A new type of micro/nanocomposite was made by using only micro fibrillated cellulose and inorganic fillers. This composite structure can contain up to 90% fillers being still mechanically stable and flexible. Calendering can be used to produce dense structures with extremely smooth surface. To study the effect of filler shape and type, both kaolin and precipitated calcium carbonate (PCC) based sheets were examined. Microscopy (cross-sectional and surface SEM images) and mechanical and morphological properties, including strength properties, surface roughness and dimensional stability as a function of moisture were analysed. After calendering the surface of the PCC containing sheets was smoother than that of photopaper and in the same level as reference plastic film Mylar A. The dimensional stability of the sheets was clearly better than that of paper sheets. The combination of a good dimensional stability with low surface roughness makes these structures potential for printed electronics applications, in which they could replace oil-based plastic substrates. Suitability for printed electronic applications was tested by inkjet printing conductors with silver nanoparticle ink. The sheet resistances of conductors printed on kaolin based sheets were close to those printed on plastic Mylar A film.

Novel lightweight cellulose fibre materials containing various strength enhancing polymeric and fibrillar components were formed with the help of foam technology. Increasing inter-fibre bond strength and local material density was attempted with unique lignin-containing wood fines (V-fines), cellulose microfibrils (CMF), TEMPO-oxidized cellulose nanofibrils (TCNF), and macromolecules such as cationic starch, polyvinyl alcohol (PVA), and locust bean gum (LBG). The investigated fibres included both long hemp bast fibres and northern bleached softwood Kraft pulp. In the low-density range of 38–52 kg/m3, the compression stress and modulus were highly sensitive to inter-fibre bond properties, the multi-scale features of the fibre network, and the foaming agent employed. Still, the compression-stress behaviour in most cases approached the same theoretical curve, derived earlier by using a mean-field theory to describe the deformation behaviour. At 10% addition level of fine components, the specific compression stress and compression modulus increased in the order of V-fines < CMF < TCNF. A tremendous increase in the compression modulus was obtained with LBG, leading to a material surface that was very hard. In general, the foams made with PVA, which acts both as foaming agent and reinforcing macromolecule, led to better strength than what was obtained with a typical anionic sodium dodecyl sulphate surfactant. Strength could be also improved by refining the softwood pulp. Graphic abstract

No abstract

No abstract

Foam technology enables the preparation of new fiber-based materials with reduced density and improved mechanical performances. By utilizing multi-scale structural features of the formed fiber network, it is possible to enhance the elasticity of lightweight cellulose materials under compressive loads. Sufficient strength is achieved by optimally combining fibers and fines of different length-scales. Elasticity is improved by adding polymers that accumulate at fiber joints, which help the network structure to recover after compression. This concept was demonstrated using natural rubber as the polymer additive. For a model network of viscose fibers and wood fines, the immediate elastic recovery after 70% compression varied from 60% to 80% from the initial thickness. This was followed by creep recovery, which reached 86% to 88% recovery within a few seconds in cross-linked samples. After 18 h, the creep recovery in those samples was almost complete at up to 97%. A similar improvement was seen for low-density materials formed with chemi-thermomechanical fibers. The formed structure and elastic properties were sensitive not only to the raw materials, but also to the elastomer stiffness and foam properties. The improved strain recovery makes the developed cellulose materials suitable for various applications, such as padding for furniture, panels, mattresses, and insulation materials.