Guiqiu Ma

Plasma treatment of electrospun PCL random nanofiber meshes (NFMs) for biological property improvement

In this article, the plasma surface modification effects on the chemical, mechanical, and biological properties of electrospun poly (ε-caprolactone) (PCL) random nanofiber meshes (NFMs) were investigated by adjusting plasma chemistry, that is, using glow discharges of N(2) +H(2), NH(3) +O(2), and Ar+O(2) gas mixtures. The surface property changes of electrospun PCL NFMs after those plasma treatments were examined by water contact angle measurements and X-ray photoelectron spectroscopy. The experimental results showed that the plasma treatments introduced polar groups onto the surfaces and thus increased the surface hydrophilicity. From tensile test data, plasma treatment had limited effect on the mechanical properties of PCL random NFMs. The biological properties of the plasma-treated PCL NFMs were examined by cell proliferation assays using mouse osteoblast cells (MC3T3-E1). It was found that the plasma-treated PCL NFMs gave a higher proliferation rate and improved cell adhesion properties as compared with the untreated controls.

PLASMA MODIFICATION OF POLYPROPYLENE SURFACES AND GRAFTING COPOLYMERIZATION OF STYRENE ONTO POLYPROPYLENE

The surface of polypropylene (iPP) is modified with glow discharge plasma of Ar, so that the modified surfaces of iPP films are obtained. The studies of scanning electron microscopy (SEM) show the surface etching pattern of iPP films. The chemical structures of iPP films are confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The wetting properties of modified surfaces of iPP films are characterized by contact angle, and the free energy of surfaces is calculated. The free radical of modification surfaces of iPP is measured by chemical method. The surfaces of iPP are achieved with Ar plasma treatment followed by grafting copolymerization with styrene (St) in St. The grafting polymer of St onto iPP is characterized by FTIR. The grafting rate is dependent on plasma exposure time and discharge voltage. The studies show that homopolymerization of St is undergone at the same time during the graftingcopolymerization of St onto iPP.

Morphological Aspects of In-Situ Compatiblized Binary Polymer Blends With Variable Viscosity Ratios of Components

The in-situ compatiblized binary polymer blend polypropylene(PP)/polystyrene(PS)/ anhydrous aluminum chloride(AlCl3) was selected as a model system of a reactive polymer blend to investigate the effect of viscosity ratio of components at a constant shear rate on the phase morphological behavior in in-situ compatibilized systems. The results showed that the well-known interfacial compatibilization effect was related to variations of viscosity ratios of components in the reactive PP/PS blends with different contents of AlCl3 catalyst. The phase morphology evolution of the in-situ compatiblized reactive blend was determined by both the interfacial compatibilization and the variation of the viscosity ratio of components under the fixed mixing conditions, which showed characteristics obviously different from and much more complex than those in binary polymer blends generally compatiblized by added compatiblizers. The results implied that the variation of the viscosity ratio of components should be checked carefully and taken into account if necessary, when the phase morphology of binary polymer blends is investigated, especially in complex in-situ compatiblized reactive polymer blends.

Low temperature plasma-initiated copolymerization of styrene and maleic anhydride

In this study we show that the plasma-initiated polymerization can be carried out at ambient temperature and pressure using the dielectric barrier discharge technology. The structure of styrene-maleic anhydride copolymer (SMA) is analyzed by Fourier transform infrared and H1 NMR. The effects of initiation time, postpolymerization time, and polymerization temperature on conversion are also discussed. The results show that SMA exhibits a dominant alternating structure, the conversion increases with increasing initiation time, postpolymerization time, and polymerization temperature, and the plasma-initiated polymerization in this experiment is proven to follow the free radical polymerization mechanism.

Rheological Characterization of in situ Compatibilized Binary Polymer Blends With Variable Steady Shear Viscosities of Components

Zero shear viscosities of binary polymer blends, η0,bc, of polypropylene (PP)/polystyrene (PS), in situ compatibilized by anhydrous aluminum chloride (AlCl3) catalyst, were obtained by fitting their shear rate sweep curves according to the modified Carreau model. The results showed that the dependence of η0,bc on AlCl3 content was complicated and obviously influenced by viscosity variations of the components as well as the interfacial compatibilization effect of the in situ formed PP-g-PS copolymer. For further investigation, η0,bc was divided into three parts: contribution of the viscosity of components, contribution of phase geometry, and contribution of the interfacial compatibilization effect. The results showed that when the apparent value of the third part was experimentally determined, the significant influence of viscosity variations of the components had to be considered, while the influence of phase morphology geometry resulting from viscosity variations of the components could be ignored experimentally and reasonably within the whole experimental range of AlCl3 content. The contribution of the interfacial compatibilization effect to η0,bc could be used as the rheological parameter to characterize the interfacial character and could be used to interpret the variations of η0,bc of the in situ compatibilized polymer blend successfully. In addition, η0,bc is more sensitive to the shear viscosity variations of the components than the phase structure geometry evolution of the reactive blends.

