A KINETIC ANAYSIS OF THE DEGRADATION OF GRAFTED ANIONIC POLYACRYLAMIDE GEL UNDER NONISOTHERMAL CONDITION

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1 Joural of gieerig Sciece ad Techology Vol. 4, No. 4 (2009) School of gieerig, Taylor s Uiversity College A KINTIC ANAYSIS OF TH DGRADATION OF GRAFTD ANIONIC POLYACRYLAMID GL UNDR NONISOTHRMAL CONDITION AYMAN ABO JABAL, ISA M. TAN, ZAKARIA MAN, SAIKAT MAITRA* Dept. of Chemical gieerig, Uiversiti Tekologi PTRONAS Badar Seri Iskadar, Trooh, Perak Darul Rizua, Malaysia *Correspodig Author: drsaikat_maitra@petroas.com.my Abstract Grafted aioic polyacrylamide gel has bee sythesised i the laboratory followig radical polymerisatio process. Kietics of thermal degradatio of sythesised gel was evaluated uder oisthothermal coditio by itegral approximatio method to determie the thermal stability of the material from thermogavometric study. The activatio eergy for the thermal degradatio was foud to be sigificatly high for the gel material. Keywords: Grafted aioic, Polyacrylamide gel, No isothermal kietics, Itegral Approximatio kietics, Thermal Degradatio. 1. Itroductio The kietics of the thermal decompositio ad degradatio of solid state materials is a highly complex ad frequetly cotroversial subject [1]. The practical importace of the subject, however, has lead to a very extesive effort to uderstad the mechaisms which cotrol such reactios. xtesive studies have bee carried out o the o-isothermal decompositio kietics of solid systems. Multiple techiques were cited i literature for determiig the reactio mechaism ad deducig the kietic parameters [2]. Solid state reactios follow complex pathway compared to liquid ad gas phase reactio. While the liquid ad gas phase reactios ca be described by order based kietics, the solid phase reactios i most of the cases follow complex diffusio or iterface cotrolled mechaism. The ifluece of heat ad mass trasfer o the phase boudaries are also to be take ito accout for such reactios. Several thermoaalytical techiques are ofte used to follow the course of solid state reactios ad amog 364

2 A Kietic Aalysis of The Degeeratio of Grafted Aioic Polyacrylamide Gel 365 Nomeclatures A Pre-expoetial factor, s -1 A o Pre-expoetial factor at 0 K, sec -1 Activatio eergy, kj/mol g(α) Itegral kietic fuctio k Reactio rate costat, s -1 m Temperature depedece of pre-expoetial factor Reactio order R Gas Costat, kj/mol/k T Reactio temperature, K w Weight at ay time, g w o Iitial weight, g Fial equilibrium weight, g w Greek Symbols α β Fractio of reactio Heatig rate, o C/mi these thermo-gravimetry (TG) is the most commo techique [3]. I differet thermoaalytic techiques, properties like heat absorptio, chage i temperature, chage i weight etc of the material are measured as a fuctio of temperature or time [4]. I thermogravometry the chage i weight is recorded as a fuctio of time or temperature for isothermal ad o- isothermal cases, respectively. May works have bee cited i the literature o the kietic studies of thermal degradatio of polymeric materials. Friedma [5] developed a kietics equatio for rate law ad kietic parameters to describe the thermal degradatio of plastic for TGA data. The equatio was successfully tested by several techiques, icludig coformatios with costat temperature data that were available i the literature. Nam ad Seferis [6] developed a composite methodology for multistage degradatio of polymer. This exteded methodology established aalytical schemes for describig complex decompositio of polymer i ratioal maer, icorporatig both experimetal ad theoretical cosideratios. Aderso ad Freema [7] used the o-isothermal method of Freema ad Carroll to ivestigate of the kietics of thermal degradatio of polyethylee ad polystyree. The authors compared the results of their ivestigatio with the kietics parameters reported by other ivestigatio for the decompositio of these polymers. Wag et al [8] studied the kietics of cotiuous thermal degradatio of poly (styree alkyl alcohol) i supercritical fluid. They iterpreted the kietics results by a mathematical model based o the cotiuous kietics for specific ad radom degradatio process, ad obtaied activatio eergies i the rage of kcal/ mole for specific degradatio process ad 35 kcal/mole for radom degradatio process. Stuggs [9] developed a theoretical framework for characterisig sigle step Arrheius degradatio kietics i terms of a characteristic temperature rage. The author developed a estimate of the average or steady mass loss rate which fully accouted for the iteractio betwee the Joural of gieerig Sciece ad Techology December 2009, Vol. 4(4)

