Moo Sung Lee

Effects of comonomers and shear on the melt intercalation of styrenics/clay nanocomposites

Abstract The effect of polar comonomers introduced into polystyrene (PS) chains on the melt intercalation into organosilicate is investigated in terms of shear and annealing time. In the case, where the interaction between polymers and silicate layers is relatively weak, e.g. PS/organosilicate hybrids, it is difficult for the polymer chains to diffuse into interlayers of organosilicate and the hybrids are unstable under shear. For hybrids in which the interaction is enhanced by incorporating polar comonomers, e.g. acrylonitrile (AN) and methylvinyl oxzoline (OZ), their structures are stable even after a long mixing time. However, they do not show an exfoliated structure under the mixing conditions used in this study. The interaction between the comonomer and the silicate surface is investigated indirectly via both X-ray diffractional and FTIR spectral analyses. It is concluded that the structural stability of polymer/organosilicate hybrids is very dependent on the relative magnitude of the interactions between polymers, organic modifiers, and silicate layers.

Compatibilization of immiscible poly(l-lactide) and low density polyethylene blends

Blends of poly(l-lactide) (PLA) and low density polyethylene (LDPE) were prepared by melt mixing in order to improve the brittleness of PLA. A reactive compatibilizer with glycidyl methacrylate (GMA), PE-GMA, was required as a compatibilizer due to the immiscibility between PLA and LDPE. It contributes to reduce the domain size of dispersed phase and enhance the tensile properties of PLA/LDPE blends, especially for PLA matrix blends. A reaction product between PLA and PE-GMA, which was formed during melt-mixing and considered to act as a reactive compatibilizer, was characterized using1H-NMR spectroscopy.

Preparation of clay-dispersed poly(styrene-co-acrylonitrile) nanocomposites using poly(ϵ-caprolactone) as a compatibilizer

Abstract Poly(styrene-co-acrylonitrile) (SAN)/organoclay nanocomposites were prepared using poly(ϵ-caprolactone) (PCL) as a compatibilizer. Two-step mixing sequence was used to prepare the SAN nanocomposites: PCL/organoclay master batches with different degree of intercalation were prepared by melt mixing first, and then they were melt-mixed with SAN, where PCL is miscible with SAN. The intercalation behavior of PCL in the master batches was investigated in terms of the type of organic modifier and mixing conditions such as shear rate, mixing temperature and mixing time. Longer mixing time and lower mixing temperature were required to prepare exfoliated PCL master batches. As the degree of exfoliation of clays becomes better, the stiffness reinforcement effect of the organoclays increases in both PCL/organoclay master batches and their blends with SAN.

Preparation of functionalized polystyrene by reactive extrusion and its blend with polyamide 6

Abstract Maleic anhydride (MAH) was grafted to polystyrene (PS) by reactive extrusion in the presence of a free-radical initiator. The grafting reaction was confirmed by spectroscopic analyses. The amount of MAH grafted on PS was evaluated by a titration method. The polystyrenes functionalized with MAH (MPSs) were blended with polyamide 6 (PA6), and the effect of MAH units incorporated in PS on the compatibility with PA6 was examined by measuring the morphology, rheological and tensile properties. Although the content of MAH in MPS prepared in this study was much less than 1 wt%, a significant change in the morphology and rheological and tensile properties of PA6/MPS blends was observed. The formation of PS-g-PA6 copolymers during melt mixing of PA6 and MPS was evaluated using spectroscopic analyses and also confirmed from the high stability of the suspension obtained by dissolving the blend in formic acid.

Melt free‐radical grafting of hindered phenol antioxidant onto polyethylene

A monomeric antioxidant (3) was prepared by reacting 3,5-di-tert-butyl-4-hydroxybenzyl alcohol (1) with N-[4-(chlorocarbonyl) phenyl] maleimide (2). This reactive antioxidant was grafted onto polyethylene (PE) by melt processing with free-radical initiators in a mini-max molder. The IR spectra of the grafted PE showed that the monomeric antioxidant was introduced onto the PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Also, the extent of crosslinking was indicated by the gel content. Grafting occurred in the following order: dicumyl peroxide (DCP) > benzoyl peroxide > 2,2′-azobisisobutyronitrile. The influences of the DCP concentration and monomeric antioxidant on the extent of grafting were studied. The effects of the reaction time and temperature were also determined.

