Chemical stopping

Dizziness, headache, mild gastric symptoms, and (in high concentration) semi-asphyxia and brief loss of consciousness have aU been reported. See ARGON for a discussion of simple asphyxiants. To fight fire, use CO2, water spray, or dr chemical. Stop flow of gas. 

At time 7 , use of the polluting chemical stops and substitution to the more expensive, clean chemical occurs. Sales of the substitute are constant over time at the level y where price equals the marginal cost c. The polluting chemical is banned in perpetuity. 

In the case of chemical stopping, the rate of formation of carboxylic acid endgroups is also proportional to the number of accessible reducing endgroups. The pseudo-first-order rate expression is given by ... 

The rate coefficients for chemical stopping decreased with time for both substrates in a pattern similar to that for peeling. Thus, as the accessible reducing endgroups occupied progressively more ordered regions of the structures, their reactivity toward chemical stopping also decreased. 

Further clarification of these differences is provided by comparing the relative rates of peeling and chemical stopping for the two substrates. Average values of kp/k(.g (Table IV) were calculated using Equation 3, derived by dividing Equation 1 by Equation 2. 

Table IV. Relative Rates of Peeling and Chemical Stopping Reaction...

In both the 60 and 80 C reactions, the fibrous hydrocellulose exhibited higher kpg values than the amorphous hydrocellulose (Table V). This appears to be due to the involvement of more molecules in crystalline domains of the fibrous substrate. The greater inhibition of chemical stopping by cellulose I than cellulose II domains may also have contributed to this effect by allowing more molecules in the fibrous hydrocellulose to peel to a point where the reducing endgroup would be inaccessible. 

Except for the later period of the 80°C reactions, the fibrous hydrocellulose exhibited a higher value of kpg (Table V) than k(-g (Table IV). Consequently the degradation of a majority of the molecules in the fibrous hydrocellulose was terminated by physical rather than chemical stopping processes. In contrast, chemical stopping was the dominant mechanism of stabilization in the amorphous hydrocellulose. 

Peeling is inhibited to similar extents by the crystalline order of both cellulose 1 and II allomorphs, while chemical stopping is significantly more inhibited in the cellulose I allomorph. This is consistent with the higher ratio of the rate of chemical stopping to that of peeling typically reported for mercerized cellulose in comparison to native cellulose... 

The rate of chemical stopping increases with temperature relative to peeling in both fibrous and amorphous hydrocellulose. This observation is consistent with previous findings ( )>... 

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