RESULTS 



Thermal Behavior of |NH4)2HP04 and |NK4)2S04 



An understanding of the thermal behavior of flame retardants will assist in 

 interpretation of the effects they have on the pyrolysis and combustion of cellulose. 

 A and B, page 11, show DTA and TGA thermograms of (NH4)2HP04 and (NHtt)2S0^ in an atmos- 

 phere of air. No significant change in their thermal behavior in nitrogen was found. 

 Changes in the heating rate (between 5° and 30° C. per minute) and gas flow rate (50 to 

 150 cubic centimeters per minute) caused minor shifts in the thermograms. 



The small endotherm at 166° C. in the thermogram for (NHi^) 2HP0[+ is caused by 

 decomposition and partial conversion to NHt+H2P0(+. The second endotherm at 190° C. is 

 produced by melting of the NH^H^POf^. TGA curves indicate about 13 percent weight loss 

 by 185° C. and is noted by a slight plateau. This weight loss corresponds closely to 

 loss of the first mole of NH3. A nearly linear weight loss of the remaining sample 

 (equivalent to NHt|H2P0i^) is observed up to 550° C. where the remaining sample is rapidly 

 volatilized. Weight loss following loss of the first mole NH3 indicates a complex 

 decomposition consisting of more products than simply NH3 and H3P0^ and probably accounts 

 for the difference in melting point between NHL1.H2PO4 and (NH|^)2HP04. It is likely that 

 polymerization of the phosphate occurs with formation of water: 



> 190° C. 



2H3P04 H2O + H4P2O7 



and 



H4P2O7 ^ 2H2O + P2O5 



Although the temperatures at which these reactions occur depend on sample size, con- 

 figuration, etc., the general reaction equations are in agreement with equations given 

 by Van Wazer (1958, p. 503) and Tang and Eickner (1968). 



Thermal analysis of monoammonium phosphate helped substantiate these possibilities. 

 DTA of NHt+H2P0i4 shows melting and decomposition to begin at 190° C. (A, page 11). The 

 TGA curve was identical to the TGA curve for QiWt^) 2^^^k after loss of its first mole 

 of NH3. 



In (NH4)2S04, the only endotherm occurs at 360° C. and is due to melting and de- 

 composition. The TGA curve shows initiation of weight loss near 225° C. with the rate 

 being nearly constant until 350° C. where rapid decomposition begins. The weight loss 

 at this point (20 percent) is less than necessary for loss of the two moles NH3. This 

 can be explained by the likely simultaneous decomposition of (NH4)2S04 and H2S0t^, a 

 possible initial product in addition to NH3. The absence of the peak in the DTA curve 

 near 225° C. indicates either the NH3 is weakly associated or the heat exchange at 

 this point is very small in comparison to the large endotherm at 360° C. 



Differential Thermal Analyses 



DTA thermograms for the pyrolysis of cellulose at several treatment levels of 

 ammonium phosphate and sulfate on cellulose are shown on page 12; those leading to com- 

 bustion are shown on page 13. The peak temperatures of primary endotherms and exotherms 

 for pyrolysis and combustion are given in tables 1 and 2. 



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