Synergetic mixtures

Figure 4.38 The DSC curves of an unstabilised polyether, a polyether stabilised with a hindered phenol and a polyether stabilised with a synergetic mixture hindered phenol...

A broad spectrum of synergetic mixtures of Cl is used to strengthen their inhibiting action and expand the range of metals protected [39,46,47]. To extend the life of inhibited plastics, they are modified by Cl mixtures of different volatility. Highly volatile components of inhibitive mixtures intensify the formation of adsorptive Cl laj ers on hardware surfaces prior to the onset of the corrosion process. Low-volatility Cl are able to prolong the anticorrosion effect of the plastics. 

Rubber-free inhibited sealants based on plasticized thermoplastics have been developed for oil and gas pipelines. A non-drying plastic material [10] in the form of a gel is based on PE and a tar of mineral and vegetable oils, which is used as a plasticizing and anticorrosion additive. PE gels are filled with fibers and powder particles to improve the strength of sealing layers [11]. For PE-compatible Cl a synergetic mixture of potassium and... 

The oxidation of p-xylene to terephthalic acid occurs by the same general mechanism as described above for alkylaromatics. Bromide ions and nitrogen-containing ligands provide synergetic mixtures with metal salts [56-58,61]. Pyridine is one of the most efficient additives [59,60j. Oxo-centered cobalt(III) clusters have been isolated from the reaction mixtures, which can be regarded as active intermediates [34,62,63]. The optimum catalytic activity was found to be associated with the composition corresponding to Co Br py = 1 2 (1-2) [64]. 

Polyepoxide plasticizers comprise two basic types. The first type is the epoxidized soybean oils (with a maximum iodine number of 6 and an oxirane oxygen minimum of 6%), which have a good affinity to vinylic polymers [45]. Compared to plasticizers of the second type, the alkylepoxy stearates (butyl, octyl), they are less volatile and are less effective for low-temperature plasticization. Polyepoxide plasticizers have less affinity to PVC than primary plasticizers. They are efficient as heat and light stabilizers and for this reason they are used in synergetic mixtures to stabilize PVC. 

Synergetic mixtures of metallic soaps (mainly Ba, Ca, Cd, and Zn) have found wide application as heat stabilizers [16,23,24,26,30,32,34-37,45,46, 48-53]. Synergism, in this case, is the action of two heat stabilizers achieving a higher stability than the best offered by only one of the two (see Section 10.2.6). 

Synergetic mixtures presenting no health hazard are worthy of mention. They are zinc-based compounds mixed mainly with calcium soaps. Since zinc-containing stabilizers function only at very low concentration in PVC (0.1-0.4% by weight), it is necessary to ensure a good dispersion of the stabilizer mixture in the polymer matrix to obtain the best stabilizing effect. Too high a concentration of zinc stabilizer decreases the heat stability of PVC appreciably [55]. To avoid this, epoxide compounds should be used as HCl acceptors in conjunction with the stabilizer mixture. 

Fig.9.4. Schematic illustration of synergism and antagonism of PVC thermal stabilizer. Curve 1 stabilizing effect of component A curve 2 stabilizing effect of component B curve 3 stabilizing effect of component C curve 4 stabilizing effect of synergetic mixture of A + curve 5 stabilizing effect of antagonistic mixture of A + C curve 6 unstabilized PVC.

Fig. 9.7. Relation between heating time at 180°C in the air and the quantity of HCl evolved from PVC stabilized by a synergetic mixture of barium and cadmium stearates [65]. Curve 1 sheet obtained by homogenization in a twin-roll mixer curve 2 homogenized powder in a turbomixer.

When the efficiency of different flame retardants is compared, phosphorus compounds are better than those containing antimony, chlorine, and bromine. The most efficient are the synergetic mixtures of phosphorus and bromine-containing compounds the bromine content can be decreased by adding an antimony compound, as shown in Table 12.6 [40]. 

PS and copolymers synergetic mixtures of brominated compounds and peroxides, terpolymers with a monomer containing a halogen. 

Formulation No 4 PEX-A pipe sample contained a synergetic mixture of phenol antioxidant (PhAO 2) and hindered phosphite antioxidant (HPhAO). 

Dependences of antioxidants consumption in Formulations No 1, No 2 and No 4 are presented in Figure 3. The eontent of phenol antioxidant in Formulations No 1 and No 2 is identical. The difference is that Formulation No 1 represents a synergetic mixture of two phenol antioxidants (PhAO+SPhAO) while Formulation No 2 contains only PhAO 2. The results received show that eonsumption of phenol antioxidants in Formulation No 1 is quieker than in Formulation No 2. 

The lifetime of industrial sacks can be doubled or even tripled using an amount of 0.25-0.5%. An additional protective effect on TPO is obtained by synergetic mixtures with nickel-containing stabilizers. 

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