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Attempts to create foamed or foamed materials from wood fibers date back to the 1940s. Wastewater containing high concentrations of lignin (a byproduct of paper and fiberboard manufacturing) was used as a source of lignin; carbonic acid was added to the process, causing the mixture to foam and solidify. Alternatively, the foaming was achieved by blowing air. Other techniques were also explored. However, none achieved commercial success, and the know-how was lost. More recently, at the beginning of the millennium, this wartime idea was revived and adapted. During World War II shortages, sawdust was added to bread dough to conserve food supplies. In 2003, Austrian researchers capitalized on this idea, mixing sawdust with wheat flour and water to form a dough that was then leavened with yeast. After baking, the product became known as "wooden bread," marketed as an industrial product rather than a food.
The current product does not have these drawbacks. It appears as a brown or colored sponge that is hard to the touch, with pores of varying size and proportion, depending on the desired density. Its sole component is wood fiber, which can be softwood or hardwood, or virtually any woody biofiber source, including agricultural waste. In the laboratory, beech and pine wood were used. To break down the wood chips into fibers through thermomechanical pulping, they were ground in a refiner at 150°C. This was then mixed with water to produce a very finely ground wood fiber suspension. To foam the aqueous suspension, protein can be added or air can be blown through it. The product's strength depends on the inherent cohesive strength of the wood fibers. For activation, hydrogen peroxide is added, and the foamed suspension is then convection-dried at 130°C for half an hour and then held at 70°C overnight. (This is, of course, a laboratory process. Commercial production is ongoing.)
Different densities of foam
To be continued