Synthesis of DOPO-based Cyclotriphosphazene Macromolecule Flame Retardant and Its Performance in Flame-retarded Epoxy Resin †

doi:10.7503/cjcu20190257

Abstract

Abstract:

A novel inorganic-organic hybrid macromolecule flame retardant, hexa-[4-(N-phenylamino-DOPO-methenyl)-phenoxyl]-cyclotriphosphazene(DOPO-PCP, DOPO=9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide) was synthesized successfully through three-step reactions including substitution, condensation and addition. The chemical structure of DOPO-PCP was characterized by Fourier transform infrared spectroscopy, ¹H and ³¹P nuclear magnetic resonance spectroscopies. All the results conformed the functional groups of the DOPO-PCP designed. Then the thermal stability of DOPO-PCP, pure epoxy(DGEBA) and their composites was analyzed by thermogravimetric analysis, and the properties of flame-retarded cured epoxy were investigated by limited oxygen index(LOI), UL-94 vertical burning test and Cone calorimeter test. Among all the samples, P-1.3 passed UL-94 V-0 level test and its LOI value reached 36.2%, while the phosphorus content in it was only 1.3%. In cone calorimeter test, the heat release rate(HRR) and the smoke production rate(SPR) of P-1.3 went down obviously, meanwhile, its residual char mass increased significantly, demonstrating that DOPO-PCP was favored to flame-retarded DGEBA. Furthermore, the SEM images showed the excellent compatibility between the additives and DGEBA matrix, which made for the formation of the continuous char layer. The mapping photographs displayed the uniform distribution of phosphorus and nitrogen elements in intumescent char layer. As a result, DOPO-PCP was evaluated as a higher efficiency flame retardant by synergistic flame retardant mechanism in both gas phase and the solidification phase.

Key words: Cyclotriphosphazene-DOPO macromolecule(DOPO=9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide), Flame retardant, Epoxy resin

CLC Number:

O631.3

TrendMD:

Minwen JIANG,Chenhui YIN,Sheng LI,Xiaoli LI. Synthesis of DOPO-based Cyclotriphosphazene Macromolecule Flame Retardant and Its Performance in Flame-retarded Epoxy Resin ^†[J]. Chem. J. Chinese Universities, 2019, 40(12): 2615.

Figures/Tables 15

Scheme 1 Synthetic routes of DOPO-PCP

Fig.1 FTIR spectra of HAPCP(a), HPA-PCP(b) and DOPO-PCP(c)

Fig.2 1H NMR spectrum of DOPO-PCP

Fig.3 31P NMR spectrum of DOPO-PCP

Sample	m(DGEBA)/g	m(DDS)/g	m(DOPO-PCP)/g	w(DOPO-PCP)(%)	w(P)(%)	LOI(%)	UL-94 rating
Sample	m(DGEBA)/g	m(DDS)/g	m(DOPO-PCP)/g	w(DOPO-PCP)(%)	w(P)(%)	LOI(%)	3.0 mm	Dripping
DGEBA	100	31	0	0	0	21.7	Fail	NO
P-1.0	100	31	13.5	9.3	1.0	35.4	V-1	NO
P-1.1	100	31	15.0	10.3	1.1	35.5	V-1	NO
P-1.2	100	31	16.6	11.2	1.2	35.8	V-1	NO
P-1.3	100	31	18.1	12.1	1.3	36.2	V-0	NO

Fig.4 TGA(A) and DTG(B) curves of DOPO-PCP(a), DGEBA(b) and P-1.3(c)

Sample	$T 1 % *$ /℃	$T 5 % *$ /℃	R_{peak 1}/T_{peak 1} (%·min^-1/℃)	R_{peak 2}/T_{peak 2} (%·min^-1/℃)	Mass fraction at 700 ℃(%)
DOPO-PCP	246.6	287.1	3.01/303.3	468.9	46.1
DGEBA	350.4	385.4	20.87/418.8		15.4
P-1.3	277.5	338.7	13.93/387.3		28.2

Sample	$T 1 % *$ /℃	$T 5 % *$ /℃	R_{peak 1}/T_{peak 1} (%·min^-1/℃)	R_{peak 2}/T_{peak 2} (%·min^-1/℃)	Mass fraction at 700 ℃(%)
DOPO-PCP	246.6	287.1	3.01/303.3	468.9	46.1
DGEBA	350.4	385.4	20.87/418.8		15.4
P-1.3	277.5	338.7	13.93/387.3		28.2

Sample	DGEBA	P-1.3
TTI/s	63	51
Av-EHC/(MJ·kg^-1)	24.43	17.93
Peak _1-HRR/(kW·m^-2)	857.9	252.4
t_{Peak 1-HRR}/s	120	60
Peak_2-HRR/(kW·m^-2)		352.1
t_{Peak 2-HRR}/s		185
THR/(MJ·m^-2)	93.0	51.1
Peak _1-SPR/(m²·s^-1)	0.36	0.20
t_{Peak 1-SPR}/s	115	60
Peak _2-SPR/(m²·s^-1)		0.19
t_{Peak 2-SPR}/s		170
TSP/(m²·kg^-1)	36.85	26.14

Fig.5 HRR(A) and THR(B) curves of DGEBA(a) and P-1.3(b)

Fig.6 SPR(A) and TSP(B) curves of DGEBA(a) and P-1.3(b)

Fig.7 Residual char mass curves of DGEBA(a) and P-1.3(b)

Fig.8 Digital photos of the char residues after cone calorimeter tests (A) Top view, DGEBA; (B) main view, P-1.3; (C) top view, P-1.3.

Fig.9 SEM images of char residue of DGEBA(A) and P-1.3(B) after Cone calorimeter tests

Fig.10 SEM images of fracture surfaces of DGEBA(A) and P-1.3(B)

Fig.11 Merged EDX elements mapping images of P-1.3 after cone calorimeter tests (A) N; (B) P.

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