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Periodate oxidation of cellulose for internal plasticization and materials design

Abstract : Cellulose, an abundant and renewable polymer, offers an interesting biosourced alternative to replace petrosourced thermoplastics commonly used in our everyday life. However, cellulose cannot be used in industrial thermoforming processes since its melting temperature is higher than its degradation temperature. Derivatives such as cellulose acetate show glass transition and melting temperatures below the thermal decomposition but still require the addition of external plasticizers to be processable. These plasticizers can exude over time, making the materials brittle and causing environmental issues due to the release of potentially toxic molecules.The present work proposes to introduce internal plasticization of cellulose, by increasing both the flexibility of the chains and the free volume using a grafting strategy, thus preventing exudation. To achieve this goal, a two-steps strategy was followed: first, a periodate oxidation was performed to cleave the glucose ring and generate aldehyde groups, resulting in dialdehyde cellulose (DAC). Second, the highly reactive aldehyde groups were used to graft plasticizing agents.The periodate oxidation of cellulose was first studied by varying parameters such as the amount of oxidant, the reaction time or the temperature, in order to precisely map the reaction conditions leading to a controlled degree of oxidation. To characterize DAC samples, an accurate and reliable quantification method based on solid-state nuclear magnetic resonance (13C CP-MAS NMR) has been developed and compared to other methods from the literature. The reduction of DAC led to colloidally stable hairy neutral nanorods suspensions, which were characterized by a combination of structural investigation techniques (light and X-ray scattering, transmission electron microscopy and turbidimetry). Casting of the suspensions led to thermoplastic films with a core-shell nanocomposite structure. Reductive amination of DAC with different amines also led to thermoplastic materials. The thermo-mechanical properties of all these materials were studied by solid-state NMR, dynamic mechanical analysis, differential scanning calorimetry and thermogravimetric analysis. Results show that materials produced from this strategy have a Tg inversely proportional to DO, between 122 and 65 °C, depending on the DO and the modification. This strategy is promising for the synthesis of processable thermoplastic materials from cellulose.
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Julien Leguy. Periodate oxidation of cellulose for internal plasticization and materials design. Material chemistry. Université Grenoble Alpes, 2018. English. ⟨NNT : 2018GREAV010⟩. ⟨tel-01852166⟩

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