Partially bio-derived phosphazene-tannic acid microspheres as fire retardant additives for an epoxy tannic acid resin system.
Topic(s) : Material science
Co-authors :
Rusheni SENANAYAKE (AUSTRALIA), Houlei GAN , Jane ZHANG , Dan LIU , Russell J. VARLEY (AUSTRALIA)Abstract :
Epoxy resins are well known for their exceptional mechanical and thermal properties making them ideal as matrices for structural composites in weight sensitive applications. However, one major disadvantage, their inherently poor fire retardancy, is increasingly problematic as polymer composites become more intertwined into the daily lives of people. In particular, for many new applications in the construction and transportation industries non-combustibility is critical, such as EV battery casings, insulation materials and building facades. For these reasons, epoxy resins with low flammability have been widely studied and actively developed.
As nations seek to reduce their Greenhouse Gas emissions, there is an urgent need to utilise sustainably derived raw materials to drive greater self-reliance and localised supply chains in the manufacture of safer materials and structures. For this reason, fire retardants which are either fully or partially bio-derived have been explored as potential replacements for fossil fuel or non-sustainably sourced fire-retardant modifiers. The most common of these include tannins, lignin and other lignocellulosic materials, phytic acid and isosorbide. Adducts and various assemblies of these chemicals combined with other well-known fire retardants to promote synergistic behaviour is also a common strategy to enhance overall performance.
In this work, partially bio-derived colloidal microspheres are synthesised from tannic acid (TA) and hexachloro-cyclophosphazene (HCCP), then investigated for their effectiveness as a fire-retardant additive to a partially bioderived epoxy resin system. The epoxy resin system is based upon diglycidyl ether of bisphenol A (DGEBA) and tannic acid (TA), a bio-derived highly aromatic phenolic curative noted for its inherent fire retardancy. This study presents the impact of increasing the concentration of the phosphazene-TA microspheres (TAPZ) and varying the DGEBA-TA stoichiometry to determine the optimum formulation required to achieve the greatest improvement in fire retardancy. At a concentration of 15wt% of TAPZ, the DGEBA-TA resin, easily achieves a V-0 rating using the UL-94 vertical burn test, has an LOI value of 29% and displays a 62% reduction in peak heat release rate (PHHR) compared with the unmodified DGEBA-TA network using cone calorimetry. TAPZ addition, however, does reduce the glass transition temperature (Tg), flexural strength and modulus, and increases viscosity significantly. Exploring the impact of stoichiometry between DGEBA and TA, suggested that the additional surface hydroxyl groups from the TAPZ microspheres accelerated the DGEBA-TA reaction through enhancing interfacial reaction between residual epoxide groups of the cured epoxy network. Overall, these results present a promising approach to the development of a highly fire retardant, high performance, and highly bio-derived epoxy network.
As nations seek to reduce their Greenhouse Gas emissions, there is an urgent need to utilise sustainably derived raw materials to drive greater self-reliance and localised supply chains in the manufacture of safer materials and structures. For this reason, fire retardants which are either fully or partially bio-derived have been explored as potential replacements for fossil fuel or non-sustainably sourced fire-retardant modifiers. The most common of these include tannins, lignin and other lignocellulosic materials, phytic acid and isosorbide. Adducts and various assemblies of these chemicals combined with other well-known fire retardants to promote synergistic behaviour is also a common strategy to enhance overall performance.
In this work, partially bio-derived colloidal microspheres are synthesised from tannic acid (TA) and hexachloro-cyclophosphazene (HCCP), then investigated for their effectiveness as a fire-retardant additive to a partially bioderived epoxy resin system. The epoxy resin system is based upon diglycidyl ether of bisphenol A (DGEBA) and tannic acid (TA), a bio-derived highly aromatic phenolic curative noted for its inherent fire retardancy. This study presents the impact of increasing the concentration of the phosphazene-TA microspheres (TAPZ) and varying the DGEBA-TA stoichiometry to determine the optimum formulation required to achieve the greatest improvement in fire retardancy. At a concentration of 15wt% of TAPZ, the DGEBA-TA resin, easily achieves a V-0 rating using the UL-94 vertical burn test, has an LOI value of 29% and displays a 62% reduction in peak heat release rate (PHHR) compared with the unmodified DGEBA-TA network using cone calorimetry. TAPZ addition, however, does reduce the glass transition temperature (Tg), flexural strength and modulus, and increases viscosity significantly. Exploring the impact of stoichiometry between DGEBA and TA, suggested that the additional surface hydroxyl groups from the TAPZ microspheres accelerated the DGEBA-TA reaction through enhancing interfacial reaction between residual epoxide groups of the cured epoxy network. Overall, these results present a promising approach to the development of a highly fire retardant, high performance, and highly bio-derived epoxy network.