Cellular Polymers

Rigid polyurethanes have been used in the manufacture of household appliances for three decades. Their use has helped turn refrigerator manufacture into a major world activity, allowing completely new approaches to design and production.

This paper reviews the polyurethane properties that have enabled the domestic refrigeration industry to grow and describes current manufacturing and assembly techniques. Issues such as CFC phase-out, and the manufacturing implications, are discussed, along with likely trends for the future. It shows that for the polyurethanes industry to be an effective supplier to the refrigeration industry, it must continue to provide strong support over the next few years.

Over the last two to three years, the automotive industry has recognised the benefits of low density structural reaction injection moulding (LDSRIM) materials in automotive interior applications. Low part weights, consolidation of parts, and improved design freedom associated with this technology help reduce material and labour costs, improve productivity and help engineers meet specific objectives such as CAFE standards.

ICI Polyurethanes has actively participated in the development of LDSRIM technology and has developed a series of resins designed for automotive interior application. These CFC-free polyurethane foams are processable on conventional RIM equipment. The resin systems are differentiated for open pour and closed mould processing techniques.

Unique processing features allow glass reinforced substrates to be moulded directly behind various vinyl composites, carpeting and fabrics, to produce parts with an aesthetically pleasing look and feel. Excellent adhesion to these substrates eliminates the need for secondary adhesive bonding operations, thereby improving productivity and lowering assembly costs. Composite door panels containing 20% by weight glass mat reinforcement weigh approximately half as much as competitive materials, such as ABS and polypropylene, with comparable physical properties. Typical door panel composite materials have flexural modulus 2370 MPa at 0.55 specific gravity. Unreinforced sections of the part, such as ribs and attachment points, are filled with a durable rigid foam material. Attachment inserts can be moulded in place to eliminate the need for post-mould assembly. Manufacturing mould residence times of 45 seconds are achievable in door panels.

American Cyanamid Company has developed a novel, high functional carbamylmethylated melamine polyol named CYUNK™ HPC polyol. The reactivity of CYUNK™ HPC polyol was studied and compared with that of an aromatic amine polyol (Pluracol® 824 polyol) and a sucrose-based polyol (Voranol® 360 polyol). A combination of the CYUNK™ HPC polyol and aromatic amine polyol was used for the preparation of rigid urethane foams. Water, CFC-11A and a mixture of CFC-11A and water (50/50) were used as the blowing agents. The k-factor of the foams containing CYUNK™ HPC was good: 0.022 W/mK for the water-blown system, 0.018 for the foam blown with a mixture of CFC-11A and water, and 0.015 for the CFC-11A blown foam. In all cases, retention of the k-factor with ageing (at room temperature and 70°C) was better for foams containing CYLINK™ HPC than for the control foams. Photomicrographs of the cell structure showed that the cell size of the foams containing CYLINK™ HPC polyol was smaller than that of the control foams. The presence of CYLINK™ HPC polyol decreased the combustibility of the water-blown rigid urethane foams. This effect was very significant in the case of foams containing sucrose-based polyol. The residue after burning of the reference foam without flame retardant was 26%, and with flame retardant (10 pbw) 48%. The residue after burning of the foam containing 30 pbw of CYUNK™ HPC polyol without flame retardant was 76%. CYUNK™ HPC polyol can thus be classified as a reactive flame retardant**. The study also included the effect of surfactant concentration and isocyanate index on the properties of water-blown rigid urethane foams containing CYUNK™ HPC polyol.