Next Generation of Non-Emissive Amine Catalysts

Dr. Michael Krebs Regional Technology Manager EMEA Evonik Nutrition&Care GmbH Uğur Can İyidir Technical Service Manager – Flexible Foam Turkey & Middle East Evonik Ticaret Ltd. Şti. The reduction of volatile organic compounds (VOC) content continues to be a significant issue in the polyurethane industry. To minimize environmental impact and improve material safety, foam manufacturers across multiple markets – including spray foam, automotive, furniture and bedding – face increasingly stringent regulations. This trend toward reducing emissions is reflected in a growing number of third-party institute certifications in the comfort market, such as LGA, CertiPUR and Ecolabel, among others. Amine catalysis is a key element in polyurethane foam formation. Although many components in PU foam are responsible for emissions, amine catalysts are commonly targeted. Tertiary amines such as bis(2-dimethylaminoethyl) ether (BDE) and triethylenediamine (TEDA) have been used for many years in flexible polyurethane foam production. However, these catalysts are fugitive compounds with considerable volatility and thus contribute significantly to VOC emissions. Evonik has invested substantial effort and resources in understanding different mechanisms to minimize amine contribution to total VOC emissions of flexible PU foams (Figure 1). Over the past few years, a variety of non-fugitive amine catalysts containing isocyanate-reactive groups have been developed.

Figure 1. Difference in reactivity of conventional amine catalysts versus non-fugitive amine catalysts

However, not all reactive catalysts are non-emissive. Although firmly bound into the polymer matrix, amine catalysts can decompose and migratory adducts can form, which can contribute to the total VOC content of the foam. Therefore, Evonik DABCO® NE catalysts typically combine reactive groups with high molecular weight and high polarity. Furthermore, it is important to reduce the amount of non-reactive, volatile by-products in the actual amine catalyst to a minimum. To address these emission concerns, the DABCO® NE series of amine catalysts meets the highest purity standards. In addition to emissions and environmental requirements, amine catalysts must perform according to established guidelines to meet high standards of physical property requirements, ensuring the mechanical performance of the finished product. The comfort industry has also developed a wide variety of tests to simulate foam performance over its life cycle. One such test relates to the chemical stability of foam, employing severe conditions of heat and humidity. These testing methodologies are used to create guidelines for foam performance over time and to simulate accelerated foam aging conditions. Typically, catalysts retained in the polyurethane polymer produce foam articles that exhibit lower chemical stability when exposed to accelerated aging conditions. Evonik has now developed new catalyst technologies to help foam manufacturers meet foam stability requirements while satisfying even more stringent emission requirements. The new catalyst technology is based on a combination of reactive blow catalyst DABCO® NE 300 and a new gel catalyst DABCO® NE 740 (Figure 2).

Figure 2. Evonik portfolio of non-emissive amine catalysts for the region EMEA

Reactive Amine Catalysts with High Blow Selectivity – DABCO® NE 300 DABCO® NE 300 is a reactive blow catalyst that exhibits zero amine emissions in various high-temperature emanation tests for the automotive industry (e.g. VDA 278) as well as in room-temperature tests for comfort applications. DABCO® NE 300 offers similar activity and foam physical properties compared to conventional blow catalysts such as DABCO® BL 11. Typically, it is possible to replace DABCO® BL 11 with DABCO® NE 300 equally or with only a minor increase in catalyst loading. This is illustrated in Figure 3, where replacement of DABCO® BL 11 in a 19 kg/m³ density formulation with DABCO® NE 300 at a ratio of 1.1:1 resulted in an equivalent rise profile.

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

Due to its chemical structure, DABCO® NE 300 generates very open, high-quality foam with excellent compression set performance and is readily miscible with polyols and polyol/water mixtures. Odour testing according to VDA 270 confirms that DABCO® NE 300 exhibits the lowest odor of commercially available reactive blow catalysts (Figure 4).

Figure 4. Odor evaluation of DABCO® NE 300

Latest Generation of Non-Fugitive Gel Catalysts – DABCO® NE 740 Besides a blowing-optimized amine catalyst, many formulations require an additional amine catalyst with improved gelling behavior to achieve balanced catalysis. In recent years, reduced and non-emissive gel amine catalysts have been developed (DABCO® NE 500, DABCO® NE 1082, TEGOAMIN® ZE types, etc.). However, they typically exhibit lower activity and insufficient gel selectivity compared to DABCO® 33 LV. Therefore, non-fugitive gel amines with similar performance have not been readily available. Evonik has extended this research and recently developed a novel next-generation non-emissive amine catalyst with high gel selectivity called DABCO® NE 740. DABCO® NE 740 is used in flexible polyether slabstock foam applications to meet comfort industry labels (LGA, OEKOTEX, etc.) as well as automotive OEM emission specifications such as the new VDA 278, and eliminates windshield fogging and vinyl staining. DABCO® NE 740 is intended for the production of various types of flexible polyurethane foam, such as standard polyether slabstock foam, viscoelastic foam and high-resilient foam. In comparison to other non-fugitive catalysts, it allows the production of flexible polyurethane foam with excellent aging properties, including thermal aging, wet aging and compression set. Due to its outstanding gel selectivity, DABCO® NE 740 is well suited for the production of low-emission viscoelastic foams (based on TDI or MDI) and hyper-soft foams. Typically, DABCO® 33 LV can be completely replaced by DABCO® NE 740 when increasing the non-fugitive catalyst loading by only 10–30%, depending on the formulation. Figure 5 shows reaction profiles of two 21 kg/m³ density foams, one made with 0.11 parts DABCO® 33 LV and one made with 0.14 parts DABCO® NE 740. Both curves are essentially identical in terms of rise time, foam height and curve progression.

Figure 5. Reaction profile of DABCO® NE 740 (red curve) compared to DABCO® 33 LV (red curve) in a 21 kg/m³ density formulation

To assess the gel selectivity of the new amine catalyst, long-curing visco foams were prepared with DABCO® NE 740 and compared to DABCO® 33 LV. The results are shown in Figure 6. To obtain a similar rise profile, an excess of 20% DABCO® NE 740 was used compared to DABCO® 33 LV. At this elevated usage level, however, the tack-free time of the foam prepared with the reactive catalyst decreased significantly from 90 s to 65 s.

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

For flexible foam products, the use of DABCO® NE 300 in combination with the newly developed gelling catalyst DABCO® NE 740 results in foam materials essentially free of amine emissions according to the thermal desorption method VDA 278 and DIN 16000-9 (chamber test). Significant improvement compared to existing non-fugitive gel amine catalysts has been achieved with the new gel-optimized amine catalyst DABCO® NE 740 in terms of activity and gel selectivity. End-curing of visco foams, for example, is comparable to the industry standard DABCO® 33 LV. The advantages of using DABCO® NE 300 with the new gel catalyst DABCO® NE 740 are: 1. This combination of catalysts allows foam producers to prepare flexible polyurethane foam materials that can satisfy physical property requirements, particularly under accelerated humid aging, with no emissions. 2. Establish non-emissive standards. 3. No impact on odor. With the broad spectrum of demands to improve comfort, durability, processability, physical properties and reduction or elimination of VOC emissions, Evonik Industries AG will continue to develop new technologies that will allow polyurethane formulators and manufacturers to meet the ever-changing requirements of the industry. Polyurethane foam consumers can certainly expect to enjoy higher standards of foam quality with the use of these newly developed polyurethane additives. Note: All foams produced for this study were made by hand pouring in the laboratory.