Crystallinity In Natural Rubber Research Articles

Comparison between x-ray diffraction and quantitative surface calorimetry based on infrared thermography to evaluate strain-induced crystallinity in natural rubber.

The crystallinity of stretched crystallizable rubbers is classically evaluated using x-ray diffraction (XRD). As crystallization is a strongly exothermal phenomenon, quantitative surface calorimetry from infrared thermography offers an interesting alternative to XRD for determining the crystallinity. In this paper, the two measurement techniques have been used for evaluating the strain-induced crystallinity of the same unfilled natural rubber. This study provides the first comparison between the two techniques. The results obtained highlight the very satisfactory agreement between the two measurements, which opens a simple way for evaluating the strain-induced crystallinity from temperature measurements.

Characterization of Natural Rubber Latex/Chitosan Blends

In an attempt to prepare novel biodegradable materials, blends of natural rubber latex/chitosan (NR/CS) with different compositions have been prepared by solution casting followed by compression. The blends were characterized by thermogravimetry, Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction, and scanning electron microscopy (SEM) techniques. The effect of thermal stability on the percentage of natural rubber latex (NR) in the blend was studied. The percentage of bound rubber content and fraction of rubber dissolved in benzene was determined. Better interfacial adhesion between chitosan and natural rubber is achieved in the blend NR95 CS5. This is reflected in the IR spectrum also. The water absorption behavior of the blends has also been studied. X-ray diffraction study shows a decrease in crystallinity in natural rubber with addition of chitosan.

Thermal reversibility of crystal surface structure and its contribution to degree of crystallinity in natural rubber and trans-polyisoprene

Abstract The small-angle X-ray and electron microscopy results of the reversible phenomena of long period and/or crystal and amorphous fold thicknesses with temperature in natural rubber and trans-polyisoprene are presented and discussed in detail. The results cannot be accounted for satisfactorily by either the premelting theory or the solid-state refolding mechanism, but can best be explained by a recrystallization by refolding from a transient liquid-crystalline state. A substantial portion of the long period reversibility is seen to arise from the changes in amorphous surface thickness with temperature. This explains to a large extent the reversibility of crystallinity with temperature and the limiting crystallinity in natural rubber and trans-polyisoprene, and probably in other materials as well.

A high-strain specimen stretching device for the Elmiskop I electron microscope

Apparatus is described which enables strains of up to 1000% to be applied to a specimen during observation in the electron microscope. The device, which was designed for use with rubbers and other highly-extensible materials, is made from an ordinary specimen capsule and requires no modification of the microscope. It is operated by means of the stereo push rod and employs a lever system to separate a pair of sliding jaws. An example of its use is the observation of strain-induced crystallinity in natural rubber.

X-Ray Diffraction Studies of Crystallization in Elastomers

Abstract In general, extension of an elastomer results in a degree of preferred orientation of the molecular chains composing the amorphous phase. Therefore the amorphous fraction of a partially crystalline elastomer must be related to the integrated intensity of the amorphous diffraction halo rather than to the intensity at any one azimuth. A noteworthy exception is natural rubber, for which simple meridional measurements suffice. A Geiger-counter apparatus, with beam monitor and temperature-controlling accessories, is described for making accurate measurements of the x-ray intensities scattered at any azimuth and at small or moderate Bragg angles. Measurements of crystallinity in natural rubber are in essential agreement with the findings of previous workers. When polybutadiene is extended at room temperature, molecular orientation occurs, but little if any crystallization. Measurements at lowered temperatures show that the crystalline fraction becomes appreciable at about 0° C and that it increases with further reduction of temperature and with increasing extension ratio. Preferred orientation of the crystalline regions in extended polybutadiene has been measured quantitatively with the object of providing jointly with birefringence measurements a value of the birefringence of a single crystal of polybutadiene.

X-Ray Diffraction Studies of Crystallization in Elastomers

In general, extension of an elastomer results in a degree of preferred orientation of the molecular chains composing the amorphous phase. Therefore the amorphous fraction of a partially crystalline elastomer must be related to the integrated intensity of the amorphous diffraction halo rather than to the intensity at any one azimuth. A noteworthy exception is natural rubber, for which simple meridional measurements suffice. A Geiger-counter apparatus with beam monitor and temperature-controlling accessories is described for making accurate measurements of the x-ray intensities scattered at any azimuth and at small or moderate Bragg angles. Measurements of crystallinity in natural rubber are in essential agreement with the findings of previous workers. When polybutadiene is extended at room temperature, molecular orientation occurs, but little if any crystallization. Measurements at lowered temperatures show that the crystalline fraction becomes appreciable at about 0°C and that it increases with further reduction in temperature and with increasing extension ratio. Preferred orientation of the crystalline regions in extended polybutadiene has been measured quantitatively with the object of providing jointly with birefringence measurements a value of the birefringence of a single crystal of polybutadiene.