Confined Crystallization in Polymer Blends: DSC Studies of the Behavior and Kinetics of Isothermal Crystallization of Polypropylene in Poly(cis-butadiene) Rubber Blends

Thermal properties of polypropylene with poly(cis-butadiene) rubber (iPP/PcBR) blends have been measured by differential scanning calorimetry (DSC), and the melting point Tm, crystallization temperature Tc, enthalpy Δ H (melting enthalpies and crystalline enthalpies), and equilibrium melting point T0 m have been measured and calculated. The variation of Tm, Tc, Δ H and T0 m with composition in the blends was discussed, showing that an interaction between phases is present in iPP/PcBR blends. The degree of supercooling characterizing the interaction between two phases in the blends and the crystallizability of the blends which bears a relationship to the composition of the blends was discussed. The kinetics of isothermal crystallization of the crystalline phase in iPP/PcBR blends was studied in terms of the Avrami equation, and the Avrami exponent n and velocity constant K were obtained. The Avrami exponent n is between 3 and 2, meaning that iPP has a thermal nucleation with two dimensional growths. The variation of the Avrami exponent n, velocity constant K, and crystallization rate G bear a relation to the composition of the blends, n increases with increasing content ofPcBR. K also increased with increasing content of PcBR. All of the K for the blends are greater than for pure iPP. The crystallization rate G (t1/2) depends on the compositions in the blends; all G of the blends are greater than for iPP.

Morphology Development in Multi‐Component Polymer Blends: I Composition Effect on Phase Morphology in PP/PET Polymer Blends

The relationship of the phase morphology of polypropylene/polyethylene‐terephthalate (PP/PET) blends and their corresponding compatibilized blends with composition was investigated using digital image analysis. A diameter, d g , was defined and calculated to discuss the phase morphology of this polymer blend system. A figure‐estimation method was introduced to determine the width of the distribution of d g . Based on the method, it is proven that the distribution of d g obeys a log‐normal distribution and consequently, the distribution width, σ was calculated. Further, a fractal dimension, D f , was introduced to describe the distribution of main sizes of the particles of the dispersed phase. The results showed that, while d g increased with the concentration of the dispersed phase, σ and D f show different dependence relations on composition;σ increases monotonously but D f shows a maximum at a PET content of 30%, indicating that, even though the whole size distribution is much broader, the distribution of the main body of size becomes more uniform when the content of PET is less than 30%.

Surface modification of polypropylene by ethylene plasma and its induced β-form in polypropylene

This study aims to investigate the chemical structure and morphology of plasmapolymers produced by deposition of ethylene on the surface of polypropylene. The deposition films (sediments) of ethylene plasma on the surface of polypropylene are nonuniform, and the characterization results indicate the existence of hydroxyl groups and aldehyde (or ketone) groups in the sediments. The sediment of ethylene plasma on the polypropylene surface could induce the growth of β-form crystals in the surface layer of polypropylene.

Shear-induced crystallization in phase-separated blends of isotactic polypropylene with ethylene-propylene-diene terpolymer

The compatibility between isotactic polypropylene (iPP) and ethylene-propylene-diene terpolymer (EPDM) in the blends was studied. SAXS analysis indicates that iPP and EPDM phases in the binary blend are incompatible. Isothermal crystallization behaviors of iPP in phase-separated iPP/EPDM were studied by in situ POM equipped with a Linkam shear hot stage. It was found that typical spherulites of iPP were formed both in neat iPP and in iPP/EPDM blends. The radial growth rate (dR/dt) of spherulites of iPP in the blend was not influenced by EPDM phases. Further investigations on isothermal crystallization of iPP in iPP/EPDM after shear with a fixed shear time showed that the crystallization rate of iPP in the blends increased with increasing shear rates, whereas, the crystallization rate was much lower than that of neat iPP. WAXD results showed that β-crystal iPP was formed in neat iPP as well as in iPP/EPDM blends after shearing and the percentage of β-crystal bore a relationship to the applied shear rate. The presence of EPDM resulted in lower percentage of β-crystal in the blends than that in neat iPP under the same constant shear conditions. SAXS experiments revealed that shear flow could induce formation of oriented lamellae in iPP and iPP in the blends, and the presence of EPDM led to a reduced fraction of oriented lamellae.

Phase Structure Characterization by SALS of In Situ Compatiblized Binary Polymer Blends and Its Relation to Rheology

Phase structures of polypropylene (PP)/polystyrene (PS) blends, in situ compatiblized by a Friedel–Crafts alkylation reaction with anhydrous aluminum chloride (AlCl3) as a catalyst, were investigated by small angle light scattering (SALS). The invariant Q, the content of compatible domain between the two phases, i.e., the interphase volume fraction, and the interphase thickness of the in situ compatiblized binary polymer blends were determined by Rayleigh scattering, as well as the phase structure parameters, such as correlation distance and average chord lengths. The results showed that the obtained blend is a partially compatible system. The invariant Q, the interphase volume fraction, and the interphase thickness all can be used to characterize the in situ interfacial compatiblization of the blends and all showed a nonlinear dependence on the in situ formed copolymer content. Further investigations revealed that the contribution of the interfacial modification to the zero shear viscosity of the in situ compatiblized blends showed exponential decay with the increasing invariant Q and showed exponential growth with the increasing volume fraction and thickness of the interphase in the blends. The nonlinear relations between the three phase structure parameters and the in situ formed copolymer content, as well as the nonlinear relations between the three phase structure parameters and the contribution of the interfacial modification to the zero shear viscosity of the blends, might be closely related to the in situ formation of the copolymer and its effect at the interfacial surface in the blends.