Dear Rezvan,

The following publications describe the stabilization of polyurethane foam:

1-Role of Silicone Surfactant in Flexible Polyurethane Foam

X. D. Zhang,* C. W. Macosko,*,1 H. T. Davis,* A. D. Nikolov,† and D. T. Wasan†

Journal of Colloid and Interface Science 215, 270–279 (1999)

Grafted copolymers which consist of a polydimethylsiloxane backbone and polyethylene oxide-co-propylene oxide pendant groups are used as surfactants to stabilize the foam cells in the flexible polyurethane foaming process. The mechanical properties of the cured polyurethane foam such as air permeability and foam cell size are affected significantly by the structure of the silicone surfactant used in the formulation. It is shown that silicone surfactant has an important impact on both the bubble generation and the cell window stabilization stage. A series of silicone surfactants with different structures was tested. Surfactants with higher

silicone content will provide lower surface tension and thus help increase the number of air bubbles introduced during mixing. These air bubbles serve as the starting point for foam cell growth. As a result, the cured polyurethane foam made with higher silicone content surfactant has a smaller bubble size. It is also shown

that silicone surfactant can reduce the cell window drainage rate due to the surface tension gradient along the cell window. The Gibbs film elasticity, the dynamic film elasticity, and the film drainage rate were measured for the first time versus surfactant composition. Surfactants with longer siloxane backbones are

shown to give higher film elasticity. Using the vertical film drainage and foam column tests, it is shown that surfactants with higher film elasticity will yield slower drainage rate and better foam cell stability.

http://research.cems.umn.edu/macosko/papers_n_shows/papers/J308.pdf

2-Cell Stabilizing Polyurethane Flexible Foam

Summary:

Polyurethane Flexible Foam Technology is a method for preparing flexible or semi-flexible polyurethane foams using stabilizing cell opening water dispersed additives. This specific method of making polyurethane foam creates numerous process benefits including:improved dimensional stability, reduction of crushing force, and low levels of dispersion additives.

Overview:

Air Products is offering for license technology which covers making polyurethane flexible foam using dimensional stabilizing, cell opening additives. Flexible molded polyurethane foam requires mechanical crushing to open cells and prevent shrinkage. Opening cells also improves dimensional stability of the foam pad. Current mechanical methods for cell opening consist mainly of crushing, vacuum rupture, or time pressure release. Other mechanical attempts have been made to achieve dimensionally stable foam such as decreasing cycle production times and time pressure release. The mechanical methods mentioned above usually result in incomplete or inconsistent cell opening and require a flexible molded foam producer to invest in additional machinery. A chemical method for cell opening would be preferred by the industry.

http://www.airproducts.com/~/media/Files/PDF/company/tech-chemcials-cell-stabilized-flexible-pi-foam.pdf?la=en

3- How silicone foam stabilizers work

Sometimes foam is a good thing. Polyurethane foams, for example, are formed by allowing a liquid mixture containing a large amount of a polyol to react, while a blowing agent generates the foam cells.

Stabilizing the foam requires the use of a surface active agent, which orients itself on the cell walls in a precise manner and causes them to thin. Many organic surfactants have a surface tension that is higher than 32 mN/m, the surface tension of the polyol in the foam mixture. Consequently, they are not able to stabilize polyurethane foam.

Silicone polyethers have such low surface tension, they can potentially lower the surface tension of the foam another 10 mN/m! This makes them ideal surfactants for use not only in polyurethane foam but also in other applications where the creation of stable foams is desired.

Silicone surfactants help stabilize foams two ways: by thinning the cell walls and by promoting the creation of large numbers of small vs. large bubbles.

http://www.dowcorning.com/content/discover/discoverchem/si-stabilizers.aspx

4-Additives for Polyurethane

Polyurethanes are among the most versatile polymers.They are used in a wide variety of applications including adhesives, sealants, coatings, fibers, reaction-injection molded components, thermoplastic parts, elastomers and both rigid and flexible foams. Polyurethanes offer an impressive range of performance

characteristics and the use of appropriate stabilizers can extend the service life of polyurethane products. Selecting the best stabilization system depends on specific production conditions, end-use environment and a knowledge of the fundamental degradation mechanisms of the polyurethane components. Degradation of both the polyol and urethane components will cause changes in the physical or mechanical properties of the polyurethane. Urethanes are susceptible to degradation by free radical pathways induced by exposure to heat or ultraviolet light. The use of primary antioxidants, such as Irganox

®, suppresses the formation of free radical species and hydroperoxides in polyols both during storage and conversion. UV absorbers and hindered amine stabilizers, such as Tinuvin ® and ChimassorbTM, protect polyurethanes from UV light-induced oxidation. Ciba Additives offers a variety of additives for improving the processing and service life of polyurethane products. For detailed information about individual products, specific application or performance requirements, please contact your local Ciba technical representative or regional agent.

http://www.mufong.com.tw/ciba/ciba_guid/additives_polyurethane.pdf

Hoping this will be helpful,

Rafik

I have nothing to add after Rafik Karaman.

Thanks Dear Rafik 

In fact, I'm using polydimethylsiloxane, but narrows foam and is not stable yet. I read some paper of Harith, I changed a catalyst, and I'm using DMEA and other amines. (Beafor i use Tin),  Foam isnt  stable  absolutely and  no resistance mecchanica. It breaks easily.

Rezvan