PURPOSE: To improve the soundproofing properties by applying plasma to a vegetable fiber in an ordinary temperature solution for converting it through a chemical reaction caused by the plasma wave to a polymer-like material and blending an inorganic material, etc., therewith so that both the organic and inorganic materials may be contained.

CONSTITUTION: Wood chips are supplied from a hopper 1 to a crushing and drying oven 2 and crushed in a frozen state at the upper part of the oven 2 so as to remove water from the wood chips. The resultant dried wood material composed of a vegetable fiber is supplied through a quantitative classifier 21 for the raw material to a polymerization reaction oven 5 by a high-pressure screw conveyor 4. Liquefied CO2 is simultaneously supplied from a CO2 bomb 7 through a flow meter 19 and a heat exchanger 8 thereto and ions accelerated by plasma from a plasma generator 14 are allowed to apply an impact to the wood at the same time. Thereby, a polymerization reaction is initiated and the fibrous glycolipid bark is converted through a chemical reaction caused by the plasma wave to a polymer-like material. The whole body of the raw material is simultaneously converted into a colloidal state and, after passage of a prescribed hour, the resultant colloidal material is supplied through a high-pressure screw driving unit 121 to a kneader 123. A coagulant such as Mg and an inorganic material such as diatomaceous earth are admixed therewith and the resultant mixture is charged under pressure through a pressure-type fixed discharge cylinder 1234 into a frame mold 1236, thus producing the objective solid material having a prescribed shape.