3 366 Ayma Abo Jabal et al. degradatio kietics, the exteral heat flux, the heat losses ad the latet heat of vaporizatio. Madras et al [10] studied the ultrasoic degradatio of polystyree ad poly (viyl acetate) i chlorobezee ad developed a model that successfully simulated the umber average molecular weight, the polydispersity of the degraded polymer ad the time evolutio of the molecular weight distributio. Lee et al [11] studied the thermal degradatio of poly(hexamethylee guaidie) phosphate by dyamic thermogravimetric aalysis ad pyrolysis GC-MS. The authors used Coats-Redfer [16] methods to ivestigate the degradatio mechaisms at differet stages. Grafted aioic polyacrylamide gel (GAPAMG) fids lots of importat applicatios, like fire extiguishig compositio, fillers ad reiforcig aget [12]. I the preset ivestigatio, GAPAMG was sythesized at the laboratory. The thermal degradatio behaviour of GAPAMG is a importat parameter for its characterizatio i various applicatios. The proposed degradatio pathway of the material is give below [21] Although may works have bee doe o the degradatio kietics of differet polymers, o literature is presetly available o the thermal degradatio kietics of GAPAMG, particularly the mechaism of the degradatio. I the preset ivestigatio, therefore, the kietics of decompositio of GAPAMG has bee studied uder o-isothermal coditios usig thermo-gravimetry to determie the kietic parameters such as order of reactio (), activatio eergy () preexpoetial factor (A 0 ) ad mechaism of degradatio. Theory The fractioal degradatio of polymeric material ca be expressed i terms of weight chage i the followig way wo w α = (1) w w o where w o, w ad w, are the iitial, at ay istat durig thermal aalysis ad fial weight of the samples, respectively. Decompositio reactio is expressed i terms of order based reactio kietics, the it ca be writte as: dα dt ( 1 α) = k (2) i.e, the rate of reactio is proportioal to the th power of u-decomposed part of the sample. The power is cosidered as the order of the reactio ad k is specific reactio rate. But the specific reactio rate is a fuctio of temperature which ca be expressed by Arrheius equatio k = Ae (3) where is the activatio eergy of the reactio. Substitutig k from q. (3) ito q. (2) results i the followig equatio: Joural of gieerig Sciece ad Techology December 2009, Vol. 4(4)

4 A Kietic Aalysis of The Degeeratio of Grafted Aioic Polyacrylamide Gel 367 dα = Ae dt ( 1α ) After separatig the variables from q. (4) the followig equatio ca be obtaied (4) dα ( 1α) = Ae dt (5) dt The rate of heatig β = or dt dt dt = (6) β Puttig the expressio of dt i q. (5) ad itegratig betwee limits T 1 ad T 2 T2 dα A = e ( 1α) β T1 dt Itegratig betwee limits α T2 dα A = e ( 1α β 0 ) T1 dt (7) (8) But the itegral at the right side T2 e T1 dt has o aalytical solutio. Therefore several approximate solutios of the equatios are available i literature [13-16]. I the preset ivestigatio the solutio give by Coats ad Redfre [16] was used to determie the kietic parameters of the degradatio reactio. The approximate solutio of the itegral as per this method is like the followig ( α ) l 1 AR 2 l = T l 1 2 β ad 1 l l 2 ( 1α ) AR ( ) T 2 = l 1 1 β (for = 1) (9) (for 1) (10) AR 2 If it is assumed that the expressio l 1 remais costat [17] β over the temperature rage of degradatio the the equatio assumes a liear form. Joural of gieerig Sciece ad Techology December 2009, Vol. 4(4)

