Prediction of failure initiation in polypropylene with glass beads

The effect of glass bead content and residual stresses on failure initiation in isotactic polypropylene composites has been investigated by finite element analysis for the cases of interfacial debonding, plastic yielding, and cavitation. Residual thermal stresses are demonstrated to have a large effect on global failure initiation stress. Yielding and cavitation occur at higher global stresses than debonding. Modeling results, as well as previous experimental data, support debonding as the initial failure mechanism.     

Microscopical damage mechanisms in glass fiber reinforced polypropylene

The damage mechanisms in two structurally different glass mat reinforced polypropylene materials were studied. In situ microscopy was applied during the tensile testing of thin notched sheets. Micrographs of the damage processes in the two materials are presented. The major points of damage initiation were transversely oriented fibers and fiber bundles. In the swirled mat material, cracks grew along the fiber bundles; crack formation and growth was relatively unaffected by macroscopical stress concentration. In the short fiber material, crack growth occurred at the notch. In both materials the maximum load was determined by the fibers oriented in the longitudinal direction. The different damage mechanisms were interpreted in terms of damage zone size. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1319–1327, 1998     

Wettability control of glass beads

Wettability plays an important role in a number of industrial applications. Often it becomes desirable to control contact angles (wettability). For this purpose, two techniques for altering the contact angles of glass beads are described. These involve chemisorption of Silicones or Hexamethyldisilazane (HMDS) on glass surfaces. The results of measured contact angles on treated glass beads indicate that by carefully controlling the treating procedure, it is possible to obtain the desired wettability.     

Viscosity and die swell of acrylonitrile-butadiene-styrene filled with glass beads and glass fibers

Shear viscosity and die swell ratio of acrylonitrile-butadiene-styrene filled with glass beads and glass fibers were measured. The relative viscosity of the composites increased with filler content, but decreased with shear rate. At low shear rates, fiber filled systems had higher relative viscosities than bead filled systems. At high shear rates, the opposite was observed. The die swell ratio of the unfilled material increased linearly with the logarithm of the shear rate. Systems highly filled with glass beads or fibers showed a maximum in the die swell ratio at medium shear rates. The magnitude of the maximum in the die swell ratio increased with the filler content and the die length, up to a certain length, in a series of dies that had the same radius. The presence of a maximum in the die swell ratio of the filled melts is explained by an order-disorder phenomenon observed earlier by Wu.     

Failure of polypropylene fibers

Conclusions A quantitative definition of the highly elastic deformation built up in extension of polypropylene fiber has been proposed.In the extension of a crystallizing polymer, under definite temperature-deformation conditions, a steady flow regime is reached (analogous to amorphous polymers). Under these conditions, breakage takes place on reaching a critical fiber diameter, regardless of the original fiber thickness.Translated from Khimicheskie Volokna, No. 4, pp. 22–23, July–August, 1983.     

Vane rheology of cohesionless glass beads

The rheology of a single coarse granular powder has been studied with shear vane rotational viscometry. The torque required to maintain constant rotation of a vane tool in a loose bed of glass beads (with a mean particle size of 203 μm) is measured as a function of vane immersion depth and rotational speed. The resulting torque profiles exhibit both Coulombic behavior at low rotational rates and fluid-like, collisional behavior at high rotational rates. Analyzing vane shaft and end effects allows the flow dynamics at the cylindrical and top and bottom disk surfaces of vane rotation to be determined. Disk surfaces show a uniform torque profile consistent with Coulombic friction over most of the rotational rates studied. In contrast, cylindrical surfaces show both frictional and collisional torque contributions, with significant dynamic torque increases at deep immersion depths and fast vane rotation.     

Mixing and enzyme reactions in a microchannel packed with glass beads

Mixing behavior in a microchannel was investigated by means of a spectrophotometer equipped with optical fiber probes. Microreactors with a Y-shaped channel were fabricated on poly(methyl methacrylate) substrates. Glass beads were packed in the intersection and the downstream regions to improve mixing performance. An NaOH solution and a BTB solution as a pH indicator were fed to the microchannel with a syringe pump. As the mixing progressed, the color of the mixed solution changed to blue. The degree of mixing was evaluated by the change in absorbance at 623 nm of the mixing solution. The packed glass beads strongly enhanced the mixing performance in the microchannels, especially in the case of packing in the intersection. The effect of mixing in the microchannel on an enzyme reaction was also investigated. The hydrolysis of o-nitrophenyl-\-D-galactopyranoside by \-galactosidase was used as a model reaction. The results showed that the enzyme reaction was enhanced in the microreactor with glass beads compared with a batch reactor. The microreactor packed with glass beads gave the highest reaction rate.     

