Synthesis of waterborne polyurethane aerogels-like materials via freeze-drying: an innovative approach

Abstract

Waterborne polyurethane (WBPUR) aerogels using acetone method and freeze-drying procedure have been successfully synthesized. The morphology, chemical structure, and thermal and mechanical properties of obtained aerogels were analysed by means of scanning electron microscopy, Fourier-transform infrared spectroscopy, contact angle, thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis. In addition, the influence of the solids content in the hydrogel (2–15 wt.%), obtained by varying the amount of water added in the suspension, on the density and thermal conductivity was evaluated. Obtained results demonstrated that the properties of aerogels strongly depend on the solids content assayed in the parent solution. As the solids content in the WBPUR aerogels increases, the density and thermal conductivity for materials with 2.5 and 10% solids content follow an upward trend, while their elasticity decreases. Materials with solids content below 2.5% and above 10% have not demonstrated adequate processability due to their high deformity and hardness, respectively. The drying methodology (freeze-drying) can be profitably used to prepare aerogels-like materials in a cost-effective way. Graphical abstract Illustration of the alternative preparation process of WBPUR aerogels and its potential industrial application.

Exploring the Impact of the Synthesis Variables Involved in the Polyurethane Aerogels-like Materials Design

“…The raw synthesis process for waterborne polyurethane (WBPUR) aerogels is described in the Materials and Methods section [ 33 ]. The impacts of key synthesis variables on the physicochemical properties of the materials were extensively assessed.…”

“…The influence of the nature of the organic solvent on the WBPUR aerogels’ properties was evaluated by adding different solvents (or their mixtures) to the reaction mixture prior to gel formation and the freeze-drying process ( Table 1 , set 1). Our previous experience using the acetone method [ 33 ] showed that it was difficult to work with this solvent due to its low boiling point in relation to the operating conditions used during the polyurethane synthesis. Thus, acetone was directly substituted by some other solvents with similar solubility parameters.…”

“…Furthermore, the samples lose their dimensional stability, particularly in terms of thickness, as they reduce to thin films resembling a coating. Previous aerogels, which were prepared using acetone as the gelation solvent and an EDA/HMDI ratio of 0.33 [ 33 ], exhibited an average shrinkage ratio of 62 ± 6% ( n = 3) 5 months after their preparation (see Figure S4 ). To overcome these limitations, it may be possible to reduce the amine content instead.…”

“…The synthesis process of WBPUR aerogels involved a slightly modified polymerization method followed by a freeze-drying process, as described in previous studies [ 33 ]. The notable variation in the procedure was the utilization of various organic solvents, including EtOAc, among others.…”

Fast Gold Recovery from Aqueous Solutions and Assessment of Antimicrobial Activities of Novel Gold Composite

“…The thermal degradation of pGME-en/Au is presented in Figure 10b. It can be seen that pGME-en/Au exhibited a weight loss of about 5% below 100 • C, due to the loss of water physically adsorbed or occluded in the pores [65]. Then, the degradation of pGMEen/Au took place in two stages.…”