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Enthalpy relaxations during physical ageing have been examined for two amorphous poly(ethylene terephthalate) (PET) samples with different thermo-mechanical glass-forming histories by differential scanning calorimetry. The relaxation behaviour of the PET glass formed by casting the drawn melts on a metal roller at 10°C can be explained from a molecular viewpoint, assuming that the glass consists of a network structure with strand chains and crosslinks. It is shown that the physical ageing of the glass gives rise to three different modes of structural rearrangement: (i) strand chain relaxation with relatively short relaxation times, associated with local segmental rearrangements within the strand chains; (ii) enthalpy redistribution, which forms the non-homogeneous dissipative structures of lower- and higher-enthalpy regions; and (iii) network rearrangements taking place slowly with long-distance, diffusive motions of the crosslinks. On the other hand, it is also shown that a single mode of structural rearrangement occurs for the ultraquenched PET glass formed by quenching directly into liquid nitrogen

Детальніше...  

This paper reports on the obtention of two extrinsic conducting polymer systems by means of copper and carbon black filler incorporation into a polymer system consisting of a poly(vinylidene fluoride)/polystyrene (PVDF/PS) blend. With the aim of analysing the influence exerted by copper and carbon black on the morphology, microstructure and compatibility of the systems under study, the glass transition temperatures as well as isothermal and non-isothermal crystallization kinetics were determined for the different systems. The dynamic mechanical and calorimetric results demonstrated on the one hand that carbon black produces partial compatibilization of the PVDF/PS system, while on the other hand they prove both copper and carbon black to be capable of modifying the microstructure and morphology of the initial system

Детальніше...  

It is shown that the structure of biaxially oriented polyester poly(1,4-phenylene-2,5-di-n-alkoxyterephthalate), with the length of the n-alkoxy side chains being n = 16, can be interpreted as a mixture of incommensurate structures. The principal one describes the ordering of rigid rods using an orthorhombic cell. The structure of side chains in a quickly stretched film is described by a monoclinic and a triclinic cell. An orthorhombic cell helps to describe the slowly stretched film. The monoclinic cell was found on the basis of our model calculations of X-ray scattering on a powder sample of this polyester, documenting that there is a clustering of side chains. Further, the ordering of side chains in the amorphous phase anticipates the interchain distance characteristic for the crystalline-like arrangements of side chains in the biaxially oriented films, because the average distance between side chains calculated from all incommensurate structures is 4.8 A, i.e. precisely the distance found between clustered side chains in the amorphous phase.

Детальніше...  

Styrene and methyl methacrylate were copolymerized at 323 K in the presence of a polybutadiene seed latex in emulsifier-free semi-continuous and, for comparison, batch processes using cumene hydroperoxide as initiator. Graft polymer characteristics were studied including the intra- and intermolecular microstructure. In contrast to expectation, the free and graft copolymers resulting from the semi-continuous processes under starved conditions appeared to have even broader distributions than the copolymers formed in the batch processes.

Детальніше...  

The thermal behaviour of a series of well defined segmented polyurethanes (PU) grafted with poly(methyl methacrylate) (PMMA) has been examined using differential scanning calorimetry. The grafts were located only in the poly(e-caprolactone) (PCL) soft segments. Three annealing schedules were employed. Grafting was found to have little effect on the hard segment domains, provided the hard segments were long enough to crystallize. Phase separation of the PCL and PMMA was incomplete. A transition, which was shifted to higher temperatures as the annealing temperature increased, was assigned to the glass transition (Tg) of a PCL/PMMA mixed amorphous phase. PCL crystalline melting and a PCL Tg were observed in the polymers with a low concentration of PMMA; an event which could be assigned to the Tg of a PMMA phase was not detected in any of the samples.

Детальніше...  

The evolution of the molecular-weight distributions in the batch miniemulsion polymerization of styrene initiated by different oil-soluble initiators (lauroyl peroxide, benzoyl peroxide and azobisisobutyronitrile) was investigated. Two series of polymerizations were carried out. In the first, miniemulsions contained only oil-soluble initiators to minimize monomer droplet degradation by molecular diffusion. In the second, the stability of the monomer droplets was reinforced with hexadecane. Also, a series of conventional emulsion polymerizations were carried out. The effect of both the type of initiator and the extent of the compartmentalization of initiator radicals between the polymer particles on the molecular-weight distributions were analysed by means of a mathematical model. A good agreement between experimental results and model predictions was achieved

Детальніше...  

