Low-GWP blowing agents are going to be introduced to the market in the next few years and it will be necessary to optimise spray foam systems to use these ingredients.
By Christian Eilbracht, Carsten Schiller, Robert Tauchen and Wiley Rowe of Evonik.
Spray foam formulations are unusual among polyurethane systems; they must have a long shelf life and they are complex mixtures of ingredients. Surfactants can have a significant impact the shelf life, chemical compatibility and physical properties, of these formulations.
We have found that surfactants play an important role in terms of spray-foam physical properties, flow, appearance and formulation shelf-life.
Additionally, this work shows that our Tergostab B84715 material gives good all-round properties in a standard formulation but that other surfactants may be more suitable if a high R-value or improved FR are required in different formulations.
To reach this conclusion we tested ten Evonik surfactants.
In July 2015, the EPA announced final regulations changing the status of several products with high Global Warming Potential (GWP) used in polyurethane foam. As a result, users have been instructed to stop using hydrofluorocarbons (HFCs) in some applications and switch to low GWP alternatives like 4th generation blowing agents, hydrofluoroolefins (HFOs). The GWP of the new HFOs is typically 1% of HFCs.
The spray foam industry has to face this change and it will be necessary to move to systems with different blowing agents.
Formulating for success
Testing took place in two parts. First, each system was compounded and sprayed shortly afterwards and physical property and appearance data was gathered.
Then samples of each liquid spray foam system were placed in a non-climate controlled environment for three months. After that time, the systems were re-sprayed several times and again tested for physical properties and appearance.
Each initial set of samples were sprayed on cardboard, and each aged set were sprayed on oriented strand board (OSB).
The foam properties of the aged and unaged resin samples were compared to assess differences in stability between the systems.
The surfactants were sprayed following the sampling schedule below.
We tested standard and a few experimental spray-foam surfactants. The surfactants tested had a wide range of silicone content, molecular weight, and polyether composition. The differences between the ten products are listed in Table 2.
Table 2. Surfactants Selected for evaluation.
Figure 1 shows how the chemical structures of different surfactants can vary. The black line represents the silicone backbone and the purple lines are the polyether pendants. The left figure shows surfactants with short siloxane chains, high degree of backbone modification, and low polyether chain length. The middle figure shows medium siloxane chain length, low modification, and medium polyether chain length. Finally, the figure on the right illustrates long siloxane chain length, medium backbone modification, and high polyether chain length.