5 368 Ayma Abo Jabal et al. l Therefore, a plot of 1 l ( 1α ) ( ) 1 T 2 l 1 l 2 T ( α ) vs. 1/T for =1 ad vs. 1/T for 1 gives the value of from the slope(-/r) AR 2 ad value of A from the itercept l 1 [18]. β 2. Materials ad Methods 2.1. Sythesis of GAPMAG Sythesis of GAPMAG was carried out by radical polymerizatio usig acrylamide moomer (.Merck), potassium persulphate (Aldrich) ad urea (Aldrich). 30 %(w/v) acrylamide was dissolved i distilled water ad residual oxyge was removed by itroge bubblig through the solutio for 45 miutes uder stirrig at 25 C. The polymerizatio was iitiated by drop wise additio of 5% (w/v) aqueous solutio of potassium persulphate to the acrylamide solutio over a period of 5 miutes. The reactio temperature was maitaied at 60 C ad the ph of the solutios was adjusted to 9 with the additio of sodium dihydroge phosphate. The polymerizatio was coducted for a period of 3 hours. The fial viscous solutio was diluted to 3 times with water. The polymer was the isolated by precipitatio with ethaol-acetoe mixture ad the precipitated mass was dried uder vacuum at 60 o C for a period of 8 hours. The plausible reactios at the differet stages of the sythesis have bee show i Fig. 1. Fig. 1. The Proposed Schematic Reactio for Sythesis. Joural of gieerig Sciece ad Techology December 2009, Vol. 4(4)

6 A Kietic Aalysis of The Degeeratio of Grafted Aioic Polyacrylamide Gel Degradatio kietics of the material A weight of 0.5 g of the sample was take i the form of powder for the thermogravimetric (TG) study with a TG apparatus (Model Perkilmer Pyris 1 TGA). The weight chage of the samples were recorded as a fuctio of heatig temperature ad TG curves were obtaied at four differet heatig rates (5, 7.5, 10 ad 12.5 C/miutes) betwee 30 to 600 C; the precisio of reported temperatures was estimated to be ±2 C. 3. Results ad Discussio From the thermo-gravimetric curves (Fig. 2) it is apparet that there are three major iflectios i the decompositio at three differet temperature rages, 250 o C, 350 o C ad 450 o C. The first stage decompositio idicates the breakage of primary bods, secod stage idicates the breakage of secodary bods ad the third stage decompositio idicates the breakage of tertiary bods i the polymer structure [8]. The fractio decompositio values (α) were calculated from the thermo-gravimetric data ad the values cotiuously icreased with the icrease i temperature (Fig. 3). Weight loss (%) 5 o C/mi 7.5 o C/mi Temperature ( o C) Fig. 2. TGA Result for Aioic Polyacrlamide Gel with Differet Heatig Rates. Fractio of Decompositio (%) 7.5 o C/mi 5 o C/mi Temperature ( o C) Fig. 3. Fractio Decompositio (α) versus Temperature C. Joural of gieerig Sciece ad Techology December 2009, Vol. 4(4)

