FL-\MUABILITY OF HERBICIDE-TREATED GUAVA FOLIAGE 



C. W. Philpot and R. IV. Mutch 



Fire is one of the most economical and effective means of clearing land. Tropical 

 forests are difficult to burn, due to the adverse environment, rapid decomposition of 

 dead fuel, and high moisture content of the vegetation. Herbicide treatments to kill 

 the trees and provide a more flammable fuel continuum have been suggested. Such treat- 

 ment will lower the moisture content of the leaves, add to the surface fuels if 

 abscission occurs, and possibly change the chemical composition of the plant material. 

 Ive have determined some of the chemical changes and changes in flammability of guava 

 leaves (Psidium guaj ava L.) treated with 2,4-D and 2,4,5-T in Puerto Rico. 



The major components of natural fuel are cellulose, usually amounting to 40-45 

 percent by weight, lignin, 30 percent, and hemicelluloses , 25 percent. Lignin does not 

 undergo pyrolysis below 400° C. Above this temperature the reaction is quite slow(6).^ 

 Therefore, lignin is probably not very important from a pyrolytic standpoint although it 

 contributes to the glowing reaction. Cellulose makes up approximately 65 percent of 

 the lignin-free fuel, and its pyrolytic mechanisms should have great influence on the 

 way the fuel burns. 



The pyrolysis of cellulose can be represented as taking place along two pathways 

 (4). The low temperature pathway leads to CO, CO2, H2O, char, and the glowing reaction. 

 The high-temperature pathway leads to about 30 volatiles and the flaming reaction (5). 

 Treatment of cellulose with inorganic contaminants favors the low temperature pathway 

 and a reduction in flammable volatile production^ (2, 3). Therefore, inorganic compo- 

 sitional changes in natural fuels could affect pyrolytic and combustion characteristics. 



In addition to the above-mentioned pyrolytic compounds, nonpyrolytic compounds also 

 exist in natural fuels. These include terpenes, resins, oils, and waxes; they can be 

 quantified by extractive content. The heat content of these extractives is about 8,000 

 cal./g. as compared to the fuel, which has approximately 4,400 cal./g. The majority of 

 these compounds volatilize at temperatures considerably lower than 200° C. Variations 

 in extractives should lead to variations in rate of energy release during burning and 

 possibly to changes in rate of spread. 



We measured the ash content, ether extractives, and higli heat content of treated 

 and untreated guava leaves. The fuels were then subjected to thermogravimetric 

 analysis (TGA) , differential thermal analysis (DTA) , and small-scale burning tests. 

 This presents the results of these tests. 



Methods 



The guava was sprayed with a mixture of 12.5 lbs. acid equivalent of 2,4-D and 

 12.8 lbs. acid equivalent of 2,4,5-T per acre. This was applied as 3 gal. herbicide 

 plus 7 gal. diesel oil per acre. Samples of treated dead leaves, untreated dead leaves, 

 and living foliage (designated in this paper "treated," "dead," and "green," respec- 

 tively) were collected in Puerto Rico, air-dried, and shipped to the Northern Forest 

 Fire Laboratory, Missoula, Montana. 



Numbers in parentheses refer to Literature Cited. 

 ^Shafizadeh, F. Pyrolysis and combustion of cellulosic materials. Advances in Carbohydrate 

 Chemistry 23: 419-474, 1969. (In press.) 



