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A new non-CFC, MDI-based flexible foam technology.



A new theory of foam reaction mechanisms that led to revised concepts of foam morphology guided the design of an MDI-based isocyanate for automotive seating and headrest applications.

The well-documented hazards of chlorofluorocarbon (CFC) blowing agents have led to a huge, worldwide development effort to produce foams without the use of CFCS. Mobay Corporation's long-term research efforts in MDI-based flexible foams has resulted in the recent development of a new class of these foams that are made without using CFCs and which meet or exceed most automotive specifications. This article discusses the steps in the development process, outlines the concepts behind the new MDI foam technology, and presents examples of the excellent physical properties of these new foams.


There are two methods for obtaining MDI-based isocyanate products suitable for use in flexible foams. Either directly produced, high-monomerpolymeric MDI products or prepolymer derivatives of polymeric MDI products may be used. In the past, directly produced polymeric MDIs have had sufficient lot-to-lot variations in composition-such as monomer content and monomer ratios-to cause unacceptable variations in flexible foam processing, especially in all water-blown systems. As a result, prepolymer MDI products of directly produced polymeric MDIs have been used to reduce the degree of process variability that might otherwise be seen with the directly produced, high-monomer materials.

Mobay Corp. has made an intensive effort in learning to control the production process for high-monomer MDI products and has developed a directly produced, high-monomer MDI product, Mondur MRS-2.5, with very consistent flexible foam processing characteristics. The advantages of this approach over the prepolymer approach are:

* A higher isocyanate concentration (% NCO) for more efficient blowing.

* A strong hardness/index response for dual hardness foams.

* Excellent storage stability.

* Low viscosity.

Coupled with the development of this directly produced polymeric MDI is the recent development of a new Mobay polyol technology for flexible MDI foams. This technology arose from a study undertaken to understand the phenomenon of humid aged compression set (HACS).

Foam Morphology Theory Our study of the extensive literature covering the mechanics of foam formulation and the HACS phenomenon revealed some current basic assumptions. In general, conventional foams are understood to be rather well organized, with discrete polyurea domains in the polyurethane matrix, while high-resilient (HR) foams are described as being rather disperse, with randomly distributed polyurea segments in the polyurethane matrix. The polyureas result from the reaction of theory is an accurate representation of what actually occurs during the synthesis of both conventional and HR flexible foams. With the use of this new technology, the actual foam morphology may be manipulated in an engineered manner, allowing enormous flexibility in designing new flexible foam products for specific applications.


The author wishes to thank J.D. Hodel, R. Zacour, and R. Zibert, without whose hard work and dedication this article would not have been possible.
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Title Annotation:chlorofluorocarbon, methylenediphenyl isocyanate
Author:Milliren, Charles M.
Publication:Plastics Engineering
Date:Jan 1, 1991
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