thermal behavior and thermal safety of nitrate glycerol ether cellulose

7/24/2019 Thermal Behavior and Thermal Safety of Nitrate Glycerol Ether Cellulose

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CHEM. RES. CHINESE UNIVERSITIES2012, 28(3), 516519

*Corresponding author. E-mail: [email protected]

Received July 13, 2011; accepted August 30, 2011.

Supported by the Foundation of National Key Laboratory of Science and Technology on Combustion and Explosion of China

(No.9140C3503011004).

Thermal Behavior and Thermal Safety of Nitrate

Glycerol Ether Cellulose

XU Si-yu1, ZHAO Feng-qi1*, YI Jian-hua1, GAO Hong-xu1, SHAO Zi-qiang2,

HAO Hai-xia1, HU Rong-zu1and PEI Qing11.Science and Technology on Combustion and Explosion Laboratory,

Xian Modern Chemistry Research Institute,Xian 710065,P.R.China;

2.School of Materials Science and Engineering,Beijing Institute of Technology,

Beijing 100081,P.R.China

Abstract The thermal behavior, nonisothermal decomposition reaction kinetics and specific heat capacity of nitrate

glycerol ether cellulose(NGEC) were determined by thermogravimetric analysis(TGA), differential scanning calori-

metry(DSC) and microcalorimetry. The apparent activity energy(Ea), reaction mechanism function, quadratic equa-tion of specific heat capacity(Cp) with temperature were obtained. The kinetic parameters of the decomposition reac-

tion areEa=170.2 kJ/mol and lg(A/s1)=16.3. The kinetic equation is f()(4/3)(1)[ln(1)]1/4. The specific heat

capacity equation is Cp=1.2856.276103T+1.581105T2(283 K


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No.3 XU Si-yuet al. 517

Micro-DSCIII apparatus(Setaram Co., France) and the amount

of sample was 76.8 mg. The heating rate was 0.10 K/min from

283.1 K to 353.2 K, in which the precisions of temperature and

heat flow were 1.0104K and 0.2 W, respectively. The prin-

ciple for measuring the continuous specific heat capacity isshown as follows:

( )s bp

s

AC

m

= (1)

where As and Ab are the heat flows of the sample and blank,

respectively, ms is the amount of the sample, and is the

heating rate.

3 Results and Discussion

3.1 Thermal Behavior and Nonisothermal Reac-

tion Kinetics

The DSC curves at different heating rates at 0.1 MPa and

TG-DTG curves at a heat rate of 10 K/min for NGEC sample

are shown in Figs.2 and 3, respectively. There is only an exo-

thermic peak on each DSC curve at 0.1 MPa. From the typical

DSC and TG-DTG curves(Figs.2 and 3), it can be seen that

NGEC has an intense exothermic decomposition process with a

mass loss of about 87.8% during thermal decomposition. From

Fig.2, some important parameters at different heating rates are

obtained, such as the beginning temperature(T0), the extrapo-

lated onset temperature(Te), peak temperature(Tp) and exother-

mic decomposition enthalpy(Hd). These parameters are listed

in Table 1.

Fig.2 DSC curves of NGEC sample at different

heating rates under 0.1 MPa

Heating rate/(Kmin1): a. 2.5; b. 5; c. 7.5; d. 10; e. 12.5;f. 15.

Fig.3 TG-DTG curves of NGEC sample at a heating

rate of 10 K/min

The data of DSC curves of NGEC at six different heating

rates were dealt with mathematic means. The values ofEawere

obtained with the conversion degree of main exothermical peak

changing from 0.08 to 0.84. Five integral methods(General

integral, MacCallum-Tanner, atava-estk, Agrawal, and

Flynn-Wall-Ozawa) and one differential method(Kissinger)

were employed[69]

. The calculated values of Ea, lgA, linearcorrelation coefficient(r) and standard mean square deviation(Q)

are listed in Table 2. The decomposition reaction mechanism

functions of NGEC sample are listed in Table 2, too.

