Experimental and Simulation Studies of Temperature Effect on Thermophysical Properties of Graphene-Based Polylactic Acid

Abstract

Overheating effect is a crucial issue in different fields. Thermally conductive polymer-based heat sinks, with lightweight and moldability features as well as high-performance and reliability, are promising candidates in solving such inconvenience. The present work deals with the experimental evaluation of the temperature effect on the thermophysical properties of nanocomposites made with polylactic acid (PLA) reinforced with two different weight percentages (3 and 6 wt%) of graphene nanoplatelets (GNPs). Thermal conductivity and diffusivity, as well as specific heat capacity, are measured in the temperature range between 298.15 and 373.15 K. At the lowest temperature (298.15 K), an improvement of 171% is observed for the thermal conductivity compared to the unfilled matrix due to the addition of 6 wt% of GNPs, whereas at the highest temperature (372.15 K) such enhancement is about of 155%. Some of the most important mechanical properties, mainly hardness and Young's modulus, maximum flexural stress, and tangent modulus of elasticity, are also evaluated as a function of the GNPs content. Moreover, thermal simulations based on the finite element method (FEM) have been carried out to predict the thermal performance of the investigated nanocomposites in view of their practical use in thermal applications. Results seem quite suitable in this regard.

Keywords: biodegradable polymers; graphene nanoplatelets; multiphysics simulations; nanocomposites; thermal transport properties; thermophysical properties.

Figure 1

Schematic summary of the production of nanocomposites, filaments, and test samples.

Figure 2

Measurement principle of laser flash method (a) and characteristic parameters for the evaluation of the thermophysical properties (b).

Figure 3

Main model definitions for the numerical study on the thermophysical properties of polymer-based heat sinks (a). Schematic representation of the numerical case study (b).

Figure 4

SEM images of neat PLA and the two nanocomposites, including 3 and 6 wt% of GNPs in (a–c), respectively. A schematic stacked arrangement of the graphene particles is depicted in (d).

Figure 5

TEM images regarding the graphene nanoplatelets adopted in the present study as reinforcement for the PLA matric are reported in (a–c).

Figure 6

Comparison of mechanical properties of pure PLA, PLA filled with 3 wt% GNP and PLA reinforced with 6 wt% GNP in terms of nanoindentation hardness and Young’s modulus in (a), scratch and wear coefficient of friction in (b), maximum flexural stress and tangent modulus of elasticity in (c).

Figure 7

Comparison of thermophysical properties of pure PLA, PLA filled with 3 wt% GNPs and PLA reinforced with 6 wt% GNPs in terms of thermal conductivity (λ), thermal diffusivity (α), and specific heat capacity (Cp) in (a–c), respectively.

Figure 8

Comparison of the temperature profiles (average values) recorded on the upper surfaces vs. time for heat sink based on pure PLA, PLA reinforced with 3 and 6 wt% of GNPs different temperatures, i.e., 298.15, 313.15, 353.15, and 373.15 K, are considered in (a–d), respectively.

Figure 9

Numerical prediction of the average surface temperature profiles (left side) and temperature isolines (right side) recorded at steady-state condition (t = 150 s), and at temperature value of 373.15 K for heat sinks based on pure PLA, PLA reinforced with 3 wt% of GNPs and 6 wt% of GNPs in (a–c), respectively.

Figure 10

Temperature multislices evaluated at steady-state condition (t = 150 s) and at temperature value of 373.15 K relatively to PLA, PLA/3 wt% GNPs, and PLA/6 wt% GNPs in (a–c), respectively.

Figure 11

Temperature profiles (evaluated at the half course of each transient phase and alongside the symmetry axis) for the different heat sinks at the different temperature values: 298.15, 313.15, 353.15, and 373.15 K in (a–d), respectively.

Figure 12

Convective heat flux trends over time for the three polymer-based heat exchanges operating at different temperature values: 298.15, 313.15, 353.15, and 373.15 K in (a–d), respectively.

Figure 13

Three-dimensional views of the conductive heat flux at steady-state condition (t = 150 s) and at temperature value of 373.15 K relatively to PLA, PLA/3 wt% GNPs, and PLA/6 wt% GNPs in (a–c), respectively.

Figure 13

Three-dimensional views of the conductive heat flux at steady-state condition (t = 150 s) and at temperature value of 373.15 K relatively to PLA, PLA/3 wt% GNPs, and PLA/6 wt% GNPs in (a–c), respectively.

Figure 14

Temperature (a) and convective heat flux (b) as a function of GNPs concentration at the different temperatures. The lines are the fitting curves of the numerical data (colored markers).