Pia Willberg-Keyriläinen

The effect of side-chain length of cellulose fatty acid esters on their thermal, barrier and mechanical properties

Abstract Currently, long-chain cellulose esters are not produced commercially because of high price, and since their preparation typically requires a large quantity of chemicals. To reduce the chemical consumption, cellulose reactivity needs to be increased without losing its quality. One way to increase the reactivity of cellulose is to decrease its molar mass in a controlled manner. In this study, we have synthesized cellulose esters with different side-chain length (C6–C18) in a homogeneous system using ozone molar mass-controlled cellulose. The target was to keep the degree of substitution as low as possible while still ensuring the suitability of cellulose esters for solvent casting. Thermal, barrier and mechanical properties were studied depending on cellulose fatty acid ester side-chain length. All our molar mass-controlled cellulose esters form optically transparent, flexible and heat-sealable films with good water barrier properties and are processable without the addition of an external plasticizer. Furthermore, the films have mechanical properties comparable to some generally used plastics. These good properties suggest that our molar mass-controlled cellulose esters could be potential candidates for various applications such as films and composites.

The effect of cellulose molar mass on the properties of palmitate esters.

Nowadays one of the growing trends is to replace oil-based products with cellulose-based materials. Currently most cellulose esters require a huge excess of chemicals and have therefore, not been broadly used in the industry. Here, we show that decreasing the molar mass of cellulose by ozone hydrolysis provides cellulose functionalization with less chemical consumption. To reveal the differences in reactivity and chemical consumption, we showed esterification of both native cellulose and ozone treated hydrolyzed cellulose. Based on the results, the molar mass of the starting cellulose has a significant effect on the end products degree of substitution and properties. Furthermore, molar mass controlled palmitate esters form mechanically strong, flexible and optically transparent films with excellent water barrier properties. We anticipate that molar mass controlled cellulose will provide a starting point for the greater use of cellulose based materials, in various application, such as films and composites.

Production of cellulose carbamate using urea-based deep eutectic solvents

Cellulose carbamate is a bio-based, biodegradable, and environmentally friendly material and thus an interesting alternative to petroleum-based polymers or fibers from cellulose produced using the viscose process for producing fibers from cellulose. In this study we described an efficient and green method to prepare cellulose carbamates by using deep eutectic solvents. Three different urea-based deep eutectic solvents were used with different molar ratios and cellulose consistency. Nitrogen content of cellulose carbamates increases when cellulose consistency increases from 5 to 20%. Also, the reaction temperature affects the nitrogen content. In addition, the cellulose crystallinity decreases during the carbamation reaction with 20% cellulose consistency using any of the three deep eutectic solvents studied, when the sample is processed in a high-consistency reactor. By selecting suitable parameters, the nitrogen content of cellulose carbamates can be easily adjusted to a desired level.

Hydrophobization and smoothing of cellulose nanofibril films by cellulose ester coatings

The Cellulose nanofibrils (CNF), also referred to as nanocellulose, is one of the most studied bio-based material in recent year, which has good potential in the future for packaging applications due to its excellent mechanical strength and oxygen barrier properties. In the future, CNF films may also find new applications for example in printed electronics, if the surface smoothness of CNF films can be improved. One way to improve surface smoothness is to use thin coating solutions with zero porosity, such as molar mass controlled cellulose ester coatings. In this study, we have coated CNF films using molar mass controlled cellulose esters with different side chain lengths forming 3-layer film (ester-CNF-ester). These coatings improved significantly the smoothness of CNF films. The 3-layer films have also good water vapor barrier and mechanical properties and the films are heat-sealable, which enable various new applications in the future.