Abstract
Ambient temperature self-blowing mimosa tannin-based non-isocyanate polyurethane (NIPU) rigid foam was produced, based on a formulation of tannin-based non-isocyanate polyurethane (NIPU) resin. A citric acid and glutaraldehyde mixture served as a blowing agent used to provide foaming energy and cross-link the tannin-derived products to synthesize the NIPU foams. Series of tannin-based NIPU foams containing a different amount of citric acid and glutaraldehyde were prepared. The reaction mechanism of tannin-based NIPU foams were investigated by Fourier Trasform InfraRed (FT-IR), Matrix Assisted Laser Desorption Ionization (MALDI-TOF) mass spectrometry, and 13C Nuclear Magnetic Resonance (13C NMR). The results indicated that urethane linkages were formed. The Tannin-based NIPU foams morphology including physical and mechanical properties were characterized by mechanical compression, by scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). All the foams prepared showed a similar open-cell morphology. Nevertheless, the number of cell-wall pores decreased with increasing additions of glutaraldehyde, while bigger foam cells were obtained with increasing additions of citric acid. The compressive mechanical properties improved with the higher level of crosslinking at the higher amount of glutaraldehyde. Moreover, the TGA results showed that the tannin-based NIPU foams prepared had similar thermal stability, although one of them (T-Fs-7) presented the highest char production and residual matter, approaching 18.7% at 790 °C.
Highlights
Tannin, because of their distinct chemical properties, are classified into hydrolysable tannins and condensed or polyflavonoid tannins [1]
In this temperature range, 44.1% of weight loss for T-Fs-2, 41.2% of weight loss for T-Fs-7, 43.7% of weight loss for T-Fs-11, and 42.9% of weight loss for T-Fs-13 take place. This step may be caused by breaking C–C bonds and the decomposition of pyrolysis residual products from the first two stages [55,67]. These results show that the tannin-based non-isocyanate polyurethane (NIPU) foams present similar pyrolysis temperature weight losses
The work presented in this case reports a novel mimosa tannin-based NIPU rigid foam using
Summary
Because of their distinct chemical properties, are classified into hydrolysable tannins and condensed or polyflavonoid tannins [1] They are natural phenolic compounds, fairly ubiquitous in the vegetable world and commonly utilized as a starting materials in many fields, such as medicine [2,3], wastewater treatment [4,5,6], activated carbon [7,8], wood adhesives [9,10,11,12], fire resistance [13,14], coatings [15,16,17], etc. This concept was inspired from the preparation of meringue from egg whites, tannin, or tannin-furan resin that were mixed with other ingredients, and a large amount of air was introduced into the mixture by vigorous mechanical stirring, forming a liquid foam with a fast expansion speed [32]
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