Rate of stabilization

At sufficiently low pressures, the reaction step 9.101 becomes fast relative to the rate of stabilization collisions (reverse direction of 9.100), that is, kd >> ks [M], and Eq. 9.105 becomes... 

At sufficiently low pressures, C undergoes few collisions with third bodies, so the decomposition step (reverse of reaction 9.132) and the reaction step 9.134 become fast relative to the rate of stabilization ... 

Determination of extractability of stabilizers should be a substantial part of the rating of stabilizer efficiency where leaching is a common deterioration effect or where legislation requires quantitative data dealing with extractability of stabilizers from packaging materials by food simulants. 

The rate of proton dissociation is controlled by three parameters the frequency of ion pair formation, the rate of stabilization of the proton by hydration, and the rate of escape out of the Coulomb cage. Measurements carried out in dilute salt solutions, that is, 10— lOOmM, will not be influenced by the two later steps. The activity of the water is invariable whereas the ionic atmosphere will screen the electrostatic attraction. Under such conditions, the rate of dissociation should be a direct function of the probability that the stretching covalent bond will reach the dissociation distance. As demonstrated in Figure 2, this expected correlation is observed over a wide range of pKs. Under these conditions, a reversible dissociation will comply with the relationship Kdiss = ki/k-i. As the recombination reaction for all acids is a diffusion-controlled reaction, we can approximate = k-t Kdlss — 1010 Kdiss(sec-1). 

Figure 10.44 shows that the rate of stabilizer loss corresponds to molecular weight of plasticizer. Lower molecular weight plasticizers seem to have a steeper relationship than the less volatile plasticizers. 

In the spinning process, the molecular chains are oriented by three effects flow orientation inside and outside the spinneret orifices, and orientation by deformation. For the orientation of the molecular chains that occurs in the spinneret to be effective in orienting the filament, the rate of stabilization of the filament must be greater than the reciprocal relaxation time. This requirement applies only to the surfaces and not to the interior of the filament. The orientation of the molecule within the spinneret thus has little influence on the orientation of the molecule in the finished filament. 

The conversion value ai(m), at the maximum dehydrochlorination rate of PVC, is 19-20 % for 100/0, 90/0, and 80/20 blends. With an additional increase in the CPE content, ai(m) decreases, and for the 30/70 blend it amounts to 9 %, though it is 25 % for the pure CPE. The maximum dehydrochlorination rates of stabilized PVC/CPE blends are achieved at higher conversion in comparison with unstabilized blends, with the exception of the 0/100 blend. 

This stabilization consists of slowly heating the stretched fiber to 200 -280°C in an oxygen atmosphere (usuaily air) under tension to maintain the orientation of the poiymer skeleton and stabilize the structure (Fig. 8.4). The addition of ammonia to oxygen increases the rate of stabilization.i i... 

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