The Effect of Ash Silanization on the Selected Properties of Rigid Polyurethane Foam/Coal Fly Ash Composites

According to the assumptions of the European Union, by 2050 it is planned to achieve climate neutrality. For this purpose, a document called the “European Green Deal” was established, which is a set of policies of the European Commission. One of the assumptions is a circular economy that takes into account the use of waste in subsequent production cycles. In order to meet the latest trends in environmentally friendly materials and use of waste in the production of building materials, composites of rigid polyurethane foam with 10 wt.% of waste were produced. Fly ash from coal combustion after modification was used as a filler. Three types of modifications were used: silanization, sieving, and both processes together. The silanization process was carried out for 1 and 2% silane ([3-(2-aminoethylamino)propyl]trimethoxysilane) concentration in relation to the fly ash mass. The sieving was aimed at reaching a fraction with a particle diameter below 75 µm. Six composites with modified fillers were compared and one material containing unchanged fly ash was used as a reference. A comparative analysis was carried out on the basis of surface analysis, thermal stability and physical properties. It turned out that the polyurethane materials modified fly ash silanized with 1% and 2% silane solution proved the best results in performed tests. On the other hand, the polyurethane foam containing sieved ash was characterized by the lowest flammability and the lowest emission of smoke and CO. The use of modified fly ash in technology of polyurethane foams can be a good method of its disposal and can increase the applicability of the composites.