Thermal Degradation Mechanism of Bio-based Polybutylactam Plasticized by Ionic Liquids

doi:10.7503/cjcu20220353

Abstract

Abstract:

Polybutyllactam（PBL） has attracted increasing attention in recent years since it can be degraded in various natural environments including water. However， due to the melting point is close to the thermal decomposition temperature， it cannot be melting processed and the application is limited. Therefore， reducing melting point and improving thermal stability of PBL becomes an urgent problem. Herein， two imidazolium-based ionic liquids（ILs）， hydrophobic 1-butyl-3-methyl-imidazolium hexafluorophosphate（［BMIM］PF₆） and hydrophilic 1-butyl-3-methyl-imidazolium tetrafluoroborate（［BMIM］BF₄）， were applied to plasticize PBL， and their effects on the crystallization and thermal properties of PBL were investigated. It was found that both ILs weakened the intermolecular hydrogen bonds of PBL， inhibited the growth of PBL crystals at the （200） crystal plane and reduced the crystallinity of PBL. When the addition mass fraction of ILs was 5%， the melting temperature of PBL was decreased by 7—8 ℃. Compared with pure PBL film， the thermal stability of ［BMIM］BF₄ plasticized PBL film decreased slightly， while that of ［BMIM］PF₆ plasticized PBL film improved. The results of thermal kinetic analysis of ［BMIM］PF₆ plasticized PBL film showed that the activation energy（E） of thermal decomposition is 46.68 kJ/mol， and the reaction order（n） is 1. The most probable mechanism function model of thermal degradation follows the Mampel power law（first order）. It indicates that when PBL is thermally stimulated， it irregularly nucleates at the interface between polymer and decomposition products. The reaction core is of reactivity and the reaction gradually expands until the end.

Key words: Polybutyrolactam, Ionic liquid, Thermal stability, Thermal degradation mechanism

CLC Number:

O631.3

TrendMD:

CHANG Sihui, CHEN Tao, ZHAO Liming, QIU Yongjun. Thermal Degradation Mechanism of Bio-based Polybutylactam Plasticized by Ionic Liquids[J]. Chem. J. Chinese Universities, 2022, 43(11): 20220353.

Figures/Tables 16

Table 1 Crystallization properties of PBL films plasticized by ionic liquids

Sample	Mass fraction of IL^* （%）	2θ/（°）		d/nm		X_c（%）
Sample	Mass fraction of IL^* （%）	（200）	（020）	（200）	（020）	X_c（%）
PBL	0	20.10	23.96	0.441	0.371	47.9
［BMIM］BF₄/PBL	3	20.26	24.20	0.438	0.367	39.2
	5	20.56	24.46	0.432	0.364	35.0
［BMIM］PF₆/PBL	3	20.28	24.20	0.438	0.367	44.6
	5	20.34	24.32	0.436	0.366	35.7

Table 2 Thermal degradation temperatures of PBL films plasticized by ionic liquids

Sample	Mass fractoin of IL（%）	T₅/℃	T_p/℃	T_end/℃	（dw/dt）_max/（%?min^-1）
PBL	0	259	300	323	26
［BMIM］BF₄/PBL	3	245	287	311	24
	5	242	287	323	17
［BMIM］PF₆/PBL	3	248	302/321	335	17/18
	5	255	306/322	336	18/20

Table 3 Thermal kinetic parameters of PBL plasticized by 5% mass fraction of [BMIM]PF6 obtained by Ozawa method

α	Linear equation	r²	E/（kJ?mol^-1）	ln（A/min^-1）
0.1	y=-2028.60x+8.12	0.92336	36.93	20.28
0.2	y=-2130.90x+8.23	0.96923	38.79	21.24
0.3	y=-2015.80x+7.72	0.97304	36.70	20.58
0.4	y=-1979.83x+7.48	0.97176	36.04	20.42
0.5	y=-2008.97x+7.46	0.97946	36.57	20.67
0.6	y=-2102.62x+7.66	0.98175	38.28	21.35
0.7	y=-2163.43x+7.74	0.98715	39.39	21.79
0.8	y=-2224.59x+7.84	0.99000	40.50	22.27
Average			37.90	21.07

Table 4 Thermal kinetic parameters in different mechanisms using C-R method

No.	Mechanism	g（α）	r²	E/（kJ?mol^-1）	ln（A/min^-1）
1	Avrami?Erofeev Equation	$[- l n (1 - α)] 12$	0.99809	19.46	3.78
2	Avrami?Erofeev Equation	$[- l n (1 - α)] 23$	0.99831	27.64	7.22
3	Avrami?Erofeev Equation	$[- l n (1 - α)] 34$	0.99838	31.73	8.91
4	Mampel power law（first order）	$- l n (1 - α)$	0.99852	44.00	13.88
5	Avrami?Erofeev Equation	$[- l n (1 - α)] 32$	0.99861	68.55	23.60
6	Avrami?Erofeev Equation	$[- l n (1 - α)] 2$	0.99866	93.10	33.19
7	Avrami?Erofeev Equation	$[- l n (1 - α)] 3$	0.99870	142.19	52.18
8	Avrami?Erofeev Equation	$[- l n (1 - α)] 4$	0.99872	191.28	71.04

Table 4 Thermal kinetic parameters in different mechanisms using C-R method

No.	Mechanism	g（α）	r²	E/（kJ?mol^-1）	ln（A/min^-1）
1	Avrami?Erofeev Equation	$[- l n (1 - α)] 12$	0.99809	19.46	3.78
2	Avrami?Erofeev Equation	$[- l n (1 - α)] 23$	0.99831	27.64	7.22
3	Avrami?Erofeev Equation	$[- l n (1 - α)] 34$	0.99838	31.73	8.91
4	Mampel power law（first order）	$- l n (1 - α)$	0.99852	44.00	13.88
5	Avrami?Erofeev Equation	$[- l n (1 - α)] 32$	0.99861	68.55	23.60
6	Avrami?Erofeev Equation	$[- l n (1 - α)] 2$	0.99866	93.10	33.19
7	Avrami?Erofeev Equation	$[- l n (1 - α)] 3$	0.99870	142.19	52.18
8	Avrami?Erofeev Equation	$[- l n (1 - α)] 4$	0.99872	191.28	71.04

Table 5 Reaction orders of PBL plasticized by 5% mass fraction of [BMIM]PF6 using Crane method

No.	Mechanism	E/（kJ·mol^-1）	Theoretical n	Calculated n	Relative error
1	Avrami?Erofeev Equation	19.46	1/2	0.38	-24%
2	Avrami?Erofeev Equation	27.64	2/3	0.54	-19%
3	Avrami?Erofeev Equation	31.73	3/4	0.62	-17%
4	Mampel power law（first order）	44.00	1	0.86	-14%
5	Avrami?Erofeev Equation	68.55	3/2	1.34	-10%
6	Avrami?Erofeev Equation	93.10	2	1.82	-9%
7	Avrami?Erofeev Equation	142.19	3	2.79	-7%
8	Avrami?Erofeev Equation	191.28	4	3.75	-6%

Table 6 Thermal kinetic parameters obtained by different methods

Method	r²	E/（kJ?mol^-1）	ln（A/min^-1）
Ozawa	＞0.92300	37.90	21.07
Coats?Redfern	0.99852	44.00	13.88
Satava	0.99878	46.68	3.75

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