Jinjun Yang

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.

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.

Crystallization behavior of biodegradable poly(ethylene adipate) modulated by a benign nucleating agent: Zinc phenylphosphonate

Zinc phenylphosphonate (PPZn), a benign and biocompatible nucleating agent, was prepared and incorporated into the biodegradable poly(ethylene adipate) (PEA) to investigate its effect on the crystallization behavior, crystallization kinetics and spherulite morphology of PEA. Upon addition of PPZn, the crystallization temperature and crystallinity of PEA in the non-isothermal crystallization process increased significantly. Analysis of crystallization kinetics by Avrami equation suggests that the crystallization time shortened greatly and crystallization rate increased markedly after addition of PPZn. In the presence of PPZn, the spherulite size decreased and spherulite density increased significantly. It suggests that PPZn is an efficient nucleating agent for the crystallization of PEA. The accelerated crystallization in the presence of PPZn is mainly attributed to the epitaxial nucleation of PEA crystals on the surface of PPZn crystals, that is, a perfect lattice matching between PEA crystal and PPZn crystal occurs.

Studies on Comonomer Compositional Distribution of Poly(propylene carbonate-propylene oxide) Copolymer and Its Effect on the Thermal, Mechanical and Oxygen Barrier Properties of Fractions

Poly(propylene carbonate) (PPC) was synthesized by the alternating copolymerization of carbon dioxide and propylene oxide (PO). However, during the polymerization, two by-products tended to produce cyclic propylene carbonate (CPC) and a polyether (PE) segment. The excess PO repeat units (PE segment) can easily insert into the PPC backbone and eventually produce the PPC–PO copolymer. The production of CPC and PE segments affected the increase of polymer chain length. In order to investigate the effects of the existence of PE segments, CPC, and molecular weight of fractions on the physical properties of PPC–PO copolymer, a series of fractions with narrow molecular weight distribution were obtained by repeated fractionation. Based on a solvent/non-solvent (chloroform/n-heptane) mixture, an original PPC–PO sample was fractionated into nine fractions with number–average molecular weights (Mn) from 0.34 × 105 to 5.56 × 105 and PE content from 0.4 to 15 mol%. The Mn of PPC–PO fractions decreased with the increase of PE content in the PPC–PO backbone, and the thermal and mechanical properties of the PPC–PO copolymers were affected by their Mn and PE contents. Furthermore, the lower the PE content, the higher the Mn value. Higher Mn means better tensile and lower oxygen permeability of PPC–PO copolymer.

Mechanical and Gas Barrier Properties of Poly(L-Lactic Acid) by Plasma-Enhanced Chemical Vapor Deposition of SiOx

ABSTRACT In this work, poly(L-lactic acid) film was coated with SiOx by the plasma-enhanced chemical vapor deposition with different deposition times. Compared with the neat poly(L-lactic acid) film, the oxygen (O2), carbon dioxide (CO2), nitrogen (N2), and water vapor permeability of the poly(L-lactic acid)/SiOx60 film (depositing for 60 min) decreased by 40.7, 30.6, 58.7, and 53.4% at 25°C, respectively. After treated by the SiOx deposition, the gas permselectivity of the poly(L-lactic acid)/SiOx60 film, such as α(CO2/O2), α(O2/N2), and α(CO2/N2), increased by 17.2, 43.9, and 67.5% at 25°C, respectively. In addition, Young’s modulus and tensile strength of poly(L-lactic acid)/SiOx60 film increased by 107.2 and 49.3%, respectively. Moreover, the poly(L-lactic acid)/SiOx60 films still kept good toughness with an elongation at break of 50.7%. GRAPHICAL ABSTRACT

Polymorphism, thermal stability and enzymatic degradation of poly(1,4-butylene adipate) tailored by a benzene-1,3,5-tricarboxamide-based nucleating agent

An organic nucleating agent (NA), N,N′,N″-tricyclohexyl-1,3,5-benzenetricarboxylamide (TMC-328), was incorporated into biodegradable poly(1,4-butylene adipate) (PBA) to prepare the PBA/TMC-328 blend system to investigate the effect of the TMC-328 NA on the crystallization kinetics, polymorphism, thermal stability and biodegradation of the PBA. Due to the excellent nucleation ability, the TMC-328 enhanced the crystallization temperature, crystallization rate, crystal density and degree of crystallinity of the PBA. The TMC-328 facilitated the formation of the alpha-crystal, accelerated the beta-to-alpha-phase transition, and tailored the polymorphic crystalline structure of the PBA. The incorporated TMC-328 increased the thermal stability and decreased the enzymatic degradation rate of the PBA. The mechanisms of the tailored polymorphism, enhanced thermal stability and decreased biodegradation rate of the PBA in the presence of the TMC-328, have also been proposed and discussed. The PBA/TMC-328 blend provides us an informative model to shed more light on the correlation of hydrogen bond interaction, polymorphism and property of polymorphic polymeric material.