Effect of dietary and synthetic chelating agents on the intestinal absorption of lead

The effect of a number of dietary and synthetic chelating agents on the intestinal absorption of lead has been examined using the everted sac preparation and the tracer isotope ²⁰³Pb. All the agents examined increased lead transport into the serosal compartment. An explanation of the way in which these agents modify the model to describe lead transport is proposed.     

The construction site as a multicultural workplace: a perspective of minority migrant workers in Brunei

Construction projects have become progressively multicultural, especially for countries with limited labour force where there is need to depend on migrant workers. This multicultural environment can easily create problems related to unfair treatment or discrimination. Focus group discussions were conducted with migrant workers from Indonesia and Thailand to examine factors directly and indirectly related to construction activities that need to be considered in a diverse nationality construction site, with a focus on the minority group. The study suggested that communication, wage segmentation, task assignment and trust, scapegoatism, and belief and religion are the important aspects needing to be carefully taken into account to have a constructive working and living environment in a multicultural project. Management should not overlook the above factors to avoid disenfranchizing minority workers.     

Antecedents of construction project coalitions: a study of the Spanish construction industry

Research into the formation of alliances, relevant in the field of strategic management and especially, in the construction industry, is often explained in terms of interdependency and complementarities (exogenous factors). In contrast, the influence of a firm’s social relations networks (endogenous factors) has hardly been studied at all. Thus, a model is needed that includes both exogenous and endogenous factors as antecedents to the formation of strategic alliances in the construction industry. Cooperation in the construction sector is especially frequent, above all in public works programmes, as their scale requires coalitions of different‐sized firms. Accordingly, to explore how both exogenous and endogenous factors influence the formation of alliances, a social network analytical method—Multiple Regression Quadratic Assignment Procedure (MRQAP)—was applied to cooperative project coalitions in the Spanish public works construction sector from 2001–2007. Empirical findings confirm that construction companies form coalitions, principally on the basis of past alliances. Membership of business associations and groups is also a key factor, though the influence of geographic proximity is the most debatable result. In the construction industry, the formation of alliances is conditioned, among other factors, by previous social and economic relations that can generate the necessary information and trust for the selection of whichever partner is considered the most suitable for the development of the joint project.     

The discourse of ‘Respect for People’ in UK construction

A competency‐based review of professional quantity surveying is important for service excellence and has continuing relevance in the built environment of the 21^st century. A survey of quantity surveyors in professional practice in South Africa has provided a new perspective on the relative importance of competencies required for current and future quantity surveying services, and revealed notable gaps between the important competencies and current proficiency levels among practitioners. The survey was based on a structured questionnaire reflecting 23 defined competencies, which were derived from the literature and from in‐depth interviews with selected practitioners. The results indicated that technically orientated competencies were rated of highest importance for current services, while management orientated competencies were rated of higher importance for future services. The profession was rated as deploying below average proficiency levels in marketing, advanced financial management, leadership and general management, and project management, although these received high current and future importance ratings. The findings suggest that initial and continuing education and training of professional quantity surveyors should emphasize the development of management‐orientated competencies.     

Shape memory crosslinked polyurethanes containing thermoreversible Diels‐Alder couplings

Crosslinked polyurethanes (PUs) containing irreversible (allophanate) and reversible Diels‐Alder chemical bonds were synthesized using various diisocyanates (methylene diphenyl diisocyanate MDI, 1,6‐hexamethylenediisocyanate HDI) and poly(?‐caprolactone) ((PCL) with different molecular weights (M_n = 10 kg/mol, 25 kg/mol, 50 kg/mol) as diol component. The melting/crystallization of PCL and the reversible DA bonds acted as temperature‐activated switches for shape memory performances, while allophanate network provided the permanent crosslinks for these PUs. The reversible DA bonds were obtained by the reaction of diisocyanate‐ended prepolymers with furfurylamine (FA) followed by the addition of bismaleimide (BMI). The permanent crosslinks between the linear chains containing DA bonds were achieved using additional amounts of diisocyanates (MDI or HDI). The above reaction path was supported by infrared spectroscopic results and swelling experiments. Tensile mechanical and shape memory properties in tension of the PUs were determined and discussed as a function of composition and crosslink densities deduced from swelling and dynamic mechanical analysis. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44145.     

Preparation and characterization of innovative cellulose diacetate/epoxy resin blends modified by isophorone diamine

Cellulose diacetate (CA)/epoxy resin (EP) blends with excellent mechanical performance were prepared with simple blending followed by curing with isophorone diamine (IPDA). The reaction between the amino groups of IPDA and epoxide groups of EP was confirmed by Fourier transform infrared spectroscopy. Scanning electron microscopy revealed that the cured EP particles gradually became larger and closer to each other to form semi‐interpenetrating polymer networks in the CA matrix; this contributed to the improved mechanical properties of the CA/EP blends. Dynamic rheological experiments indicated that the CA/EP blends with semi‐interpenetrating polymer networks retained processability. After the introduction of a low content (5–10 phr) of IPDA, the mechanical properties of the CA/EP blends were significantly enhanced. With the addition of 20–30‐phr IPDA, the CA/EP blend exhibited a tensile strength of 77 MPa, a flex strength of 65 MPa, a flex modulus of 2.6 GPa, and a hardness of 94 HD; these values were much higher than those of the pristine CA/EP binary blend. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44151.     

