Effect of Support Material Properties on Dynamic Membrane Filtration Performance

A dynamic membrane is defined as a cake layer which forms on a support material, for example, filter cloth or mesh when the liquid to be filtered includes suspended particles. Formation of an effective dynamic cake layer is highly related with the retention of particles on the support material surface. Therefore, support material properties are considered to be of prime importance in the performance of dynamic membrane treatment systems. This study investigates the effect of support material properties including pore size and structure of the material on dynamic membrane formation and performance. In this concept, a comparative evaluation was made between support materials which have different yarn types. The results showed that high total suspended solids removal efficiency (>98%) could be achieved by using dynamic membrane filtration technology. Mono-monofilament and staple filter cloths were determined as the most appropriate materials in terms of the critical fluxes which were 9.2 L/m² · h and 17–19 L/m² · h for mono-mono filament and staple materials, respectively. However, considering the results of more long-term experiments, mono-monofilament filter cloth was found more suitable for cake layer accumulation. Therefore, we postulate that mono-monofilament cloth can be used in dynamic membrane filtration systems as an alternative to traditional membranes in anaerobic membrane bioreactors.     

Borofloat and Starphire Float Glasses: A Comparison,

Borofloat^® borosilicate float glass and Starphire^® soda-lime silicate float glass are used in transparent protective systems. They are known to respond differently in some ballistic and triaxial loading conditions, and efforts are underway to understand the causes of those differences. Toward that, a suite of test and material characterizations were completed in this study on both glasses so to identify what differences exist among them. Compositional, physical properties, elastic properties, flaw size distributions and concentrations, tensile/flexure strength, fracture toughness, spherical indentation and hardness, transmission electron microscopy, striae, high-pressure responses via diamond anvil cell testing, laser shock differences, and internal porosity were examined. Differences between these two float glasses were identified for many of these properties and characteristics, and the role of three (striae, high pressures where permanent densification can initiate, and submicrometer-sized porosity) lack understanding and deserve further attention. The contributing roles of any of those properties or characteristics to triaxial or ballistic loading responses are not definitive; however, they provide potential correlations that may lead to improved understanding and management of loading responses in glasses used in transparent protective systems.     

Ballistic performance of armour ceramics: Influence of design and structure. Part 1

The use of advanced ceramics for armour systems allows the defeating of the projectile and ballistic impact energy dissipation providing adequate ballistic protection. The development of lightweight and inexpensive ceramics and armour designs is under ongoing attention by both ceramic armour manufacturers and armour users. This paper summarizes the results of extensive studies of ballistic performance of different armour ceramics, mostly obtained during development, as well as of the materials manufactured by other recognized armour ceramic suppliers, and the designed ceramic-based armour systems. The studied armour ceramics include homogeneous oxide and carbide ceramics and heterogeneous ceramic materials. Composition, structure and main properties of the considered ceramics, which affect ballistic performance, are examined and analyzed. Only a combination of all relevant physical properties and microstructure, including the ability to dissipate ballistic energy, as well as optimization of manufacturing processes, should be considered for proper selection and evaluation of ceramic armour. Ballistic performance of the studied ceramics as function of their structure and properties, armour system design and type of projectile has been discussed.     

Comparison of mechanical and ballistic performance of composite laminates produced from single‐layer and double‐layer interlocked woven structures

Textile structures have become quite popular as reinforcement materials in composite laminates due to their high impact‐damage tolerance and energy absorption ability. The impact performance of textile composites is not only affected by the type of fiber/matrix but also by the fabric structure used as reinforcement. The aim of this study was to compare the mechanical and ballistic performance of composite laminates reinforced with single‐layer and double‐layer interlocked woven fabrics. Kevlar^®−29 multifilament yarn was used for preparation of all the fabric structures and epoxy resin was used as the matrix system. The composites were produced using a hand lay‐up method, followed by compression molding. The mechanical and ballistic performance of composites reinforced with single‐layer and double‐layer interlocked woven fabrics was investigated in this study. The energy absorption and mechanical failure behavior of composites during the impact event were found to be strongly affected by the weave design of the reinforcement. The composites reinforced with double‐layer interlocked woven fabrics were found to perform better than those comprising single‐layer fabrics in terms of impact energy absorption and mechanical failure. POLYM. COMPOS., 35:1583–1591, 2014. © 2013 Society of Plastics Engineers     

