This Small Business Innovation Research Phase I project investigates the properties of mesoporous silicate nanoparticles and the use of these particles as non-toxic, char-forming flame retardants (FRs) for thermoset and thermoplastic polymers. The project elucidates the relationship between the physiochemical properties of the silicate compositions (e.g., surface area, pore size, pore volume, surface polarity and chemical composition) and the effectiveness of the mesophases in forming carbonaceous and ceramic chars that function as a barrier toward the three components that support combustion (heat, oxygen, and volatile fuel). In order to accomplish this objective, the quality of the two forms of char is being improved by doping the silicate surfaces to enhance catalytic surface acidity (carbonaceous char) and by integrating the silicates with low temperature inorganic sintering aids (ceramic char). The research program also investigates the dispersion of conventional FR agents within the framework's pores and surfaces for improved flame retardant efficacy through synergistic and additive interactions with the silicate mesophase. The multi-component FR formulations of interest include agents that function in the condensed phase (e.g., intumescent polyphosphates, endothermic metal hydroxides) and the gaseous phase (e.g., molecular phosphorus agents and halogenated compounds).
The broader impact/commercial potential of this project is to further the global efforts to reduce the consumption of halogenated flame retardant agents in polymers, due to their negative impact on the environment when they are produced, discarded, and/or burned. Manufacturers are further challenged because the addition of all existing FR compounds diminishes the mechanical properties of the polymer into which they are compounded. The outcome of this project will directly address both of these concerns. Our completely non-toxic, silica-based, mesoporous nanoparticles provide both flame retardation and mechanical property enhancement for a broad range of polymers. The proposed research provides a number of broad, societal and commercial impacts. Further improving the efficacy of mesoporous silicate compositions as FR agents for polymers will advance knowledge by yielding a better understanding of the mechanisms underlying the combustion of plastics. Scaling our production facility to meet customer demand will result in job creation and increased use of environmentally friendly and domestically sourced raw materials. As these products become broadly adopted, both domestically and around the world, human exposure to endocrine-active chemicals will be reduced, in accord with the anticipated reduction of dependence on halogenated FR agents.
The general objective of this Phase I program was to investigate the effectiveness of micelle-templated mesoporous silicates (SilaporeTM) as flame retardant (FR) agents and as FR synergists when combined with conventional FR agents in composites of representative thermoset (epoxy) and thermoplastic (polypropylene and polyamides) polymers. To summarize, our SBIR Phase I studies have provided the following principle technical advancements: Silapore silicates are effective char forming agents for improving the effectiveness of intumescent epoxy and other thermoset coatings for the protection of steel structures against thermal failure during a fire. A Silapore loading of a few parts per hundred parts of polymer can reduce the peak heat release rate of a coating by 40%, even more if the loading is increase proportionately. Our additives are strong synergists for phosphorus-based intumescent formulations for representative highly flammable plastics such as polypropylene and for less flammable polymer compositions such as glass fiber-reinforced PA-6 (a.k.a., Nylon-6). In the case of polypropylene and other polyolefins, which require in addition to a phosphorus reagent the incorporation of a carbon source and a blowing agent as part of the formulation, as much a 28 parts of the conventional FR components can be replaced per part of Silapore with retention of a UL94 rating of V0. For glass-filled PA-6, which requires only a phosphorus catalyst for char formation, 1.0 phr of Silapore can replace 10 phr of the molecular phosphorus reagent with retention of a V0 rating. Silapore silicate additives also are effective synergist for FR reagents that operate via a radical quenching mechanism in the gas phase. Such pathways require a halogen, most preferably bromine, as the radical source and a heavy element such as antimony to facilitate the transport of the halogen into the flame. In the case of polypropylene as the representative polymer fuel, the incorporation of 0.8 to 1.7 phr Silapore silica in the polymer, allows the organo-bromine content to be reduce 5 phr (20% reduction) and the antimony oxide component to be reduced as much as 7.6 phr (90 % reduction). With regard to a value proposition, the above technical advancements clearly demonstrate the economic potential of our FR additive technology. However, there is broader societal value in our technology. Phosphorus is an important element for use as a plant fertilizer, yet the global availability of phosphate rock as the primary source of phosphorus is dwindling rapidly and its price is ever increasing. Reducing the widespread use of phosphorus in FR applications will make much more of the element available as a resource for food production. Likewise, antimony is in tight global supply and the market for this element is controlled by a few major suppliers, causing the price to continually increase. Although there are growing concerns over the health and environmental effect of organic bromides and antimony, these reagents provide FR safety benefits that have proven difficult to replace completely. The reduction in halogen and antimony levels made possible by our additive technology will lower both the health risk and environmental impact of these two elements. As a further feature of our value proposition, we note that the addition of conventional FR agents to a polymer matrix almost always compromises mechanical properties. By replacing substantially larger quantities of these mechanically antagonistic reagents with several-fold smaller quantities of Silapore silicates, users of our FR additive technology can realize an improvement in the mechanical performance of their composites at no additional cost.
