Preparation and Evaluation of Glucose Based Non-Isocyanate Polyurethane Self-Blowing Rigid Foams

Abstract

A partially biobased self-blowing and self-hardening polyurethane foam from glucose-based non-isocyanate polyurethanes (g-NIPU) was prepared by reaction of glucose with dimethyl carbonate and hexamethylene diamine. However, these foam types generally require a high foaming temperature. In this paper, a self-blowing foam based on g-NIPU was prepared at room temperature by using maleic acid as an initiator and glutaraldehyde as a crosslinker. Water absorption, compression resistance, and fire resistance were tested. Scanning electron microscopy (SEM) was used to observe the foam cells structure. Middle infrared (ATR FT-MIR) and Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF) mass spectrometry were used to help to analyze the reactions during the foaming process. The results obtained showed that self- blowing rigid foams have good compression, this being directly proportional to the foam density. Increasing the amount of glutaraldehyde or reducing maleic acid thickens the cell walls and increases the density of the foams. MALDI-TOF analysis showed that g-NIPU reacts with both maleic acid and glutaraldehyde. The foams presented poor fire resistance indicating that, as for isocyanate based polyurethane foams, addition of a fire retardant would be necessary.

Preparation and Characterization of Condensed Tannin Non-Isocyanate Polyurethane (NIPU) Rigid Foams by Ambient Temperature Blowing

“…On account of the high reactivity between citric acid and -NH 2 groups (HDMA or tannins-based NIPU), the possible reaction products can be detected. This series of reactions is also the source of energy for foam volume expansion [53]. These peaks are such as 313.1 Da in Figure 5a Figure 5d.…”

“…The self-blowing energy for foaming (cf. Scheme 1) comes from the reaction of citric acid and the amino groups of both the hexamine and possibly with some still free amino groups of the tannin NIPU resin, resulting in the volume expansion of the liquid foams [53]. Glutaraldehyde functions as cross-linker, ensuring that the liquid foams system does not collapse and maintains itself self-supporting.…”

“…Glutaraldehyde functions as cross-linker, ensuring that the liquid foams system does not collapse and maintains itself self-supporting. Again, glutaraldehyde cross-links by reacting with the amino groups and with the reactive aromatic ring sites of the tannins [53], which contributes to form the three-dimensional structure of the tannin-based NIPU foam. Furthermore, hexamine participates to cross-linking by forming bridges between tannin molecules during the periods of foaming and heating.…”

“…Comparing T-Fs-2 with T-Fs-11 shows that the foam apparent density decreases slightly with the increasing amount of citric acid, from 0.15 g•cm −3 to 0.12 g•cm −3 . This is attributed to the foaming energy originating from the reaction of citric acid with the -NH 2 groups [53]. Thus, a larger expansion volume can be obtained by increasing the amount of citric acid to obtain a smaller apparent density.…”

“…This can be seen when a larger proportion of citric acid was used, as shown in Figure 2c (8 g of citric acid) and Figure 2d (9 g of citric acid). The reason for this might be that more citric acid can react with amino groups to provide more energy for foaming, which leads to a better volume expansion of the liquid foam [53]. Simultaneously, this resulted in a smaller foam density, as shown in Table 2.…”