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Blends of poly(butylene terephthalate) (PBT) with thermotropic liquid crystalline polymer (LCP) concentration down to 0.2 wt.% were prepared to investigate the effects of LCP component on the crystallization behavior of PBT. The crystal structure of PBT in the blends was not deteriorated by the presence of LCP. The regularity of PBT crystals in the blends with lower LCP content appeared to be more perfect, compared with that of pure PBT sample and of blends with high LCP content. The experimental results revealed that the LCP component may affect, to a great extent, the crystallization process of the blends due to the inhomogeneous nature of the LCP used. The crystallization process of PBT in the blends was very sensitive to the LCP content and its microstructures existing in the melt before the start of crystallization, with the nucleation effect of the LCP component in its crystalline state being more efficient than that in its nematic state. The favorable content at which the LCP microdomains show ''the most efficient nucleation’’ is more likely to occur at lower LCP content for these systems. Based on the fact that the addition of the LCP component leads to higher crystallization temperature, crystallinity and degree of perfection of the crystallites formed, it is proposed that the effects of heterogeneous nucleation dominate in the crystallization process of the blends with lower LCP concentration.

Детальніше...  

We present results from a series of molecular dynamics simulations for adsorption and spreading of polymer chains onto a flat surface. We consider both homopolymer chains and “protein-like” copolymer chains in the simulations. For homopolymer chains, we have considered both good and poor solvent conditions, and for copolymer chains, we have considered several conformations of the non-adsorbing monomers. Our results indicate that when the adsorption strength is strong enough, a scaling description of the adsorption kinetics works well for homopolymers in both good and poor solvent conditions. When the adsorption strength is not strong enough, the chains adsorb partially, and one needs to consider effects of this partial adsorption in the scaling description. For each of the three primary structures of the copolymers considered in this study, the polymer chain does get adsorbed to the surface but the kinetics of the adsorption process depends on the specific structures of the copolymer chains.

Детальніше...  

A series of zinc-neutralized ethylene-methacrylic acid ionomers was studied using X-ray absorption spectroscopy. Neutralization methodology, neutralization level and methacrylic acid content were varied to test whether any of these factors affected the local environment of the zinc cations. Three different neutralization methods were tested: melt neutralization with zinc oxide, melt neutralization with zinc acetate and solution neutralization with zinc acetate. Neutralization levels varied between 2.5 and 100% of stoichiometric, and methacrylic acid contents varied between 10 and 20% by weight. Samples were prepared and handled to rigorously exclude water. Despite the substantial differences in sample preparation procedures, the local environments around the zinc atoms were identical in all materials, resembling the arrangement of atoms in the crystal structure of monoclinic anhydrous zinc acetate. In this compound, four oxygen atoms surround the zinc atom with distances ranging from 1.950 to 1.965 A

Детальніше...  

This study comprises a detailed morphological study of cold-drawn polyethylene materials by Raman spectroscopy and other techniques. Cold-drawn polyethylene is recently being used as a model material for studying and characterising the environmental stress cracking resistance (ESCR) behaviour of polyethylene grades. The cold-drawn structure was shown to be highly oriented and a large decrease in the Raman orthorhombic crystallinity was observed. Also other Raman and i.r. vibrational split modes pointed to the orthorhombic crystallinity decrease. No corresponding crystallinity changes were seen using the i.r. active -CH 2- bending doublet or DSC. WAXS and Raman did not give evidence for large scale phase transformation from orthorhombic to monoclinic or triclinic. The results suggest an ill-defined orthorhombic crystalline structure with dislocations and disrupted crystals formed by cold-drawing, probably as a result of molecules being pulled through the crystals. In situ Raman straining experiments were carried out on the cold-drawn material at 240 K (in order to suppress molecular relaxation). Further orthorhombic crystalline disruption was evident with strain. No disruption was seen in fibrils created during environmental stress crack resistance (ESCR) tests carried out at 348 K. Temperature was confirmed as an important factor in determining the crystalline phase recovery of the orthorhombic crystallinity and disappearance of the monoclinic phase occurred when the cold-drawn structure was annealed.

