Seeking Approaches To Reduce R-Value Loss With Aging Of Rigid Polymeric Foams

• A technology
• A Material

A SpecialChem Client is seeking a technology to reduce cell wall permeability of rigid polymeric foams with a backbone of polyurethane (PUR) / polyisocyanurate (PIR).

When rigid foams are manufactured, a PUR or PIR matrix is expanded using a combination of blowing agents to form a cellular network that comprises an efficient temperature insulating material (monitored with the k-factor metric). These rigid PIR/PUR foam boards are known to exhibit an aging effect in which thermal insulation performance decreases over time.

Because the PIR/PUR reaction is exothermic, as the foam board cools to ambient temperature the cell gasses also cool. Condensation of these gasses creates a partial vacuum in the closed cells of the foam and pulls air into the cell. The smaller molecules in the air are not good contributors to thermal insulation and the foam board loses some k-factor rating as a result.

In most cases, the gasses are also soluble in the polymer matrix to varying degrees, which further contributes to the loss of the desired blowing agent in the cells.

The SpecialChem Client is ready to consider chemical, filler, and manufacturing process modifications to improve their current formulations. The Client is willing to work with the solver to make and test prototypes. Depending on the nature of the solution, the Client is willing to purchase or license the technology.

A typical manufacturing process to make the backbone of PUR/PIR follows these steps:

- Only liquid reactants are used.

- Raw materials are formulated with tertiary amine and potassium trimer catalysts, water, auxiliary hydrocarbon blowing agents, and surfactants.

- The rigid foam board is produced by pouring the reactants onto a heated conveyor to make boards. For applications in walls, these boards are 0.5 – 2.0 inches thick (1,2 – 5 centimeters) and for roof applications they are 1.5 to 4.0 inches thick (3,8 – 10 centimeters).

• Conveyor is heated to the temperature of 60 - 70°C (140 - 160 °F)
• This is generally done with a 2-stream mixhead, where the isocyanate is one stream and the formulated polyol/additives blend is the second stream, but the hydrocarbon blowing agents are often added as a third stream.

- Typical hydrocarbon auxiliary blowing agents:

• HCFO 1233zd(E): initial k-factor of ~0.125 BTU-in/hr-ft2-°F @ 75°F
• Normal-pentane: initial k-factor of ~0.135 BTU-in/hr-ft2-°F
• These hydrocarbons are used because they provide high impedance to the flow of heat through the foam board.

- The conveyor is usually lined with a facing material (fabric, aluminum, paper, etc.)

- Formulation additives are typically combined with the polyol component or added as a separate reactant stream.

PIR/PUR foam formulations are adjusted to produce the desired physical/mechanical properties for the targeted application. Composition of raw materials will also directly impact the desired foam physical properties.

Approaches to reduce this effect, for example, by reducing cell wall permeability to air or reducing the diffusion of blowing agents from the cell into the matrix are solicited.

Chemical solutions may include novel surfactants or additives to the matrix that reduce migration of cell gases into the matrix or air into the cells.

Ideas for reducing the loss of cell pressure during cooling may also be beneficial.

Solutions may also suggest modifications to the isocyanate and/or polyol intermediates used to make the foam if these would reduce migration or solubility of gasses in the cell wall or foam matrix.

As soon as realistically possible.

• Ready to use solutions
• Proven concepts
• Partners

• Buy
• License