Polyol Stabilization

Polyol producers are looking for additives which stabilize the polyether polyol against oxidation during neutralization, storage and transport. On the other hand flexible foam manufactures are looking for a high level of scorch resistance since halogenated blowing agents are replaced with other auxiliary blowing agents such as water leading to higher exothermic reactions and therefore to more severe scorch especially in low density foams.
Antioxidant packages have two functions:

1. They are added to protect the polyether polyol from oxidation (hydroperoxide formation) during manufacture, transportation and storage. The state-of-the-art stabilization of polyether polyol against oxidation is the use of 300-500 ppm of a hindered phenol. Many polyol producers prefer Ciba® IRGANOX® 1076 and Ciba® IRGANOX® 1135 due to their lower volatility compared to BHT.
The effectiveness of antioxidants in polyols is often assessed by  differential scanning calorimetry (DSC). At constant heating rate, the temperature is determined at which the exothermic reactions starts (oxidation temperatures). The temperature at the onset of the exotherm can be used as a measure of the thermooxidative stability of the polyol sample, with a higher temperature indicating improved stability
Influence of stabilization on the oxidation temperature of a polyether polyol, determined by DSC Measurements:  Dynamic 50 - 250 °C / Heating Rate: 5 °C / min under Oxygen
   

2. They should prevent scorching during foaming of large foam blocks; therefore a higher amount of antioxidant is necessary. In practice, the stabilization of slabstock polyols is based on combinations of hindered phenols and secondary aromatic amines like Ciba®IRGASTAB®PUR 55. In slabstock polyols where outstanding resistance to scorch, low VOC emissions and low foam discoloration after gas and / or light exposure is required, two new liquid BHT free packages Ciba®IRGASTAB®PUR 67 and Ciba®IRGASTAB®PUR 68 are recommended.

Flexible PUR Foam Scorch Evaluation. YI after Dynamic Heat Test

Fogging / Low VOC emissions

In recent years there has been a dramatic change of mind in the automotive market regarding emissions in car interiors. Extensive fogging, e.g., on the windscreen, is not acceptable anymore. Beside cyclic polyols - widely recognized as a major factor in fogging - amine catalysts , silicone surfactants and BHT antioxidants are also contributors. Flexible PUR Foam Fogging Evaluation: VOC emissions (Method: PB VWL 709)
  

Foams have been produced using the new emanation free catalyst system TEGOAMIN ZE 1 and KOSMOS EF.

Gas fading and Textile staining

Foam discoloration resulting from gas fading is an issue in BHT stabilized materials. Under foam storage conditions, where nitroxide (NOx) gases are involved, phenolic antioxidants can lead to a yellow discoloration. BHT-containing foams when subjected to gas fading induce textile (e.g. mattresses, shoulder pads) or carpet staining. The low molecular weight molecules - yellow nitrophenol derivatives resulting from BHT in presence of nitroxide gases - can migrate to the surface and to the textile wrapping the foam block. This phenomenon is not observed with higher molecular weight antioxidant. High concentrations of aromatic amines have also a negative contribution.

Flexible PUR Foam Textile Staining Evaluation: Delta E on Textile Exposure: 6-8 ppm NOx / Oven: 24 h at 40 °C
   

Flexible PUR Foam: Gas Fading (0.5 h / 6-8 ppm NOx / 40 °C / 65 % rel. Humidity)

Light stability of PUR foams

Flexible PUR foams based on aromatic isocyanates are known to turn yellow after exposure to light. Samples containing different types of stabilizers were exposed in the WOM (B.P. 63 °C, dry). Samples containing aromatic amines tend to discolor faster than samples containing the amine free system Ciba® IRGASTAB® PUR 68.

WOM Exposure of Flexible PUR Foam            

The light stability of flexible foams can be improved by using liquid light stabilizers blends, e.g. Ciba® TINUVIN® B 75.

For further information, please contact us.