Direct Measurement of Temperature Diffusivity of Nanocellulose-Doped Biodegradable Composite Films

• Main Authors: Hiroki Fujisawa, Meguya Ryu, Stefan Lundgaard, Denver P. Linklater, Elena P. Ivanova, Yoshiaki Nishijima, Saulius Juodkazis, Junko Morikawa
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Series: Micromachines
• Subjects: thermal properties; temperature diffusivity; nano cellulose
• Online Access: https://www.mdpi.com/2072-666X/11/8/738

The thermal properties of novel nanomaterials play a significant role in determining the performance of the material in technological applications. Herein, direct measurement of the temperature diffusivity of nanocellulose-doped starch–polyurethane nanocomposite films was carried out by the micro-contact method. Polymer films containing up to 2 wt%. of nanocellulose were synthesised by a simple chemical process and are biodegradable. Films of a high optical transmittance <inline-formula><math display="inline"><semantics><mrow><mi>T</mi><mo>≈</mo><mn>80</mn><mo>%</mo></mrow></semantics></math></inline-formula> (for a 200 <inline-formula><math display="inline"><semantics><mi mathvariant="sans-serif">μ</mi></semantics></math></inline-formula>m thick film), which were up to 44% crystalline, were characterised. Two different modalities of temperature diffusivity based on (1) a resistance change and (2) micro-thermocouple detected voltage modulation caused by the heat wave, were used for the polymer films with cross sections of ∼100 <inline-formula><math display="inline"><semantics><mi mathvariant="sans-serif">μ</mi></semantics></math></inline-formula>m thickness. Twice different in-plane <inline-formula><math display="inline"><semantics><msub><mi>α</mi><mo>‖</mo></msub></semantics></math></inline-formula> and out-of-plane <inline-formula><math display="inline"><semantics><msub><mi>α</mi><mo>⊥</mo></msub></semantics></math></inline-formula> temperature diffusivities were directly determined with high fidelity: <inline-formula><math display="inline"><semantics><mrow><msub><mi>α</mi><mo>‖</mo></msub><mo>=</mo><mn>2</mn><mo>.</mo><mn>12</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup></mrow></semantics></math></inline-formula> m<inline-formula><math display="inline"><semantics><msup><mrow></mrow><mn>2</mn></msup></semantics></math></inline-formula>/s and <inline-formula><math display="inline"><semantics><mrow><msub><mi>α</mi><mo>⊥</mo></msub><mo>=</mo><mn>1</mn><mo>.</mo><mn>13</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup></mrow></semantics></math></inline-formula> m<inline-formula><math display="inline"><semantics><msup><mrow></mrow><mn>2</mn></msup></semantics></math></inline-formula>/s. This work provides an example of a direct contact measurement of thermal properties of nanocellulose composite biodegradable polymer films. The thermal diffusivity, which is usually high in strongly interconnected networks and crystals, was investigated for the first time in this polymer nanocomposite.