Showing papers on "Differential scanning calorimetry published in 1971"

Thermal Properties of the Starch/Water System Part I. Measurement of Heat of Gelatinisation by Differential Scanning Calorimetry

Abstract: The application of Differential Scanning Calorimetry to the gelatinisation of concentrated starch/water suspensions produced a well-defined endotherm under suitable conditions. Measurement of the peak area enabled the heat of gelatinisation to be calculated. The method has been applied to the following aspects of gelatinisation: — 1 Intercomparison of different starches, 2) Effect of granule size, 3 Application to wheat flour, 4 Effect of starch damage, 5 Staling of starch gels, 6 Amylose and amylopectin.

Side‐chain crystallinity. I. Heats of fusion and melting transitions on selected homopolymers having long side chains

Abstract: Heats of fusion, melting transitions, and the derived entropies of fusion were obtained by differential scanning calorimetry for examples from three homologous series of homopolymers having long side chains. Homopolymers having side-chain lengths between 12 and 22 carbon atoms were chosen from the poly(n-alkyl acrylates), the poly(N-n-alkyl-acrylamides) and the poly(vinyl esters). The data demonstrated that only the outer paraffinic methylene groups were present in the crystal lattice. This was concluded because phase diagrams obtained for mixtures of structurally different monomers and homopolymers, as well as for selected copolymers, showed only isomorphism in the polymeric examples. In addition, scanning curves, reflecting the distribution of crystallite sizes, became narrower as the side chains became longer. The critical chain length required to maintain a stable nucleus in the bulk homopolymers was a constant value for each homologous series. It varied between 9 to 12 carbon atoms. When heats of fusion were determined in the presence of methanol, main-chain restraints were freed, thus permitting more methylene groups to enter the crystal lattice. Hence, the heats of fusion, the crystallinity, and melting points increased above that of the bulk state. The magnitude of the contribution to the heats of fusion by each methylene group indicated that the hexagonal paraffin crystal modification prevailed in these homopolymers, in agreement with x-ray data from the literature.

Hydrodynamically induced crystallization of polymers from solution

Abstract: This paper deals with a study on the melting behaviour of polyethylene crystals showing a fibrillar morphology. These crystals were prepared by hydrodynamically induced crystallization from xylene solutions. Use was made of several techniques, such as differential scanning calorimetry, polarizing microscopy and infrared dichroism. The experimental observations indicate that the melting process of the fibrous crystals can only partly be related to morphological structures. The infrared dichroism and persistent birefringence up to temperatures of 200 °C are due mainly to the molecular orientation in the melt. The shrinkage on melting was found to depend on the thickness of and fibre orientation in the sample, as well as on the molecular weight of the polyethylene. A maximum shrinkage value of 93% was measured on fibrillar crystals of Marlex (M w =90 · 103). Calorimetric studies on the fusion of fibrillar crystals of high molecular weight polyethylene (M w =1.5 · 106) revealed that extendedchain backbones melt at 150 °C and even at 180 °C. The melt of these crystal structures remains partly oriented, as could be inferred from the constant temperature position of the melting peak on repeated crystallizing and melting.

Complex plane analysis of heat capacity of polymers in the glass transition region

Abstract: A method is described which enables the direct measurement of relaxation times and relaxed and nonrelaxed heat capacities as a function of temperature. The apparatus designed is to be used as additional equipment to the Perkin-Elmer differential scanning calorimeter DSC-1B. The specimen is heated periodically with time instead of proportionally. The amount and phase of differential heat flow are measured. The parameters of an 'equivalent circuit' of a heat capacity model are fitted to the measured complex Cp values obtained at various frequencies and appropriate amplitudes of temperature. Further applications of the 'oscillating thermal analysis' are proposed.

Direct observation of the double glass transition in a phase-separated glass

Abstract: Heat capacity measurements have been performed for the phase-separated pseudobinary chalcogenide glass system X PbSe-(1− X )Ge 1.5 As 0.5 Se 3 in the composition range X = 0.0 to 0.6. The heat capacity versus temperature plots for the phase-separated glasses exhibit two glass transition breaks. The composition dependences of the heat capacity changes, ifΔC p , at the two transitions are shown to be in accord with the behavior predictable from the phase diagram of a glass-forming system exhibiting liquid-liquid immiscibility and with the structure of these glasses as determined by electron microscopy. The two composition points on the immiscibility dome at which the temperature is equal to the higher glass transition temperature have been determined from the composition dependence of the ΔC p 's and indicate that the dome spans almost the entire composition range for this system.

