Research Progress and Prospect on Lignin-based Polyurethane Thermal Insulation Foam

As global building energy consumption continues to rise, polyurethane foam has become a crucial material for reducing energy consumption in the construction sector due to its superior thermal insulation properties. However, the current production of polyurethane foam relies heavily on non-renewable petroleum-based polyols, posing significant challenges to environmental sustainability and resource availability. Lignin, an abundant natural polymer in nature, offers a promising alternative to petroleum-based polyols due to its complex three-dimensional structure and an abundance of hydroxyl and other functional groups. Polyurethane foams based on lignin not only maintain the excellent thermal insulation properties of conventional materials but also considerably reduce the dependence on petroleum-based feedstocks, thereby advancing the low-carbon transformation of building materials. This paper systematically reviews the latest research developments in the field of lignin-based polyurethane thermal insulation foams from three perspectives: the preparation technology of polyurethane foams, the liquefaction and modification of lignin, and the relationship between the structure and thermal insulation properties of lignin-based polyurethane foams. It delves into the characteristics of the one-step foaming method and its dynamic regulation mechanisms of bubble nucleation, expansion, and gelation. Additionally, it explores the research and application of modification technologies such as hydroxymethylation and oxyalkylation. It also provides an in-depth discussion on the thermal insulation and heat transfer mechanisms of foams as well as the optimization paths for improving thermal insulation performance. In light of current research bottlenecks, this paper outlines future development directions from five aspects: green lignin modification technologies, key properties enhancement, multi-function collaborative optimization, application scenario expansion, and standardization of industrial applications. This review aims to provide a robust theoretical foundation for promoting the large-scale application and sustainable development of lignin-based polyurethane foams.