Stepwise cure and properties of silicone resin for high‐ultraviolet‐transmission optical elements

A new high‐ultraviolet (UV)‐transmission silicone‐resin polymeric material was prepared via curing during hydrosilylation of tetramethyltetravinylcyclotetrasiloxane with tetramethylcyclotetrasiloxane by a liquid‐surface supernatant method, using a stepwise heating program to avoid spontaneous combustion of the reaction mixture. The relationships were investigated in detail between reactive groups, cross‐linking density, mechanical and UV‐transmission properties. For this purpose, UV transmittance and dynamic mechanical properties, respectively, of the silicone resin were measured with UV–visible spectrophotometry and dynamic mechanical thermal analysis. In addition, surface roughness was evaluated with an atomic force microscope as well as an interferometer. The curing process was monitored by Fourier transform infrared spectroscopy and rotational rheometry. The cyclic silicone oils were compared with linear ones in structure and product properties. The results indicated that stepwise temperature control during curing process was particularly indispensible due to the presence of active Si? H bonds, and that the silicone resin of high modulus, high UV transmittance (92.7%) and low surface‐roughness was largely homogeneous in cross‐linking points distribution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43308.     

The effect of tunable modification parameters on the structure and properties of polypropylene with cyclotrimerization surface of isocyanates

The cyclotrimerization of methylene diphenyl 4,4‐diisocyanate (MDI) and 3‐isopropenyl‐α,α′‐dimethylbenzene isocyanate (TMI) was applied on the bead/membrane surfaces of a polypropylene (PP)‐bearing isocyanate group to synthesize a protective networked polymer. Chemical structures of these molecules were characterized through attenuated total reflectance–Fourier transform infrared spectroscopy. Results showed that the absorption peak of isocyanate group at 2255 cm^?1 became negligible after the reaction was completed. The absorption peaks of the isocyanurate groups appeared simultaneously at 1600 cm^?1 and at 1510–1560 cm^?1; this result indicated that the grafted isocyanates were almost consumed, thereby forming isocyanurates. Energy X‐ray dispersive spectroscopy revealed that oxygen content increased; indeed, isocyanurate was formed on the PP surface. Pure PP beads, PP‐g‐TMI, and cyclotrimerization products were also subjected to thermal property tests to investigate their corresponding thermal stabilities. Cyclotrimerization could result in the increase in PP‐grafted decomposition temperature, even slightly higher than pure PP. Rheological behavior in oscillatory flow was also evaluated; the storage modulus, loss modulus, and complex viscosity of cyclotrimerization products were higher than those of the PP‐grafted membranes. Surface morphology was further observed through field‐emission scanning electron microscopy and atomic force microscopy. The cyclotrimerization products contained blocks and exhibited a rough surface. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43327.     

Elastic constants of lamellar and interlamellar regions in α and mesomorphic isotactic polypropylene by AFM indentation

A study of the nanoscale mechanical properties of isotactic mesomorphic and semi‐crystalline polypropylene (iPP) is presented. Two iPPs produced with metallocene and Ziegler‐Natta catalyst polymerization are used. The resulting fibers are characterized by wide angle X‐ray scattering, small‐angle X‐ray scattering (SAXS), and Raman spectroscopy. The spatial variability of the percentage crystallinity is evaluated based on the SAXS data. AFM indentation is performed to measure the elastic modulus of the fibers in the direction perpendicular and parallel to the fiber axis. Since the AFM probing is performed on a scale larger than the lamellar thickness, a statistical analysis of the AFM and SAXS data is necessary to infer the elastic moduli of the α crystals and of the inter‐lamellar regions. The elastic modulus of the crystalline lamellae in the direction perpendicular to the c‐axis of the α crystal probed in compression is estimated at approximately 3.3 GPa, while the effective modulus of the interlamellar regions ranges from 1.5 to 2.2 GPa. The method proposed can be applied to other material systems with similar layered structure to measure elastic moduli or hardness on length scales smaller than the resolution of the indentation test. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43649.     

Synthesis and characterizations of hydrophobically associating water‐soluble polymer with nonionic surfmer

In this article, a hydrophobically associating copolymer (2‐acrylamido)‐2‐methylpropanesulfonic acid (AMPS)/AA‐EO₂₅C₁₂ was synthesized by AMPS and nonionic surfmer AA‐EO₂₅C₁₂ through free radical copolymerization. The structure of copolymer was characterized by FT‐IR and ¹H‐NMR. The properties of copolymer were studied and the results indicated that the copolymer exhibits good thickening ability due to intermolecular hydrophobic associations as the apparent viscosity of the copolymer solution increases sharply with increasing polymer concentration. Compared with homopolymer PAMPS, the rheological test indicates that the copolymer solution shows shear thickening behavior at low shear rate region. Besides, the copolymer exhibits interfacial activity as it can reduce the interfacial tension to 10° level, and ability to form emulsion with good stability, which is due to successfully introducing the structure of nonionic surfmer AA‐EO₂₅C₁₂ to the polymer chain. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43195.