Available online at www.sciencedirect.com PHYSICA A ELSEVIER Physica A358(200)212-217 www.elsevier.com/locate/physa TG and DSC studies of natural and artificial aging of polypropylene M.RjebA.LabzourA.RjebS.Sayouri Y.Claire,A.Perichaud Laboratoire de Chimle Macromolecaire.UMR CNRS6171 13397 Marselle Cedex20.Framce Available online 5 July 2005 Abstract natural one under the impact of the solar environment and the artificial one which was carie out by exposing the sample o radiations of a 100 W commerc degradation is more important in the artificial aging case than it is in the natural one and is an reasing tunction of aging.I prolonged and continu us therm d by th odpou evolution unn heating and coong of the samples.using the ho of the phase transition temperatures and the corresponding enthalpies of melting 2005 Elsevier B.V.All rights reserved. Keywrd:Polymer:Polypropylene:Aging:TG:DSC Coremponding athor. @yahoo.com(A.Rjeb)
Physica A 358 (2005) 212–217 TG and DSC studies of naturaland artificial aging of polypropylene M. Rjeba,b, A. Labzourb , A. Rjebb,, S. Sayouric , Y. Clairec , A. Pe´richaudc a Laboratoire de Physique Corpusculaire, Faculte´ des Sciences et Techniques, BP 2202 Fe`s, Morocco b Laboratoire de Physique The´orique et Applique´e, Faculte´ des Sciences DM, BP 1796 Fe`s Atlas, Morocco c Laboratoire de Chimie Macromole´culaire, UMR CNRS 6171 13397 Marseille Cedex 20, France Available online 5 July 2005 Abstract We study the evolution of thermal degradation of samples of polypropylene (PP), during their aging for two periods of 60 and 80 days. The study, using thermogravimetric analysis (TG) and differential scanning calorimetric (DSC) analyses, focused on two types of aging: the naturalone under the impact of the solar environment and the artificialone which was carried out by exposing the sample to radiations of a 100 W commercial lamp. The comparative study of these two types of aging shows that the thermaldegradation of the PP increases as a function of time of aging. Indeed, for a same duration, this thermal degradation is more important in the artificialaging case than it is in the naturalone and is an increasing function of aging. The prolonged and continuous thermal effect produced by the lamp, in the case of the artificial aging, weakened the polymer and implies very important acceleration of the process of degradation. The results obtained during heating and cooling of the samples, using the DSC, show an evolution of the phase transition temperatures and the corresponding enthalpies of melting and crystallization. r 2005 Elsevier B.V. All rights reserved. Keywords: Polymer; Polypropylene; Aging; TG; DSC ARTICLE IN PRESS www.elsevier.com/locate/physa 0378-4371/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physa.2005.06.023 Corresponding author. E-mail address: arjeb@yahoo.com (A. Rjeb)
M.Rjeb et al Physica A358(2005)212-217 213 1.Introduction The polymer material industry is today showing great expansion due to the ion.Pur chers in the area e of nufacture polym are ofter the The photo-oxidation phenomenon during the natural aging process has been recently studied extensively [1-5].It was shown that oxygen has a great impact vis-a- vis polymers,that is capable of producing varieties of species oxygenated on the surface of polypropylene (PP). During the last decades,various studies concerning thermal polymer degradation have been carried out [6-10],focusing mainly on the kinetic study of the degradation under inert or oxygenated atmosphere,and,in particular,members of our research group have studied the aging of PP by thermogravimetric(TG).thermal differential (TD)and differential scanning calorimetric (DSC)analyses [11.121. Recently.we investigated.using xPS and infrared s ectroscopy (IR)methods [1.21,the natural aging of PP during a period of five years.whose chemical formula is (CH2-CH(CH3) As a cons we have that is the on the of PP,incre nng t the aging proces th -0 the oxidation o e surface by th breaking of C-H bonds [1.3.13-16]. 2.Experimental procedure TG and TD experiments were performed using a SETARAM TGA 92 apparatus. by a debit of compressed air of 20 ml/min.Crucibles (reference and sample)were of silica type.During experiments,we begun with a constant temperature of 25C for a few minutes,then we increased the temperature from 25 to 650C with a heating rate of 10C/min.followed by a cooling stage till 50C with a cooling rate of 90C/min Sizes of the PP samples studied (Cambridge mark).manufactured in France.with unspecified purity and weighing approximately 35mg.were approximately 21cm2 A SETARAM DSC 92 was e placedn used for the DSC measure n35 to mples weighing 7.5C nin cooled from 190 to 45C atmosphere of flowing air. In the present work,a comparative study using TG and DSC focused on two types of aging,one natural and the other artificial,of many PP samples.These samples were exposed,during two periods of time (60 and 80 days),either to both solar radiations and rain effects(with a temperature ranging between 5 and 30C),or to artificial radiations (sample placed in a dark room,about 10cm away from a commercial power lamp of 100 W,the measured temperature near the sample was 45C).A third untreated sample was kept as reference for this comparative study
