Thermal oxidation in polyethylene

It is well known that thermal oxidation in polyethylene (PE) in the presence of oxygen leads to sudden and deep embrittlement, in which oxidative chain scission plays a key, but perhaps indirect, role. We have developed a kinetic model, derived from a branched radical chain mechanistic scheme, able to predict accurately molecular structural changes (7). 

Nomenclature for branch caihon resonances Determination of crosslinking in polyethylene Determination of thermal oxidation in polyethylene Determination of stcreoregulariiy of polymers... 

U.W. Gedde, B. TerseUus and J-F Jansson, Polymer Testing 2, A New Method for the Detection of Thermal Oxidation in Polyethylene Pipes , 85-101, 1981. 

The products of thermal oxidation of polyethylene films can be characterized by C FTNMR furthermore, using the spin-lattice relaxation technique, quantitative estimates can be made of the oxidized functional groups. Observation of the development progress of the various functional groups leads to the postulation of hydroperoxides as the primary oxidation products, which undergo further transformations to the other derivatives in a complex scheme . 

One additive that improves both long-term photo and thermal stability of polyethylene Is carbon black. The ability of carbon black to retard destructive thermal oxidation In polyethy-lenes at elevated temperatures Is well known(17) and, as was seen In the earlier section of this paper on photo oxidation. It Is effective at lower temperatures also. Our studies of the thermal oxidation of low-density polyethylene show black samples to be outstanding, even In the presence of copper. For example black low-density polyethylene wire Insulation Is still Intact after 7 years at 80°C while all other colors. Including unplg-mented, failed mechanically due to oxidation after only about 3 months. 

The high efficiency of Irganox 1010, as a long-term thermal stabilizer in polyethylene film, was evidenced by the increased oxidation induction time (OIT) (Table 3.4). 

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. 

Other reinforcing agents either have been used to reduce the thermal degradation of polymers or do not have an effect on it. These include calcium carbonate in polyvinyl acetate [65,73] and polymethyl methacrylate [69,71] and titanium dioxide-magnesium oxide in polyethylene [78]. 

Iring, M., Tiidos, F. Thermal Oxidation of Polyethylene and Polypropylene Effects of Chemical Structure and Reaction Conditions on the Oxidation Process, Progress in Polymer Science, 15 (1990) 2, p. 217-262... 

Barabas K, Iring M, Kelen T, Tudos F. Smdy of the thermal oxidation of polyolefines volatile products in the thermal oxidation of polyethylene. Degradation and Stab cf Polyolefins, lUPAC Microsymp on Macromol, 15th 1977 57 65-71. 

Hoang EM, AUen NS, Liauw CM, Fontan E, Lafuente P The thermo-oxidative degradation of metaUocene polyethylenes part 2 thermal oxidation in the melt state, Polym Degrad Stab 91(6) 1363-1372, 2006. 

E.M. Hoang, N.S. Allen, C.M. Liauw, E. Fontan, P. Lafuente. The thermo-oxidative degradation of metallocene polyethylenes. Part 1 Long-term thermal oxidation in the solid state. Polymer Degradation and Stability 91(6), 1356-1362 (2006). 

Polythiosemicarbazide disulfide is the most efficient aliphatic polyamine disulfide for inhibiting the thermal oxidative breakdown of polypropylene, while polyimi-noaniline disulfide and polydiiminodiphenyloxide disulfide (Fig. 3) are the most efficient aromatic polyamine disulfides. In contrast to polyethylene, the thermal oxidative breakdown period increases as the concentration increases (Fig. 4), Depending on the concentration, the flow-melt index at 230°C increases at a lower rate than in the case of commercial stabilizer Santanox (Table 2)-... 

Synthesis of comb (regular graft) copolymers having a PDMS backbone and polyethylene oxide) teeth was reported 344). These copolymers were obtained by the reaction of poly(hydrogen,methyl)siloxane and monohydroxy-terminated polyethylene oxide) in benzene or toluene solution using triethylamine as catalyst. All the polymers obtained were reported to be liquids at room temperature. The copolymers were then thermally crosslinked at 150 °C. Conductivities of the lithium salts of the copolymers and the networks were determined. 

As part of a multi-technique investigation (see also discussion under mid-infrared spectroscopy later), Corrales et al. [13] plotted the carbonyl index for films prepared from three grades of polyethylenes a high-density PE (HDPE), a linear low-density PE (LLDPE) and a metallocene PE (mPE) (see Figure 5). In this study, the data trend shown in Figure 5 correlated well with activation energies derived from the thermal analysis, which showed that the thermal-oxidative stability followed the order LLDPE > mPE > HDPE, whereas the trend... 

Composite-based PTC thermistors are potentially more economical. These devices are based on a combination of a conductor in a semicrystalline polymer—for example, carbon black in polyethylene. Other fillers include copper, iron, and silver. Important filler parameters in addition to conductivity include particle size, distribution, morphology, surface energy, oxidation state, and thermal expansion coefficient. Important polymer matrix characteristics in addition to conductivity include the glass transition temperature, Tg, and thermal expansion coefficient. Interfacial effects are extremely important in these materials and can influence the ultimate electrical properties of the composite. 

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