综述：木质纤维素基聚氨酯的制备与应用研究进展

本综述系统阐述了利用可再生木质纤维素生物质开发生物基聚氨酯（BPU）以应对资源短缺与环境问题的有效策略，详细总结了木质纤维素基聚氨酯（LCPU）的合成策略（如作为填料或生物基多元醇）、性能增强（如力学性能、热稳定性）及赋予的特殊功能（如抗菌、自修复、阻燃、生物降解性），并探讨了其环境可持续性、技术经济可行性及未来挑战，为LCPU作为可持续材料的进一步探索提供了重要见解。

　　

Abstract

The development of bio-based polyurethane (BPU) using renewable lignocellulosic biomass instead of petroleum-based raw materials has become an effective strategy to cope with resource shortage and environmental problems. However, few of lignocellulose-based polyurethane (LCPU) have been synthesized and used at industrial scales. As such, this review paper intends to provide insight into the recent advances in the fabrication and potential applications of LCPU and discuss the existing challenges. The strategies and synthesis pathways to prepare LCPU are summarized and discussed. The roles of lignin, cellulose, and hemicellulose as either fillers or bio-based polyols in the synthesis of BPUs are discussed in detail. The incorporation of lignocellulose component not only enhances mechanical property and thermal stability of PU but also endows PU with special characteristics such as antibacterial activity, self-healing, flame retardancy, and biodegradability. Discussion on the features or functions of the corresponding PU inherited from lignocellulose, the structure–function relationships and their potential applications are included. Moreover, the recent advance in the environmental sustainability and techno-economic feasibility of LCPU are summarized and explored. Finally, we offer perspectives on challenges and the future prospects of LCPU. This review will contribute to the further exploration of LCPU as sustainable materials.

Introduction

Polyurethane (PU) is a class of synthetic polymers distinguished by the urethane groups within their chemical structures and has been ranked among the sixth most manufactured worldwide polymers due to its efficient synthesis chemistry, customizable molecular structure and versatile properties. The global market volume of PU reached 26 million metric tons in 2022, accounting for almost 8% of total global plastics production. It is predicted that this volume is expected to exceed 31 million tons over the next decade. Financially, the global polyurethane market size was valued at USD 89.82 billion in 2025 and is projected to reach around USD 128.95 billion by 2034, reflecting a compound annual growth rate (CAGR) of 4.10% from 2025 to 2034. PU can be manufactured in various forms, including foams, films, coatings, adhesives, lubricating greases, elastomers, and fibers. Consequently, PU products have been widely used in numerous industries, ranging from biomedical field and aerospace to construction, textiles, automotive, and electronics, demonstrating their versatility and wide-ranging adaptability.

Polyurethane can be classified into conventional isocyanate-based PU and non-isocyanate polyurethane (NIPU). Conventional polyurethanes are commonly synthesized by the step-growth polymerization of a di- or polyisocyanate with a polyol and chain extenders, and the synthesis process can be carried out via one-shot or two-step methods (e.g., prepolymer synthesis routes) according to the addition sequence of reactants. In the one-shot method, all reagents are added simultaneously during the initial reaction. In the two-step synthesis method, the pre-polymerization reaction between isocyanate and polyol is first conducted to create a prepolymer with terminal NCO-groups. Then, the prepolymer is reacted with the chain extender (usually diamines or diol compounds) to complete the synthesis of polyurethane. Compared with the one-shot method, which is a commonly used industrial technique due to its simplicity, the two-step method is more controlled, and the chemical structures of the corresponding polyurethanes are more regular. In contrast to these conventional polyurethanes which have already been well-established, NIPU emerges as a novel kind of PU and is found beneficial for limiting isocyanate handling risks. Without the use of isocyanates, the synthesis methods of NIPU can be divided into three categories, including polycondensation reaction, ring-opening polymerization and polyaddition. Among them, the polyaddition reaction via cyclic carbonates with amines is the most general approach used for the synthesis of NIPU because it offers flexibility in choosing reactants, enabling the customization of NIPU properties for special purposes.

