Strontium Hydroxystannate Nanorods Encapsulated by Hybrid Polyphosphazene: Synthesis and Flame Retardancy on Epoxy Resin

doi:10.15541/jim20180493

Abstract

Abstract:

To develop a novel hybrid organic-inorganic flame retardant and smoke suppressant, strontium hydroxystannate (SrSn(OH)₆) nanorods were synthesized via a co-precipitation method, and then the SrSn(OH)₆ were encapsulated by cyclomatrixpolyphosphazene (PZS) to prepare a novel core-shell organic-inorganic hybrid nano-flame retardant (PZS@SrSn(OH)₆). The micromorphology and chemical structure were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FT-IR). The thermal degradation of PZS@SrSn(OH)₆and EP/PZS@SrSn(OH)₆ composites was investigated by thermogravimetry analysis (TGA). The flame retardancy properties were studied by limited oxygen index (LOI) and CONE calorimetry tests. The flame retardant mechanism was determined by X-ray diffraction (XRD), SEM, energy-dispersive X-ray spectroscopy (EDS), and FT-IR. The results showed that PZS@SrSn(OH)₆ exhibited high flame retardant and smoke suppression efficiency. Significant synergy between PZS and SrSn(OH)₆ was found to enhance the flame retardancy of EP compared with pure EP, the LOI value was increased from 26.2% to 29.6% with 3wt% addition of PZS@SrSn(OH)₆. CONE calorimetry tests indicated that 3% incorporation of PZS@SrSn(OH)₆ brought about 29% and 37% maximum reduction in peak heat release rate and peak smoke production rate, and 242% improvement of char residue, respectively. A dense char structure is formed after combustion under elevated temperature for PZS@SrSn(OH)₆, and the char layer blocks the exchange between the decomposed fragments and oxygen, then protect EP matrix and improve the flame retardancy.

Key words: polyphosphazene, strontium hydroxystannate, hybrid, flame retardancy, nanocomposites

CLC Number:

O631

ZHANG Chong, GENG Xiao-Wei, GAO Xiang-Di, ZHANG Xin, GUO Rao, WANG Yu-Jing, XU Jian-Zhong, MA Hai-Yun. Strontium Hydroxystannate Nanorods Encapsulated by Hybrid Polyphosphazene: Synthesis and Flame Retardancy on Epoxy Resin[J]. Journal of Inorganic Materials, 2019, 34(7): 761-767.

Figures/Tables 10

Fig. 1 Synthetic routes of the SrSn(OH)6 and PZS@SrSn(OH)6

Fig. 2 Morphologies and element distribution map of SrSn(OH)6 and PZS@SrSn(OH)6

Fig. 3 TG (a) and DTG (b) curves of SrSn(OH)6, PZS and PZS@SrSn(OH)6 tested in N2 atmosphere

Fig. 4 TG (a) and DTG (b) curves of EP nanocomposites tested in N2 atmosphere

Table 1 Thermogravimetric properties of PZS, SrSn(OH)6, PZS@SrSn(OH)6 and EP nanocomposites

Sample	T_5%/℃	T_max/℃	Residue at 800 ℃/wt%	Theoretical residue at 800 ℃/wt%
PZS	442.8	507.9	48.2	—
SrSn(OH)₆	217.3	237.7	80.4	—
PZS@SrSn(OH)₆	218.5	487.5	69.4	—
Pure EP	364.2	375.3	13.0	—
3% EP/SrSn(OH)₆	354.0	367.3	16.2	15.0
3% EP/PZS@SrSn(OH)₆	360.0	368.6	17.0	14.7

Fig. 5 LOI values and residue chars at the end of LOI tests of EP, EP/SrSn(OH)6 and EP/PZS@SrSn(OH)6 nanocomposites

Fig. 6 Heat release rate (HRR) (a), specimen mass (b), smoke production rate SPR (c), and CO production rate (d) curves of the samples in CONE tests

Table 2 Cone calorimetry data for EP composites

Sample	Pure EP	1wt% EP/SrSn(OH)₆	3wt% EP/SrSn(OH)₆	1wt% EP/PZS@SrSn(OH)₆	3wt% EP/PZS@SrSn(OH)₆
Char residue/g	5.6	13.2	12.4	13.8	19.2
THR/(MJ·m^-2)	100.4	93.2	92.6	93.1	88.9
PHRR/(kW·m^-2)	1141.1	971.7	888.9	777.3	809.7
PSPR/(m²·s)	0.33	0.25	0.24	0.22	0.21
TSP/m²	27.6	23.7	23.9	25.1	21.2

Fig. 7 Digital photos of the char residues for composites after cone calorimeter tests (a,f) EP; (b,g) 1wt% EP/SrSn(OH)6; (c,h)3wt% EP/SrSn(OH)6; (d,i) 1wt% EP/PZS@SrSn(OH)6; (e,j) 3wt% EP/PZS@SrSn(OH)6

Fig. 8 XRD (a), EDS (b) and FT-IR (c) spectra of the char residue of EP samples

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