On the degree of crystallinity in natural rubber

A recent theory, developed by Flory, allows the degree of crystallization to be calculated from thermodynamical measurements if certain parameters are properly evaluated. Such evaluation is possible by combining Wildschut's thermodynamical measurements with the X-ray results presented in previous papers. Thus, the average length of molecule chains between cross-linkages can be derived; it closely corresponds to the results of swelling measurements, carried out by Gee. Other parameters are also evaluated in agreement with their physical meaning.

The Degree of Crystallinity in Natural Rubber. IV. The Degree of Crystallization in Frozen Raw Rubber and Stretched Vulcanized Rubber

Abstract An improved x-ray technique has been worked out to determine the degree of crystallinity in natural rubber. Inaccuracies which sometimes occur in quantitative x-ray measurements were eliminated, and it has been shown that the amount of crystalline rubber, both in frozen samples of raw rubber and in stretched vulcanized rubber, could be determined fairly accurately. More experiments were carried out and the results are described. These results, which confirm the current views on the problem of crystallization, point to relatively low degress of crystallization, even in highly stretched rubber, and they agree with some other experimental evidence and with a recent theoretical investigation.

The Degree of Crystallinity in Natural Rubber. III. Correlation between X-Ray and Density Measurements

Abstract In 1925 Katz discovered the crystallization of stretched rubber. In the following years several investigators tried to determine the structure of rubber crystallites. The densities of the rubber crystallites calculated from the results of these investigations varied strongly. The results of x-ray and density measurements on crude rubber carried out by the author can be made to correspond only when the latter are based on the unit cell of Bunn. It is shown by experiment that, to measure the correct degree of crystallization, it is necessary to use monochromatic x-rays.

The Degree of Crystallinity in Natural Rubber. V. A Discussion of the X-Ray Results on Natural Rubber in Connection with the Work of Flory, Gee and Wildschut

Abstract A recent theory, developed by Flory, makes it possible to calculate the degree of crystallization from thermodynamical measurements if certain parameters are properly evaluated. Such evaluation is possible by combining Wildschut's thermodynamical measurements with the x-ray results presented in previous papers. Thus the average length of molecule chains between cross-linkages can be derived; it closely corresponds to the results of swelling measurements carried out by Gee. Other parameters are also evaluated in agreement with their physical meaning.

On the degree of crystallinity in natural rubber III

An improved X-ray technique has been worked out to determine the degree of crystallinity in natural rubber. Inaccuracies which sometimes occur in quantitative X-ray measurements were eliminated and it has been shown that the amount of crystalline rubber, both in frozen samples of raw rubber and in stretched vulcanized rubber, could be determined fairly accurately. More experiments were carried out and the results are described. These results, which confirm the current views on the problem of crystallization, point to relatively low degrees of crystallization, even in highly stretched rubber, and they agree with some other experimental evidence and with a recent theoretical investigation.

On the degree of crystallinity in natural rubber I

There are indications that the degree of crystallization in highpolymeric substances is of importance for the study of the mechanical properties. With regard to the crystallization of rubber up to now only few measurements have been made, mainly bij Field. The results, however, are in contradiction with some estimates of earlier date and therefore the necessity was felt to have them checked. An X-ray method, in some respects differing from Field's, was developed, the results of which diverged considerably from the figures reported by Field. The present article deals with the description of the method.

On the degree of crystallinity in natural rubber IV

On the degree of crystallinity in natural rubber IV

On the degree on crystallinity in natural rubber II

In a foregoing article a description has been given of a method for determining the amount of crystalline rubber in stretched samples. A complication due to varying crystallite orientation in different samples appeared to interfere with the application. A simple relation is given here between the degree of orientation and an empirical constant which makes possible a rapid determination of the degree of crystallization, regardless of the orientation in the sample under investigation.

On the Degree of Crystallinity in Natural Rubber. II. The Orientation of Rubber Crystallites in Stretched Samples

Abstract In the foregoing article a method for determining the proportion of crystalline rubber in stretched samples has been described. A complication due to varying crystallite orientation in different samples appeared to interfere with the application. A simple relation is given between the degree of orientation and an empirical constant which makes possible a rapid determination of the degree of crystallization, regardless of the orientation in the sample under investigation.

On the Degree of Crystallinity in Natural Rubber. I. An Improved Method to Determine the Degree of Crystallization in Rubber

Abstract There are indications that the degree of crystallization in high polymeric substances is of importance in studying mechanical properties. With regard to the crystallization of rubber, few measurements have been made, mainly by Field. The results, however, are in contradiction to estimates of an earlier date, and therefore the necessity was felt to have them checked. An x-ray method, in some respecta differing from that of Field, was developed, the results of which diverged considerably from the figures reported by Field. The present article deals with a description of the method.