Polyethylene Avrami exponent

Acronyms and variables cold crystalhzation (CC) cobalt molybdenum catalyst (CoMoCAT) chemical vapor deposition (CVD) dichlorobenzene (DCB) high-pressure carbon monoxide (HiPCO) isotactic polypropylene (iPP) melt crystalhzation (MC) melt flow index (MFl) poly( -caprolactone) (PCL) polydispersity index (PDD polyethylene (PE) polyethylene oxide (PEO) poly (ethylene-propylene-diene) [P(E-PP-diene)] poly(ethylene 2,6-naphthalate) (PEN) poly(ethylene terephthalate (PET) poly(L-lactic acid) (PLLA) poly(trimethylene terephthalate (PTMT) poly(vinyl alcohol) (PVA) 1,1,2,2-tetrachloroethane (TCE) tetrahydrofuran (THE) weight-average molecular weight = ] number-average molecular weight Avrami exponent for neat polymer = Avrami exponent for CNT composite = Avrami rate constant for neat polymer = Avrami exponent for composite = neat polymer crystalhzation... 

Eder and Wlochowicz [192] crystallized PE at constant cooling rates ranging from 0.5 to 10°C/min. Their experimental data did not conform to the theoretical treatment developed by Ozawa [177]. The authors attributed the deviation from the equation to factors such as secondary crystallization (for polyethylene it may be greater than 40% of the total [140]), dependence of the lamellar thickness on crystallization temperature, and occurrence of different mechanisms of nucleation. However, it is worth commenting that the occurrence of different kinds of nucleation would not affect the validity of Ozawa s equation, but only the value of the Avrami exponent. 

Godovsky et al. found Avrami exponent values of 2 0.6 for the polyethylene glycols studied. The Avrami equation. 

Results from extensive dilatometric measurements of the crystallization of polyethylene from the melt are shown in Fig. 3.100. Without normalization, the data for different molar masses are first matched to Avrami curves of different exponents. Higher molar mas ses seem to fit better to lower exponents, but deviate earUer from the calculated curves. At later times the crystallization is not described by the Avrami expression. It is then governed by secondary crystallization within the spherulites. 

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