A major difference in thermograms for the pyrolysis of the two cellulose treatments 

 is indicated. As (NHt+)2HP04 is added to cellulose and pyrolyzed in nitrogen (page 12), 

 the strong endotherm at 364° C. in untreated cellulose gradually shifts to lower temper- 

 atures. However, as the (NHi4)2SO^ concentration is increased to 0.50 percent, a new 

 endotherm appears near 250° C; this endotherm dominates the DTA curves at higher con- 

 centrations. The endotherm near 210° C. for (NHit)2HP0i^ treatments of cellulose greater 

 than 4.00 percent is attributed to the inorganic fraction. Monoammonium phosphate 

 NHl,H2P0l,, which could be formed as the sample was dried, has an endotherm near 210° C. 

 (A, page 11). An endotherm due to the presence of (NH4) 2SOL, is not readily discernible. 



The DTA thermograms for combustion in air (page 13) of both (NHi+)2HP0^ and (NHl,)2S0i+ 

 treated cellulose are dominated by a strong exotherm from about 300° to 450° C. The 

 endotherm near 250° C. for (NH^)2S0i^ treated samples is apparent at a concentration of 

 0.70 percent, and above, but is small compared to the latter exotherm. A prominent 

 difference between the effects of the two chemicals on the combustion of cellulose is 

 that (NHL^)2S0t+ causes a larger exotherm (note the difference in the AT scale used, pages 

 12 and 13) . 



Thermogravimetric and Derivative Thermogravimetric Analyses 



The cellulose samples, treated with (NHi4)2HP0i+ and (NH^)2S0i^ in concentrations from 

 to 25 percent by weight were investigated for thermal behavior in air and nitrogen 

 by TGA and DTG . After initial water loss and setting of sample weight to 100 percent, 

 the TGA curves are horizontal until pyrolysis (pages 14, 15) and combustion (pages 16,17) 

 begin. As the chemical percent is increased, there is a lowering of the pyrolysis 

 and combustion threshold temperature. The threshold temperature was determined using 

 the DTG curves and arbitrarily denoted as the temperature required to produce a weight 

 loss rate of 0.09 milligram per minute (< 1 percent of the maximum weight loss rate). 

 Table 3 shows the effect of amount of (NHlj)2HP0^ and (NH^)2S0i+ on the threshold tempera- 

 ture for pyrolysis and combustion. The slight difference (8° C.) in the threshold 

 temperatures for untreated cellulose in nitrogen and air is probably due to the dif- 

 ference in procedures for obtaining the environmental temperature in nitrogen and air. 

 The lowering of threshold temperatures for treated fuels in air and nitrogen is also 

 accompanied by a lowering of the temperature at which the maximum weight loss or reac- 

 tion rate is observed. The temperature of the maximum weight loss was equally useful 

 in comparing the effect of the different chemical concentrations. 



Although the trends in TGA curves appear very similar for both chemicals, the DTG 

 curves (pages 18, 19, 20, 21) which were run simultaneously with TGA, were much more 

 sensitive to small differences in weight loss rates. These DTG curves, as well as the 

 TGA curves, were very reproducible. In both air and nitrogen, the DTG curves show 

 (NHi+)2SCi+ treatment causes a rate of weight loss peak at about 250° C. In nitrogen, 

 treatments as low as 0.500 percent cause this peak; in air, 1.00-percent treatments 

 have the same effect. The curves for (NH4)2HP04 show a much more gradual shift of the 

 peak to lower temperatures, with a peak at 250° C. developing only with high (greater 

 than 10.0 percent) concentrations of chemical. Tables 4, 5, 6, and 7 give data for the 

 rate of weight loss for peaks in the DTG curves and the temperature at which those 

 peaks occur. Although numerical data are useful for comparison purposes, viewing the 

 entire DTG thermograms (pages 18-21) provides a better picture of reaction differences. 



The rate was normalized to correct for decreasing initial cellulose weights with 

 increasing chemical treatment. The normalized rate was determined by: 



, . , Actual peak rate (mg. per minute) 



Normalized peak rate (mg . per minute) = ■= —r—^ — ~ rr. — r— ^ — £ 



^ V t. r Fraction of cellulose in sample 



5 



