Abstract
In order to develop an effective flame retardant for poly(vinyl chloride) (PVC), a core@double-shell structured magnesium hydroxide@9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide@melamine formaldehyde resin (MH@DOPO@ MF) encapsulated flame retardant was prepared. Its flame retardancy and smoke suppression effects in flexible PVC were investigated. Results show that the PVC/10 wt% MH@DOPO@MF composite has the best flame retardancy and smoke suppression performance in comparison with pure flexible PVC and the PVC/20 wt% MH composite. The limiting oxygen index (LOI) of the PVC/10 wt% MH@DOPO@MF composite was ∼30.8%, achieving a V-1 rating in the UL-94 test. MH@DOPO@MF in PVC remarkably increases the yields of the residual char and drastically decreased the heat release rate (HRR), total heat release (THR), smoke production rate (SPR) and total smoke production (TSP). The mechanical property testing showed that MH@DOPO@MF had slight damage on the tensile strength and elongation at break of PVC. This is ascribed to the synergistic flame-retardant effects of MH coordination with DOPO and MF. The present work demonstrates that the core@double-shell structured microcapsule (MH@DOPO@MF) prepared in this efficient manner has good flame retardancy and smoke suppression, and may provide a candidate flame retardant for applying in flexible PVC.
Highlights
The mechanical properties, ame retardancy and smoke suppression mechanism of poly(vinyl chloride) (PVC)/magnesium hydroxide (MH)@DOPO@melamine formaldehyde (MF) composites were characterized by multiple test instruments such as electronic universal testing instrument, UL-94 horizontal burning level (UL-94), limiting oxygen index (LOI), cone calorimeter test (CCT), scanning electron microscope (SEM), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and thermogravimetry analysis coupled with Fourier transform infrared spectroscopy (TGA-FTIR) tests
Test samples of pure exible PVC and its PVC/MH were fabricated by the same procedure
The as-prepared core@double-shell structured MH@DOPO@MF was incorporated into exible PVC materials by a melt-blending method and pure exible PVC, PVC/MH and PVC/MH@DOPO@MF composites were prepared for comparison
Summary
Flexible poly(vinyl chloride) (PVC) is widely used in the elds of electrical insulation, sealing, toys and medical devices, and is an ideal substitute for rubber and elastomer materials with low cost and easy fabrication.[1,2] most exible PVC composites are ammable, generating toxic gases and heavy black smoke during combustion, which dramatically limit their practical applications, especially in the electrical elds.[3,4] the improvement of ame retardancy and smoke suppression will make exible PVC materials more suitable. Among the halogen-free polyphosphate ame retardants, 9,10-dihydro-9-oxygen-10-phosphoheterophene-10-oxide (DOPO) has been found to have excellent gas-phase high efficiency ame retardance.[28] Compared with other linear low molecular weight aliphatic phosphates and phosphorous compounds, DOPO presents higher thermal stability, chemical stability, excellent ame retardancy and low toxicity owing to the existence of diphenyl cyclophosphate groups in its molecular structure It has high char forming ability and ame-retardant effect in condensed-phase.[29] Besides, owing to the active P–H bonds in the molecule of DOPO, it can react better with unsaturated groups, i.e., epoxy group, Schiff base, carbon–nitrogen double bond (C]N) and triple (C^N), carbon–carbon double bond (C]C), etc., so that various types of DOPO-based synergistic ame retardants and smoke suppressants can be synthesized with others.[30,31] In addition, melamine formaldehyde (MF) resin is an environment-friendly Nbased ame retardant and its thermal stability is above 380 C.32. The mechanical properties, ame retardancy and smoke suppression mechanism of PVC/MH@DOPO@MF composites were characterized by multiple test instruments such as electronic universal testing instrument, UL-94 horizontal burning level (UL-94), limiting oxygen index (LOI), cone calorimeter test (CCT), scanning electron microscope (SEM), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and thermogravimetry analysis coupled with Fourier transform infrared spectroscopy (TGA-FTIR) tests
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