Lignin-derived core-shell flame retardants for fire-safety rigid polyurethane (RPU) insulations

• Published in: Construction & building materials Vol. 451; p. 138749
• Main Authors: Tian, Feiyu, Wu, Yutao, Xu, Haocheng, Chen, Hao, Wang, Bingbing, Zhu, Chunfeng, She, Yanan, Jin, Yuanyuan, Liu, Yingpeng, Wang, Shaocong, Xu, Xinwu
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15-11-2024
• Subjects: Biobased-flame retardant; Core-shell; Flame retardant mechanism; RPU; Biobased-flame retardant; Core-shell; RPU; Flame retardant mechanism
• ISSN: 0950-0618
• DOI: 10.1016/j.conbuildmat.2024.138749

How to ensure the fire safety of rigid polyurethane (RPU) insulation materials remains a challenge. Herein, alkali lignin (AL) and 4,4′-diphenylmethane diisocyanate (MDI) were used as raw materials to construct bio-based cross-linked polyurethane structures on the surface of ammonium polyphosphate (APP) to obtain APP@AL flame retardants. APP@AL was combined with expandable graphite (EG) in varying proportions and applied to rigid polyurethane (RPU) foam to modify its flame retardancy and physico-mechanical characteristics. Compared with untreated RPU, the high interfacial compatibility increased the compressive strength of the flame-retardant RPUs by 10.8 %, and the thermal insulation coefficient reached 22.8 mW·m−1·K−1. The addition of flame retardant for each flame-retardant RPU was 30 wt% of the polymethylene polyphenyl isocyanate. Owing to the P/C/O hybridized char layer in the combustion residues and the capture of gas by EG after expansion, APP@AL/EG not only reached the limiting oxygen index (LOI) of 27.1 % but reduced the mean heat release rate and smoke release rate by 70.3 % and 58.9 %, respectively. This work presented a novel approach to designing environmentally friendly flame retardants for RPU foams with enhanced fire safety and superior overall performance. Additionally, it offers a novel strategy for the high-value conversion of lignin.
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•A lignin-based polyurethane network was developed on the surface of APP.•A green flame-retardant RPU foam was prepared.•The mean HRR and SPR of RPU were reduced by 70.3 % and 58.9 %, respectively.