New Generation Emission-Free Amine Catalysts

Reducing the content of Volatile Organic Compounds (VOC) remains an important issue in the polyurethane industry. To produce more environmentally friendly products and enhance material safety, PU spray manufacturers and automotive producers, as well as companies manufacturing polyurethane foam for the furniture and bedding sectors, are implementing stricter regulations. This trend in reducing volatile organic compounds is also reflected in the increasingly growing third-party institute certifications in the flexible foam market, such as LGA, CertiPUR, and Ecolabel. Amine catalysts are one of the key catalysts during polyurethane foam formation. Amine catalysts are the compounds receiving the most attention in emission studies alongside many components that create emissions in PU foam. Tertiary amines such as bis(2-dimethylaminoethyl) ether (BDE) and triethylenediamine (TEDA) have been used for many years in flexible polyurethane foam production. However, since these catalysts have significant volatility, they cause an increase in VOC emissions. Evonik has contributed to understanding different mechanisms and created numerous resources to minimize amine contribution to total VOC emissions generated in flexible PU foams (Figure 1). In recent years, Evonik has developed various non-volatile amine catalysts containing isocyanate-reactive groups.

Figure 1. Difference in reactivity between conventional amine catalysts and non-volatile amine catalysts

However, not all reactive catalysts are emission-free. Although tightly bound to the polymer matrix, amine catalysts can decompose and create carried additives that lead to an increase in the foam's total VOC amount. For this reason, Evonik DABCO® NE catalysts typically have reactive groups with high molecular weight and high polarity. Additionally, it is important to reduce to a minimum level the amount of non-reactive, volatile by-products in the actual amine catalyst. The DABCO® NE series is a product group containing a high degree of purity to solve high emission problems. In addition to emission and environmental requirements, amine catalysts must be synthesized according to specific rules to meet high physical property standards. The mechanical performance of the final product can only be guaranteed under these conditions. In the flexible foam industry, various tests have been developed to simulate the performance of foam over its life cycle. These tests are conducted under high heat and humidity conditions and relate to the chemical stability of the foam. These test methodologies are used to create guides for foam performance over time and also to simulate accelerated conditions of foam aging. Generally, foams made with catalysts retained in the polyurethane polymer have lower chemical stability when exposed to accelerated aging conditions. Evonik aims to assist foam production by developing new catalyst technologies. With these new technologies, foam producers meet stricter emission requirements while simultaneously meeting foam stability requirements. Evonik's new catalyst technology consists of a combination of DABCO® NE 300, a reactive blowing catalyst, and DABCO® NE 740, a gel catalyst (Figure 2).

Figure 2. Non-volatile amine catalysts for the EMEA region

Reactive Amine Catalysts with High Blowing Selectivity - DABCO® NE 300

DABCO® NE 300 is a reactive blowing catalyst that exhibits zero amine emissions in various high-temperature emission tests (such as VDA 278) for the automotive industry and also in room temperature tests for flexible foam applications. DABCO® NE 300 has similar activity and similar physical properties in foam compared to conventional blowing catalysts such as DABCO® BL 11. In formulations where DABCO® NE 300 replaces DABCO® BL 11, DABCO® NE 300 can be used in equal amounts as DABCO® BL 11. (In some formulations, DABCO® NE 300 may be used in slightly higher amounts). Figure 3 shows the rise profiles of DABCO® BL 11 and DABCO® NE 300 in a formulation with a density of 19 kg/m³. In this formulation, DABCO® NE 300 was used somewhat more than DABCO® BL 11.

Figure 3. Reaction profile of DABCO® NE 300 (blue curve) compared to DABCO® BL 11 (red curve) at 19 kg/m³ density

Due to its chemical structure, DABCO® NE 300 produces foam with low deformation values, very open cells, and high quality. Additionally, DABCO® NE 300 mixes easily with polyols and polyol/water mixtures. According to the VDA 270 odor test, DABCO® NE 300 has lower odor compared to other commercially available reactive blowing catalysts (Figure 4).

