Investigation of the Flame Retardant Properties of High-Strength Microcellular Flame Retardant/Polyurethane Composite Elastomers

Abstract

Flame retardants (FRs) often reduce the mechanical properties of polymer materials, and FR/microcellular polyurethane elastomer (MPUE) composite materials have not been systemically studied. Hence, we conducted this study on FR/MPUE composites by using multiple liquid FRs and/or expandable graphite (EG). Compared with liquid flame retardants, the LOI of an expandable graphite/dimethyl methylphosphonate (EG/DMMP) (3:1) combination was significantly increased (~36.1%), and the vertical combustion grade reached V-0 without a dripping phenomenon. However, the corresponding tensile strength was decreased by 17.5%. With the incorporation of EG alone, although the corresponding LOI was not a match with that of DMMP/EG, there was no droplet phenomenon. In addition, even with 15 wt% of EG, there was no significant decline in the tensile strength. Cone calorimeter test results showed that PHRR, THR, PSPR, and TSR were significantly reduced, compared to the neat MPUE, when the EG content surpassed 10 wt%. The combustion process became more stable and thus the fire risk was highly reduced. It was found that flame retardancy and mechanical properties could be well balanced by adding EG alone. Our proposed strategy for synthesizing FR/MPUE composites with excellent flame retardancy and mechanical properties was easy, effective, low-cost and universal, which could have great practical significance in expanding the potential application fields of MPUEs.

Analysis of mechanical and flame‐retardant properties of flexible polyurethane foams

“…MC decomposed into melamine and cyanuric acid after heat treatment. The resulting melamine diluted oxygen and heating gases, which are elements of the combustion process, thereby improving flame retardancy 52 . The urethane foam with expandable graphite loses 10% of its total weight at 297°C.…”

“…As an additive flame retardant, it has various flame‐retardant mechanisms, such as halogenated flame retardants that stabilize radicals. Phosphorous flame retardants induce decomposition, combustion reactions that reduce the heat of combustion 52 . When expanded graphite is added to a specimen and encounters a flame, it expands to produce char, which retards combustion by blocking oxygen and heat 53 .…”

Microporous Polyurethane Elastomer’s Comprehensive Properties Affected by Flame Retardant EG/APP

“…As mentioned in the previous article, due to the "popcorn effect" of expanded graphite widely recognized in the field of flame retardant, adding EG alone, the expanded carbon layer was easy to fall off, and the flame-retardant effect was general [13] . Still, the synergistic effect was more obvious when combined with APP.…”

“…As a result of EG's relatively large particle size, it was difficult to adequately disperse it throughout the substrate. When it was added to a certain amount, the closed-cell ratio of MPUE would decrease, resulting in a decrease in its tensile strength 13 . However, APP, with only a few microns, could be evenly dispersed in the matrix, which did not affect the closed-cell ratio of the product.…”

“…We successfully created MPUE with outstanding flame retardancy and mechanical qualities by using EG as a common and affordable flame retardant. The synthesis method was simple and offered strong versatility [13] . However, it was shown that the vibration reduction and fatigue resistance capabilities of MPUE were dramatically diminished by the addition of EG.…”