Sung Chul Kim

Effect of compatibilizer on the crystallization, rheological, and tensile properties of LDPE/EVOH blends

The effect of the compatibilizer on the crystallization, rheological, and tensile properties of low-density polyethylene (LDPE)/ethylene vinyl alcohol (EVOH) (70/30) blends was investigated. Maleic anhydride-grafted linear low-density polyethylene (LLD-g-MAH) was used as the compatibilizer in various concentrations (from 1 to 12 phr). The interesting effect of compatibilization on the crystallization kinetics of the blends was noted, and the correlation between the morphology and the rheological and tensile properties was also discussed. Morphological analysis showed that the blends exhibited a regular and finer dispersion of the EVOH phase when LLD-g-MAH was added. Nonisothermal crystallization exotherms of the compatibilized LDPE/EVOH blends showed the retarded crystallization of the dispersed EVOH phase, which probably resulted from the constraint effect of the grafted EVOH (EVOH-g-LLD) as well as the size reduction of the EVOH domains. The blends exhibited increased melt viscosity and storage modulus and also enhanced tensile properties with the addition of LLD-g-MAH, which seemed to be attributable to both dispersed particle-size reduction and improved interfacial adhesion.

Laminar Morphology Development Using Hybrid EVOH-Nylon Blends

Properties of blends having two types of hybrid dispersed phases as laminar morphology were investigated. The hybrid dispersed phases were prepared by preblending nylon and ethylene–vinyl alcohol (EVOH) in solid state (E + N) and in melt state (E/N). Oxygen and toluene barrier properties through the hybrid-dispersed phases in low-density polyethylene (LDPE) matrix were analyzed considering the morphological changes (number and size of layers). Oxygen barrier properties of the blends of LDPE–E + N hybrid dispersed phase having separate domains of nylon and EVOH were found to be linearly dependent on EVOH composition in the blend, but toluene barrier properties of the blends exhibited negative deviation. The other hybrid dispersed phase (E/N) in LDPE matrix, having comingled dispersed phase of nylon and EVOH, exhibited positive deviations in both oxygen and toluene barrier properties. Tensile properties also showed positive deviation. Basic studies on the melt blend (E/N) of EVOH and nylon 6 showed some miscibility, which was revealed from melting point depression, and positive deviation in complex viscosity and tensile properties of the blend.

Gas transport in polyurethane-polystyrene interpenetrating polymer network membranes. II: Effect of crosslinked state and annealing

A series of polyurethane(PU)-polystyrene(PS) interpenetrating polymer network (IPN), semi-IPN (only PU component crosslinked) and linear blend membranes were prepared with varying synthesis temperature and composition. PU was first thermally polymerized, and then PS was polymerized by photolytic methods at two different temperatures, 0°C and 40°C. The permeability coefficient decreased and the separation factor increased when preparation took place at the lower temperature due to the increase in homogeneity of PU and PS as shown in the previous papers. The minimum permeability coefficient and the maximum separation factor were observed at a composition with ca. 25 wt.% PU. The permeability coefficient increased in the following sequence; IPN, semi-IPN and linear blends. Thermal annealing was adopted to study the effect of homogeneity of the two polymer components in the membrane on the gas permeation characteristics. Annealing was found to increase the permeability coefficients, while it caused a decrease in selectivity and the extent of synergistic behavior. The annealing effect on the permeation characteristics depended on the nature of crosslinking of the membrane (IPN <semi-IPN<linear blends). It was shown that a change in homogeneity, modulated by change of composition, state of crosslinking, synthesis temperature and annealing temperature etc., could play an important role in controlling the gas transport characteristics through the multicomponent polymeric membranes. The observed permeability characteristics were also substantiated by considering the densities and the degree of relative intermixing (by means of Tg variations).

Interlaminar fracture toughness of carbon fiber/epoxy composites using short Kevlar fiber and/or Nylon-6 powder reinforcement

Mode I (GIC) and Mode II (GIIC) interlaminar fracture toughness of carbon-fiber/epoxy composites have been investigated as a function of the amount of short Kevlar-29 fiber (SKF) and/or Nylon-6 powder (N6P) between continuous fiber layers. GIIC increased with increasing crack length as a consequence of the presence of SKFs bridging in the wake of propagating crack. GIIC of SKF alone could reach the maximum at an intermediate amount of SKF. GIIC of SKF and N6P was lower than that of SKF alone because N6P prevented the orientation of SKF to out-of-plane. The extent of SKFs bridging phenomenon may be influenced by the amount and orientation of SKF. GIC showed no significant effect with SKF and uniform irrespective of crack length. Scanning electron microscopy after GIIC test showed that new surfaces were created by extensive fiber bridging, pull-out and fracture of SKF in random direction without any fixed pattern.

Computer simulation for the pervaporation process of wate/ethanol mixture through interpenetrating polymer network (IPN) membranes

Abstract In this study, the pervaporation behavior of EtOH-water mixture through interpenetrating polymer network (IPN) membranes was predicted. The pervaporation characteristics of single component membranes were modelled according to the “six coefficients model” proposed by Brun [J. Membrane Sci., 23 (1985) 257]. In the case of the IPN membrane, two models were proposed according to the phase structure of the IPN. For a uniphase membrane with no phase separation, the compositional averages of the single component membrane coefficients were used. In the case of the phase separated IPN, two cases exist. The first is the island and sea model: one phase is continuous and the other is discrete. The second is the cocontinuous model, in which two continuous phases exist. For these cases the permeation rate and separation factor of the IPN membrane were calculated using the experimental sorption data and pure component values for each IPN composition. Comparison with the experimental data indicates that these models could be to predict the performances of IPN membranes depending on the morphology of the IPN.