碳纤维布/玻纤布增强聚氨酯复合材料的研究

以聚氨酯为基体树脂,分别以碳纤维布、玻璃纤维布和这两种纤维布交替铺叠作为增强材料,采用真空辅助灌注成型工艺制备了4种复合材料.考察了纤维布的铺层结构对复合材料的弯曲、拉伸和冲击性能的影响.结果显示,复合材料的拉伸模量和弯曲模量随碳纤维含量增加而增加,冲击强度则降低.分别采用TGA、DMA和SEM对复合材料的热性能、界面...     

Morphological effects of ballistic impact on fabrics of highly drawn polyethylene fibers

Changes in crystalline structure of high-tenacity ultra-high-molecular-weight polyethylene fabric brought on by ballistic impact from a small projectile were determined by X-ray diffractometry. A suitable X-ray diffraction method that averages out the fiber orientation effects in the diffraction pattern was used. The Spectra 1000? polyethylene fabrics were successfully characterized in terms of both the predominant orthorhombic and the minor monoclinic crystal content. Crystallinity values for the undamaged fabric are consistent from sample to sample and show an average orthorhombic fraction of 0.61 and an average monoclinic fraction of 0.04. Fabric damage by the projectile impact results in either an increase in monoclinic fraction, attributed to recrystallization at temperatures nearing the normal polyethylene melting point, or disappearance of monoclinic material as that temperature is exceeded. The latter predominates where ballistic penetration is complete. However, actual melting need not be involved: Transformation to the hexagonal (“rotator”) phase and the disappearance of the monoclinic phase could have occurred rather than true melting. © 1993 John Wiley & Sons, Inc.     

Energy loss partitioning during ballistic impact of polymer composites

The objective of this study is to determine the energy dissipation processes in polymer-matrix composites during impact of ballistic projectiles. These processes include heat, fiber deformation and breakage, matrix deformation and fracture, and interfacial delamination. In this study, experimental measurements were made, using specialized specimen designs and test methods, to isolate the energy consumed by each of these processes during impact in the ballistic range. Using these experiments, relationships between material parameters and energy dissipation were examined. Composites with the same matrix but reinforced with Kevlar, PE, and graphite fabric were included in this study. These fibers were selected based on the differences in their intrinsic properties. Matrix cracking was found to be one of the most important energy absorption mechanisms during impact, especially in ductile samples such as Spectra-900 PE and Kevlar-49 reinforced polymer. On the contrary, delamination dominated the energy dissipation in brittle composites such as graphite reinforced materials. The contribution from frictional forces also investigated and the energy partitioning among the different processes evaluated.     

Ballistic performance of armour ceramics: Influence of design and structure. Part 2

The use of advanced ceramics for armour systems allows the defeating of the projectile and ballistic impact energy dissipation providing adequate ballistic protection. The development of lightweight and inexpensive ceramics and armour designs is under ongoing attention by both ceramic armour manufacturers and armour users. This paper summarizes the results of extensive studies of ballistic performance of different armour ceramics, mostly obtained during development, as well as of the materials manufactured by other recognized armour ceramic suppliers, and the designed ceramic-based armour systems. The studied armour ceramics include homogeneous oxide and carbide ceramics and heterogeneous ceramic materials. Ballistic performance of the studied ceramics as function of their structure and properties, armour system design and type of projectile has been discussed. Depending on the requirements for ballistic protection, armour systems may be designed to various configurations and weights based on the most suitable ceramic materials and backing. The examples of successful designs of lightweight armour systems with adequate ballistic performance, including satisfactory multi-hit performance, have been demonstrated.     

