Kinetics of dehydrochlorination of polyvinylchloride in the presence of some stabilizers

228

K.S. Mr~SK~R and V. P. ]VrAT.rNSKAYA

(2) The a d d i t i o n of OG-20 reduced the particle dimensions of the dispersions a n d h a d an irregular effect on the e l e c t r o - c o n d u c t a n c e a n d the viscosity. (3) The r e l a x a t i o n processes were tastest during t h e r m o s e t t i n g of the SC; it v e r y m u c h shortened the time of f o r m a t i o n a n d gave rise to a material with stable physical-mechanical properties. (4) H i g h mechanical s t r e n g t h and d e f o r m a t i o n properties a t relatively small a-values were o b t a i n e d w h e n the p o l y u r e t h a n e h a d a n o p t i m a l s u r f a c t a n t conc e n t r a t i o n o f u p to 1-1.5%. (5) The mechanical s t r e n g t h a n d d e f o r m a t i o n characteristics of the SC as a f u n c t i o n of the s u r f a c t a n t c o n c e n t r a t i o n correlate well, w i t h the c o n c e n t r a t i o n d e p e n d e n c e of a a n d the variations are due to the different degree of dispersion of t h e m a c r o m o l e c u l a r structures. Translated by K. A...AT.T,I~,S REFERENCES

1. M. R. KISELEV, L. A. SUKHAREVA, A. R. NARINSKAYA and P. I. ZUBOV, Sb.: Mekhanism protsessov plenkoobrazovaniya iz polimernykh rastvorov i dispersii (The Mechanism of Film Formation from Polymer Solutions and Dispersions). p. 95, Izd. "Nauka", 1966 2. P. I. ZUBOV and L. A. I,EPII,I(INA, Vestnik Akad. Nauk SSSR, No. 3, 49, 1962 3. L. A. SUKHAREVA, M. R. KISELEV and P. I. ZUBOV, Kolloid. zh. 29: 266, 1967

KINETICS OF DEHYDROCHLORINATION OF POLYVINYLCHLORIDE IN THE PRESENCE OF SOME STABILIZERS* K. S. M.II~SKER a n d V. P. M~Lr~SKAYA 40th Anniversary of October State University, Bashkiria (Received 14 June 1971) ~rHE production of plastic materials based on polyvinylchloride (PVC) normally makes use of compositions containing various other products, primarily metal-containing "primary" thermostabilizers (TS). All such TS have the reaction capacity with HC1, liberated by the PVC during thermal degradation, in common, and thus the elimination of the detrimental effect of HC1. Some of the features of the PVC dehydrochlorination kinetics in the presence of TS based on M 1+ metals have been described [1]. To this type of TS belong, for example, alkali metal stearates [2]. PVC is more frequently stabilized with TS based on bivalent metal ~salts, i.e. the basic sulphates and phosphites of Pb, metallic soaps based on Ca, Cd, Ba, Zn, etc. An examination of the dehydrochlorination kinetics of PVC in the presence of TS based on M z+ is therefore of considerable interest. * Vysokomol. soyed. A15: 51o. 1, 200-212, 1973.

Kinetics of dehydrochlorination of polyvinylchloride

229

The reactions of such TS with HC1 can be described either by a trimolecular reaction, MX2+ 2HC1 ~ MC12-t-2HX,

(A)

or as a process consisting of two parallel and consecutive reactions of second order, MX2%HC1 -~ MXCl~-HX MXCI-~HC1 -* MC12~HX

(B)

