Coupled effect of self-assembled nucleating agent, Ni-CNTs and pressure-driven flow on the electrical, electromagnetic interference shielding and thermal conductive properties of poly (lactic acid) composite foams

Abstract

Biobased and biodegradable poly (lactic acid) (PLA) composite foams with good mechanical properties, a low percolation threshold, and absorption-dominant shielding properties with little reflection are considered suitable substitutes for traditional petroleum-based polymer composite foams in various applications. However, fabricating PLA composite foams that simultaneously satisfy all the above properties remains a significant challenge, particularly at low conductive filler addition. In this study, we successfully fabricated high-performance multifunctional PLA/self-assembled nucleating agent (TMC-306)@Ni-CNTs composite foams. In the ternary composites system, PLA and 0.5 wt% TMC-306 were melt mixed first to prepare granules and used as a polymer matrix, while Ni-CNTs were employed as a conductive segregated filler. To determine the coupled effect of TMC-306, Ni-CNTs, and pressure-driven flow on PLA composite foams, rheological, crystallization, and morphological properties of ternary composites were initially investigated. The results demonstrated that the increased complex viscosity of composites with increasing Ni-CNTs content affected the flow orientation under pressure-driven flow and the pore growth of the subsequent foaming process. The low content of Ni-CNTs could play a synergistic role with TMC-306 to improve PLA crystallization ability, whereas the nucleating agent effect was inhibited at high Ni-CNTs content. Additionally, pressure-driven flow induced the formation of segregated oriented conductive networks and ordered crystalline structures in the matrix, which significantly impacted on the low-temperature foaming performance of PLA composites. After supercritical carbon dioxide (Sc-CO2) foaming treatment, the composite foams exhibited an ultralow percolation threshold of 0.076 vol% and high electrical conductivity of 7.58 × 10−2 S/cm at an ultralow Ni-CNTs content of 0.805 vol%. Moreover, the composite foams containing 0.805 vol% Ni-CNTs achieved a high electromagnetic interference (EMI) shielding effectiveness (SE) of 25.2 dB and an absorption-dominant shielding mechanism with a high absorptivity of 86%. It also had a low density of 0.36 g/cm3, a high compressive strength of 5.42 MPa and a good thermal conductivity of 62.3 mW·m−1·K−1. In summary, this study may provide a facile and cost-effective strategy for developing high-performance PLA composite foams with broad applications.