Converting HCFC-141b-Based Polyol Systems to SOLKANE® 365/227-Based Systems

  Due to the Montreal Protocol and national regulations, the use of HCFC-141b as a blowing agent in polyurethane (PU) foams was placed on a phase-down schedule and was terminated in Turkey as of 1 January 2013, as specified in the Official Gazette dated 12 November 2008 and numbered 27052. Although many alternative chemicals exist, only a limited number of chemicals can provide the technical properties required by the polyurethane industry. This article has been prepared to serve as a guide in appropriately modifying the most commonly used formulations with HCFC-141b blowing agent in accordance with new regulations and in optimizing the use of SOLKANE® 365/227 and SOLKANE® 365mfc blowing agents. The first section introduces the product properties, while the second section describes how polyol formulations can be modified in the most suitable manner.

1. Product Properties of SOLKANE® 365/227 and SOLKANE® 365mfc

SOLKANE® 365mfc is a hydrofluorocarbon and is a liquid with a boiling point of 40 °C under normal conditions. When SOLKANE® 365mfc is mixed with SOLKANE® 227ea, it can be used as a non-flammable liquid, making it the preferred method in many applications. Table 1 presents the physical properties of SOLKANE® 365mfc-based blowing agents offered by SOLVAY.

Table 1 / Table 1:

The flash points of SOLKANE® 365/227 mixtures offered by SOLVAY have no flash point according to ISO 1516/1523 standards and are not subject to flammable substance regulations. Since the mixtures are non-azeotropic, their composition may change during use. When the concentration of SOLKANE® 227ea falls below 5%, the mixture becomes flammable. The flash point of pure SOLKANE® 365mfc is below -27 °C according to the DIN 51755 method. It is quite difficult to ignite SOLKANE® 365mfc. The minimum ignition energy is approximately 50 times higher than that of pentane. The ignition energy of SOLKANE® 365mfc is 10.4 mJ (25 °C, 1 bar in air at 8% volume ratio). Explosion limits in dry air under standard conditions are as follows:

Table 2 / Table 2:

Compared to HCFC-141b, the thermal and chemical resistance of SOLKANE® 365mfc is relatively even better. It should not be exposed to strong alkaline compounds or alkali metals. At high temperatures or under pressure, harmful reactions may occur with reactive metals such as zinc, aluminum and alloys, magnesium, and even with air. Since SOLKANE® 365mfc has been observed to be stable in pre-prepared PU foam systems, stabilizers are not required. SOLKANE® 365mfc should be stored in cool and well-ventilated areas. Contact with heat sources, open flames or sparks should be avoided. SOLKANE® 365mfc is a compound compatible with many materials. Its compatibility with a wide range of gasket materials is shown in Table 3. *Weight % change was determined after being held in liquid for 7 days. Its solubility in polyols* is lower than HCFC-141b and generally higher than hydrocarbons. The following table shows the solubility of the blowing agent in grams per 100 g of polyol. * Similar values can be assumed for SOLKANE® 365/227 mixtures. 2. Modification of Formulations Many polyols, flame retardants, catalysts, surfactants and isocyanates used with SOLKANE® 365mfc and other PU raw materials are fully compatible, and therefore replacing HCFC-141b with SOLKANE® 365mfc or SOLKANE® 365/227 is a fairly straightforward application. Our recommendation is that during this replacement, the type of surfactant used should preferably be one developed for medium-solubility blowing agents rather than one developed for high-solubility blowing agents. For example, the use of pentane-type surfactants should be appropriate. The correct selection of the conversion recipe varies for each application or special case and depends on the target parameters specified below: 1. Density 2. Thermal conductivity 3. Compressive strength 4. Adhesion The advantage of using SOLKANE® 365mfc and SOLKANE® 365/227 is that they give the best results when mixed with water in a wide ratio range in formulations. For this reason, we recommend the following steps in optimizing the replacement of HCFC-141b.

2.1 First Step: Replacement of HCFC-141b with SOLKANE® 365/227

The first step is to replace HCFC-141b with SOLKANE® 365/227 at a ratio of 1.27 or a molecular weight ratio of 117:149. Example: For every 10 units of HCFC-141b, 12.7 units of SOLKANE® 365/227 or SOLKANE® 365mfc should be used. Based on our experience, the foam will very likely exhibit the following properties: 1. Better mechanical properties such as compressive strength and dimensional stability. This is because SOLKANE® 365mfc is less soluble within the foam matrix. The softening effect resulting from HCFC-141b has been almost completely eliminated in foams containing SOLKANE® 365mfc. As a result, it is possible to reduce foam density when SOLKANE® 365/227 is used instead of HCFC-141b. 2. Somewhat higher thermal conductivity values (λ or k-value). The reason for this change is the difference in the specific heat conductivity of the compounds and possibly the condensation of SOLKANE® 365mfc. 2.2 Second Step: Gradual Replacement of SOLKANE® 365/227 with Water This step will allow optimization of thermal conductivity while limiting the additional cost resulting from the use of SOLKANE® 365/227 in place of HCFC-141b. This will be possible by gradually replacing part of the SOLKANE® 365/227 to be used with water. This replacement should be applied at a molecular weight ratio of 8.28 or 149:18. An additional amount of water can be added to compensate for the reduction in foam density. The replacement with water should be continued until values obtainable with HCFC-141b are reached. Example: To reduce the amount of SOLKANE® 365/227 by 4.14 units, first 0.5 units of water should be added. Then, to compensate for the 17.5% reduction in foam density, an additional 0.5 units of water should be added. To achieve optimum results in accordance with the target specifications of the final foam, the replacement with water should be done gradually.

3. Foam Example

In the above example, the second column presents information on the first step, namely the replacement of HCFC-141b with SOLKANE® 365/227, while the third column presents data from the second step, namely the gradual replacement of part of the SOLKANE® 365/227 to be used with water. First, as mentioned, the amount of HCFC-141b is replaced with SOLKANE® 365/227 at a 1.27 molecular weight ratio: for 17 units of HCFC-141b (17 x 1.27 =) 21.59 units of SOLKANE® 365/227 should be used. Then 0.5 units of water should be replaced with SOLKANE® 365/227 at a ratio of 8.28 (149:18), that is, when 0.5 units of water is added, SOLKANE® 365/227 should be reduced by 4.14 units. As a result, the amount of SOLKANE® 365/227 to be added (21.59 – 4.14 =) 17.45 units. To reduce the density of the foam at 40 g/dm3 by 17.5% and bring it down to 33 g/dm3, an additional 0.5 units of water is added. This can be done because foams made with SOLKANE® 365/227 have better mechanical properties.

4. Conclusion

Using the guide explanation described above, HCFC-141b in your formulations can be replaced with SOLKANE® 365/227 or SOLKANE® 365mfc. This makes it possible to obtain similar foams used in different application areas. The new formulation should be optimized according to your polyurethane specifications. Optimization should be performed separately for each formulation and application. In addition to reducing the total cost of the formulation by adding water as recommended in the second step, the "condensation effect" of SOLKANE® 365mfc has also been resolved and thermal conductivity values will also decrease (λ or k-value). The replacement of the blowing agent with SOLKANE® 365/227 has an additional effect in integral foams and mold-cast foams. After removal from the mold, the shrinkage effect is lower compared to foams made with HCFC-141b in a manner similar to formulations previously made with CFC-11.

Dr. Ercan Ünveren / Regional Sales and Marketing Manager - SOLVAY Fluor GmbH

Kris Schauvliege / Business R&D Specialist - SOLVAY SA