Volume 23, Issue 4

Miscibility of styrene-acrylonitrile (SAN) and ethylene-propylene-diene (EPDM) blends containing high impact polystyrene (HIPS) as a compatibilizer were studied. Blends were characterized by determination of mechanical properties, glass transition temperatures and their morphology was inspected by scanning electronic microscopy. Blends were separated into components to clarify the effects of the extrusion process and the obtained components were characterized by FTIR spectroscopy and by gel permeation chromatography. It was observed that significant fraction of in situ formed graft copolymer is formed during extrusion, which contributes to the homogeneity of the studied systems. The results show finer morphology and size reduction of the dispersed phase due to enhanced interface adhesion in compatibilized blends, with enhanced mechanical properties.

Multi-cavity injection molding has been regarded as low cost mass-production method for producing plastic products such as optical elements. However, the flow imbalance during filling a multi-cavity mold using symmetrical runner system is a serious problem. This paper is devoted to improving the flow balance by modifying the runner system design. For this purpose, four eight-cavity molds with four modified symmetrical runner systems are designed, constructed and tested. They are tapering H-type runners, pinned H-type runners, curved A runners, and curved B runners. The flow imbalance in each runner system is observed and measured with the aid of short-shot experiments. The experimental results indicate that the tapering H-type runner system can improve flow balance. The pinned H-type runner system fails to improve flow balance. The curved A and B runner system can reverse the imbalance trend, but the stability of the curved systems is poor at high melt temperature.

High molecular weight poly(ethylene terephthalate) (HMW-PET) (intrinsic viscosity of 0.809 dL/g) and its nanocomposites with 1 wt.% organoclay C 12 PPh-Cl − and 1 and 2 wt.% trisilanol isobutyl-poly(hedral oligomeric silsesquioxane) (POSS) were high-speed melt spun over the range of take-up speeds 1 to 4.5 km/min, and the effects of nanoparticle type on the fiber properties were investigated. The clay and POSS nanocomposites exhibited quite different melt spinning behaviors. The neat PET and PET/POSS nanocomposites showed a neck-like deformation distinctly from the take-up speed of 3.5 and 3 km/min while PET/clay nanocomposites did not show any neck-like deformation over the entire spinning speed range. In comparison with nanocomposite chips clay gave rise to re-aggregation of nanoparticles whereas POSS made little change in dispersion. Clay suppressed the crystallization of PET during high-speed spinning although it had more effective nucleation effects at the static state than POSS. Clay nanocomposite fibers gave lower modulus and higher elongation at break than PET fibers. On the other hand, the mechanical properties of POSS nanocomposite fibers were almost equal or slightly better than PET fibers.

We investigate effects of electric current on formations of beads in electrospinning by changing an electric conductivity of a poly(vinyl alcohol) (PVA) aqueous solution and spinning conditions, such as applied voltage, distance between a tip of needle and a collector, and relative humidity. From the results of experiments done by changing the conductivity of PVA aqueous solution and spinning conditions, we found that a beads formation is suppressed at a lower electric current. Furthermore, when the electrospinnings are performed at a certain constant electric current in various spinning conditions where the applied voltage and tip-collector distance are changed so as to give the same constant electric current, resultant PVA fibers have no beads and almost the same distribution of fiber diameter.

The processing behavior of a number of LLDPE/LDPE blends with emphasis on the effects of manufacturing technology of LLDPE and long chain branching is presented. A single low-density polyethylene was blended with two Ziegler-Natta linear-low-density polyethylenes LLDPE's and two metallocene-LLDPE's having distinctly different molecular structures. The weight fractions of the LDPEs used in the blends were 1 wt.%, 5 wt.%, 10 wt.%, 20 wt.%, 50 wt.% and 75 wt.%. Capillary extrusion reveals that the onset of sharkskin and gross melt fracture are slightly influenced with the addition of LDPE into LLDPE. However, the amplitude of the oscillations in the stick-slip flow regime was found to scale well with the weight fraction of LDPE even at amounts as low as 1 wt.%. Furthermore, it was observed that the onset of this flow regime was shifted to higher shear rates with increase of LDPE content. Shear rheology was found to be insensitive to detect small levels of LDPE. On the other hand, extensional rheology was found to be capable of detecting levels of LDPE as low as 1 wt.% at high Hencky strain rates (typically greater than 5 s −1 ) although only for certain blends.

A novel method for the continuous dispersion of carbon nanofibers (CNFs) in a polymer matrix for manufacturing high performance nanocomposites was developed using an ultrasonically assisted single screw extrusion process. The effect of ultrasound on die pressure, electrical and thermal conductivity, rheological, morphological and mechanical properties of polyetherimide (PEI) filled with 1 to 20 wt.% CNFs was studied. A reduction in the die pressure and percolation threshold of CNF/PEI nanocomposites with a permanent increase in the viscosity and a permanent decrease in tan δ was achieved through ultrasonic treatment. Morphological studies of the treated nanocomposites revealed their improved homogeneity leading to an increase of the Young's modulus and electrical and thermal conductivity.