Thermal Degradation Kinetics of a Linked Polyureth

Testing and Evaluation

Jianfu Chen,1,2Weiying Zhang,1Xiao Li,1and Yimin Chen2

DOI:10.1520/JTE20120251

Thermal Degradation Kinetics of a Linked Polyurethane Acrylate Film

VOL.42/NO.2/MARCH2014

Jianfu Chen,1,2Weiying Zhang,1Xiao Li,1and Yimin Chen 2

Thermal Degradation Kinetics of a Linked Polyurethane Acrylate Film

Reference

Chen,Jianfu,Zhang,Weiying,Li,Xiao,and Chen,Yimin,“Thermal Degradation Kinetics of a Linked Polyurethane Acrylate Film,”Journal of Testing and Evaluation ,Vol.42,No.2,2014,pp.298–304,doi:10.1520/JTE20120251.ISSN 0090-3973

ABSTRACT

Linked polyurethane-acrylate (LPUA)emulsions with good stability were synthesized by seed swelling emulsion polymerization.We then investigated the thermal degradation process of the LPUA film by means of thermogravimetry-derivative thermogravimetry (TG-DTG)at different heating rates.It was shown that the heating rate had obvious influence on the thermal weight loss of LPUA.Both the starting and ending temperatures of decomposition shifted to a higher temperature with increased heating rate.The most probable kinetic parameters of decomposition were obtained from the Coats-Redfern integral equation and Achar differential equation.It was shown that the optimum

mechanism functions of the decomposition reaction were 3D diffusion,spherical symmetry,D4,and deceleration type a–t curve.The thermal decomposition mechanism function of the LPUA film was f ða Þ¼3=2½ð1Àa ÞÀ1=3À1 À1;G ða Þ¼ð1À2a =3ÞÀð1Àa Þ2=3.Keywords

linked polyurethane-acrylate,thermal degradation kinetics,model fitting method

Introduction

Thermal analysis kinetics allows measuring the change in a material’s physical feature with tem-perature in order to obtain the kinetic information of this dynamically changing process [1].The popular thermal analysis technologies include DSC,DTA,and TG [2].Due to the reaction kinetic information hidden in the recorded thermal analysis curves,the related kinetic parameters can be obtained from mathematical treatment for the reaction curves.

When heated in an oxygen atmosphere experience,polymeric materials change their physical mechanism and degrade in long term usage due to aging.Therefore,it is necessary that polymeric materials possess excellent thermal stability [3–5].Thermal decomposition includes various

Manuscript received August 17,2012;accepted for publication August 8,2013;published online January 21,2014.

1

College of Chemistry and Chemical Engineering,Fuzhou Univ.,Fuzhou Fujian 350108,China (Corresponding author),e-mail:lxzwy@126.com 2

Dept.of Food and Biology Engineering,Zhangzhou Institute of Technology,Zhangzhou Fujian 363000,China.

Copyright V C 2014by ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.298

Journal of Testing and Evaluation

doi:10.1520/JTE20120251/Vol.42/No.2/MARCH 2014/available online at www.astm.org

Journal of Testing and Evaluation 300

measure the typical FT-IR spectra of the dried LPUAfilm.As seen in Fig.1,the spectrum showed absorption bands at 3350cmÀ1for the N-H stretching that reveals the hydrogena-tion of the N-H on the carbamido was essentially complete.It also implied the hydrogenation of acrylate modified polyur-ethane could push an orderly arrangement in a hard segment of a polyurethane molecular chain.The absorption bands at 2960cmÀ1were for the C-H stretching vibration of methyl and methylene.The IR spectrum also indicated the completion of reaction between di-isocyanate and polyol by disappearance of-NCO absorption band at2750and1850cmÀ1.Bands at 1730and1600cmÀ1were for the carbonyl stretching absorp-tion and-COOÀantisymmetric stretching.Bands at1150and 940cmÀ1were the characteristic peaks of methyl methacrylate and butyl acrylate,respectively,that suggested that LPUA had both features of polyurethane molecules and acrylate molecules.THERMAL DECOMPOSITION OF THE LPUA FILM

Figures2and3demonstrated the TG and DTG curves of LPUA film under N2environment at different heating rates.

The experimental results showed that there were two weight loss stages in the thermal decomposition process at dif-ferent heating rates and the weight loss peak moved to a higher temperature with increased heating rate.According to the ther-mal analysis,on one hand,the movement of the molecular chain became more active with increased temperature.On the other hand,the increased temperature transferred heat through the media–container–sample.The temperature difference was developed between the oven and the sample and temperature gradients were formed inside the sample.This nonequilibrium process and the temperature differential became more

TABLE1Classification of kinetic mechanisms of thermal decomposition[11,20].

