Polyamide 6/cork composites by in situ polymerization: Effect of cork surface modification

Polyamide 6 (PA6) thermoplastic composites reinforced with cork residues were processed using Thermoplastic Resin Transfer Molding (T-RTM) by in situ polymerization of caprolactam (ε-CL) due to the use of PA6 thermoplastic precursors, whose processing using conventional thermoplastic processing techniques is challenged by the high melting temperature of PA6 and the limited thermal stability of cork. The cork surface was chemically modified using alkaline and acetylation treatments to enhance interfacial adhesion with the matrix. This study revealed that the cork alveolar structure was not deteriorated with the use of T-RTM, a low-pressure process, and with the adopted compatibilization treatments. Overall, the addition of cork residues led to a favorable effect on density (from 1.14 to 1.05 g.cm −3 ), Izod impact strength (from 10 to 24 kj.m −2 ) and thermal conductivity (from 0.47 to 0.38 W.m −1 . K −1 ) of the composite and to a detrimental effect on flexural and compressive properties, as well as in the polymer degree conversion (98.2% to 74.8%). The formulations with 10 vol% cork presented superior flexural properties/density ratio in comparison to PA6 (up to 25%) and other formulations (up to 65%). Superior outcomes were achieved with acetylation treatment at 10% vol% cork, while the alkaline treatment demonstrated superior stability at 20 and 30 vol% cork. These composites produced by T-RTM represent a more sustainable and lightweight material, offering a promising alternative for advanced composite applications.