Crystallization kinetics of stretched natural rubber

Abstract

Studies of the crystallization kinetics of natural rubber networks held in simple extension are reported. In these experiments the length of the specimen was held constant, and the crystallization process was followed by the decay in stress that occurred. A wide range of extension ratios and crystallization temperatures was encompassed by these experiments. From an analysis of the shapes of the crystallization isotherms, it can be concluded that major changes take place in the nucleation and growth processes as the extension ratio is increased. This conclusion is in accord with reports in the literature of changes in the crystallite morphology with extension ratio. Analysis of the temperature coefficient of crystallization, by means of nucleation theory, indicates a substantial increase in apparent interfacial free energies with increased deformation. This latter observation is interpreted to indicate a departure from a correlated crystallization process to one where isolated crystallites are formed.

Strain-Induced Crystallization of Crosslinked Natural Rubber As Revealed by X-ray Diffraction Using Synchrotron Radiation

“…In most classic studies, the stretched sample was equilibrated at elevated temperature and then quenched to predetermined crystallization temperature to start SIC. 11,62,63 Relatively slow kinetics of SIC have been studied under the condition of small s and in long time scales ranging from several minutes to several months, because the rate of SIC at high elongation is too fast for typical X-ray or volume measurements to follow. Probably, the only exception reporting the fast kinetics of SIC has been the thermal study by Mitchell & Meier.…”

The maximum melting temperatures in strain-crystallized van der waals networks

“…Simplifying the actual situation the disparity in c-sequence lengths is on average characterized by Ay = Ay + B (see text). Using the equivalent two-phase model, it it is evident from the (4) sketch that nc-units "are built into this crystal". The concentration of these units is uniquely dependent upon Ay(y).…”

“…Gaylord improved the theory by taking into account finite chain lengths and the orientational distribution of the crystallites found in strained networks [2,3]. A discussion of melting temperatures at different elongations has also been given by Mandelkern [4], Krigbaum, Flo W, Oth, and Gent [5][6][7][8][9]. However, one essential problem was not solved in all of these approaches: the finite degree of crystallinity and its well known dependence on temperature and strain [6][7][8][9] is a priori not described.…”

Crystallization of polymers in oriented state

“…Since that moment, a number of investigations have been performed using the stress relaxation as a tool for measuring crystallization kinetics (6,7,8,9). The results have shown that crystallization rate increases drastically with an increase of deformation.…”