Synthesis and Properties of a Novel Bio-based Benzoxazine†

doi:10.7503/cjcu20180751

Abstract

Abstract:

A novel bio-based benzoxazine resin(phenolphthalein-furfuramine-benzoxazine, PTL-F-BOZ), used bio-based furfurylamine, phenolphthalein, and paraformaldehyde as raw materials, was synthesized and characterized by Fourier transform infrared spectroscopy(FTIR), nuclear magnetic resonance(¹H NMR and ¹³C NMR). The curing, thermal and flame retardant properties were analyzed by differential scanning calorimetric(DSC), thermogravimetric analyzer(TG), limiting oxygen index(LOI), vertical burning test, microscale combustion calorimetry(MCC), cone calorimeter(Cone) and scanning electron microscope(SEM). The DSC curve of PTL-F-BOZ showed a two-stage curing with two maxima at 224 and 251 ℃ respectively, and had lower curing temperature than that of the traditional fossil-based bisphenol benzoxazine bisphenol A-aniline benzoxazine(bisphenol A-aniline-benzoxazine, BPA-A-BOZ). The presence of the furan ring in the furfurylamine increased the cross-linking density of polymer, retarded the rearrangement reaction from the phenoxy structure to the phenol structure, and resulted in two curing peaks in the DSC curve of PTL-F-BOZ. Under nitrogen and air atmospheres, the temperatures of 5% mass loss(T_5%) for PPTL-F-BOZ resin were 380 and 370 ℃, respectively and the residual chars at 800 ℃ were 63.0% and 10.5%, respectively. Compared with PBPA-A-BOZ resin, PPTL-F-BOZ resin both possessed higher T_5% and residual char of 800 ℃. From the DTG curve, the maximum mass loss rates of two decomposition stage(Peak 1 and Peak 2 values) of PPTL-F-BOZ resin were 0.67%/min and 3.28%/min, which were only 7.38% and 63.44% of PBPA-A-BOZ(9.07%/min and 5.17%/min) under nitrogen atmosphere, and those were also the same under air atmosphere. LOI of PPTL-F-BOZ resin was 36.2%, which was higher than that of PBPA-A-BOZ resin. Meanwhile, in the UL-94 test, PPTL-F-BOZ resin extinguished quickly and released less smoke during combustion process, and the original morphology was kept well and a stable carbon layer was formed after burning. Its first ignition time(t₁) and second ignition time(t₂) were 1.4 and 8.5 s, respectively, far smaller than the maximum permissible values of 10 s, and a UL94 V-0 rating was also achieved. Hence, PPTL-F-BOZ resin showed excellent thermal and flame retardant properties.

Key words: Bio-based benzoxazine, Phenolphthalein-furfuramine-benzoxazine resin, Curing reaction, Thermal property, Flame retardancy

CLC Number:

O631

TrendMD:

YIN Ping,YAN Hongqiang,CHENG Jie,FANG Zhengping. Synthesis and Properties of a Novel Bio-based Benzoxazine^†[J]. Chem. J. Chinese Universities, 2019, 40(5): 1071.

Figures/Tables 21

Scheme 1 Synthetic route of PTL-F-BOZ

Fig.1 FTIR spectrum of PTL-F-BOZ

Fig.2 1H NMR spectrum of PTL-F-BOZ

Fig.3 13C NMR spectrum of PTL-F-BOZ

Fig.4 DSC curves of BPA-A-BOZ(a) and PTL-F-BOZ(b)

Table 1 Curing characteristics of BPA-A-BOZ and PTL-F-BOZ*

Sample	T_on/℃	T_p1/℃	T_p2/℃	T_off/℃
BPA-A-BOZ	209	260	—	321
PTL-F-BOZ	196	224	251	269

Fig.5 Probable sites of H-bonding in PPTL-F-BOZ

Fig.6 DSC curves of PTL-F-BOZ treated by different temperatures

Fig.7 In-situ FTIR spectra of PTL-F-BOZ

Scheme 2 Polymerization mechanism of PTL-F-BOZ

Fig.8 TGA curves of PPTL-F-BOZ(a) and PBPA-A-BOZ(b) resins under N2 atmosphere(A) and air atmosphere(B) Insets are the corresponding DTG curves.

Table 2 Thermal degradation results of PPTL-F-BOZ and PBPA-A-BOZ resins measured by TGA*

Sample	Atmosphere	T_5%/℃	T_max1/℃	Peak 1 value (%·min^-1)	T_max2/℃	Peak 2 value (%·min^-1)	Char yield at 800 ℃(%)
PPTL-F-BOZ	N₂	380	312	-0.67	457	-3.28	63.0
	Air	372	437	-2.70	674	-7.03	10.5
PBPA-A-BOZ	N₂	331	406	-9.07	476	-5.17	30.6
	Air	350	398	-4.82	651	-7.90	0

Fig.9 Structures of four different benzoxazine monomers

Table 3 Thermal degradation results of four different resins measured by TGA under N2 atmosphere

Sample	T_5%/℃	Char yield at 800 ℃(%)
PBPA-A-BOZ	331	31
PPTL-F-BOZ	380	63
PPTL-A-BOZ^[14]	305	51
PBPA-F-BOZ^[18]	347	47

Fig.10 Images of PPTL-F-BOZ(A, A') and PBPA-A-BOZ(B, B') resins after UL-94 burning over top view(A, B) and side view(A', B')

Table 4 UL-94 vertical burning test and LOI values for PPTL-F-BOZ and PBPA-A-BOZ resins*

Resin sample	LOI(%)	t₁/s	t₂/s	UL-94 rate
PBPA-A-BOZ	32.2	Fail	Fail	NR
PPTL-F-BOZ	36.2	1.4	8.5	V-0

Fig.11 Heat release rate results measured by MCC

Table 5 Data recorded during MCC measurement*

Sample	PHRR/(W·g^-1)	THR/(kJ·g^-1)	T_max/℃	HRC/(J·g^-1·K^-1)
PBPA-A-BOZ	165.7	23.6	417.2	169
PPTL-F-BOZ	22.2	8.9	420.5	30

Fig.12 Heat release rate results measured by Cone

Table 6 Data recorded during Cone measurement*

Sample	PHRR/(kW·m^-2)	THR/(MJ·m^-2)	T_ign/s
PBPA-A-BOZ	292.5	74.3	87
PPTL-F-BOZ	25	0.4

Fig.13 SEM images of the surface char residues of PBPA-A-BOZ(A, C) and PPTL-F-BOZ(B, D) after UL-94 burning in different magnification

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