Distribution by Scientific Domains

Kinds of Curing

  • light curing
  • microwave curing
  • thermal curing
  • ultraviolet curing
  • uv curing

  • Terms modified by Curing

  • curing agent
  • curing behavior
  • curing condition
  • curing kinetics
  • curing light
  • curing process
  • curing rate
  • curing reaction
  • curing system
  • curing temperature
  • curing time
  • curing unit

  • Selected Abstracts


    Signe Vikkels
    Performance standards and accountability pervade modern healthcare. According to Michael Power, this may signify a new rationality of governance characterized by control of controls, which affects practices not by direct intervention, but through the processes by which practices are made auditable. The paper addresses this thesis by exploring the construction of a Danish standard for electronic patient records. It is shown that making healthcare auditable activates deep tensions between programs of clinical practice, quality control, evidence based medicine, and casemix funding, resulting in an ambiguous and unstable standard. During this process, however, particular notions of patients, diseases, and diagnoses emerge as undisputed innovations, which may come to survive the subsequent career of the standard. The paper discusses the performative effects of these innovations and argues that information infrastructure has become an analytically important site for exploring the substantial effects of new rationalities of governance in healthcare. [source]

    Effects of Oxidation Curing and Sintering Additives on the Formation of Polymer-Derived Near-Stoichiometric Silicon Carbide Fibers

    Lifu Chen
    The effects of oxygen pick-up and sintering additives on the formation of silicon carbide (SiC) fibers from polyaluminocarbosilane are studied. It has been found that the strict control of oxygen pick up during the oxidation curing is essential to produce near-stoichiometric SiC fibers. When the molar ratio of oxygen to excess carbon in the pyrolyzed fibers (SiCxOy) is slightly over 1 (O/CExcess=y/(x,1)>1), the excess carbon is eliminated during the subsequent sintering as CO and CO2 as a result of the decomposition of SiCxOy; the remaining oxygen is removed as SiO and CO vapor, leaving near-stoichiometric SiC as the residue. However, with still increasing oxygen pick up, the final ceramic fibers become more porous and rich in silicon. The evolution of CO, CO2, and SiO generates high porosity in the absence of a sintering additive, leading to low fiber density. The inter-connected and open porosity favors the formation of CO. In contrast, for the fibers containing aluminum (Al) or Al/B sintering additives, the pores are much smaller and essentially closed, favoring the formation of CO2. Therefore, after sintering at 1800C, the fibers without sintering additives contain excess silicon, while those with sintering additives are near stoichiometric. Al is beneficial to the densification but it alone cannot produce fibers of high density. When B is added in addition to Al, the fibers can be sintered to nearly full density. [source]

    Curing of four different plasmids in Yersinia pestis using plasmid incompatibility

    B. Ni
    Abstract Aims:, Plasmids are critical for the pathogenicity of Yersinia pestis. In order to carry out a systematic investigation of their role in pathogenesis, we cured plasmids from Y. pestis. Methods and Results:, Each plasmid's replicon of Y. pestis was cloned into plasmid pEX18Gm containing a counter-selectable sacB gene, and was then introduced into Y. pestis strain 201 by electroporation. Strains containing recombinant plasmids were cultivated under antibiotic selection. The resultant plasmid-curing colonies, identified by specific polymerase chain reactions, were then cured off pEX18Gm under sucrose pressure. This method was used to successfully cure all four plasmids of Y. pestis, singly or in different combinations. Conclusions:, Naturally evolving plasmids in Y. pestis are difficult to remove by conventional curing methods. We employed a method based on plasmid incompatibility to cure the plasmids from Y. pestis, which confirmed the efficacy of this method for curing plasmids with different types of replicons from one bacterium. Significance and Impact of the Study:, There have been no reports on the curing of multiple plasmids by using replication mechanisms from one bacterium with this technique. In the present study, we were able to successfully apply this methodology to cure four plasmids from Y. pestis, confirming its feasibility. [source]

    Synthesis of a New Hyperbranched Polyaminoester and Its Use as a Reactive Modifier in Anionic Curing of DGEBA Thermosets