The polymerization of acetylene, using [Rh(1,5-Cod)C1]2, where 1,5-Cod is cis,cis-cycloocta-l,5-diene or [Rh(NBD)C1] 2, where NBD is bicyclo(2,2,1)hepta-2,5-diene, has been followed by u.v.-vis, spectroscopy in solution. The growing polyacetylene was identified by three fine structure maxima in the spectrum, at 500, 544 and 590 nm, which were obtained by subtracting the catalyst spectrum from that of the reaction mixture. In addition, by using the first-order derivative of the absorption spectrum of the growing polyacetylene it is possible to detect vibrational maxima at 480, 515, 550 and 600 nm for the cis isomer and at 640, 670 and 710 for the trans isomer. U.v.-vis., as well as Fourier transform infra-red (FTi.r.) spectroscopy, was used to study the structure of the thin free-standing films of cis-rich and trans-isomerized polyacetylene obtained by using Rh(I) complexes. The absorption spectrum of thin films of polyacetylene produced in this way reveals the absence of the vibrational structure which has been detected in ethanolic solutions during acetylene polymerization. The microstructure of the polyacetylene is very similar to that formed when using a Luttinger catalyst, in terms of defects, which are present as sp 3 hybridized carbon atoms in the polymer, and which can be detected by FTi.r. spectroscopy.

Детальніше...  

Raman microline focus spectrometry has been utilized to record spatially resolved and spatially averaged Raman spectra from degraded poly(vinyl chloride) (PVC) sheet. Characteristics of simultaneous thermal and chemical degradation occurring in commercial polyurethane (PU)-foam-backed PVC sheet have been inferred from the observed Raman data. From a comparison of the data recorded across a section of the sheet, the presence of PU foam is shown to increase the degradation rate of PVC. In addition, higher concentrations, higher rates of formation and longer conjugation lengths of those polyenes formed during degradation are found at the PVC/PU contact interface. This is attributed to the extra chemical degradation occurring at the PVC/PU interface due to catalysis of dehydrochlorination by amine residues in the PU.

Детальніше...  

A blend of poly(hydroxy ether of bisphenol A) (phenoxy) and poly(vinyl methyl ether) (PVME) was investigated by inverse gas chromatography (i.g.c.) over a wide temperature range. Specific retention volumes were measured for a variety of probes in pure and mixed stationary phases and interaction parameters were calculated. It was found that the polymer-polymer interaction parameter was probe-dependent. Two methods of data analysis recently proposed were applied in an attempt to eliminate this dependence. In both cases similar results were obtained with similar and large confidence intervals. I.g.c. experimental results were compared with theoretical calculations of an association model for polymer mixtures with specific interactions. A reasonable agreement was found

Детальніше...  

N,N'-(1,6-Hexanediyl)bisurea oligomerizes thermally in the melt (> 190°C) to urea-terminated poly(1,6- hexamethyleneurea) with the volatilization of ammonia and isocyanic acid. At higher temperatures (225-250°C) in the liquid phase, the trimerization of isocyanic acid to cyanuric acid also occurs.

Детальніше...  

Корисні статті

Вибір професії

Кожна людина зіштовхується у своєму житті з вибором, який найсильніше вплине на все її подальше життя. Йдеться про вибір професії та вибір вищої освіти. Закінчуючи школу, молоді люди стикаються з величезним вибором професій та спеціальностей: інженер, економіст, юрист, менеджер, маркетолог, логіст, фінансист і т.д. При цьому навколо можна чути безліч стереотипних фраз: "Юристи багато заробляють", "Фінансисти працюють з грошима, тому у них хороші зарплати", "Маркетолог - основний людина в будь-якому бізнесі", а часом і просто без обґрунтування - "Менеджер - це круто ". Часом, такі "поради" впливають на вибір професії.

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.

Як стати інженером?

Кожна людина в процесі свідомого життя стикається з проблемою вибору професії. Найбільш актуальною ця проблема є для учнів старших класів – випускників, які добровільно або примусово здають шкільні іспити та зовнішнє незалежне оцінювання, за результатами чого приймають участь в конкурсному відборі на навчання у ВНЗ. Щоб обрана професія не стала важким випробовуванням, потрібно ще у шкільні роки зважити всі «за» і «проти», оцінити свої здібності, схильності, можливості.

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.

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?