Silicone surfactants polyurethane

The unique surface characteristics of polysiloxanes mean that they are extensively used as surfactants. Silicone surfactants have been thoroughly studied and described in numerous articles. For an extensive, in-depth discussion of this subject, a recent chapter by Hill,476 and his introductory chapter in the monograph he later edited,477 are excellent references. In the latter monograph, many aspects of silicone surfactants are described in 12 chapters. In the introduction, Hill discusses the chemistry of silicone surfactants, surface activity, aggregation behavior of silicone surfactants in various media, and their key applications in polyurethane foam manufacture, in textile and fiber industry, in personal care, and in paint and coating industries. All this information (with 200 cited references) provides a broad background for the discussion of more specific issues covered in other chapters. Thus, surfactants based on silicone polyether co-polymers are surveyed.478 Novel siloxane surfactant structures,479 surface activity and aggregation phenomena,480 silicone surfactants application in the formation of polyurethane foam,481 foam control and... 

Snow, S. A. Stevens, R. E. The Science of Silicone Surfactant Application in the Formation of Polyurethane Foam. In Silicone Surfactants-, Hill, R. M., Ed. Surfactant Science Series Dekker New York, 1999 Vol. 86, Chapter 5, pp 137-158. 

Industrially, silicone surfactants are used in a variety of processes including foam, textile, concrete and thermoplastic production, and applications include use as foam stabilisers, defoamers, emulsifiers, dispersants, wetters, adhesives, lubricants and release agents [1]. The ability of silicone surfactants to also function in organic media creates a unique niche for their use, such as in polyurethane foam manufacture and as additives to paints and oil-based formulations, whilst the ability to lower surface tension in aqueous solutions provides useful superwetting properties. The low biological risk associated with these compounds has also led to their use in cosmetics and personal care products [2]. 

The high hydrophobicity of silicones can complicate their use in some applications. For example, proteins can undergo denaturation in contact with silicones [1]. In such cases, the siloxane can be modified to include a hydrophilic domain. This is typically accomplished by functionalizing the silicone with a hydrophilic polymer such as poly(ethylene oxide)(PEO). Silicone surfactants of this type have found widespread use as stabilizers for polyurethane foams, and have been investigated as a structurant to prepare siloxane elastomers for biomaterials... 

The surface activity of silicones is often exploited by using them as additives. For this reason, aspects of the two most important additive forms, copolymers and surfactants, are also included in this discussion. These two classes come together in the relatively low molecular weight PDMS-poly(alkylene oxide) block and graft copolymers that are commonly used as polyurethane foam stabilizers. Other short-chain silicone surfactants designed for aqueous systems and other silicone-organic copolymers are also available. 

The surfactants employed for polyurethane foams can be also used for preparing foamed composites. The surfactants include silicone surfactants, which consist of polysiloxane-polyoxyalkylene block-copolymers. 

Dabco( DC. [AirPro. ] Silicone surfactants additives fot flexible mdded polyurethane foams. 

Tegostab . [Goldschmidt] Silicone surfactants stabilizer for polyurethane foams. 

The real challenge in polyurethane foam formation is to control the chemical and physiochemical processes up to the point where the material finally sets. The sequence and the rate of the chemical reactions are predominately a function of the catalyst and the reactivity of the basic raw materials, polyol and isocyanate. The physiochemical contribution to the overall stability and processability of a system is provided by the silicone surfactants. Optimum foaming results will be achieved only if the correct relationship between chemistry and physics exists [4]. 

The effect of a silicone surfactant on the burning behaviour of the polyurethane foam can be quite significant even though they normally represent less than 1 % of the plastic material. It is due to the fact that in any case the decomposition of a polyurethane foam starts at the surface. Because of the surface activity of the foam stabilisers it is easy to rationalise their enrichment on the surface and it is the surface that is the most influential part of the polymer regarding flame spread development. 

Modelling the Stabilising Behaviour of Silicone Surfactants During the Processing of Polyurethane Foam The Use of Thin Liquid Films... 

Intermolecular adhesion between the polyether chains of a typical silicone surfactant and the underlying polyurethane liquid matrix could increase the surface viscosity contribution in PU films and foams. 

X. Zhang, Role of Silicone Surfactant in Polyurethane Foaming Process, University of Minnesota, USA, 1998, [Ph.D Thesis]. 

One of the technically and commercially most interesting applications of silicone surfactants is their use in the production of polyurethane (PU) foams (Fig. 13). These foams are formed by the reaction of polyols and isocyanates. The finished foams typically have cell sizes in the millimeter range and below with densities mostly less than 50 kg/m, thus forming systems with very large surfaces. The process of foam formation is complex and consists of different phases, which require a variety of properties of the used surfactants. The flexibility of silicone chemistry, especially the broad variety of silicone polyether chemistry, is particularly suited to meet these different requirements. 

Figure 6a and c show typical structures of silicone surfactants for the production of polyurethane foam, i.e., comb-like and branched siloxanes. Siloxanes that are modified with polyether groups are important surfactants for rigid, ester, or flexible slabstock foams. 

Inverse structures have been published for use in polyurethane foam formation [43]. Monofunctional siloxane chains are attached to a multifunctional polyether backbone. However, significant advantages over classical silicone surfactant structures could not demonstrated. A major drawback of this approach is the difficult synthesis of monofunctional siloxanes. 

Domingo et al. evaluated immobilization of trichloroethylene-degrading Burkholderia cepacia bacteria using hydrophilic polyurethane foam. The influences of several foam formulation parameters upon cell retention were examined. Surfactant type was a major determinant of retention a lecithin-based compound retained more cells than Pluronic- or silicone-based surfactants. 

Other companies have also produced condoms made from the polymer styrene-ethylene-butylene-styrene which has the advantage of being even stretchier than polyurethane, thereby reducing the risk of tearing during use. There are also condoms lubricated with a combination of silicone oil and nonoxynol-9 which acts as a spermicide. Nonoxynol-9 is also used as a surfactant in cosmetic products, but it has the ability to interfere with the acrosomal membrane which covers the head of a sperm, causing it to become paralysed, which is why nonoxynol-9 has been widely used in lubricants for condoms and es-... 

This reaction yields surfactants in which the polar group is linked to the silicone through an SiOC linkage. These materials have found widespread use in nonaqueous applications such as manufacture of polyurethane foam (PUF) but in an aqueous system the SiOC linkage hydrolyses (rapidly away from pH = 7). 

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