ࡱ> SUR @H-bjbj5*5* $NW@W@ 4444444Hppp8\\Hllllllll$R":]4lllll:44llDDDl4l4lDlDD44Dl` @fbpND0D#(#DHH4444#4DllDlllll::HH$ l DHHl KINETIC ANALYSIS OF THE ISOTHERMAL DEGRADATION OF PHB/OMMT NANOCOMPOSITES Matko Erceg*, Tonka Kova i, Ivka Klari Faculty of Chemistry and Technology, Department of Organic Technology, Teslina 10/V, 21 000 Split, Croatia * E-mail: merceg@ktf-split.hr; tel: ++ 385 21 329 459; fax: ++385 21 329 461 Polymer nanocomposites consisted of biodegradable poly(3-hydroxybutyrate) (PHB) and organically modified montmorillonite Cloisite25A (OMMT) as nanofiller with compositions PHB/OMMT 100/0, 100/1, 100/3, 100/5, 100/7 and 100/10 by weight were prepared by solution intercalation method [1]. These samples were degraded isothermally for 120 min at 230, 235, 240 and 245C in the nitrogen atmosphere. The addition of OMMT increases the thermal stability of PHB. The most pronounced effect has the addition of 7 wt. % of OMMT where the occurrence of the constant mass plateau is shifted for 30 min to longer degradation times compared to pure PHB. The kinetic triplets (activation energy, E; pre-exponential factor, A; kinetic model g(a)) of the isothermal thermogravimetric (TG) degradation of pure PHB and PHB/OMMT nanocomposites are obtained without making any assumption about g(a). For the determination of kinetic triplets the so called reduced time plots (RTP) method is used. This method is broadly used in solid state kinetics [2]. Each theoretical g(a) [3] has unique RTP plot and the true g(a) of the investigated process can be obtained by comparison of the experimental RTP curves with the theoretical ones. Isothermal degradation of PHB/OMMT nanocomposites occurs through mechanism described with Avrami-Erofeev kinetic model g(a)=[-ln(1-a)]1/n. To calculate the values of parameter n, i.e. empirical kinetic models, this expression is introduced into logarithmic form of general kinetic equation, lnt = ln[g(a)] -lnk. From the slope and intercept of the plots lnt vs. ln[-ln(1-a)] parameter n and reaction rate constants, lnk for each degradation temperature are obtained, respectively. By plotting -lnk vs. 1/T, a straight line is obtained and(6 8 x  - / S a I M R T j w , ӻӳ˳Ӡ˘ˠxphhh-mH sH h)=mH sH h^a mH sH hNpmH sH hRYmH sH himH sH hTCmH sH he9+hJmH sH hmH sH hMgmH sH h}mH sH he9+mH sH hJmH sH he9+he9+mH sH he9+he9+5mH sH hdhe9+5mH sH hMg5mH sH (x . / B'D'' (((2(J(b(h(( $$Ifa$gdTgde9+$a$gde9+D-F-, - 6 [ x  r"$(*,0bXźЂŚŲzrjh:mH sH h\mH sH hJmH sH h>7mH sH he9+hbr:6OJQJmH sH he9+hbr:6mH sH he9+h6mH sH hbr:mH sH he9+hmH sH he9+he9+mH sH hmH sH h)=mH sH h mmH sH hmH sH himH sH h-mH sH &X^bl퍹qqf^VhR[mH sH h9kmH sH h9k6H*mH sH hh6OJQJmH sH hh6mH sH hmH sH h\mH sH he9+he9+6OJQJmH sH he9+he9+6mH sH hahmH sH he9+hT6OJQJmH sH he9+hT6mH sH h mmH sH hTmH sH he9+he9+mH sH h\cymH sH !,.0n"$(*,.8<>Zvz|̼̼ܰxxxog[h mh m6mH sH h mmH sH h m6mH sH he9+he9+mH sH hNlmH sH hahh9k6OJQJmH sH hahh9k6mH sH hah6mH sH hahhah6mH sH hkmH sH hahmH sH h9kmH sH h7emH sH h:mH sH hR[hR[6mH sH hR[mH sH hmH sH  n$ $$&$:$<$>$F$H$L$N$l$$$ǿ㠬yph`hkmH sH h>7mH sH h8j6mH sH hh6mH sH Uhd6mH sH hNlmH sH h9kmH sH he9+he9+6mH sH he9+he9+mH sH h mmH sH hmH sH hh m6mH sH hR[mH sH himH sH h mh m6mH sH h mh m6OJQJmH sH # from its slope and intercept E and lnA are calculated, respectively. The values of kinetic triplets (E, lnA, g(a)) obtained by RTP method are shown in Table 1. Eiso values are obtained by model-free integral isoconversional method, i.e. without assumption of g(a). The results in Table 1 show that E values obtained by RTP method are almost identical to Eiso values, what proofs the correctness of kinetic analysis. Table 1. Values of kinetic parameters obtained by RTP and integral isoconversional methods PHB/25AConversion, ag(a)E / kJmol-1lnA / min-1r2Eiso / kJmol-1100/010-90[-ln(1-a)]1/3,33111,123,09610,99482107,9100/110-90[-ln(1-a)]1/3,54136,929,01160,99581136,3100/330-90[-ln(1-a)]1/4,28123,725,84400,99818123,4100/530-90[-ln(1-a)]1/3,98118,824,56190,99669118,8100/730-90[-ln(1-a)]1/3,15101,520,22660,99769101,9100/1040-90[-ln(1-a)]1/1,9996,719,60630,9942997,5 [1] M. Erceg, T. Kova i, I. Klari, J. Appl. Poly, Sci. (in press) [2] S. Vyazovkin, C. A. Wight, Thermochim. Acta 340-341 (1999) 53-68. [3] K. Pielichowski, J. 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