A Fast Estimation of Activation Energy of Low Density Polyethylene (LDPE) Widad H. Jassim Department of Physics /College of Education for Pure Science( Ibn Al- Haitham) ,University of Baghdad Received in :18 November 2013, Accepted in : 2 February 2014 Abstract A dynamic experimental study of thermal decomposition of low density polyethylene has been carried out with two different heating rates .As usual , we can determine the activation energy of any polymer using( 3 - 6 ) TGA experiment as minimum , but in this work , we estimate the activation energy of LDPE using two of TGA experiments only. Key words : Low density polyethylene (LDPE), activation energy ,thermal decomposition and thermogravimetric analysis . 128 | Physics @a@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹127@@ÖÜ»€a@I2@‚b«@H2014 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 27 (2) 2014 Introduction The determination of activation energy of a polymer is very useful since its used to predict the kind of a polymer using the thermo gravimetric analysis (TGA) which is the one of the members of the family of thermal analysis techniques used to characterize a wide variety of materials. There have recently appeared several publications which describe some methods of estimation activation energy for the thermal decomposition of polymers using two methods : Flynn -Wal l-Ozawa (FWO) and Kissinger - Akahira – Sunose (KAS) [1-6] . These methods are time - consuming and involve curve fitting , a prior knowledge of reaction order and type of kinetic process in addition to using between (3-6) curves of thermo-gram of polymer degradation with different heating rates [7,8]. In present work , we can overcome some of these objections and estimate the activation energy of low density polyethylene using only a two curves of thermogravimetry with two different heating rates ,so we can get a rapid estimation of activation energy for any polymer. Experimental We cut two samples of the same water pipe which is made of low density polyethylene and characterize them by thermogravimetric teqnique, where this polymer is heated from temp. (approx. 23 oC) to 600 oC, the weight of samples is loss with time /temperature . These samples with weight (30 - 35 mg) are heated with heating rate (5 oC/min ) for the first sample and (9 oC / min ) for the second. In (TGA) a thermo balance is used to measure the mass change of a sample as a function of temperature or time . The thermal decomposition of polymer is generally assumed to be as in eq.(1) A( solid ) → B( volatiles ) + C( solid ) ----------------(1 ) [ 4 ] The rate of polymer degradation is generally assumed to be proportional to the concentration of reactants which is defined as r = - dα/ dt -----------------------------( 2 ) [9 ] Where : dα /dt is the rate of mass loss α is the fraction of material reacted We may write - ≈∫ α α αα o nd / RTE T e A / 0 −∫ β dT ----------------(3) [4,10] So we can write 129 | Physics @a@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹127@@ÖÜ»€a@I2@‚b«@H2014 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 27 (2) 2014 - ≈∫ α α αα o nd / RTEe E RTA / 2 )( − β ------------------- (4) Where : A is the exponential factor ( sec-1 ) β is the heating rate R is the universal gas constant ( 8.314 J/mole .oK) T is the absolute temperature (oK ) Utilizing two thermo grams for the same material possessing different heating rates ( β ) we can write 21 /2 22 /2 11 )/(/)/(/ RTERTE eERTAeERTA −− = ββ ----------------(5) Or ) 11 (])(ln[ 21 2 2 1 1 2 TTR E T T −= β β ---------------------(6) So ) 11 ( ])(log[303.2 21 2 2 1 1 2 TT T T R E − = β β ----------------------(7 Where E is the activation energy of a polymer. Results and Discussion Displayed in figures 1 and 2 are the TGA results generated on the LDPE at an applied heating rate β1 ( 5 oC/min ) and β2 (9 oC/min ) respectively , these plots show the mass loss as a function of temperature . To get the conversion levels in weight , we must take the percent of mass loss as a function of temperature as in figures 3 and 4 , where the conversion level 20% is at 80 of weight% and the decomposition temperatures T1 is 435 oC for the first sample at heating rate 5 oC/min as in (figure 3) and T2 is 448 oC/min for the second sample at heating rate 9 oC/min as in (figure 4) then all the decomposition temperatures (T1 and T2 ) are fixed at any conversion levels as in table 1 , where the decomposition temperatures are pushed to higher with the increase of the heating rate and the conversion rate ,which agreed with [5]. From TGA results and using equation 7 , the activation energy of LDPE can be established as in table 2 , where the activation energy is changed with temperature . In figure (5) , we can see that the activation energy began to be constant at conversion rate 30% so this conversion level is very suitable to get the value of activation energy in our work . The activation energy of LDPE is (215 – 221 KJ/ mol) using the friedman , Kissinger - Akahira –Sunose and Flynn - Wall- Ozawa [2,11] but in our study the activation energy of LDPE is a bout 227 KJ / mole , because the activation energy is influenced by estimation method and the operating condition [12]. Conclusion 1- The value of activation energy depends on conversion levels. 2-The decomposition temperatures increase with the increase of the heating rate. 3- The advantage of this method is to consume relatively little time. 4- The conversion level 30% is suitable to estimate the activation energy . 