    Mireia Morell
    Abstract The synthesis and characterization of a new hyperbranched PAE with a flexible structure and terminal hydroxyl groups is reported. The influence of PAE in the anionic curing of DGEBA with 1-methylimidazole was studied. The curing reaction was investigated by DSC and FT-IR. The covalent incorporation of the modifier in the matrix was proven. The addition of PAE to the formulation reduced the contraction on curing. The modified materials were more thermally degradable than neat DGEBA thermosets, which is advantageous from the point of view of their reworkability. Their Tgs were reduced by the flexibility introduced by the aliphatic structure of PAE. SEM microscopy on the fractured surface of cured samples revealed a homogeneous morphology and a possible effect of PAE as a toughness enhancer. [source]

    Novel Triaromatic Ester Mesogenic Liquid Crystalline Epoxy Resin Containing Both Methyl Substituent and Ethoxy Flexible Spacer: Synthesis and Curing

    Guo-dong Liu
    Abstract A novel triaromatic ester liquid crystalline epoxy resin (LCER) that contains both a methyl substituent and an ethoxy flexible spacer, p -methylphenylene di{4-[(2,3-epoxypropoxy)ethoxy]benzoate} (MPEPEB), has been synthesized. The mesotropic property has been investigated by differential scanning calorimetry (DSC) and polarized light optical microscopy (POM). MPEPEB shows a lower melting temperature at 78.7,C and a broad nematic mesophase temperature range of about 55,C. Meanwhile MPEPEB shows a mesophase to ,50,C upon cooling. The curing behavior of MPEPEB with 2,6-diamino-3,5-diethyltoluene (DAE) has been investigated by means of DSC and POM during isothermal and dynamic processes. Although there is little difference between the activation energies obtained from the kinetic data, a marked difference is found between the isothermal and dynamic investigation. The curing reaction in the isothermal investigation roughly obeys n- th order kinetics, while two exothermal peaks appear in the dynamic DSC curves of MPEPEB/DAE. A comparison of the isothermal and dynamic data shows that the curing rate is not a unique function of temperature and curing degree. The cured networks have lower glass temperatures and show a mesophase at room temperature which disappears at about 86,88,C. [source]

    Ring-Opening Metathesis Polymerization Based Post-Synthesis Functionalization of Electron Beam Curing Derived Monolithic Media

    Rajendar Bandari
    Abstract Monolithic materials were prepared via electron-beam curing from ethyl methacrylate, trimethylolpropane triacrylate, and norborn-5-ene-2-ylmethyl acrylate. Reaction of the norborn-2-ene groups with either RuCl2(PCy3)2(CHPh) (1) or RuCl2(PCy3)(1,3-dimesityl-4,5-dihydroimidazol-2-inylidene)(CHPh) (2) resulted in the surface attachment of the initiators. The extent of initiator immobilization was found to be substantially higher for 1 than for 2. Reaction of the surface immobilized initiators with various monomers resulted in the desired surface modification of EB-derived monoliths. The amounts of grafted monomer were determined by elemental analysis and ICP-OES. [source]

    Kinetic Study and New Applications of UV Radiation Curing

    Christian Decker
    Abstract Highly crosslinked polymers can be readily synthesized by photoinitiated polymerization of multifunctional monomers or functionalized polymers. The reaction can be followed in situ by real-time infrared (RT-IR) spectroscopy, a technique that records conversion versus time curves in photosensitive resins undergoing ultrafast polymerization upon UV exposure. For acrylate-based resins, UV-curing proceeds with long kinetic chains (7700 mol/radical) in spite of the high initiation rate. RT-IR spectroscopy proved very valuable in assessing the influence of various parameters, such as initiation efficiency, chemical structure of the telechelic oligomer, light intensity, inhibitory effect of oxygen, on polymerization kinetics. Interpenetrating polymer networks can be rapidly synthesized by means of UV irradiation of a mixture of difunctional acrylate and epoxy monomers in the presence of both radical and cationic-type photoinitiators. The same UV technology can be applied to crosslink solid polymers at ambient temperature, which bear different types of reactive groups (acrylate and vinyl double bonds, epoxy ring). UV radiation curing has been successfully used to produce within seconds weathering resistant protective coatings, high-resolution relief images, glass laminates and nanocomposites materials. Photoinitiated crosslinking polymerization. [source]

    Interpenetrating Polymer Networks with Spatially Graded Morphology Controllable by UV-Radiation Curing

