Volume 18, Issue 1-2

Stochastic dynamics simulations were performed to investigate the viscoelastic properties of polymer blends. In this simulation, three model systems with different intermolecular interactions are used to examine the effect of intermolecular interaction on the viscoelastic properties of polymer blends. Structural information such as the radius of gyration, orientation factor and radial distribution function of polymers is calculated from computer simulations as a function of shear rate and then is related to simulated viscoelastic properties of polymer blends. The effect of intermolecular interaction on the viscosity becomes different depending upon the magnitude of shear rate. At lower shear rate regions, more attractive intermolecular interaction results in lower viscosity due to chain stretching. But, at higher shear rate regions, more attractive interaction results in higher viscosity due to more dense packing of chains induced by the intermolecular attraction.

Structure-property relationships of poly(butylene terephthalate) (PBT) / polyolefin (PO) (80/20) blends modified by a reactive compatibilizer, ethylene-acrylic ester-glycidyl methacrylate terpolymer (BAG), were investigated as part of studies on toughening of PBT. POs used for the study were ethylene propylene rubber (EPR), low-density polyethylene (LDPE), and high-density polyethylene (HDPE), whose deformabilities were different at room temperature. It was observed that the particle size of PO in the discrete phase was the smallest when the EAG content was 8~12 wL%. Shear viscosity of the blends increased as the particle size was decreased. It seems that the morphology and rheological properties of the blends were affected by graft copolymers formed in situ from EAG and PBT during melt mixing. Brittle-tough transition of impact strength of the PBT/EPR/EAG blends was observed when the EAG content was increased from 0 to 4 wt% at room temperature. However, blends of PBT/LDPE/EAG and PBT/HDPE/EAG showed brittle-tough transition with increasing the EAG content from 8 wt% to 12 wt%. It is postulated that toughening of the PBT depends on the deformability of the discrete PO particle as well as its size.

Novel silicon-containing nonlinear optical (NLO) polyesters were prepared by condensation polymerization as well as a new carbodiimide polycondensation of bis(4-chlorocarbonylphenyl)dimethylsilane (DCMS) with 4-(N, N′- bis(2-hydroxyethyl)amino-4′-nitrostilbene (DANS-diol). The NLO polyesters were obtained in relative yields with a high intrinsic viscosity of 0.60 dL/g. The intrinsic viscosity was increased by adding a small amount of a highly reactive diol (bisphenol-A). Molecular structural characterization of the resulting polymers was achieved by typical analytic methods, such as 1 H- and 13 C-NMR, FT-IR, and UV-vis spectroscopies. These silicon-containing side chain NLO polyesters were highly soluble in aprotic polar solvents, such as DMAc, DMF, NMP, γ-butyrolactone, etc. These polymers were found to be amorphous from DSC analysis. They exhibited a relatively higher T g and thermal stability up to 220°C. The value of the electro-optic coefficient measured at the wavelength of 1.3 μm is in the range of 2 to 5.5 pm/V, and the refractive indices measured at the wavelength of 1.3 pm is in the range of 1.6213 to 1.6233.

The surface area change of UHMWPE fibers which underwent oxygen plasma treatment was measured as a function of plasma power and plasma treatment time. The interfacial adhesion of oxygen plasma treated UHMWPE fibers was evaluated via micro-droplet test and double cantilever beam test Surface area increased with plasma treatment time at 30 and 60W, but showed a maximum at 100 and 150W. The interfacial adhesion of UHMWPE fibers to vinylester resin exhibited the same trend as the surface area. SEM analysis revealed that oxygen plasma treatment roughened UHMWPE fibers by forming micro-pores leading to increased surface area. However, 1S0W plasma treatment led to degradation of the fibers and thus resulted in failure within the fiber surface layers, producing ribbon-like strips of fiber.

Relationships between fatigue behavior and nonlinear dynamic viscoelastic properties for the annealed, isothermally crystallized, and oriented high-density polyethylenes (HDPEs) with different molecular aggregation states were intensively discussed. Nonlinear dynamic viscoelasticity under cyclic fatigue was estimated on the basis of nonlinear viscoelastic parameter (NVP) which was defined as the contribution of higher harmonics of Fourier expanded stress signal. Fatigue strength of specimens decreased with an increase in the magnitude of NVP. Thus, NVP can be used as an index of fatigue strength for polymeric solids. Also, higher-order structural changes of specimens by cyclic straining were investigated and it was concluded that the nonlinear dynamic viscoelasticity under cyclic fatigue became dominant with an increase in cyclic straining concentration at the amorphous and/or spherulite or crystallite boundary regions.

