components respectively.