    Hideyuki Nakanishi
    Abstract Interpenetrating Polymer Networks (IPNs) composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) were synthesized from a precursor mixture by using dissimilar photo-cross-link reactions. When the reation yields exceeded a certain threshold, the mixture was quenched from one-phase region into two-phase region, leading to phase separation. Upon irradiation with strong UV-light, an intensity gradient was formed along the propagating direction of the exciting light, generating a gradient of quench depth via the spatial inhomogeneity of the cross-link reactions. As a consequence, a gradient of the characteristic length scales was continuously generated from the top to the bottom of the mixture. The resulting three-dimensional (3-D) morphology was in-situ observed at different depths of the mixture by using a laser-scanning confocal microscope (LSCM). From this 3-D observation, it was found that phase separation was accelerated at the bottom of the mixture and proceeded in an autocatalytic fashion. The mechanism for the formation of the graded morphology was discussed in conjunction with the kinetics of the autocatalytic phase separation. [source]

    Curing and Healing: Medical Anthropology in Global Perspective; Everyday Spirits and Medical Interventions: Ethnographic and Historical Notes on Therapeutic Conventions in Zanzibar Town; Some Spirits Heal, Others Only Dance: A Journey into Human Selfhood in an African Village; The Straight Path of the Spirit: Ancestral Wisdom and Healing Traditions in Fiji; Healing Makes Our Hearts Happy: Spirituality and Cultural Transformations among the Ju!'hoansi

    Helle Samuelsen
    Curing and Healing: Medical Anthropology in Global Perspective. Andrew Strathern and Pamela J. Stewart. Durham, NC: Carolina Academic Press, 1999. vii+224 pp. Everyday Spirits and Medical Interventions: Ethnographic and Historical Notes on Therapeutic Conventions in Zanzibar Town. Tapio Nisula. Saarijanjarvi: Transactions of the Finnish Anthropological Society 43,1999. 321 pp. Some Spirits Heal, Others Only Dance:. Journey into Human Selfhood in an African Village. Roy Willis with K. B. S. Chisanga. H. M. K. Sikazwe. Kapembwa B. Sikazwe. and Sylvia Nanyangwe .Oxford: Berg, 1999. xii. 220pp. The Straight Path of the Spirit: Ancestral Wisdom and Healing Traditions in Fiji. Richard Katz. Rochester, VT. Park Street Press, 1999.413 pp. Healing Makes Our Hearts Happy: Spirituality and Cultural Transformations among the Ju!'hoansi. Richard Katz. Megan Biesele. and Verna St. Denis. Rochester, VT: Inner Traditions, 1997. xxv. 213 pp. [source]

    A fiber optic thermoset cure monitoring sensor

    POLYMER COMPOSITES, Issue 4 2000
    Michele Giordano
    Curing determines the chemical and physical properties of a reacting resin. Among these, the optical properties strongly correlate with the structural features of the developing polymeric network. By monitoring changes of the refractive index, it is possible to analyze the polymerization of thermoset resin. In this work, a fiber optic sensor system has been designed and developed (based on the optical time domain reflectometry principle) to measure the reflection coefficient at the interface between the fiber optic and the resin during a curing process. Correlation between the sensor output and conversion has been proposed, following the Lorentz-Lorenz law. Isothermal data from the sensor have been compared with calorimetric analysis of an epoxy-based resin. [source]

    Curing of diglycidyl ether of bisphenol-A epoxy resin using a poly(aryl ether ketone) bearing pendant carboxyl groups as macromolecular curing agent

    Fuhua Liu
    Abstract BACKGROUND: Reactive thermoplastics have received increasing attention in the field of epoxy resin toughening. This paper presents the first report of using a novel polyaryletherketone bearing one pendant carboxyl group per repeat unit to cure the diglycidyl ether of bisphenol-A epoxy resin (DGEBA). The curing reactions of DGEBA/PEK-L mixtures of various molar ratios and with different catalysts were investigated by means of dynamic differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy methods. RESULTS: FTIR results for the DGEBA/PEK-L system before curing and after curing at 135 C for different times demonstrated that the carboxyl groups of PEK-L were indeed involved in the curing reaction to form a crosslinked network, as evidenced by the marked decreased peak intensities of the carboxyl group at 1705 cm,1 and the epoxy group at 915 cm,1 as well as the newly emerged strong absorptions of ester bonds at 1721 cm,1 and hydroxyl groups at 3447 cm,1. Curing kinetic analysis showed that the value of the activation energy (Ea) was the highest at the beginning of curing, followed by a decrease with increasing conversion (,), which was attributed to the autocatalytic effect of hydroxyls generated in the curing reaction. CONCLUSION: The pendant carboxyl groups in PEK-L can react with epoxy groups of DGEBA during thermal curing, and covalently participate in the crosslinking network. PEK-L is thus expected to significantly improve the fracture toughness of DGEBA epoxy resin. Copyright 2009 Society of Chemical Industry [source]