Single crystals of poly(2,6-dimethyl-1,4-phenylene)oxide

Abstract: Poly(2,6-dimethyl-1,4-phenylene)oxide crystals obtained from 0.1%α-pinene solutions by isothermal growth at temperatures from 80–90 as well as 100 °C, were investigated by optical and X-ray diffraction techniques. A study has been made by differential scanning calorimetry in order to measure the melting point, glass transition and melting point depression temperatures of mixtures of the polymer withα-chloro-naphthalene. The densities of the dry mats of single crystals were measured by a flotation method.

Ethylene-propylene copolymers: Degree of crystallinity and composition

Abstract: X-ray, differential scanning calorimeter, and density measurements of the degree of crystallinity have been made on ethylene—propylene copolymers which range in composition from 60 to 100 mole-% ethylene. At 23°C the degree of crystallinity was found to vary from zero to approximately 75 wt-% in a regular manner with composition. A systematic difference exists between the x-ray and heat of fusion measurements if a simple two-phase model is assumed in order to calculate the per cent crystallinity from heats of fusion. The apparent heat of fusion of the crystalline fraction detected by the x-ray method is as low as 30 cal/g. This discrepancy increases with comonomer content. It is suggested that large surface or defect energies are present. The broad melting behavior of the samples is also consistent with such a description of the system.

The dissolution and stability of cellulose triacetate in acetone

Abstract: The solubility behaviour of primary cellulose acetate in acetone has been investigated and it has been found that samples with a degree of substitution (DS) between 2.80 and 2.90 can be completely dissolved by first cooling the polymer-liquid mixtures to about 190°K then warming to ambient. The efficiency of this process deteriorates rapidly for DS of 2.90–3.0 when only partial solution can be effected. Upper and lower critical solution temperatures have been estimated for these solutions, which provide an indication of the extent of total miscibility for the system. Approximate values for the enthalpy of fusion, together with glass and melting temperatures have been determined by means of a differential scanning calorimeter. The data suggest that acetone can dissolve the smaller crystallites and the associated amorphous regions in the fully acetylated material, but cannot dissolve the larger well ordered regions, unless the sample contains a significant number of hydroxyl groups.

Preparation and thermodynamics of Some Homologous Nitrones, a New Group of Liquid Crystals

Abstract: To investigate the mesomorphic behavior of aldonitrones, a series of 13 homologs of N-(p-alkoxyphenyl)-α-anisylnitrones was prepared and characterized. Although most of these substances exhibit normal nematic or smectic mesophases, the trend in nematic-isotropic transition temperatures to increase as a function of alkoxy chain length is an exceptional occurrence. Comparison of our data with that of analogous compounds previously reported indicates that thermal persistence of the nematic phase of these compounds increases in the following order : 4, 4′-dialkoxybenzylideneaniline, 4, 4′-dialkoxyazobenzene, N,α-di-(4-alkoxyphenyl)-nitrone, 4, 4′-dialkoxyazoxybenzene. In addition, the phase transitions were investigated by means of differential scanning calorimetry. The entropies of the mesophase-isotropic transitions of the nitrones imply that the long alkoxy chains, in contrast to a widely held belief, are not restricted to a single conformation in the mesophase.

Influence of temperature-induced phase transitions on fat emulsions

Abstract: The polymorphic behavior of a commercial monoglyceride emulsifier together with a liquid vegetable oil and water has been investigated by means of microscopic examination and differential scanning calorimetry. The results show that the stability regions of the liquid crystalline phases formed are highly dependent on the temperature and related both to the solubility of the monoglyceride emulsifier in the oil phase and to its polymorphic behavior. The formation and stability of emulsions are discussed in connection with the results obtained.

Preparation and thermodynamics of some homologous nitrones, a new group of liquid crystals

Abstract: To investigate the mesomorphic behavior of aldonitrones, a series of 13 homologs of N-(p-alkoxyphenyl)-a-anisylnitrones was prepared and characterized. Although most of these substances exhibit normal nematic or smectic mesophases, the trend in nematic-isotropic transition temperatures to increase as a function of alkoxy chain length is an exceptional occurrence. Comparison of our data with that of analogous compounds previously reported indicates that thermal persistence of the nematic phase of these compounds increases in the following order: 4,4′-dialkoxybenzylideneaniline, 4,4′-dialkoxyazobenzene, N,α-di-(4-alkoxyphenyl)- nitrone, 4,4′-dialkoxyazoxybenzene. In addition, the phase transitions were investigated by means of differential scanning calorimetry. The entropies of the mesophase-isotropic transitions of the nitrones imply that the long alkoxy chains, in contrast to a widely held belief, are not restricted to a single conformation in the mesophase.

A Differential Scanning Calorimeter Study of Phase Transitions in Alkali Metal Stearates

Abstract: Differential scanning calorimeter thermograms have been obtained for the alkali metal stearates from 25 to 200 °C. Four different samples of different thermal history were studied for each soap, an...