An investigation on the frictional performance of a natural rubber compound containing polynorbomene (PN) vulcanizate powder was carried out at various temperatures between -20°C and 60°C. The glass transition temperature, T g , of the PN vulcanizate was 15°C. At temperatures below its T g , the frictional coefficient of the composite significantly increased to the extent of 10% with a 10 phr addition of PN vulcanizate powder, while the wear rates were not greatly affected. The wear behavior of the composite was strongly dependent on the frictional work input.

The compatibilizing effect of three kinds of poly(styrene-co-glycidyl methacrylate) (SGMA) in a modified poly(2,6-dimethyl-1,4-phenylene oxide) (MPPO)/poly(butylene terephthalate) (PBT) blend was studied based on the morphology observed by scanning electron microscopy, dynamic mechanical properties, rheological properties, and mechanical properties. When the content of SGMA in the blend was fixed at 3 phr, the compatibilizing effect of SGMA increased as the GMA content in SGMA was increased. When the content of the reactive GMA monomeric unit in the blend was fixed at 0.37 phr, SGMA containing 4 mol% of GMA unit was most effective for compatibilization among three kinds of SGMAs.

Limiting oxygen index (LOI) value, glass transition temperature (T g ), thermal degradation profile, morphology, and tensile strength and elongation at break of the flame-retarding polycarbonate (PC)-poly(acrylonitrile- butadiene-styrene) (ABS) (7/3) blends were studied. The flame retardants used were huntite-hydromagnetite compounds (HHM), triphenyl phosphate (TPP), zinc stannate, and antimony trioxide. The LOI values were increased with the increase of TPP content, but they did not change significantly when the HHM was used as a flame retardant Glass transition temperatures of the flame-retarding PC-ABS (7/3) blends were decreased significantly when TPP was added to the blends. This is mainly due to the plasticizing effect of the TPP on the PC-ABS (7/3) blends. In the flame-retarding PC-ABS (7/3) blends, the LOI value, tensile strength, and elongation at break were measured and found to be 24.6 - 31.6%, 41.4 - 50.3 MPa, and 2.16 - 33.7%, respectively. These LOI values and mechanical properties were achieved when the TPP, zinc stannate, and antimony trioxide were used as flame retardants, and when dodecylbenzenesulfonic acid sodium salt and dimethylsulfone were used as additives into the PC-ABS (7/3) blends.

Composite membranes made of β-chitosan extracted from squid were prepared and crosslinked with sulfuric acid with various crosslinking times. Dehydration performance of the water/ethanol and water/isopropanol mixtures by pervaporation experiments using β-chitosan composite membranes was investigated. Crosslinking and deacetylation degree of the membrane were confirmed by ATR-FT-IR and elemental analysis (EA), respectively. Pervaporation experiments were investigated under various feed concentrations and temperatures. β-Chitosan showed a higher degree of swelling in water than a-chitosan, resulting in a higher flux of β-Chitosan than that of α-chitosan. β-Chitosan composite membranes showed good dehydration performance in pervaporation of a water/alcohol mixture. For water/ethanol mixtures, separation factor (α) - 270; flux (J) - 700 g/m 2 hr, for water/isopropanol, α - 150; J -1800 g/m 2 hr, respectively.

Melt blends of SAN with acrylonitrile-styrene-acrylic ester copolymer (ASA) were prepared using a twin-screw extruder. Morphology, mechanical and viscoelastic properties of the SAN/ASA blend were studied in the full range of compositions. TEM micrographs showed a bimodal distribution of the rubber particles with 0.7 μm and 0.2 μm in diameter. The transition from brittle to ductile mode of failure occurred in the range of 20~30 wt% ASA The blends showed typical behavior of an immiscible system where melt viscosity exhibited a positive deviation from the log additivity. The glass transition temperature (Tg) of blends did not shift with increasing ASA content, indicative of complete phase separation.