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The crosslinking reaction of tetraglycidyl-4,4'-diaminodiphenylmethane with 27% 4,4'-diaminodiphenylsulphone at 150°C and 170°C was studied by near-i.r, spectroscopy while simultaneously recording the heat flow by isothermal differential scanning calorimetry (d.s.c.). From the absolute concentrations of primary, secondary and tertiary amine groups and the epoxy, hydroxyl and ether groups measured throughout the reaction, instantaneous rate curves were obtained and used along with reported reaction enthalpies to calculate heat flow curves for comparison with the d.s.c, data. It was found that previous assumptions of a constant reaction enthalpy were incorrect and values of -83___2, -131+9 and -65 _+ 6 kJ mol-1 for epoxide reaction with primary amine, secondary amine and hydroxyl, respectively, gave the best fit between near-i.r, and d.s.c, data. Deviations between fitted and experimental data after gelation were attributed to heat capacity changes on vitrification and allowed a 'true' isothermal baseline to be constructed. From the corrected isothermal d.s.c, data and the absolute concentration of epoxide consumed, an average reaction enthalpy of -92 + 1 kJ mol-i was obtained. Reasons for discrepancies between these and scanning d.s.c, data are considered.

Детальніше...  

This study deals with the determination of the role of carbon fibre in the thermal ageing of PMR 15 polyimide matrix composite. The gravimetric behaviour of a neat resin is compared with that of a composite based on the same resin, both polymerized with a very similar cure schedule. Rates of degradation in the stationary stage of gravimetric curves are analysed with an Arrhenius model.

Детальніше...  

Five isotactic polypropylenes, produced by different polymerization processes and with different heterogeneous catalyst systems, were fractionated according to stereoregularity. One of the samples was also fractionated according to molecular weight, to obtain a set of narrow fractions of different molecular weights. Crystallization and melting behaviours of the whole samples and the fractions were studied as a function of tacticity and molecular weight. Crystallization and melting experiments were performed using d.s.c. For tacticity determinations FTi.r. spectroscopy was applied. The thermal properties studied in this work were mostly dependent on tacticity and a linear correlation between crystallinity and i.r. isotacticity was found. In the main part of the molecular weight range studied (~, ~ 22 000-947 000) molecular weight had no or only a small influence on crystallization behaviour. In addition to detecting correlations between thermal properties and molecular structure, small differences between the samples produced with different processes and catalyst systems were also observed.

Детальніше...  

End-capped poly(p-phenylenebenzobisthiazole) structures containing randomly distributed 2,6-dimethylphenoxy pendants along the rigid-rod backbone were synthesized through the copolycondensation of 2,5-diamino-l,4-benzenedithiol dihydrochloride with terephthaloyl chloride and 2-(2,6-dimethylphenoxy)- terephthaloyl chloride in polyphosphoric acid. End-capping was accomplished through the addition of 2,4,6-trimethylbenzoic acid to the reaction mixture. Through control of reaction stoichiometry, copolymer intrinsic viscosities were limited to 8.6 dl g- ~ (methanesulphonic acid, 30°C) or less. The 2,6-dimethylphenoxy moiety served as a graft site for grafting reactions with 3-phenoxybenzoic acid in a methanesulphonic acid/phosphorus pentoxide medium. Incorporation of the resultant thermoplastic poly(ether ketone) side-chains into the rigid-rod poly(p-phenylenebenzobisthiazole) structures was substantiated through infra-red spectroscopy and analysis of model reactions

Детальніше...  

A polyethylene cylindrical rod with lamellar structure is loaded with tension-torsion combined stress. The orientation behaviour of the crystallites is evaluated by an improved orientation distribution function. The function assumes affine deformation and that the orthogonal relation of the three crystallographic axes is maintained during deformation. The improved function is achieved by assuming that slippage deformation occurs in a crystallite block. For cases in which twist is strong and samples are highly deformed, the orientation behaviour is interpreted by taking into account the slippage deformation of the (1 1 0) plane. This, with the assumption of spiral orientation of the chain axis and rotation of the a- and b-axes around the c-axis, results in good agreement between calculation and experimental results.

Детальніше...  

The appearance of double melting endotherms in dynamic d.s.c, runs of polypropylene fractions was studied with the aim of relating their appearance to the structure of the polymer. Fractions obtained by fractionation either according to stereoregularity or to molecular weight were investigated. Double peaks were detected for low molecular weight, non-isotactic fractions, as well as for low molecular weight fractions with isotacticities around 90%. Fractions consisted of pure ~ crystal form and those showing double melting endotherms had low average isotactic sequence lengths, generally below 80 propylene units. The occurrence of double-peak shapes was attributed to two different processes, one characteristic of highly stereoirregular material, and probably constituted by melting of two different crystalline species, and the other consisting of reorganization or recrystallization of less-ordered domains of crystalline material taking place during the melting scan.

Детальніше...  

