kpilogo shields

The effect of fibre reinforcement, industrial processing and subsequent annealing on the structure of polyamide-6,6 was analysed in this paper from the correlation between photoacoustic Fourier transform infra-red (PA FTi.r.) spectroscopic and differential scanning calorimetry (d.s.c.) thermal measurements. Using the band situated at 1650cm-1 as an internal reference band, no spectral change was detected in the bands at 936 and 1146 cm- 1. Furthermore, the bands centred at 1335 and 1224 cm- 1, which are related to chain-folding, appear in the unannealed composite, whereas in the matrix these were only detected at the highest annealing temperatures. It seems that the manufacturing process used for the composite determines its microstructure and the subsequent annealing does not produce further conformational changes. On the other hand, the composite satisfies a two-phase conformational model, different from that of the matrix, which can be related to the strong interactions between the polymer and the glass fibres with surface treatment. In the thermal analysis, in contrast to the spectroscopic results, substantial changes in the endothermic melting peaks and in the degree of crystallinity can be noted. Up to an annealing temperature of ~ 120-150°C, the composite crystallinity is constant and lower than the matrix crystallinity, but above this temperature the value rises and tends towards the values of the matrix. Furthermore, there was a more homogeneous crystalline distribution detected in the unannealed matrix, along with a greater size and perfection of the crystals than that seen in those of the unannealed composite. We suggest that the d.s.c, variation in the crystallinity can be attributed to an improvement in the fibre-matrix interface, in which the crystals of the interfacial phase change to more perfect ones as a result of the annealing treatment

Детальніше...  

A high temperature thermosetting aryl dicyanate resin was modified with thermoplastic polysulfone and/or poly(ether imide) at various compositions. Differential scanning calorimetry was used to characterize the phase behaviour, while the morphologies and continuities of the thermoplastic/dicyanate networks were investigated by using dynamic mechanical analysis, scanning electron microscopy, fracture toughness testing, and solvent sorption studies. The phase structure was found to change from a thermosetting continuity to a co-continuity of both thermoplastic and thermosetting domains. The mechanical and physical properties of the modified polycyanates exhibited a step change at the shift of the phase structure.

Детальніше...  

A novel procedure for the treatment of sedimentation velocity data by the method of moments is proposed for determination of polydispersity indices, such as M,JM,, etc. This method is based on linear approximations and enables the reliable exclusion of diffusion and concentration effects. It is particularly effective when applied to polymer solutions with strong intermolecular interactions and noticeable diffusion mobility of the macromolecules.

Детальніше...  

A series of semi-interpenetrating polymer networks (IPNs) based on poly(zinc acrylate) and polyacrylonitrile were synthesized by a sequential mode of synthesis. The IPNs were characterized by scanning electron microscopy, i.r. spectroscopy and by measuring crosslink density. Divinyl benzene was used as the crosslinking agent for acrylonitrile, and azobisisobutyronitrile as initiator. Variation in composition of the IPN was achieved by varying the concentration of polymer, monomer, crosslinker, initiator and the viscosity average molecular weight of polymer, and their effects on morphology and crosslinking were examined. The increase in concentration of linear polymer and initiator decreases crosslinking and increases incompatibility, while the increase in concentration of crosslinker increases both crosslinking and phase separation.

Детальніше...  

Poly(butylene terephthalate) (PBT), poly(ether ester) (PEE) based on PBT and poly(ethylene glycol) (PEG) (PBT/PEG=49/51 wt%) and their blend are extruded with quenching, drawn x 5 and annealed together with undrawn samples at 170, 180, 190 and 200°C for 6 h in vacuum. All samples are characterized by differential scanning calorimetry (d.s.c.), small-angle and wide-angle X-ray scattering, dynamic mechanical thermal analysis and static mechanical measurements. D.s.c. and X-ray results show the absence of complete cocrystallization of homo-PBT and PBT from PEE in the blend in accordance with other reports. The drawn blend annealed at 200°C reveals much higher (by 30°C) T m than the PEE component (49/51). Also the mechanical properties of the blend are in between those of the components (homo-PBT and PEE 49/51) but improved compared to those of PEE with the same chemical composition (PEE 75/25). Both observations are explained by partial cocrystallization, i.e. formation of crystallites consisting of two populations of crystallites differing in their size, perfection, origin and time of appearance. The lack of complete cocrystallization and miscibility in this particular blend as well as in other cases with PEE containing less than 75 wt% PBT is explained by the insufficient length of PBT hard segments in PEE necessary for the formation of lamellar thickness typical of the crystallites of homo-PBT.

Детальніше...  

