Crystallization of unvulcanized rubber at different temperatures

Abstract

The crystallization and melting of un vulcanized natural rubber in the unstretched state have been investigated at different temperatures. Change of volume has been used as a quantitative measure of the extent of crystallization, and mercury-filled dilatometers containing the rubber have been u sed for the volume measurements.Crystallization was observed to occur at temperatures between -50° and + 15° C and to be most rapid at about -25° C. The final decrease of volume on crystallization was usually found to lie between 2.0 and 2.7 percent. The melting of the crystalline rubber was found to occur over a range of temperature and to be strongly dependent on the temperature at which the crystals were formed. The temperature at which the beginning of melting occurs is fro m 4 to 7 degrees above the temperature of crystallization. The range of melting is about 35 degrees at the lowest temperatures and decreases to about 10 degrees at the highest. The same range of temperature of melt ing is obtained regardless of the extent of the crystallization. CONTENTS P age

Low Temperature Behavior of Silicone and Organic Rubbers

“…This is in contrast to the behavior of natural rubber under similar circumstances (9, 10). The data presented by Weir, Leser, and Wood further indicate that crystallization of Silastic is a rapid process in contrast to the crystallization of natural rubber studied by Bekkedahl and Wood (3,10). These facts help explain why the special short-term aging technique for Silastic appears to be an Temperatures for Natural Rubber R-860 adequate substitute for long-term aging.…”

Observing Nucleation Transition in Stretched Natural Rubber through Self-Seeding

“…Although hot press would undermine naturally occurring network, numerous such networks still remain. 2,17 Third, for NR-1, in order to introduce residual TIC-melting crystallites, the prepared NR film was subjected to TIC-melting process: 19 the film was stored in a fridge at 2−6 °C for 6 weeks, and then taken out and preserved under room temperature (25 °C) for about 48 h just before sample characterization. For NR-2, the film was preserved under room temperature without suffering TIC-melting process.…”

The effect of strain-induced crystallization (SIC) on the physical properties of natural rubber (NR)

“…Crystallization of un-vulcanized NR in a 24-hour period has been measured in a temperature range from -50°C to 2°C; the maximum rate of cold crystallization is at -25°C, with a time to crystallization of around 2.5 hours. The maximum crystalline content of cold crystallizing NR is around 27% by density (Wood and Bekkedahl, 1946;Treloar, 1975). The broad range of crystallization temperatures and the low value of the maximum crystalline content suggest that the high molecular weight, broad molecular weight distribution and the gel component of NR may decrease the mobility of molecules, impeding crystal formation.…”