Table 1 Values of T0, Te, Tpand Hdof the thermal

decomposition process determined by DSC

curves at different heating rates()

/(Kmin1)Initial value

T0/K Te/K Tp/K Hd/(Jg1)

2.5 422.6 474.8 492.0 1709

5.0 427.5 483.0 498.6 1834

7.5 432.4 487.4 502.6 1939

10.0 435.6 490.9 505.3 192012.5 439.4 493.3 507.6 1942

15.0 442.3 494.6 510.4 1782

Table 2 Kinetic parameters for the decomposition

process of NGEC sample at 0.1 MPa*

Method /(Kmin1) Ea/(kJmol

lg(A/s1) r Q

General- 2.5 161.5 15.4 0.9864 0.3613

integral 5 166.5 16.0 0.9854 0.3887

7.5 165.4 15.9 0.9852 0.3940

10 171.4 16.6 0.9845 0.426

12.5 176.2 17.1 0.9847 0.4079

15 175.5 17.1 0.9872 0.3406

MacCallum- 2.5 161.8 15.4 0.9876 0.0679

Tanner 5 167.0 16.0 0.9867 0.0730

7.5 165.9 15.9 0.9865 0.0740

10 172.1 16.6 0.9859 0.0775

12.5 176.9 17.2 0.9860 0.0766

15 176.2 17.1 0.9884 0.0640

atava-estk 2.5 161.0 15.4 0.9876 0.0679

5 165.8 16.0 0.9867 0.0730

7.5 164.9 15.8 0.9865 0.0740

10 170.6 16.5 0.9859 0.0775

12.5 175.2 17.0 0.9860 0.0766

15 194.5 17.0 0.9884 0.0640

Agrawal 2.5 161.5 15.4 0.9864 0.3613

5 166.5 16.0 0.9854 0.3887

7.5 165.4 15.9 0.9852 0.3940

10 171.4 16.6 0.9845 0.4126

12.5 176.2 17.1 0.9847 0.4079

15 175.5 17.1 0.9872 0.3406

Mean 170.2 16.3 0.9862 0.2287

Flynn-Wall-Ozawa 178.2(EpO) 0.9987(EpO) 0.0010

148.6(EeO) 0.9986(EeO)

Kissinger 179.5 17.7 0.9986 0.0056

Mechamism function f()(4/3)(1)[ln(1)]1/4

*Ewith the subscript of eO, and pO is the apparent activation energyobtained from the extrapolated onset temperature(Te) and the peak tempera-

ture(Tp) by Ozawas method.

3.2 Self-accelerating Decomposition Temperature

(TSADT)

The values(T00, Te0and Tp0) of the initial temperature point

at which DSC curve deviates from the base line(T0), onset


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518 CHEM. RES. CHINESE UNIVERSITIES Vol.28

(8)

temperature(Te) and peak temperature(Tp) corresponding to

0 were obtained by Eq.(2), and the self-accelerating de-

composition temperature(TSADT) was obtained by Eq.(3)[1015].

The values of T00, Te0(or TSADT) and Tp0 are 416.9, 459.6 and

481.5 K, respectively.T0(or e or p)=T00(or e0 or p0)+a+b

2+c3+d4 (2)

TSADT=Te0 (3)

where a, b, cand dare coefficients.

3.3 Thermal Ignition Temperature(TTIT) and

Critical Temperature of Thermal Explosion(Tb)

The thermal ignition temperature(Tbe0 or TTIT) was ob-

tained by substitutingEeOand Te0into Eq.(4)[9,10], and the criti-

cal temperatures of thermal explosion(Tbp0or Tb) was obtained

by substitutingEpOand Tp0into the equation. The values of TTIT

and Tbare 472.1 and 492.8 K, respectively. The values of Tbfor

NGEC show that the threshold for ignition and thermal explo-

sion is larger.2

O O O 0b

4

2

E E E RTT

R

= (4)

whereEOis the value of Eobtained by Ozawas method andR

is the gas constant.

3.4 Thermodynamic Parameters of Activation

Reaction

The entropy of activation(S), the enthalpy of activation

(H), and the free energy of activation(G) of the main exo-

thermic decomposition process corresponding to T=Tp0, A=AK,

and E=EKwere obtained by Eqs.(5)(7)[1113]. The values of

S, Hand Gare 114.5 J/(molK), 167.7 kJ/mol and 133.6

kJ/mol respectively. The positive vales of Gindicate that the

exothermic decomposition of NGEC must proceed under the

heating condition.

B expk T S

Ah R

=

(5)

Bexp exp expk TE S H

ART h R RT

=

(6)

= STHG

(7)where kBis the Boltzman constant and his the Plank constant.

3.5 Specific Heat Capacity

Fig.4 shows the determination results of the specific heat

capacity of NGEC by a continuous specific heat capacity mode

of Micro-DSCIII apparatus. It can be seen that the Cpof NGEC

presents a good linear relationship with temperature in the de-

termined temperature range. And the specific heat capacity

equation is obtained by the result. It is shown as Eq.(8).

Cp=1.2856.276103T+1.581105T2

(283 K


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No.3 XU Si-yuet al. 519

The specific heat capacity equation of NGEC is

Cp=1.2856.276103T+1.581105T2(283K

thermal behavior and thermal safety of nitrate glycerol ether cellulose

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