Dehydrochlorination of CPE

The appeiratus used for mecisuring the rates of dehydrochlorination of CPE has been described elsewhere [ ]. It allows for the volvimetric measurement of HCl evolved from the polymer with time at a constant temperature. 

Dehydrochlorination of CPE Crosslinked with Peroxides and 2-Mercaptoimidazoline, Measured at 180°C in Oxygen... 

Effects of Radiation Crosslinking on Dehydrochlorination of CPE at 180°C in Oxygen. Four CPE compounds were Chosen for radiation curing and subsequent dehydrochlorlnation eigperiments. The first compound Rad 1) was pure CPE, the second (Rad 2) contained 8 phr TMPT, the third (Rad 3) contained 8 phr TMPT and... 

The main degradation reaction of PVC at moderate temperatures is dehydrochlorination, which is also the dominant reaction in CPE degradation. While dehydrochlorination of PVC is an autocatalytic reaction, the dehydrochlorination of CPE is statistical (Jimenez 1993 Stoeva et al. 2000). 

The maximum rate of autocatalytic PVC dehydrochlorination is considerably higher than the maximum rate of statistical dehydrochlorination of CPE, and it decreases as the ratio of CPE increases from 0 % to 50 %. In the PVC/CPE 30/70 blend, the maximum dehydrochlorination rate of CPE is higher than that of PVC. In the second degradation step, the dehydrochlorination rate of CPE is the highest, but it is lowered by increasing the ratio of PVC in the blends. 

The results of this study are shown in Figure 1. Pure CPE, which luider above conditions underwent degradation reactions and very little crosslinking resulted in a maximum rate of dehydrochlorination of 0.117 mg. eq. HCl/g. polymer-hour. Most of the weight loss from the sample after degradation can be accounted... 

Effects of Antioxidants and Stabilizers on Dehydrochlorination of Chemically Crosslinked CPE at 150°C in Nitrogen. 

The beneficial effects of these systems were not observed for the NA-22 crosslinked CPE. Without the stabilizers and antioxidants a high maximum rate of dehydrochlorination of 140x10 mg. eq. HCl/g. polymer-hour was measured cund with these stabilizing additives the maximum rat of dehydrochlorination rose to a higher value namely 150x10. It is apparent that this... 

Pyrolysis GC has been used in the determination of compositional analysis and microstructure of chlorinated polyethylene (CPE). This method utilized specific aromatic compounds which were formed through dehydrochlorination of trimers after pyrolysis of CPE polymers at elevated temperatures. The composition and microstructure calculation was based on the difference between the levels of ethylene and vinyl chloride trimers formed [19-22]. 

The CPE material used in this study is CM 0342 supplied by The Dow Chemical Ccxnpany. This CPE grade has a specific gravity of 1.25, a chlorine content of 42 percent, an average Mooney Viscosity [HLl-i-4 (lOO C) ] of 65 eind a residual crystallinity of less than 2 percent. Molded slabs of the pure and compounded polymer were used. Molding was conducted at 163 C for ten minutes which for most compounds is an optimum cure condition. Samples molded under other conditions will be so noted in the text. For dehydrochlorination measurements the samples were cut into ediout 2 mm cubes. 

Figure 3. Effects of anlioridants and stabilizers on dehydrocHlorination (ISO C, 0< of chetnicaUy crossdinked CPE containing (O), uncross-titJced control (%),...

Beyond that the two amine groups on the molecule of the NA-22 evidently accelerate the dehydrochlorination by abstracting and eventually releasing HCl from the CPE due to heat. Addition of ZnO with NA-22 reduces the maximum rate of dehydrochlorinatlon to... 

Thermal degradation of stabilized and unstabilized PVC/CPE was studied by Stipanelov Vrandecic et al. (Stipanelov Vrandecic et al. 2001). Dynamic TGA was performed for the thermal degradation of PVC/CPE blends between 50 °C and 600 °C at a heating rate 2.5 °C min. It was found that the thermal degradation of the pure unstabiUzed and stabilized polymers, as well as the PVC/CPE blends, occurs in two degradation steps dehydroclorination of PVC or/and CPE and the degradation of the dehydrochlorinated residues. 

In immiscible polymer blends, one polymer is dispersed in the form of domains in the continuous phase of the other. The degree of dispersion depends upon the mixing ability of the polymers, which decreases with an increase in concentration of the other polymer in the blend. Therefore, the quantity of domains and the degree of dispersion in PVC/CPE blends determine the progress of the degradatimi. The evolved HCl partially lags in the bulk sample, due to inefficient diffusion and, consequentially, has a catalytic effect on dehydorchlorination at low level of dehydrochlorination, as well as on the secondary reactions of polyene residues (Mahmood and Quadeer 1994). 

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. 

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