Functions Mechanisms f(a)G(a)

1Mampel power rule power function m¼1/44a3/4a1/4

2Mampel power rule power function m¼1/33a2/3a1/3

3Mampel power rule power function m¼1/22a1/2a1/2

4Mampel power rule power function m¼11a

5Parabola rule1D diffusion1/(2a)a2

6Valensi Eq2D diffusion[Àln(1Àa)]À1aþ(1Àa)ln(1Àa) 7Ginstling-Broushtein Eq3D diffusion,spherical symmetry,D4,deceleration type a–t curve(3/2)[(1Àa)À1/3À1]À1(1À2a/3)À(1Àa)2/3 8Avrami-Erofeev Eq Random nucleation and subsequent growth n¼1/2,m¼22(1Àa)[Àln(1Àa)]1/2[Àln(1Àa)]1/2

9Avrami-Erofeev Eq Random nucleation and subsequent growth n¼1/3,m¼33(1Àa)[Àln(1Àa)]2/3[Àln(1Àa)]1/3 10Avrami-Erofeev Eq Random nucleation and subsequent growth n¼1/4,m¼44(1Àa)[Àln(1Àa)]3/4[Àln(1Àa)]1/4 11Phase boundary reaction Contraction cylinder2(1Àa)1/21À(1Àa)1/2

12Phase boundary reaction Contraction cylinder3(1Àa)2/31À(1Àa)1/3

13Chemical reaction First order reaction1ÀaÀln(1Àa)

14Chemical reaction Third order reaction(1Àa)3/22[(1Àa)À1/2À1] 15Chemical reaction Second order reaction(1Àa)2(1Àa)À1À1

FIG.1FT-IR spectra of the dried LPUAfilm.FIG.2The TG plots employed for studying the effect of heating rate:

a¼5 C/min;b¼10 C/min;and c¼20 C/min.

CHEN ET AL.ON THERMAL DEGRADATION KINETICS301

pronounced with increased heating rate,the movement of mo-lecular chain,and its decomposition energy reflected indirectly the relation between the relaxation of the molecular chain and

temperature.Due to the nature of thermal decomposition being the same under various heating rates the DTG curve was chosen to analyze the thermal decomposition kinetics of the LPUAfilm.

TG KINETICS CALCULATION

Freeman-Carroll Method

Combining the TG-DTG curves of the LPUAfilm,the thermal decomposition activation energy E and reaction order n were calculated by the Freeman-Carroll method.This method does not require preknown or assumptions of the reaction order and it can greatly simplify kinetic analysis.Its advantage is to calcu-late E in a thermal decomposition stage based simply on a noni-sothermal TG curve.The basic data from TG-DTG curves of the thermal decomposition of LPUAfilm are given in Table2.

Table3gives the results from the Freeman-Carroll method for LPUA.The calculated deviations of activation energies were minimal at three heating rates,the average E was206.81kJ/mol, and the reaction order n was1.311.

Kissinger Method

Based on Figs.2and3,the thermal decomposition temperature of the LPUA at the maximum weight loss velocity at different heating rates could be obtained.From the plot of ln(b/T p2)ver-sus1/T p,the value of E was calculated as141.93kJ/mol as the slope in Fig.4,ln A is equal to24.16from the intercept of the regression line in Fig.4,and the relation coefficient R as 0.99823.

Flynn-Wall-Ozawa Method

The apparent activation energy was estimated by the Flynn-Wall-Ozawa model and the results are shown in Table4.When a was within0.1to0.9,the E value increased monotonically from112.04to171.93kJ/mol.The average value of E was 148.46kJ/mol.

THE MOST PROBABLE MECHANISM FUNCTION

Based on thermal decomposition TG and DTG curves of the LPUAfilm,Coasts-Redfern integral formula and Achar differ-ential method were used tofit the kinetic data from15mecha-nism functions that are shown in Table1and thefitting results shown in Tables5and6.

Compared with the results in Tables5and6that were cal-culated from the Coasts-Redfern integral formula and Achar differential method,we found that the E and ln A from the two methods were quite close to each other with the best relation coefficients when using the No.7function from Table1.There-fore,according to the judging basis of the most probable mecha-nism function,thermal decomposition mechanism functions of the LPUAfilm were as follows:

FIG.3The DTG plots employed for studying the effect of heating rate: a¼5 C/min;b¼10 C/min;and c¼20 C/min.TABLE2Basic data from TG-DTG curves of the thermal decompo-sition of the LPUAfilm.

