Nanostructured rigid polyurethane foams with improved specific thermo‐mechanical properties using bacterial nanocellulose as a hard segment

Abstract

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.

In‐situ thermal aging of biobased and conventional rigid polyurethane foams nanostructured with bacterial nanocellulose

“…In fact, for the case of immersion at 25°C, we can observe that increasing contents of BNC caused a monotonous increase of cell size in the L direction, which was the exactly opposite case in the T direction. These results reinforce the hypothesis that BNC was increasing the anisotropic behavior of the foams, 14 causing more heterogeneity in the variation of cell size.…”

“…It is important to highlight that, in all cases, water immersion produced and increased amount of open cells, but, the observation of the micrographs of the pristine foams clearly indicated that BNC acted as a cell opener. Such result were completely logical and it has already been observed by our group as well as other researchers 14,35,55,56 . Nowadays, it is known that BNC has a substantial role in the formation and rupture of cell windows during foaming and this aspect is clearly affected by the insertion route 14,39 .…”

“…One phenomena which took place was foam cure. As already noticed above and in previous study of our group, 14 RPUFs can have post‐foaming cure, causing either an increase in cell size due to further reaction of remnant isocyanate with humidity or, in the other hand, shrinkage due to foam cell collapse 3 . In addition to these effects, the permeation of water into the cells further complicates the analysis.…”

“…The incorporation of BNC in the polyurethane foam derived from a conventional polyol (RPUF) and castor oil (RPUF RIC ) was performed using the “polmix” route described in previous works of our group 14,39 . It is important to highlight that the BNC had to be lyophilized and subsequently dispersed in the polyol, giving rise to a colloidal dispersion.…”

“…Our group has addressed this important issue by using the NPs as a hard segment. Using this technique, it is possible to increase significantly specific thermomechanical properties while also increasing sustainability 14 . However, a key aspect towards the implementation of nanostructured RPUFs in industry relies on the impact of such NPs on the stability and mechanical properties of the RPUFs in service.…”