Yunsheng Ding

A well-defined biodegradable 1,2,3-triazolium-functionalized PEG- b -PCL block copolymer: facile synthesis and its compatibilization for PLA/PCL blends

A novel biodegradable 1,2,3-triazolium-functionalized PEG-b-PCL copolymer (TAPEC) was synthesized by the “click” coupling of methoxypolyethylene glycol azide and α-propargyl-ω-hydroxyl-poly(ε-caprolactone), followed by the quaternization of the 1,2,3-triazole moiety with iodomethane. All the intermediates and TAPEC were characterized by 1H NMR, FT-IR, and gel permeation chromatography (GPC). Taking advantage of the characteristics of ionic liquid and block copolymer, this ion-containing diblock copolymer is expected to be used as a novel compatibilizer in mixed biopolyester for regulating the interface and crystallization behaviors. Hence, the TAPEC was evaluated as a compatibilizer and an interface emulsifier in the blends of polylactic acid (PLA) and poly(ε-caprolactone) (PCL). Non-isothermal crystallization experimental results showed that the TAPEC with the higher amount of ε-caprolactone units induces a plasticization and nucleate effect that increased the crystallization ability of the PLA phase; meanwhile, in the PCL phase, the agminated ionic cluster acting as a nucleating agent significantly increased the crystalline of PCL.

Enhancement of polar phase and conductivity relaxation in PIL-modified GO/PVDF composites

To investigate the effect of graphene oxide (GO) modified by polymerized ionic liquid (PIL) on the crystallization and dielectric relaxation of poly(vinylidene fluoride) (PVDF), a series of PVDF composites have been prepared using the solution casting method. The ion-dipole interaction between PIL and >CF2 and the π-dipole interaction between GO and >CF2 can induce synergistically the polar phase, and the π-ion interaction between GO and PIL can strengthen the induction effect of the polar phase and decrease the degree of crystallization of PVDF. The electric modulus and conductivity relaxation are employed to analyze the experimental complex dielectric permittivity. In the frequency spectra of complex permittivity of PVDF composites, space charge polarization and conductivity lead to a large value of dielectric permittivity. The temperature dependence of relaxation time of conductivity relaxation accords with the Arrhenius equation. A low degree of crystallization, more ion concentration, and polar phase in PVDF/PIL/GO enhance the movement of the polymer chain segment and charge carriers.

Improved dielectric properties of PVDF nanocomposites: a comparative study of noncovalent and covalent functionalization of MWCNTs

Polyvinylidene fluoride (PVDF) based nanocomposites with γ-oxo-pyrenebutyric acid-noncovalent modified multiwalled carbon nanotubes (denoted as PACNTs) and stearic acid-covalent modified MWCNTs (SACNTs) as nanofillers, were fabricated using solution-blending method and their dielectric properties were carefully investigated. γ-Oxo-pyrenebutyric acid (PA) or stearic acid (SA) can improve the dispersion of MWCNTs in PVDF matrix because of strong physical π–π interaction and the surface of MWCNTs grafted with SA respectively. The values of percolation threshold for PVDF/PACNTs and PVDF/SACNTs were determined to be 5.7 and 6.3xa0vol%, respectively. Higher dielectric permittivity and lower loss tangent of PVDF/PACNTs originates from remarkable interfacial polarization because PA have more contact area with MWCNTs and can reduce leakage current compared with SA.

Thermal stability and crystallization behavior of cellulose nanocrystals and their poly(l-lactide) nanocomposites: effects of surface ionic group and poly(d-lactide) grafting

Construction of stereocomplexation on the interface of cellulose nanocrystal (CNC) and poly(l-lactide) (PLLA) has been proven to be an efficient way to strengthen interfacial interaction of the nanocomposite. However, the surface structure variation of CNC with different types of ionic group after grafting of poly(d-lactide) (PDLA) and its influence on the properties of their PLLA nanocomposites are still unrevealed. In this current work, the sulfonated CNC (SCNC) and phosphorylated CNC (PCNC) are prepared and grafted with PDLA by surface-initiated ring-opening polymerization. The removal of ionic groups is observed on the surface of SCNC and PCNC after modification, but it has an opposite effect on the thermal stability of the grafted CNC particles. The thermal stability of SCNC-g increases compared with SCNC while PCNC-g decreases compared with PCNC. Consequently, the large difference in thermal stability of the pristine CNCs disappears after grafting and PCNC-g only shows slightly higher thermal stability than SCNC-g. Although the average PDLA grafting content is similar, the number and length of grafted chains are different on SCNC-g and PCNC-g. The grafted chain length on SCNC-g is 4 times as large as that on PCNC-g, which facilitates the formation of interfacial stereocomplex (SC) crystallites in the SCNC-g/PLLA nanocomposites. The SC crystallites improve the thermal stability of the nanocomposites and accelerate the matrix crystallization kinetics. PCNC-g/PLLA samples contrarily show earlier decomposition and lower crystallinity due to the absence of SC crystallites. This study could provide some insights into the effects of ionic groups in the surface grafting process of CNC and the influences on interfacial structure and property of the PLLA nanocomposite.Graphical abstract