EMPLOYMENT OF ZERO ODP BLOWING AGENTS FOR POLYURETHANE RIGID FOAMS FOR THERMAL INSULATION

The problem of ozone depletion in the atmosphere is becoming more and more important. Consequently, many countries introduced more restrictive regulations in comparison with the Montreal Protocol and its subsequent revisions, anticipating the phaseout of CFC. The introduction of HCFCs, whose molecules are less harmful to the ozone, is entering a transitional period awaiting more conclusive solutions (e.g., zero ODP systems). In this respect EniChem has been concentrating its efforts on setting up systems for the production of PU rigid foams blown with HFC-134a for thermal insulation. Significant progress has been made on the employment of this blowing agent in the refrigeration application. Initial thermal conductivity values at 23-degrees-C of about 21 mW/mK in real cabinets were obtained, comparable to that of reduced CFC-11 systems currently used in the market. Energy consumption data were also equivalent to reduced CFC-11-containing refrigerators. Further research allowed us to also extend the employment of this blowing agent for production of continuous panels, overcoming the problem of excessive ''frothing effect'' that unitl now limited the use of low boiling agents in this field. Good material distribution and mechanical characteristics were obtained, and in particular again a thermal conductivity value at 23-degrees-C of 21 mW/mK. The most interesting alternative, from the technological and scientific point of view, however, is the blowing obtained only by CO2, which is produced by the reaction between water and isocyanate. EniChem/PU Division research in this respect has been basically directed to the reduction of initial and aged lambda value, without leaving out other important aspects, like dimensional stability and adhesion to facers. The results of this research allowed the achievement of interesting performances both in the continuous panels and in the refrigeration cabinets production, demonstrating the possibility of strongly reducing initial thermal conductivity down to 22 mW/mK at 23-degrees-C. Moreover, use of PU matrixes of lower permeability to CO2, with respect to normally accepted values, limited the aging problem so that after 3 months at room temperature a panel without skin, 40 mm thick, increased its thermal conductivity value only 10%.