Testing the Effect of the Reactivity of Silicone Surfactants in Polyurethane Rigid Foams

Concentrol has conducted a study of 15 new surfactants used in formulations of rigid polyurethane foams to analyze the effect of the reactivity of the surfactant on their properties. The study was conducted with the aim of providing surfactants with the best performance and minimum cost to produce polyurethane.

The study was carried out in Concentrol’s labs and was led by Josep Nadal, Doctor of Chemical Sciences and Technical Director in PU Additives.

Rigid polyurethane foams have different applications in industry, construction and the domestic sphere, including refrigerators, freezers, refrigeration chambers, wall coverings and roofs. Polyurethane in these applications must have specific properties to obtain good results in terms of thermal isolation, consistency, flammability and adhesion. Silicone surfactants are essential components for the production of polyurethane foams because they allow foaming to be stabilized while also improving other properties.

From a chemical perspective, silicone surfactants are formed by a polyether and a polysiloxane. The study carried out by Concentrol focuses on the synthesis of different groups of surfactants, where the only difference is the terminal group of the polyether, thereby modifying its reactivity.

Thanks to its synthesizing capabilities, Concentrol can produce surfactants with different terminal groups, reactive and non-reactive, to obtain specific properties in rigid polyurethane foams, such as improving adhesion or to produce one- component foams (for use with spray guns). In this study, three different situations altering the reactivity were analyzed:

  • Non-capped (-OH)
  • Methoxy capped (-OCH3)
  • Acetoxy capped (-OCOCH3)

Each of the three types of resulting surfactants have different applications depending on the type of polyurethane desired. The preparation of polyurethane panels is where these three types of surfactants are most often used. For this reason, and to obtain comparable results between three variations of surfactants, Concentrol focused this study on analyzing the effects of reactivity in PUR/PIR formulations in particular.

The study is divided into two parts. In the first, 15 samples of new experimental surfactants using different types of polysiloxane (based on molecular weight and ramification) and different types of polyethers (based on molecular weight and on the percentage of ethylene oxide EO) are synthesized, where the only difference is the reactivity. This part of the study observed the synthesis and characterization of these surfactants using different technologies to analyze:

  • Polarity (cloud point analysis)
  • Infrared spectrum
  • Molecular weight

The second part involved the physical analysis of the foams prepared with the surfactants resulting from the first part of the study, to link the chemical structure with the resulting physical parameters. To do so, the following characteristics were taken into account:

  • Lambda values (thermal conductivity)
  • Flammability
  • Measurement of dimensional stability
  • General appearance

The results provided by the different analyses show that, in the chosen formulations for polyurethane panels, the most important changes in the foam come from the different combinations of chemical components of the surfactants (EO, PO, siloxane %); altering the reactivity of the terminal group of silicone surfactants does not show an effect on the quality and performance of polyurethane panel foams.

Therefore we can conclude that in the three silicone surfactants synthesis technologies developed by Concentrol’s lab for this study (non-capped -OH, -OCH3 capped and -OCOCH3 capped) no negative effects were detected in the properties (thermal conductivity, flammability, dimensional stability and overall appearance) of the resulting polyurethane panels.

Capping the reactivity of a surfactant is a synthesis process that makes the resulting product more expensive. This study demonstrates that this process is not necessary to improve the properties of the different formulations of PUR/PIR panels studied.

To continue this study, we plan to evaluate the effect of different surfactants in the resulting foam by analysing parameters such as adhesion of the foam on the metal sides of the panel and the effect on the flowability of the foam.

This study was presented to the public in April 2016 by Josep Nadal during the bi-annual CONCENTROL UTECH North America event.

Concentrol exhibited at Foam Expo North America 2018.