Classification of aliphatic-butylene terephthalate copolyesters in relation to aliphatic/aromatic ratio

Abstract

Aliphatic-aromatic copolyesters containing: butylene terephthalate ester and a mixture of butylene esters: adipate, succinate and glutarate, (PBASGT), were synthesized and classified according to their chemical composition and physical performance. Several such mixtures of aliphatic dimethyl esters are available on the market. Structures and properties of PBASGTs were characterized by various techniques including 1H NMR spectrometry, calorimetry, x-ray scattering and diffraction, dynamic mechanical analysis and tensile testing. All copolyesters were nearly random copolymers. Surprisingly, only the aromatic component is able to crystallize in the form characteristic for poly (butylene terephtalate). The increase of aromatic units content did not change the crystallographic form, however, a stronger crystallinity develops. The dramatic changes of thermal and mechanical properties of PBASGT were observed with the increase of aliphatic units content, e.g. from brittle to tough behavior. Copolyesters with aromatic content of 30% and below exhibit single relaxation peak of aliphatic rich amorphous components. At the concentration of 40% and above the aromatic component is segregated while the amorphous aliphatic units form joint pools. A partial segmental miscibility of aromatic and aliphatic components is suggested. It was shown that PBASGT with 40% of aromatic units is biodegradable.