    Yielding behaviour of thermoplastic/elastomer blends cured by gamma irradiation

    A Shaltout
    Abstract Mechanical blends of thermoplastic medium density polyethylene (MDPE) and elastomeric ethylene propylene diene monomer (EPDM) have been prepared with a fixed composition of 60/40,wt%. They have been used either in their gum form or loaded with two different reinforcing fillers, high abrasion furnace (HAF) carbon black or precipitated SiO2 (Hi Sil) of concentration 25,100,phr (parts per hundred parts of resin) with respect to the blend. Curing was achieved by gamma irradiation. Yielding properties (yield stress, yield strain and cold drawing) have been followed as a function of irradiation dose for different blend compositions. Yield stress values increased with irradiation dose and with the content of the reinforcing filler, but yield strain and cold drawing values decreased with irradiation dose and also with the filler content. The data obtained reveal that Hi Sil is more effective as a reinforcing filler, and the prepared blends are suitable for load-bearing applications. 2001 Society of Chemical Industry [source]

    The expansion of the south-western fisheries in late medieval England

    Maryanne Kowaleski
    This article argues that the expansion of marine fishing in south-western England from the late fourteenth century to the early sixteenth was part of the maritime sector's critical, but unappreciated, contribution to the rising prosperity of the region. Revenues from fishing represented a substantial supplement to the income of the fisher-farmers who dominated the industry; promoted employment in ancillary industries such as fish curing; improved the seasonal distribution of maritime work; and stimulated capital investment in ships, nets, and other equipment because of the share system that characterized the division of profits within fishing enterprises. In offering what was probably the chief source of employment within the maritime sector, fishing also provided the ,nursery of seamen' so prized by the Tudor navy, and built the navigational experience that underpinned later voyages of exploration. [source]

    Influence of light energy and power density on the microhardness of two nanohybrid composites

    Kerstin Gritsch
    The purpose of this study was to investigate the role of light parameters on nanohybrid composite curing. Two nanohybrid resins were cured by two light-emitting diode (LED) devices and by one quartz-tungsten-halogen (QTH) device using different combinations of energy density and power density (8 J cm,2 and 400 mW cm,2; 8 J cm,2 and 1,000 mW cm,2; 16 J cm,2 and 400 mW cm,2; and 16 J cm,2,1,000 mW cm,2). The effects of these combinations on polymerization were assessed by measuring the Vickers microhardness. Data differed for the two composites and varied according to the light parameters and the nature of the curing device. For both resins, an energy density of 16 J cm,2 yielded the best microhardness values at both the top and the bottom of the sample, independently of the power density. When using a lower energy density of 8 J cm,2, a modulated power density was required to achieve proper curing at the bottom of the sample: 8 J cm,2 and 400 mW cm,2 induced greater values at the bottom surface. At an energy density of 16 J cm,2, the power density was not relevant (no significant differences were found between 400 and 1,000 mW cm,2), except when the emission spectra of the light-curing units (LCUs) did not match exactly with the absorption spectra of the photoinitators included in the resins (greatest values with 16 J cm,2 and1,000 mW cm,2). These results suggest that above a certain energy density threshold, the power density may not significantly influence the polymerization kinetics. [source]

    Resin composite shrinkage and marginal adaptation with different pulse-delay light curing protocols

    Ivo Krejci
    The aims of this study were, first, to measure shrinkage induced by different methods of pulse-delay light curing and, second, to verify their influence on the marginal adaptation of class V restorations in enamel and dentin. Eight groups, comprising seven groups (n = 6) with different pulse-delay parameters and a control group, were compared for dynamic linear displacement and force by using a fine hybrid composite. Based on these results, the pulse-delay curing procedure with the lowest shrinkage force was chosen and tested against the control group with respect to marginal adaptation in class V restorations (n = 8) before and after simultaneous thermal and mechanical loading. Statistically significant differences between groups were found for both shrinkage properties tested, with one pulse-delay group giving the lowest overall shrinkage values. However, the percentages of ,continuous margin' of this group, and of the control before and after loading, were not significantly different in dentin, whereas a significantly lower percentage of ,continuous margin' was detected in the pulse-delay group in enamel after loading. [source]

