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Waste and scraps, from polyurethane elastomers, mainly from the shoe sole production, can be conveniently converted by a transesterification process into polyols which can be reused in the production of rigid foams, with both economical and ecological advantages.In the transesterification process, secondary reactions leading to amine formation, can be controlled by means of the reaction conditions.In the production of rigid foam the recovered products are mixed with fresh polyol; the recovered/fresh polyol ratio must be moderate in order to obtain materials with sufficiently high dimensional properties.

Rigid polyurethane foams filled with alumina trihydrate (ATH) exhibit, in comparison with non-filled foams, higher fire resistance when evaluated using the oxygen index (O.I.) test method.The hydrate particle size within a certain range, does not have any effect on the oxygen index. The efficiency of the treatment increases with the concentration of ATH in the foam and, by using simultaneously flame resistant agents containing phosphorous, it is possible to obtain polyurethane foams with O.I. of the same order of those of polyisocyanurate foams.Thermogravimetric analysis has shown that the ATH does not modify the thermal-oxidative degradation in the polymer.The reduction in the smoke density of the ATH filled foams can be attributed to the action in gas phase of an intermediate in the ATH decomposition process and to the slower thermal-oxidative degradation of the polymer.

Alumina trihydrate (ATH) is an active filler in various polymer systems with respect to flame resistance and smoke emission.It does not modify substantially the morphology of the foam in the density range normally used for heat insulation when it is utilised as filler for rigid polyurethane foams.The physical properties of the foams are only slightly affected by the filler and it would not seem necessary to treat the surface of the filler in order to improve its coupling with the polymer.A certain amount of care must be taken in order to maintain the volumetric yield during expansion.

Glycolysis products from microcellular elastomer polyurethane were used in the preparation of PUR-PIR rigid foams.Foams were generally good but, with a low NCO index, showed insufficient dimensional stability.The foam stability can be improved by an increase in the crosslinking density of the polymer, by using polyol components with an increased functionality or by increasing the isocyanurate content.The improved crosslinking induced by trimerisation is more efficient for stability than that derived by higher polyol functionality.The use of MDI with a high average functionality and glycolysis products with a relatively high equivalent weight, permit a more favourable MDI/polyol ratio and are therefore economical.

The substitution of CFC-11 with blowing agents with low environmental impact, for the production of PU thermal insulating materials, implies the variation of several properties of the material. The worsening of fire behaviour of material, based on Ixol B 251, with flammable blowing agents (HCFC-141b, 2-chloro propane and n-pentane) can be reduced by modifying the formulation, i.e. by increasing the amount of flame retardants.The results of the Oxygen Index test were compared with the data obtained from the ISO 3582, DIN 4102 - B2 and UNI 9177 test and gave a good correlation.The initial thermal conductivity of the various foams is strictly linked with the thermal conductivity of the gas phase and increases with the new blowing agents and particularly in the case of n-pentane reaches values which are about 20% higher than that of foams blown with CFC-11.Hydrocarbon type blowing agents do not change significantly the mechanical properties of the materials; small variations in mechanical properties with HCFC-141b should be attributed to the solvent action of the compound on the polymer matrix.

The mechanisms of degradation of rigid Polyurethane foams (PU) filled with Ammonium Phosphate (AP) as inorganic flame retardant, have been studied using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) both in inert (N2) and oxidizing (air) atmospheres.TGA analyses have shown that the filler modifies the thermal and the thermaloxidative decomposition of the polymer, but the formation of much more stable thermal structures with respect of unfilled PU can be obtained only in an oxidizing atmosphere.The phosphoric acid formed by the endothermic decomposition of AP, acts as a dehydrating catalyst of the polymeric substrate, leading towards the formation of thermally stable structures (char precursors).The reduction in the smoke density of the AP filled foams can be attributed to the actions in the solid phase of the H3PO4that produce a slower thermaloxidative degradation of the polymer decreasing the flammable volatile and potentially toxic products and also producing a protective layer on the surface of burning material.

Flexible water blown polyurethanes are polymers with repeating urethane and urea groups. When they undergo heating in the presence of glycols the reaction of these groups leads to soluble products. The transesterification reaction of the urethane groups, that leads to the formation of new carbamate is faster than that of the urea groups. Carbamates in turn undergo aminolysis due to the amines formed in the glycolysis of the urea groups.The use of ethylene glycol (EG) allows the process to be carried out with high polymer/glycol ratio (up to 4:1). A polyphase product is obtained with a top liquid phase mainly formed by the polyether polyol from the polymer, an intermediate liquid phase formed by the solution of carbamates, ureas and amines in EG and a bottom solid phase with compounds with prevalent urea bonds.