Polyethylene with antioxidants

Efforts to modify polyethylene with antioxidants have been in progress since the 1960s [6-16]. 

Oxidation of polyethylene with the formation of carbonyl groups can lead to a serious increase in power factor. Antioxidants are incorporated into compounds for electrical applications in order to reduce the effect. 

Used as a secondary accelerator with antioxidant, antiozonant, and stabilizing function in synthetic rubber and high polymer materials in the plastics and rubber industries. Mainly used in styrene-butadiene rubber (SBR), chloroprene rubber (CR), epichlorohydrin, and chlorosulfonated polyethylene rubber. Promotes heat-resistance of chlorosulfonated polyethylene rubber, EPDM and CSM and sunshine resistance of CR. 

The origin of chemiluminescence in polyolefins has been profoundly analyzed and it has contributed to the better understanding of their complex mechanism of thermooxidation The thermal oxidation of polyethylenes with different manufacturing histories has been compared, which allowed to establish a relationship between CL and some structural characteristics of the polymers. Modification of their stability in the presence of antioxidants, or other additives such as the activity of nano- and micron particles of pigments has been evaluated. 

Zhang and Xu [1993] blended EVAc and CPE (chlorinated-polyethylene) with PE (Table 11.9), because crosslinked PE has low flexibility for use as cable insulation. They mixed 30-70% HDPE with 70-30% EVAc or CPE, along with 0.5-1.0% of the antioxidant 1010 and 0.5-1.0% of zinc stearate in a SK-160B double roller mixer at 130-140°C. The blends so made were either hot-pressed into sheets or extruded into tubes, and irradiated with 1.5-MeV electrons to a dose of 100 kGy. Some properties of the irradiated blends and PE are compared in Table 11.21. As the data in this Table show, the flexibility and the elongation of the HDPE/EVAc and HDPE/CPE blends are better than those of the PE but their hardness and softening points are lower. The two blends also show the memory effect better than that shown by the PE. Moreover, the heat-shrunk tubes of the PE/EVAc and PE/CPE blends were more flexible than those of the heat-shmnk PE. 

Polyethylene can be applied as a hot melt coating to metals. Poor adhesion has been found with conventional pre-treatments when the polymer was stabilized with antioxidant. By contrast, adhesion to microflbrous surfaces is good even in the presence of antioxidant (Table 1). ... 

The mechanism of synergism in pairs of carbon black and sulfur-containing compounds is quite unknown. It is assumed only that the structure of the carbon black plays an important role here. Carbon blacks subjected to pyrolysis entirely lose their protective action and their ability to manifest synergism with antioxidants. It has been shown [76] that polyacenes (model of deactivated carbon black), for example, tetracene, pentacene, and perylene possess high effectiveness in conjunction with phenol sulfides and thiols. Thus, the addition of 0.1% perylene and 0.1% iS-naphthyl mercaptan greatly decelerates the oxidation of polyethylene at 140°C. In this case autocatalysis is not observed for more than 2000 hr. 

Low amounts of stabilizer are necessary for improving the stability of polymers [06C1]. The most used polymer, polyethylene, needs antioxidants in its product formulation, even though it is saturate polymer and the oxidation in any conditions starts more slowly than in many other polymer materials. A comparative study on the effect of two additives (hydrolysis-conditioned phosphate and IRGANOX 1076) on the thermal stability of medium density polyethylene (MDPE) and low density polyethylene (LDPE) (Fig. 71) illustrates the performances of material modified with carbon black (CB) and dicumyl peroxide (DCP), respectively [02F1]. This figure demonstrates that the same antioxidants promote differently thermal protection in the direct relation with material formulation. 

Figure 10.24 Oxidation temperature as a function of antioxidant concentration (Irganox 1010 in a medium-density polyethylene). With permission from Elsevier (Karlsson, Assargren and Gedde 1990).

The method is capable of determining down to 0.01% antioxidant in polyethylene with an accuracy of 5%. 

Berzen J. Luketic D. Stabilised polyethylene moulding materials, esp. for implants containing polyethylene with molecular wt. 10 5-10 7. antioxidant, and toco[4ierol, esp. alpha- tocopherol or vitamin E. as stabiliser. European Patent 613,923 1994. 

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