Highly transparent biaxially oriented poly(ester amide) film with improved gas barrier properties and good mechanical strength

Poly(ethylene terephthalate) (PET) reinforced with hydrogen bonding is prepared by incorporating 4 mol% amide units formed by 1,12-dodecanediamine and terephthalic acid. Structurally modified PET (PETA) containing amide units is extruded and biaxially stretched to make biaxially oriented (BO) PETA films with high performance. The formation of hydrogen bonds in BOPETA is detected, and the effect of the incorporated amide units on the performance is discussed. Attractive interchain forces are increased through the hydrogen bonds formed in BOPETA, and its crystallinity and mechanical properties are improved. The fabricated BOPETA film exhibits lower water and oxygen permeabilities than that of BOPET because the free volume was reduced. The optical properties of the BOPETA film remain good after incorporating amide units into the PET backbone, and its light transmittance reaches 88.8%. Moreover, BOPETA with 4 mol% amide units absorbs somewhat ultraviolet (UV) light and exhibits slight anti-UV performance. A facile approach for the preparation of PET films with good mechanical strength, high transparency, and improved gas barrier properties for packaging is discussed in this work.