Initiation and termination of crazes in high impact polystyrene

Initiation and termination of crazes in high impact polystyrene (HIPS) were studied by transmission electron microscope. Instead of the first initiation of crazes in the vicinity of the equator or rubber particles, ribbon-shaped crazes beyond the region were observed on the TEM photos. The starting point and the end point of each ribbon were noticed not to be randomly located on the surface of the cellar particles in HIPS. The spots connecting to the ligaments between the PS rigid inclusions in the cellar particle are found to be the locations where crazes were initiated and terminated preferentially. In addition, the crazes generated at those spots were much thicker and longer. The thoughness of high impact polystyrene was enhanced by the multiple crazes formed in the matrices, through the reduction of the craze stress at room temperature with increasing the volume fraction of polybutadiene at these spots in the dispersed phase. These results conducted that not only the cell structure of the domains in HIPS was not homogeneous but also the polybutadiene ligaments between PS rigid inclusions in the domains were inhomogeneous. Therefore, the responsibility of those polybutadiene ligaments with different thickness to the stresses was different and it forced the crazing initiation and growing preferentially. The crazes were created in some regions in the matrices; On the contrary, rare crazes were formed in the other regions in spite of these regions surrounded around the same dispersed particles. The relation between the spots on the surface and the inner structure of the cellar particle was discussed in this paper.

Radiation effects on the immiscible polymer blend of nylon1010 and high-impact polystyrene (HIPS) I: Gel/dose curves, mathematical expectation theorem and thermal behaviour

This paper studies the radiation properties of the immiscible blend of nylon1010 and HIPS. The gel fraction increased with increasing radiation dose. The network was found mostly in nylon1010, the networks were also found in both nylon1010 and HIPS when the dose reaches 0.85 MGy or more. We used the Charleby-Pinner equation and the modified Zhang-Sun-Qian equation to simulate the relationship with the dose and the sol fraction. The latter equation fits well with these polymer blends and the relationship used by it showed better linearity than the one by the Charleby-Pinner equation. We also studied the conditions of formation of the network by the mathematical expectation theorem for the binary system. Thermal properties of polymer blend were observed by DSC curves. The crystallization temperature decreases with increasing dose because the cross-linking reaction inhibited the crystallization procession and destroyed the crystals. The melting temperature also reduced with increasing radiation dose. The dual melting peak gradually shifted to single peak and the high melting peak disappeared at high radiation dose. However, the radiation-induced crystallization was observed by the heat of fusion increasing at low radiation dose. On the other hand, the crystal will be damaged by radiation. A similar conclusion may be drawn by the DSC traces when the polymer blends were crystallized. When the radiation dose increases, the heat of fusion reduces dramatically and so does the heat of crystallization. (C) 1999 Elsevier Science Ltd. All rights reserved.

Radiation effects on the immiscible polymer blend of nylon1010 and high-impact strength polystyrene (II): mechanical properties and morphology

The paper studies the morphology and mechanical properties of immiscible binary blends of the nylon 1010 and HIPS through the radiation crosslinking method. In this blend, the HIPS particles were the dispersed phases in the nylon 1010 matrix. With increasing of dose, the elastic modulus increased, However, the tensile strength. elongation at bleak and the energy of fracture increased to a maximum at a dose of 0.34 MGy, then reduced with the increasing of dose. SEM photographs show that the hole sizes are not changed obviously at low dose and at high dose, remnants that cannot be dissolved in formic acid and THF can be observed in the holes and on the surface. TEM photographs showed that radiation destroys the rubber phases in the polymer blend. (C) 2001 Elsevier Science Ltd. All rights reserved.

Blends of polyamide 1010 with ungrafted and maleic anhydride grafted high impact polystyrene

The crystallization, dynamic mechanical properties, tensile properties and morphology features of polyamidel 1010(PA1010) blends with the high impact polystyrere (HIPS) and maleic anhydride (MA) grafted HIPS(HIPS-g-MA) were examined at a wide composition range. By comparison the PA1010/HIPS-g-MA and PA1010/HIPS binary blends, it was found that the size of the domains of HIPS-g-MA was much smaller than that of HIPS at the same compositions. It was found that the mechanical properties of PA1010/HIPS-g-MA blends were obviously higher than those of PA1010/HIPS blends. When the content of PA1010 is more than 50wt% in the blends, the crystallization temperatures, T-cs, of PA1010 increase with increasing the content of HIPS-g-MA. On the other hand, when the content of PA1010 in the blends is less than 35wt% the fraction crystallization is observed. The same result is not obtained for the blends of PA1010/HIPS. These behaviors could be attributed to the chemical interactions between the two components and good dispersion in PA1010/HIPS-g-MA blends.

Blends of polyamide1010 with unmodified and maleic-anhydride-grafted high-impact polystyrene

The crystallization behaviors, dynamic mechanical properties, tensile, and morphology features of polyamide1010 (PA1010) blends with the high-impact polystyrene (HIPS) were examined at a wide composition range. Both unmodified and maleicanhydride-(MA)-grafted HIPS (HIPS-g-MA) were used. It was found that the domain size of HIPS-g-MA was much smaller than that of HIPS at the same compositions in the blends. The mechanical performances of PA1010-HIPS-g-MA blends were enhanced much more than that of PA1010-HIPS blends. The crystallization temperature of PA1010 shifted towards higher temperature as HIPS-g-MA increased from 20 to 50% in the blends. For the blends with a dispersed PA phase (less than or equal to 35 wt %), the T-c of PA1010 shifted towards lower temperature, from 178 to 83 degrees C. An additional transition was detected at a temperature located between the T-g's of PA1010 and PS. It was associated with the interphase relaxation peak. Its intensity increased with increasing content of PA1010, and the maximum occurred at the composition of PA1010-HIPS-g-MA 80/20. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 857-865, 1999.

