In the modern construction and industrial sectors, rigid polyurethane foam and polystyrene foam are widely used as primary insulation materials for applications such as wall insulation and cold storage. This article provides a detailed comparative analysis of these two materials from the perspectives of foaming mechanisms, physical and chemical properties, and application methods, aiming to offer insights for practical use.

1. Different Foaming Mechanisms

The foaming mechanism of rigid polyurethane foam involves the thorough mixing of two-component liquids (commonly referred to as “A” and “B” components), leading to a rapid chemical reaction and curing within a short time frame ranging from seconds to minutes. Rigid polyurethane foam is a lightweight thermoset foam with high closed-cell content (>90%) due to the addition of blowing agents, catalysts, and dispersing agents. On the other hand, the foaming of polystyrene foam (EPS, XPS) occurs through the expansion of bead or powder materials upon heating, with the blowing agent vaporizing and expanding, followed by molding using molds or extrusion machinery, resulting in a granular structure characteristic of a thermoplastic foam. Polystyrene foam is sensitive to temperature and carries a risk of secondary foaming.

2. Different Physical and Chemical properties

a) Insulation Performance

Polystyrene foam exhibits good insulation properties, but its thermal conductivity (λ) is still relatively high compared to rigid polyurethane foam. For example, the λ value of EPSis around 0.04 W/k·m, and that of XPS is about 0.031 W/k·m, while rigid polyurethane foam only has a thermal conductivity value of approximately 0.022 W/k·m. Under the same energy-saving standards, rigid polyurethane foam can reduce the thickness of insulation panels, enhancing the quality and stability of the insulation system.

b) Thermal Stability

Rigid polyurethane foam can achieve thermal stability of up to 120°C, whereas the polystyrene foam only withstands 70°C. In China, during summer, the surface temperatures of exterior walls often reach or exceed 70°C, which can easily trigger secondary foaming of polystyrene, leading to crack formation.

c) Surface Adhesion

Rigid polyurethane foam contains a certain amount of -OH bonds (hydrophilic genes) in its molecular chain, enabling it to bond with cement-based mortar. Polystyrene lacks -OH bonds, making it a hydrophobic material that is challenging to integrate with cement-based mortars and other inorganic materials. This difficulty leads to the susceptibility of polystyrene exterior insulation systems to cracking, delamination, and detachment.

d) Combustion Principle

Rigid polyurethane foam is a thermoset material that forms a carbonized layer when burned, which acts as a barrier against further heat and oxygen infiltration, hindering the foam from extensive burning and reducing fire risks. Polystyrene foam, being a thermoplastic material, shrinks, melts, and drips when heated, failing to form a carbonized barrier, thus making it prone to flame spreading and flashover accidents.

e) Corrosion Resistance

Rigid polyurethane foam exhibits resistance to water, oil, and solvents, whereas polystyrene only resists water but not solvents. Polystyrene is especially sensitive to benzene and ester solvents, making it susceptible to rapid corrosion.

3. Different Application Methods and Scope

Polystyrene foam can only be produced through expansion or extrusion process in a factory setting, while rigid polyurethane foam can be constructed by spraying, pouring and pasting prefabricated foam, making its application methods more flexible and diverse. Rigid polyurethane foam can be used not only for building insulation systems but also in various insulation fields such as cold storage, pipelines, and ships, offering the advantages of easy construction and high efficiency.

In conclusion, rigid polyurethane foam and polystyrene foam each have their own advantages and disadvantages. In practical applications, the choice of insulation material should be based on specific needs and environmental conditions. Rigid polyurethane foam, with its excellent insulation performance, thermal stability, surface adhesion, and corrosion resistance, is particularly suitable for situations requiring high insulation effectiveness and durability. On the other hand, polystyrene foam finds widespread use in areas with lower insulation performance requirements due to its lower cost and easy installation. Through proper selection and scientific application, energy conservation and environmental friendliness can be achieved, enhancing the lifespan and safety of buildings and industrial facilities.