    Effect of irradiation type (LED or QTH) on photo-activated composite shrinkage strain kinetics, temperature rise, and hardness

    Norbert Hofmann
    This study compares commercially available light-emitting diode (LED) lights with a quartz tungsten halogen (QTH) unit for photo-activating resin-based composites (RBC). Shrinkage strain kinetics and temperature within the RBC were measured simultaneously using the ,deflecting disc technique' and a thermocouple. Surface hardness (Knoop) at the bottom of 1.5-mm thick RBC specimens was measured 24 h after irradiation to indicate degree of cure. Irradiation was performed for 40 s using either the continuous or the ramp-curing mode of a QTH and a LED light (800 mW cm,2 and 320 mW cm,2, respectively) or the continuous mode of a lower intensity LED light (160,mW cm,2). For Herculite XRV and Filtek Z250 (both containing only camphoroquinone as a photo-initiator) the QTH and the stronger LED light produced similar hardness, while in the case of Definite (containing an additional photo-activator absorbing at lower wavelength) lower hardness was observed after LED irradiation. The temperature rise during polymerization and heating from radiation were lower with LED compared to QTH curing. The fastest increase of polymerization contraction was observed after QTH continuous irradiation, followed by the stronger and the weaker LED light in the continuous mode. Ramp curing decreased contraction speed even more. Shrinkage strain after 60 min was greater following QTH irradiation compared with both LED units (Herculite, Definite) or with the weaker LED light (Z250). [source]

    Bonded aircraft repairs under variable amplitude fatigue loading and at low temperatures

    Bonded repairs can replace mechanically fastened repairs for aircraft structures. Compared to mechanical fastening, adhesive bonding provides a more uniform and efficient load transfer into the patch, and can reduce the risk of high stress concentrations caused by additional fastener holes necessary for riveted repairs. Previous fatigue tests on bonded Glare (glass-reinforced aluminium laminate) repairs were performed at room temperature and under constant amplitude fatigue loading. However, the realistic operating temperature of ,40 C may degrade the material and will cause unfavourable thermal stresses. Bonded repair specimens were tested at ,40 C and other specimens were tested at room temperature after subjecting them to temperature cycles. Also, tests were performed with a realistic C-5A Galaxy fuselage fatigue spectrum at room temperature. The behaviour of Glare repair patches was compared with boron/epoxy ones with equal extensional stiffness. The thermal cycles before fatigue cycling did not degrade the repair. A constant temperature of ,40 C during the mechanical fatigue load had a favourable effect on the fatigue crack growth rate. Glare repair patches showed lower crack growth rates than boron/epoxy repairs. Finite element analyses revealed that the higher crack growth rates for boron/epoxy repairs are caused by the higher thermal stresses induced by the curing of the adhesive. The fatigue crack growth rate under spectrum loading could be accurately predicted with stress intensity factors calculated by finite element modelling and cycle-by-cycle integration that neglected interaction effects of the different stress amplitudes, which is possible because stress intensities at the crack tip under the repair patch remain small. For an accurate prediction it was necessary to use an effective stress intensity factor that is a function of the stress ratio at the crack tip Rcrack tip including the thermal stress under the bonded patch. [source]

    Doc-mediated cell killing in Shigella flexneri using a C1/LacI controlled expression system

    David A. Schofield
    Abstract In this report we describe the development of a highly stringent and dually regulated promoter system for Shigella flexneri. Dual regulation was provided by utilizing a promoter susceptible to control by the bacteriophage P1 temperature-sensitive C1 repressor that in turn was under the transcriptional control of LacI. The level of induction/repression ratios observed was up to 3700-fold in S. flexneri. The general utility of this promoter system was evaluated by demonstrating that the bacteriophage P1 post-segregational killer protein Doc mediates a bactericidal effect in S. flexneri. This represents the first report of Doc (death on curing)-mediated killing in this Gram-negative species. [source]

    Changing Fire Management in the Pastoral Lands of Cape York Peninsula of northeast Australia, 1623 to 1996

