Light Foam Biocomposites
VTT (Technical Research Centre of Finland) is developing two types of light foam biocomposites: Fibrous foam and foamed bio-based thermoplastics.
Fibrous foam is intended mostly for surface panels in façade and interior walls. These are manufactured from porous wood fibre webs produced by foam-laid forming technology, possibly impregnated with biopolymers to achieve panels with good mechanical and sound absorption properties.
Foamed bio-based thermoplastics are intended for the middle layer of interior walls. They are physically expanded, bio-based, closed-cell foam produced by a thermoplastic extrusion process and it will enhance the thermal and sound insulation properties of the wall and stabilise the wall structure.
Porous wood fibre webs with varied densities are manufactured by the foam-laid forming technology. To achieve sufficient mechanical properties the fibre webs are sometimes strengthened using a small amount of additive.
Foam-laid forming: Aqueous foam is an excellent suspending medium
- foam is generated by foaming agents
- material is located in “bubble pockets” (vertex) leading to excellent structure formation
- the pseudo-plastic nature of foam allows for the dispersion of relatively long fibres (up to 200 mm), but also nanoscale fibres are possible.
Using this technology it is possible to manufacture a wide range of densities and thicknesses of materials from paper thin to tens of mm thick. In the OSIRYS project the target is to develop board-like material with thickness in an order of 10 mm and strength comparable to normally used wall boards (gypsum board mostly).
Good strength compared to gypsum boards with a clearly lower weight were achieved. The highest bending strength was achieved with wood fibres and a small amount of polymer binder. The bending strength was higher than that of normal gypsum board, but slightly lower than the strength of hard gypsum board. The weight of this new solution was approximately 3.5 – 4 kg/m2 – approximately 2 to 3 times lower than traditional gypsum board at 8.8 – 11.3 kg/m2.
In OSIRYS, extrusion foamed bio-based thermoplastics are being developed as a core for an internal insulation board. The research has up to now focused on the optimisation of foam and process parameters in lab-scale extrusion foaming, and in initial trials using a pilot-scale tandem extrusion line. The biobased materials are developed by TECNARO GmbH.
In laboratory scale tests lignin-based thermoplastic materials were foamed to find preliminary processing parameters. For these bio-based materials, the optimum temperature for successful foaming was found. The foam density reached 40-100 kg/m3 depending on the material used and the process parameters. The foam structures of selected samples are visible in the figures above, showing a closed-cell structure with mean cell size about 100 µm when a die temperature of 125°C is used. At higher temperatures the density too high for our application.
For the up-scaling of polymer foaming, a pilot-scale tandem extrusion line owned by VTT is used. The trials so far have been done using lignin-based thermoplastic material and PLA. In the initial experiments with PLA, a foam board with a thickness of 10 mm, width of 70 mm, density of 60 kg/m3 and average cell size of 500 µm was obtained (see image below). Throughput in the experiments was 7.2 kg/h, and the dimensions can be increased by using higher throughput rate.