Increase In Melting Point Research Articles

Phase relationships, electrical conductivities and vaporization rates in the system La(Fe 0.5Cr 0.5)O 3Sr(Fe 0.5Cr 0.5)O 3SrZrO 3 in air

The properties of the mixed perovskite (La,Sr)FeO 3SrZrO 3 with LaCrO 3 additions were investigated. In general, an increased melting point is achieved with these additions without significant change of the electrical conductivity. However, phase separation into end-member compounds was observed up to 1700°C. The vaporization rates were measured for several compositions by the weight loss at 1700°C in still air, and it has been found that the additions of SrZrO 3 up to 20 mol% reduced the vaporization rate greatly.

Digestibility of fat and fatty acids in rainbow trout and mink

The digestibility of different fats in rainbow trout and mink showed somewhat higher values in mink than in fish. Digestibility coefficients in fish did not exhibit distinct differences between two water temperatures (3 and 11°C). Rainbow trout and mink responded very similarly to digestibility differences between dietary fats and fatty acids. Both species revealed decreasing digestibility of total lipids and fatty acids with increasing melting point. Thus soybean oil, cod liver oil and capelin oil were efficiently digested, while hydrogenation of capelin oil resulted in decreased digestibility. Mild hydrogenation to 21°C melting point had a slight effect. The digestibility of saturated and unsaturated fatty acids were similarly influenced by hydrogenation. The digestibility of individual fatty acids decreased with increasing chain length up to C 18. A further increase in chain length up to C 22 caused increased digestibility. Unsaturated acids showed higher digestibility than their saturated counterparts.

Low molecular weight peptidic fraction in the chromatin from normal and cancer cells: control of transcription.

DNA isolated from cell nuclei by intensive deproteinization with chloroform/isoamyl alcohol and phenol extractons contains a low molecular weight peptidic fraction in a quantity of about 20 micrograms/mg DNA. These peptides were characterized by chromatography on CM-Sephadex, Sephadex G-25, high performance liquid chromatography on microBondapak C18 and amino acid composition. The peptides control transcription in a reconstituted cell-free system with prokaryotic and eukaryotic RNA polymerase and stabilize the structure of double stranded DNA, while increasing its melting point. Their level is markedly decreased (by about 40%) in DNA prepared from tumor cells as compared to normal cell DNA. Transcriptional studies showed only a slightly increased template activity of DNA extracted at pH 9.5 versus DNA extracted at pH 6.0 for DNA preparations from tumor cells. However, there was a marked increase in template activity for DNA preparations treated at pH 9.5 from normal cells--232%, 124%, 97% and 78% for rat liver, mouse liver, mouse thymus and fibroblast L-929 cells, respectively. Also there was no difference in the melting point between these two preparations of DNA from tumor cells; normal cell DNA preparations showed increased melting point of preparations treated at pH 6.5. The data obtained indicate that the loss of low molecular weight peptides from tumor DNA during carcinogenesis is responsible for uncontrolled gene expression observed in cancer.

Thermal transitions in cold-crystallized blends of isotactic and static polystyrene

Solution-cast blends of isotactic and atactic polystyrene were stripped of casting solvent and heated above the glass transition temperature to temperatures below the equilibrium melting point of the respective blends to induce the development of crystallinity of the isotactic polystyrene. The samples, maintained at these crystallization temperatures for various times, were subsequently characterized by differential scanning calorimetry. The amount of crystallinity, the crystalline melting point, and the rate of crystallization were determined for each of the blends from the d.s.c. scans. The development of crystallinity, characterized by increased melting points, resulted from annealing at progressively higher temperatures. The maximum rate of crystallization for each of the blends was observed at a temperature corresponding closely to 8 9 of the absolute equilibrium melting temperature. The decrease in the melting point of the isotactic polymer, crystallized in the presence of atactic diluent, resulted primarily from weak enthalpic interactions between isotactic and atactic polystyrene homopolymers. Scanning electron photomicroscopy revealed that atactic-rich blends, immersed in n-hexane at 40°C, developed a non-intercommunicating network of microvoids. Similar solvent treatment of isotactic rich blends had little effect on the samples. D.s.c. measurements confirmed recently published results which indicated that n-hexane, at modest temperatures, does not induce the development of crystallinity in isotactic polystyrene.

