Polymer-diluent Systems Research Articles

Role of Neutral Salts on the Denaturation Temperature of Biopolymers

IN recent years, a great deal of attention has been devoted to the study of the effect of salts on the denaturation of biopolymers, both in the bulk state (for example, shrinkage of fibrous collagen) and in dilute solutions (for example, helix-coil transitions)1,2. Recent work in this laboratory3 has demonstrated that two main factors must be considered in describing the effects of both salt type and salt concentration on the shrinkage of collagen at neutral pH (when polyelectrolyte effects are absent). These are: the diluent and the specific effect. The former effect is predominant for salting-out agents, such as potassium chloride and magnesium sulphate, whereas the latter occurs with salting-in agents, such as potassium thiocyanate and lithium bromide. The diluent effect is satisfactorily described by the conventional melting point depression theory developed for binary polymer-diluent systems where Tm is the melting temperature of the polymer in the presence of the diluent, Tm° the melting temperature of the undiluted polymer, ΔHu is the heat of fusion per mole of repeating unit, Vu the molar volume of the repeating unit, V1 the molar volume of the diluent, ζ1 the volume fraction of diluent, and χ1 represents a polymer–diluent interaction parameter which can be interpreted3 in terms of conventional salting-out theories4.

Study of the effect of fillers on the thermal behaviour of polycaproamide by a method of differential thermal analysis (DTA)

THE method of differential thermal analysis (DTA) has recently found increasing application in the investigation of the thermal properties of polymers. Attention has mainly been given to melting processes and polymer crystallization [1-5]. Bacon Ke [6] from results obtained by studying the effect on the melting point of polyethylene of several low-molecular weight diluents, both liquid and solid which melt on heating, draws the conclusion that DTA is highly accurate even for the evaluation of the degree of interaction in the polymer-diluent system. The purpose of our investigations was to examine the possibility of using DTA to determine the effect of natural fillers, which do not undergo any transformations in the range of temperatures studied, on the thermal behaviour of polycaproamide, and finally to determine the degree of interaction of the latter on adding a filler.

Molecular interpretation of glass temperature depression by plasticizers

AbstractThe view that the glass transition is basically thermodynamic in nature is used to derive an expression for glass temperature depression by plasticizers. The second‐order transition temperature is given as that temperature at which the configurational entropy first becomes zero as we cool the polymer–diluent system. The concentration of plasticizer, size of the plasticizing molecule, and its flexibility are found to be the main determinants of glass temperature depression. Available experimental data confirm the predictions of the theory, and it is thereby concluded that the thermodynamic view is sufficient to explain glass temperature depression. It is pointed out that data exist which contradict the free volume theory, as applied to glass temperature depression.