Preparation and Properties of Flame Retardant Waterborne Polyurethane Nanocomposites via Click Reaction†

doi:10.7503/cjcu20160177

Abstract

Abstract:

Polyurethane bearing the alkyne functions as pendant groups was synthesized via functional monomer 2,2-di(prop-2-ynyl) propane-1,3-dio as chain extender. Flame retardant waterborne polyurethane(WPU) nanocomposites were prepared by the Click reaction between alkyne-functionalized PU and azido-modified nano-montmorillonite(MMT), nano-aluminum hydroxide(ATH) and magnesium hydroxide(MH). The structures of the flame retardant WPU nanocomposites were characterized by Fourier transform Infrared spectrometer(FTIR), proton nuclear magnetic resonance spectroscopy(¹H NMR) and scanning electron microscopy(SEM). The influence of the ratio of nano flame retardants and preparation methods on limit oxygen index, dynamic combustion performance and thermal degradation behavior of the WPU nanocomposites were studied by the comparative study. The findings on flame resistance study indicated that when the mass fractions of MMT-N₃, MH-N₃ and ATH-N₃ were 7%, 2% and 1%, respectively, the oxygen index of the composites prepared by Click reaction was 7% higher than that of pure WPU, time to ignition was lengthened from 10 s to 29 s, and the peak heat release rate and smoke release rate were reduced by 41% and 42%, respectively. TGA results showed that when the mass fraction of MMT-N₃of 10%, the temperature at 50% mass loss of MMT/WPU composites prepared by Click reaction increased 21 ℃ compared with the WPU. SEM analysis of the composite section and combustion residue showed that Click reaction is an effective method to disperse nanomaterials in polymer matrices.

Key words: Flame retardant waterborne polyurethane, Nano-montmorillonite, Nano-hydroxide, Click reaction, Dynamic combustion behavior

CLC Number:

O631

TrendMD:

LI Xingjian,JU Yunpeng,CHANG Degong,ZHANG Yiheng. Preparation and Properties of Flame Retardant Waterborne Polyurethane Nanocomposites via Click Reaction^†[J]. Chem. J. Chinese Universities, 2016, 37(8): 1580.

Figures/Tables 16

Scheme 1 Synthesis of 3-azidopropyltriethoxysilane

Scheme 2 Synthesis of DPPD

Scheme 3 Strategy for the azidation of MMT, ATH and MH

Scheme 4 Click reaction between alkyne-functionalized PU and azido-nano fillers

Table 1 Recipes of WPU flame retardant nanocomposites

Sample	Component(mass fraction, %)			Composite mechanism
Sample	MMT-N₃		MH-N₃	ATH-N₃
WPU
MMT/WPU	10	0	0	Click reaction
PBWPU	7	2	1	Physical blending
CRWPU	7	2	1	Click reaction

Fig.1 FTIR spectra of DPPD(a) and alkyne-functionalized PU(b)

Fig.2 FTIR spectra of MH(A), ATH(B) and MMT(C) befor(a) and after(b) modification of N3

Fig.3 FTIR spectra of alkyne-WPU(a) and functionalized WPU after Click reaction(b)

Fig.4 1H NMR spectra(500 MHz, DMSO-d6) of alkyne-functionalized WPU before(a) and after(b) Click reaction

Fig.5 SEM images of WPU(A), MMT/WPU(B), PBWPU(C) and CRWPU(D)

Table 2 LOI, tign, pkHRR and pkSPR of WPU nanocomposites

Sample	LOI(%)	t_ign/s	pkHRR/(kW·m^-2)	pkSPR/(m²·s^-1)
WPU	17.0	10	397.1	0.033
MMT/WPU	19.8	9	293.3	0.024
PBWPU	22.2	17	274.6	0.023
CRWPU	24.0	29	235.6	0.019

Fig.6 HRR curves for WPU(a), MMT/WPU(b),PBWPU(c) and CRWPU(d)

Fig.7 Smoke production rate curves of WPU(a), MMT/WPU(b), PBWPU(c) and CRWPU(d)

Fig.8 SEM residue images of WPU(A), MMT/WPU(B), PBWPU(C) and CRWPU(D) after the cone calorimeter tests

Fig.9 TGA(A) and DTG(B) curves of WPU nanocomposites a. WPU; b. MMT/WPU; c. PBWPU; d. CRWPU.

Table 3 Temperature of thermal lost weight of the film and the final char yield of WPU nanocomposites

Sample	T_5%/℃	T_50%/℃	T_max/℃	Char yield(500 ℃)(%)
WPU	158	317	325	-2.9
MMT/WPU	183	338	339	11.5
PBWPU	247	320	321	12.6
CRWPU	253	325	323	13.3

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