Characterization and property correlations of amorphous poly(alpha olefin)

Amorphous poly(alpha olefins)® (APAOs) with various types and contents of comonomers, and molecular weight were characterized by general, thermal, rheological, and mechanical methods and their properties were correlated with their molecular parameters. It was found that they can be used as a modifier for isotactic polypropylene. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Spectra composite that withstands torch flame test

In recent years, the development of high performance Spectra® fibers has received increasing attention in industry. Because of the outstanding capability to absorb energy, these polyethylene fibers are frequently used in damage tolerant composite materials to protect equipment, apparatus, and/or people against blast and debris of explosion or projectiles. Since the fiber is thermally stable, it is possible to design composite structures that are suitable for use in applications where prolonged exposure to flame is anticipated. In this paper, we report the findings obtained in a recent flammability evaluation of a Spectra composite subjected to a torch flame, and to hot metal balls. The Spectra composite structures that will be discussed were found to withstand these exposures without burning and the smoke generation and toxic gas emission were far below the limits set in the standard for current aircraft interior materials.     

Review of ballistic performance of alumina: Comparison of alumina with silicon carbide and boron carbide

Ceramic armour materials are designated to protect personnel and vehicles against ballistic damage. The main effort is now focused on developing ceramics with difficult-to-obtain properties, such as high ballistic performance and light weight. Over the past 30 years, the development of ceramic materials has led to a sustained improvement in their properties and structural homogeneity. Nevertheless, the relation of these properties with the ballistic performance of ceramics remains unclear.This paper reviews the current understanding regarding the failure stages of ceramic armour and the methods used to evaluate ballistic performance. A comparison of alumina with silicon carbide and boron carbide was performed.     

氧化锆纤维布的研究

氧化锆纤维布是大容量碱性电池的理想隔膜材料.本文研究了氧化锆纤维布的制备工艺,原料纤维、浸渍工艺参数、热处理工艺等对氧化锆纤维布性能的影响.所研制的氧化锆纤维布在大容量镍氢电池中作为隔膜得到了应用,电性能及吸碱速率和吸碱量优于美国产品,但强度低于美国产品.     

Penetration of double-layer targets with an outer ceramic layer and optimization of their structure

Analytical formulas for calculating the maximum velocity of penetration of doublelayer cermet and ceramic/organic-plastic targets are obtained taking into account the structural characteristics of the target and the physical and mechanical properties of the projectile and target materials. Using these formulas, the ballistic resistance of targets was studied and the possibility of optimizing their structure was shown. The results agree qualitatively with available experimental data. The optimal relative thickness of the ceramic layer which provides maximum penetration velocity was determined at areal densities of the target of 30–50 kg/m² for different substrate materials. It is found that these velocity values depend weakly on the areal density of the target and are mainly determined by the properties of the substrate material.     

滤布材质及微观结构与透水性能的关系

机织滤布的透水性能会直接影响过滤设备的生产效率。为理清滤布材质、微观结构与过水通量之间的相互关系,定制一批控制变量的滤布用于实验。对不同材质的滤布进行了FTIR,动、静态接触角和表面能测定,从机理分析了材质影响过水通量的关键性指标。对滤布微观结构进行了SEM表征,并分析了编织方式、厚度、孔径对过水通量的影响,建立了滤布微观结构与过水通量的半经验模型。结果表明:材质亲水性大小顺序为聚丙烯>聚碳酸酯>聚酰胺,对应的过水通量分别为6.34、5.75、5.46 m/min,亲水性强的材质具有更大的过水通量;微观结构中,过水通量大小顺序为缎纹滤布>斜纹滤布>平纹滤布,孔径、厚度分别与过水通量呈正、负相关关系,拟合的微观结构与过水通量的半经验模型可以为机织滤布的选型提供理论参考。     

Effects of the injection‐molding temperatures and pyrolysis cycles on the butadiene phase of high‐impact polystyrene

