Yanmo Chen

Study on Phase‐Change Characteristics of PET‐PEG Copolymers

Polyethylene glycol (PEG) was selected as a phase‐change material (PCM) and the phase‐change fibers of its copolymers with polyethylene terephalate (PET), PET‐PEG, were successfully prepared by melt spinning. The PET‐PEG copolymers have solid‐solid phase change characteristics at 10–60°C without obvious liquid substance appearing, while PET/PEG blends will lose their phase‐change characteristics since the PEG of the blends may melt and leak under high temperature. By controlling the molecular weight and relavent proportion of PEG added, the phase‐change temperature range and the enthalpy can be adjusted.

Synthesis and properties of a spinnable phase change material CDA-IPDI-MPEG

Abstract A comb like phase change material (PCM) CDA-IPDI-MPEG, based on cellulose diacetate (CDA) as a backbone, with methoxy polyethylene glycol (MPEG) grafted onto it, was synthesized by a two-step reaction in the presence of dibutyltin dilaurate (DBTDL) catalyst system, using acetone as solvent and isophorone diisocyanate (IPDI) as crosslinking reagent. Size exclusion chromatography (SEC) was used to characterize the molecular weight distribution of each step reaction products. Back titration was utilized for determination of free isocyanate. The molecular structures were confirmed qualitatively using FTIR and H1-NMR measurements. Phase change properties were characterized by differential scanning calorimetry (DSC).

Poly(m‐Phenylene Isophthalamide) Ultrafine Fibers from an Ionic Liquid Solution by Dry‐Jet‐Wet‐Electrospinning

Ultrafine poly(m‐phenylene isophthalamide) (PMIA) fibers from PMIA solution in an ionic liquid via dry‐jet‐wet electrospinning technology are described. The morphology of the fibers with and without treatment in a coagulation water bath in the dry‐jet‐wet‐electrosinning process was observed by scanning electrical microscopy (SEM) and a high resolution optical microscope. The crystal structure of the fibers was analyzed by wide angle X‐ray diffraction (WAXD). The differences of morphologies and properties between the ultrafine fibers obtained by the electrospinning process and fibers from conventional wet‐spinning technology are discussed. The thermal properties of the ultrafine PMIA fibers were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

Crystallization Behavior and Crystal Morphology of PTT/PBT Blends

The crystallization behavior and crystal morphology of the poly(trimethyl terephthalate) (PTT)/poly(butylene terephthalate) (PBT) blends were investigated by means of differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD) and polarized light microscopy (PLM) techniques. It was found that the two components crystallized simultaneously in the crystalline regions. The degree of crystallinity changed with PTT content. Crystalline properties were worse when the ratio of PBT and PTT contents was close to 50:50, but were better when PBT content was greatly different from PTT content.

Mechanism of the Formation of Concentric Ring-like Patterns on PHBV Spherulites

Abstract Polymers of the 3-hydroxybutyrate-co-3-hydroxyvalerate type are ideal systems for the study of spherulite morphology. The growth of spherulites was studied using polarizing microscopy with heat-stage and scanning electron microscopy (SEM). Some concentric ring features on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV spherulite were observed. The SEM photos proved that the concentric rings occur on the surface of spherulite. And its a “Z”-shape feature, the outer ring is higher than the inner. The factors that influence the phenomenon include the temperature, the thickness of film, and the radius of the spherulite, etc. The possible mechanism of this phenomenon is given. It is postulated that the concentric rings are formed by the change on physical parameters when crystallizing.

Toughened Poly(Trimethylene Terephthalate) by Blending with a Functionalized Metallocenic Poly(Ethylene-Octene) Copolymer

New toughened poly(trimethylene terephthalate) (PTT) materials were obtained by melt blending with maleic anhydride grafted poly(ethylene-octene) (POEg). Rheological properties, mechanical properties, and morphological characteristics of PTT/POEg blends at four different compositions—95/5, 90/10, 80/20, and 70/30—were studied. The melt viscosity of the blends shows a linear decrease on increasing the POEg content. The addition of rubbery POEg to the PTT matrix increases the impact strength, while tensile properties decrease. Scanning electron microscopy (SEM) displayed a very good dispersion of POEg particles in the PTT matrix. Differential scanning colorimetry (DSC) experiments showed that for all samples the melting point was almost constant and the crystallinity did not show obvious differences. SEM results showed shear yielding of the PTT matrix was the major toughening mechanism.

