Flame-retardant Properties and Transformation of Flame-retardant Mechanisms of EVA: Effect of ATH/ADP Ratio

doi:10.15541/jim20230502

Abstract

Abstract:

To improve the flame-retardant properties of ethylene-vinyl ecetate copolymer (EVA) with aluminum hydroxide (ATH), a blend of aluminum diethylphosphite (ADP) and ATH was used. The flame-retardant properties of the composites were evaluated by using vertical burning (UL-94), limiting oxygen index (LOI), and cone calorimeter (CONE) tests. The results indicated that at the mass ratio of ATH to ADP of 2∶1 and 1∶2, compared to the EVA/ATH composites, the vertical burning rating improved from no rating to V-0, and the LOI increased from 34.5% to 37.8% and 42.8%, respectively. Different methods were used to analyze the flame-retardant mechanisms of samples with these two ratios. For the sample with a mass ratio of ATH to ADP of 2∶1, the content of phosphorus-containing compounds released during thermal decomposition was extremely low, and the formation of aluminum phosphate (AlPO₄) strengthened the char layer, made it more continuous and dense, resulting in higher residue mass than theoretical value. Therefore, the proposed flame-retardant mechanism at this ratio is dominated by the condensed phase. For the sample with a mass ratio of ATH to ADP of 1∶2, the char layer had more pores, and the residue mass was lower than theoretical value, but high content phosphorus-containing compounds appeared in the gaseous products. Hence, the proposed flame-retardant mechanism at this ratio is dominated by gas phase.

Key words: aluminum hydroxide, aluminum diethylphosphite, ethylene-vinyl acetate copolymer, flame-retardant mechanism

CLC Number:

TB321

CHENG Bo, AN Xiaohang, LI Dinghua, YANG Rongjie. Flame-retardant Properties and Transformation of Flame-retardant Mechanisms of EVA: Effect of ATH/ADP Ratio[J]. Journal of Inorganic Materials, 2024, 39(5): 509-516.

Figures/Tables 11

Fig. 1 Flow chart of EVA composites preparation

Table 1 Formulations of EVA composites and test results of UL-94 and LOI

Sample	EVA/% (in mass)	ATH/% (in mass)	ADP/% (in mass)	LOI/%	UL-94
EVA1	40	60	0	34.5	NR
EVA2	40	55	5	34.7	NR
EVA3	40	50	10	36.8	NR
EVA4	40	45	15	37.4	V-1
EVA5	40	40	20	37.8	V-0
EVA6	40	30	30	39.2	NR
EVA7	40	20	40	42.8	V-0
EVA8	40	15	45	41.6	NR
EVA9	40	10	50	39.8	NR
EVA10	40	0	60	34.0	NR

Fig. 2 Photos of samples EVA5 (up) and EVA7 (down) for the UL-94 test

Table 2 Results of CONE test for EVA composites

Sample	TTI/s	PHRR/ (kW·m^-2)	THR/ (MJ·m^-2)	TSR/ (m²·m^-2)	Residue mass/%
EVA1	75	167.95	72.37	417.74	43.71
EVA5	80	253.00	89.65	928.12	40.22
EVA7	67	399.91	97.30	1895.28	26.92
EVA10	45	498.11	106.14	2586.84	16.71

Fig. 3 (a) HRR, (b) THR, (c) SPR, and (d) TSR curves of EVA composites Colorful figures are available on website

Table 3 TG data for ATH, ADP, EVA,and EVA composites

Sample	T_5%/℃	T_max1/℃	T_max2/℃	Residue mass at 800 ℃/%	Theoretical mass of residue/%
ATH	250.7	279.7	—	66.2	—
ADP	409.8	466.8	—	18.8	—
EVA	342.5	355.1	472.3	0.0	—
EVA1	296.2	324.9	470.8	39.2	39.7
EVA5	306.4	318.6	471.2	31.8	30.2
EVA7	322.5	326.5	467.5	16.6	20.7
EVA10	362.8	361.5	467.3	3.4	11.3

Fig. 4 (a) TG and (b) DTG curves of ATH, ADP, EVA and EVA composites Colorful figures are available on website

Fig. 5 Digital images of char after CONE test for EVA1, EVA5, EVA7, and EVA10 composites (a) Top view; (b) Side view; (c) SEM images

Fig. 6 XRD patterns of char after CONE test Colorful figure is available on website

Fig. 7 FT-IR spectra of EVA5 and EVA7 composites at 330 and 580 ℃ Colorful figures are available on website

Fig. 8 Schematic diagram of flame-retardant mechanisms for EVA5 and EVA7 composites

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