Guayule

The flow of natural rubber from Southeast Asia was cut off in World War II. As an emergency measure, the U.S. Department of Agriculture planted tens of thousands of acres of guayule for the Emergency Rubber Project. In all, about 8000 tons of such rubber was produced during World War II, about 6000 tons from Mexico and 2000 tons form the United States (7). Since then little has been done to increase the production of this rubber. Mexico built a small plant in 1976 in Saltillo to produce the rubber from shrubs growing wild in the area. It had two objectives to lessen dependence on imported natural rubber and to provide work in northern Mexico. In terms of production quantity, it must still be considered a pilot plant. 

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Guayule, potentially a source of natural mbber, is an unusual crop in that it has been an article of commerce in the past. Guayule grows wild in northern Mexico and the southwestern United States. When the leaves are milled in water, a latex is released that coagulates into natural mbber worms. These can easily be collected and relatively easily refined to give a product that is almost identical to the natural mbber from southeast Asia. During World War II there were several thousand acres of guayule planted in California and a small plant estabUshed to extract the mbber for military use. After the war. 

In the United States and in Mexico there has been recent renewed interest in the guayule shrub as a source of natural rubbber. Whilst this shrub could provide an indigenous source of supply to these countries the rubber is more difficult to obtain. At present it is necessary to pull up the bush, macerate it, extract the rubber with solvent and then to preeipitate it from solvent. 

Encelia farinosa (27), and rmw-cinnamic acid from guayule (Par-thenium argentatum) 5). Some chemical and biological properties of natural herbicides from Thanmosma montana are described in this... 

Yanez-Flores et al. have studied the shear properties of blends of PE with polyisoprene rubber (Guayule mbber) [50]. The blends were prepared using a cam-type mixer at 50 rpm for 10 min at 140°C. The blend compositions ranged from 10% to 70% mbber content. 

The hypothesis of Gray and Bonner (31, 32) that 3-acetyl-6-methoxybenzaldehyde, which is found in the leaves of Encelia farinosa and in the soil beneath these plants, is responsible for the suppression of other plant species has not been substantiated by Muller (33, 34). The same is true for the presumed role of trans-cinnamic acid in "soil sickness associated with guayule (Parthenium argentatum), for the amygdalin of peach roots, and for the phlorizin of apple roots or its breakdown products (35), which were thought to be associated with the "soil sickness" of orchards. 

Rubber obtained from the shrub, Parthenium argentatum, native to north central Mexico and the adjacent part of Texas. The rubber is not obtained by tapping but by harvesting the shrubs and crushing the woody tissue to separate it from the rubber. Intensive research, started in 1942, has not succeeded in making guayule competitive with Hevea rubber, and since 1962 there has been no commercial production. 

Rubber obtained from botanical sources. The bulk of natural rubber is obtained from the Hevea Brasiliensis free with small amounts from other vines, shrubs and plants mainly the Guayule shrub and the Kok-Saghyz plant. See Isoprene. 

PAN, Z., DURST, F, WERCK-REICHHART, D., GARDNER, H.W., CAMARA, B., CORNISH, K., BACKHAUS, R. A., The major protein of guayule rubber particles is a cytochrome P450. Characterization based on cDNA cloning and spectroscopic analysis of the solubilized enzyme and its reaction products, J. Bio. Chem., 1995, 270, 8487-8494. 

Synthesis and Characterization of Chlorinated Rubber from Low-Molecular-Weight Guayule... 

The chlorination of low molecular weight natural rubber from Guayule (Parthenium Argentatum Grey) has been accomplished. The structure of the chlorinated product is consistent with that of chlorinated Hevea rubber. The use of Azo-bis-isobutyronitrile was as a catalyst resulted in increased chlorine content with a concomitant reduction in molecular weight, thereby allowing the preparation of lower viscosity grades of chlorinated rubber. 

Batch No. Amount of Guayule Rubber Used, g Amount of Chlorinated Rubber Isolated, g Cl%... 

The FTIR spectra of Figure 3 comparing a commercial grade rubber (Alloprene CR-20 from ICI) with guayule CR shows the two materials to be essentially identical. Absorption bands characteristic of CR appear near 780 cm" and 736 cm" and represent the secondary C-Cl and the CI rocking... 

Figure 1 HNMR of Purified Guayule Natural Rubber...

Figure 3 FTIR Spectrum of Chlorinated Rubber (a) Guayule CR (b) Commercial CR...

The major NMR chemical shifts of guayule CR are shown in Table II the spectra are displayed in Figure 4. 

TABLE II. Characteristics of NMR Spectra of Guayule CR And Commercial Grade CR... 

Figure 6 Gel permeation Chromatograms of Chlorinated Rubber (a) Guayule CR prepared with AIBN, Ecess Chlorine (b) Guayule CR prepared with AIBN (Cl - 63.7%) (c) Commercial grade CR-5 (Cl - 64-65%)...

The DSC spectrum of guayule CR with 60% chlorine content (Table I, batch 1), is shown in Figure 7. The glass transition temperature (T ) of guayule CR is approximately lOtf C, while the T s are 12tf C and 128 C for CR-5 and CR-20 respectively. The lower Tg values for guayule CR may be due to traces of waxy materials which can act as a plasticizer and reduce the glass transition temperature. 

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