Enhanced Crystallization of Poly(Pentylene Adipate‐Co‐Terephthalate) via Ionomer Nucleation: Toward Biodegradable Flexible Packaging

ABSTRACT Various Li, Mg, and Na‐neutralized ethylene‐methacrylic acid copolymer ionomers and an un‐neutralized ethylene‐methacrylic acid copolymer were used as nucleating agents for poly(pentylene adipate‐co‐terephthalate) (PPeAT). The mixtures were tested for isothermal and non‐isothermal crystallization in a differential scanning calorimeter. Neat PPeAT showed a minimum crystallization half‐time of 28 min at 40°C. The addition of 0.05 wt% nucleating agents led to a decrease in crystallization half‐time at 40°C to an average of 2.3, 2.4, 1.9, and 0.7 min for Li, Mg, and Na‐neutralized ionomers and the unneutralized acid copolymer, respectively. The only difference found in nucleating ability was for cation type; for example, resin molecular weight and neutralization level for a given cation showed no difference in nucleation ability. Further investigations with the Na ionomer showed that a minimum in crystallization half‐time of 0.6 min at 40°C was found at 0.5 wt% ionomer content; an increase in the acid copolymer to 0.5 wt% caused a slight increase in crystallization half‐time to 0.76 min. Fully crystallized PPeAT without added ionomer nucleating agent had statistically significantly higher elongation at break and nearly double the tensile strength than fully crystallized PPeAT with 0.05 wt% ionomer nucleating agent; the former did have ~20% higher fractional crystallinity. Moduli for the ionomer nucleated PPeATs were about 15% higher than the non‐nucleated PPeAT. With 0.5 wt% Na ionomer or acid copolymer nucleating agent, however, mechanical property and crystallinity values were about the same as for non‐nucleated PPeAT. Because the crystallization half‐time of PPeAT ~matches that of poly(butylene adipate‐co‐terephthalate), which is currently being used to replace linear low‐density polyethylene (LLDPE) in flexible film applications, PPeAT is also a viable biobased biodegradable alternative to LLDPE for these applications.