Nature of stark rubber

Abstract

TI;,e melting behavior: and X-ray diffrac.tion patterns of four different samples of "stark rubbel: have been Illvestigated. The meltmg temperatures, 39° to 45 .5° C, a re s ubstantially hif?her than th.at .observed for natural. rub.ber crystallized by coo ling. The X-ray d iffractIOn patterns 1I1clicate that the crystallites 111 stark rubber are oriented. This observati.op ~an ex plaip the higher meltin~ temperatures. Thus, t he prev ious assignment of an eq UIlibrium melt1l1g temperature, 28 ± 1° C, to unoriented crystalline natural rubber is shown. to be appropriate. Several different methods that have been used successfully in prepanng stark rubber under controlled conditions in the laboratory are outlined.

Long Time Evolution of Structural Hierarchy in Uniaxially Stretched and Retracted Cross-Linked Natural Rubber

“…This is not surprising since these crystals were grown very slowly over long periods of time at room temperature. Similar high-temperature crystallites were found in stark natural rubber stored for long periods of time . Crystallites formed at low (−25 °C) and high temperature (room temperature) are distinguished by the degree of their development and perfection but pertain to the same crystallographic form .…”

“…Similar high-temperature crystallites were found in stark natural rubber stored for long periods of time. 38 Crystallites formed at low (-25 °C) and high temperature (room temperature) are distinguished by the degree of their development and perfection but pertain to the same crystallographic form. 39 Although long-term slow crystallization at room temperature is necessary, it is not sufficient to grow high temperature crystallites in natural rubber.…”

The Crystallization Of Flexible Polymer Molecules

“…The melting temperatures obtained in this manner are reproducible and are invariably found to be significantly higher than those obtained employing fast heating rates. In these experiments care must be taken to insure that the crystallites are randomly oriented relative to one another, for if they are not an abnormally high melting temperature may be observed (140). The observation that on slow heating reproducible melting temperatures are obtained is the first indication that an equilibrium melting temperature may exist.…”

Preferred orientation in stark rubber

“…The specimen was approximately a I-mm cube, cut with one edge perpendicular to the surface of a sheet of H evea rubber d esignated as sample III in the previous investigation [1]. Reference should be made to this earlier paper for details concerning the preparation and history of the sample.…”

“…When stark rubber is heated , t he obseJ:ved mel ting temperature is ap preciably higher than t hat usually ass igned Lo natural rubber. It has been s hown recently [1]1 t hat these higher rndting temperatures are a consequence of Lhe fact that the crystall ites are not randoml.\T arran ged relative to one another in stark rubber. These conclusions were based on the X-ra.\r diffraction paLterns for several different samples wherein the intensities around the cirC"umferences of diA'racLion haloes we re found to be nonlmifonn.…”