Emerging Technologies for Materials and Chemicals from Biomass

Chapter 16

Polymeric Materials from Agricultural Commodities S. F. Thames and P. W. Poole

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Department of Polymer Science, University of Southern Mississippi, Hattiesburg, MS 39406-0076

The guayule shrub (Parthenium Argentatum Grey) is processed into the following five major components of potential utility as polymeric materials: (1) high molecular weight natural rubber, (2) low molecular weight natural rubber, (3) organic soluble resins, (4) water soluble extracts, and (5) bagasse. This research has emphasized the isolation, characterization, and derivation of guayule coproducts.

The entire natural rubber demands of the United States are currently met via importation. It is important, therefore that a domestic supply of natural rubber, a strategic material, be available. The current demands for natural rubber are being met via imported Hevea rubber to the extent approximating 800,000 metric tons per year. The demands for the 1990's are projected to reach 920,000 metric tons per year at an estimated cost of one dollar per pound (1). With no anticipated decline in demand and the ever present increasing conversion of rubber plantations into more profitable crops (i.e., coffee or coconut), short supply and accompanying price escalations for natural rubber are apparently inevitable. It is clear, therefore, that the factors of long term projected demands, market availability, and lack of a domestic source strongly supports the development of a U.S. natural rubber industry. Guayule as a Source Among rubber producing plants, Guayule provides high molecular weight natural rubber of high quality, with similar, if not identical properties, to those of Hevea (Malaysian rubber) (2,5). In contrast, however, guayule rubber ( G R ) is one of five fractions obtained via a selective solvent extraction process. Currently, the value and quantity of the high molecular weight rubber is insufficient to offset the costs of planting, cultivating, harvesting, and processing.

0097-6156/92/0476-0273$07.50A) © 1992 American Chemical Society

In Emerging Technologies for Materials and Chemicals from Biomass; Rowell, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

274

MATERIALS AND CHEMICALS FROM BIOMASS

Therefore, if Guayule is to become the basis of a domestic, natural rubber industry, value added products must be developed from guayule co-products.


Rubber Extraction Process Strands of guayule generally found in semi-arid regions such as Texas, Arizona, California and northern Mexico provide a promising source of natural rubber. Approximately five to twenty percent of the shrub's dry weight contains high molecular weight rubber. Low molecular weight natural rubber, guayule resin, a water soluble component, and bagasse make up the remainder of the fractions. Though the molecular structure of guayule is very similar to Hevea, the process for rubber isolation is quite different. For instance, guayule rubber is extracted from the walls of individual parenchyma cells requiring the destruction of the entire shrub (4,5,6,7). While our efforts center about the use of guayule coproducts, cost effective processing methods are necessary. These efforts are currently under investigation by Dr. John Wagner and co-workers at Texas A & M University. In particular, they have conducted research in sequential and simultaneous solvent extraction processes. Sequential Solvent Extraction (7). The sequential solvent extraction process involves two primary steps. First, polar solvent with acetone and a variety of alcohols are used to de-resinate the material, after which it is re-extracted with non-polar solvents from which the natural rubber is obtained. Flash evaporation of solvent with steam injection is necessary, with the water being removed from the rubber slurry via a combination of dewatering operations of thermal or mechanical origin. The authors do not considered this process economically favorable due to the high cost of water and solvent removal. Simultaneous Solvent Extraction (7). Simultaneous extraction is a single step process and separates resins and rubber, thereby minimizing processing time. Filtration and/or centrifugation are used to remove particulate matter, while deresination and rubber recovery are affected via the addition of polar solvent(s). The natural rubber precipitates while the resins remain in solution. The polar solvent(s) is removed to insure high quality rubber. Separation of Low Molecular Weight Rubber. The process used to isolate high molecular weight guayule rubber results in the formation of a resinous byproduct containing, among other components low molecular weight guayule rubber ( L M W G R ) . The guayule resin is dissolved in acetone and upon its removal provides a sticky, black residue. Further treatment with 90% ethanol results in precipitation of L M W G R as a solid mass, while the solvent, containing the remaining resinous material(s), is removed by décantation. * H and C N M R analysis of the rubber fraction has served as structural identification for L M W G R or poly(cis-isoprene) (8). A n alternative separation process involves the use of xylene, with subsequent rubber precipitation by addition of ethanol. This process insures the isolation of rubber of high purity, grey color and essentially no 1 3


