Flexible Foam Surfactants

Many different types of surfactants have been employed for flexible foams, but usually nonionic and anionic surfactants and silicones are used. The choice of surfactant depends upon the method of foam 

In the prepolymer method for one-shot polyether flexible urethane foams the primary role of the silicone surfactant is to lower surface tension and to provide film (cell-wall) resilience. Resilient films prevent the collapse of the foam during foam rise and continue to stabilize it until the foam is self-supporting. A secondary, but nevertheless important role of the silicone surfactant is cell-size control. The silicones can be added to the formulation in any of the 2 to 6 streams usually fed to the mixing head in the one-shot process. Usually, however, the silicone is metered separately, in combination with the polyol, or added as a wa-ter/amine/silicone mixture. It can also be added in the fluorocarbon blowing agent (52). 

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In more recent years, molded flexible foam products are becoming more popular. The bulk of the molded flexible urethane foam is employed in the transportation industry, where it is highly suitable for the manufacture of seat cushions, back cushions, and bucket-seat padding. TDI prepolymers were used in flexible foam mol ding ia conjunction with polyether polyols. The introduction of organotin catalysts and efficient siHcone surfactants faciHtates one-shot foam mol ding, which is the most economical production method. 

Formulations for one-shot polyether systems are similar to those used for flexible foams and contain polyether, isocyanate, catalyst, surfactant and water. Trichloroethyl phosphate is also often used as a flame retardant. As with polyesters, diphenylmethane di-isocyanate is usually preferred to TDI because of its lower volatility. Tertiary amines and organo-tin catalysts are used as with the flexible foams but not necessarily in combination. Silicone oil surfactants are again found to be good foam stabilisers. Volatile liquids such as trichlorofluoro-methane have been widely used as supplementary blowing agents and give products of low density and of very low thermal conductivity. 

Many choices of surfactants are commercially available for use in various foams such as flexible foams, HR foams, rigid foams, etc. 

In recent years, the ban on the use of CFCs resulted in major changes in foam formulations. A number of studies were carried out on the use of 100% water-blown foams for both rigid and flexible foams. These studies required modifications or improvements in raw materials, e.g., polyisocyanates, polyols, catalysts and surfactants. 

Uses Raw material, combined with iso anates, to produce urethanes such as rigid foam, flexible foam, coatings, adhesives, sealants, elastomer systems for furniture, car seating, bedding, refrigerator insulation, paints/coatings, ski suits, playground surfaces, waterproof leisure wear also in surfactants and oil demulsifiers Carbalink HPC [Huntsman]... 

CAS 61788-62-3 EINECS/ELINCS 262-990-2 Synonyms Dicocoalkyl methylamine Classification Dialkyl methylamine Properties Cationic Uses Chemical intermediate for quat. ammonium derive., acid scavenger in petrol, prods. epoxy hardener, catalyst in mfg. of flexible PU foams surfactant industrial detergent chemical intermediate for mfg. of oil-sol. betaines and quat. ammonium salts in cosmetics... 

Table 5.1 A comparison of commercial flexible slabstock PU foam surfactants in PU thin liquid films (1 pph surfactant) ...

The formation of cellular products also requires surfactants to facilitate the formation of small bubbles necessary for a fine-cell structure. The most effective surfactants are polyoxyalkylene-polysiloxane copolymers. The length and ethylene oxide/PO (EO/PO) ratio of the pendant polyether chains determine the emulsification and stabilizing properties. In view of the complexity of the interaction of surfactant molecules with the growing polymer chains in foam production, it is essential to design optimal surfactants for each application. Flexible polyurethane foams require surfactants that promote improved cell-wall drainage. This allows the cell walls to become more open during the foaming reaction. Also, the shift away from TDI to MDI in molded HR foams adds new demands on foam surfactants (97). 

We see that the two amine catalysts, DABCO and N-ethylmorpholine, are added in the amount of about 1 % based on the polyol component, while the amoimt of Sn-octoate is 0.15%. While DABCO is a balanced catalyst, which promotes both gelation and foaming, N-ethylmorpholine favors open cell formation. The surfactant has multiple role, to lower surface tension and facilitate division of cells, and since it is a separate phase, to act as a nucleant. Increasing the amount of surfactant gives finer cells with thinner walls until the limit is reached above which it causes foam collapse. Density of flexible foams is usually between 30 and 80kg/m. Density of the polyurethane itself is about llOOkg/m. ... 

Before the discovery of the catalytic activity of tin compounds, polyether foams were prepared by the pre-polymer technique. In this two-stage process, the low reactivity of the polyether secondary hydroxy groups is compensated for by carrying out the reaction between isocyanate and diol before the addition of water. The polyether is treated with excess of isocyanate to give an isocyanate-terminated pre-polymer which is stable in the absence of moisture. Addition of water, tertiary amine and surfactant to the pre-polymer results in a flexible foam of good quality. The pre-polymer process has been largely displaced by the more economical one-shot process but is still occasionally used since it offers more scope in the design of compounds. 

Silicone polyethers with end-capped polyethers are standard for the production of flexible foam. This type of foam requires a high number of open cells thus, chemical cross-linking by the surfactant has to be avoided. The complex need for controlled cell sizes, high physical stabilization, and timely cell opening typically is met by products with a low degree of substitution (Fig. 3, mjn > 7), long silicone chains m + n > 40), and often by using mixtures of two, three, or even more polyethers, which are attached to the same siloxane backbone. 

The lower molecular weight polymers of propylene oxide and propylene oxide adduct copolymers are used as surfactants, hydraulic fluids, and machine and metal-working lubricants. Propylene oxide adducts of polyhydroxy compounds, such as glycerine, trimethylolpropane, or pentaerythritol or sorbitol, are principal polyols used in making polyurethane elastomers, rigid thermal insulation, flexible foams, and coatings. 

Uses Surfactant for use in high resiliency flexible foams in TDI, MDI / TDI and MDI based cold-cure flexible molded PU systems cell regulator and surface stabilizer Features Eliminates basal cell formation low vise. exc. vent stability and foam surface appearance, even at broad mold temp, latitude (55-70 C)... 

Another important year for the advancement of oscillatory structural forces at mesoscopic length was 1996. Three independent studies emerged that year which reported the observation of oscillatory force interactions involving polyelectrolytes. Two of these studies dealt with polymer-surfactant mixtures [23,24], and one used only polyelectrolyte solutions [25]. Also noteworthy is that one study dealt with flexible foam Aims [23] and the other two measured forces between rigid solid surfaces [24,25]. Two different phenomena were revealed oscillatory force interactions originating from bulk solution organization and from surface-specific complexation. What follows is an overview of these different force-structure relationships. 

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