Abstract
In this work, the effects of a chitosan-based derivative (CSA), DOPO (9, 10-dihydro-9-oxa-10- phosphaphenanthreene-10-oxide) and CSA-DOPO additives on the flammable properties of EP (epoxy resin) composites were systematically studied, where CSA was synthesized by a facile condensation between chitosan (CS) and 9-anthralaldehyde. The mass ratio of CS and 9-anthralaldehyde in CSA was determined by elemental analysis and theoretical calculation. Under the 8% addition in EP, EP/2.66%/5.34%DOPO sample was the only one passing the UL-94 V-0 rating and exhibiting the highest LOI value of 36.4%. The cone calorimeter test (CC) showed that the total smoke emission value and the peak heat release rate of the EP/2.66%/5.34%DOPO decreased by 36.0% and 61.9%, and the residual char amount increased by 151%, respectively, when compared with EP. Moreover, the incorporation of CSA/DOPO effectively improved the flexural strength by 52.3%. According to the results obtained from Py-GC/MS analyses for EP and EP/2.66%CSA/5.34%DOPO samples, together with Raman spectra, XPS (X-ray photoelectron spectra) for their char residues, and the real time FTIR (Fourier-transform infrared) spectra at different pyrolysis temperatures and cone calorimeters, it was proposed that CSA/DOPO played roles in both gaseous and condensed phases, and the synergistic effect of CSA and DOPO significantly improved the flame retardancy and mechanical strength of EP. Graphical abstract
Highlights
Epoxy resin has been frequently used in many fields owing to its superior chemical resistance, excellent adhesion and good mechanical properties (Zhu et al 2020; Tang et al 2019; Yu et al 2016)
The effects of a chitosan-based derivative (CSA), DOPO and CSA-DOPO additives on the flammable properties of EP composites were systematically studied, where CSA was synthesized by a facile condensation between chitosan (CS) and 9-anthralaldehyde and
A flame retardant synergist (CSA) was successfully synthesized, and the EP/CSA/DOPO thermosetting material obtained by compounding DOPO and CSA with EP had good flame retardant properties
Summary
Epoxy resin has been frequently used in many fields owing to its superior chemical resistance, excellent adhesion and good mechanical properties (Zhu et al 2020; Tang et al 2019; Yu et al 2016). Wang Xin et al (Wang et al 2010, 2011a, b, c, d) used phosphorus oxychloride, pentaerythritol and DOPO-based dihydric phenolic compounds as raw materials to synthesize a series of DOPO-based oligomers. When these oligomers were added in EP using 4, 4'-diaminodiphenylmethane as a curing agent, the amount of combustible gas, the total heat release and the maximum heat release rate in the combustion process were reduced significantly, and the LOI value was greatly increased. Some DOPO-based derivatives modified EP composites exhibited good flame retardancy, the complicated preparation process as well as the drawbacks in mechanical properties limited their industrial application. The better flame retardancy of EP composites promoted by the combined action of several substances was worth to further study for industrial applications
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