    G.M. Crowley
    Accounts of European explorers between 1623 and 1880 indicate that fires were lit by Aboriginal people on Cape York Peninsula in northeast Australia throughout the dry season (May,October). Diaries kept by three generations of pastoralists in the Musgrave area (1913,1952, 1953,1974 and 1976,1992) show that burning activities were largely confined to a two to six week period between May and early August. The timing of burning depended on the amount and date of cessation of wet season rainfall. More rarely, ,storm-burning', burning under hot conditions within a few days of the first heavy rains of the wet season, was undertaken. Long-term pastoralists felt a responsibility to use fire wisely and had a detailed knowledge of the role of fire in land management. Their decisions to burn were based on the extent of grass curing, and soil and weather conditions, all of which affected the extent of each burn. They used early dry season fires mainly to maintain forage and control cattle movements. Storm-burns were reputed to control woody weeds, but were used infrequently because of difficulty in controlling their spread and uncertainty as to when the next rains would stimulate new grass growth. [source]

    Cycloaddition approach to the curing of polyimides via precursor containing thiophene- S,S -dioxide

    Andrew Magyarosy
    A new method for linear polymerization of maleimides via the Diels,Alder reaction has been developed. This method involves use of a new cross-linking agent, benzene-3,4-dimethylenesuccinimide, which can be generated in situ from its thiophene precursor, benzene-2,5-dihydrothiophene-3,4-dicarboximide- S,S -dioxide. This new cross-linking agent is reasonably reactive, readily prepared, and stable at room temperature. A controlled molecular weight oligomer has been synthesized and applied to the polymerization to yield a highly thermal stable polyimide. 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:648,652, 2006; Published online in Wiley InterScience ( DOI 10.1002/hc.20249 [source]

    Phenotypic profile and functional characterization of rat lymph node-derived ,, T cells: implication in the immune response to cytomegalovirus

    IMMUNOLOGY, Issue 2 2003
    Larissa Dyugovskaya
    Summary ,, T cells are unique, and their localization at sites of infection is considered critical in immune defence. We demonstrate the accumulation of ,, T cells in rat regional popliteal lymph nodes (PLNi) starting 2 days after inoculation of cytomegalovirus (CMV) into the footpad. Early-appearance PLNi ,, T cells significantly inhibited plaque development and the spread of CMV infection. These ,, T cells were negative for CD4 and CD8beta receptors, proliferated in response to interleukin-2 (IL-2) and contained high levels of interferon-, (IFN-,), the appearance of which correlated with the curing of fibroblasts from virus infection. The addition of anti-IFN-, abolished the ability of fibroblast monolayers to be cured from CMV infection. In contrast, this protection was not abolished by the addition of anti-rat IL-2 or anti-rat TNF-,, or by the depletion of NKR-P1-bearing cells within ,, T cells. In addition, the present study shows that while ,, T cells derived from naive and CMV-infected rats are able to kill both YAC-1 targets and CMV-infected syngeneic fibroblasts in vitro, only the latter are able to clear CMV-infected fibroblast monolayers. Finally, our data suggest that the expression of NKR-P1 by ,, T cells is critical for cytotoxicity, but its contribution to the curing from CMV infection was limited. [source]

    Fabrication of Polyimide-Blend Thin Films Containing Uniformly Oriented Silver Nanorods and Their Use as Flexible, Linear Polarizers

    ADVANCED MATERIALS, Issue 18 2005
    S. Matsuda
    Fully aromatic polyimide films containing uniformly oriented Ag nanorods (see Figure) have been prepared by a simple method consisting of thermal curing and uniaxial drawing of submicrometer-scale phase-separated polyimide-blend films containing dissolved AgNO3. The films exhibit outstanding optical dichroism, over 20,dB (see inset), in the near-IR region due to the high aspect ratio of the nanorods and the high transparency of the matrix. [source]

    Effects of storage aging on the cure kinetics of bismaleimide prepregs

    M. Frigione
    The effects of room temperature aging on the subsequent polymerization kinetics of a bismaleimide (BMI) matrix prepreg, for high performance composites, have been characterized by different time and storage conditions. The study has focused on the stability of BMI matrix carbon fiber prepregs, when exposed to controlled environmental conditions before being used in composite manufacturing. The effects of aging on glass transition temperature, reactivity, and processability have been investigated by calorimetry through dynamic, isothermal, and cure-simulating tests. A theoretical kinetic model for epoxy matrix prepregs, developed in previous studies, has been applied to the polymerization of both aged and unaged BMI matrix. The model is able to satisfactorily describe the effect of processing variables such as temperature and degree of reaction during the curing of the composite under different conditions (curing temperature and heating rate). The effects of diffusion-controlled phenomena on the reaction kinetics, associated with changes in glass transition temperature as a function of the degree of polymerization and cross-linking, have been taken into account in the formulation of an nth-order kinetic model. 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 253,265, 2005; Published online in Wiley InterScience ( DOI 10.1002/adv.20048 [source]

