Abstract
Although films of microfibrillated cellulose (MFC) have good oxygen barrier properties due to its fine network structure, properties strongly deteriorate after absorption of water. In this work, a new approach has been followed for actively tuning the water resistance of a MFC fiber network by the inclusion of dispersed organic nanoparticles with encapsulated plant wax. The modified pulp suspensions have been casted into films and were subsequently cured at 40 to 220 °C. As such, static water contact angles can be specifically tuned from 120 to 150° by selection of the curing temperature in relation with the intrinsic transition temperatures of the modified pulp, as determined by thermal analysis. The appearance of encapsulated wax after curing was followed by a combination of morphological analysis, infrared spectroscopy and Raman mapping, showing balanced mechanisms of progressive release and migration of wax into the fiber network controlling the surface properties and water contact angles. Finally, the appearance of nanoparticles covered with a thin wax layer after complete thermal release provides highest hydrophobicity.
Highlights
Microfibrillated cellulose (MFCs) possesses numerous interesting properties attributed to the formation of a dense fibrous network with high surface area and aspect ratio, high stiffness and tensile strength, and good oxygen barrier properties
The thermal properties of these materials were analyzed by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), as discussed below
Films has been developed in such a way, that a single chemical process is found to be sufficient for the surface modification of the MFC and depending on the required user properties the static water contact angles can be “actively” tuned from 120 to 150°upon selective curing
Summary
Microfibrillated cellulose (MFCs) possesses numerous interesting properties attributed to the formation of a dense fibrous network with high surface area and aspect ratio, high stiffness and tensile strength, and good oxygen barrier properties. The nanotechnological approaches enable to “actively” tune the surface functionalities of papers and/or cellulose fibers after deposition of a basic coating material. The formation of functional papers has been reported for different applications, e.g., fragrance papers [12], anti-bacterial paper [13], insect-repellant paper [14], color-producing paper [15] and photoactive papers [16] These papers utilize the native properties of the functional materials that were initially protected from environmental factors by microencapsulation techniques, but can be used for the controlled release of functional materials in response to external stimuli applied such as mechanical stress [12], temperature [14], light [16] and humidity [15], as such, desired “user-properties” can be delivered “on-demand”. It will be shown that the obtained water contact angles depend on the combined release and migration effects of the hydrophobic agent, leading to maximum hydrophobicity
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