icaii 



THE INDIA RUBBER WORLD 



"09 



Experiments \\ ith a New Cactus Rubber. 



By Emmet S. Loiii;. 



IT HAS RECENTLY bccii the writer's privilege to experiment with 

 ■A gum extracted Irom the American cactus and the resuhs 



have so far been so entirely satisfactory that the subject should 

 undoubtedly be of interest to every one connected with the rubber 

 industry. The war has certainly disclosed the necessity, or at 

 least the desirability, of producing on as large a scale as possible 

 a portion at least of the rubber require- 

 ments of this country and for this rea- 

 son, as well as for the economic better- 

 ment of the rubber industrj- itself, there 

 has resulted considerable activity in the 

 investigation of this important question. 



Several j'ears ago the writer had occa- 

 sion to do considerable experimenting 

 with the extraction and compounding 

 with rubber of a gum derived from the 

 Ocotillo plant, more particularly for the 

 purpose of obtaining a gum which 

 would replace guayule. This plant 

 ranges from five to twenty-five feet in 

 height, growing extensively in certain 

 parts of Arizona and California. The 

 results were satisfactory to a certain 

 extent, but due to the solvent-distilla- 

 tion method of extraction employed, the 

 gum contained a large percentage of 

 resins which seriously affected the cure 

 when used in large percentages in the 

 compound. Later the destructive-dis- 

 tillation process with subsequent refin- 

 ing was evolved with the assistance of 

 government chemists, and it is reported 

 that a much superior product is now 

 being produced in large quantities at the 

 large plant in Arizona. 



The cactus gum mentioned at the be- 

 ginning of this article is found in pay- 

 ing quantities in two different varieties 



of cactus, one the spineless, or cultivated cactus developed by 

 Burbank and the other the prickly pear or wild species. Spineless 

 cactus has been raised in many parts of Southern California as 

 food for cattle. It was soon learned, however, that many cattle 

 died, probably as a result of the insoluble gum content. The 

 plant consists of a number of lobes somewhat similar in shape to 

 an inverted hot water bottle, each lobe projecting outward and 

 upward from the edge of the one underneath, the number of 

 lobes depending upon the age of the plant. It is easily propa- 

 gated by breaking off these lobes and planting them in the ground. 

 The plant is very hardy and has the advantage of being easily 

 cultivated upon practically worthless soil or in localities where 

 the rainfall is very slight. 



Prickly pear or Opuntia zmlgaris grows extensively in many 

 parts of Arizona, California, Nevada and other tropical parts of 

 the United States. It is somewhat similar in structure to the 

 spineless cactus, but is covered with long, sharp needles. It bears 

 an edible fruit of a purplish color also covered with spines. Like 

 the spineless, it is very easily propagated and attains a height 

 of seven or nine feet. Unlike Ocotillo and many other gum- 

 bearing plants, the rubber in these two varieties of cactus occurs 

 as a latex and >'ields a sticky, white liquid from the abraded 

 surface if pressure be applied by the fingers. By special treatment 

 nf the latex and subsequent refining, an amber colored gum re- 

 sembling smoked sheet in color and guayule in physical properties 



is obtained, although tlie gum when thoroughly dried is consider- 

 ably less plastic than guayule. It is reported that the gum can 

 be produced at a price to compete favorably wHth guayule and 

 crude rubber. 



Following is a summary of some of the experiments made 

 with gum from the spineless cactus : 



Smoked sheet 

 'actus rubber 



Sample 1. 



rubbe 



Per Cent. 

 .. 50 



ngredients) 10 



This compound was mixed upon the 

 mill in the usual manner and contained 

 only the amount of sulphur usually re- 

 quired to vulcanize a stock having 90 

 per cent smoked sheet. It mixed easily 

 on the rolls at a much lower tempera- 

 ture than that which would have been 

 required for pure smoked sheet. The 

 next day test strips were cured in the 

 press and were found to have high ten- 

 sile strength and elasticity, showing that 

 the gum vulcanizes perfectly in about 

 the same length of time required for 

 plantation rubbers. Another portion 

 was used to friction a sample of belting 

 duck which was found upon examina- 

 tion to be thoroughly impregnated with 

 the gum A very tack-y cement was 

 made from the remaining portion by 

 dissohing in benzol. 



Sample : 



Smoked sheet 

 \uto reclaim , 

 Cactus rubber 

 Compound 



In spite of the fact that this stock ' 

 was mixed on a relatively cold mill, it 

 retained a sticky surface after calendering and showed no ten- 

 dency to bloom in the raw state. It would seem from this that 

 the use of the gum in repair stocks and especially in those contain- 

 ing large amounts of carbon black would be advantageous, due to 

 the necessity of preserving a tacky surface indefinitely, and the 

 lower temperature at which the stock conld be milled would 

 minimize the danger of burning when use is made of certain 

 organic accelerators. Part of Sample 2 was used to skim-coat 

 and cover the fabric mentioned above, which was then made into 

 a piece of belting. 



Sample 3. 



Per Cent. 



Smoked sheet . 

 Cactus rubber 



It was the object of this mixture to estimate the value of the 

 gum in a cheaper compound containing a larger percentage oi 

 minerals. No difficulty was encountered in milling and the stock 

 was made into various kinds of articles of comparatively good 

 quality. 



Samf 



Cactus rubber 

 declaimed . . 

 Compound 



Cent. 



regular heel compound in which 10 percent smoked 