1. Introduction The polymer material industry is today showing great expansion due to the numerous advantages and areas of application. Pure and applied researchers in these areas are of particular interest to manufacturers and researchers. Polymer materials are often used in the atmospheric environment and undergo multiple degradations during their aging. The photo-oxidation phenomenon during the naturalaging process has been recently studied extensively [1–5]. It was shown that oxygen has a great impact vis-a`- vis polymers, that is capable of producing varieties of species oxygenated on the surface of polypropylene (PP). During the last decades, various studies concerning thermal polymer degradation have been carried out [6–10], focusing mainly on the kinetic study of the degradation under inert or oxygenated atmosphere, and, in particular, members of our research group have studied the aging of PP by thermogravimetric (TG), thermaldifferential (TD) and differential scanning calorimetric (DSC) analyses [11,12]. Recently, we investigated, using XPS and infrared spectroscopy (IR) methods [1,2], the naturalaging of PP during a period of five years, whose chemicalformula is –[(CH2-CH(CH3)]n–. As a consequence, we have shown that oxygen, the element that is the major contaminant on the surface of PP, increases during the aging process. The mechanism of the photo-oxidation shows that radiations contribute to the oxidation of the surface by the breaking of C–H bonds [1,3,13–16]. 2. Experimental procedure TG and TD experiments were performed using a SETARAM TGA 92 apparatus, by a debit of compressed air of 20 ml/min. Crucibles (reference and sample) were of silica type. During experiments, we begun with a constant temperature of 25 C for a few minutes, then we increased the temperature from 25 to 650 C with a heating rate of 10 C/min, followed by a cooling stage till 50 C with a cooling rate of 90 C/min. Sizes of the PP samples studied (Cambridge mark), manufactured in France, with unspecified purity and weighing approximately 35 mg, were approximately 2 1 cm2. A SETARAM DSC 92 was used for the DSC measurements. PP samples weighing 15 mg were placed in a crucible, heated from 35 to 190 C with a heating rate of 7.5 C/ min and cooled from 190 to 45 C with a cooling rate of 3 C/min, in an atmosphere of flowing air. In the present work, a comparative study using TG and DSC focused on two types of aging, one natural and the other artificial, of many PP samples. These samples were exposed, during two periods of time (60 and 80 days), either to both solar radiations and rain effects (with a temperature ranging between 5 and 30 C), or to artificial radiations (sample placed in a dark room, about 10 cm away from a commercialpower lamp of 100 W, the measured temperature near the sample was 45 C). A third untreated sample was kept as reference for this comparative study. ARTICLE IN PRESS M. Rjeb et al. / Physica A 358 (2005) 212–217 213
214 M.Rjeb et al Physica A358(2005)212-217 3.Results and discussion TG curves corresponding to the naturally aged PP samples,during 80 days,named NA80(c).and 60 days,named NA60 (b),are shown in Fig.1.as well as the one corresponding to the nonexposed sample,named NE (a).The samples degrade in a single step from 275 to about 425C for the unaged sample,and to about 443C for the samples aged during 60 and 80 days. These curves represent the percentage of mass loss as a function of the tempe one n otices that the material that is more aged degrades all the m rapidly, and thus the end of degradation te mperat ase during the aging th e pe of the corr ng mas n or (Fig.(1) ang poncd e ge of mass loss,the corresponding temperature is a decreasing function Fig.1(2)shows the effect of the artificial aging on the PP sample.The same behavior observed in the case of the natural aging is present in that of the artificial aging(samples named AA60 and AA80 for the artificial aging during 60 and 80 days, respectively). Table I illustrates the diminution of the end of degradation temperatures observed for the two aging types. A comparative study of the influence of the duration of exposition on the degradation and therefore on the type of the PP aging,for the same duration,60 and (a) -40 (b) 60 300 350 400 450 1) 2 Tceofthethm deompPp amp ()andifc Table 1 End of degradation temperatureC of different PP samples:aged during 60,80 days and new sample Reference PP aged naturally PP aged artificially NE 60days 80 days 80 days 452.0 443.8 441.9 435.8 433.8