The study of the PVC reaction with basic sulphur salts of Pb showed [3] that the PbO is converted to PbCll without the alkalinity of the salt changing. I t seems that the binding of the HC1 takes place here by reaction (A). The bimolecular mechanism (B) is more likely where organic acid salts are used. The likely mechanism of the reaction of TS with HC1 during PVC dehydrochlorination is described by the kinetic equations I - V (Table 1). The symbols used there mean: a0--number of HC1 mole/mole polymer before dehydrochlorination (de-HC1); x - - n u m b e r of liberated HC1, mole/mole PVC at time t; co, c--initial and current concentration of TS respectively (g-equiv-TS/equiv.PVC); z, y--current concentrations of MC12 and MXC~ (mole Cl-/mole PVC); do--reactive additive concentration not utilized during reaction, mole/mole PVC; dx/dt and dz/dt, dy/dt and de/dr--rates of HC1 elimination, MCI~ and MXC1 accumulation, and TS consumption respectively; kl--rate constant of PVC de-HC1, see-l; k2--rate constant of the trimolecular I-IC1 reaction with TS, mole ~ PVC/mole2.sec; k~, k~'-rate constants of the seond-order reaction of TS with HC1 and of MXC1 with HC1 respectively (mole PVC/mole. see); ks, k~, k~'--rate constants of the catalytic PVC de-HC1 in the presence. of the metal salt, the reaction products, PR and TS respectively, mole PVC/mole. sec. I t was a s s u m e d for d e r i v a t i o n of e q u a t i o n s I - I V t h a t t h e P V C de-HC1 is a r e a c t i o n of zero order [4, 5]. This a s s u m p t i o n m u s t be correct since t h e c h e m i s t r y of p o l y m e r s t a b i l i z a t i o n is t h a t of infinitely small conversions. T h e TS c o n t e n t o f t h e P V C - b a s e d c o m p o s i t i o n n o r m a l l y is less t h a n 2 - 3 % , i.e. t h e changes in chlorine c o n t e n t during t h e a c t i v i t y of TS is so small t h a t it can be n e g l e c t e d . T h e s t u d y of t h e P V C de-HC1 kinetics in later phases is n o t so essential as e v e n v e r y slight chemical changes of t h e m a c r o m o l e c u l e s will result in a n almos~ c o m p l e t e loss o f a n u m b e r of v a l u a b l e p r o p e r t i e s b y t h e p o l y m e r . To solve t h e s y s t e m of differential e q u a t i o n s I - I V we m a d e use of t h e n u m e r i c a I i n t e g r a t i o n m e t h o d on a "l~lairi-C" c o m p u t e r , as t h e y could n o t be a c c u r a t e l y solved a n a l y t i c a l l y . Value kl was t a k e n to be 1.2 × 10 -6 sec -1, c o r r e s p o n d i n g t o t h e e x p e r i m e n t a l c o n s t a n t of p u r e P V C de-HC1 a t 175°C. T h e values of k3, k~, a n d k~ were chosen w i t h i n t h e r a n g e 10 -5 to 10-1mole P V C / m o l e . s e c ; v a l u e s k2, k'2 a n d k~ are e x p e r i m e n t a l l y u n k n o w n a n d were selected during i n t e g r a t i o n . T h e initial TS c o n c e n t r a t i o n (co) was t a k e n to be of t h e order of 2 × 10-3g-equiv. T S / e q u i v . PVC, w h i c h is t h a t n o r m a l l y used in p r a c t i c e to stabilize t h e P V C compositions. T h e r e q u i r e d a c c u r a c y of t h e i n t e g r a t i o n series was a u t o m a t i c a l l y selected (Af/f<, 0.03, f - - f u n c t i o n resulting f r o m t h e i n t e g r a t i o n of t h e differential e q u a t i o n s , i.e. x, y , z, a n d c, Af - - e r r o r of function). T h e results of c o m p u t i n g t h e differential e q u a t i o n s 1A a n d 1B ( v a r i a n t I) as a f u n c t i o n of k 2 for a c o n s t a n t k~ are r e p r o d u c e d in Fig. 1. Fig. l a shows t h a t t h e curves of P R a c c u m u l a t i o n , TS c o n s u m p t i o n a n d free HC1 ( u n b o u n d TS) libera-

230

K . S . MINS~B a n d V. P. MALII~SKAXA

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FIe. 1. Diagrams of the computer solutions of differential equations: a - - I A , b, c, d - - I B ; k , = l . 2 × 1 0 -e sec-1; c 0 = 2 × 1 0 - ' g-equiv. TS/equiv. PVC; a--k= (mole = PVC/mole.sec): 1--104 , 2--105 , 3--106 , 4--10 ~ a n d 108; b--k'~k~': 1--1, 2--10, 3--100, 4--1000; c--k~ =1000; k:': 1--1, 2--10, 3--100, 4--10,000, 5--100,000; d - - k : ' = 1 0 0 0 ; k',: 1--1, 2--10, 3-- I00, d-- 10,000, 5-- 100,000 mole PVC/mole TS.see.

231

Kinetics of dehydroohlorination of polyvinylohloride DO

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232

K.S.