Recycling is a thermal process in which polymers are melted to produce new products. It is possible that these thermal processes could modify their mechanical and thermal properties. Polymer degradation can be characterized with thermogravimetric analysis and differential scanning calorimetry. Recycled materials tested with these methods have shown variations in some thermal properties, such as the glass‐transition temperature and thermal degradation onset, but the sensitivity of these methods is not sufficient to investigate the changes in the characteristics of polymers when materials are exposed to moderate temperature conditions or several thermal cycles. To study these structural changes, a much more sensitive technique, such as pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS), is needed. Small variations in the structure can be determined by Py–GC/MS. Each pyrolysis product can be identified by its retention time and mass spectrum with the use of reference literature. In this work, we have studied structural changes in high‐impact polystyrene as a function of the injection‐molding temperature and pyrolysis cycles. The results do not show significant changes in samples processed at different temperatures with Py–GC/MS, but the values of the pyrolysis products differ as a function of the pyrolysis cycles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of preform architecture on the mechanical properties of 2D C/C composites prepared using rapid directional diffused CVI processes

The substrate architecture of carbon-carbon (C/C) composites has an effect on both the mechanical properties and the cost of the products. Four kinds of substrate materials, 1K and 3K plain carbon cloth, carbon paper, and carbon felt, were used in this study, and from them four different 2D preforms were produced, namely, 1K plain carbon cloth, carbon paper+1K plain carbon cloth, carbon felt+1K plain carbon cloth, 3K plain carbon cloth, using a spreading layer method. The preforms were densified using the rapid directional diffused CVI processes. A three-point bend test was used to investigate the influence of preform architecture on the flexural properties and microstructure of the C/C composites. The results show that all samples have an obvious pseudo-plastic fracture behaviour, and the macroscopic appearance of the bent fractured section shows as an Z shape. The samples prepared using 1K plain carbon cloth have a uniform microstructure, and consequently possess the highest flexural strength, while the composites produced from 3K plain carbon cloth possess the lowest value due to their poor microstructure and lower strength fibers. In general the flexural properties of the C/C composites are improved with an increase of the carbon fiber volume fraction in the preform. All the C/C composites manufactured from the four preforms fail by delamination when broken.     

Thermal and mechanical degradation during polymer extrusion processing

Polymer processing often activates material degradation, which affects to some extent the performance or the life cycle of the obtained products. Polymer degradation is usually evidenced by molecular weight variations as consequence of exposure to high processing temperature and to relevant mechanical stresses. The degrading effects of melt extrusion under different thermo‐mechanical conditions on polymethyl‐methacrylate and polystyrene are investigated. Materials were processed at different temperatures and rates in a single screw extruder and in a capillary rheometer. Processed and as‐received materials were analysed by Gel permeation chromatography, solution viscosity, and melt rheology. Evaluations of molecular weight and rheological behavior changes after processing, as compared with as‐received materials, evidenced the extent of degradation in the different conditions. Experimental analysis was accompanied by finite elements simulation of the polymer flow and heat transmission within the extruder. This allowed an estimation of the expected shear stresses and temperatures distributions, thus indicating potentially critical situations. It was found that the materials processed at the highest rates in extruder presented lowest molecular weight reductions. This was attributed to the shorter residence time in the extruder and to the possibility of wall slip phenomena, which likely reduce the actual shear stress and viscous dissipation in the fast processing conditions. POLYM. ENG. SCI., 47:1813–1819, 2007. © 2007 Society of Plastics Engineers     

Processing and properties of modified polyamide 66-organoclay nanocomposites

Binary polyamide 66 nanocomposites containing 2 wt % organoclay, polyamide 66 blend containing 5 wt % impact modifier, and ternary polyamide 66 nanocomposites containing 2 wt % organoclay and 5 wt % impact modifier were prepared by melt compounding method. The effects of E-GMA and the types of the organoclays on the interaction between the organoclay and the polymer, dispersion of the organoclay, morphology, mechanical, flow, and thermal properties of the nanocomposites were investigated. Partial exfoliation and improved mechanical properties are observed for Cloisite® 15A and Cloisite® 25A nanocomposites. On the other hand, the organoclay was intercalated or in the form of tactoids in Cloisite® 30B nanocomposites. Components of the nanocomposites containing Cloisite® 15A and Cloisite® 25A were compounded in different addition orders. Mixing sequence of the components affected both the dispersion of the organoclay and the mechanical properties drastically. SEM analyses revealed that homogeneous dispersion of the organoclay results in a decrease in the domain sizes and promotes the improvements in the toughness of the materials. Melt viscosity was also found to have a profound effect on the dispersion of the organoclay according to MFI and XRD results. Crystallinity of the nanocomposites did not change significantly. It is only the type of the constituents and their addition order what dramatically influence the nanocomposite properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Reinforcing effect of organoclay in rubbery and glassy epoxy resins,part 1: Dispersion and properties

