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The remarkable properties of poly(3-hydroxyalkanoate)s (PHAs) have resulted in a growing interest in these polymers. They offer a wide variety of useful mechanical properties and show excellent biodegradability. However, they are still expensive and poly(3-hydroxybutyrate) (PHB) in particular is quite brittle. Polymer blending offers interesting possibilities to prepare less expensive biodegradable materials with useful mechanical properties. In this review the literature concerning PHA-containing blends has been summarized. Blends incorporating either PHB or copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate (P(HB-HV)) were discussed. The thermal and crystallization behaviour of the blends, their mechanical properties, morphology and biodegradability have been reviewed. Among the conclusions drawn from the literature, it is evident that PHAs can form miscible blends with polymers containing the appropriate functional groups via hydrogen bonding and/or donor-acceptor interactions. The crystallization behaviour of the PHAs is influenced by both the miscible and immiscible components. Immiscible PHA-containing blends show improved apparent biodegradability when compared to miscible blends. Their apparent biodegradability (weight loss) is mostly controlled by the blend morphology. Blends of PHA with other biodegradable polymers also usually show improved biodegradability when compared with pure PHAs

Детальніше...  

Blends of poly(p-phenylenebenzo[1,2-d:5A-d']bisoxazole) (PBO) dispersed in poly(ether ether ketone) (PEEK) have been prepared by casting and coagulating methanesulfonic acid (MSA) solutions containing different fractions of each polymer. At PBO fractions greater than about I%, the fluorescence spectra resemble that of 'bulk' PBO coagulates; but at lower PBO concentrations, the spectra show a sharper, blue-shifted peak, close to the 0-0 peak of dilute PBO/MSA. This emission most likely originates from PBO chains that have been isolated in a photophysical sense. This result, along with the solvent shift seen in a model compound, suggests that the deprotonation minimally perturbs the emission spectrum of PBO relative to the changes caused by aggregation.

Детальніше...  

Although the 'crystal modulus' of most semicrystalline polymers has been estimated by measuring the displacement of meridional X-ray reflections on application of a stress to an oriented specimen, this method has not been applied to polyacrylonitrile (PAN). The X-ray diffraction behaviour and the long-range order in PAN are very controversial. Several reports state that the diffraction pattern of oriented PAN contains only equatorial peaks and therefore the material is only laterally ordered. However, there are a few papers that mention or imply sharp meridional and off-axis reflections. We have produced two samples of PAN which were oriented by different production methods. Both our specimens always produced the 'standard' fibre pattern of PAN which consists of just two equatorial peaks and weak, diffuse meridional scattering. The standard pattern has been assumed in the literature to arise from a hexagonal packing of chains with no chain-axis order. One of our specimens had a preferred double orientation of crystallographic axes and when the X-ray beam was passed along the fibre axis of this sample, a six-arc pattern was obtained. This result is new evidence for hexagonal symmetry in a bulk sample of PAN. As we were unable to reproduce the claims made by a few authors regarding sharp meridional peaks, the crystal modulus of PAN could not be measured in the same way as has been done with other polymers. However, by considering the rod-like conformation adopted by the PAN chains, and comparing it with polymers which adopt a helical form, it was estimated that the maximum tensile modulus of atactic PAN would be about 55 GPa.

Детальніше...  

The phase behaviour of mixtures of acrylate based side-chain liquid crystal polymers is examined. The constituent polymers differ only in the number of alkyl units in the coupling chain between the mesogenic units and the polymer backbone. Mixtures composed of such materials exhibit both a lower critical solution temperature in the isotropic phase range and a upper critical solution temperature in the nematic phase range. The miscibility gap for 50/50 mixtures is of the order of ~ 30°C but there is minimal miscibility in the nematic phase range. This behaviour is observed for both mixtures involving nematic phases with the same sign of orientational coupling between the mesogenic units and the polymer chains and mixtures involving polymers with opposite signs of coupling. There is an asymmetry in the miscibility curve for a mixture containing polymers of opposite signs of coupling

Детальніше...  

The various dipolar relaxation mechanisms of a liquid-crystalline side-chain polymer have been studied in detail by the technique of thermally stimulated currents. The ~ relaxation, or glass transition relaxation, showed a compensation behaviour, i.e. a correlation between the activation enthalpy and the activation entropy of its components. Two sub-glass relaxations were observed. The lower-temperature one shows a small activation enthalpy (5-6 kcal mol- ~), and is attributed to slightly hindered internal rotations in the side group. The higher-temperature one, on the other hand, shows a higher activation enthalpy (23 kcal mol-1) and a low positive activation entropy, and is attributed to restricted internal rotations of the side groups around bonds near the main chain, eventually in cooperation with the movements of the main-chain segments. An upper glass relaxation was also observed. This relaxation shows a Williams-Landel-Ferry or Vogel behaviour and high values of its mean activation enthalpy and entropy. The attribution of this discharge at the molecular level is discussed

Детальніше...  

