Low Emission Catalysts

Automobile manufacturers have high performance requirements for vehicle materials. In addition to indicators such as mechanical properties, flame retardancy, and riding comfort, the interior environment of vehicles, especially odor and fog within the cabin, has become a new standard for assessing comfort in recent years. Polyurethane flexible foam used in car seats often involves the use of tertiary amine catalysts during production. These catalysts can emit an amine odor in the confined vehicle environment and volatilize at higher cabin temperatures. Some volatiles may condense on car windows, causing fogging. As a result, the polyurethane industry has introduced low-emission (also known as low-fogging or low-volatility) catalysts and foam stabilizers in recent years.

Low-volatility amine catalysts or non-emissive amine catalysts are typically either high molecular weight (high boiling point) catalysts or reactive catalysts. Reactive catalysts contain active hydrogen groups, such as hydroxyl groups, which integrate into the polyurethane resin during foam reaction molding, rendering them non-volatile. Several specialized polyurethane additive companies, including Air Products in the United States, Nitroil in Germany, GE Silicones’ OSI Polyurethane Additives division in the United States, Tosoh Corporation in Japan, and Huntsman Polyurethanes in the United States, offer low-volatility and reactive catalysts.

Reactive catalyst types include:  

- 2-(2-Dimethylaminoethoxy)ethanol  

- Bis(3-dimethylaminopropyl)amine  

- Trimethylhydroxyethyltriamine  

- Trimethylhydroxyethyl ethylenediamine  

- N,N-Bis(dimethylaminopropyl)isopropanolamine  

- N,N,N'-Trimethyl-N'-hydroxyethylbis(aminoethyl)ether  

- N-(Dimethylaminopropyl)diisopropanolamine  

- N-Methyl-N'-hydroxyethylpiperazine  

- Bis(dimethylamino)-2-propanol  

The OSI division's low-fogging catalysts include gelling amine catalysts such as Niax EF-600, EF-602, and UAX-1180. Among these, Niax EF-602 is a medium-activity delayed-action catalyst. Tertiary amine foaming catalysts include Niax EF-708, EF-705, and EF-700. These catalysts are reported to not only delay reactions and improve foam openness but also maintain or enhance the wet aging performance of the foam products.

Volatility performance tests were conducted on molded foam using the Daimler Chrysler PB VW 709L method. Test results for MDI-based and TDI-based foam formulations revealed that when traditional catalysts (A1, A-33) were used, the mass fraction of volatile amines in foam products was 232×10⁻⁶. In contrast, when low-fogging catalyst combinations EF-602 and EF-708 were used, no volatile amines were detected.