MINsx~R and V. P. ~SKAyA

TABLE 1. THE XI~rE~OS OF TH~ PVC DEHYDROCHLORINATION I1~"THE PRESENCE OF T S (EQUATIONS)

Effects of TS a n d its reaction products w i t h HC1 (PR) o n . t h e PVC de-HCl N e i t h e r TS nor P R affect t h e r a t e of HC1 f o r m a t i o n

Kinetic equations Trimolecular reaction of TS w i t h HC1 (A)

dx

dx ~ - ~ klao-- ksx~c

dc dt

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dy

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TS accelerates PVC de-HC1, while P R has no effect on t h e r a t e of HC1 formation

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dz dt

dc dt dz dt

-

k'~xc k'~" x y

tion a t fairly small b2 values is a f u n c t i o n of t w o constants, ]c1 a n d k 2 . The difference b e t w e e n t h e curves b e c o m e s g r a d u a l l y smaller as k 2 increases; t h e y will finally coincide w h e n k~>~ 10 7, t h e P R a c c u m u l a t i o n a n d TS c o n s u m p t i o n will

Kinetics of dehydrochlorination of polyvinylchloride

233

t h e n be i n d e p e n d e n t o f ks a n d will o n l y d e p e n d on k 1, F r e e H01 starts t o a p p e a r w h e n all t h e TS has been utilized. T h e r a t e c o n s t a n t of a n effective TS r e a c t i o n with HC1 m u s t t h e r e f o r e be 12-13 times larger t h a n t h e r a t e c o n s t a n t of the

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234

K. S. MINSKERand V. P. ~AT.r~SKAyA

PVC de-HC1. This large difference between the rate constants is the consequence of the used TS content of PVC compositions not exceeding 2 - 3 ~ . We examined the kinetic curves of the bimolecular reaction (1B) for various ratios of constants k~ and k~, namely k~----]~ (Fig. lb) and k~Xk~ (Fig. lc, d). The MXC1 accumulation curves passed through a peak in the first case t~k,~ k,,~ 2J and its position depended on the value of the constants, while its amplitude was independent of them. The MC12 accumulation curve was sigmoid in shape; the spontaneous acceleration coincided here with the time required to reach the maximum concentration of MXC1. The C1- accumulation curves (MXC1-]-MC12) which characterize the efficiency of the TS become independent of /c~ and k~ when ]c~----]c~~ 1000. The TS absorbed all the liberated HC1 in this case and the rate of the P R accumulation was completely determined b y kl. The MC12 will start accumulating at k'2>>k"2 only after the peak had been reached on the MXC1 accumulation curve (curves 1, 2 in Fig. lc and 3, g in Fig. ld). The maximum of MXC1 will depend on the k'2: k"2 ratio; when k ~ 1 0 0 0 , k~k', b y two orders of magnitude will make the activity of a bivalent TS like that of a monovalent stabilizer. The P R accumulation curve will be independent of k2 before the MXC1 peak is reached on its curve, i.e. the TS will absorb all the liberated HC1. There will be subsequently a large inflexion on the curve, the reaction of P R formation will slow down, and free tiC1 will appear in the system at the same time (curves 1, 2 in Fig. lc). k~ larger than k~ b y two or more orders of magnitude will cause MXC1 to be almost instantaneously converted to MC1s and the (]l-ion accumulation curves will coincide with those of MCls over the whole time interval of TS activity (curve 5 in Fig. lc). The analysis of the kinetic curves characterizing the HC1 binding according to reaction (B) thus made it clear that the smallest of the rate constants of the MX s and MXC1 reactions with HCI must be larger than 100 if the second constant is at least 1000, because the PVC de-HC1 will become the limiting stage only if this is the case. In order that the above condition is fulfilled, the k~ : k", ratio will only effect the MXC1 and MC1s ratio and the rate of MX s consumption, but n o t the shape of the P R accumulation curve. The system of differential equations I I A and I I B (variant II) differs from that of systems IA and IB only in that the first kinetic equation of variant II contains an additional term, i.e. kaao%, which is identical with the rate constant of PVC de-HC1 k~----lcl~kaC0 in the differential equation system of variant I. Figure 2 shows the machine solution diagram of systems I I A and I I B as a function of k3 and only those ]c2-values (]c~:k~) at which the rate of P R accumulation starts to be independant of ks (/c~). The diagram makes it clear that each los value will have its corresponding ks (k~), and that the P R accumulation rate will become independent of the rate constant of HC1 formation when k s is greater then ]c~(~kl~k3%)b y a factor of 12-13 (trimolecular reaction of HC1 with MXs) , or when k's:k"s is greater then k~ b y a factor of 7-8 (parallel-consecutive second-

