(Au gus t 1] , 1966)Theoreti ca l equ a ti o ns ar e de ve lo pe d for typi cal decompositions of polyme rs including th ose in whi c h the vola tilization does not folJ ow a simpl e "re action orde r" a nd those made up of a composite of seve ral reac tions of diffe rin g e ne rgies of ac tivation. The e ffects of orde r, activation ene rgy, heatin g ra te and te mpe ra ture de pe nd e nce upon th e calc ulated th ermogram s is illu strated. The lite rature on th ermogravim e tri c kine ti cs is c riti cally re vi ewed and coalesced into a logi cal and cohere nt de velopme nt stressin g the inte rrelation of me th ods a nd e mplo yin g a co ns iste nt sys te m of nota tion . As a res ult , a nu mbe r of impro ved me th ods and ne w me thod s for the a nalys is of kineti c data a ppli ca ble to th e co mpl e x sys te ms me nti oned a bove are developed . It is co nc lu de d th at me thods involvin g a va riabl e rate of hea tin g or invo lving seve ra l the rm ogra vime tri c traces at d iffe re nt ra tes of hea tin g a re capa bl e of es tabli s hing th e unique ness of kine ti c pa ra me te rs. A ne w me th od of de te rminjn g init ial pa ra me te rs from rate·conve rs ion data is de veloped . A novel co nce pt is e mpl oyed of programmin g reac ti on va ri a bles (i n thi s case, th e heatin g ra te) in a ma nne r whi c h great ly simplifies th e mathe mati cs of the kin e ti c s'ys te m and whic h shows pro mise of a wide ra nge of a pp lj ca bilit y in th e area of rate processes. Ke y Word s : Degrad a tion, no ni sothe rm al kine ti cs, polyme rs, pyrolys is, th e rm a l deco mp os iti o n, th e rmogra vim e try, th e rm olys is, sta bilit y of po lyme rs.
The isoconversional method for the determination of energies of activation from the reciprocal temperature at which a fraction of conversion was reached in experiments at differing constant heating rates is reviewed and amplified. The error introduced into the calculation of activation energy by the use of a linear approximation of the logarithm of the temperature integral is discussed. Methods for the correction of this error are developed and a table of correction factors are given.Since its formulation by Ozawa.[1] and independently by Flynn and Wall [2], the isoconversional method has been used extensively to calculate energies of activation from thermoanalytical experiments at constant heating rate. Its popularity is due mainly to its capability of yielding activation energies without the necessity of one positing what often turn out to be incorrect models for the reaction mechanism. Such an incorrect model for the relationship between rate and conversion will give a grossly incorrect value for the activation energy since temperature and fraction conversion are changing simultaneously in nonisothermal experiments [3].The use of Doyle's linear approximation of the temperature integral [4] often introduces a sizable error in the activation energy calculated from the isoconversional method. This was pointed out in the 1966 paper by Flynn and Wall [2], and an iterative method was given to correct for this error. It has been made obvious by a high frequency of inquiries about the above correction method that its explanation was inadequate in the original letter [2]. Therefore, we shall briefly review the isoconversional method, discuss the errors involved in the linear approximation of the logarithm of the temperature integral, and develop a method for improving the accuracy of this approximation in a more simple and comprehensible manner. With the increased sensitivity of modern thermoanalytical equipment, activation energies are often calculated to an imprecision of less than one percent. It will be demonstrated that errors in the calculation of activation energy using the Doyle approximation in many cases will be considerably greater than these experimental limits of precision.
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