Детальніше...  

The imidization kinetics of nanocomposites of poly(amic acid) and organoclay were analyzed with in situ Fourier Transform Infrared spectra at several temperatures. The poly(amic acid) studied consisted of pyromellitic dianhydride and 4,4 0 -oxydianiline. It was found that by dispersing a small amount of organoclay in nanometer scale in the poly(amic acid), both the imidization temperature and the imidization time of the poly(amic acid) can be reduced dramatically. In specific, when two parts of exfoliated silicate layers of organoclay was dispersed in the poly(amic acid), the imidization temperature was lowered by 50°C (250°C versus 300°C) for achieving a complete imidization. Additionally, the imidization time of the poly(amic acid) at 250°C can be reduced to 15 min when the amount of organoclay increased to seven parts.Using a first-order reaction to model the imidization kinetics of poly(amic acid)/organoclay, a 20% drop in the activation energy for imidization of PMDA-ODA/organoclay (7 phr) was obtained as compared to that for imidization of neat PMDA-ODA.

Детальніше...  

This article reviews the application of FTIR methods (attenuated total reflection, specular reflectance and photoacoustic detection) to orientation measurements of polymers, and to thermotropic liquid crystalline polymers (LCPs) in particular. FTIR specular reflectance dichroism studies are then applied to determine molecular orientation from the surface of injection mouldings (square plaques with dimensions 60 × 60 × 2 mm, unfilled polymer; 60 × 60 × 4 mm, filled polymer) of a LC copolyester based on hydroxybenzoic acid, terephthalic acid, 4,4 0 -oxydibenzoic acid and chlorohydroquinone. The effects of the melt temperature (265–3158C) and of the addition of fillers (mica, silica or glass beads) on the development of orientation are investigated. Scans are presented showing the quality of orientation with respect to orthogonal axes. The orientation profiles are related to the flow behaviour of LCPs during processing (spreading radial flow at the entrance to the mould, converging flow in the first half of the mould and fountain flow). At some positions, orientation minima occur which assume parabolic profiles and are associated with an arc-like band-pattern consisting of dark and brownish white bands at the surface of the mould. The light-coloured arcs correspond to regions in which the chains are not planar and tend to lie with their long axis in the thickness direction.

Детальніше...  

Transcrystallization of polypropylene (PP) on various fibres (Kevlar, PET, carbon and PTFE fibres) was investigated using a polarized optical microscope. The nucleation rate, induction time and nucleation density at saturation were determined at various crystallization temperatures. Results show that the inverse proportion relation between induction time and nucleation rate which is held valid for PTFE and carbon fibre systems is not applicable to Kevlar and PET fibre systems. This is attributed to the different types of nucleation sites resulting from the non-uniformity of surface roughness of Kevlar and PET fibres. Based on the theory of heterogeneous nucleation, the interfacial free energy difference functions Au of PP on different fibres were determined and compared to that in the bulk matrix. It has been found that AU KeV,ar = 3.35 ? 0.24, AupET = 5.87 + 0.54, AuCarbon= 1.14 + 0.25, Au= 0.75 + 0.12, and AubUlk= 1.23 + 0.07 erg cm-'. From a thermodynamic point of view, PP transcrystallinity is most likely to take place on PTFE fibres due to the lowest value of Au, which is consistent with the experimental findings. Moreover, induction time, nucleation rate and nucleation density at saturation are also used to characterize quantitatively the nucleating ability of fibres. A simple mechanism, based on thermal stress-induced orientation and relaxation of polymer chains, has been proposed to account for the nucleation of transcrystallization. The topography of the fibre surface plays an important role as well. It is suggested that the presence of small-scale grooves at the fibre surfaces will cause the concentration of thermal stresses and enhance the nucleation process

Детальніше...  

