Abstract
This paper demonstrates the application of a modified Avrami equation in the analysis of crystallisation curves obtained using differential scanning calorimetry (DSC). The model incorporates a square root of time dependence of the secondary process into the conventional Avrami equation and, although previously validated using laser flash analysis and infrared spectroscopy, is not currently transferable to DSC. Application of the model to calorimetric data required long-duration isotherms and a series of data treatments. Once implemented, the square root of time dependence of the secondary process was once again observed. After separation of the secondary process from the primary, a mechanistic n value of 3 was obtained for the primary process. Kinetic parameters obtained from the analysis were used in the model to regenerate the fractional crystallinity curves. Comparison of the model with experimental data generated R2 values in excess of 0.995. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was used as model polymer due to the prominent secondary crystallisation behaviour that this polymer is known to display.
Highlights
IntroductionThe method developed by Hillier [20] assumes an initial constant radial growth of spherulites, followed by a first-order increase in crystallinity at time θ
Poly(3-hydroxybutyrate) (PHB) and its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) have shown promise as sustainable and biodegradable alternatives to current oil-derived, single-use plastics [1]
The mechanical properties can be improved by rapidly cooling the polymer to yield microstructure that is composed of relatively small spherulites, but to enable this, knowledge of the crystallisation kinetics is required [9]
Summary
The method developed by Hillier [20] assumes an initial constant radial growth of spherulites, followed by a first-order increase in crystallinity at time θ This leads to the standard Avrami equation for the primary process (Equation (1)) and a modified version for the secondary process (Equation (2)). On completion of the primary process, the crystallisation n rate will depend solely on the square root of time as the term e−Zp t becomes negligibly small This leads to the following equation: Xt = Xp,∞ (1 + ks t1/2 ). PHBV was chosen as it is well known to display secondary crystallisation over time [7,8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