中空玻璃微珠在泡沫塑料中的应用研究

概括了中空玻璃微珠(HGB)在泡沫塑料中应用的研究进展。着重HGB对泡沫塑料的加工过程、泡孔结构、不同性能的影响进行了研究,并介绍了其在复合泡沫功能化方面的进展。研究表明HGB在泡沫基体中易分散,易加工,能够显著提高泡沫塑料的压缩性能,并对其耐热性能、保温性能、阻燃性能有一定的促进作用。此外,HGB在功能化方面也展现了日益突出的作用,显示出广阔的应用前景。     

釜式法制备聚丙烯发泡珠粒研究进展

概述了聚丙烯发泡珠粒的性能及用途,釜式法制备聚丙烯发泡珠粒的机理(即过饱和气体原理)以及一般的工艺流程,着重介绍了发生泡孔成核、膨胀过程的原理以及温度、压力、保温时间、冷却方式、降压速率等工艺参数对发泡效果的影响.综述了发泡配方、基体树脂的选择方法和后成型加工过程的特点,发泡珠粒主要的性能指标.展望了聚丙烯发泡材料的发展趋势.     

玻璃纤维增强聚丙烯复合材料的研究进展

综述了长、短玻璃纤维增强聚丙烯（GFRPP）复合材料的研究进展,总结出纤维含量、纤维长度及分布、纤维取向及分布、纤维与基体界面结合和改性等均为影响GFRPP性能的因素。在复合材料中,长度大于临界长度的玻璃纤维对材料的强度才有作用;增强玻璃纤维与聚丙烯的界面结合也是提高增强效果的有效手段。     

Coupling of glass fiber with polypropylene by gamma radiation

The effect of ⁶⁰CO gamma radiation on polypropylene and glass-fiber-reinforced polypropylene was investigated. The glass fiber content in the reinforced polypropylene was observed to influence the mechanical properties of the original polypropylene. The initial modulus and off-set yield strength (at 0.25% strain) increased with the dose and glass fiber content. The tensile strength showed an initial decrease with the increase in glass fiber content followed by an increasing trend. A similar behavior was found with increasing dosage. The extent of fiber breakage during processing was higher at higher glass fiber content. However, the fiber length distribution became narrower beyond 2.45% glass fiber content in the polypropylene.     

Mechanical degradation of glass fibers during compounding with polypropylene

The objective was to study the fiber length degradation during compounding of glass fiber with polypropylene. The effect of parameters such as viscosity, total work, concentration on fiber length and dispersion was studied using an automatic particle size analyzer. The length degradation is most severe during the very first stage of the process, i.e., when fiber bundles are being filamentized. The mode of glass fiber incorporation into the melt (fiber addition to the molten resin versus to polypropylene powder prior to compounding) was found to have no effect on the final fiber length. Matrix resin viscosity affects the fiber length significantly. Concentration dependencies of fiber length for different times of compounding suggest that the degradation results from both fiber-fiber and fiber-melt interactions.     

Photocatalytic inactivation of algal growth in eutrophic water with hollow glass beads

Photocatalytic inactivation of algae,Anabaena, Microcystis, andMelosira, was performed with TiO₂-coated pyrex glass beads under the illumination of UV light (370 nm wavelength). After being irradiated with UV light in the presence of the TiO₂-coated pyrex glass beads,Anabaena andMicrocystis, known as typical cyanobacteria, lost their photosynthetic activity, and the string ofAnabaena cells and the colonies ofMicrocystis cells were completely separated into individual spherical ones. In the case ofMelosira, which is a typical diatom, however, somewhat lower photocatalytic inactivation efficiency was obtained, which was believed to be due to the presence of the inorganic siliceous wall surrounding the cells ofMelosira.     

Transcrystallinity in injection molded polypropylene glass fibre composites

The occurrence of transcrystallinity in polypropylene in the presence of glass fibres under stress was studied. An experiment was designed on a hot-stage polarizing microscope in which it was found that slight mechanical stress at the fibre polymer interface gives rise to surface nucleation and growth of transcrystalline regions. Composites of polypropylene with various concentrations of glass fibres were prepared by injection molding. The observed transcrystalline regions in the injection molded samples were attributed to the availability of sufficient inherent internal stresses. Moreover, an increase in fibre concentration was found to enhance transcrystallinity. This indicated that the internal stresses were increased with increasing fibre population.     