3. Results and discussion TG curves corresponding to the naturally aged PP samples, during 80 days, named NA80 (c), and 60 days, named NA60 (b), are shown in Fig. 1, as well as the one corresponding to the nonexposed sample, named NE (a). The samples degrade in a single step from 275 to about 425 C for the unaged sample, and to about 443 C for the samples aged during 60 and 80 days. These curves represent the percentage of mass loss as a function of the temperature; one notices that the materialthat is more aged degrades allthe more rapidly, and thus the end of degradation temperatures decrease during the aging process. Indeed, for the same temperature, the percentage of the corresponding mass loss is an increasing function of duration (Fig. (1)), and conversely, for the same percentage of mass loss, the corresponding temperature is a decreasing function (Fig.1(1)). Fig. 1(2) shows the effect of the artificialaging on the PP sample. The same behavior observed in the case of the naturalaging is present in that of the artificial aging (samples named AA60 and AA80 for the artificial aging during 60 and 80 days, respectively). Table 1 illustrates the diminution of the end of degradation temperatures observed for the two aging types. A comparative study of the influence of the duration of exposition on the degradation and therefore on the type of the PP aging, for the same duration, 60 and ARTICLE IN PRESS 275 300 325 350 375 400 425 450 475 -100 -80 -60 -40 -20 0 Mass loss (TG %) Temperature (˚C) 300 350 400 450 -100 -80 -60 -40 -20 0 (a) (a) (c) (b) (b) (c) Mass loss (TG %) Temperature (˚C) (1) (2) Fig. 1. TG curves of the thermal decomposition of PP: samples aged naturally (1) and artificially, (2) during 80 days, (c) 60 days (b) and new sample (a). Table 1 End of degradation temperature C of different PP samples: aged during 60, 80 days and new sample Reference PP aged naturally PP aged artificially NE 60 days 80 days 60 days 80 days 452.0 443.8 441.9 435.8 433.8 214 M. Rjeb et al. / Physica A 358 (2005) 212–217
M.Rjeb et al.Physica A358(2005)212-217 215 80 days (Fig.2).shows that the thermal degradation is important and more rapid in the case of the artificial aging than in the natural one for the 60 days period,with more emphasis for the 80 days period. Fig.3illustrates the DSC s for PP degradation under natural conditions (NA60 and NA80 sa mples)and artificial。 (AA60 and AA80 on heating and cooling of the samples Table 2 temperatur and the enthalpies variations (AH deduced from he analysis of thes curves. This table reveals that the parameter AH orresponding to melting and crystallization of the samples decreased,for the two types of aging,as a function of 20 20 b (b) 00 300 350 450 000 35d 400 Fie.2 TGu of the thermal dee n of PP for the e duration of 60(1)and 80 (2)days artificially (c).naturally(b)and new sample (a). 80100120140160180200 10012010160180 20 Temperature (C) Fig.3.DSC curves corresponding to the naturally (1)and artificially (2)aged samples
80 days (Fig. 2), shows that the thermaldegradation is important and more rapid in the case of the artificialaging than in the naturalone for the 60 days period, with more emphasis for the 80 days period. Fig. 3 illustrates the DSC curves for PP degradation under natural conditions (NA60 and NA80 samples) and artificial ones (AA60 and AA80 samples) obtained on heating and cooling of the samples. Table 2 gathers the phase transition temperatures and the enthalpies variations (DH) deduced from the analysis of these curves. This table reveals that the parameter DH corresponding to melting and crystallization of the samples decreased, for the two types of aging, as a function of ARTICLE IN PRESS -100 -80 -60 -40 -20 0 Mass loss (TG %) -100 -80 -60 -40 -20 0 Mass loss (TG %) 300 350 400 450 (a) (b) (c) (a) (b) (c) Temperature (˚C) 300 350 400 450 (1) (2) Temperature (˚C) Fig. 2. TG curves of the thermaldecomposition of PP for the same duration of 60 (1) and 80 (2) days: artificially (c), naturally (b) and new sample (a). -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 60 80 100 120 140 160 180 200 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 Exo Cooling Heating Heating Heating Heating curves curves curves Cooling Cooling curves PP new PP new PPna60 PPna60 PPna80 PPna80 Heat flow (a.u) Heat flow (a.u) Heat flow (a.u) Heat flow (a.u) Temperature (˚C) Temperature (˚C) 60 80 100 120 140 160 180 200 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 Cooling Exo (1) (2) Fig. 3. DSC curves corresponding to the naturally (1) and artificially (2) aged samples. M. Rjeb et al. / Physica A 358 (2005) 212–217 215