16. THAMES & POOLE

Polymeric Materials from Agricultural Commodities

275

tackiness for which gel permeation chromatography ( G P C ) has confirmed a molecular weight of 40 to 50 thousand.


Other Constituents of the Extraction Process. The organic soluble resins remaining after extraction and isolation of L M W G R are separated into several fractions. Moreover, the water soluble resinous portion and bagasse, a woody pulp containing lignins and cellulosics, are fractions of potential utility. The extraction process provides materials useful for derivation, and thereby allows for the development of value added materials. The following sections will emphasize derivation and formulation of guayule coproducts into useful and economically important products. High Molecular Weight Guayule Rubber ( H M W G R ) The H M W G R from the guayule shrub is high quality poly(cis-isoprene) of approximately 1,000,000 molecular weight with properties equal to those of Hevea. Vulcanized H M W G R , utilized in the formation of high quality rubber products, possesses properties equal or superior to those of Hevea products. Low Molecular Weight Guayule Rubber ( L M W G R ) L M W G R does not possess mechanical properties equal to the H M W G R and thus, functional derivatives have been synthesized for application in a variety of uses. Moreover, since the traditional mastication or molecular weight reduction process used with Hevea rubber is not necessary with L M W G R , impetus is given to the development of products which otherwise require mastication. The alkene character of L M W G R affords the opportunity for chlorination, epoxidation, maleinization, cyclization, and hydrogénation. Consequently, we have employed this functionality in the synthesis of a number of derivatives and have shown that they can be utilized in surface coating formulations and in crosslinking reactions. Characterization of L M W G R . L M W G R can be characterized by several methods; among them are N M R , IR, and G P C . *H and C N M R spectra are shown in Figure 1. L M W G R typically contains wax and other hydrocarbons and must be purified before derivation. Purification can be monitored by *H spectroscopy with the peak assignments in Figure 1 used to document purity (S): 1 3

1.67 ppm 2.00 ppm 5.12 ppm

(cis double bond methyl protons) (methylene protons) (vinyl proton)

The small peak at 1.25 ppm is characteristic of an impurity that can be removed by additional precipitation from an ethanolic solution (S). The assignments are in excellent agreement to literature values for Hevea as is the infrared spectrum (Figure 2).



276


ΤΓ-ι—ι—ι 9.0

8.0

ι ι ι ι 7.0

6.0

ι—ι—ι—ι—;—I—ι—I—ι—Γ—«—Γ*" 5.0

4.0

3.0

2.0

1.0

0.0

ΡΡΜ

b

I

Figure 1. (a) Ή N M R spectrum of L M W G R , (b) LMWGR.

1 3

C N M R spectrum of


Polymeric Materials from Agricultural Commodities 277


16. THAMES & POOLE

33NVQU0S8V


278


In summary, low molecular weight G R of high purity can be readily isolated and avoids the mastication process required with Hevea rubber. Chlorination of L M W G R . Hevea rubber has been successfully chlorinated (9) and yields a product useful as a result of its chemical resistance and increased adhesion due to its polar nature. It was therefore of interest to determine the efficacy of chlorinating unmasticated L M W G R . The reaction of chlorine with L M W G R produces a fine white powder recoverable by steam distillation of the inert reaction solvent, carbon tetrachloride( Figure 3)(70). The empirical formula for chlorinated natural rubber is ΰ Η α , suggesting more than one isoprene unit reacts (Figure 4) (11) to form a soluble, cyclized product, rather than one of a high crosslink density (Figure 5) (10). Azo-bis-isobutyronitrile (AIBN) and L M W G R produces grades of chlorinated rubber lower in viscosity than that from Hevea rubber (Table I). It is significant that more than two pounds of chlorinated product is produced from one pound of L M W G R , a result of the addition of chlorine. The higher market value of chlorinated- in comparison to natural-rubber clearly establishes chlorinated L M W G R as a value added coproduct for the emerging domestic Guayule industry. Product yields of chlorinated guayule rubber, using A I B N as a catalyst, have approached the literature cited theoretical chlorine contents of 64.7% (S).


