Mechanical properties improvement and fire hazard reduction of expandable graphite microencapsulated in rigid polyurethane foams

Abstract

Nowadays, reducing the fire hazard and improving the mechanical strength of rigid polyurethane foams (RPUFs) at the same time are important research direction in the fields of safety materials. Expandable graphite (EG) is an effective flame retardant for RPUF, but would destroy the compatibility of the matrix. In this article, EG is capsuled by melamine cyanurate (MCA) and then microencapsulated expandable graphite (MCEG) is obtained, which is added into RPUF. The mechanical properties of composites were evaluated by compressive strength test, torsion strength test and shear stress test. The fire characteristics including smoke and heat production of RPUF composites were studied using cone calorimeter test. And the thermal decomposition and flammable properties were further evaluated using thermogravimetric analysis and limiting oxygen index. The results show that the mechanical properties of RPUF containing MCEG are similar with RPUF and better than RPUF containing EG. Furthermore, MCA cover would impede expanding of EG, which weakens the protective and insulation effects of expanding layer. Therefore, the composites containing MCEG decompose faster and produce more smoke than the composites containing EG. However, MCA and EG have the synergistic enhancing effect on the flame retardant property of composite. POLYM. COMPOS., 40:E1006–E1014, 2019. © 2018 Society of Plastics Engineers

Structure and Flame-Retardant Actions of Rigid Polyurethane Foams with Expandable Graphite

“…It can be viewed that LOI of RPUF is increased via increasing the EG until a threshold value is obtained at 15 phr EG, where the LOI is 22.2% when compared to 19.2% of pure RPUF. EG could expand to be carbon layer and adsorb onto the surface of the materials [19,25], which stops the migration of air or heat. All of the samples after adding EG display the promotions of LOI value to be 20.8%, 21.9%, 22.2%, and 20.8%, respectively, implying the positive effect of EG on the flame-retardant performance of RPUF.…”

“…For the moment, the additive flame retardants, such as magnesium hydroxide [13], aluminum hydroxide [14], red phosphorus [15], nitrogen flame retardant, and intumescent flame retardants [16,17] were widely used in RPUF. Expanded graphite (EG) is a loose and vermiculate material that was obtained from the intercalation, puffing on natural graphite, and it could promote the flame retardancy of polymers [18,19,20,21]. Khalili demonstrated that EG incorporated with natural fiber could improve the fire resistivity of epoxy, especially at 5 wt % loading of EG, and that the material obtained a sufficient self-extinguishing property [22].…”

Enhanced Fire Safety of Rigid Polyurethane Foam via Synergistic Effect of Phosphorus/Nitrogen Compounds and Expandable Graphite

“…This compact and firm char layer has a distinguished obstructing effect on smoke and heat. As a prominent flame retardant, EG was universally applied in various polymeric materials, especially in RPUF [ 30 ]. Wang et al introduced 6.67 wt.% EG and 13.33 wt.% MP into polystyrene and found that the peak of heat release (PHRR) was reduced by 40.4% [ 31 ].…”

Steam Exploded Peanut Shell Fiber as the Filler in the Rigid Polyurethane Foams

“…When heated to a certain temperature, EG expands rapidly, becoming a wormlike structure with huge insulation effect [15][16][17]. Cheng et al [18] used EG microencapsulated by Melamine cyanurate (MCA) to improve the safety (mechanical properties improvement and fire hazard reduction) of RPUF. The results showed that the composites containing microencapsulated expandable graphite (MCEG) decompose faster and produce more smoke than the composites containing EG.…”