Fully Aliphatic Copolyesters Based on Poly(butylene 1,4- cyclohexanedicarboxylate) with Promising Mechanical and Barrier Properties for Food Packaging Applications

Poly(butylene cyclohexanedicarboxylate/diglycolate) random copolymers (P(BCEmBDGn)) of various compositions were synthesized and characterized from the molecular, thermal, structural, and mechanical point of view. Barrier properties to different gases (oxygen and carbon dioxide) were also evaluated. All the polymers showed good thermal stability and appeared as semicrystalline materials at room temperature. The main effect of copolymerization was a lowering in the crystallinity and a decrease of Tm with respect to homopolymers. The dependence of Tm on composition for copolymers with high butylene cyclohexanedicarboxylate unit content was well described by Baur’s equation. X-ray diffraction (XRD) measurements indicated that two different crystalline phases are present, depending on composition: copolymers with high BCE unit content were characterized by PBCE crystal phase, whereas those rich in BDG counits crystallized in PBDG lattice. The samples displayed different surface hydrophilicity: the water contact angle regularly decreased with the increasing mol % of BDG. The mechanical properties were found strictly related to crystallinity degree (χc); the copolymers containing 60−75 mol % of BDG showed the lowest elastic modulus and the highest elongation at break. Lastly, the chemical composition of the copolymer strongly influenced permeability to CO2 and O2. Moreover, the selectivity ratios for the examined samples increased with the increasing of BDG mol %, confirming the existence of a correlation between the permeability and the chemical composition. Almost all copolymers showed improved barrier properties with respect to polylactide films tested under the same conditions.