Superior, processing-dependent thermal conductivity of cellulose Nanocrystal-Poly(vinyl alcohol) composite films

• Published in: Polymer (Guilford) Vol. 164; pp. 17 - 25
• Main Authors: Chowdhury, Reaz A., Rai, Amit, Glynn, Evan, Morgan, Patrick, Moore, Arden L., Youngblood, Jeffrey P.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.02.2019; Elsevier BV
• Subjects: Alcohol; Alcohols; Anisotropy; Cellulose; Cellulose nanocrystals; Chemical industry; Electronics; Flexible components; Flexible electronics; Heat conductivity; Heat transfer; Hermans order parameter; Nanocrystals; Order parameters; Organic composites; Substrates; Thermal conductivity; Thermal management; Thermal resistance; Hermans order parameter; Thermal conductivity; Organic composites; Flexible electronics; Cellulose nanocrystals
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2019.01.006

The in-plane thermal conductivity of cellulose nanocrystal (CNC) – poly(vinyl alcohol) (PVA) composite films containing different PVA molecular weights, CNC loadings and varying order parameters (S) were investigated as an eco-friendly, renewable and sustainable alternative to commonly used petroleum-based polymeric materials for potential application in thermal management of flexible electronics. Isotropic CNC-PVA bulk films with 10–50 wt% PVA solid loading showed significant improvement in thermal conductivity compared to either one component system. Further, anisotropic composite films exhibited in-plane thermal conductivity as high as ∼3.45 W m−1 K−1 in the chain direction, which is higher than most polymeric materials used as substrates for flexible electronics. Such an improvement can be attributed to the inclusion of PVA as well as to a high degree of CNC orientation. Further, a theoretical model was used to study the effect of CNC arrangement (both isotropic and anisotropic configuration) and interfacial thermal resistance on the in-plane thermal conductivity of the CNC-PVA composite films. In order to demonstrate an application for flexible electronics, thermal images of a concentrated heat source on both neat PVA and CNC-PVA composite films were taken that showed the temperature of the resulting hot spot was lower for the composite films at the same power dissipation. [Display omitted] •CNC-PVA composite films were prepared with a variation of order parameter between 0 and 0.85 for anisotropic films.•PVA molecules act as an interstitial filler between the CNCs, hence improving the effective κ of the CNC-PVA composite films.•Anisotropic CNC-PVA films showed κ as high as ∼3.45 W m−1 K−1, the highest value reported for a CNC-based material to-date.•Our CNC-PVA composite films exhibited ∼ 4–14 fold higher κ than that of films for flexible electronic devices.