7 370 Ayma Abo Jabal et al. Usig differet values qs. (5) ad (6) were plotted as discussed above. From these plots the value, which resulted i the best correlatio coefficiet was selected as the order of the reactio. The activatio eergy ad the preexpoetial factors of the degradatio reactio were determied from the slope ad the itercept respectively of the liear plot for this particular value. By itegral approximatio method we have determied the activatio eergy ad reactio order for the degradatio assumig that the reactio follows a order based kietics. But i reality solid state reactios follow differet complex reactio mechaisms, like diffusio cotrolled, iterface cotrolled, ucleatio ad growth cotrolled etc. The actual mechaism of the degradatio reactio i this case was determied usig the method developed by Maitra et al [19]. I this method the itegral form of kietic fuctio is expressed i the followig form, ( ) = [ ] + k T T g α (11) 2 1 where, T 2 ad T 1 are the maximum ad miimum values of the temperature for the degradatio reactio. l{( A0 / T k = exp[ m ) / β} ( / m + 1 max ) ] (12) where A o is the pre-expoetial factor, m shows the temperature depedece of the expoetial factor. Cosiderig the validity of trasitio state theory the value of m was take as 1 [20]. The right had side of q. (11) therefore ca be evaluated at differet T values ad it is the compared with all possible g(α) fuctios with α values at these T s. A list of all possible g(α) values is listed i Table 1. ach of this fuctio describes the relevat mechaism for solid state reactios [22]. The fuctio that results miimum differece betwee the L.H.S ad the R.H.S is chose as the kietic fuctio of the cocered heterogeeous reactio. I the preset case it was foud to follow mostly two dimesioal diffusio cotrolled reactio (D 2 ). Table 1. Classificatio of Kietic Models for Reactio Mechaism [22]. Kietic classificatio g(α) = dα /ƒ(α) (1) Sigmoidal α-t curves Avrami-rofeev (A 2 ) [-l(1- α)] 3/2 Avrami-rofeev (A 3 ) [-l(1- α)] 1/3 Avrami-rofeev (A 4 ) [-l(1- α)] 1/4 Prout-Tompkis (B 1 ) [-lα(1- α)]+c (2) Acceleratory α-t curves Power law (P 1 ) α 1/ xpoetial Law ( 1 ) l(α) (3) Deceleratory α-t curves (3.1) Based o Geometrical Models Cotractig area (R 2 ) 1-(1-α) 1/2 Cotractig volume (R 3 ) 1-(1-α) 1/3 Joural of gieerig Sciece ad Techology December 2009, Vol. 4(4)

8 A Kietic Aalysis of The Degeeratio of Grafted Aioic Polyacrylamide Gel 371 Table 1. (cot d). Kietic classificatio g(α) = dα /ƒ(α) (3.2) Based o diffusio mechaism Oe-dimesioal (D 1 ) 1/2 α 2 Two dimesioal (D 2 ) (1-α)l(1-α)+ α Three Dimesioal (D 3 ) [1-(1-α) 1/3 ] 2 Gistlig-Broushtei (D 4 ) (1-2α/3)-(1-α) 2/3 (3.3) Based o order of reactio First-order (F 1 ) -l(1-α) Secod order (F 2 ) (1-α) -1 Third order (F 3 ) (1-α) -2 The results are show i Table 2. The decompositio reactios of the grafted polymer followed mostly 1.3 order reactio kietics. The reaso for fractioal order may be ascribed to the icomplete availability of the gel surface for degradatio, which ca be related to the coverage of the u-degraded gel particles with the decomposed products. So, the degradatio reactio of GAPAMG was likely to follow multi-stage process. The ucleatio ad growth of the decomposed product at the surface of the gel ad the diffusio of volatiles like, CO 2 ad other volatiles through the u-degraded material cotrols the rate of reactio. The activatio eergy for decompositio was foud to be quite high (94.43 kj/mol) compared to the data available for other polymers i literature [7-11]. The relatively higher value of activatio eergy for the degradatio reactio is idicative of the sigificat thermal stability of the gel. The value of the pre-expoetial factor was observed to be quite low ( s -1 ), which idicate the gel is relatively iert towards the formatio of thermally iduced activated complex. Table 2. Variatio i Stadard rror (S) for Grafted Aioic Polyacrylamide Gel (GAPAMG) with Differet Values. Correlatio Coefficiet (S) Joural of gieerig Sciece ad Techology December 2009, Vol. 4(4)

