Poly(ε-caprolactone-co-ε-decalactone)/carbon black or carbon nanofiber composites. Synthesis, morphological, and thermal/electrical properties

Abstract

Much of the research on biodegradable polymers is currently aimed at developing alternative materials to fossil fuel plastics. Among the biodegradable polymers, the bio-based aliphatic polyesters (e.g. poly-ε-caprolactone, PCL) have had important success in replacing single-use plastics as well as durable consumer goods, mainly in the packaging and biomedical sectors. In other sectors, like electronics, the use of bio-based plastics has received little attention, despite e-waste (pollutant and difficult to handle) being the fastest growing solid waste stream in the world. In this work, P(CL–DL)/carbon black and P(CL–DL)/carbon nanofiber composites with enhanced thermal and electrical properties were prepared and studied. P(CL–DL) copolymers were synthesized via ring opening polymerization (ROP) at CL/DL molar compositions of 95/5, 90/10, 80/20, and 70/30. Their number-average molecular weight (_n) and dispersity index (Đ) lie between 17.5 and 21.8 kDa, and 1.72 and 1.99, respectively. They are thermally stable to up to 300 °C, and show a melting temperature (T_m) and a crystalline degree (X_c) that decrease with increasing contents of DL in the polymer chains. The thermal (k) and electrical (σ) conductivities of copolymers were enhanced by adding, through melt blending, carbon black (CB) or carbon nanofibers (CNF) at 1.25, 2.5, and 5.0 wt%, reaching a maximum value of 0.55 W m⁻¹ K⁻¹ and 10⁻⁷ S cm⁻¹, respectively. The frequency-dependence of the dielectric constant (ε′) and dielectric losses (tan δ) was also measured. Two of the composites showed a marked increase of ε′ near percolation whereas their tan δ remained low. The thermal and electrical conductivity performances, as well as the increment found in ε′ near percolation, are discussed in terms morphology changes produced by variations in both the DL mol% and the nanoparticles wt%. Finally, biodegradable composites with heat and electron dissipative capacities are materials that can contribute to alleviating the problem of e-waste.