    Isolation and characterization of a bacterial strain of the genus Ochrobactrum with methyl parathion mineralizing activity

    X.-H. Qiu
    Abstract Aims:, To isolate and characterize a methyl parathion (MP)-mineralizing bacterium, and to elucidate the degradative pathway of MP and localize the responsible degrading genes. Methods and Results:, A bacterial strain, designated B2, capable of mineralizing MP was isolated from the MP-polluted soil. Analysis of the 16S rRNA gene sequence and phenotypic analysis suggested that strain B2 had a close relationship with Ochrobactrum anthropi. B2 could totally degrade MP and four metabolites [p -nitrophenol (PNP), 4-nitrocatechol (4-NC), 1,2,4-benzenetriol (BT) and hydroquinone (HQ)] were identified by HPLC and gas chromatography-mass spectrometry analyses. Plasmid curing of strain B2 resulted in the loss of ability of B2 to degrade PNP, but not the ability to hydrolyse MP. Conclusions:,Ochrobactrum sp. B2 can mineralize MP rapidly via PNP, 4-NC, BT and HQ pathway. B2 harbours a plasmid encoding the ability to degrade PNP, while MP-hydrolysing activity is encoded on the bacterial chromosome. Significance and Impact of the Study:, This new bacterial strain (B2) capable of mineralizing MP will be useful in a pure-culture remediation process of organophosphate pesticides and their metabolites such as nitroaromatics. [source]

    Preparation and flame retardancy of 2-EHA/n -BA acrylic PSA containing single and combined flame retardants

    Eun-Young Park
    Abstract UV curable acrylic PSAs (pressure-sensitive adhesives) were modified with organic and inorganic flame retardants to improve flame retardancy of PSAs minimize the sacrifice of adhesion properties. The flame retardancy (UL-94 test) of acrylic PSAs were enhanced by the addition of 5,30 wt % of an organic flame retardant such as TCEP (Tris(2-chloroethyl)phosphate), PBPE (pentabromophenyl ether), and TBBPA(3,3,5,5,-tetrabromobisphenol A). Especially, TBBPA is the best flame retardant for acrylic PSAs when it works alone. However, PSAs compounded with aluminum trihydroxide (Al(OH)3) showed a little reduction in burning time up to 30 wt %. An apparent synergic effect was observed only for an acrylic PSAs with a combination of TCEP and PBPE flame retardants. The addition of flame retardants brought a no significant effect on curing even in high amount. It was surmised that the miscibility between PSAs and flame retardant was closely related with flame retardancy and adhesion properties of acrylic PSAs. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

    Reactive mold filling in resin transfer molding processes with edge effects

    Yanyu Ding
    Abstract Reactive mold filling is one of the important stages in resin transfer molding processes, in which resin curing and edge effects are important characteristics. On the basis of previous work, volume-averaging momentum equations involving viscous and inertia terms were adopted to describe the resin flow in fiber preform, and modified governing equations derived from the Navier,Stokes equations are introduced to describe the resin flow in the edge channel. A dual-Arrhenius viscosity model is newly introduced to describe the chemorheological behavior of a modified bismaleimide resin. The influence of the curing reaction and processing parameters on the resin flow patterns was investigated. The results indicate that, under constant-flow velocity conditions, the curing reaction caused an obvious increase in the injection pressure and its influencing degree was greater with increasing resin temperature or preform permeability. Both a small change in the resin viscosity and the alteration of the injection flow velocity hardly affected the resin flow front. However, the variation of the preform permeability caused an obvious shape change in the resin flow front. The simulated results were in agreement with the experimental results. This study was helpful for optimizing the reactive mold-filling conditions. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

    Investigation of the postcure reaction and surface energy of epoxy resins using time-of-flight secondary ion mass spectrometry and contact-angle measurements

