Solution casting of cellulose acetate films: influence of surface substrate and humidity on wettability, morphology and optical properties

Abstract

Variations on the processing conditions of conventional methods for polymeric film preparation may allow tuning certain properties. In this work, different casting surfaces and humidity are presented as variables to consider for cellulose acetate (CA) film preparation using conventional solution casting method. Specifically, borosilicate glass, soda-lime glass and Teflon (PTFE) dishes have been used for casting and their influence on various properties on CA films assessed. The surfaces of glass dishes are smooth, while PTFE surface has a pattern constituted by concentric channels of micro dimensions (as seen by optical microscope), which is adopted by cast films upon drying. The resulting patterned films are translucent while films produced using smooth surfaces are transparent. The effect of the environment humidity (35%, 55% and 75% RH) in the properties of the CA films during the evaporation of solvent from solution has been evaluated. Higher humidity produces smoother surfaces and increased crystallinity as shown by XRD and DSC; however, the wettability of the films does not seem to be influenced by this variable. Due to the specific morphology of the patterned films, changes in material opacity upon wetting are detected, from translucent to transparent, while the removal of water from the surface restores the translucency. This micropatterning effect that causes different visual appearance of the material can find use as a humidity sensor in food packaging applications.

Photopolymerization Pattern of New Methacrylate Cellulose Acetate Derivatives

“…CA and CA derivatives were dissolved in THF in six vials, stirred on a magnetic hob, and coated as films on which six droplets of water were added per film. The measured angle value for the CA was 62 ± 1° which was very close to the value described in the scientific literature (~60°) for the pure CA membranes (M = 50,000 g/mol having 29–45% acetyl group) [ 48 , 49 ]. Modification in the angle values may refer to the fact that 2-IEMA reacted with CA, affecting the existing hydrogen bonds between polymeric chains, either by decreasing their number or by increasing their length.…”

Active Cellulose Acetate/Chitosan Composite Films Prepared Using Solution Blow Spinning: Structure and Electrokinetic Properties

“…At this point, it is important to highlight the influence of the preparation route of these CA/CS composites. As stated in earlier works, CA is a hydrophilic polymer which, in the form of cast films, usually exhibits a contact angle in the range of 60–70° [ 24 , 45 , 51 ], and the addition of chitosan can further reduce the contact angle, making the final material very hydrophilic [ 24 ]. In another work by our group, it was shown that CA films prepared by SBS can result in various levels of hydrophobicity, depending on the morphology [ 28 ].…”

“…As can be seen in Figure 4 , all spectra show the typical absorption bands of cellulose acetate. The broad weak band around 3490 cm −1 corresponds to non-esterified hydroxyl groups (OH stretching) of cellulose; the weak bands at 2945 cm −1 and 2886 cm −1 are associated with the CH antisymmetric and symmetric stretching of the methyl group, CH 3 , respectively [ 11 , 45 , 54 ]. The high-intensity absorption band at 1735 cm −1 corresponds to carbonyl stretching in the acetyl group, as expected for cellulose acetate, which does not change upon the addition of chitosan.…”

“…Solution casting onto a glass petri dish was performed with the same solutions of cellulose acetate/chitosan in formic acid or acetic acid simply by leaving the solutions to evaporate under controlled humidity at 35% RH for 72 h. Before casting, the glass was coated with chlorotrimethylsilane to prevent strong adherence of films to the glass surface [ 45 ]. The cast films were used to compare the electrokinetic properties of the films prepared by the two different methods: the novel SBS method and the traditional casting method.…”

Valorization of waste paper sludge as a sustainable source for packaging applications

“…The acetylated sludge had WCA > 90°, a surprising result that is inconsistent with the previous explanations since the hemicellulose content of the sludge was higher than that of the purified samples (13% vs 9%). Therefore, WCA must also be affected by film appearance (unevenness or defects) and surface roughness [59].…”