High-value copolyamide 6 materials with colorless transparent and low water absorption upgraded from upcycled and biomass comonomers

Abstract

Polyamide 6 (PA6) is a semicrystalline polymer with excellent wide application for filament and packing materials. However, the use in filament and packing materials of PA6 with high crystallinity and rich hydrogen bonds is limited because of its low optical properties and poor anti-water absorption. In this work, a series of partially sustainable PA6 copolymers with high value were synthesized by melt polycondensation from fatty dimer acid (FDA) and upcycled chemical bis(6-aminohexyl) terephthalamide (BAHT). The chemical structure of partially sustainable PA6 copolymers was characterized by 1 H NMR, FT IR, relative viscosity, and amine value. The mechanical properties, optical properties, and anti-water absorption of high-value PA6 copolymers depended on the BAHT salt loading and the chain length of aliphatic dicarboxylic acids. The tensile strength of PA6 copolymers was decreased, but the tensile toughness, optical transmittance, and anti-water absorption of that were significantly improved. Overall, this easy method opens up new avenues for devising excellent optical transmittance and low water absorption of polyamide materials, whereas providing the new strategy for carbon-neutral through rPET upcycling and biomass use, and these PA6 copolymers have the potential and economy to be widely applied. • Combining both upcycling and biomass segments in polycaprolactam copolymers (CoPAs). • Bis(6-aminohexyl) terephthalamide (BAHT) upcycled from rPET bottle to promote spherulite shrinkage of CoPAs. • Fatty dimer acid influenced the optical behavior of the polyamide (transparency level > 80% and haze level < 10%). • Fatty dimer acid increased the anti-water absorption of CoPAs. • CoPAs prepared transparent monofilaments and films by twin-screw extrusion and hot-pressing.