Eco-design of biobased poly(butylene succinate-b-pentamethylene 2,5-furanoate) copolymers with optimized mechanical, thermal and barrier properties for flexible food-packaging

Poly(butylene succinate) and poly(pentamethylene 2,5-furanoate) homopolymers have been combined, both physically as well as chemically, to optimize the final material’s functional properties for flexible food packaging applications. The two parent homopolymers were synthesized through two-step bulk polycondensation, then they were physically mixed in an equiponderal blend by solvent casting. The blend was subjected to reactive blending at high temperature and in presence of the catalyst, for different times, to prepare several copolymers with tuned molecular architecture, i.e. different block lengths. After molecular characterization, the polymers were processed in form of films and subjected to thermal (TGA and DSC), structural (SEM and XRD), mechanical and gas barrier characterization. All the materials show very high thermal stability (Tonset > 360 ◦C; Tmax > 390 ◦C) and modulated melting temperatures (43 ◦C < Tm < 113 ◦C). Even if not miscible, the two homopol- ymers reveal good compatibility, reflected in enhanced flexibility (elastic modulus reduced up to one order of magnitude) and elongation (up to five times higher) already in the physical blend, together with surprising elastic capability in the copolymers (shape recovery > 70 %). The presence of furan moieties in the final ma- terials leads to reduced permeability of CO2 and, particularly, of O2 (up to Barrier Improvement Factor (BIF) ≈ 8). The results obtained highlight the possibility of modulating the material response by playing with composition and repeating unit distribution along the macromolecules.