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Issue 01/2023

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Cover Story Research on

Cover Story Research on biobased polyurethane The need to get away from fossil resources has triggered the development of biobased thermoset and thermoplastic polyurethanes which can be used for applications in many sectors. Biobased polyurethanes can be synthesised in different ways, e.g. by conventional chemical synthesis or solventfree synthesis and using different biomass-derived reagents, as shown in Figure 1. for the production of biobased polyurethane in collaboration with the company Tecno Caucho Rolls & Covers (Quart de Poblet, Spain) during the DICKENS project. To realize partially biobased polyurethanes, it is possible to partially substitute the isocyanates traditionally used, in other words, to replace the methylene diphenyl diisocyanate (MDI) or the toluene diisocyanate (TDI) by some commercial biobased isocyanates. On the other hand, it can be possible to obtain biobased polyurethane by partially or totally substituting the fossil-based polyol commonly used. A biobased polyol can be synthesized from biomass products such as lignin or plant oils. Figure 1: Image of the different derived biomass reagents for the synthesis of polyurethane (Source: nova-Institute) The thermosets polyurethanes are obtained by the crosslinking of two prepolymers, which are commonly a polyester or polyether polyol and isocyanates under basic or acidic catalyst system. Polyurethanes can be obtained from compact to expanded (foamed) state and from flexible to rigid form. This variety of forms makes polyurethanes a group of very versatile polymers used in many industries. To reduce the environmental problems associated with these materials, research on the development of biobased polyurethane is booming. In this context, AIMPLAS had the opportunity to drive the research on the substitution of products of fossil origin As part of the project, the first objective is to replace fossil-based polyols with biobased synthesized polyols. To complete this goal, the first step was to choose the most adapted biomass product for the formulation of polyurethanes suitable for the final application. The oils chosen for this development are available in large quantities, moreover, there is no price fluctuation of these resources, and they are available at a rather low cost. In addition, their chemical structure allows for many chemical modifications, so they are very versatile and interesting for the development of polyurethanes. The polyols were obtained from oils undergoing c h e m i c a l modifications to replace the fossil-based reagent in the formulation of the thermoset polyurethane. By experimenting with the starting reagents used, it was possible to synthesise several biobased polyols with different properties, such as the molecular weight, viscosity, or hydroxyl index of each of these samples, from a single oil. This panel of polyols has not only allowed the formulation of several polyurethanes that are with varying levels of rigidity but also different mechanical properties, which opens up their use for several kinds of applications. 28 bioplastics MAGAZINE [01/23] Vol. 18

By: Ana Mangas Roca, Mechanochemistry Researcher Juliette Thomazo-Jégou, Synthesis Researcher AIMPLAS, Plastics Technology Centre Paterna, Valencia, Spain Cover Story such as the synthesis and/or modification of polymers, with their segregation, reinforcement, and/or degassing in a single step. With REX, the raw materials are continuously fed into the extruder and subjected to a shear reaction at high temperatures. The ability to eliminate the use of solvents is a significant environmental benefit. Photography of biobased polyurethanes This project showed that it was possible to develop polymers, in particular polyurethane thermosets, which were partially biobased without reducing the mechanical properties required for thermosetting and without significantly increasing the price of their production. In summary, the sustainability of polyurethane (PU) in terms of chemical composition and production technology is an important topic in the polymer industry, driven by circular economy strategies. That is why over time, new technologies are being developed that allow a more sustainable process in terms of solvents used, origin of the materials, energy consumption, environmental impact etc. This is where reactive extrusion processes are positioned as a process superior to most polymerization processes. REX (Reactive Extrusion) is based on the use of an extruder as a continuous chemical reactor which makes it possible to combine several typical processes of the polymer industry, Synthesis of TPU by reactive extrusion To achieve this, polyurethane can be developed from its individual components or from a premix of the selected diols. Residence times range from 2 to 5 minutes, so it is a quick and effective reaction, which can be developed on a continuous mode in a pilot and industrial plant scale. Success studies are reported in which solvent-free synthesis can also be done with materials of biobased origin even at room temperature. Some examples include the use of polyols derived from natural oils, which have reactive functional groups such as diols and diisocyanates, but also from furan-based diols such as BHMF, cellulose-derived 5-hydroxymethylfurfural (HMF) and furfural . Even several diols and diamines from C5 and C6 sugars can be used to make copolymers to form furan-based PUs. The development of biobased polyurethane is currently not very well established as there are many factors limiting their production such as access to feedstock, competition with established fossil-based materials, regulatory barriers, social barriers , finance and investment, and also Research & Development [1]. However, current research shows that there is a real technical and economic opportunity to produce these polymers using biomass. Presented as an alternative to petroleum-derived resources, it could also be synthesized with higher molecular weight (Mw) and controlled physical properties by greener and solvent-free reactions, being extended to large-scale and industrial productions, generating the necessary positive impact on the environment. [1] Source: RoadToBio-European Union’s Horizon 2020 research and innovation programme under grant agreement No 745623 bioplastics MAGAZINE [01/23] Vol. 18 29

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