摘要:

This study investigated the effects of a common superplasticizer, ligno-sulfonate, on the hydration of Portland cement Type V. Samples of plain cement and superplasticizer-treated cement have been examined by x-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive spectroscopy. Lignosulfonate has been observed to retard the hydration of cement through specific surface chemical reactions which involve Ca2+ions in pore solution. The admixture has been found to retard the formation of Ca(OH)2and stabilize ettringite [Ca6(Al22O6)(SO4)3.32H2O]. The inhibition of the rate of conversion of ettringite to monosulfate [Ca4Al2(OH)12.SO4.6H2O] is attributed to charge-controlled reactions caused by large quantities of Ca2+ions from initial hydration reactions. Leaching of the admixture doped cement by water-removed lignosulfonate and caused complete hydration of cement. A charge-controlled-reaction model involving the Ca2+ions is proposed to explain the role of the admixtures during hydration of cement.

ISSN:0360-2559    

DOI:10.1080/03602559909351619

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An approximate analytical solution for tube-coating wire with a highly viscous Newtonian fluid is developed (high Froude and capillary numbers). Acute extrusion angles for the annular slit are considered. We obtain expressions for the melt cone shape, coating thickness, contact length, contact pressure, drawing force, apparent contact angle, and contact convexity. In this article, we identify a process indeterminacy that arises in classical tube coating which employs a parallel annulus, and this necessitates applying an internal vacuum. We show that with a rapidly converging extrusion annulus, this indeterminacy vanishes and so does the need for an internal vacuum. Thus, a unique solution for the contact length is always obtained. The extension to a viscoelastic fluid is also briefly considered.

ISSN:0360-2559    

DOI:10.1080/03602559909351620

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this article, a comprehensive review of important enclosure design issues in electronic systems is given. Use of various polymer-based materials and materials selection criteria based on mechanical and electrical properties are reviewed. Structural design models for electronic enclosures are presented. Shielding effectiveness of a printed wiring board and gasketing are examined. A cost-estimation technique is summarized and future trends are discussed.

ISSN:0360-2559    

DOI:10.1080/03602559909351621

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

New semi-interpenetrating (semi-IPN) polymeric networks from commercial polysulfone (UDEL RP-1700) and thermosetting bismaleimide (4, 4'-bismaleimidodiphenylmethane) (BMDM) and maleimide terminated polyaminobismaleimide prepolymer based upon BMDM and 4, 4'-diaminodiphenylmethane were prepared. The chemistry, processing, physical and mechanical properties, phase morphology, thermal stability and solvent resistance of the neat resins are presented. The interrelationships among structure, processing, propcrties, and morphology are also discussed.

ISSN:0360-2559    

DOI:10.1080/03602559909351622

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In the quest to improve the thermooxidative aging of the poly(vinyl chloride)/epoxidized natural rubber (PVC/ENR) blend, nitrile rubber (NBR) was incorporated into the blend to yield a ternary blend of PVC/ENR/NBR. A Brabender Plasticorder with a mixing attachment was used to perform the melt mixing at 150°C and 50 rpm followed by compression molding. The mechanical properties, dynamic mechanical properties, and thermooxidative aging behavior of the ternary blend were compared with those of the binary blends (i.e., PVC/ENR and PVC/NBR). It was found that the ternary blend exhibits mechanical properties which are superior to those of PVC/ENR. A single glass transition temperature (Tg) obtained from dynamic mechanical analysis coupled with synergism in the modulus and some other mechanical properties indicate that PVC, ENR, and NBR form a single phase (miscible system) in the ternary blend. Di-2-ethyl hexylphthalate (DOP) plasti-cizer improves the aging resistance of the blends generally, whereas the presence of CaCO3as a filler only imparts minor influences on the properties and aging resistance of the blends.

ISSN:0360-2559    

DOI:10.1080/03602559909351623

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Injection-molding part designers are frequently faced with multiple quality and cost issues. These issues are usually in conflict with each other; thus, a trade-off needs to be made to reach a final compromised solution. Because evaluation of part quality and cost via injection-molding simulation is very time-consuming, implementation of a conventional multicriteria optimization procedure for injection-molding problems is economically unfavorable. However, many injection-molding problems dealing with multiple quality and cost issues can be modeled as constrained problems, with the total cost as the objective function and quality quantities as the constraints. By introducing a concept of penalized total cost, such constrained problems are further simplified into bounded single-criterion problems. The bounded single-criterion problems are then optimized using a direct search-based optimization procedure. Strategies of modeling, transformation, and optimization for these problems are discussed in this article. A case study is provided.

ISSN:0360-2559    

DOI:10.1080/03602559909351624

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The graft copolymerization of maleic anhydride (MAH) onto a acryloni-trile-butadiene-styrene (ABS) terpolymer was carried out using benzoyl peroxide (BPO) as an initiator and toluene as a solvent. The effects of various parameters such as monomer concentration, initiator concentration, reaction time, and temperature on graft yield were studied. Addition occurs in the butadiene region of the polymer, either by the loss of vinylic hydrogen and subsequent radical formation and addition of monomer or by addition to the double bond. The graft copolymers were characterized by infrared, thermogravirnetric analysis, and differential scanning calorimetry. Thermal stability was improved andTgwas increased.

ISSN:0360-2559    

DOI:10.1080/03602559909351625

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Ethylene-propylene-diene terpolymer rubberlnatural rubber blends (EPDM/NR) in different proportions (100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100) reinforced with 20 phr semireinforcing furnace carbon black have been studied. The permittivity ε' and dielectric loss ε″ for these samples were determined in the frequency range 102–107Hz. Also, their physico-mechanical properties were investigated.

ISSN:0360-2559    

DOI:10.1080/03602559909351626

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Polypropylene hybrid composites were made using coconut and glass fibers as reinforcing agents in the polypropylene matrix. The incorporation of both fibers into the PP matrix has resulted in the reduction of flex-ural, tensile, and impact strengths and elongation at break. The reduction has been attributed to the increased incompatibility between the fibers and the PP matrix, and the irregularity in fiber size, especially for biofibers as shown by scanning electron micrographs. Both the flexural and tensile moduli have been improved with the increasing level of fiber loading. Most of the properties tested for Composites with high glass fibers/low biofiber loading are comparable with the ones with low glass fiber/high biofiber loading. The results show that more biofibers could be incorporated in hybrid composites which would give the same range of properties as the composites with higher loading of glass fibers.

ISSN:0360-2559    

DOI:10.1080/03602559909351627

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Of the various oxidizing agents available. never have the tetrabutyl ammonium permanganate or the potassium psrmanganate been used for the oxidation of polyolefins in the molten state. The effects of time and temperature on the oxidation reaction were studied using an internal mixer. The reaction was performed in the presence of traces of hexadecyl alcohol as an accelerator. In certain cases, biphenyl was uscd as a conipatibilizing agent in the molten state. The oxidized polyethylene was purified by sol-ubilization in order to eliminate the MnOlformed from the reaction between KMnO4, tetrabutyl ammonium permanganate, and low-density polyethylene (LDPE). The presence of MnO2was confirmed by chemical tests and by electron spectroscopy for chemical analysis (ESCA).

ISSN:0360-2559    

DOI:10.1080/03602559909351628

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor