COMBUSTIBILE SOLIDO SINTETICO E SUO IMPIEGO COME SOSTITUENTE DELLA LEGNA

1. A solid, log-shaped fuel prevalently consisting of synthetic material which can be used as a substitute for wood, obtained by a process characterized in that the following products are mixed in the molten state: a) thermoplastic resin with a high molecular weight, having a density of between 0.8 and 1.0 g/cm and a melting point equal to or less than 230 degree C , in a quantity of between 70% and 97% by weight; b) a resin with a low molecular weight in a quantity of between 3 and 30% by weight; c) a blowing agent selected from inorganic or organic compounds in a quantity of between 0.02 and 0.5 moles per Kg of thermoplastic resin, this molten mixture is extruded through a matrix; and finally the extruded mass is cut into cylindrical form. 2. The fuel according to Claim 1, characterized in that the thermoplastic resin is a polyolefin selected from polyethylene, olypropylene, polybutene or their copolymers. 3. The fuel according to Claim 2, characterized in that the thermoplastic resin has a melting point equal to or lower than 180 degree C. 4. The fuel according to Claim 1, characterized in that the resin with a low molecular weight: be selected from waxes of petroleum origin or derivatives from synthesis of the Fischer-Tropsch type. 5. The fuel according to Claim 4, characterized in that the resin with a low molecular weight is used in a quantity of between 5 and 15% by weight with respect to the thermoplastic resin. 6. The fuel according to Claim 1, characterized in that the blowing agent is selected from inorganic compounds such as CO2, N2, Ar, steam or organic compounds such as aliphatic hydrocarbons with from 1 to 9 carbon atoms or chemical substances such as azodicarbonamide, azodisobutyronitrile, N,N'-dimethyl-N,N'-dinitrousterephthalamide and trihydrazinotriazine. 7. The fuel according to Claim 6, characterized in that the blowing agent is CO2. 8. The method of obtaining a solid synthetic fuel according to Claim 1 by mixing thermoplastic resin with a high molecular weight, having a density of between 0.8 and 1.0 g/cm and a melting point equal to or less than 230 degree C, in a quantity of between 70% and 97% by weight; a resin with a low molecular weight in a quantity of between 3 and 30% by weight and a blowing agent, extrusion the molten mixture and cutting of the extruded mass into pieces of cylindrical form characterized in, that the quantity of blowing agent is between 0.05 and 0.3 moles per kg of thermoplastic resin. 9. The fuel according t