Insight into glass transition of cellulose based on direct thermal processing after plasticization by ionic liquid
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Ionic liquid plasticized cellulose (IPC) materials were prepared with microcrystalline cellulose (MCC) and 25–70 wt% 1-butyl-3-methylimidazolium chloride (BmimCl) by direct thermal processing. Their chemical, morphological and crystalline structures were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction, and their glass transition behaviors and mechanical properties were discussed. The results show there is no chemical reaction between cellulose and the ionic liquid. BmimCl only acts as a plasticizer to improve the thermal processability of MCC, the IPC materials show only one glass transition terrace and can be processed repeatedly. Based on the free volume transition and the percolation of continuous hydrogen bonding networks, the effects of free volume and H-bonding interactions on the glass transition have been differentiated. Furthermore, the phase diagram with four regions has been plotted for IPC materials, which is useful to optimize the thermal processing and modulate the properties of cellulose materials.
KeywordsCellulose Ionic liquid Plasticization Thermal processing Hydrogen bonding Glass transition
Glass transition temperature
Ionic liquid plasticized cellulose
Fourier transform infrared spectroscopy
Differential scanning calorimetry
Scanning electron microscopy
- G-T/K-B equation
The authors acknowledge the financial support of the National Basic Research Program of China (973 Program, 2012CB025903), the National Natural Science Foundation of China (51210004, 51373060) and the Chinese Ministry of Education (NCET-11-0174). We also thank the Analytical and Testing Center of HUST for SEM and XRD measurements.