ADVERTISEMENT

The Kinetics Of Melting And Recrystallization Using Normal Differential Scanning Calorimeter

The Differential scanning calorimeter (DSC) is a widely applied tool to study the thermal behavior of various materials, including melting and recrystallization. However, it is not an easy task to interpret the DSC results of polymer lamellar crystals since they will melt, recrystallize and remelt during heating. Consequently, the endothermal and exothermal peak are combining results with melting and recrystallization. In addition, the baseline is difficult to determine.

Our research group (Prof. Xuā€™s group, Tsinghua University, Beijing, China) has developed a method to extract the kinetics of melting and recrystallization via step-heating program using normal DSC. The samples were originally isothermally crystallized for sufficient time. The following step-heating program consists of alternative heating and temperature holding stages, which allows for melting and recrystallization, respectively.

ADVERTISEMENT

The results show that the studied poly(butylene succinate) homopolymers and copolymer show different recrystallization behavior. The homopolymer, whether of low or high molecular weight, demonstrate considerable recrystallization. In contrast, the block copolymer does not exhibit observable recrystallization.

Even for the block copolymer without recrystallization, melting occurs at several heating stages, which may reflect the different stability of the isothermally crystallized polymer lamellar crystals. Poly(butylene succinate) homopolymers isothermally crystallized at lower temperatures can show 2 to 4 recrystallization exotherms during step heating, which is hard to distinguish using the normal DSC with continuous heating.

The kinetics of the most obvious melting, recrystallization and remelting have been quantitatively fitted via physical models. It is of particular interest that the remelting shows quite different power law index y of the superheating.Ā  The y value for the melting of the originally formed crystals ranges from 5 to 9, much larger than the values, around 1, for the remelting of the recrystallized crystals.

Previously, Toda et al. (Toda, A., Androsch, R., and Schick, C., Polymer, 2016, 91: 239) observed that melting of the lamellar crystals of different polymers shows the different power-law indices. This is the first report that the different crystals of the same polymer show such large difference in melting kinetics. We suspect that the difference may result from different mechanisms of stabilization during crystallization and recrystallization, which deserves further study.

ADVERTISEMENT

The recrystallization kinetics was fitted as well. The results show that the recrystallization follows the law of the secondary nucleation after melting a considerable part of the originally formed crystals.

To summarize, we have developed a new method to study the phase transitions, melting, recrystallization and remelting, of polymer lamellar crystals using normal DSC. The results reveal that the metastability of polymer lamellar crystals varies with the thermal history and physical constraints of the neighboring chain segments.

The study,Ā Study on melting and recrystallization of poly(butylene succinate) lamellar crystals via step heating differential scanning calorimetry was recently published in theĀ Chinese Journal of Polymer Science.

Comments

READ THIS NEXT

A Wolf Was Spotted In Belgium For The First Time In Over A Century

Indicating itsĀ hopeful recovery,Ā a Eurasian wolf has been seen in the forests of Belgium for the first time in 100 years. […]

Ultra-Precise Measurements Of Electron Field Shape Confirms Standard Model Of Particle Physics

A new experiment allowing scientists to measure an electron to a previously unprecedentedĀ level of precision has offered novel insight into […]

Peridynamic Unit Cell For HomogenizationĀ 

Composite materials are inherently anisotropic and heterogeneous at the micromechanical scale, and its microstructure provides the bridge between manufacturing and […]

The Unusual Cellulose Utilization System Of Cytophaga hutchinsonii

Cellulose, a component of the plant cell wall, is the most abundant renewable organic resource on Earth. Cellulose is insoluble […]

One-way Sound Propagation: Breaking Acoustic Reciprocity In 2D Materials

Phononic materials with elastic or acoustic ļ¬elds that travel simultaneously in space and time have been shown to break elastodynamic […]

Wild Winds On Neptune

Neptuneā€™s upper atmosphere contains some of the fastest winds in the solar system, reaching speeds upwards of 400 m/s (900 […]

A Network Of Possibilities Beyond Age

When we are young, visual stimuli in the outer world ā€” faces, objects, scenes ā€” seem slow. But as we […]

Science Trends is a popular source of science news and education around the world. We cover everything from solar power cell technology to climate change to cancer research. We help hundreds of thousands of people every month learn about the world we live in and the latest scientific breakthroughs. Want to know more?