    Firas Awaja
    Abstract Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to investigate correlations between the molecular changes and postcuring reaction on the surface of a diglycidyl ether of bisphenol A and diglycidyl ether of bisphenol F based epoxy resin cured with two different amine-based hardeners. The aim of this work was to present a proof of concept that ToF-SIMS has the ability to provide information regarding the reaction steps, path, and mechanism for organic reactions in general and for epoxy resin curing and postcuring reactions in particular. Contact-angle measurements were taken for the cured and postcured epoxy resins to correlate changes in the surface energy with the molecular structure of the surface. Principal components analysis (PCA) of the ToF-SIMS positive spectra explained the variance in the molecular information, which was related to the resin curing and postcuring reactions with different hardeners and to the surface energy values. The first principal component captured information related to the chemical phenomena of the curing reaction path, branching, and network density based on changes in the relative ion density of the aliphatic hydrocarbon and the C7H7O+ positive ions. The second principal component captured information related to the difference in the surface energy, which was correlated to the difference in the relative intensity of the CxHyNz+ ions of the samples. PCA of the negative spectra provided insight into the extent of consumption of the hardener molecules in the curing and postcuring reactions of both systems based on the relative ion intensity of the nitrogen-containing negative ions and showed molecular correlations with the sample surface energy. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

    Morphology and thermal and dielectric behavior of cycloaliphatic epoxy/trimethacrylate interpenetrating polymer networks for vacuum-pressure-impregnation electrical insulation

    Jingkuan Duan
    Abstract Vacuum pressure impregnation has been known as the most advanced impregnation technology that has ever been developed for large and medium high-voltage electric machines and apparatuses. We developed one new type of vacuum-pressure-impregnation resin with excellent properties by means of a novel approach based on in situ sequential interpenetrating polymer networks resulting from the curing of trimethacrylate monomer [trimethylol-1,1,1-propane trimethacrylate (TMPTMA)] and cycloaliphatic epoxy resin (CER). In this study, the influence of the concentrations of the components and their microstructures on their thermal and dielectric behaviors were investigated for the cured CER/TMPTMA systems via atomic force microscopy, dynamic mechanical analysis, thermogravimetric analysis, and dielectric analysis. The investigation results show that the addition of TMPTMA to the CER,anhydride system resulted in the formation of a uniform and compact microstructure in the cured epoxy system. This led the cured CER/TMPTMA systems to show much higher moduli in comparison with the pure CER,anhydride system. The thermogravimetric analysis results show that there existed a decreasing tendency in the maximum thermal decomposition rates of the cured CER/TMPTMA systems, which implies that the thermal stability properties improved to some extent. The dielectric analysis results show that the cured CER/TMPTMA systems displayed quite different dielectric behaviors in the wide frequency range 0.01 Hz,1 MHz and in the wide temperature range 27,250C compared with the cured CER,anhydride system. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Moisture curing kinetics of isocyanate ended urethane quasi-prepolymers monitored by IR spectroscopy and DSC

    Ana Lusa Daniel-da-Silva
    Abstract The study of the kinetics of the curing of isocyanate quasi-prepolymers with water was performed by infrared spectroscopy and differential scanning calorimetry. The influence of the free isocyanate content, polyol functionality, and of the addition of an amine catalyst (2,2,-dimorpholinediethylether) in the reaction kinetics and morphology of the final poly(urethane urea) was analyzed. A second-order autocatalyzed model was successfully applied to reproduce the curing process under isothermal curing conditions, until gelation occurred. A kinetic model-free approach was used to find the dependence of the effective activation energy (Ea) with the extent of cure, when the reaction was performed under nonisothermal conditions. The dependence of Ea with the reaction progress was different depending on the initial composition of the quasi-prepolymer, which reveals the complexity of the curing process. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]

    Water-repellent finishing of cotton fabrics by ultraviolet curing

    F. Ferrero
    Abstract Cotton fabrics were water-repellent-finished by radical ultraviolet curing of silicone and urethane acrylates with different formulations. The fabrics were impregnated with undiluted resins and with toluene solutions or water emulsions. Moreover, cationic ultraviolet-curable systems were also investigated, such as an epoxy-functional polysiloxane and mixtures of an epoxy resin with hydroxyl-containing silicone additives. The gel content and polymerization yield were considered for the ultraviolet-curing process evaluation. Water-resistance properties were determined in terms of the contact angle, wettability, moisture adsorption, and water vapor permeability measurements, whereas the morphology and surface composition of treated fabrics were examined with scanning electron microscopy and energy-dispersive X-ray analysis. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]