Renewable, Cashew Nutshell Liquid-Based Polyols: Their Benefits in CASE and Polyurethane Foams
Evaluating the performance and key characteristics of CNSL-based polyols in the formulation of various PU systems, including protective coatings, adhesives, and foams.
Polyurethanes (PU) have been extensively used in a broad range of industrial applications, such as foams, textiles, composites, adhesives, sealants, and coatings. For example, the polyurethane demand worldwide in 2017 was about 16.9 million tons, and it is forecasted to grow close to 22.5 million tons by 20241. In the CASE applications, polyurethane chemistry has become more and more attractive because of its valued properties of superb durability and toughness, excellent abrasion resistance, adhesion strength on various substrates, as well as desired aesthetic finishes2. Most of the polyols currently used in polyurethane applications such as foams, coatings, adhesives, and elastomers, derive from petroleum-based feedstock, but the growing interest in materials from renewable sources has led to the development of several bio-based polyols3. There are no significant examples at industrial scale of bio-based polyols with an aromatic backbone, as the majority of bio-based materials currently available are soybean-, palm-, or castor oil-based, which can offer hydrophobicity and good flexibility but lack chemical and thermal performances. The structures and properties of polyols or isocyanates as raw materials can significantly affect the physical, mechanical, and chemical properties of the final polyurethane systems. Therefore, the proper design and modification to the raw materials, especially polyols, is an effective way to enhance the performances of polyurethane systems to meet requirements for various applications.
Cashew Nutshell Liquid (CNSL) is a sustainable and non-food-chain biomaterial that is contained in the honeycomb structure of the cashew nutshell4,5. Shown in Figure 1, cardanol is the main component derived from CNSL via decarboxylation and distillation. Cardanol (average structure illustrated in Figure 2) is a penta-decadienyl phenol with a long aliphatic side chain that consists of a mixture of one, two, and three double bonds in a linear chain. Such unique and versatile structure enables this natural oil to become a very important chemical building block for numerous bio-based products including polyols.