Polyolefins thermo-oxidative

Ethanox 376 is a stabilizer that provides heat stability by preventing thermo-oxidative degradation during processing and service life. It provides compatibility with resins and extraction resistance. It can be applied in polyolefins, such as polyethylene, polypropylene, polybutene-1 and other polymers such as engineering plastics, styrenes, polyurethanes, saturated and unsaturated elastomers, styrenics, rubber modified styrenics, segmented block copolymers, and PVC. 

Captodative Compounds in the Stabilization of Polyolefin s Melt and Their Potential Application in UV and Thermo-oxidation Stabilization [23-29]... 

Both this study and later work by Botelho and co-workers [13] showed that, unlike polyolefins, the thermo-oxidative degradation of PET involves non-oxidative thermal degradation processes, especially in the early stages. The overall thermo-oxidative process in PET is therefore extremely complex. Recent studies [19,20] using state-of-the-art mass spectroscopic techniques have provided further evidence for the role of hydroxylated terephthalate fragments in PET discoloration. 

Polyolefins are susceptible to several degradative mechanisms, out of which thermo-oxidative and thermomechanical are dominant. The PO stability depends on macromolecular configuration and it follows the order HOPE > LLDPE > LDPE > i-PP. Chemiluminescence, FT-IR, mechanical properties, and Ihermogravimetty have been used for detecting and quantifying degradations (Cran 2004). 

Two review articles have been published, one relating to the thermo-oxidative degradation and stabilization of polyolefins and the other to the effect of thermal and thermo-oxidative breakdown of polyethylene and polypropylene upon overall properties. The latter paper specifically considers the effects of reprocessing. A... 

Generally, non-pressurized pipes contain carbon black (CB) as a pigment. However, CB may have a negative effect on the thermo-oxidation of polyolefins. The influence of CB on the long term thermal behavior of irrigation pipes (for vineyards in Cap Province, South Africa) based on LLDPE/LDPE recyclate is shown in Figure 21. 

Crystalline starch beads can be used as a natural filler in traditional plastics [3]. They have been particularly used in polyolefins. When blended with starch beads, polyethylene films biodeteriorate upon exposure to a soil environment. The microbial consumption of the starch component leads to increased porosity, void formation, and loss of integrity of the plastic matrix. Generally, starch is added at fairly low concentrations (6-15 wt%). The total disintegration of these materials is obtained using transition metal compounds, soluble in the thermoplastic matrix, used as pro-oxidant additives to catalyze the photo and thermo-oxidative processes [4]. These products belong to the first generation of degradable polymers that biodeteriorate more than mineralize to CO2 and H2O in a time... 

Over the last few years a number of applications on the analysis of olefin copolymers have been published that make use of the LC-Transform system. These include the SEC-FTIR analysis of ethylene/vinyl acetate copolymers [117], ethylene/ methyl methacrylate copolymers [118, 119], ethylene/styrene copolymers [120], HOPE and PP [121]. A number of studies used SEC-FTIR for monitoring the thermo-oxidative degradation of polyolefins [122-126] and a combination of TREE and SEC-FTIR to investigate the complex structure of olefin copolymers [127,128]. 

Another interesting feature of HT-AF4 is that the thermo-oxidative degradation of polyolefins in solution can be visualized [203]. This approach can be used to evaluate effects that are caused by improper sample treatment including sample preparation for HT-SEC. 

In Table 4 some data concerning thermal and thermo-oxidative stabilities of polyolefins are presented. It can be seen that, with some exceptions, the thermal stabilities, judged by values, roughly correlate with T)r r and values. Thermo-oxidative degradation occurs at lower temperatures than the thermal degradation. 

TABLE 4 Thermal and thermo-oxidative stabilities of some polyolefins... 

TABLE 7 Products identified as resulting from thermal (T) and thermo-oxidative (TO) decomposition and combustion (C) of some polyolefins... 

In the composition of the combustion products, most products of thermal and thermo-oxidative decomposition appear in very low concentrations. Their composition depends on the mode of operation, e.g., in closed or open space, flameless or flame combustion, oxygen concentration, etc. The major products of combustion are distinguished by higher concentrations of the thermally stable compounds (CO2, H2O, CO, low molecular weight compounds, aromatics, etc.) and also by some toxic products. The apparent lethal concentrations (ALC50, 30 min exposure period) of pyrolysis products of polyolefins is about 11.8 mg, which indicates that they are not unusual or extremely toxic [205, 222, 232]. 

Both thermal and thermo-oxidative decomposition of polyolefins are characterized by a set of kinetic parameters. 

The high moleeular mass of phenolic antioxidants confers substantial proteetion against thermo-oxidative damage. If required, long-term heat resistance of polyolefin fibers may be increased by addition of an extra amount of phenolic antioxidant, the performanee in this respeet inereasing with the square root of antioxidant eoneentration. Improved long-term heat resis-tanee of polyolefin fibers can also be achieved with polymerie HAS [8-10]. 

Research devoted to the flammability of polyolefin insulating tape showed that thermo-oxidative aging... 

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