Blending of a poly(4-vinylpyridine) core-polystyrene shell polymer microsphere with lamellar poly(styreneb- 4-vinylpyridine) block copolymers gave novel, microphase-separated films which were examined in two dimensions using transmission electron microscopy (TEM). The TEM results showed that the poly(styrene-b-4-vinylpyridine) block copolymer was arranged as a honeycomb-like bilayer around the ordered microspheres

Детальніше...  

The 19F n.m.r, spin-lattice relaxation times in both the laboratory and the rotating frame have been measured in a 70/30mo1% random copolymer of vinylidene fluoride and trifluoroethylene, over a range of pressures from 0.1 to 200 MPa in the paraelectric phase. Molecular motions have been investigated in this condis phase, and correlation times were obtained as a function of pressure and temperature. Activation parameters have been determined and discussed in terms of a thermally activated model and compared with literature data.

Детальніше...  

An association model is used to predict phase behaviour in mixtures of poly(hydroxy ether) of bisphenol A (phenoxy) (PH) with poly(alkylene oxide)s, poly(vinyl alkyl ether)s, aromatic polyethers and related copolymers. Equilibrium constants and enthalpies corresponding to self-association of PH and interassociation of PH with the second component were calculated from a Fourier transform infra-red spectroscopy study of low molecular weight analogues in dilute solutions. Transferability of the association constants between model compounds and polymer blends, as well as model predictions of blend miscibility and phase diagrams, are discussed.

Детальніше...  

The determination of the conformation of molecular chains and modes of packing of poly[ethylene-l,2- bis(phenoxy)ethane-4,4'-dicarboxylate] and its chlorinated derivatives is assisted by the X-ray crystallographic analysis and energy calculations of three model compounds. Molecules of dimethyl 1,2-bis(phenoxy)ethane- 4,4'-dicarboxylate are packed in an orthorhombic crystal system, space group Pbca, with a = 6.374(4) A, b = 35.094(6) A, c = 7.124(5)A, and z = 4. The molecule has a crytallographic centre of symmetry at the centre of the CH2-CH2 bond and the two ether O atoms are oriented anti to each other. Molecules of dimethyl 1,2-bis(2-chlorophenoxy)ethane-4,4'-dicarboxylate are packed in a monoclinic crystal system, space group C2/c, with a = 12.712(2)A, b = 7.594(1),~, c = 18.709(2)A, fl = 100.06(1) °, and z = 4. The molecule has a crystallographic two-fold axis at the centre of the CH2-CH2 bond and the O-CH2-CH2-O torsion angle of 69.9 ° makes the conformation of this part of the molecule gauche. Molecules of dimethyl 1,2-bis(2,6-dichlorophenoxy)ethane-4,4'-dicarboxylate are packed in a monoclinic crystal system, space group P21/n, with a = 4.041(2)/~, b = 12.799(1)•, c = 18.8528(9)/It, fl = 91.36(1) ° and z = 2. The molecule has a crystallographic centre of symmetry at the centre of the CH2-CH 2 bond and the two ether O atoms are oriented anti to each other. CH2-CH 2 bond shortenings were observed in the three model compounds. The crystal structures were compared with energy-minimized molecular structures using the semi-empirical quantum-mechanical method MNDO, giving results in substantial agreement

Детальніше...  

Two unexpected phenomena have been observed during the study of the growth of ~t and fl spherulites of a poly(ethylene oxide)-resorcinol complex: an overgrowth rate (denoted as Gi) of the fastest, namely the or-form, along the interface of the r-form, and a transformation of the E-form into the or-form, which propagates as a dynamic front at a constant rate G t. The evidence for these two phenomena is demonstrated, and possible explanations are discussed. Measurements of the two rates, G i and Gt, are also reported.

Детальніше...  

Корисні статті

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.

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.

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.

Полімерні матеріали

Полімер це велика молекула, або макромолекула, котра складається з багатьох субодиниць. Через їх широкий спектр властивостей, синтетичні і природні полімери відіграють найважливішу і всюдисущу роль в повсякденному житті. Полімери в діапазоні від знайомих синтетичних пластмас, таких як полістирол природний біополімер, таких як ДНК і білки, які є основоположними для біологічної структури і функцій. Полімери, як природні і синтетичні, створюються за допомогою полімеризації багатьох малих молекул, відомих як мономери.

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.