Kinetics of dehydroohlorination of polyvinylchloride

235

order reaction). The shape of the kinetic curves in Fig. 2 is identical with that in Fig. 1. The solution of system I I B equations is given in Fig. 2b only for t h e case ]¢~-----/¢~because the shape of the P R accumulation curve, as pointed out 2/ 2 ratio if these constants assure the complete earlier, is independent of the ]Eqd' binding of the liberated HC1. 3

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The machine solution of the system of differential equations I I I A and IVA (variants I I I and IV of the trimolecular reaction of MX2 with HC1) are illustrated in Fig. 3 as a function of k~ and k~ which quantitatively characterize the extent of the P R and TS effects on the HCI elimLaation. Here, like in Fig. 2, the only curves given are those with k2 values at which the rate of P R accumulation clearly starts to be determined b y the kl and k~ (k~) values. The shape of the MC12 accumulation curves for system I I I A is typical of an autocatalytic reaction. The free HC1 is liberated with the rate constant /c~=/cl+k~% after the TS has been utilized. The rate of P R accumulation in the case of system IVA decreases as the TS is utilized and the tIC1 is afterwards liberated at rate constant kl. The kinetic equations of system I I I B are slightly more complicated. We remarked earlier that the correlations between MXCI and MC12 depend on the k~/k~ ratio. One could assume these products to have the same catalytic activity in the PVC de-HC1 (as described b y the first kinetic equation in system IIIB),

236

K. S. M~NSXER and V. P. i ~ a ~ , r ~ s ~ y A

or t h a t the catalysis is produced either by MC12 or MXC1 alone. The second term in the first kinetic equation of system I I I B can then be written as k~aoz or ]4aoy. This makes it clear that the shape of the kinetic curves of P R accumulation will depend significantly on the Ic'/lc"~/~ratio. The machine solution of system I I I B for k~= 10-3 (examining the catalysis of MXC1, MCL, and MXCI+MC12) and for k~ ~>k~, ensuring the complete binding of HCI, is reproduced in Fig. 4a. I t shows that the catalytic activity of MXCI+MCI~ ,",

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k~-- 10-a, k~-- 1000, 1, 3--MCll catalysis, 2--MCI~+MXCI catalysis, g--MKCI catalysis; b, c--k~', mole PVC/mole.sec: 1--10 -4, 2--10 -a, 3--10 -~, 4--10-1; b--Xc:~--k~', mole PVC/mole.sec: 1, 2--1000, 3, 4--10,000; c--k~--~lO0, k~'-----lO0,O00mole PVC/mole. sec,

Kinetics of dehydrochlorination of polyvinylchloride

237

' " at k2=#2, a n d of MC12 and k"2> #'~ will produce a shape of kinetic curve of P R accumulation typical of an autocatalytic reaction (curves 2 and 3). The shape will be the same also in the MC12 catalysis for k'--k"2--~ (curve 1), but its position is below curve 2. The rate constant of HC1 elimination will be #~----#1+#3c0 after TS exhaustion for all the cases examined.

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FIe. 5. The effect of some of the TS and the PVC de-HC1 (in prackets are the TS quantities as mg-equiv./g-equiv.PVC): 1--Ba stearate (1--4, 1'--10), 2--Ca stearate (2--5, 2'--10), 3--Mg stearate (3--10, 3'--20), 4--tribasic Pb sulphate (5--5, 5'--10). O-points got by solving the differential equation system IA and IB for k,~-~l.2× I0 -e sec-1; k2= 107 (IA); k ~ = k ~ ' ~ 1000 (IB) and also calculated according to eqn. (1) for the same kl-value. I f only the MXCI has catalytic activity (k~=k~), the kinetic curve of P R accumulation will have the characteristics of variants I I I and IV (curve 4). I t will be identical at the start with the respective curve 2 and then digress, but approach kinetic curve 1 as the MXCI concentration becomes smaller (for the corresponding k'~ and k~). The HC1 will be eliminated at rate constant k 1 as soon as the TS is exhausted. The shape of the kinetic curves of P R accumulation for the system IVB solution is identical with t h a t of the curves for system IVA (Fig. 4b, c). However, as the rate of TS utilization depends on the ratio of these constants, the shape of the kinetic curves of P R accumulation will also depend on it. For identical #~ the rate of P R accumulation (and correspondingly the PVC de-HC1 rate during the period of TS activity) will be larger for k2>k2 t h a n for k~=k~. The explanation is t h a t the TS is more rapidly utilized in the latter case and the actual constant of PVC de-HC1, k ~ = k l + k ~ c , will also decrease more rapidly and approach kl in value. The proposed kinetic equations and the proposed mechanisms can be easily

