Effect of Molecular Orientation on the Cold Crystallization of Amorphous–Crystallizable Polymers: The Case of Poly(trimethylene terephthalate)

Microcrystalline cellulose grafted hyperbranched polyester with roll comb structure for synergistic toughening and strengthening of microbial PHBV/bio-based polyester elastomer composites

The brittle feature of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is the major challenge that strongly restricts its application at present. Successfully synthesized bio-based engineering polyester elastomers (BEPE) were combined with PHBV to create entirely bio-composites with the intention of toughening PHBV. Herein, the 2,2-Bis(hydroxymethyl)-propionic acid (DMPA) was grafted onto microcrystalline cellulose (MCC) and then further transformed into hyperbranched polyester structure via polycondensation. The modified MCC, named MCHBP, had plenty of terminal hydroxyl groups, which get dispersed between PHBV and BEPE. Besides, a large number of terminal hydroxyl groups of MCHBP can interact with the carbonyl groups of PHBV or BEPE in a wide range of hydrogen bonds, and subsequently increase the adhesion and stress transfer between the PHBV and BEPE. The tensile toughness and the elongation at break of the PHBV/BEPE composites with 0.5phr MCHBP were improved by 559.7 % and 221.8 % in comparison to those of PHBV/BEPE composites. Results also showed that MCHBP can play a heterogeneous nucleation effect on the crystallization of PHBV. Therefore, this research can address the current issue of biopolymers' weak mechanical qualities and may have uses in food packaging.

Tailoring compatibility and toughness of microbial poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/bio-based polyester elastomer blends by epoxy-terminated hyperbranched polyester

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a type of promising bio-based thermoplastic for food packaging but find restricted industrial applications due to its brittleness and poor processability that is caused by its large spherulite sizes. In this study, for the purpose of toughening PHBV, bio-based engineering polyester elastomers (BEPE) were synthesized and blended with PHBV to prepare fully bio-based blends. In order to improve the compatibility and toughness of the BEPE/PHBV blends, epoxy-terminated hyperbranched polyesters (EHBP) were synthesized, which could be homogeneously dispersed into the PHBV/BEPE blends and improve the compatibility between the two phases of the matrix. The results showed that compared to those of the PHBV/BEPE blends, the elongation at break, impact strength and tensile toughness of the PHBV/BEPE blends with 3.0phr EHBP were enhanced by 134.2 %, 76.8 %, and 123.5 %, respectively. The crystallization study demonstrated the crystallization rate of PHBV/BEPE blends decreased due to the addition of EHBP. The reasons lied in that the addition of EHBP leads to chemical cross-linking between PHBV and BEPE. Meanwhile, the formation of hydrogen bonding, co-crystallization and chain entanglement increased the adhesion between PHBV and BEΡE, which generated the superior toughness of the blends.

The Importance of Nonequilibrium to Equilibrium Transition Pathways for the Efficiency and Stability of Organic Solar Cells

Controlled morphology of solution-processed thin films have realized impressive achievements for non-fullerene acceptor (NFA)-based organic solar cells (OSCs). Given the large set of donor-acceptor pairs, employing various processing conditions to realize optimal morphology for high efficiency and stable OSCs is a strenuous task. Therefore, comprehensive correlations between processing conditions and morphology evolution pathways have to be developed for efficient performance and stability of devices. Within the framework of the blend system, crystallization transitions of NFA molecules are tracked utilizing the first heating scan of differential scanning calorimeter (DSC) measurement correlating with respective morphology evolution of blend films. Real-time dynamics measurements and morphology characterizations are combined to provide optimal morphology transition pathways as NFA molecules are shown to be released from the mixed-phase to form balanced ordered packing with variant processing conditions. Polymer:NFA films are fabricated using blade coating incorporating solvent additive or thermal annealing as processing conditions as a correlation is formulated between performance and stability of solar cells with morphology transition pathways. This work demonstrates the significance of processing condition-controlled transition pathways for the realization of optimal morphology leading to superior OSC devices.

Processing-property relationships of biaxially stretched poly(L-lactic acid) sheet for application in coronary stents

The development of coronary stents from poly(L-lactic acid) requires knowledge of its mechanical properties and the effects of manufacturing processes on those properties. The effects of the biaxial stretching procedure on the mechanical and microstructural properties of poly(L-lactic acid) are hereby investigated. The mechanical properties were evaluated before and after biaxial stretching, with a Design of Experiments methodology employed to identify processing parameters that had the most significant effect on the elastic modulus and yield strength of the biaxially stretched sheets. Microstructural characterisation was performed using differential scanning calorimetry to evaluate crystallinity and thermal transitions of the biaxially stretched sheets. The results show that the mechanical properties of the stretched sheets are highly dependent on the extent of stretch ratio applied during processing; however, neither the elastic modulus nor yield strength are directly attributable to crystallinity, but are affected by the degree of amorphous orientation. The results of this study have the potential to be applied in the design of high stiffness, thin-strut polymeric expandable scaffolds for the application of coronary stents.

Effects of Poly(cyclohexanedimethylene terephthalate) on Microstructures, Crystallization Behavior and Properties of the Poly(ester ether) Elastomers

To understand the role of molecular structure on the crystallization behavior of copolyester in thermoplastic poly(ether ester) elastomers (TPEEs), series of poly(butylene-co-1,4-cyclohexanedimethylene terephthalate) (P(BT-co-CT))-b-poly(tetramethylene glycol) (PTMG) are synthesized through molten polycondensation process. The effects of poly(cyclohexanedimethylene terephthalate) (PCT) content on the copolymer are investigated by Fourier transform infrared spectroscopy (FT-IR), ¹H and 13C nuclear magnetic resonance (NMR), gel permeation chromatographs (GPC), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), mechanical, and visible light transmittance tests. FT-IR and NMR results confirm the incorporation of PCT onto the copolymer. WAXD and DSC indicate that the crystalline structure of the copolymers changed from α-PBT lattice to trans-PCT lattice when the molar fraction of PCT (MPCT) is above 30%, while both crystallization and melting temperatures reach the minima. An increase in MPCT led to an increase in the number sequence length of PCT, the thermal stability and the visible light transmittance of the copolymer, but to a slight decrease in tensile strength and elastic modulus.

Photodegradation behavior and mechanism of poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate) (PETG) random copolymers: correlation with copolymer composition

Norrish type I and II mechanisms occurred in PETG copolymers. The inherent photostability of PETG decreased with increasing CHDM content. The higher CHDM content resulted in the higher crosslinking degree.

Poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate) random copolymers: effect of copolymer composition and microstructure on the thermal properties and crystallization behavior

The glass transition temperature of the statistically random PETG copolymers increased linearly with the increasing CT content. An increase in the average sequence length resulted in a higher melting temperature.