Nowadays, the majority of polyurethane are synthesized from petroleum-based feedstock and are predominantly disposed of via incineration or landfill at end-of-life, contributing to global warming through carbon dioxide emissions. With the increasing concern about environmental and resource issues as well as the requirements of the bioeconomy, interest and efforts have been directed toward the synthesis of BPU. Studies on preparing BPU by using biomass such as turpentine, vegetable oil, cellulose, lignin, phenolics, sugars, proteins, and starches have been reported. Among them, some raw materials for the synthesis of bio-based polyurethanes are derived from food crops, raising concern over the risk of food shortages. It is worth noting that lignocellulosic biomass is the most abundant renewable resource in the world. Leveraging lignocellulosic biomass to produce biofuels, biochemicals, and biomaterials is a foundational pathway toward a sustainable bioeconomy and could play a critical role in reduction of greenhouse gas emissions. It is mainly composed of cellulose (30% ~ 35%), hemicellulose (15% ~ 35%) and lignin (20% ~ 35%), all of which are rich in active hydroxy groups, enabling their incorporation into PU via synthesis procedures. Lignocellulose is considered to have significant potential for BPU preparation due to their excellent biocompatibility, degradability, low cost, and renewability. Previous studies show the possibility of incorporating lignocellulose into PU materials by three different ways: synthesis of lignocellulose-based polyol, incorporation as fillers, or use as raw materials for the synthesis of NIPU. To the best of our knowledge, even though there are some reviews focusing on BPU derived from vegetable oil, sugar, lignin, there are no works specially focusing on the synthesis strategies of lignocellulose-based polyurethanes (LCPUs) and the impact of incorporated lignocellulose on the properties of resultant polyurethanes. In this review, we aim to highlight the latest advancements in LCPU and emphasize the approaches for introducing lignocellulose and their contribution to the function and properties of polyurethanes materials. Initially, we provided a comprehensive overview of synthesis strategies for different types of LCPU. Secondly, the effects of lignocellulosic raw material selection and process optimization on the specific functions and potential applications of BPU were thoroughly discussed, along with environmental sustainability and techno-economic assessment (TEA) of LCPU. At the end of this review, the challenges and future development directions for the development of a new generation of lignocellulose-based polyurethanes are highlighted.

The synthesis strategies of lignocellulose-based polyurethane

Lignocellulose is a collective term for natural plant fiber materials derived from a wide array of sources, including logs, residues from wood processing, bamboo, vines, agricultural straws, husks, hemp, and other similar organic fibers. This work mainly focuses on recent advances in the synthesis of cellulose-based polyurethane, lignin-based polyurethane and hemicellulose-based polyurethane.

Mechanical performance and thermal properties of lignocellulose-based polyurethane

In recent years, increasing efforts have been made to synthesize LCPU with excellent mechanical properties. The type of lignocellulose significantly affects the mechanical properties of resultant PUs. On the other hand, it is known that the degree of reinforcement in mechanical performance of LCPUs is strongly related to the interfacial interaction between the lignocellulose and the PU matrix. Therefore, the strategies to improve the interfacial compatibility, such as chemical modification of lignocellulose, are crucial for achieving high-performance LCPU materials. Regarding thermal properties, the incorporation of lignocellulose components generally enhances the thermal stability of PU, which is attributed to the inherent thermal resistance of lignocellulosic structures and the formation of stronger interfacial bonds.

Life cycle assessment of lignocellulose-based polyurethane

Life cycle assessment (LCA) is a widely accepted and standardized approach that evaluates the potential environmental impacts related to a product by compiling and evaluating inputs (including energy, raw and ancillary materials), outputs (emissions to air, water, and soil), and corresponding impacts over the life cycle of the PU. Extensive studies have been conducted with the aim of enhancing the sustainability of PU materials. The predominant solution explored is the substitution of petroleum-based raw materials with renewable resources like lignocellulose. LCA studies on LCPU aim to quantify the environmental benefits, such as reduced global warming potential and fossil resource depletion, compared to conventional PU. However, the environmental footprint of LCPU is also influenced by factors like the energy intensity of lignocellulose processing and chemical modification routes. Therefore, a comprehensive LCA is essential for identifying hotspots and guiding the sustainable development of LCPU technologies.

Conclusions and prospects

So far, previous studies on LCPU have demonstrated the feasibility of synthesis pathways and their potential across various applications. This is due to the enrichment in functional groups of lignocellulose such that it offers opportunities for chemical modification to meet the synthesis requirements of PU and diverse application requirements. Moreover, the feature and functions of lignocellulose endow polyurethanes with favorable multi-functionality and further enhances its practical or potential application value. Nevertheless, challenges remain in scaling up the production of LCPU, optimizing the cost-effectiveness, and fully understanding the long-term performance and degradation behavior. Future research should focus on developing more efficient and green modification methods for lignocellulose, designing LCPU with tailored properties for specific high-value applications, and conducting more comprehensive LCA and TEA studies to validate the sustainability and economic viability of LCPU. The continuous exploration of LCPU is expected to contribute significantly to the development of a sustainable bioeconomy.