Expendable Graphite as an Efficient Flame-Retardant for Novel Partial Bio-Based Rigid Polyurethane Foams

Abstract

The rigid polyurethane foam (PU) is a versatile material, used especially for construction and household applications. The current situation demands a facile, cost-efficient, and greener approach for developing the polyurethanes from bio-derived materials. In this study, we present a novel bio-polyol synthesized using carvone, an extract from caraway, spearmint, or dill seeds via facile thiol-ene reaction. Our one-step reaction uses a UV irradiation to allow the room temperature conversion of the carvone to a high purity bio-polyol, as confirmed from the standard analytical characterizations. The hydroxyl number of 365 mg KOH/g close to its theoretical limit confirms the high conversion yield of the polyol for rigid PU synthesis. To overcome the flammability issues in PU, expandable graphite (EG) powder was used as an additive flame-retardant during the synthesis step. The resulting foams with EG maintained the uniform closed cell structure (>95%) with a high compression strength of 175 kPa. The addition of EG in PU results in the formation of a protective char layer during the flammability test and reduces the weight loss from 40.70% to 3.55% and burning time from 87 to 11 s. Our results confirm that the carvone-based polyol can be a novel alternative to the petroleum polyols for an industrial-scale application.

Waste to Resource: Synthesis of Polyurethanes from Waste Cooking Oil

“…The addition of EG also led to an overall decrease in compressive strength, which could also be attributed to the increase in cell size along with partial disruption of the cellular structure. On top of that, EG interacts poorly with the RPUF along with the presence of a flake-like structure that can more easily lead to microphase separation which can weaken the RPUF’s mechanical strength. , …”

“…This loose layer has good heat-insulating properties that protect the rest of the foam from burning. It can also filter or absorb any flammable fragments generated, thereby limiting the transfer of heat and mass from the heat to the polymer which prevents further decomposition of the foams and improves their FR characteristics. ,− …”

Recent Advancements in Flame-Retardant Polyurethane Foams: A Review

“…Therefore, the market size for PU foams was primarily categorized into furniture, construction, electronics, automotive, packaging, and footwear among others. However, accompanied by this market growth, a large consumption of petrochemical-based raw materials has raised the concerns for the environment. − To address such issues, there has been a push to introduce biobased and renewable sources into the manufacturing of PU. ,− The industries have also made efforts to increase the overall biobased content in the PU, which resulted in production of ∼1634 tons of biobased PU in 2013, which was expected to reach ∼2546 tons in 2020 …”

Effects of Various Types of Expandable Graphite and Blackcurrant Pomace on the Properties of Viscoelastic Polyurethane Foams

“…As a result, nanoparticles are used with other commercial flame retardants directly added to the polyol [ 25 , 27 ] or used for the synthesis of new systems [ 28 , 29 , 30 ]. To obtain flame retardant polyurethane foams, expanding graphite is also used and well known as an independent, effective flame retardant [ 31 , 32 , 33 ]. During the combustion of foams with graphite, the scale increases due to the expansion of graphite, which creates a thermal barrier limiting oxygen diffusion and heat and mass transfer.…”

“…Moreover, the addition of approximately 30 parts per 100 of polyols by weight ensures that the oxygen index of rigid polyurethane foams is 25% [ 38 , 39 ]. However, the addition of graphite also increases the viscosity of the reaction mixture which may result in the deterioration of mechanical properties [ 32 , 33 , 37 ]. Therefore, in recent years, researchers have focused on finding synergistic effect of expandable graphite (EG) with other additive flame retardants [ 40 , 41 , 42 ] or nanofillers [ 43 , 44 , 45 ].…”