238

K . S . MINSK~.]~ and V. P. lVfATJr~SKAYA

verified b y experiment. A criterion of the adequacy of the mathematical model and the actual progress of the process is the agreement of the experimental a n d theoretical diagrams. The experimental curves of P R accumulation in the presence of Ba, Ca and Mg stearates, of Pb monostearate and tribasic P B sulphate are reproduced in Fig. 5 which shows that the P R accumulation has a constant rate for some time and is independent of the TS amount or its chemical nature, but practically stopped after this time. The points at which the line curves away from the straight are those of TS utilization to value ~, i.e. the effective amount of TS which depends on the stabilizer type [6]. The time at which free HC1 will appear in the volume above the polymer, as indicated b y "Congo-red" paper, corresponded with the time at which the curvature appeared on the kinetic curves. The comparison of experimental with theoretical findings showed the experimental curves to be near those obtained on solving the differential equation system IA and IB for k~= 1.2 × 10 -6 sec -1 and those for a k~ at which the rate of P R accumulation became independent of these constants, and was just a function of k 1. It therefore follows from the kinetic data that the PVC de-HC1 follows the scheme of variant I under experimental conditions, and t h a t the rate of P R accumulation is independent of the rate constants of the TS reaction with HC1. To clarify the effect of diffusion on P R formation we plotted the kinetic curves of P R accumulation at various temperatures as a function of the dispersity of the system. The independence of the rate of P R accumulation on the latter (only slightly varying the absolute value of ~) and the temperature coefficient indicated the progress of the process in the kinetic range [2, 5]. The rate constants of P R accumulation and the Eact were equivalent to the rate constant of de-HC1 and the Eact of pure PVC respectively (Table 2). The limiting stage under experimental conditions was thus the HC1 liberation b y PVC. The stationary concentration method could therefore be applied to the differential equation system IA and IB, so that the following equation was obtained for the P R accumulation z= k ~ 0 t (1) and for the TS consumption, C=co--k~aot

.

(2)

The data contained in Fig. 5 show good agreement of the curve calculated from eqn. (1) for k 1 = 1 . 2 × 10 -e see -1 with the experimental findings, and with the curves resulting from solving the system of differential equations IA or IB for the same kl and the respective ks (k~ and k~). The P R accumulation (or the HC1 liberation during the time of TS activity) in PVC de-I-IC1 studies, using the salts of Pb, Ca, Ba or Mg as TS, can thus be calculated from eqn. (1). We had already mentioned that the time after which free HC1 will appear

Kinetics of dehydroehlorination of polyvinylehloride

239

c o i n c i d e d w i t h t h e e x h a u s t i o n o f t h e e f f e c t i v e T S q u a n t i t y . A n e q u a t i o n for t h e t i m e o f h e a t r e s i s t a n c e (~), i.e. t h e t i m e i n t e r v a l t o t h e p o i n t o f free HC1 a p p e a r i n g , c a n b e e a s i l y a r r i v e d a t f r o m e q n . (2), k l a o l : = c o - (c o - ~co)----~¢c0 ~c o

(3)

T = kxao

The above equation agrees with the formula for T proposed b y Minsker [6] who based it on experimental findings. The determination error of T based on the time of curvature appearing on the kinetic curves, established b y the indicator method, or b y using eqn. (3), did not exceed 20/o. The comparison of the described kinetic equations with the experimental stabilization data for PVC given in the literature showed that the de-HC1 proceeds in the presence of the majority of P b salts [6] and Sr stearate [2] as described b y the kinetics of variant I, and that the limiting stage is the PVC de-HC1. TABLE 2. THE E F F E C T S OF S O M E O F T H E T S O N T H E R A T E OF P V C DEHYDROCHLORINATION

TS

Ba stearate Ca stearate Mg stearate Monobasie stearate of P b Tribasic stearate of P b

kl X 10e , sec -1

Eact, keal/mole

1"20 1"18 1"10

30 31 31

TS

Zn stearate Cd stearate

k~ × 108, mole PVC/ /mole. see

Eact, kcal/mole

5.8/1.4 *

34

0.1/0"07"

34

1 "00

1.20

34

* As a functionof k's x 10' mole PVC/molo.secfor the respective MC1,.

