Tae-Kyu Kang

Microstructure, tensile properties, and biodegradability of aliphatic polyester/clay nanocomposites

Novel biodegradable aliphatic polyester (APES)/organoclay nanocomposites were prepared through melt intercalation method. Two kinds of organoclays, Cloisite 30B and Cloisite 10A with different ammonium cations located in the silicate gallery, were chosen for the nanocomposites preparation. The dispersion of the silicate layers in the APES hybrids was characterized by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile properties and the biodegradability of the APES/organoclay nanocomposites were also studied. APES/Cloisite 30B hybrids showed higher degree of intercalation than APES/Cloisite 10A hybrids due to the strong hydrogen bonding interaction between APES and hydroxyl group in the gallery of Cloisite 30B silicate layers. This leads to higher tensile properties and lower biodegradability for APES/Cloisite 30B hybrids than for the APES/Cloisite 10A hybrids.

Preparation and Characterization of Poly(butyleneterephthalate)/Organoclay Nanocomposites

PBT/organic montmorillonite (MMT) nanocomposites were prepared via melt intercalation and their nanostructure was characterized by means of X-ray diffraction and transmission electron microscopy. Nanocomposite formation requires sufficiently hydrophobic organically modified layered silicates, as well as the presence of polar interactions between silicate and polymer. Three different alkylammonium surfactants were used to modify MMT. In addition, epoxy resin was added as a third component, and the effects on the intercalation and exfoliation behavior of the PBT nanocomposites were investigated.

Effect of processing variables on the crosslinking of HDPE by peroxide

In this work, the effect of processing variables such as temperature, shear rate, and the content of crosslinking agent on the melt torque behavior in a mixer, the degree of crosslinking, the thermal properties and density of high density polyethylene (HDPE) was investigated. Di-ter-butyl peroxide (DTBP) was used as a crosslinking agent. It was concluded that the crosslinking behavior of HDPE by peroxide was an overall function of temperature, shear rate in terms of mixer rpm, and the peroxide content. Crosslinking termination time was shortened on increasing the reaction temperature, regardless of the mixer rpm. As the mixer rpm increases, the crosslinking reaction time was shortened by the effect of shear heating. As a result, athough the crosslinking reaction termination time of HDPE depends on both the temperature and shear rate at constant peroxide contents the temperature was the more dominant. It was found that there is an optimum peroxide content, here 0.6 phr, to crosslink HDPE. In addition, the crosslinking of HDPE gives rise to a decrease in crystallinity, followed by a decrease in density.

Syntheses and characterization of poly(ethylene terephthalate) modified with p-acetoxybenzoic acid

Though the structure and properties of a copolyester of 40 mole % of polyethylene terephthalate (PET) and 60 mole % p-hydroxybenzoic acid (PHB) (PET/60PHB) and their blends have been well documented, no work has been reported in an open literature on the systematic investigation of the PET copolymers modified with broad range of p-acetoxybenzoic acid (PABA) composition as yet. In this study, several PETA-x copolyesters having various PABA compositions from 10 to 70 mole % were prepared by the melt reaction of PABA and PET without a catalyst, where x denotes the mole % of PABA. And the modified polyesters obtained were characterized by 1H-NMR spectrophotometry, X-ray diffraction pattern, polarizing microscopy, thermal analysis, and rheometry. The anisotropic phase appeared when x is above 50 mole % of PABA, and especially for the xs of 60 and 70 mole %, the nematic liquid crystalline texture appeared clearly on the whole matrix. As the mole % of PABA increased, melting temperature, heat of fusion, crystalline temperature, degree of crystallinity, and the glass transition temperature of the modified PET were decreased, but the thermal stabilities of those copolyesters were increased. The dependence of melt viscosity on the shear rate for PETA-50 ∼ 70 followed the typical rheological behavior of liquid crystalline polymers. Finally, it was concluded that the PETA-x copolyesters having compositions of higher than 50 mole % of PABA exhibit the behavior of thermotropic liquid crystalline polymers.

Gelation Behavior of Three-functional Silanes for Preparation of Mesoporous Silicas (I)

We studied on the gelation behavior in a sol-gel reaction of three-functional silanes under various reaction parameters such as solvents, concentration of catalyst, and gelation time. Trimethoxyvinylsilane(TMVS) or Triethoxyvinylsilane(TEVS) was used as a precursor and poly(ethylene oxide- b -propylene oxide- b -ethylene oxide)(EPE) was used as a structure directing agent.