5

8

3 3 >

Experimental (S). A dilute solution (5-10%) of L M W G R in carbon tetrachloride is placed in a three neck round bottomed flask equipped with a condenser, gas dispersion tube, and adaptor. A chlorine cylinder is fitted with two gas traps and connected to the reaction flask with Teflon tubing that is changed periodically for safety purposes. Ice-cooled traps of 2 Ν sodium hydroxide solution are used to collect any residual chlorine and/or hydrogen chloride. Oxygen is purged from the reaction vessel via nitrogen at the outset of the reaction and is maintained as a continuous nitrogen blanket for the duration of the experiment. The solution is allowed to reflux at 79°C with stirring. The addition of ethanol provides chlorinated rubber in the form of a fine, white precipitate. Characterization of the Chlorinated Guayule Rubber (CR) (8). *H N M R and C N M R spectra of chlorinated L M W G R were obtained on a 300 M h z Bruker fourier transform spectrometer. The spectra were prepared in CDC1 and tetramethylsilane was used as an internal standard. Major C N M R chemical shifts of L M W G R chlorinated rubber agree with literature values (Table II)(Figure 6). Fourier transform infrared spectroscopy (FT!R)(Figure 7) is likewise consistent with the N M R data. G e l permeation chromatography ( G P C ) was performed on a Waters Associates, Inc. G P C equipped with a refractive index detector. Operating conditions were: mobile phase, T H F ; flow rate, 1 ml/min; columns ΙΟ , 10 ,500 ,100 E. Calibration curves were obtained from polystyrene standards. Figures 8 and 9 show relative elution times and volumes as compared to commercially available chlorinated rubber products. 1 3

3

1 3

6


4

16. THAMES & POOLE


279

CH CH

C = C H

CI — C I

CH

2

2


CHLORINATED GUAYULE RUBBER Figure 3. Reaction of L M W G R with chlorine gas.

CH

CH« ο

C

^

CH

2

\' C =

Cl CH

2

->

CH ^ 2

CHU CH / CI

^CHg

CHg^^

C I CH

3

CHg^ CHg-^

CH—C C* I I CH CHo / \ / Cl CH2

2

3

CH—C I CH CI

C'^CH CH

C I CHo \ / * CH

CH

•

C, II CH CH

2

Figure 4. Mechanism of the chlorination of L M W G R .

CI

CI \

CH — CH

/ CI-C-CHo \ — CH — C / \ CI CI 3

/

\ CH-CI / C—CH — I \ CH CI 3

Figure 5. Final proposed structure of chlorinated L M W G R .


280


Table I Experimental Conditions Used in the Synthesis of Chlorinated Guayule Rubber


Batch No.

Amount Guayule Used, grams

1"

3.20

6.00

b

5.00

11.80

C

5.00

13.14

2 3

a

Amount of Chlorinated Rubber Isolated, grams

C C l , 200 ml C C l , 100 ml CCl4, 100 ml and 37.5 mg of AIBN 4

b

4

c

Table II Characteristic Shifts of Guayule Chlorinated Rubber and Commerical CR Guayule CR, ppm

Literature value.ppm

21.5, 28.7, 34.7,

21.5, 28, 34.7,37.4

37.6

Assignment

215,38,37.4

CH* CH

45.4,48.01

45.4,48

-CH -C1

62.25,6437

62-64

=CHC1

75.1,77.18

74-77

2

=CC1


3



16. THAMES & POOLE


281

282



Wavelength (μπΟ

4000

3600

3200

2600

2400

2000

1600

1200

800

Wave numb ers Figure 7. FTTR spectra: (a) guayule chlorinated rubber, (b) commercial chlorinated rubber.

