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The crystalline morphology of oriented films of poly(butylene terephthalate) (PBTP) was characterized by wide-angle X-ray diffraction and scanning electron microscopy. The PBTP films were drawn to different draw ratios at various drawing temperatures. Transformation of the lamellar spherulites into a microfibrillar structure occurred in the necking region. The microfibrillar structure appeared at the end of the plateau region. Transformation to perfect microfibrillar structure and the subsequent drawing of this structure were observed in the strain hardening region. The orientation of crystals occurred above the yield point and continued rapidly with draw ratio, while the rate of orientation was decreased by drawing the microfibrillar structure. An optimal drawing temperature of about 423 K (which lies between the glass transition and melting temperatures) was found to provide the highest degree of crystalline orientation. In the glass transition region the strong movement of the non-crystalline chain segments influenced the orientation of crystals. The formation of the microfibrillar structure and the orientation of crystals were also disturbed at the drawing temperature near the melting point. Etching of PBTP films allowed the observation of the stacked lamellae oriented more or less perpendicular to the draw direction as well as the microfibrils existing between the stacked lamellae.

Детальніше...  

Water uptake in the system M(CF3SO3)2PEO,, where M=Ni, Zn and Pb, and n=6-24, has been investigated at room temperature using i.r. spectroscopy and X-ray diffraction. It has been found that the ion-pairing/clustering involving M 2 + and CF3SO 3 is highly affected by hydration, with water replacing CF3SO 3 at the cation. At intermediate degrees of hydration, the CF3SO 3 ions are hydrogen bonded to metal-ion coordinating water molecules. In conditions of water excess, features typical of CF3SO 3 ions in aqueous solution are observed. The interaction between PEO and M 2 + is also affected by hydration for M = Ni and Zn. The v(COC)a stretching band is shifted to higher wave numbers, indicating a weakening in the interaction between PEO and a hydrated cation. X-ray diffraction has shown that any crystalline component present in the anhydrous form is destroyed by water uptake.

Детальніше...  

The thermal shrinkage behaviour of poly(ethylene terephthalate) fibres and films with varying amounts of orientation and crystallinity and different degrees of crystal disorder is reported. It is shown that the shrinkage of undrawn and drawn samples with low orientation can be considered as the contraction of a rubber-like network which arises from disorientation of the oriented amorphous phase. However, in the highly drawn samples with significantly higher orientation, interaction between shrinkage and crystallization can occur, particularly in samples produced at low speeds. X-ray diffraction and thermal studies show that these samples have crystals with high defect density and also contain tiny nuclei; these factors can result in rapid crystallization at relatively high temperatures and thus impede shrinkage.

Детальніше...  

Surface enrichment of one-phase and phase-separated blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) by the latter component, which has the lower surface free energy, has been examined using attenuated total reflectance infra-red spectroscopy. The apparent surface concentration of PVME, determined by assuming compositional homogeneity within the depth probed, as a function of blend composition, agrees well with data derived by other methods. Although no effect due to variations in the PS molecular weight was evident, star-shaped PS appears to behave differently from linear PS.

Детальніше...  

X-ray photoelectron spectroscopy and static secondary ion mass spectrometry (s.i.m.s.) have been used to characterize plasma polymers of perfluorobenzene (PFB), perfluorotoluene (PFT), perfluorocyclohexene, perfluorocyclohexane and benzene. The plasma polymers of PFB and PFT appear to be based on a perfluoroalkylbenzene-type structure, with lesser amounts of other ring systems and very few aliphatic chains. The polymers derived from perfluorocyclohexene and perfluorocyclohexane were found to be much more aliphatic in nature, with fewer aromatic and other ring systems. The s.i.m.s, analysis of plasma-polymerized benzene was almost identical to that of polystyrene, but this probably does not reflect the true nature of the plasma polymer.

Детальніше...  

Dynamic thermomechanical properties of composite polymer films obtained from poly(vinyl acetate) (PVAc) latexes which are sterically stabilized by poly(vinyl alcohol) (PVA) are investigated. These films exhibit dramatic changes in their dynamic mechanical response after annealing. The effects of various parameters (volume fraction and features of PVA in the latex, mean size of the PVAc particles) on this behaviour are discussed. The results are interpreted on the basis of a phase rearrangement during annealing, which results in a strong enhancement of the degree of connectivity of the PVA matrix within the films. Finally, it is shown that qualitative and semiquantitative information can be gained from inspection of dynamic thermomechanical spectra concerning, respectively, the features of the interphase between PVAc particles and the PVA matrix and the actual volume fraction of PVA involved in the continuous matrix.

