Cellular Polymers

MDI based, CFC free, moulded polyurethane foam floor pan carpet composites are in production world wide. They will play an increasingly important role as a versatile and economic solution to the reduction of interior vehicle noise. This paper reviews current processing experience with ICI all-MDI acoustic foam systems and describes some of the results of the acoustic development programme which has been underway for the past two years. Simple model representations for airborne and structure borne noises are presented and analysed. A laboratory test rig is described which is used for the evaluation of the airborne noise and vibration radiated noise Insertion Loss of non-bonded carpet composites. Data are presented showing how system and material design parameters affect acoustic performance. Analysis of data shows that performance is controlled primarily by system parameters, namely area mass of heavy layer and thickness of foam isolating core. It is shown that control of foam properties such as density, stiffness, and clamping can be used to optimise system performance for a vehicle having a particular noise and vibration signature.

Polyester based microcellular polyurethanes are usually dimensionally unstable at low densities and show shrinkage.

Polyether based polyurethane soling materials however are usually dimensionally stable at these lower densities but exhibit unacceptably low mechanical properties. The density of these soles is therefore limited by the required properties.

Shrinkage occurs, at lower densities, because there is insufficient strength to support the foam and because of inherently high closed cell content. Problems of shrinkage have been overcome by the development of a new ICI prepolymer. This product acts as a reactive surfactant thereby controlling reactant compatibilities, cell size and open/closed cell ratios. Stable foams down to the free rise density are now possible.

The nature of the product is such that the derived products maintain satisfactory properties even at densities down to ca. 200 – 250 kg/m³. This constitutes a major weight saving per sole. Conventional midsoles have densities of ca. 400 – 500 kg/m³, so achieving, with the new prepolymer, a weight saving of ca. 50 %.

The low density midsole system can be used in conjunction with almost any outsole material. But of special interest is the use of the recently developed, high slip resistant outsole. The construction of this combi-sole allows direct replacement of EVA/Rubber soles - but with the usual all-PU processing/handling advantages. The high slip resistant PU outsole system is a soft formulation, which employs novel hydrophobic soft blocks and retains excellent mechanical properties.

The problems associated with the testing of fibre reinforced polymer composites arise because of the anisotropic and inhomogeneous nature of the material. The nature of these problems, the approach historically which has been taken to overcome some of them and the current situation with regard to tests and standards are discussed. The effect on test data of specimen design, composite fabrication, test method and the environmental history of the material, are discussed and experimental data taken from the author's own research is used to illustrate the influence of some of these factors.

This paper describes how Celotex, a manufacturer of a product with an environmental problem, is improving its products.

First, the background to Rigid Urethane Foams and the CFC issue.

Second a guide to the most popular applications for CFC-blown Rigid Urethane Foams in construction, highlighting the essential features of the product necessary for satisfactory performance in these applications.

Finally, an overview as to how successfully these essential characteristics are being reproduced in the new generations of CFC free foam boards now being introduced into the market, and some of those yet to come.