Figure 4. Odor evaluation of DABCO® NE 300

Next Generation Non-volatile Gel Catalysts - DABCO® NE 740

In PU formulations, in addition to an amine catalyst with blowing properties, amines with gelling behavior are also required to create catalyst balance. In recent years, reduced emission-free gel amine catalysts have been developed, such as DABCO® NE 500, DABCO® NE 1082, TEGOAMIN® ZE types, etc. These products have lower activity and insufficient gel selectivity compared to DABCO® 33 LV, which is widely used in the industry. For this reason, the use of non-volatile gel amines is not very straightforward. Evonik expanded this research and recently developed a new generation "emission-free amine catalyst with high gel selectivity" called DABCO® NE 740. DABCO® NE 740 is used in flexible polyether foam applications to meet some regulations used in the flexible foam industry (LGA, OEKO-TEX, etc.). In addition to this application, it is also used in the new VDA 278 test standards used in the automotive industry. In addition to emission properties, DABCO® NE 740 also eliminates windshield fogging or vinyl staining. DABCO® NE 740 can be used in the production of various flexible polyurethane foams such as standard polyether foam, viscoelastic foam, or HR foam. DABCO® NE 740 provides improved thermal aging, aging, and permanent deformation properties of foam compared to other non-volatile catalysts. Due to its strong gel selectivity, DABCO® NE 740 is also highly suitable for the production of low-emission viscoelastic foams (TDI or MDI-based) and hypersoft foams. In general, when compared to DABCO® 33 LV, we need to increase the amount of DABCO® NE 740 by 10 to 30 percent depending on the formulation. Figure 5 shows the formation curve of two different foams at a density of 21 kg/m³. One of these curves was made with 0.11 part DABCO® 33 LV and the other with 0.14 part DABCO® NE 740. In both tests, the rise time, foam height, and rise curve were examined primarily.

Figure 5. Comparison of reaction profile with DABCO® NE 740 (red curve) and DABCO® 33 LV (blue curve) at 21 kg/m³ density

To determine the gel selectivity of the new amine catalyst compared to DABCO® 33 LV, viscoelastic foam was prepared with DABCO® NE 740. The results are shown in Figure 6. DABCO® NE 740 was used 20 percent more than DABCO® 33 LV to achieve a similar rise curve. On the other hand, with the formulation prepared at this increased usage level, the skin tack-free time decreased from 90 seconds to 65 seconds.

Figure 6. Formulation and properties of two TDI 80 viscoelastic foams made with DABCO® NE 740 and DABCO® 33 LV

In cases where the newly developed gel catalyst DABCO® NE 740 is used together with DABCO® NE 300 in flexible foam production, no amine emissions were observed in tests conducted according to VDA 278 and DIN 16000-9 (Cup) thermal desorption method. The most notable significant advancement is that DABCO® NE 740 has much better activity and gel selectivity compared to existing emission-free amines. For example, the final cure of viscoelastic foams is comparable to DABCO® 33 LV.

The advantages of using DABCO® NE 300's new gel catalyst DABCO® NE 740 can be listed as follows:

1. Providing success to foam producers under accelerated aging tests, 2. Meeting emission standards/requirements, 3. Not creating odor effects. With a broad range of requirements; Evonik Industries AG will continue to develop new technologies to meet the continuously changing requirements of polyurethane system houses, manufacturers, and the polyurethane industry for comfort, durability, processability, improvement of physical properties, reduction or elimination of VOC emissions. End consumers can enjoy high-standard products manufactured with continuously developed polyurethane additives. Note: All foams produced for this study were made by hand casting in the laboratory. Dr. Michael Krebs Technology Manager, EMEA Region Evonik Nutrition&Care GmbH     Uğur Can İyidir Technical Service Manager – Flexible Foam Turkey & Middle East Evonik Ticaret Ltd. Şti.