No TS acting according to the variant II mechanism were found, but this variant describes the PVC de-HC1 in the presence of additives which are not consumed during the reaction (e.g. metal chlorides). Earlier work [1] described the .effects of chlorides on de-HC1 in the presence of Na stearate as TS. The replacement of the latter b y Ba stearate or tribasic P b sulphate did not alter the shape of the kinetic curves. The experimental curves agreed with the theoretical obtained on solving differential equation system I I A and I I B for a kl--1.2 X × 10 -e see -1 and the respective k 8 and ks (k;, k~) ensuring the complete binding of the liberated HC1. One can therefore conclude that the rate of P R accumulation will here also be independent of the rate constant of TS reaction with HC1 and will be determined only b y k ' l = k l ~ - k 3 d o. The application of the stationary state method to the differential equation

240

K . S. MII~SKEBand V. P. l~ffAr,rt~lSKAYA

systems I I A and 1I]3 led to the following equation for P R accumulation:

z = (kx + k3do)aot or z

aot

--~l-[-kado,

(4)

i.e. a n y PVC de-HC1 described by variant I I must show a linear dependence of z/aot on do; this was confirmed by experiments. The ks values determined b y the use of eqn. (4) for LiC1, CdCI~ and ZnCl=, when using Ba stearate or tribasic P b sulphate as the TS, agreed with the respective constants determined earlier [1].

]

I ~3.o I-

g

5.0 _

b

2

&O

,

_

['0

!

i'O

I

2OO

t/O0 600 T[rne , sec

I 800

20

/./0

60 80 Time, min

I I00

FIG. 6. Effects of the stearates of: a--Zn, b--Cd on the PVC de-HC1 at 175°(3. a: 1--5, 2--10, 3--15; b: 1--5, 2--15 mg-equiv, stearate/g-equiv. PVC). The dark dots are experimental, the light ones theoretical points of solving the differential equation system IIIB for k1=1"14× 10-6, c0=15 m-equiv. TS/equiv. PVC; k.'= 100, k~=100,000, a: k~=5.8× 10-*; b: k~= 1-0 x 10-~. The triangles are points calculated from eqn. (5) for the same kx- and/¢~values. The kinetic curves of P R accumulation during the PVC de-HC1 in the presence of Zn- or Cd-stearates are reproduced in Fig. 6. Their shape is typical of an autocatalytic reaction, which means t h a t the PVC de-HC1 takes place according to variant I I I . The same curves for variants I and I I will coincide where the HC1 is bound by TS according to reactions (A) and (B), and accumulation is independent of the /c'/k" 3/ 2 ratio where these constants are sufficiently large for the complete binding of the liberated HC1. As regards variant III, we proved above t h a t the ratio of the constants can affect the shape of the kinetic curves. Th at of the experimental curves reproduced in Fig. 6 exclude any MXC1 catalysis (k~----k~, HC1 binding by reaction B). The work b y Nagatomi and Saeki [2] on the PVC de-HC1 in the presence of Ba-, Cd- and Zn-stearates had given the same results over the whole activity period of the TS. This indicated t h a t there is no

Kinetics of dehydrochlorination of polyvinylchloride MXCl present in the system.

The HCl binding

by these TS therefore

241 proceeds

either according to reaction (A), or that of (B) when k’!>kL. The sigmoid shape of the. curves in Fig. 6 is therefore due to the catalytic activity of MCI,. The comparison of the experimental curves with the theoretical calculations showed the PR accumulation

curves to coincide with those obtained

by solving

the differential equation system IIIA and IIIB for the respective kl, k& and k, (k’i>kL), ensuring the complete binding of liberated HCl (Fig. 6). The limiting stage is thus the PVC de-HCl under experimental conditions. The use of the stationary concentration method with IIIA and IIIB led to the following equation for the PR accumulation: X=k’

