The effect of a secondary process on crystallization kinetics – Poly (є-caprolactone) revisited

Phillipson, Kate; Jenkins, Michael J.; Hay, J. N.

doi:10.1016/j.eurpolymj.2016.09.037

Cited by 16 publications

(23 citation statements)

References 13 publications

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“…In the limited polymer system we studied, the same conclusions concerning primary and secondary crystallization were made, which are contrary to observations in the literature . In particular, we found the following.…”

Section: Introductioncontrasting

confidence: 97%

“…We have argued that rate is limited by the sensitivity of the detectors while with direct measurement crystallinity can always be detected provided you are prepared to wait long enough for the change. In the past micro‐dilatometers were successfully used but, with improved software and better analytical procedures, computer control and improved detectors, Fourier transform infrared spectroscopy coupled with a thermostatted hot stage can have the necessary accuracy to measure the development of crystallinity over extended periods …”

Section: Introductionmentioning

confidence: 99%

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The role of a secondary process in polymer crystallization: 4 − Polyethylene revisited

Hay

2018

Polymer International

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It is suggested that the overlap of primary and secondary crystallization is a cause of the repeated observation of non‐integer n values in polymer crystallization. The possibility that two concurrent crystallization processes occurring during the crystallization of polyethylene may account for anomalous fractional values of the Avrami exponent, of no theoretical significance, is reconsidered using data from the classical paper by Banks et al. (Polymer 4: 61 − 74 (1963)) on the kinetics of crystallization of polyethylene fractions which placed emphasis on evaluating the secondary crystallization stage. In general constant n values in excess of that expected for the crystallization mechanisms can readily be interpreted in terms of the additional crystallinity developed by the secondary process and these values increase commensurate with the rate constant of secondary crystallization. Constant n values close to but below n = 4.0 are interpreted as due to the presence of an induction period present in the presence of homogeneous nucleation. It is not possible to separate the effect of incorporating both an induction period, lowering the value of n, and secondary crystallization, raising the value of n, in the kinetic equation. © 2017 Society of Chemical Industry

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Section: Introductioncontrasting

confidence: 97%

Section: Introductionmentioning

confidence: 99%

The role of a secondary process in polymer crystallization: 4 − Polyethylene revisited

Hay

2018

Polymer International

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“…More recently, Hay et al further evaluated the secondary crystallisation kinetics of poly(ethylene terephthalate) (PET) [22] and poly(caprolactone) (PCL) [26] and derived a different approach to the previous authors. Hay noted that the models discussed above indicated a dependence of log (X s , t ) on time; however, the opposite is seen when plotting the data [26]. Through a series of experiments on PET and PCL, Hay discovered a square root time dependence on the growth of lamella stem length following primary crystallisation [19,27].…”

Section: Introductionmentioning

confidence: 99%

“…In addition, as the thickness of the lamellae is greater at the centre of the spherulite, it was postulated that secondary crystallisation occurs as soon as the lamellae has been formed and proceeds with and beyond the primary process [22]. These factors have led to the formation of a new model for the crystallisation of polymers, which has been validated using infra-red spectroscopy [22,26] and laser flash analysis [28].…”

Section: Introductionmentioning

confidence: 99%

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The Effect of a Secondary Process on the Analysis of Isothermal Crystallisation Kinetics by Differential Scanning Calorimetry

et al. 2019

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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 R 2 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.The crystallisation kinetics of a polymer are generally described by the following Avrami equation [15]:where X p,t is the fractional primary crystallinity; X p,∞ is the final primary crystallinity; Z p is the Avrami primary crystallisation rate constant; t is time and n an integer combining values attributed to both the geometry and mechanism of nucleation. Although this equation is widely used, it often generates non-integer n values. In addition, it does not take into account the secondary crystallisation process, which has been proven to occur during polymer crystallisation [16][17][18][19]. Numerous authors have proposed modifications to the Avrami equation to account for these issues, with the most notable being Hillier [20,21], Velisaris [17] and Hay [22].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)) in which the n exponent is taken as 1:where X s,t−θ is the fractional crystallinity formed after time θ; X s,∞ is the final fractional crystallinity; and z s is the secondary rate constant. These two equations can then be combined to give an expression for the total crystallinity at time t. X t = X p,t + t 0

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Volumetric Printing of Thiol‐Ene Photo‐Cross‐Linkable Poly(ε‐caprolactone): A Tunable Material Platform Serving Biomedical Applications

et al. 2023

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Current thoroughly described biodegradable and cross‐linkable polymers mainly rely on acrylate cross‐linking. However, despite the swift cross‐linking kinetics of acrylates, the concomitant brittleness of the resulting materials limits their applicability. Here, photo‐cross‐linkable poly(ε‐caprolactone) networks through orthogonal thiol‐ene chemistry are introduced. The step‐growth polymerized networks are tunable, predictable by means of the rubber elasticity theory and it is shown that their mechanical properties are significantly improved over their acrylate cross‐linked counterparts. Tunability is introduced to the materials, by altering Mc (or the molar mass between cross‐links), and its effect on the thermal properties, mechanical strength and degradability of the materials is evaluated. Moreover, excellent volumetric printability is illustrated and the smallest features obtained via volumetric 3D‐printing to date are reported, for thiol‐ene systems. Finally, by means of in vitro and in vivo characterization of 3D‐printed constructs, it is illustrated that the volumetrically 3D‐printed materials are biocompatible. This combination of mechanical stability, tunability, biocompatibility, and rapid fabrication by volumetric 3D‐printing charts a new path toward bedside manufacturing of biodegradable patient‐specific implants.

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The effect of a secondary process on crystallization kinetics – Poly (є-caprolactone) revisited

Cited by 16 publications

References 13 publications

The role of a secondary process in polymer crystallization: 4 − Polyethylene revisited

The role of a secondary process in polymer crystallization: 4 − Polyethylene revisited

The Effect of a Secondary Process on the Analysis of Isothermal Crystallisation Kinetics by Differential Scanning Calorimetry

Volumetric Printing of Thiol‐Ene Photo‐Cross‐Linkable Poly(ε‐caprolactone): A Tunable Material Platform Serving Biomedical Applications

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