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     

Tensile deformation mechanisms of polypropylene/elastomer blends reinforced with short glass fiber

Polypropylene hybrid composites reinforced with short glass fiber (SGF) and toughened with styrene–ethylene butylenes–styrene (SEBS) elastomer were prepared using extrusion and injection‐molding techniques. Moreover, hybrids compatibilized with SEBS‐grafted maleic anhydride (SEBS‐g‐MA) and hybrid compatibilized with PP grafted with maleic anhydride (PP‐g‐MA) were also fabricated. The matrix of the latter hybrid was designated as mPP and consisted of 95% PP and 5% PP‐g‐MA. Tensile dilatometry was carried out to characterize the fracture mechanisms of hybrid composites. Dilatometric responses showed that the elastic deformation was the dominant deformation mechanism for the SGF/SEBS/PP and SGF/SEBS‐g‐MA/PP hybrids. However, cavitation deformation prevailed over shearing deformation for both hybrids at the higher strain regime. The cavitation strain resulted from the debonding of glass fibers and from the crazing of the matrix in the SGF/SEBS/PP hybrid. In contrast, the cavitation was caused by the debonding of SEBS particles from the matrix of the SGF/SEBS‐g‐MA/PP hybrid. The use of PP‐g‐MA resulting in elastic deformation was the main mode of deformation in the low‐strain region for the SGF/SEBS/mPP and SEBS/SEBS‐g‐MA/mPP hybrids; thereafter, shearing appeared to dominate at the higher strain regime. This was attributed to the MA functional group improving the bonding between the SGF and PP. The correlation between fracture morphology and dilatometric responses also is presented in the article. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 441–451, 2003     

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 mechanisms of Al2O3 with different glass phase content at cryogenic temperatures

The effects of glass phase and temperature on the mechanical properties of 99%, 92%, 85% and 75% Al₂O₃ are investigated. The in-situ XRD results revealed that the lattice constants of Al₂O₃ single crystals were reduced when temperature decreased from room temperature (RT) to 30 K. The results of mechanical properties were analyzed by Weibull equation. It can be concluded that for the samples containing same content of glass phase, the bending strength and fracture toughness increased as temperature decreased from RT to 77 K. While at the same test temperature, the mechanical properties degraded when the glass phase content increased. The statistical analysis of indentation crack propagation paths of 99% Al₂O₃ indicated that the proportion of transgranular fracture was increased at 77 K.     

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.     

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.     

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。     

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。     

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.     

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.     

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.     

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.     

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.     

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.     

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.