9 372 Ayma Abo Jabal et al. 4. Coclusios The degradatio kietics reactios of the grafted polymer was studied uder oisothermal coditio usig Coats ad Redfer itegral approximatio method was used to determied the kietics parameters. The degradatio kietics reactio of the gel followed mostly 1.3 order reactio kietics. The kietic fuctio for the degradatio reactio was also determied, which was foud to follow mostly two dimesioal diffusio cotrolled reactio. The activatio eergy for decompositio was foud to be quite high (94.43 kj/mol) compared to the data available for other polymers i literature which is a idicatio of relative thermal stability of the gel. Refereces 1. Maitra, S.; Badyopadhyay, N.; Das S.; Pal, A.J. ad Pramaik, J. (2007). No-isothermal decompositio kietics of alkalie earth metal carboate. Joural of the America Ceramic Society, 90(4), Vyazovki, S. ad Wight, C.A. (1997). Kietics i solids. Aual Review of Physical Chemistry, 48, Maitra, S. ad Dutta, B.K. (2008). Kietics of solid phase reactios. Idia Chemical gieer, 50(4), Vyazovki, S. (2000). Kietic cocepts of thermally stimulated reactios i solids: A view from a historical perspective. Iteratioal Reviews i Physical Chemistry, 19(1), Friedma, H.L. (1964). Kietic of thermal degradatio of char-formig plastics from thermogravometry. Applicatio to a pheolic plastic. Joural of Polymer Sciece Polymer Symposium, 6(1), Nam, J.D. ad Seferis, J.C. (1991). Composite methodology for multistage degradatio of polymer. Joural of Polymer Sciece: Part B, Polymer Physics, 29(5), Aderso, D.A. ad Freema,.S. (1961). The kietics of thermal degradatio of polyethylee ad polystyree. Joural of Polymer Sciece, 54(195), Wag, M.W.; Smith J.M. ad McCoy, B.J. (1995). Cotiuous kietics for thermal degradatio of polymer i solutio. AlCh Joural, 41(6), Staggs, J.. (1999). Modellig thermal degradatio of polymers usig sigle step first order kietics. Fire Safety Joural, 32(1), Madracar, G.; Kumar S. ad Chattopadhyay, S. (2000). Cotiuous distributio of kietics for ultrasoic degradatio polymer. Polymer Degradatio ad Stability, 69(1), Lee, S.; Ji, B.S. ad Lee, J.W. (2006). Thermal degradatio kietics of ati microbial aget, poly(hexamethylee guaidie) phosphate. Macromolecular Research, 14(5), Biswal, J.K.; Bhardwaj, V.; Goel, N.K.; Dubey, K.A.; Chaudhari, C.V. ad Sabharwal, S. (2007). Radiatio-iduced graftig of acrylamide oto guar gum i aqueous medium: Sythesis ad characterizatio of grafted polymer guar-gum-acrylamide. Radiatio Physics ad Chemistry,76(10), Joural of gieerig Sciece ad Techology December 2009, Vol. 4(4)

10 A Kietic Aalysis of The Degeeratio of Grafted Aioic Polyacrylamide Gel Tag, W.; Liu, Y.; Zhag, H. ad Wag, C. (2003). New approximate formula for Arrheius itegral. Thermochimica Acta, 408(1-2), Hsig, L.C. (1985). A itegral approximatio formula for kietic aalysis of o isothermal TGA data. AICh Joural, 31(6), Agarwal, R.K. ad Sivasubramaiam, M.S. (1987). Itegral approximatio for o-isothermal kietics. AICh Joural, 33(7), Coats, A.W. ad Redfer, J.P. (1964). Kietics parameters from thermogravimetric data. Nature, 201(1), Judd, M.D. ad Pope, M.I. (1972). ergy of activatio for the decompositio of alkalie earth carboates from thermo-gravimetric data. Joural of Thermal Aalysis, 4, Maitra, S.; Bustam, A. ad Dutta, B.K. (2008). A kietic model for the thermal decompositio of CaCO 3 ad MgCO 3. Proceedig of the Symposium of Malaysia Chemical gieers, (SOMChe), 4-5 th December, 2008, Kuala Lumpur. 19. Maitra, S.; Badyopadhyay, N.; Das, S.; Pal, A.J. ad Pramaik, J. (2007) No-isothermal decompositio kietics of alkalie earth metal carboates. Joural of the America Ceramic Society, 90(4), Shao, R.D. (1964). Activated complex theory applied to the thermal decompositio of solids. Trasactio of the Faraday Society, 60, Caulfield, M.J.; Qiao, G.G. ad Solomo, D.H. (2002). Some aspects of the properties ad degradatio of polyacrylamides. Chemical Reviews, 102(9), Brow, M..; Dollimore, D. ad Galwey, A.K. (1980). Reactios i the Solid State. I Comprehesive Chemical Kietics. ds., C.H. Bradford ad C.F.H. Tipper, Vol. 22, lsevier, Amsterdam, 340. Joural of gieerig Sciece ad Techology December 2009, Vol. 4(4)