Complete ligament yielding before crack advance is one of the criteria in the essential work method. It is found that this criterion also holds when the essential work method is used to obtain the fracture toughness of polymeric films. This is done by using two specimen geometries to test each of two nylons. The criterion is then used to find the fracture toughness of three polyethylenes, a cast, amorphous poly(ethylene terephthalate) and two kaptons. In addition, the effects of specimen width and strain rate on the specific essential work of fracture we are studied.

Детальніше...  

Sedimentation velocity data obtained for solutions of monosubstituted carboxymethyl cellulose samples with molecular weights from 1.2 x l0 s to 3.8 x l0 s in a water/cadoxene mixture were used to determine the heterogeneity parameters. Linear dependence has been established for the x-spectrum standard deviation of the distribution of macromolecules in the ultracentrifugal field, as a function of the sedimentation boundary shift. This result proved the applicability of the novel method for elimination of the diffusion and concentration effects by a more reliable and convenient method than other known methods. The parameter M,JMw for different polymer samples was determined to lie between values of 1.8 and 3.5.

Детальніше...  

It has been shown that, in various thermoset/thermoplastic and monomer/polymer mixtures, demixing is induced by polymerization and it proceeds via the spinodal decomposition (SD) to yield the regularly phase-separated morphology. However, the SD is expected to take place under successive increases in quench depth. To evaluate the demixing process under the non-isoquench depth condition, we carried out computer simulations of the time dependent concentration fluctuations using the Cahn-Hilliard non-linear diffusion equation. The simulations revealed that the SD under successive increases in quench depth yields the regular two-phase structure as in the case of the SD under isoquench, the structure coarsening is suppressed by the increase in quench depth, and the final morphology is highly dependent on the quench rate. The results adequately describe the characteristic features of structure development in the reaction-induced SD.

Детальніше...  

The temperature dependence of the electrical conductivity of a conducting polymer composite is reported from 77 to 450 K. The relationship between the temperature dependence of the conductivity and the structure of the composite is discussed. The low-temperature electrical resistivity of low-density polyethylene/polypyrrole composite was also investigated and a linear relationship between the resistivity and T-1/4 was found in the liquid-nitrogen temperature range

Детальніше...  

Five isotactic polypropylenes produced with different processes and different heterogeneous Ziegler-Natta catalyst systems were fractionated using n-heptane extraction in a Soxhlet apparatus. The unfractionated polymers and their heptane-soluble and heptane-insoluble fractions were analysed with size exclusion chromatography, ~3C nuclear magnetic resonance (n.m.r.), differential scanning calorimetry and Fouriertransform infra-red spectroscopy. The composition of the heptane-soluble fraction was somewhat dependent on the molecular structure of the original polymer. On the other hand, the heptane-insoluble material was not completely isotactic, and some syndiotactic and heterotactic polymers were found in it. Heptane extraction as a method for isotacticity determination is discussed and compared with other methods. One of the samples was also divided into four fractions using successive extractions with n-heptane, n-octane and xylene. Based on the 13C n.m.r, spectroscopic pentad analysis carried out on the fractions, possible structures for stereoblock polymers are suggested. Fractionation results are also compared with an earlier fractionation performed on the same sample using fractional solution with solvent/non-solvent mixtures and vibromixer agitation.

Детальніше...  

Корисні статті

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).

Інженер-конструктор

Хто такий інженер-конструктор? Даним питанням задаються багато людей, які бажають пов'язати своє життя з цією професією. Варто відзначити, що ця професія однією з найбільш високооплачуваних на сучасному ринку праці, яка характеризується високим попитом з боку роботодавців. Інженер-конструктор машинобудування повинен володіти аналітичним складом розуму, підвищеною уважністю до деталей і відповідальним підходом до роботи. Дана діяльність пов'язана з прорахунками і різноманітним обладнанням. Першокласний інженер-конструктор механік володіє також такими рисами характеру, як раціональність і ерудованість. Важливу роль відіграє стресостійкість, адже робочий процес є досить трудомістким і при потребі замовника вимагає готовності швидко вносити зміни в готові креслення.

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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.

ВНЗ України

Вища освіта є невід'ємним елементом перспективного кар'єрного росту, тому перед кожним абітурієнтом виникає проблема, в які інститути подавати документи. Варто відзначити, що в Україні існує велика кількість вузів. Всі навчальні заклади поділяються на державні та приватні, пропонуючи різноманітні освітні програми по різних профілів. Щоб пошук інститутів дав задовільні результати, слід визначитися з найбільш прийнятними спеціальностями. Також підбір університету передбачає вибір підходящої форми навчання, наявність високої акредитації у вузу і рівень його престижності.