Heating

Rate b,

C minÀ1

Weight

Loss W a d a/dT t, C1/TÂ103,1/K 50.390.4101570.79734368.26 1.55907

0.4980.512962 1.1029378.846 1.53375

0.597770.614626 1.27035387.041 1.51471

0.69970.719440 1.2217395.056 1.49654

0.80.8225480.9596004.041 1.47669 100.399260.4290380.876777385.094 1.51919

0.4998660.537147 1.19467394.781 1.49716

0.5930.3599 1.348402.438 1.48019

0.697950.75 1.311409.77 1.43

0.79460.858533 1.04853418.093 1.44667 200.3992330.4226020.788052400.255 1.48499

0.49910.528319 1.082310.942 1.46179

0.598140.63315 1.242419.343 1.44406

06984760.739361 1.24775427.236 1.42778

0.80.846820.987188436.075 1.40999

TABLE3The kinetic parameters obtained by using the Freeman-Carroll method.

b, C/min Kinetic Parameter Value Average Standard Deviation 5E,kJ/mol206.54206.81 4.41 10211.35

20202.55

5n 1.538 1.3110.197

10 1.196

20 1.199

Journal of Testing and Evaluation 302

f ða Þ¼3=2½ð1Àa ÞÀ1=3À1 À1G ða Þ¼1À2a =3ðÞÀ1Àa ðÞ2=3

The functions were 3D diffusion,spherical symmetry,D4,and deceleration type a–t curve.

The differential formula of mechanism function was f(a ),where b ¼dT /dt ,E ¼168.34kJ/mol,and ln A ¼26.67.The aver-age values in Table 7were introduced into Eq 4,the thermal decomposition kinetic differential equations of the LPUA film could be obtained as

d a dt

¼5:73Â1011

ð1Àa Þ

À1=3À1h i À1e À20:25

T Conclusions

(1)The thermal decomposition process of the LPUA film

at different heating rates was studied by using TG and DTG methods.The results showed that the heating rate greatly affected the weight loss of the LPUA thermal and both the starting and ending temperature shifting to a higher temperature with the increased heat-ing rate.

FIG.4Curve f

ln(b /T p 2)

versus 1/T p .

TABLE 4The kinetic parameters obtained using the Flynn-Wall-Ozawa method.

T ,K

Average

a b ¼5

C/min b ¼10

C/min b ¼20

C/min E ,kJ/mol E ,kJ/mol

0.1539.400560.9575.403113.13148.46

0.2580.958601.520615.363112.040.3622.347638.584656.709130.330.40.183654.965670.547154.750.5650.8356.934681.550158.110.6659.076672.5716.961160.810.7666.679679.443697.4661.330.8675.009686.535705.112170.710.9

687.193

692.475

715.803

171.93

TABLE 5The calculated results by using the Coats-Redfern equa-tion for different solid state reaction mechanisms for the decomposition of the LPUA film.Number Correlation Coefficient

SD E ,kJ/mol

ln A 1À0.993370.003637.21À3.422À0.9960.0047413.25À1.753À0.998010.0069725.348.234À0.998710.0136661.628.265À0.9930.02704134.1621.766À0.999590.01998159.5226.147À0.999590.02133170.2826.778À0.997240.0157748.69 6.159À0.996580.0103928.8 2.0110À0.9950.007718.86À0.2211À0.999460.0117982.6211.9112À0.99910.0167790.639.6913À0.997720.03191108.2417.7914À0.994590.06308138.6623.8615

À0.99095

0.10247

173.7

31.28

TABLE 6

The calculated results by using Achar equation with dif-ferent solid state reaction mechanisms for the decompo-sition of the LPUA film.Number Correlation Coefficient

SD E ,kJ/mol ln A 10.449680.1654719.13À2.8120.324080.1663313.08À1.4630.025760.168080.99 1.0À0.663140.1733935.288.115À0.930870.18427107.8221.526À0.977710.14442154.4529.87À0.986870.12416174.232.078À0.980740.0761187.7718.059À0.9470.08167.9114.0310À0.949460.0834657.9811.9311À0.959070.117491.3218.1612À0.979380.0988111021.3313À0.995370.06194147.3629.5814À0.999860.01499203.440.3215

À0.99885

0.05429

259.44

51.05

TABLE 7Kinetic parameters obtained by using different methods.

Methods

E ,kJ/mol ln A

Freeman-Carroll 206.81Kissinger

141.9324.16Flynn-Wall-Ozawa 148.46Coats-Redfern 170.2826.77Achar 174.232.07Average

168.34

26.67CHEN ET AL.ON THERMAL DEGRADATION KINETICS 303

differential equation,the most probable mechanism function for the LPUAfilm was identified as3D diffu-sion,spherical symmetry,D4,and deceleration type a–t curve.The thermal decomposition mechanism functions of the LPUAfilm were fðaÞ¼3=2½ð1ÀaÞÀ1=3À1 À1;

GðaÞ¼ð1À2a=3ÞÀð1ÀaÞ2=3.

(3)According to model calculation,the average E was equal

to168.34mol/l and the thermal decomposition kinetic differential equation of the LPUAfilm was as follows:

d a dt ¼5:73Â1011ð1ÀaÞÀ1=3À1

h iÀ1

eÀ20:25T

ACKNOWLEDGMENTS

This project was supported by the major project of regional sci-ence and technology of Fujian Province(No.2009H4005).

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