β-cyclodextrin modified aliphatic waterborne polyurethane-based intumescent flame-retardant coatings: Experiments and pyrolysis kinetics

Abstract

Herein, the synthesis of β-cyclodextrin (β-CD) modified aliphatic waterborne polyurethane (AWP)-based coatings via the sol-gel method. The investigation aims to determine the appropriate dosage of surface-modified ammonium polyphosphate (APP) by using β-CD and the Di(dioctyl pyrophosphate) ethylene titanate (KR-238S). The flame retardancy of β-CD modified APP on AWP-based coatings is evaluated by quantitative analysis. Results show that adding 2 wt% β-CD enhances the flame retardancy of AWP-based coatings, as evidenced by an increase in the flame retardancy index (FRI) and a decrease in the peak of heat release rate (p-HRR). The FRI increases from 1.00 to 3.26, while p-HRR decreases from 133.30 kW·m−2 to 75.21 kW·m−2. Then, the modified APP improves the resilience and compatibility of AWP-based coatings using microscopic analysis. Moreover, the pyrolysis kinetics is modeled using the 3D Jander model, revealing an increase in Eα from 165.74 kJ·mol−1∼197.44 kJ·mol−1 in the stage of 352 °C∼394 °C. The superior flame retardancy benefits from the dispersed β-CD and KR-238S co-modified APP: hydrogen bonding, inclusion complex, and electrostatic interaction. Generally, it prepares a non-toxic and cleaner coating and provides a new strategy to solve the problem of coating performance degradation caused by excessive flame retardants.