The reinforcing effect of organoclay in two epoxy matrices, one rubbery and one glassy, was studied. The rubbery and glassy epoxy matrices were chosen to have a very similar chemistry to minimize its impact on the comparison of properties. The epoxy resin was EPON? 828, and the two hardeners were amine‐terminated polyoxypropylene diols, having different average molecular weights (MW) of 2000 and 230 g/mol, namely Jeffamine® D‐2000 and Jeffamine® D‐230, respectively. The nanocomposites were prepared with the organoclay Cloisite® 30B from Southern Clay Products. The quality of dispersion and intercalation/exfoliation was analyzed by means of X‐ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM), and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the curing reactivity and the thermal stability of the epoxy resin systems, respectively. Tensile properties and hardness of epoxy resin and epoxy nanocomposites were measured according to ASTM standards D638‐02 and D2240‐00, respectively. Fracture surfaces were also analyzed by FEGSEM. These two epoxy systems as well as their nanocomposites display totally different physical and mechanical behavior. It is found that the quality of clay dispersion and intercalation/exfoliation, and the mechanical behavior of the glassy and rubbery epoxy nanocomposites are distinct. The results also indicate that the presence of the clay does not significantly affect the T_g of either the rubbery or the glassy epoxy; however, the fracture surface and mechanical properties were found to be influenced by the presence of nanoclay. Finally, several different reinforcing mechanisms are proposed and discussed for the rubbery and glassy epoxy nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Headspace solid‐phase microextraction with gas chromatography/mass spectrometry reveals a correlation between the degradation product pattern and changes in the mechanical properties during the thermooxidation of in‐plant recycled polyamide 6,6

The increased susceptibility of in‐plant recycled polyamide 6,6 toward thermooxidation was shown by headspace solid‐phase microextraction with gas chromatography/mass spectrometry (HS‐SPME/GC‐MS), tensile testing, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). A correlation between the deterioration in mechanical properties and the formation of degradation products due to thermooxidation was found, and the most prominent decrease in mechanical properties coincided with the largest increase in the abundance of degradation products. The recycled materials had a shorter induction period toward oxidation, and their mechanical properties deteriorated faster than the mechanical properties of virgin material. The same trend was observed with HS‐SPME/GC‐MS because degradation products were found for recycled materials after oxidation times shorter than those for virgin material. Furthermore, larger amounts of degradation products were formed in the recycled materials. The high sensitivity of HS‐SPME/GC‐MS as an analytical tool was demonstrated because it was able to detect changes caused by oxidation considerably earlier than the other methods. Unlike DSC and FTIR, it could also show differences between samples recycled for different times. Four groups of degradation products—cyclic imides, pyridines, chain fragments, and cyclopentanones—were identified in thermooxidized polyamide 6,6. After 1200 h of thermooxidation, 1‐pentyl‐2,5‐pyrrolidinedione was the most abundant degradation product. Approximately four times more 1‐pentyl‐2,5‐pyrrolidinedione was formed in polyamide recycled three times than in virgin polyamide. Pyridines and chain fragments behaved toward oxidation and repeated processing like cyclic imides; that is, their amounts increased during oxidation, and larger amounts were formed in recycled materials than in virgin material. The cyclopentanone derivatives were present already in unaged material, and their amounts decreased during oxidation. Cyclopentanones were not formed because of the thermooxidation of polyamide 6,6. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3396–3407, 2002