540 Chemie und zugeordnete Wissenschaften
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Presently, about 8 million metric tons of polyurethanes are produced in the world annually. During production of precursors, semi-finished products and final products about 5 to 10 % of this amount is waste, i. e. an amount of about half a million tons. To this add the products after their life cycle. This is a large source of material which should not be given to landfills or incinerators but be used as secondary materials for the production of new polyurethanes.
The synthesis of polyurea dispersion polyols (PHD) was developed using a new route via depolymerization of polyurethane polyureas by a mixture of at least two glycols in the presence of a consumable catalyst, i. e. a secondary aliphatic amine. On this way such polyols were produced with a particle size distribution with a maximum in the 120 to 400 nanometer region with hydroxyl numbers of 180 to 300 mg KOH/g being optically clear and highly reactive. The exact adjustment of the ethylene oxide content of the reaction mixture together with that of the polyether polyol originally present in the polyurethane polyurea used in a predetermined range of surface tension as well as specific reaction conditions leads to these polyols which will give in turn polyurethanes with exceptional properties.
This paper is directed to the development of a new type of branched aromatic polyester polyols (APP) based on PET wastes designed to produce high quality polyurethanes (PUR). To this end, a modifi ed transesterification of PET by a glycol mixture was used and simultaneously small amounts of triols were incorporated into the reaction mixture. By this method, a series of branched APP’s with hydroxyl numbers in the range of 260 to 380 mg KOH/g and hydroxyl functionalities between 2.00 and 2.30 was received. The viscosity of the products increased slowly with the functionality in the range of 2.03 to 2.12 and sharper beyond this value. An optimum of properties was found in each series of APP with hydroxyl numbers of 260, 320, and 380 mg KOH/g, resp. with respect of viscosity, long term stability and hydroxyl functionality. APP with a higher hydroxyl functionality are useful to produce cast polyurethane resins, those with lower hydroxyl numbers for coatings, e. g. of leather.