The present invention relates to the extrusion process of polymeric foams with controlled density and granulometry, by using post-consumer or recycled heterogeneous plastic as a raw material, as, for example, polyolefines coming from the recycling of solid urban or industrial waste. These foams can be added to concrete instead of expanded clay or Polystyrene or other limestone inert materials.
Examples of applications of other concrete fillers based polymers and polymer foams can be found in the following patents/patent applications:
The major drawback of the known applications is that the product obtained cannot be used as building structural element, because the properties are compromised by complex mixture formulation and dosage. The high entrapment of air during the mixing operation, due to the crushed shape of the polymeric flakes and to the kind of the polymer, also creates a remarkable porosity, that causes the short lifetime of the product. In addition, poor mechanical properties can arise from poor properties of light polymer fillers.
The present invention as defined in claims 1 and 8 solves the above mentioned problems being an extrusion process of polymeric foams with controlled density and granulometry; such foams can be added to cement to create concrete to be used for different purposes, as, for example, building and/or high insulating material. The invention makes use of heterogeneous plastic as a raw material, such as polyolefines, both washed or not, coming from the waste differentiate collection (for example, solid urban or industrial waste).
According to the invention, is the use of a foamed chemical agent, bi-hydrate calcium sulphate (known as gypsum), which is also a waste material, a by-product of smoke treatment of power plants. It is produced in large quantities thanks to the removal of Sulphuric and Sulphurous anhydride produced during the combustion of solid and liquid fuels containing Sulphur. These and other advantages will be pointed out in the detailed description of the invention that will refer to a preferred way of carrying out.
Subject-matter of the invention, as defined in claims 1 and 8, is a process to obtain a polymeric foam with controlled density and granulometry, which, according to the needs, can be added to the cement to produce concretes, to be used for different purposes, as, for example, building and/or high insulating material. Infact, the lenticular shape of the expanded polymer allows to remarkably reduce the air entrapment and, as a result, to increase the concrete lifetime. Each component of the plastic mixture can be substituted, in part or as a whole, by the corresponding virgin polymer. The heterogeneous polymer expansion is realized by means of a chemical agent, bi-hydrate calcium sulphate (commonly known as "gypsum"), never used before for this purpose, which produces only steam as a dissociation gas with a better environmental impact with respect to other known chemical expansion agents. The bi-hydrate calcium sulphate is a waste material deriving from the treatment of power plants smoke (also carbon ones) and, therefore, is available in a large quantities and free of charge.
According to a preferred solution, a crosslinking agent is to be used, to increase the melt strength of the fused polymer to avoid the polymer collapse under the gas pressure produced by the dissociation of the expanding agent.
The desired characteristics of the polymeric foam, density and granulometry, are obtained by optimizing the following parameters:
Several formulas, optimized with different density range (air to cement ratio, paste volume), have been developed to obtain the best possible properties of the final product; with respect to the known concretes additivated with not-expanded heterogeneous plastic, this new product shows:
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