Polyurethane (PU) foams are commonly used in construction for a number of purposes, but with the drive to net zero, the sustainability of these materials is under increasing scrutiny. Improving their green credentials is paramount.
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What is Polyurethane Foam?
Polyurethane foam is a polymer that is composed of carbamate-linked organic monomer units. A lightweight material with a large air content, polyurethane has an open-cell structure. Polyurethane is made by a reaction between di- or tri-isocyanate with a polyol and can be modified by the incorporation of other materials.
Foams can be constructed from polyurethane with varying degrees of hardness, and other materials can be used in their manufacture. Thermoset polyurethane foams are the most common type, but some thermoplastic polymers exist. The key benefits of thermoset foams are their flame resistance, versatility, and durability.
Uses of Polyurethane Foam in Construction
The construction industry makes widespread use of polyurethane foams due to their flame resistance, lightweight construction, and insulating properties. It is used to construct strong and lightweight building elements and can enhance a building’s aesthetic properties.
Many types of furniture and carpeting products contain polyurethane due to its versatility, cost-effectiveness, and durability. Materials must be fully cured to stop the initial reactions and avoid any toxicity issues in line with EPA regulations. Additionally, PU foams improve the flame resistance of bedding and furniture.
Spray polyurethane foams (SPFs) are a major type of insulating material that increases the energy efficiency of buildings and comfort for occupants. The use of these insulating materials reduces greenhouse gas emissions and improves indoor air quality.
PU-based binders are also used to create wood-based products such as MDF, OSB, and particleboard. The versatility of PU means that it can be used for a wide range of purposes, such as soundproofing and abrasion, extreme temperature, mildew, and aging resistance. Many applications for this material in construction exist.
Issues With Sustainability and Recyclability
Whilst it is eminently useful and has found application in many facets of building construction, PU foam is not without its issues. Primarily, the sustainability and recyclability of this material have been called into question in recent years, with research to overcome these issues becoming more commonplace in the literature.
A main factor that restricts the sustainability and recyclability of this material is the use of highly reactive and toxic isocyanates in its manufacture. Multiple types of catalysts and surfactants are also used to produce PU foam with a variety of properties.
According to some estimates, approximately 30% of all recovered PU foam is sent to landfills, representing a major environmental challenge for the construction industry as this material is not readily biodegradable. Around a third of PU foams are recycled.
Improving the Sustainability and Recyclability of PU Foam
There is major scope for improving these issues, and to this end, many studies have explored new approaches for the recovery and re-use of PU foams and other PU materials. Physical, chemical, and biological recycling methods are commonly used to recover PU foams for value-added uses.
Currently, however, no recycling options can provide a high-quality, reusable, and consistent end product. Hurdles such as cost, low yield, and a critical lack of recycling infrastructure must be addressed before PU foam recycling can be considered to be a viable option in the construction and furniture industries.
A paper published in November 2022 has explored routes to improving the sustainability and recyclability of this key construction material. The research, published in Angewandte Chemie International Edition has been conducted by scientists at the University of Liège in Belgium.
The innovative approach involves replacing the use of highly toxic and reactive isocyanates with more environmentally friendly materials. CO2, another environmentally damaging chemical, is used as a raw material in this novel green PU foam manufacturing method.
Water is used to generate the blowing agent in this sustainable manufacturing process, which mimics the foaming technology in conventional PU foam processing and successfully avoids the use of environmentally damaging isocyanates. The end result is a green polyurethane foam the authors have termed “NIPU.”
Alongside water, the process uses a catalyst to convert cyclic carbonates, a more environmentally friendly alternative to isocyanates, into CO2 to blow the matrix. Simultaneously, the foam is cured via a reaction with amines in the material.
The novel process demonstrated in the paper produces a low-density, solid PU material with regular pore distribution. Chemical transformation of waste CO2 provides a facile obtention of cyclic carbonates for the manufacturing process. The result is a dual role, generating the blowing agent and forming the PU matrix.
The research team has created a simple, easy-to-implement, and modular technology which, in combination with readily available and low-cost, sustainable starting products, provides the impetus for a new generation of green PU foams for the construction industry. This would, therefore, enhance the sector’s push to net zero.
Whilst there is no single “silver bullet” approach to improving sustainability in the construction industry, research is ongoing, taking multiple approaches to this key environmental problem.
Innovative approaches, such as the team at the University of Liège’s new technology, will help to vastly improve the sustainability and recyclability of PU foam. Replacing conventional, highly toxic chemicals used in processing and improving the biodegradability of PU foams is crucial.
If the construction sector is to meet its net zero commitments in line with the international aim to reduce the impact of humanity on climate change and the natural world, approaches that improve circularity must be front and center of new research. It is clear that a “business as usual” approach is no longer feasible.
More from AZoBuild: Recycled and Alternative Materials for Concrete Production
References and Further Reading
University de Liege (2022) Developing more sustainable and recyclable polyurethane foams [online] phys.org. Available at:
Building With Chemistry (website) Polyurethane in Building and Construction [online] buildingwithchemistry.org. Available at:
Gadhave, R.V et al. (2019) Recycling and Disposal Methods for Polyurethane Wastes: A Review Open Journal of Polymer Chemistry 9 pp. 39-51 [online] scirp.org. Available at:
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