Effects of Crystallization Temperature of Poly(vinylidene fluoride) on Crystal Modification and Phase Transition of Poly(butylene adipate) in Their Blends: A Novel Approach for Polymorphic Control

Abstract

Effects of the isothermal crystallization temperatures of poly(vinylidene fluoride), T(IC,PVDF), on polymorphic crystalline structure, phase transition, fractional crystallization, and enzymatic degradation of poly(butylene adipate) (PBA) in crystalline/crystalline blends have been investigated. The crystal modifications of PBA can be regulated by T(IC,PVDF). Lower T(IC,PVDF) (e.g., 80 °C) facilitates the formation of PBA α crystals in both the isothermal and nonisothermal melt crystallizations and also favors the β-to-α phase transition of PBA upon annealing at elevated temperatures. This might be attributable to the decreased equilibrium melting temperature of PBA when T(IC,PVDF) is decreased. Higher T(IC,PVDF) is favorable for the fractional crystallization of PBA, which tends to segregate in the interlamellar regions of the PVDF matrix under these conditions. PBA shows faster enzymatic degradation in the blends with a lower T(IC,PVDF) than those with a higher T(IC,PVDF), attributable to the preferential formation of α crystals at a lower T(IC,PVDF). This study provides a new method to control the crystal modification and physical properties of polymorphic polymers in their blend systems.

Crystalline and Spherulitic Morphology of Polymers Crystallized in Confined Systems

“…A higher Tc favors the formation of thermodynamically-stable α polymorph; yet, a lower Tc facilitates the growth of the metastable β polymorph. Interestingly, the polymorphic structure of PBA could be regulated upon blending with Confined crystallization behavior was also reported for the PVDF/PBA [79,80] and PVDF/PBS [84,85] crystalline/crystalline miscible blends. Yang et al systematically investigated the fractional crystallization kinetics, crystalline morphology and polymorphic structure of PVDF/PBA blends [79,80].…”

“…Interestingly, the polymorphic structure of PBA could be regulated upon blending with Confined crystallization behavior was also reported for the PVDF/PBA [79,80] and PVDF/PBS [84,85] crystalline/crystalline miscible blends. Yang et al systematically investigated the fractional crystallization kinetics, crystalline morphology and polymorphic structure of PVDF/PBA blends [79,80]. In the PVDF/PBA blends, a small amount of PVDF could act as the nucleating agent and accelerate the crystallization of the PBA component; while a large amount of PVDF hindered the crystallization of PBA due to the confinement effects.…”

“…The presence of PVDF facilitated PBA to form the thermally more stable α crystals and also accelerated the phase transition from β to α crystals of PBA during the annealing process (48 • C) [79]. For the PVDF/PBA blends with a fixed composition, further investigations of Yang et al also demonstrated that the polymorphic crystalline structure of the PBA component was influenced by the crystallization conditions of PVDF component; this may account for the different segregation areas of the PBA component during the crystallization of PVDF [80]. For a certain PVDF/PBA blend, a higher T c of PVDF was favorable for the fractional crystallization of PBA component, which tended to segregate in the interlamellar regions of PVDF crystals under these conditions; this was similar to the case of the PBS/PEO blend [90].…”

“…Researchers have found that the binary miscible crystalline/crystalline polymers show the confined and fractional crystallization behavior because of the phase separation and segregation in different length scales during crystallization process. These crystalline/crystalline polymer blends included poly(ethylene terephthalate) (PET)/poly(butylene terephthalate) (PBT) [75], poly(3-hydroxybutyrate) (PHB)/poly(ethylene oxide) (PEO) [76,77], poly(vinylidene fluoride) (PVDF)/poly(butylene adipate) (PBA) [78][79][80], PVDF/poly(butylene succinate-co-butylene adipate) (PBSA) [81], PVDF/PHB [82], PVDF/poly(butylene succinate) (PBS) [83][84][85], PBS/PEO [86][87][88][89][90][91][92], PBS/PBA [93,94], poly(butylene adipate-co-butylene succinate) (PBAS)/PEO [95], poly(ethylene succinate) (PES)/PEO [96], PLLA/poly(oxymethylene) [97,98], and so on. Expect for the miscible blends with one or two crystalline homopolymers, the miscible copolymer/copolymer blends having crystalline components or blocks could also show the confined crystallization behavior [99,100].…”

“…However, PBA showed faster enzymatic degradation in the PVDF/PBA blends with a lower T c of the PVDF component, attributable to the preferential formation of α crystals under these conditions. This study has provided a new method to control the crystal modification and physical properties of polymorphic PBA in their miscible blend systems [80].…”