The structure and properties of ultra-high modulus polymers

The first successful preparation of homogeneous continuous high modulus polyethylene was carried out at Leeds University in 1972. Compression moulded sheets of comparatively low molecular weight polyethylenes were drawn 30 times to give thin tapes with initial moduli ∼ 70 GNm −2. Though these materials were of high modulus, they showed comparatively poor creep and strength properties. Supsequently, it has proved possible to extend the range of polyethylenes that can be highly drawn, and high modulus products have been obtained with considerably enhanced properties. Moreover, guidelines have been established for the development of small scale manufacture of fibres and tapes on a continuous basis. In addition, similar materials may be made in large sections by hydrostatic extrusion. It has been clearly established that high draw is essential in the preparation of high modulus by solid phase deformation. The preparation of the material is also affected by the initial structure (molecular weight, chemical composition and morphology) as well as by the drawing conditions (temperature, strain rate). Moreover, although the initial modulus depends only on the draw ratio, other properties such as melting behaviour, creep and strength depend on the initial structure and drawing conditions. Other interesting properties of these materials include increased melting points, a high thermal conductivity (comparable with stainless steel), high shrinkage force and a very high resistance to chemical attack (associated with very low permeability to gases). A wide range of structural techniques have been applied to examine these materials, including wide angle and small angle X-ray diffraction, laser Raman spectroscopy, broad line nuclear magnetic resonance and nitric acid etching followed by gel permeation chromatographic analysis of the degradation products. The results obtained suggest that although the end product features a periodicity corresponding to an initial lamellar structure formed in the early stages of stretching, high degrees of deformation are attributable to the formation of a large number of intercrystallite bridge bonds. The highly drawn polymer accordingly represents a continuous crystal phase, which serves as a strengthener for the structure as a whole. It is the degree of crystallinity, which may be determined from the X-ray data, which would account for a high elastic modulus and for thermal conductivity. A special study was made of the creep and of the recovery behaviour, since these are most significant properties for possible applications of ultra-high modulus PE fibres as reinforcing materials. It can be demonstrated that the creep consists of a recoverable part and an irrecoverable part and is satisfactorily described as an Eyring activated rate process. The link between creep and drawing can be established and leads to a comprehensive view of the plastic deformation processes. It has also proved possible to achieve high modulus in polypropylene fibres by high draw, although the results are less spectacular because of the much lower theoretical modulus of this material, and the highest modulus values obtained are only ∼ 20 GNm −2.

Crystallization‐induced reactions of copolymers. V. Important reaction variables in the reorganization of random to block copolyesters

AbstractThe effects of reaction parameters including copolyester composition, catalyst type and amount, temperature, time, endgroup concentration (molecular weight), and degree of crystallinity were determined for the reorganization of random to block poly(ethylene terephthalate‐co‐succinate). The crystallization‐induced reactions, which were the basis of these ordering processes, were carried out at temperatures at or below the terephethalate unit melting points of the initial copolyester. All samples so treated showed increased melting points, recrystallization temperatures, and degrees of crystallinity which correlated with increased blockiness of the terephthalate units, as determined by nuclear magnetic resonance spectroscopy. At reaction temperatures greater than 15°C below the initial copolyester melting point, those parameters which controlled the rate of the ester interchange reaction also controlled the extent of the reorganization. Within approximately 15°C of the melting point, the reaction rate was apparently less important than physical factors related to the crystalline properties of the initial copolyester.

Effect of chain structure on the melting of low molecular weight poly(ethylene oxide)

Linked poly(ethylene oxide) samples have been prepared by the condensation of α-methoxy-ω-chlorocarboxy-poly(ethylene oxide) with alcohols of various functionalities. Melting points (by dilatometry) and lamella spacings (by small-angle X-ray scattering) have been determined. The linked polymers have higher melting points than their unlinked precursors. The increased melting point is interpreted in the light of the model of Flory and Vrij.

Change in the electrical conductivity of organic semiconductors close to the melting point

Experimental data relating to the temperature dependence of the electrical conductivity of aromatic organic compounds are discussed within the framework of the zone (band) model. The electrical conductivity of these compounds is determined by the bond energy of the molecular compounds and diminishes with increasing melting point. The Mott formula is satisfied for anthracene, phenanthrene, and naphthalene, while the dependence of σs/σl on the change in thermal activation energy established by Gubanov for inorganic semiconductors also applies to those organic semiconductors for which δe is equal to or less than 2 eV. An analysis of the experimental data indicates than zone (band) theory may be used for organic semiconductors in the melting region if the character of the conductivity is similar in the solid and liquid states and the change in thermal activation energy is small.

The polymorphism of poly(vinylidene fluoride) IV. The structure of high-pressure-crystallized poly(vinylidene fluoride)

Abstract A detailed study of high-pressure-crystallized poly(vinylidene fluoride) has indicated that a mixture of low-melting phase II and high-melting phase I is present, rather than a new crystalline phase (phase III) as originally suggested. The relative amounts of phase I and phase II resulting from crystallization under pressure are a function of pressure and the degree of supercooling. Pressure crystallization at 285°C and 5500 atm results in samples which were pure phase I with an increased melting point of 187°C.

