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Dynamical characterization of a cellulose acetate polysaccharide
Miriam Sousa1, Ana Rita Brás, Helena Isabel M Veiga
1REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
The Journal of Physical Chemistry. B
|August 10, 2010
Summary
This study reveals how water content and polymer structure affect cellulose acetate
Area of Science:
- Polymer Science
- Materials Science
- Physical Chemistry
Background:
- Cellulose acetate (CA) properties are complex, with secondary relaxation mechanisms debated.
- Understanding these mechanisms is crucial for material applications.
Purpose of the Study:
- To investigate the molecular-level dynamics and structure of cellulose acetate.
- To clarify controversial secondary relaxation mechanisms in cellulose acetate.
- To compare the behavior of cellulose acetate with cellulose acetate structured as an asymmetric membrane (CAmb).
Main Methods:
- Dielectric relaxation spectroscopy (DRS) from 10(-1) to 10(6) Hz.
- Fourier-transform infrared spectroscopy (FTIR).
- Thermogravimetric analysis (TGA).
- Differential scanning calorimetry (DSC).
- Scanning electron microscopy (SEM).
Main Results:
- Two secondary relaxation processes (Process I and II) were identified in cellulose acetate below the glass transition temperature.
- Process I is significantly influenced by water content, showing plasticizing effects in CA compared to CAmb.
- Process II is less affected by water, exhibiting antiplasticizing effects upon hydration.
- Drying leads to a merged relaxation (gamma(dry)), which evolves slower in CA due to its more disordered structure.
- Annealing CAmb above 353 K causes skin densification and pore collapse.
Conclusions:
- Polymer arrangement and water uptake capacity dictate secondary relaxation behaviors.
- Hydration plasticizes cellulose acetate, enhancing molecular mobility.
- Water molecules can hinder side group motions through hydrogen bonding.
- Structural differences between CA and CAmb influence drying dynamics and water interaction.
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