Cocrystallization Model for Synthetic Biodegradable Poly(butylene adipate-co-butylene terephthalate)

Abstract

Synthetic biodegradable poly(butylene adipate-co-butylene terephthalate), P(BA-co-BT), with 56 mol % butylene adipate, BA, was characterized by solid-state NMR spectroscopy, thermal analysis, X-ray diffraction, computer modeling, and polarization microscopy. The NMR study showed the presence of BA and butylene terephthalate, BT. T(1C) NMR measurements proved that some BA and BT units were in crystalline regions. Thermal analysis showed one glass-transition temperature and a single diffuse melting endotherm corresponding to a large melting-point depression of about 100 degrees C compared with poly(butylene terephthalate), PBT. These results suggest that there is only one crystalline phase. An X-ray fiber diagram of a stretched film could be indexed with the same unit cell as that for PBT. Computer modeling showed that the adipate unit fits into the crystal structure of PBT by adopting a TTGTG dihedral angle sequence in the crystalline conformation proposed for the cocrystallization model. The predicted fiber diagram from the proposed model qualitatively agrees with the experimental one. Polarization microscopy revealed that the spherulite growth rate of P(BA-co-BT) was similar to that for poly(butylene adipate), PBA.

Solid-State NMR Study of Poly(3-Hydroxybutyrate) and Ecoflex reser Blends

“…2 are given by the material used in the rotor cap. These results are consistent with those published in literature [13][14][15][16][17][18]. As the repetition time used by spectrum acquisition is long enough for relaxation of carbonyl and methylene groups [14], the fractions of adipic, butanediol and terephthalic units in Ecoflex ® can be determined by means of intensities of the individual peaks as well as by means of the deconvolution of the spectrum.…”

“…Both mentioned peaks are obviously composed of two overlapping peaks. In the case of Ecoflex ® these peaks correspond to the methylene carbons in butanediol and adipic units which may be built in crystalline or amorphous region of Ecoflex ® [13][14][15][16][17]. In the case of PHB the methyl signal at 21 ppm is composed of a narrower signal at higher ppm of CH 3 groups in the crystalline regions with the trans conforma-tion of the backbone and a broader one at lower ppm corresponding to methyl groups in amorphous region with the trans/gauche dominant conformation of the backbone [1,4,7].…”

“…Solid-state NMR study of PBAT employed 13 C CP MAS techniques [13][14][15][16][17]. The existence of two components of the spin-lattice relaxation times T 1 (C) for butylene-terephthalate units revealed incorporation of these units in both, amorphous and crystalline regions of polymer.…”

“…The existence of two components of the spin-lattice relaxation times T 1 (C) for butylene-terephthalate units revealed incorporation of these units in both, amorphous and crystalline regions of polymer. However, there is no uniform opinion on the presence of butylene-adipate units in crystalline regions of PBAT [14][15][16][17]. Relatively short relaxation times T 1 (C) ascribed to butylene-adipate units in crystalline regions of PBAT implied their high mobility or possibly incorporation of these units into an interface between crystalline and amorphous regions of PBAT [15].…”

“…However, there is no uniform opinion on the presence of butylene-adipate units in crystalline regions of PBAT [14][15][16][17]. Relatively short relaxation times T 1 (C) ascribed to butylene-adipate units in crystalline regions of PBAT implied their high mobility or possibly incorporation of these units into an interface between crystalline and amorphous regions of PBAT [15]. Based on the existence of only single component of the proton spinlattice relaxation time in the rotating frame T 1ρ (H) measured via CP method for butylene CH 2 peak, the size of crystalline regions of PBAT was estimated to be less than 3 nm [16].…”