Polymorphism of cocoa butter.

AbstractLargely by x‐ray diffraction six crystalline states, I舑VI, in order of increasing melting point, have been identified for cocoa butter. Of these states II, IV, V and VI are pure and identifiable with previously (or presently) identified polymorphs of 2‐oleoylpalmitoyl stearin (POS), namelyॅ‐2,ॆ艂‐2,ॆ‐3 (舠V舡) andॆ‐3 (舠VI舡); V and VI representing distinct but very closely related crystalline structures. State I is a definite but fleeting and not readily characterized subॅ state and may be a phase mixture, as state III may be also.Melting points, heats of fusion and dilatometric data are reported for all states to the extent that their stability permits.The normal state of cocoa butter in chocolate is apparently V, certainlyॆ‐3. While it is true that 舠bloom舡 has not been observed for pure V nor observed to exist in the absence of VI, it is premature to say that VI is specifically the phase of chocolate 舠bloom舡.

Differential thermal analysis of divalent metal 8-hydroxyquinoline chelates

DTA curves were obtained for a number of anhydrous metal chelates derived from the important analytical reagent 8-hydroxyquinoline. The compounds were heated in an inert atmosphere to avoid interaction with oxygen or water vapor. The Cu, Pb, Zn, Ni and Co chelates melted without decomposition, under the conditions used, while the remainder of the compounds underwent partial decomposition upon melting. The order of increasing melting point is Pb < Cu < Zn < Ni < Co < Ba < Mn < Cd < Sr < Mg < Ca. The order of decreasing heat stability is Ca >Mg > Sr > Cd > Mn > Ba > Co > Ni > Zn > Pb > Cu.

Interfacial polycondensation. VI. Polyamides based on 4,4′‐sulfonyldibenzoic acid

AbstractThe preparation of eleven soluble polyamides based on 4,4′‐sulfonyldibenzoic acid by interfacial polycondensation with the use of aliphatic and alicyclic diamines is reported. Polymer melt temperatures of those polyamides prepared from aliphatic diamines decreased with increasing chain length and amount of chain branching in the diamine. The usual odd‐even alternation of melting points was noted. Cyclic secondary diamines gave higher‐melting polyamides than straight‐chain diamines, despite the lack of hydrogen bonding. Solubility decreased with increasing melting point, except for the polyamides based on cyclic diamines, which were both soluble and high‐melting. Fiber properties are reported for those polymers which were spun.

Effects of ingestion of paraffins by ruminants

Summary The effect of various paraffins and other non-digestible or poorly absorbed materials on the utilisation of carotene has been further investigated. Paraffins, waxes, and a sterol were found to depress carotene utilisation, the effect being related to the concentration present in the vehicle. The depressant effect decreased with increasing melting point. The triglyceride composition of the vehicle was also found to be important, carotene being less efficiently utilised from the softest and hardest fats investigated.

Some Effects of Irradiation on Nylon and Polyethylene Terephthalate

IN a detailed paper by Charlesby1 on the effects of irradiation on polyethylene, he suggested that the main effect was ‘cross-linking’, that is, the formation of covalent bridges between neighbouring molecular chains, with the consequent loss of hydrogen. Since then, there has been a tendency to refer to the effect on any polymer as ‘cross-linking’ when low irradiation doses show changed solubilities in normal solvents, increased melting points, and no gross chemical breakdown2, although other possible causes for these changes have been suggested3. It seems appropriate, therefore, to describe experiments on two of the polymers which have been specifically mentioned by Charlesby and Lawton, 66 nylon and ‘Terylene’.

The valencies of the transition elements in the metallic state

The melting-points, interatomic distances and compressibilities of the transition elements are reviewed, and are shown not to be in complete agreement with the valency scheme proposed by Pauling. In all three Long Periods on passing from Groups I A to IV A there is a steady rise in melting-point, and decrease in interatomic distance and compressibility, and for these elements Pauling’s view of a metallic valency equal to the Group number is correct. In the First Long Period there is comparatively little increase in melting-point on passing from Ti to V and Cr, in contrast to the behaviour of the corresponding elements in the later Periods where the melting-points rise steeply to a maximum in Group VI. This suggests that in Groups V A and VI A the metallic valency is less for the elements of the First Long Period than in the later Periods, and this agrees with the general inorganic chemistry of the elements. The same principle is shown to hold for the elements of Groups VII A and VIII, and a new scheme of metallic valencies is suggested which appears attractive in several ways.