216 M.Rjeb et al Physica A358(2005)212-217 Table2 AH and the correspo ing temperatures of melting and crystallization for the two types of aging of PP samples PP new PP na60 PP na80 PP aa60 PP aa80 68.03 62.49 48.66 59.26 51.09 6.46 -60.81 -61.6( -71.87 -57.7 166 122 126.34 127.53 126.56 Te onset (C) 155.1 160.3 162. 185.1 Tg (C) 67.82 103.13 81.83 91.97 presence of an amorphous state,increases during the aging period,for the two types of aging. 4.Conclusion TG and DSC analyses have been used to study two aging types,of the polypropylene(PP).during two periods,60 and 80 days.The first is natural under solar radiations and rain effects,and the second is artificial by exposition to the light of a 100 W commercial lamp types shows that the polymer material degrades all the and thus the of the end of degradation the 09o uoranposd degradation is important,more pronounced in the case of the artificial aging than in the natural one,especially for the period of 80 days.The prolonged and continuous thermal effect caused by the lamp does weaken the polymer in the case of the artificial aging compared to the natural one,where the phenomenon of oxidation, that leads,nevertheless,to a continuous and progressive degradation of the polymer, allows this one to better resist the process of degradation. Concerning the study of the two types of aging using the DSC technique,the results obtained during heating and cooling of the samples show a similar evolution of the phase transition temperatures and the corresponding enthalpies of melting and crystallization. Acknowledgements
the aging process; however, the corresponding temperatures (Tf and Tc) show a slight increase. Moreover, the glass transition temperature (Tg), which indicates the presence of an amorphous state, increases during the aging period, for the two types of aging. 4. Conclusion TG and DSC analyses have been used to study two aging types, of the polypropylene (PP), during two periods, 60 and 80 days. The first is natural under solar radiations and rain effects, and the second is artificial by exposition to the light of a 100 W commerciallamp. The study of the two aging types shows that the polymer material degrades all the more rapidly the more it is aged, and thus the evolution of the end of degradation temperatures is decreasing with more emphasis in the artificialcase. The comparative study of the influence of the duration of the aging processes, 60 and 80 days, on the degradation and on the type of PP aging shows that the thermal degradation is important, more pronounced in the case of the artificialaging than in the natural one, especially for the period of 80 days. The prolonged and continuous thermal effect caused by the lamp does weaken the polymer in the case of the artificialaging compared to the naturalone, where the phenomenon of oxidation, that leads, nevertheless, to a continuous and progressive degradation of the polymer, allows this one to better resist the process of degradation. Concerning the study of the two types of aging using the DSC technique, the results obtained during heating and cooling of the samples show a similar evolution of the phase transition temperatures and the corresponding enthalpies of melting and crystallization. Acknowledgements The experimentalpart was done at the Laboratoire de Chimie Macromole´culaire Universite´ de Provence, 3 place V. HUGO, F -13331 Marseilles Cedex 3. Our thanks ARTICLE IN PRESS Table 2 Parameters DH and the corresponding temperatures of melting and crystallization for the two types of aging of PP samples PP new PP na60 PP na80 PP aa60 PP aa80 DHf (J/g) 68.03 62.49 48.66 59.26 51.09 DHc (J/g) 56.46 60.87 61.66 71.87 57.71 Tf peak (C) 165.62 171.89 173.21 171.4 171.57 Tc peak (C) 122.67 122.28 123.73 123.76 122.77 Tf onset (C) 126.58 126.34 127.53 127.5 126.56 Tc onset (C) 155.1 156.15 160.34 162.5 185.15 Tg (C) 67.82 93.81 103.13 81.83 91.97 216 M. Rjeb et al. / Physica A 358 (2005) 212–217
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