In this study we present a rapid method to prepare robust, solvent resistant nanofibrillated (NFC) cellulose films that can be further surface modified for functionality. The oxygen, water vapor and grease barrier properties of the films were measured and in addition mechanical properties in dry and wet state, and solvent resistance were evaluated. The pure unmodified NFC films were good barriers for oxygen gas and grease. At relative humidity below 65%, oxygen permeability of the pure and 2 unmodified NFC film was below 0.6 cm 3 µmm -2 d -1 kPa -1 , and no grease penetrated the film. However, the largest advantage of these films was their resistance to various solvents, like water, methanol, toluene and dimethylacetamide. Although they absorbed a substantial amount of solvent, the films could still be handled after 24h of solvent soaking. Hot-pressing was introduced as a convenient method to increase not only the drying speed of the films but also enhance the robustness of the films. The wet strength of films increased due to the pressing. Thus they can be chemically or physically modified through adsorption or direct chemical reaction in both aqueous and organic solvents. Through these modifications the properties of the film can be enhanced introducing e.g. functionality, hydrophobicity or bioactivity. Herein a simple method using surface coating with wax to improve hydrophobicity and oxygen barrier properties at very high humidity is described. Through this modification the oxygen permeability decreased further and was below 17 cm 3 µmm -2 d -1 kPa -1 even at 97.4 % RH and the water vapor transmission rate decreased from 600 to 40 g/m 2 day. The wax treatment did not deteriorate the dry strength of the film. Possible reasons for the unique properties are discussed. The developed robust NFC films can be used as a generic, environmentally sustainable platform for functional materials.

No abstract

No abstract

No abstract

Furthermore, hydrogels exhibited self-healing ability, being able to be broken apart and reformed manually into a single continuous piece without additional external stimuli. This behaviour was attributed to the break-down and reformation of hydrogen bonds within the hydrogel. NFC fibrils contributed towards enhancing gel content and retarding swelling, essentially restricting segmental motion and water penetration. Increasing borax content had a similar effect due to closer PVA chain proximity and higher crosslink density. Compressive mechanical properties were enhanced with additions of up to 40 %·wt NFC and increased borax concentrations, while creep was retarded due to the influence of NFC on flow and viscosity and greater chain restrictions via crosslinking at increased borax loadings. Both PVA:borax complexes (crosslinking) and hydrogen bonding contribute to the mechanical performance of the hydrogels. Concentrations of NFC above 40 %·wt diminished structural properties, due to the nanofibrils preventing effective crosslinking and disrupting the network structure of the hydrogels.

Three-dimensional printing (3DP) refers to a group of additive manufacturing techniques that can be utilized in tissue engineering applications. Fused deposition modeling (FDM) is a 3DP method capable of using common thermoplastic polymers. However, the scope of materials applicable for FDM has not been fully recognized. The purpose of this study was to examine the creation of biodegradable porous scaffold structures using different materials in FDM and to determine the compressive properties and the fibroblast cell response of the structures. To the best of our knowledge, the printability of a poly(ε-caprolactone)/bioactive glass (PCL/BAG) composite and L-lactide/ε-caprolactone 75/25 mol % copolymer (PLC) was demonstrated for the first time. Scanning electron microscope (SEM) images showed BAG particles at the surface of the printed PCL/BAG scaffolds. Compressive testing showed the possibility of altering the compressive stiffness of a scaffold without changing the compressive modulus. Compressive properties were significantly dependent on porosity level and structural geometry. Fibroblast proliferation was significantly higher in polylactide than in PCL or PCL/BAG composite. Optical microscope images and SEM images showed the viability of the cells, which demonstrated the biocompatibility of the structures.

No abstract

In this work, the rheological properties of microfibrillated cellulose suspensions under stepped flow and constant shear were studied using a combination of rotational dynamic rheometer and digital imaging. During each rheological measurement, the structure of the suspension was monitored through a transparent outer cylinder with a digital camera. This enabled simultaneous analysis of the suspension floc size distribution and traditional rheological characterization. In stepped flow conditions, a good correlation between suspension floc structure and flow curve measurement was found. At constant shear, the suspension structure was dependent on the shear rate and concentration of the suspension. A low shear rate resulted in heterogeneous floc structure, which was also detected by an increase in the ratio of the viscous component to elastic component in the rheological measurement. At low concentrations and 0.5 s -1 shear rate, flow induced a formation of floc cylinders between the rotating cylinder and stationary cup surface.