Abstract
A new strategy for the preparation of an integrated three-source intumescent flame retardant (IFR) has been developed to improve the flame-retardant and smoke suppression performance of epoxy resin (EP) with a synergistic flame retardant effect. Herein, the synthesis of a macromolecular spirocyclic phosphorus/nitrogen-containing IFR poly sulfonamide spirocyclic pentaerythritol bisphosphonate (SAPC) is reported via a two-step method that uses pentaerythritol, phosphorus oxychloride and sulfonamide (SAA) as raw materials. Subsequently, the SAPC was incorporated into EP to prepare the composite to investigate its thermal stability, flame retardancy, and smoke suppression performance. Herein, a differential scanning calorimetry (DSC) analysis showed that the addition of SAPC increased the glass transition temperature (Tg) of the composite. Cone test results indicated that the incorporation of 8 wt % SAPC significantly improved the flame-retardant performance for the composite, with a 43.45% decrease in peak of heat release rate, a 28.55% reduction in total heat release, and a 30.04% decrease in total smoke release. Additionally, the composite received the V-0 rating in a UL-94 vertical burning test, accompanied by the “blowout” phenomenon. After the addition of SAPC, the amount of flammable gas products from the EP composite decomposition was obviously suppressed, and the amount of non-flammable as was increased. All of this suggests a good dilution role of SAPC. There are enough reasons to believe that the enhanced flame-retardant and toxicity suppression performance for the EP composite can be attributed to the good coordination of carbonization agent, acid source, and blowing agent in the SAPC structure.
Highlights
The industrial production of epoxy resin (EP) has been in practice for more than 60 years
For the SAPC spectrum, there was no significant P–Cl absorption peak at 551 cm−1, but a new secondary amino group appeared at 3476 cm−1
A flame retardant mechanism for the EP/SAPC composites was speculated based on the analyses of char residues and pyrolysis products (Scheme 4)
Summary
The industrial production of epoxy resin (EP) has been in practice for more than 60 years. SPDPC (3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro-[5,5] undecane-3,9-dioxide) is prepared through the nucleophilic substitution of pentaerythritol and phosphorus oxychloride, and it is a flame retardant intermediate that is widely used in spirocyclic phosphates. It is a double-ring rigid structure with high symmetry, which gives it a high thermal stability [19,20]. The prepared EP composite exhibited a good flame retardant effect, but the addition amount was relatively high [21]. EPmechanism composites.ofThe thermal stability, flame retardancy, and flame retardant mechanism of EP composites were analyzed
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