Elution Volume 8

1

r

16

24

1 32

I 4 0

Figure 8. G e l permeation chromatograms: (a) guayule C R , (b) commercial CR.


Polymeric MaterialsfromAgricultural Commoditie


16. THAMES & POOLE


284



Thermal analyses were performed on a Dupont Model 9900 thermal analyzer in a nitrogen atmosphere. The lower transitions for guayule C R are likely a result of the presence of trace amounts of waxy materials acting as plasticizers. The glass transition temperature (Tg) of the chlorinated rubber of Figure 10. Utility of Guayule Chlorinated Rubber (CR). Chlorinated rubber is typically employed in applications where chemical resistance and adhesion are important, i.e., marine paints, floor finishes, pool paints, and clear coatings. Accordingly, we have shown that guayule C R is equal or superior to commercial grades of chlorinated Hevea natural rubber (Tables ΙΠ and I V ) . In all cases, paints prepared with chlorinated G R were comparable in performance to those containing Hevea chlorinated rubber or Alloprene. The clear, non-pigmented coating contained only C R dissolved in toluene. It is noteworthy that the clear coat derived from guayule chlorinated rubber showed higher impact resistance than the Alloprene clear coat; indicating that chlorinated G R provides a superior combination of flexibility and adhesion. In summary, L M W G R can be successfully chlorinated to obtain coating grade C R . Elemental analysis and other characterization techniques confirm that the chemical structure of the material is equivalent to that of commercial grades. The use of A I B N lowers the apparent molecular weight and allows the formation of lower viscosity grades of C R . The Epoxidation of L M W G R Oxirane rings are formed by the reaction of olefinic bonds with peracids, a reaction commonly known as the "Prilezhaev reaction" (12). Reactions of this type utilize a variety of peracids such as metachloroperbenzoic acid, 3,5 dinitroperbenzoic acid (13) and trifluoroperacetic acid (14). The generally accepted mechanism of epoxidation (15,16) is shown (Figure 11) with the epoxidation typically being conducted in a solvent of low ionization potential (i.e., Benzene). In our case, the reaction was conducted in the less toxic hydrocarbon, toluene. The reaction rate is rapid and the product easy to separate, yet care must be taken to insure that no crosslinking occurs in the system. The epoxidation of L M W G R provides a functional natural rubber derivative with potential utility in the coatings, adhesives and elastomers industries. A commercial epoxidized Hevea rubber is available in the form of ENR-50 (available from Guthrie Latex, Inc., Arizona). Thus, it was of interest to determine the feasibility of producing and evaluating epoxidized L M W G R . Experimental. Initially two products have been synthesized: a 50 mole percent epoxidized rubber and a 25 mole percent epoxidized rubber. This is accomplished by preparing a 5% solution of L M W G R in toluene. The solution, in a three neck round bottomed flask, is cooled in an ice bath to reduce unwanted side reactions (11). After addition of molar amounts of sodium carbonate, to consume the side product m-chlorobenzoic acid, the reaction is allowed to equilibrate with stirring after which m-chloroperbenzoic acid is slowly added to the reaction vessel. The product is precipitated into ethanol and washed with water to remove the benzoic acid salt. Purified by recrystallization from ethanol gives a grey, non-tacky, rubber like product.



