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. 2019 Jun 3;4(6):9615-9628.
doi: 10.1021/acsomega.9b00346. eCollection 2019 Jun 30.

Thermal Stability, Pyrolysis Behavior, and Fire-Retardant Performance of Melamine Cyanurate@Poly(cyclotriphosphazene- co-4,4'-sulfonyl diphenol) Hybrid Nanosheet-Containing Polyamide 6 Composites

Kuruma Malkappa  1 , Suprakas Sinha Ray  1   2
Affiliations

Thermal Stability, Pyrolysis Behavior, and Fire-Retardant Performance of Melamine Cyanurate@Poly(cyclotriphosphazene- co-4,4'-sulfonyl diphenol) Hybrid Nanosheet-Containing Polyamide 6 Composites

Kuruma Malkappa et al. ACS Omega. .

Abstract

A novel halogen-free highly cross-linked supramolecular poly(cyclotriphosphazene-co-4,4'-sulfonyl diphenol) (PZS)-functionalized melamine cyanurate (MCA) (MCA@PZS) hybrid nanosheet fire-retardant (FR) was synthesized and thoroughly characterized using scanning electron microscopy, Fourier-transform infrared (FTIR), X-ray diffraction, and X-ray photoelectron spectroscopy analyses. The polyamide 6 (PA6) composites comprising MCA, PZS, and the MCA@PZS hybrids were prepared via the melt-blending technique. The thermogravimetric analysis combined with FTIR and mass spectroscopy revealed that during thermal degradation, the PA6/MCA@PZS composites released less toxic gases and small organic volatile compounds than the neat PA6 and composites containing MCA or PZS solely. Moreover, compared to neat PA6, the PA6 composite with a 5 wt % MCA@PZS hybrid exhibited enhanced fire retardation properties, with a 29.4 and 32.1% decrease in the peak heat and total heat release rates, respectively. Besides, the PA6 composites with MCA@PZS-5% content achieved a V-0 rating in the UL-94 test. Finally, based on the obtained results from gaseous and condensed phases, the possible mechanism responsible for improved FR properties of the PA6/MCA@PZS composites was proposed.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Schematic Model for the Formation of Highly Cross-Linked Supramolecular PZS-Functionalized MCA (MCA@PZS) Hybrid Nanosheets
Figure 1
Figure 1
Respective field emission-SEM (FE-SEM) and TEM images of (a,b) the synthesized PZS, (c,d) MCA, and (e,f) MCA@PZS hybrid.
Figure 2
Figure 2
(a) FTIR spectra, (b) powder XRD patterns, (c) TGA data, and (d) XPS plots of MCA, PZS, and the MCA@PZS hybrid; high-resolution C 1s spectra of (e) MCA and (f) the MCA@PZS hybrid.
Figure 3
Figure 3
TGA and derivative thermogravimetric (DTG) curves of PA6, PA6/MCA-3%, PA6/PZS-3%, PA6/MCA@PZS-3%, and PA6/MCA@PZS-5% in (a,b) N2 atmosphere and (c,d) air atmosphere.
Figure 4
Figure 4
FTIR spectra of neat PA6 and its composites with different FR contents at the maximum decomposition stage.
Figure 5
Figure 5
Absorbance spectra of the pyrolysis products from PA6, PA6/MCA-3%, PA6/PZS-3%, and PA6/MCA@PZS-5%. (a) Gram–Schmidt plots and plots of the released volatile components versus time: (b) CO, (c) CO2, and (d) NH3.
Figure 6
Figure 6
Mass spectra of (a) PA6, (b) PA6/MCA-3%, and (c) the PA6/MCA@PZS-5% composite at the maximum degradation stage.
Figure 7
Figure 7
Proposed possible thermal degradation mechanism of the PA6/MCA@PZS composite during combustion. At the high-temperature range, the MCA and PZS interact with PA6 degraded components in different paths with the release of nonflammable gases and various nitrogen-based small volatile components. The PZS part mainly involves during dehydration of polymer chains to form an insulating char through the formation of phosphoric acids, pyro-phosphoric acids, etc. The MCA exhibits the flame-retardant action through endothermic degradation and release of nonflammable gases through the creation of condensed compounds of melamine-derivatives.
Figure 8
Figure 8
Time-dependence (measured at 200 °C in air atmosphere) (a) storage modulus (G′), (b) loss modulus (G″), and (c) complex viscosity (η*) of neat PA6 and various composites.
Figure 9
Figure 9
Cone colorimetry plots of PA6 and its composites with different FRs indicated in the figure: (a) HRR, (b) THR rate, (c) CO2P, and (d) COP vs time.
Figure 10
Figure 10
Respective digital photographs of the residual char from the cone colorimetry test and FE-SEM images of the char residues: (a,b) PA6, (c,d) PA6/MCA-3%, and (e,f) PA6/MCA@PZS-5%.
Figure 11
Figure 11
Photographs of specimen samples of PA6 composites after the UL-94 test: (a) PA6, (b) PA6/MCA-3%, (c) PA6/PZS-3%, (d) PA6/MCA@PZS-3%, and (e) PA6/MCA@PZS-5%. The digital pictures reported in this figure were taken by K.M. who is the first author of this work.
Figure 12
Figure 12
Schematic presentation of the proposed fire-retardant mechanism of the PA6/MCA@PZS composite. PA6, polyamide 6; MCA, melamine cyanurate; PZS, poly(cyclotriphosphazene-co-4,4′-sulfonyl diphenol).
See this image and copyright information in PMC

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