Study on pyrolysis mechanism of intumescent flame⁃retardant system based on reaction force field

doi:10.19491/j.issn.1001-9278.2024.05.012

Abstract

Abstract:

The pyrolysis and combustion mechanisms of polypropylene （PP） containing different flame retardants were investigated by using a reactive force field method. The pyrolysis reactions and flame retardancy of block copolymers （PAPO⁃MP） and blends （PAPP/MPP） were compared through the simulations in a molecular level. The results indicated that the difference between the calculation and the experiment in the mass residual yield was less than 2.1 %. The activation energy of the reaction decreased from 200.16 （pure PP） to 154.64 （PAPO⁃MP） and 159.14 kJ/mol （PAPP/MPP）. This indicated that there was a prior response in the thermal decomposition of flame retardants to protect the substrate. Furthermore， the gas molecules decreased by 10 % for PAPO⁃MP and 17.5 % for PAPP/MPP. The P—O—P structure facilitated the generation of macromolecular agglomeration， thus reducing the toxic gases and improving the char residue. Moreover， the potential energy of the system was reduced by 11.6×10³kcal/mol with the addition of PAPO⁃MP compared to PAPP/MPP. In this case， the block copolymers exhibited a better stability.

Key words: ReaxFF reaction molecular dynamics, polypropylene, intumescent flame?retardant system, flame?retardant mechanism

CLC Number:

TQ320.2

ZHANG Yi, HUANG Yating, WEI Yongbao, TANG Wei, QIAN Lijun. Study on pyrolysis mechanism of intumescent flame⁃retardant system based on reaction force field[J]. China Plastics, 2024, 38(5): 66-72.

Figures/Tables 9

Fig.1. Preparation process of PAPO⁃MP

Fig.2. FTIR spectra of the samples

Fig.3. Models of PP，PAPO⁃MP，PAPP，MPP molecule and the blends

Fig.4. TG curves and simulation results of the samples

T/K	k₁（PP）/fs^-1	k₂（PP/PAPO⁃MP）/ fs^-1	k₃（PP/PAPP/MPP）/ fs^-1
2 000	1.84×10^-3	7.74×10^-4	3.82×10^-4
2 500	6.57×10^-2	7.36×10^-4	4.02×10^-4
3 000	8.16×10^-2	7.12×10^-3	6.25×10^-3
3 500	3.75×10^-1	4.27×10^-2	1.88×10^-2

Tab.1. Pyrolysis reaction rates of PP，PP/PAPO⁃MP and PP/PAPP/MPP systems at different temperature

Fig.5. Log⁃fitting lines and parameters of the reaction rate and temperature

Fig.6. （a）~（b） initial molecular structure of PP/PAPO⁃MP system pyrolysis，（c） final molecular structure of PP/PAPO⁃MP system pyrolysis， molecular structure of （d） PP，（e） PP/PAPP/MPP and （f） PP/PAPO⁃MP systems at pyrolysis termination

Fig.7. Variation curves of the pyrolysis products

Fig.8. Evolution of potential energy of PP，PP/PAPO⁃MP and PP/PAPP/MPP systems at different temperature

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