THAMES & POOLE


Table III Guayule C R Formulated Marine Coating

MATERIALS

AMOUNT (grams)

Grind: Alloprene R20 Chlorafin 40 Chlorowax 70 Epi-Rez 510 Ti-Pure R-960 Zinc Oxide International 3 X Mica, 325-mesh Xylene

28.6 143 7.1 0.425 5.0 6.4 12.6 13.4 50.0

Letdown: Epi-Rez 510 Xylene

0.425 50.0


286


Table IV Comparative Impact Resistance Tests

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REVERSE IMPACT (in-lbs)

DIRECT IMPACT (in-lbs)

Guayule Marine Alloprene Marine Guayule Clear Alloprene Clear Guayule Floor Alloprene Floor

ADHESION

160+ 160+ 10 .L i 41U ^4ϋ iU M. ~

£ ;£ ϋ JyJ £ £ j£ jj; i i 2£

8*

2sE


CARBON.001 DATE B-9-90 SF 75.469 BY 75.0 01 B053.594 SI 16384 TO 16384 SM 22727.273 HZ/PT 2.774 PH R0 AQ R6 NS TE

5.0 2.000 .360 20 185 302

FN 28500 02 6100.000 DP 12L BB LB 2.700 6B 0.0 CX 15.00 CY 10.00 Fl 200.0IBP F2 -4.B63P HZ/CM 1.031E3 PPN/CN 13.665 BR 596.21

1B0

160

140

Figure 13.

120 1 3

100 PPM

BO

60

40

20

C N M R spectrum of E G R .


289



290


16. THAMES & POOLE



0.20-1

C H'3 .

H

\ c=c/ etc.

AW

CHg

CH

2

/WV

etc. Ο

GUAYULE RUBBER

HC

CH

C

C °

Ο

MALEIC ANHYDRIDE

GUAYULE RUBBER - MALEIC ANHYDRIDE GRAFT CO-POLYMER Figure 16. Maleination conditions of G R . In Emerging Technologies for Materials and Chemicals from Biomass; Rowell, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

291

292

MATERIALS AND CHEMICALS FROM BIOMASS CH3

ι

GR — C =

CH

GR +

MALEIC ANHYDRIDE

>

I GR — C

CH

GR

HC = C H


C D

C 0

Ο

MALEIC ANHYDRIDE GRAFTED LMW GUAYULE RUBBER Figure 17. Maleination mechanism of G R .

range of applications including their use as high performance coatings with outstanding adhesion, low shrinkage during cure and excellent chemical resistance. Thus, high performance, yet strippable coatings were prepared. Great latitude in coating formulations is provided by flexibility of cure temperatures including ambient to elevated conditions (27). Thus, epoxides are an excellent polymer type for physical property modification. Formulating Conditions. Formulations of epoxy strippable coatings include E P O N 828, the diglycidyl ether of Bisphenol A from the Shell Chemical Company, and guayule resin dissolved in a solvent mixture of n-butanol and xylene to which Jeffamine D-400, a diamine product of the Texaco Chemical Company, has been added. A flow control agent, Byk-341 supplied by BykChemie U S A , is added with subsequent filtration through glass wool to remove traces of insoluble materials. The films were cast on several substrates such as pretreated steel, phosphatized steel, cold rolled steel, and aluminum in order to test its adhesion to a wide variety of substrates. Coatings were cured at 150°C for 3h in an air forced oven. Table V shows typical coating formulations. Characterization of Films. D S C measurements were used to determine Tg of the films, with the plasticization providing a marked decrease in the glass transitions (Figure 18). The decrease in Tg for guayule resin containing formulations is consistent with the plasticization by the addition of guayule O S R . In the case of guayule O S R modified epoxy coatings, surface treatment of panels improves adhesion to the substrate. In contrast, epoxy resin control coatings do not show noticeable changes in film performance, regardless of whether the coated panels are treated or untreated. For untreated panels, such


16. THAMES & POOLE


293

Table V Formulation of Guayule Modified Epoxy Coatings


Epon-Amine/Guayule resin (wt/wt) 90/10

80/20

(g)

(g)

(g)