The undrainable water in quartz sand and glass beads

The extent to which the magnitude of the undrainable water depends on its surface tension in sand and glass beads is studied by a free drainage column and a pressure porous ceramic plate. Undrainable water consists of two main elements or ‘types’: (a) film water, the thickness of which could be as high as 1 μm, depending on the unevenness of the surface, and (b) ring water retained by capillary forces at the points of contact of the particles. Film water predominates in the fine particles, whereas ring water predominates in the coarse particles. When there is some dispersion, both film and ring water should be present in the same proportion in undrainable water. From a simple consideration (h ≈ 1 μm; A_o/A = 1.5 – 2.0), it follows that this dispersion lies within particle diameters of 4 – 6 × 10^?4 m. Both methods show that a decrease in water content is observed concomitantly with a decrease in surface tension only when fine (<0.4 mm) particles are involved, while there is no such decrease with particles >0.4 mm. Apparently, with a decrease in the size of particles due to the overlaying and overlapping of ring and film water, fine capillaries are formed from which drainage is more dependent on surface tension. In any case, the magnitude of the undrainable water increases when the size of the particles decreases.     

Weldline strength in injection molded glass fiber-reinforced polypropylene

Weldlines are inescapable byproducts of the injection molding process. They represent potentially fatal flaws particularly in multiphase materials. In this work weldlines in injection molded glass fiber-reinforced polypropylene (0 to 40wt%) were studied as a function of the cavity shapes and depths. It was found that the weldline is a zone between 2 and 8 mm wide extending throughout the thickness in which the fibers are oriented almost perfectly in a plane parallel to the weldline. While the strength of moldings without weldlines depends on the mold shape and on the fiber concentration, the weldline strength is a function of fiber content only. A simple model based on the assumption of complete debonding of the fiber-matrix interface when failure occurs can be used to predict the strength loss in the weldline.     

Plasma-CVD-coated glass beads as photocatalyst for water decontamination

Amorphous TiO₂ films were deposited on glass microbeads using a specially designed circulating fluidized bed plasma-CVD reactor. The film thickness was varied between 7 and 120 nm. While only little carbon impurity was found, XPS analysis revealed the presence of silicon, sodium and alkaline earth elements in the titania coating. Reduced amounts of these substrate-originating impurities were observed in the thicker films. By ToF-SIMS imaging, cross-sectional TEM and time-resolved dissolution, the titania coatings were proven to be uniform, both per particle and in terms of the film thickness distribution.

The photocatalytic performance of the composite particles was evaluated in a fully irradiated fluidized-bed photoreactor. The thinnest films had some photocatalytic activity in the as-deposited state, possibly induced by the high specific power of the microwave plasma or silicon doping. The thicker films needed a post-deposition calcination at 723 K to achieve catalytic activity. Both the degree of anatase crystallization and the activity were improved by applying thicker films and after UV irradiation-plus-calcining. All films showed good adhesion and abrasion resistance during the photocatalytic tests. The best plasma-CVD films were about 70% as efficient (per unit reactor volume) as the reference material, P-25 immobilized on quartz sand.     

Instrumented impact testing of glass reinforced polypropylene

The impact response of a glass fiber reinforced polypropylene was studied in a 3-point drop-weight impact test between ?15 and 85°C and at a constant impact velocity of 2.2 m/s (5 mph). The response is a combination of tension and shear and can be expressed in terms of an apparent modulus, E_A: 1 . Where E₁₁ is the tensile modulus, G₁₂: shear modulus, d: specimen thickness, and l: specimen length. For a 40 weight-percent glass reinforced polypropylene, E₁₁ was found to have a room temperature value of 5.8 GPa, and shear modulus of 0.43 GPa. Both decreased with temperature increase, with the shear modulus showing greater sensitivity to a temperature change. The fracture initiation and propagation energies were relatively independent of temperature. The fracture initiation energy per unit deformed volume was of the order of 1 MJ/m³. The total fracture energy was found to be sensitive to l/d: about 7 MJ/m³ at l/d of 5.3 and about 1.7 MJ/ m³ at l/d of 16.