Детальніше...  

The miscibility of blends containing poly(vinyl methyl ether) (PVME) and one of three different styrene/(styrene derivative) copolymers was investigated by light scattering and Fourier-transform infra-red (FTi.r.) spectroscopy. For this purpose copolymers of styrene with o-methyl-, p-methyl- or m-methylstyrene were synthesized by radical polymerization. The copolymer compositions were fixed at 10% and 20% (by weight) in the monomer feed ratio. The light scattering studies revealed that all the blends showed lower critical solution temperature (LCST) behaviour. In the F Ti.r. results, the relative intensity of the 1080 cm- 1 peak was greater than that of the 1108 cm- 1 peak, due to the COCH 3 bond of PVME, in all the blends studied in this work. It is concluded that all the blends are miscible at room temperature over the entire concentration range studied, and the miscibility of the styrene/(styrene derivative) copolymers with PVME decreases in the order poly(styrene-co-o-methylstyrene) > poly(styrene-co-p-methylstyrene) > poly(styreneco- m-methyistyrene ).

Детальніше...  

Well-defined poly(styrene-b-2-vinylpyridine) diblock copolymers (about 50 wt% polystyrene blocks) were prepared by sequential anionic addition. The cast films showed a tendency where the alternating lamellar structures of two microphases were orientated with their interfaces parallel to the surface that contacts the air or Teflon substrate. Poly(2-vinylpyridine) microdomains were not only quaternized but also effectively crosslinked with 1,4-diiodobutane vapour. Subsequently, colloidal silver was introduced into quaternized poly(2-vinylpyridine) phases by the reduction of silver iodide. The element distributions on the vertical section of the modified films were measured by means of energy-dispersive X-ray spectrometer and transmission electron microscopy. These materials showed a highly anisotropic conductivity with ca. six orders of magnitude.

Детальніше...  

The results of moving die rheometry studies show that in contrast to sulfur vulcanization of carboxylated nitrile rubber (XNBR), where the loss component of the torque (S") decreases with curing time, the zinc oxide (ZnO) crosslinking of XNBR is accompanied by a gradual increase in S", which becomes more pronounced in the presence of reinforcing high abrasion furnace carbon black filler. In dynamic mechanical studies, the sulfur-vulcanized XNBR shows a single peak around -5°C. The peak height reduced in the presence of the reinforcing filler with no shift in the peak position. However, the ZnO-vulcanized XNBR shows one extra peak around 54°C, in addition to the main transition around -5°C. Incorporation of reinforcing filler causes lowering of the peak height of the main transition, while the peak height of the high-temperature transition gradually increases. For the crosslinking system consisting of both sulfur and ZnO, the characteristics of the high-temperature transition are retained. These results have been explained on the basis of the formation of ionomers of XNBR during crosslinking by ZnO. Reinforcing carbon black filler favours the stabilization of these ionomers.

Детальніше...  

The study of the simultaneous grafting of ethyl acrylate with methyl methacrylate onto amylose with Ce(IV) ammonium nitrate as initiator was attempted. Grafting yields obtained using gravimetric and 13C n.m.r. spectroscopic methods were compared and similar results were obtained. A study of the microstructure of the grafted products obtained involving either the quantitative determination of the grafted copolymer composition or the qualitative study of the sequence distribution and the stereochemical configuration of grafted copolymer sequences has been carried out. The ~t-methyl group carbon, the quaternary carbon and the carbonyl group carbon have been found to be sensitive to the relative stereochemical configuration of the chain segments.

Детальніше...  

Корисні статті

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).

Комп'ютер для інженера

У сучасному світі комп'ютери дуже поширені. Складно уявити людину, не знайому з цим поняттям. Багато професій зобов'язані своїм виникненням саме комп'ютеру, вони б просто не з'явилися без створення електронно-обчислювальної техніки.

І хоча відносно недавно, на початку XX століття, комп'ютери були розкішшю і використовувалися лише для самих складних розрахунків, у наш час комп'ютери та комп'ютерна техніка дуже глибоко інтегрувалися у наше життя. Сучасне людство залежить від комп'ютерів, що викликає подиву, якщо розглянути, коли і в яких випадках вони використовуються.

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.

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.

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.