k, (ek~(V_l). 3

The theoretical curves based on it for the respetive k; and k6 agreed with the experimental ones (Fig. 6). The Eact and rate constants of the catalytic PVC de-HCl, using Cd- or Znstearate, were similar to those for the polymer de-HCl in the presence of CdCl, or ZnCl, (Table 2). This is also proof of metal chlorides accelerating the PVC de-HCl, and of de-He1 in the presence of Cd- or Zn-stearates as described by the variant III scheme. The larger rate constants of the PVC de-HCl in the presence of Cd- or Znstearate, compared with those of a polymer decomposition in the presence of metal chlorides, are explained by being a heterogeneous catalytic process depending on the dispersity of the additive and its distribution within the system. The kinetic equations described here thus agree with the experimental findings. The PVC de-HCl in the presence of Ba-, Ca-, Mg- or Sr-stearate, as well as the majority of Pb salts, is thus described by the variant I scheme, neither TS nor PR having any effect on the HCl liberation. The introduction into the system of Li-, Cd- or Zn-chloride will cause the de-HCl process to be described by the variant II scheme, the additive catalyzing the de-HCl without being utilized. The variant III scheme describes the HCl elimination in the presence of Cd- or Zn-stearate, which is accelerated by them as the PR accumulates. No TS were found having a summary activity as described by variant II and IV schemes. A considerable amount of experimental material on the PVC stabilization by various types of compounds is available. Its quantitative interpretation, based on the examination of strict kinetic principles, will assist the clarification of the mechanism of action of stabilizers (TS). / This report describes the results for PVC obtained by suspension polymerization in the presence of azo-isobutyric acid din&rile as initiator and sodium styro-maleate aa emulsifier. The PVC had a Fikentscher value RF= 70, d= 1.41 g/cmS, bulk weight 0.53 and sol fraction content=O*OOl.

The results did not fundamentally

differ from those obtained with the C-65

type PVC. The PVC compositions with the TS and MCl, were prepared by thoroughly milling and mixing the components. All the tests were made with 1 g PVC samples. The ther-

242

K. 5. MINSKER end V. P.

MALINSKAYA

ma1 dehydrochlorinationwas carried out in the range 150-190°C by the method described by Minsker [6], the temperature being maintained within fO-6% Potentiometric titration of the aqueous extract was used to determine the Cl ions. The duration of heat resistance 7 and the TS accepting capacity factor a were determined by the same method [6]. CONCLUSIONS (1) Kinetic equations are given for the polyvinylchloride (PVC) dehydrochlorination (de-HCI) in the presence of thermostabilizers (TS) based on Mzf

for variants taking into account

the catalytic

activities

of the TS, its reaction

products with HCl, and reactive additives. (2) The rate constants of the TS reaction with HCl were estimated. It was found that the rate constant of the TS reaction will be effective in a third-order reaction if it is 12-13 times larger than the rate constant of the PVC de-HCI. Binding the HCl by a bimolecular mechanism (two parallel-consecutive reactions) requires the smallest of the constants to be 7-8 times larger than that of PVC de-HCl. (3) The stearates of Ba, Ca, Mg and Sr, and the majority of the Pb salts will produce a mechanism of PVC de-HCl in which neither the TS nor its reaction product with HCl (PR) will influence the rate of HCl formation. (4) The de-HCl will progress in the presence of Cd- or Zn-stearate by a scheme according to which the de-HCl is accelerated by the PR. (5) The comparison of the theoretical with the experimental curves proved the process of PR accumulation to be limited in all cases by the polymer dehydrochlorination. Translated

by K. A.

ALLEN

REFERENCES 1. II. S. MINSK& V. P. MALINSKAYA and V. V. SAYAPINA, Vysokomol. soyed. A14: 560, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 3, 628, 1972) 2. R. NAGATOMI and Y. SABKI, Japan Plastics Age 5: 51, 1967 3. Ye. N. ZIL’BERMAN, A. Ye. KIJLIKOVA, S. B. NElMAN, N. A. OKLADNOV, V. P. IRBEDEV and A. P. PAVLINOVA, Vysokomol. soyed. All: 1612, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 7, 1514, 1969) 4. W. GEDDES, Europ. Polymer J. 3: 267, 1967 6. A. A. BERLIN, R. M. ASEYEVA, Z. S. SMUTKINA and V. I. KASATOCHKIN, Izv. Akad. Nauk SSSR, Seriya khim., 1974, 1964 6. K. S. MINSKER and L. D. BUBIS, Vysokomol. soyed. A9: 52,1967 (Translatedin Polymer Sci. U.S.S.R. 9: 1, 57, 1967); Plast. massy, No. 8, 17, 1967