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Polyurethanes are among the most versatile polymers because of the wide range of monomers, particularly diols or polyols, that can be utilized in their synthesis. This Review focuses on the most recent advances made in the production of polyurethane materials from vegetable oils. Over the past several years, increasing attention has been given to the use of vegetable oils as feedstocks for polymeric materials, because they tend to be very inexpensive and available in large quantities. Using various procedures, a very broad range of polyols or diols and in some cases, poly- or diisocyanates, can be obtained from vegetable oils. The wide range of vegetable oil-based monomers leads to a wide variety of polyurethane materials, from flexible foams to ductile and rigid plastics. The thermal and mechanical properties of these vegetable oil-based polyurethanes are often comparable to or even better than those prepared from petroleum and are suitable for applications in various industries.

Bio-based polyols from epoxidized soybean oil and castor oil fatty acid were developed using an environmentally friendly, solvent-free/catalyst-free method. The effects of the molar ratios of the carboxyl to the epoxy groups, reaction time, and reaction temperature on the polyols' structures were systematically studied. Subsequently, polyurethane films were prepared from these green polyols. Properties of the new, soy-castor oil based polyurethane films were compared with two other polyurethane films prepared from castor oil and methoxylated soybean oil polyol, respectively. Thermal and mechanical tests showed that the polyurethane films prepared from the new polyols exhibited higher glass transition temperatures, tensile strength, Young's modulus, and thermal stability because of the higher degree of cross-linking in the new polyols. Moreover, the novel polyols, prepared using the solvent-free and catalyst-free synthetic route, were 100% bio-based and facilitate a more environmentally friendly and economical process than conventional soy-based polyols used for polyurethane production.Footnotes † Electronic supplementary information (ESI) available. See

Novel biorenewable, waterborne, castor oil-based polyurethane dispersions (PUDs) were successfully synthesized via homogeneous solution polymerization in methyl ethyl ketone followed by solvent exchange with water. Small-amplitude oscillatory shear flow experiments were used to systematically investigate the rheological behavior of these environmentally friendly, biorenewable, aqueous dispersions as a function of angular frequency, solid content, and temperature. In addition, the morphology of the dispersions was investigated at 60 °C for different time intervals using transmission electron microscopy (TEM). The solid content and temperature were found to significantly affect the rheological behavior of the PUDs. The composition dependency of the complex viscosity (η*) was found to be well described by the Krieger–Dougherty equation. Thermally induced gelation was observed for PUDs with a solid content ≥27 wt %. Although the viscoelastic behavior of the PUDs was well described by the time–temperature superposition (TTS) principle in a temperature range lower than the gel point, TTS failed to represent the behavior of the PUDs at temperatures near the critical gel point. The real time gelation behavior was also studied for different solid contents of PUDs under isothermal conditions over a wide range of angular frequencies. Furthermore, both G′ and G″ showed a power law relationship with the angular frequency at the gel point, with critical power law exponents similar to those predicted theoretically by percolation theory. Aggregation and interconnection of the nano-PU particles caused the formation of fractal gels at a critical temperature, as confirmed by TEM.

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