Rigid polyurethane foams (RPUFs) were synthesized with bacterial nanocellulose (BNC) at concentrations of up to 0.5 wt% using two insertion routes based on its reaction with the isocyanate precursor (ISO route) and the formation of a colloidal dispersion in the polyol precursor (POL route). The results indicated that, for BNC concentrations of only 0.1 wt%, drastic improvements of the specific elastic compressive modulus (+244.2%) and strength (+77.5%) were measured for foams with apparent density of 46.4+/− 4.7 Kg.m−3. The chemical reaction of BNC with the precursor was corroborated through the measurement of the isocyanate number and FTIR analysis. The BNC caused a significant nucleation effect, decreasing the cell size up to 39.7%. Differential scanning calorimetry analysis revealed that the BNC had a strong effect on post‐cure enthalpy, particularly for the POL route. Dynamical mechanical thermal analysis under flexural conditions proved that, regardless of BNC concentration, the incorporation of BNC caused anisotropy and that the ISO route contributed to an enhanced damping factor at high temperatures. These results prove that the ISO route is a key aspect to achieve foamed nanocomposites with improved specific mechanical properties.

Thermosetting polyurethanes were obtained using an aromatic isocyanate and a hydrophobic polyol formulation obtained from epoxidized soybean oil (ESO) crosslinked with glycerin. A systematic DSC analysis of the effect of catalyst type, crosslinker concentration, isocyanate index and ESO crystallization on cure kinetics was conducted. The combination of a stannic catalyst at 0.2 wt% and glycerin at 20 wt% produced a cure kinetics governed by an autocatalytic heat flow where vitrification played a key role in the formation of chemical bonds. The evolution of T g as a function of conversion, which followed Di-Benedetto's predictions, supported the hypothesis that vitrification was a preponderant phenomenon during cure. Dynamic Mechanical Analysis (DMA) of a post-cured sample revealed a Tg centered at 220 C, whereas quasi-static flexural mechanical tests shown a flexural modulus of 2.14 GPa and a flexural strength of 99.4 MPa. Rheological experiments at isothermal conditions supported the hypothesis that vitrification played a key role in the evolution of apparent viscosity. A master model using Kim-Macosko equations was obtained for the proposed formulation. The results presented in this work will serve to further extend the use of biobased polymers applied in the polymer composite industry.

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A systematic study of the post‐cure cycle of soy‐based polyurethane thermosets was conducted as a function of crosslinker content, post‐cure temperature and time. An improvement of 207% of the flexural strength, up to 175 MPa, was measured by increasing the crosslinking content to 60 wt% and by using a post‐cure cycle temperature of 110°C. Similarly, the flexural modulus also increased by 199%, up to 3.2 GPa, while maintaining a flexural strain to failure of 6.60%. In situ studies of the post‐cure cycle using dynamical mechanical analysis revealed the interplay between the two interpenetrating polymer networks as a function of crosslinker content. At a crosslinker content below 40 wt%, two rubbery to glass transition temperatures (Tg) were found at 60 and 200°C, respectively. At 60 wt%, only one Tg at temperatures close to the degradation temperature was identified (250°C). Scanning electron microscope micrographs of the fracture surface revealed the formation of stress induced cracks which were mitigated through the use of a temperature stepped post‐cure cycle. The formation of soft segments with high degradation temperatures (485°C) were revealed by thermogravimetric analysis, which can be attributed to the presence of additional covalent bonds such as allophanate and carbodiimide that were also identified through Fourier transform infrared analysis. The results revealed in this work are key for the development of biobased polyurethanes applied for the polymer composite industry. In this regard, this study represented the first analysis of the post‐cure cycle of a soy‐based polyurethane thermoset.