Influence of molten-state annealing on the phase structure and crystallization behaviour of high impact polypropylene copolymer

The phase structure evolution of high impact polypropylene copolymer (IPC) during molten-state annealing and its influence on crystallization behaviour were studied. An entirely different architecture of the IPC melt was observed after being annealed, and this architecture resulted in variations of the crystallization behaviour. In addition, it was found that the core-shell structure of the dispersed phase was completely destroyed and the sizes of the dispersed domains increased sharply after being annealed at 200 degrees C for 200 min. Through examination of the coarseness of the phase morphology using phase contrast microscopy (PCM), it was found that a co-continuous structure and an abnormal 'sea-island' structure generally appeared with an increase in annealing time. The original matrix PP component appeared as a dispersed phase, whereas the copolymer components formed a continuous 'sea-island' structure. This change is ascribed to the large tension induced by solidification at the phase interface and the great content difference between the components. When the temperature was reduced the structure reverted to its original form. With increasing annealing time, the spherulite profiles became more defined and the spherulite birefringence changed from vague to clear. Overall crystallization rates and nucleation densities decreased, but the spherulite radial growth rates remained almost constant, indicating that molten-state annealing mainly affects the nucleation ability of IPC, due to a coarsened microstructure and decreased interface area. (C) 2011 Elsevier Ltd. All rights reserved.

Existing and emerging high impact invasive species are characterized by higher functional responses than natives

Predicting ecological impacts of invasive species and identifying potentially damaging future invaders are research priorities. Since damage by invaders is characterized by their depletion of resources, comparisons of the ‘functional response’ (FR; resource uptake rate as a function of resource density) of invaders and natives might predict invader impact. We tested this by comparing FRs of the ecologically damaging ‘world's worst’ invasive fish, the largemouth bass (Micropterus salmoides), with a native equivalent, the Cape kurper (Sandelia capensis), and an emerging invader, the sharptooth catfish (Clarias gariepinus), with the native river goby (Glossogobius callidus), in South Africa, a global invasion hotspot. Using tadpoles (Hyperolius marmoratus) as prey, we found that the invaders consumed significantly more than natives. Attack rates at low prey densities within invader/native comparisons reflected similarities in predatory strategies; however, both invasive species displayed significantly higher Type II FRs than the native comparators. This was driven by significantly lower prey handling times by invaders, resulting in significantly higher maximum feeding rates. The higher FRs of these invaders are thus congruent with, and can predict, their impacts on native communities. Comparative FRs may be a rapid and reliable method for predicting ecological impacts of emerging and future invasive species.

Moist singular vectors and the predictability of some high impact European cyclones

The ECMWF full-physics and dry singular vector (SV) packages, using a dry energy norm and a 1-day optimization time, are applied to four high impact European cyclones of recent years that were almost universally badly forecast in the short range. It is shown that these full-physics SVs are much more relevant to severe cyclonic development than those based on dry dynamics plus boundary layer alone. The crucial extra ingredient is the representation of large-scale latent heat release. The severe winter storms all have a long, nearly straight region of high baroclinicity stretching across the Atlantic towards Europe, with a tongue of very high moisture content on its equatorward flank. In each case some of the final-time top SV structures pick out the region of the actual storm. The initial structures were generally located in the mid- to low troposphere. Forecasts based on initial conditions perturbed by moist SVs with opposite signs and various amplitudes show the range of possible 1-day outcomes for reasonable magnitudes of forecast error. In each case one of the perturbation structures gave a forecast very much closer to the actual storm than the control forecast. Deductions are made about the predictability of high-impact extratropical cyclone events. Implications are drawn for the short-range forecast problem and suggestions made for one practicable way to approach short-range ensemble forecasting. Copyright © 2005 Royal Meteorological Society.

Creating High-Impact Workforce Development Programs

As communities across the nation continue to face persistent unemployment, many states are turning to community college workforce development programs to combat joblessness. However, state governments and community colleges alike are often unable to devote significant resources to building new workforce initiatives. This brief examines how community colleges in four states have worked with state governments and other partners to overcome budget constraints and create effective workforce development programs, highlighting funding models and innovative practices to make efficient use of limited resources.

Effect of thermocycling on the flexural and impact strength of urethane-based and high-impact denture base resins

Objective: Mechanical properties of the acrylic resins used for denture fabrication may be influenced by water and temperature. Thus, the aim of this study was to evaluate the effect of thermocycling on the flexural and impact strength of a high-impact (Lucitone 199) and a urethane-based denture material (Eclipse).Materials and methods: Flexural strength (64 x 10 x 3.3 mm) and impact strength (60 x 6 x 4 mm) specimens were made following the manufacturers' instructions and assigned to two groups (n = 10): control (C) - not thermocycled - and T - thermocycled (5000 cycles between 5 and 55 degrees C). Specimens were submitted to three-point bending and Charpy impact tests.Results: Flexural strength (MPa) and impact strength (kJ/m(2)) data were analysed with two-way ANOVA (p = 0.05). The flexural strength of material Eclipse (C, 136.5; T, 130.7) was significantly higher than that of resin Lucitone 550 (C, 99.4; T, 90.1). Material Eclipse exhibited significantly higher impact strength (C, 6.9; T, 5.3) than the resin Lucitone 550 (C, 3.5; T, 3.0). For both materials, a significant decrease in flexural and impact strengths was observed when the specimens were thermocycled.Conclusion: Flexural and impact strengths were higher for Eclipse than for Lucitone 550, in both groups. Thermocycling decreased the flexural and impact strengths of Eclipse and Lucitone 550.