10.00

10.00

10.00

10.00

6.185

6.185

6.185

6.185

100/0

95/5

(g) Epon828 (Epoxy ether resin) Polyoxy propylene amine (Jeffamine D-400) Guayule resin (Firestone facility)

:

—

0.855

1.798

4.050

Solvent Mixture (n-Butanol-xylene, 50/50)

:

6.890

7300

7.710

8.670

Byk - 341 (Byk Chemie)

:

0.180

0.180

0.180

0.180

as cold rolled steel, guayule O S R acts as an effective surface modifier rendering epoxy systems strippable (see Table VI). This characteristic of Guayule O S R and epoxy resins is a unique application for the O S R extracts and offers significant potential for commercialization. The modification with guayule O S R provides a viable and economically feasible approach to formulate strippable epoxy coatings for use in harsh environments (27). Impact resistance was determined (Table VI) and found to remain quite acceptable with the incorporation of guayule resin modification. Tensile and elongation properties were likewise ascertained to determine the extent of change on physical properties by guayule resin modification (Table VII). The Efficacy of Guayule O S R as a Pesticide. The United States armed forces employ the use of large quantities of treated wood in marine and terrestrial environments with the annual cost of repair and replacement of these products amounting to approximately 25 million dollars (28,29). Consequently, guayule O S R is currently under evaluation as a wood protectant against termites, fungi and marine borers such as barnacles (29). Guayule O S R treated pine, exposed to termites for 33 to 44 months in the Panamanian rain forest at Chiva, shows no damage. However, the resin did not act as a repellant since the termites tube over it in order to reach the control baitwood. It is felt that since guayule resin is active against wood fungi, a


294



C o n t r o l - 3 8 * C (Tg)


16. THAMES & POOLE


295

Table VI Film Properties of Guayule Modified Epoxy Coatings on Non-Treated Panels * **


Substrate

Cold Rolled Steel Panels Untreated Aluminum Panels

Solvent

Xylene/Butanol 50/10 (wt/wt)

Cure Cycle

12^C/3 h

Flow Control Agent

Byk 341 (Byk Chemie) 80/20

100

95/5

90/10

Thickness (mils)

1.5

1.5

1.5

1.5

Pencil Hardness

H H

2B 2B

2B 2B

2B 2B

Epoxy-Amine Guayule (wt/wt)

Film came off after 30 mins.

Resistance to boiling water Impact Resistance (in. -lbs) Direct

150 60

- film released at 5

Reverse

150 60

- film released at 5 -

* Cold Rolled Steel Panels ** Untreated Aluminum Panels

Table VII Tensile Properties of Guayule Modified Epoxy Films* Epoxy-Amine/Guayulc (wt/wt):

100

95/5

90/10

Tensile Strength (MPa)

4137

40.00

39.29

% Elongation At Break

3.5

3.6

4,000

•Substrate:

Cold Rolled Steel Panels


296



condition required for termite activity, the wood resists termitic attack yet does not act as a termite repellant. Furthermore, the exposed samples do not show weathering patterns characteristic of heavy rainfalls (29). The majority of Guayule O S R treated wood, exposed to the marine environments of l i m o n Bay in Panama, remains unattacked after 45 months of exposure. This phenomenon appears to be guayule resin concentration dependent, as the wood most highly impregnated with O S R shows increased resistance to attack. The wood specimens have become lighter in color and some surface leaching of the resin has occurred. A l l untreated wood panels, however, were heavily damaged. Work is underway to identify the exact components of the resin responsible for this wood protective activity. Water Soluble Resins The processing fraction remaining the least explored is the water soluble portion. Fractionation of the water soluble materials is accomplished by membrane separation technology. Dr. Wagner and co-workers at Texas A & M are currently performing separation and characterization of fraction components. Characterization techniques include N M R , IR, DSC, and G P C . Bagasse Guayule bagasse (GB) has been mentioned as a potential fuel feedstock, a cellulosic provider, and a source of fermentable sugars or fibers. Direct combustion of G B gives a fuel value of 18,200 kJ/kg or 7,838 Btu/lb (30). It has been reported that a gas containing olefins, hydrogen and carbon monoxide can be formed when G B is passed into a fluidized bed gasification system (31). Various G B cellulosic derivatives have been prepared; these include but are not limited to cellulose acetates, cellulose nitrates and regenerated cellulosics (rayon). Pulping and bleaching of G B are necessary prior to derivation. The authors utilized contemporary wood pulping processes and therefore concluded that the process was efficient for GB(32). Pulping. Iignin and other non-cellulosics must be removed from the G B i n order to purify the cellulosics for subsequent use. A convenient laboratory method involves the Kraft pulping process carried out in a Parr reaction vessel allowing mild reaction conditions so as to protect the cellulose from degradation. After pulping, the G B is separated by filtration and squeezed with a hand press to remove all pulping liquor. Water and acetone washes are then performed until a Ph of 7 1 1 is reached with subsequent air drying to insure complete removal of residual acetone. The pulping liquor contains tall oil and sulfate turpentine that offer other potential uses (32). Bleaching. The bleaching process removes lignins and colored matter without adversely affecting the cellulose. Sodium hypochlorite is employed as the bleaching reactant while the reaction mass is monitored for Ph. Upon completion of bleaching, the product is washed with acetone and air dried to insure high purity and high yield (32).


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Polymeric Materiah from Agricultural Commodities

297

Cellulose Acetate. Acetylation is performed on pulped, bleached G B . Glacial acetic acid, acetic anhydride and concentrated sulfuric acid (catalyst) make up the acetylating solution. After 20h in solution, the remaining solids are removed via filtration and centrifugation. The filtrate is poured into distilled water whereupon a white gelatinous material, cellulose acetate, immediately forms. The infrared spectrum of this product is essentially identical to that of cotton cellulose acetate. Cellulose acetates are used in lacquers, plastics, safety film, and fabrics, and therefore, provide attractive product areas for the guayule industry (32).


Summary Ongoing research and development efforts on guayule are focused to provide a better understanding of the numerous guayule components, their chemistry and ultimately, their commercialization. The success of developing value added products from guayule components will dictate the fate of guayule as a domestic source of natural rubber. By isolating, identifying and utilizing the majority of guayule's processing fractions a domestic, natural rubber industry is likely to become a reality. Acknowledgements We acknowledge the continuous support and helpful comments of Dr. Daniel Kugler of the U S D A Office of Agricultural Materials and M r . George J. Donovan of the Department of Defense. Literature Cited 1.

2.

3. 4. 5. 6. 7. 8.

9.

Bragg, D . M . ; Lamb, C. W., Jr. The Market for Guayule Rubber; Center for Strategic Technology, Texas Engineering Experiment Station, Texas A & M University: College Station, T X , 1980. Hammond, B . L . ; Polhamus, L . G . Research on Guayule (Parthenium Argentatum Grey): 1942-1959; U.S.D.A. Agr. Res. Ser. Tech. Bill. No. 1327, U . S. Dept. of Agriculture: Washington, D C , 1965; p. 143. Backhaus, R . Α.; Nakayama, F. S. Rubber Chem. and Tech. 1986, 61, 78-85. Guayule: An Alternative Source of Natural Rubber; National Academy of Science, 1977. Hager, T. Α.; et al. Rubber Chem. and Tech. 1979, 52, 693. Soltes; et al. Report on N S F Grant No. P F R 78-12713; Texas A & M Univ.; College Station, T X , 1979; pp 77-99. Wagner J . P.; et al. Presentation to Fourth Int. Conf. on Guayule Research and Development, Tucson, A Z . Thames S. F.; Kaleem, K . In Agricultural and Synthetic Polymers; Glass, Edward; Swift, Graham, Eds.; A C S Symposium Series; A C S : Washington, D C , 1990; pp 230-241. Bloomfield, G . F. J. Chem Soc. 1943, 289.



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