5- We can estimate the activation energy of any polymer using two curves of TGA only. 130 | Physics @a@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹127@@ÖÜ»€a@I2@‚b«@H2014 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 27 (2) 2014 6- As future work , we can use this method to predict the kind or the grade of a polymer in some applications that we do not know the kind of polymers that are made. References 1. Sergey Vyazovkin and Charles , A.Wight (1999 ) Kinetics of thermal decomposition of Cubic Ammonium perchlorate , Chem. Mater , 11, 3386-3393 . 2.Aboulkas , A.; harfi, K.E.L and Bouadila, A.EL (2010) Thermal degradation behaviors of polyethylene and polypropylene , Energy conversion and Management ,51, 1363-1369. 3. Elena ,V.Bystritskaya ; Oleg N.Karpukhin and Alla, V.Kutsenova (2011) Simulation of Linear polymer thermal depolymerization under Isothermal and dynamic modes , International Journal of polymer science.2011 , 6. 4.Almustapha, M.N. and Andresen, J.M (2011) catalytic conversion of high density Polyethylene polymer as a means of recovering valuable energy content from the plastic wastes , International conference on petroleum and sustainable development . 26 , press, Singapore. 5.Aigbodion ,V.S. ;Hassan , S.B.; Atuanya and Atuanya , C.U. (2012) Kinetics of Isothermal Degradation studies by thermogravimetric data , J.Mater .Environ. Sci 3 ( 6 ):1027-1036. 6. Goswami , S . and Kiran ,K .(2012) Application of Kissinger analysis to glass transition and study of thermal degradation kinetics of phenolic - acrylic , Bull. Mater. Sci. , 35(4):657-664. 7.Jelica zelic; leticija Ugrina and Drazan Jozic(11th-13th) (2007) Application of thermal methods in the chemistry of cement: kinetic analysis of portlandite from non – iso thermal thermogravimetirc data , The first International proficiency testing conference. 8.Jean – Louis Dirion , Cedric Reverte and Michel Cabassud (2008) Kinetic parameter Estimation from TGA : Optimal design of TGA experiment Chemical Engineering research and design ,86 , 618 – 625. 9.Guo, J. and Lua ,Ac (2001) Kinetic study on pyrolytic process of oil- palm solid wate using Two-step consecutive reaction model , Biomass and Bionergy , 20 , 223-233. 10. Reich ,L. and Levi ,D.W.,(1963) Evaluation of Rate Constants from TGA , Chem., 66 , No.102 11.Celina, M. ,Gillen ,K.T and Assink ,R.A.(2005), Accelerated aging and lifetime Polymer degradation and stability ,90 , pp.395-404. 12.Malek ,J.; Mitsuhashi, T. and Criado ,J.M .(2001) Kinetic analysis of solid- state Processes , Journal of Materials Research , 16 , 1862-1871. 131 | Physics @a@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹127@@ÖÜ»€a@I2@‚b«@H2014 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 27 (2) 2014 Table No.(1): The decomposition temperatures at different conversion levels at two heating rates for (LDPE) Rate 9 ( oC.min-1 ) Rate 5 ( oC.min-1) Conversion levels % T2 (oK ) T2 ( oC ) T1 (o K ) T1 (oC ) 721 448 708 435 20 735 462 726 453 30 743 470 732 459 40 748 475 735 462 50 759 486 743 470 60 Table No.(2): The values of activation energies at different conversions levels of (LDPE ) 60 50 40 30 20 Conversion levels % 160.19 193.9 228.56 227.10 179.81 Activation energy (KJ. mol-1) 132 | Physics @a@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹127@@ÖÜ»€a@I2@‚b«@H2014 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 27 (2) 2014 .Figure1.Low density polyethylene decomposition with heating rate 5c0/min .Figure 2.Low density polyethylene decomposition with heating rate 9 co/min .Figure 3.the percentage decomposition with different conversion levels at heating rate 5 c0/min 0 10 20 30 40 0 100 200 300 400 500 600 w ei gh t( m g) Temp.(c O) Rate 5 0 10 20 30 40 0 100 200 300 400 500 600 w ei gh t ( m g) temp. (c0 ) Rate 9 0 20 40 60 80 100 120 0 100 200 300 400 500 600 W ei gh t% Temp.(c) rate 5 133 | Physics @a@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹127@@ÖÜ»€a@I2@‚b«@H2014 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 27 (2) 2014 .Figure 4. the percentage decomposition with different conversion levels at heating rate 9co/min .Figure 5.the relation of activation energy with different conversion levels 0 20 40 60 80 100 120 0 100 200 300 400 500 600 W ei gh t % Temp.(c ) Rate 9 0 50 100 150 200 250 0 10 20 30 40 50 60 70 E (K J/ m ol ) Conversion levels% 134 | Physics @a@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹127@@ÖÜ»€a@I2@‚b«@H2014 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 27 (2) 2014 )LDPEالحساب السریع لطاقة التنشیط للبولي أثیلین واطئ الكثافة( وداد حمدي جاسم جامعة بغداد / )ابن الھیثم ( للعلوم الصرفة كلیة التربیة /قسم الفیزیاء 2014شباط2، قبل البحث في 2013تشرین الثاني 18استلم البحث في : الخالصة درست دینامیكیة التحلل الحراري للبولي أثیلین واطئ الكثافة بشكل عملي باستخدام أثنین من معدالت التسخین المختلفة . عادة نستطیع أن نحسب طاقة التنشیط ألي بولیمر باستخدام ما بین ثالث إلى ست تجارب للتحلیل الحراري للبولي أثیلین واطئ الكثافة باستخدام البحث تمكنا من حساب طاقة التنشیط) حدا أدنى ولكن في ھذا TGAالوزني ( . اثنین من ھذه التجارب اقة التنشیط ، التحلل الحراري ، التحلیل الحراري الوزني.) ،طLDPEالكلمات المفتاحیة:البولي أثیلین واطئ الكثافة ( 135 | Physics @a@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹127@@ÖÜ»€a@I2@‚b«@H2014 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 27 (2) 2014