Effect of molecular weight of functionalized polystyrene on the compatibility of blends of polyamide 6 and polystyrene

Abstract The effect of polystyrene modified with maleic anhydride (MPS) on the compatibility of the immiscible blends of polyamide 6 and polystyrene was investigated as a function of the molecular weight of MPS. The MPS was prepared by melt extrusion in a twin screw extruder and the content of maleic anhydride in the MPS was below 1 wt%. The compatibilizing ability of the MPS was examined through several experimental techniques such as scanning electron microscopy and measurements of mechanical and rheological properties. The interfacial adhesion between two separated phases was also measured using a butt joint test. The compatibilizing ability of the MPS was very dependent on the molecular weight of the MPS. The MPS of high molecular weight seems to be more effective in reducing the domain size of dispersed phase and in increasing the interfacial adhesion.

Miscibility of poly(ether imide)/poly(ethylene terephthalate) blends

SummaryMiscibility of blends of poly(ether imide) (PEI) and poly(ethylene terephthalate) (PET) were studied by differential scanning calorimetry (DSC). Single and composition-dependent Tgs are observed over the entire composition range, indicating that the blends are miscible in the amorphous region. The overall crystallization rate of PET in the blends decreased with increasing the PEI content. The interaction energy density B, which was calculated from the melting point depression of the blends using Nishi-Wang equation, was-5.5 cal/cm3.

Effect of Matrix Viscosity on Clay Dispersion in Preparation of Polymer/Organoclay Nanocomposites

The viscosity effect of matrix polymer on melt exfoliation behavior of an organoclay in poly(ε-caprolactone) (PCL) was investigated. The viscosity of matrix polymer was controlled by changing the molecular weight of poly(ε-caprolactone), the processing temperature, and the rotor speed of a mini-molder. Applied shear stress facilitates the diffusion of polymer chains into the gallery of silicate layers by breaking silicate agglomerates down into smaller primary particles. When the viscosity of PCL is lower, silicate agglomerates are not perfectly broken into smaller primary particles. At higher viscosity, all of silicate agglomerates are broken down into primary particles, and finally into smaller nano-scale building blocks. It was also found that the degree of exfoliation of silicate layers is dependent upon not only the viscosity of matrix but thermodynamic variables.

Segmented block copolyetheramides based on nylon 6 and polyoxypropylene. III. SAXS analysis

Morphologic characteristics of segmented block copolyetheramides based on nylon 6 and polyoxypropylene ( POP ) were investigated as a function of the compositions and block lengths of the hard and soft segments using small angle X-ray scattering (SAXS). Three POPs with different molecular weights were used as a soft segment. One-dimensional correlation functions were obtained from the desmeared intensity SAXS curves using the method developed by Vonk and Kortleve. The interdomain spacings were determined from the correlation distance at the peak position of the correlation function. From the dependence of the correlation distance on soft segment content, we deduced that an increase in the hard-segment length may lead to crystal formation by a chain-folding mechanism. The thickness of phase boundary was determined from the smeared intensity data using the method of Koberstein. A decrease in the phase boundary thickness with increasing soft-segment content suggests that an increase in the chain mobility by soft segment facilitates the regular arrangement of the hard segment, resulting in the formation of the hard domain with a narrow interfacial region.

Effect of interchange reactions on the molecular weight distribution of poly(ethylene terephthalate) : a Monte Carlo simulation

The effect of the interchange reactions of poly(ethylene terephthalate) (PET) on its molecular weight distribution (MWD) was analyzed using a Monte Carlo simulation method. Three kinds of motions, which correspond to the direct ester(SINGLEBOND)ester interchange reaction, alcoholysis, and internal alcoholysis in polyester, were performed in this simulation: bond flip, end attack, and backbite. Two systems with two different types of nonequilibrium distribution (monodisperse and bimodal distribution) were initially prepared. The initial biases from equilibrium MWD are rapidly relaxed to an equilibrium MWD as the reaction progresses. The MWD at equilibrium is well described by the most probable MWD proposed by Flory. From the polydispersity data, it is concluded that about 0.3 interchanges per segment are sufficient to equilibrate the nonequilibrium system. For the validity of the simulation, the variation of MWD of the mixtures of two PETs having different molecular weights were monitored using gel permeation chromatography. The agreement between simulation and experiment is remarkably good.