Wood fibre based thermal insulation and sound absorption materials made by foam forming

Highly porous materials with gas containing open pores are used both as thermal insulation material and in noise control as a sound absorber material. The main use is in buildings, vehicles, industrial machines and home appliances. The materials currently used are glass and rock wool and different types of polymer foams. Only 1 % of thermal insulation materials used in Europe is based on the use of natural cellulose materials including agro and wood fibres. There is growing interest, however, in developing sustainable and easily recyclable thermal insulation and sound absorbing materials. These materials have a lower environmental impact than the conventional materials, which are based on synthetic oil based raw materials and/or where the embodied energy content is high. We will introduce a new type of manufacturing process for creating highly porous fibre structures. Foam forming technology utilises small air bubbles containing aqueous foam as a process fluid. In the foam forming process fibres, water and foaming agent are mechanically mixed and the aqueous fibre-containing foam is generated with air content between 50-70%. The air bubbles effectively prevent flocculation of fibres. After foam generation phase the fibre foam is spread on a wire. Highly porous, non-paper like materials can be produced by using small vacuums in the drainage phase and by using non-contact drying methods to prevent the collapse of the fibre network. Highly porous fibre structures were made from common papermaking pulps including softwood and hardwood cellulose pulps and thermomechanical (TMP) wood pulp to bulk density levels 25-80 kg/m3 with thicknesses varying from 10-40 mm. These materials showed similar thermal conductivity values compared to the current fibrous insulation materials and the open cell polymer foams, being significantly better than the current wood or agro cellulose based insulation products. Sound absorption was analysed from foam formed softwood cellulose materials. Their sound absorption coefficient was as well at a similar level with a commercial product made from glass wool and significantly better than that of a non-woven polyester product. A suitable application for the foam formed materials could be acoustic wall and ceiling panels at homes and offices. When further developed, the foam formed wood-fibre based materials will offer a sustainable addition to the current insulation and sound absorber material palette.