Films of poly(3-hydroxybutyrate) (PHB) were crystallized from the melt by different thermal treatments and submitted to enzymatic degradation by using a PHB depolymerase purified from Aureobacterium saperdae culture. The morphology and the supermolecular structure of PHB films were investigated to explain differences in the kinetics of enzymatic degradation. Differential scanning calorimetry, optical microscopy, wide-angle X-ray diffraction and small-angle X-ray scattering were employed to characterize the PHB films. A decreasing of enzymatic degradation rate was observed with the increasing of crystallinity and crystal dimension of the PHB films. PHB samples showing the same degree of crystallinity and similar value of lamellar thickness were prepared using different isothermal crystallization and annealing temperatures. The differences in the enzymatic degradation rate of these films were explained in terms of morphological parameters.

Детальніше...  

Mechanical properties of binary melt mixed blends of various polyamides (Nylon 11; 6,6; 6,10; 6,12) with a block copolyetherester (PEE) were investigated. All the blends prepared had very good mechanical properties and in some cases even better than those of the respective pure polyamides. Two of the systems (Nylon 11/PEE and Nylon 6,12/PEE) were selected to be studied further in terms of morphology, viscoelastic and thermal properties. These blends showed two distinct but mutual shifting Tg’s and low extracted amount of PEE during extraction experiments, supporting the view that a very good interfacial grafting had been achieved in these two-phase systems. This assumption was further evaluated on the cryofractured and selectively etched blends where the existence of the grafted PEE was justified by Fourier transform infrared as well as by micro-Raman spectroscopy.

Детальніше...  

An FTIR method was used to investigate the thermal cyclization process in synthesis of polyetherimidazopyrrolones from dietherdianhydrides and 3,3 0 -diaminobenzidine. It was concluded that the highest degree of cyclization to imidazopyrrolone structure is observed in the case of polymer with bisphenol A group having electron-donating character after dynamic heating, though for the all polyether-imides investigated even at 3208C cyclization are not complete.

Детальніше...  

Корисні статті

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.

Інженер-машинобудівник

Ні для кого не секрет, що при сучасних умовах життя, темпах розвитку промисловості, безперервній автоматизації та оптимізації роботи механізмів та виробничих процесів, великою популярністю та попитом на ринку праці користується професія інженера, особливо інженера-машинобудівника.

Щоб відповісти на питання «Хто такий інженер-машинобудівник?», необхідно розуміти , що несе в собі кожне з цих слів окремо. Інженер – це людина, яка отримала освіту з визначеного фаху. Інженер – це творець техніки. Інженер – це особа, що професійно займається інженерією, тобто на основі поєднання прикладних наукових знань, математики та винахідництва знаходить нові рішення технічних проблем. Тобто, виходячи з цих загальновживаних визначень слова «інженер» зрозуміло, що цій професії може присвятити себе лише людина з неабиякими здібностями, які ґрунтуються на знанні точних наук, логічному мисленні, невичерпному терпінні і постійному бажанні вдосконалювати світ інженерії. Від латини ingenium — здатність, винахідливість, що є свідченням того, що інженером перш за все є людина-думаюча, яка знаходиться в безперервному пошуку відповідей на складні технічні завдання.

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.

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).

Рейтинг вищих навчальних закладів

На даний час в світі існує маса університетів з дуже великою кількістю кваліфікацій, спеціальностей та спеціалізацій. Одні з них більш престижні університети, інші менш.

Рейтинг вищих навчальних закладів переписується щорічно, в зв'язку з тим, що всі прагнуть стати краще в освіті, вдосконалитися в технологіях і підвищити свій рівень акредитації. Рейтинг навчальних закладів варіюється в залежності від предметної області, це природничі науки і математика, техніка/технологія і інформатика, життя і сільськогосподарська наука, клінічна медицина і фармація, соціальні науки.