Studies on melt spinning of sea-island fibers. II. Dynamics of melt spinning of polypropylene/polystyrene blend fibers

A two-dimensional (2-D) model for melt spinning of iPP/aPS blend fibers is proposed based on two-phase models on density and crystallinity and log-additive rule on elongational viscosity. A computer program is developed based on a hybrid method of fourth-order Runge-Kutta method and implicit Crank-Nicolson method to solve the model equations to obtain the axial profiles of fiber diameter, velocity, gradient of velocity and crystallinity, and the 2-D profiles of temperature, elongational viscosity and elongational stress. The simulated fiber diameters are compared with the measured diameters to verify the certainness of the simulation. The simulated results show that polymer melt jets solidify at the positions of about 40 cm beneath the spinneret which is verified by on-line measurement of fiber diameter. And the radial gradient of temperature, elongational viscosity and elongational stress reaches to 104 to 105 °C/m, 105 to 106 Pa·s/m and 105 to 106 Pa/m, respectively, at the discussed take-up velocities.

Morphological and Rheological Properties of Poly(Trimethylene Terephthalate)/Maleic Anhydride Grafted Poly (Ethylene-Octene)/Organoclay Ternary Nanocomposite

Poly(trimethylene terephthalate) (PTT)/poly(ethylene-octene) POE-g-MA/organoclay ternary nanocomposites were prepared using melt blending in order to simultaneously improve the toughness and stiffness of PTT. The phase morphology and dispersion of organoclay were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), and transmission electron microscopy (TEM). The melt rheological behavior of the ternary nanocomposites was determined by plate/plate rheological measurements. XRD and TEM analysis indicated that the ternary nanocomposites contained exfoliated nanoparticle when a small amount of organoclay (1 part per hundred) was added. The high aspect ratio of the organoclay platelets induced the average size of the dispersed domain to become smaller. Melt rheological studies revealed that the ternary nanocomposites exhibited strong shear thinning behavior and showed good processability.

Microstructures and Mechanical Properties of Poly(Trimethylene Terephthalate)/Maleic Anhydride Grafted Poly(Ethylene-octene)/Polypropylene Blends

A range of blends based on 70 wt% of poly(trimethylene terephthalate) PTT with 30 wt% dispersed phase were produced via melt blending. The dispersed phase composition was varied from pure maleic anhydride grafted poly(ethylene-octene) (POE-g-MA) over a range of POE-g-MA:polypropylene (PP) ratios. The micromorphology and mechanical properties of the ternary blends were investigated. The results indicated that the domains of the POE-g-MA are dispersed in the PTT matrix, and at the same time the POE-g-MA encapsulate the PP domains. The interfacial reaction between the hydroxyl-end group of PTT and maleic anhydride (MA) during melt blending changes the formation from “isolated formation” to “capsule formation,” where the PP domains are encapsulated by POE-g-MA. Compared to the PTT/POE-g-MA blends, mechanical properties of ternary blends, such as tensile strength and Youngs modulus, were improved significantly.

Effect of Organoclay Platelets on Crystallization of PTT/EPDM-g-MA Blends: Isothermal Crystallization

The effects of organoclay platelets and ethylene-propylene-diene copolymer grafted with maleic anhydride (EPDM-g-MA) on the isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT) were investigated by differential scanning calorimeter (DSC) over the crystallization temperature range of 164°C–180°C. The crystallization kinetics under isothermal conditions could be described by the Avrami equation, with values of the Avrami exponent between 2.4 and 2.9 for all samples. The crystallization rate parameters (K) decrease with increasing of the melt crystallization temperature for all samples. The activation energies were determined by the Arrhenius equation for isothermal crystallization. The equilibrium melting point of isothermally crystallized samples was also evaluated.