Potential use of black liquor as lignin source for synthesis of polyurethane foam
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ORIGINAL PAPER
Potential use of black liquor as lignin source for synthesis of polyurethane foam Raziye Mohammadpour1 · Gity Mir Mohamad Sadeghi1 Received: 24 May 2020 / Accepted: 27 October 2020 © The Polymer Society, Taipei 2020
Abstract This study was conducted to recover lignin from black liquor for synthesis of lignin-based polyurethane foam (LPUF). To do so, lignin was precipitated from black liquor through acid precipitation at different pH values. The precipitated lignin samples were characterized by mid-infrared spectroscopy (MIR), thermogravimetric analysis (TGA), proton nuclear magnetic resonance (1H-NMR), and ultraviolet–visible (UV–Vis) spectroscopy (UV–Vis) techniques. After that, lignin sample with higher purification and lower molecular weight was selected for preparation of lignin polyol. Then, microwave-assisted liquefaction was employed to liquefy lignin sample. The obtained lignin polyol was used successfully to synthesize LPUF samples in different 4, 4′-diphenylmethane diisocyanate (MDI) indexes. The effect of MDI index on properties of LPUF samples was investigated through MIR, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and compressive strength tests. The results demonstrated that MDI content could change morphology of the prepared LPUF samples and caused reduction of cell size and more regularity of cellular structure. Also, thermal and mechanical properties of LPUF samples were found to be influenced by MDI index. Keywords Lignin recovery · pH of precipitation process · Lignin polyol · Lignin-based polyurethane foam
Introduction Black liquor is generated in pulp and paper industry as a waste stream. Lignin is the main component of this alkaline liquid obtained after pulping process [1]. Although, this waste stream has a high potential for lignin recovery [2] but generally, it burns in recovery boilers to generate steam energy, and recover substances used in pulping process [1]. Therefore, lignin recovery from black liquor can be an attractive occasion to extend development of green and value-added products from pulp and paper industry. Acidic precipitation of lignin from black liquor waste stream was started from the 1960s in a very small industrial scale. Many researchers have also studied this process to produce more lignin with higher Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10965-020-02334-8) contains supplementary material, which is available to authorized users. * Gity Mir Mohamad Sadeghi [email protected] 1
Department of Polymer Engineering and Color Technology, Amirkabir University of Technology, Tehran, Iran
purification. It has been reported that more solid yield with lower molecular weight is precipitated from black liquor by increasing ion strength or decreasing pH and temperature of process [1]. Wang et al., [3] reported sequential extraction of Kraft-AQ pulping lignin by organic solvent. The obtained lignin samples were characterized by chemical degradation, gel permeation chro
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