Dynamic and tensile mechanical properties of a series of graft rigid-rod copolymers were studied. The copolymers were single-component rigid-rod molecular composites consisting of a rigid-rod poly(pphenytenebenzobisthiazole) backbone grafted with flexible-coil poly(oxy-l,3-phenylenecarbonyl-l,4-phenylene) side-chains. Dynamic storage moduli of the graft copolymers showed three characteristic regions: an initial plateau region, a transition zone and a second plateau region. The peak transition temperatures of the dynamic loss modulus curves were independent of the rigid-rod backbone length but decreased with increasing side-chain lengths, suggesting that the transition was a secondary transition associated with localized motions of the flexible side-chains. The graft rigid-rod copolymers were compression moulded into tensile test specimens at temperatures above their peak transition temperatures. Although the specimens appeared well consolidated as evidenced by the scanning electron micrographs of tensile-fractured surfaces, their tensile properties were relatively poor compared with those reported for rigid-rod molecular composite blends. The significance of poor tensile properties is discussed based on the structural characteristics of the graft copolymers, namely the length of rigid-rod backbone, the frequency of graft sites, and the average contour length of flexible-coil side-chains.

Детальніше...  

The fluorescence has been measured in dilute solution and in glassy poly(methyl methacrylate) for polyesters of 2,6-naphthalene dicarboxylate and HO-(CH2CH20),,-H, m = 1-4. The model compounds in which the glycol connects two molecules of 2-naphthoate were also studied. Intramolecular energy migration is implied by the anisotropy of the fluorescence in rigid media. The results are consistent with F6rster radii of about 12 A in the model compounds and 14 A in the polyme

Детальніше...  

Poly[(R)-3-hydroxybutyrate] (PHB) is a bacterial storage polymer, currently receiving much attention because of its potential as a biodegradable plastic. A major drawback of PHB is its intrinsic brittleness. Although as-moulded PHB shows ductile behaviour, upon storage at ambient temperature a detrimental ageing process seriously embrittles the material and restricts its application possibilities. This remarkable embrittlement is delineated in the present study and could be attributed to progressive crystallization. Strikingly, we found that by using a simple annealing treatment PHB can be rejuvenated while subsequent ageing is prevented to a large extent. This observation might considerably enlarge the applicability of PHB.

Детальніше...  

Wilhelmy plate experiments were performed with carbon fibres submitted to different degrees of surface treatment and various viscous fluids. The relative solid-liquid velocity was varied between 20 and 260pm s-~. The recorded force shows contributions from hydrodynamics (connected to the fluid nature and viscosity and to the interfacial velocity) and surface-related effects (surface energetics of fibres and liquids). The use of viscous fluids in the simulation of the fibre-liquid interaction involving hot polymer melts and reactive monomers is discussed.

Детальніше...  

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Хто такий інженер

Інженер - професія нелегка, але одночасно з цим дуже цікава і захоплююча. Адже інженер це людина, у якого народжуються в голові нові ідеї і тому він здатний винаходити.

У багатьох виникає питання: хто такі інженери? Інженер (франц. Ingénieur) - фахівець з вищою технічною освітою. Спочатку інженерами називали людей, які керували військовими машинами. Поняття громадський інженер з'явилося в XVI столітті в Голландії, застосовано до сфери будівництва мостів і доріг, потім інженери з'явилися в Англії, а потім в інших країнах.

Види та функції сучасної упаковки

Різноманітна упаковка щільно увішла у життя кожної людини. На полицях магазинів, в інтер'єрах помешкань можна побачити десятки пляшочок, коробок, аерозольних болончиків. Термін існування упаковки в нашому житті може продовжуватися від кількох хвилин до кількох років. Що ж таке сучасна упаковка? Чому вона займає стільки місця в нашому житті?

Хімічне машинобудування

Хімічне машинобудування багатопрофільна галузь машинобудування, що поєднує в собі природні та експериментальні науки (наприклад, фізика і хімія), разом з науками про життя (наприклад, біологія, мікробіологія та біохімія). Математику та економіку вокористовують для розробки, перетворення, транспортування, управління виробничими процесами, які перетворюють сировину в цінні продукти.

Інженер-механік

Інженер-механік (від лат. Ingenium – талант, обдарованість, і mēchanicus – механік) – це технічний чи технологічний фахівець з вищою освітою, який застосовує отримані знання для конструювання, проектування, моделювання та експлуатації машин, апаратів та технічного обладнання в різних галузях сільського господарства та технічного виробництва. Першими з інженерів були саме механіки; вони розробляли і збирали різноманітні машини і механізми, в яких використовували принципи і закони механіки.

Що таке КПІ?

На сьогоднішній день багатьох випускників, ще недавно – школярів, цікавить наступне питання – куди поступити, куди піти навчатися? В нашій країні є дуже багато ВНЗ, які пропонують свої послуги з підготовки і навчання студентів. Одним з таких ВНЗ є Київський політехнічний інститут (КПІ).