Enhancing thermal conductivity and near‐infrared radiation reflectance of poly(ε‐caprolactone)/poly(lactic acid)‐based nanocomposites by incorporating hexagonal boron nitride

Abstract

This work aims to develop multifunctional biodegradable ternary nanocomposites with heat dissipation capability. The effects of adding hexagonal boron nitride (hBN), regarding phase morphology, near-infrared radiation (NIR) reflectance and thermal conductivity of poly (ε-caprolactone) (PCL) and poly(lactic acid) (PLA) blends were investigated. The hBN nanoparticles were selectively localized in the PCL phase. Scanning electron microscopy showed that the increased hBN concentration in the PCL/PLA blend led to a more fibrillar PLA phase and, after compression molding, its morphology presented a co-continuous structure. Adding hBN nanoplatelets increased the reflectance in the NIR region by 184%, the thermal conductivity of the PCL/PLA by 400%, and increased the blend's thermal stability. The co-continuous morphology could favor the heat flow, because it promotes the confinement of the hBN nanoplatelets in the PCL phase, favoring the conductive thermal pathway formation. POLYM. COMPOS., 40:3464-3471, 2019.

Effects of processing conditions on hybrid filler selective localization, rheological, and thermal properties of poly(ε‐caprolactone)/poly(lactic acid) blends

“…In our previous studies with ternary systems, we observed that TiO 2 was selectively localized at the PCL/PLA interface and a compatibilization effect was seen, while hBN nanoplatelets were selectively localized in the PCL phase . According to the calculated wettability coefficient, the TiO 2 has a thermodynamic preference for the PLA phase, and the hBN has a preference for the PCL/PLA interface .…”

“…According to the calculated wettability coefficient, the TiO 2 has a thermodynamic preference for the PLA phase, and the hBN has a preference for the PCL/PLA interface . However, since the polymers' melting points largely differ, 59 °C for the PCL and 168 °C for the PLA, as well as their viscosities, 43 Pa s for the PLA and 3 Pa s for the PCL (the capillary rheometer curve is shown in Supporting Information Section S1), and since all blend components were simultaneously added into the extruder, the TiO 2 or the hBN were expected to be first localized in the PCL phase, and, through the driving force generated by the thermodynamic preference, they would migrate to the PLA phase or to the interface, respectively. Such behavior can be related to the nanoparticle's geometry, which hinders the migration through the interface .…”

“…Such behavior can be related to the nanoparticle's geometry, which hinders the migration through the interface . The migration was obstructed by the hBN tactoids, impairing the movement through the PCL polymer chains …”

“…The samples of the PCL/PLA/TiO 2 and the PCL/PLA/hBN ternary systems were prepared according to the methods used in our previous works . The quaternary systems were prepared in a co‐rotating twin‐screw extruder (AX Plasticos, Brasil), set to 100 rpm while the temperature ranged from 120 to 170 °C in the heating zones, then compression‐molded into 0.170 ± 0.02 mm‐thick sheets at 170 ± 5 °C for 3 min under 15 MPa of pressure using a hydraulic press.…”

“…Furthermore, such properties of PCL/PLA blends can be further enhanced with the addition of nanoparticles. For example, TiO 2 presents an excellent ultraviolet blocking and hexagonal boron nitride (hBN) has a high thermal conductivity and can reflect infrared radiation . Their addition into the PCL/PLA blend can improve such properties, showing application potential in biodegradable agricultural films, packaging, and among others.…”