Discussion 



Differential thermal (DTA) , thermogravimetric (TGA) , and derivative thermogravi- 

 metric (DTG) methods of analyses show significant differences in the effects ammonium 

 sulfate and ammonium phosphate have on the degradation of cellulose in either nitrogen 

 or air atmosphere. Some of the general effects and the differences can be summarized: 



1. Both ammonium sulfate and ammonium phosphate lower the threshold temperature 

 and activation energy required to initiate cellulose decomposition in nitrogen and air. 



2. Increasing the amount of either retardant chemical decreases the maximum weight 

 loss rate occurring during decomposition until the temperature of the peak nears 250° C. 

 An increase in the amount of either retardant beyond the concentration required to ob- 

 tain a maximum rate at 250° C. causes an increase in the peak rate without shifting its 

 temperature. Any additional increase further reduces the maximum weight loss rate. 



3. Increasing retardant chemical causes an increase in the residue or char 

 production. 



4. Ammonium phosphate is more effective in increasing char production in an air 

 atmosphere than is ammonium sulfate. 



5. Uliile a 2-percent treatment of ammonium sulfate causes a shift to near 250° C. 

 in the maximum decomposition rate, five times this quantity of ammonium phosphate (on 



a molar fraction basis) is required to produce the same effect, indicating a sizable 

 difference in the action of the two chemicals on cellulose. 



It is theorized that the differences ammonium sulfate and phosphate have on cellu- 

 lose pyrolysis and combustion are either due to the availability of the inorganic frac- 

 tion involved in the reaction or to a different mechanism by which these chemicals alter 

 pyrolysis and combustion. 



1. Such theorizing is based on the fact that ammonium sulfate decomposes at a low- 

 er temperature than ammonium phosphate and may not be available in similar concentrations 

 or at the necessary time. For instance, ammonium sulfate is completely decomposed by 

 420° C, a temperature which may preclude glowing combustion reactions. This is borne 

 out by the fact that ammonium sulfate treated cellulose produces less residue at 450° 



C. than does ammonium phosphate. 



2. Major shifts in cellulose decomposition occurred prior to losses of significant 

 amounts of the sulfate or phosphate portion of the compound. Because the molecular weight 

 is the same for both compounds (132.05 and 132.14 for (NHi+)2HP04 and (NH(^)2S0tj, respec- 

 tively), the treatments can be considered as being on a molar basis. Thus, provided 



the difference in NH3 production rates is not responsible for the difference (equal 

 total amounts of NH3 are produced by both compounds) it is likely there is a difference 

 in the mechanism by which these compounds alter both pyrolysis and combustion. It is 

 unlikely that NH3 is important in the process since (NHlj)2HP0^ and NH^HgPOi^ have the 

 same effect on pyrolysis and combustion when the comparison is made on an equivalent 

 PO1+ basis. This is also supported by the fact empirical fire tests have shown H3PO1+ 

 as well as (NHlj)2HP0^ and NHLjH2P0tj to be equally effective when compared on an equiv- 

 alent PO1+ basis. 



It is possible that the differences in the effects of (NHi^)2S0i^ and (NHi+)2HP0it can 

 be attributed to both theorized causes previously mentioned. A different mechanism by 

 which pyrolysis and combustion are altered may exist at lower temperatures for the com- 

 pounds while the difference in high temperature availability of a portion of the com- 

 pound may affect glowing combustion, and thus residue, differently. 



9 



