Open Access
ARTICLE
Phosphorylated Salicylic Acid as Flame Retardant in Epoxy Resins and Composites
Lara Greiner1,*, Philipp Kukla2, Sebastian Eibl1, Manfred Döring3
1
Bundeswehr Research Institute for Materials, Fuels and Lubricants, Erding, 85435, Germany
2
Fraunhofer Institute for Structural Durability and System Reliability LBF, Darmstadt, 64289, Germany
3
Schill+Seilacher GmbH, Böblingen, 71032, Germany
* Corresponding Author: Lara Greiner. Email:
(This article belongs to the Special Issue: Bio-based Halogen-free Flame Retardant Polymeric Materials)
Journal of Renewable Materials 2022, 10(7), 1931-1950. https://doi.org/10.32604/jrm.2022.019548
Received 29 September 2021; Accepted 01 December 2021; Issue published 07 March 2022
Abstract
A novel, versatile flame retardant substructure based on phosphorylated salicylic acid (SCP) is described and used
in the synthesis of new flame retardants for HexFlow
® RTM6, a high-performance epoxy resin used in resin
transfer molding processes as composite matrix. The starting material salicylic acid can be obtained from natural
sources. SCP as reactive phosphorus chloride is converted with a novolak, a novolak containing 9, 10-dihydro-9-
oxa-10-phospha-phenanthrene-10-oxide (DOPO) substituents or DOPO-hydroquinone to flame retardants with
sufficient thermal stability and high char yield. Additionally, these flame retardants are soluble in the resin as well
as react into the epoxy network. The determined thermal stability and glass transition temperatures of flame
retarded neat resin samples as well as the interlaminar shear strength of corresponding carbon fiber reinforced
composite materials showed the applicability of these flame retardants. Neat resin samples and composites were
tested for their flammability by UL94 and/or flame-retardant performance by cone calorimetry. All tested flame
retardants decrease the peak of heat release rate by up to 54% for neat resin samples. A combination of DOPO
and SCP in one flame retardant shows synergistic effects in char formation and the mode of action adapts to neat
resin or fiber-reinforced samples, so there is efficient flame retardancy in both cases. Therefore, a tailoring of SCP
based flame retardants is possible. Additionally, these flame retardants efficiently reduce fiber degradation during
combustion of carbon fiber-reinforced epoxy resins as observed by scanning electron microscopy and energy dispersive X-ray spectroscopy.
Keywords
Cite This Article
APA Style
Greiner, L., Kukla, P., Eibl, S., Döring, M. (2022). Phosphorylated salicylic acid as flame retardant in epoxy resins and composites. Journal of Renewable Materials, 10(7), 1931-1950. https://doi.org/10.32604/jrm.2022.019548
Vancouver Style
Greiner L, Kukla P, Eibl S, Döring M. Phosphorylated salicylic acid as flame retardant in epoxy resins and composites. J Renew Mater. 2022;10(7):1931-1950 https://doi.org/10.32604/jrm.2022.019548
IEEE Style
L. Greiner, P. Kukla, S. Eibl, and M. Döring "Phosphorylated Salicylic Acid as Flame Retardant in Epoxy Resins and Composites," J. Renew. Mater., vol. 10, no. 7, pp. 1931-1950. 2022. https://doi.org/10.32604/jrm.2022.019548