Polypropylene thermo-oxidation

Le Bras, M., Bourbigot, S., Delporte, C., Siat C., and Le Tallec, Y. 1996. New intumescent formulations of fire retardant polypropylene Discussion about the free radicals mechanism of the formation of the carbonaceous protective material during the thermo-oxidative treatment of the additives. Fire Mater. 20 191-203. 

Ozonization of the polypropylene powder creates the peroxidic species in the polymer, as well. The activation energy [41] of the thermal decomposition of these peroxides is 100 kJ/mol. In the decomposition of peroxides more than one type of radicals was trapped. Moreover, the three exotherms (peak at 40,90, and 130 °C) were observed on DSC thermograms of ozonized sample which also indicates the presence of several types of peroxides. Besides the peroxidic bonds in polymer, selective thermal decomposition may occur also with such bonds in the polymer as, e.g., with end groups containing the initiator moieties [42], This, however, takes place at higher temperatures than it corresponds to usual temperatures at which the thermo-oxidation starts. 

Figure 9. Distribution of nitroxyl radicals concentration by thickness of sample underwent thermo-oxidative destruction at 120°C a - poly(acrylonitril-butadiene-styrene (ABS) copolymer), thickness of sample is 3,8mm b - polypropylene copolymer with polyethylene, thickness of sample is 3,4mm. The inset is the example of EPR-spectrum of nitroxyl radical in ABS-copolymer.

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. 

Non-discoloring, sulfur containing phenolic antioxidant and stabilizer that provides long-term heat stability by preventing thermo-oxidative degradation. Used for the process stabilization of polyethylene wire and cable resins for polyethylene during extruder compounding. Can also be applied in styrenic polymers, polypropylene, elastomers such as EPDM and SBR and for carboxylated SBR latex, polybutadiene rubber and polyisopropene rubber. 

Another important attribute of a HALS is its effect on the thermo-oxidative stability of polypropylene multifilaments. This property is important in certain end-use applications where elevated temperature over a period of time is experienced, such as in automobile rear shelf fabrics. The excellent performance of the oligomeric HALS 4 and 6, as determined by 120°C oven aging, is shown in Figure 2. The superior activity of these products may be due not only to their low volatility but also to the presence of a triazine moiety in the structure, which appears to have a positive effect on the thermo-oxidative stability of polypropylene. 

Osawa et al. [465] found an inhibiting effect of cobalt (III) diethyl-selenocarbamate on the thermo-oxidative degradation of polypropylene both in the absence and presence of cupric stearate or cobalt (II, III) acetyloacetonate. 

It was found that the presence of titanium- compounds shortens the induction period of thermo-oxidation of polypropylene [350, 549]. The... 

As a result of this extensive experimental program, it has been found that in rotational molding, polyethylene and polypropylene polymers show different degradation behavior. While in polypropylene the thermo-oxidative degradation causes mainly chain scission, in polyethylene crosslinking dominates. The use of increased amounts of antioxidant in the... 

Bikiaris, D., Vassiliou, A., Chrissafis, K., Paraskevopoulos, K. M., Jannakoudakis, J., and Docoslis, A. 2008. Effect of acid treated multi-walled carbon nanotubes on the mechanical, permeability, thermal properties and thermo-oxidative stability of isotactic polypropylene. Polymer Degradation and Stability 93 952-967. 

Yang, L., Thomason, J.L., Zhu, W. The influence of thermo-oxidative degradation on the measured interface strength of glass fibre-polypropylene. Compos. A Appl. Sci. Manuf. 42, 1293-1300 (2011)... 

Polypropylene (PP) has wide acceptance for use in many application areas. However, low thermal resistance complicates its general practice. The new approach in thermal stabilization of PP is based on the synthesis of PP nanocomposites. This paper discusses new advances in the study of the thermo-oxidative degradation of PP nanocomposite. The observed results are interpreted by a proposed kinetic model, and the predominant role of the one-dimensional diffusion type reaction. According to the kinetic analysis, PP nanocomposites had superior thermal and fireproof behavior compared with neat PP. Evidently, the mechanism of nanocomposite flame retardancy is based on shielding role of high-performance carbonaceous-silicate char which insulates the underlying polymeric material and slows down the mass loss rate of decomposition products. 

These results show that the second step in thermo-oxidative degradation of PP-MAPP-Cloisite 20A is described by one-dimensional diffusion (DO reaction type which is liable for the overall process of the carbonization in nanocomposite polypropylene structure. 

With respect to recycling, it is to be mentioned that tensile properties of oriented polypropylene tapes can be affected following the addition of recycled process waste at various concentrations. A significant loss in tape strength occurs when recycled or waste PP is added because of thermo-oxidative degradation. Useful tapes with acceptable tenacities can be achieved using up to 25% w/w of some recycled waste PPs in the absence of stabilizers. 

Fig. 26, Induction period of the thermo-oxidative destruction of polypropylene stabilized by mixtures of SAG-6 and pyro-catechol phosphite with ionol. Summary concentration of the stabilizers 0.015 mole/kg T = 200 C Pq = 200 mm Hg.

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... 

The catalytic effect of various metals, metal oxides, and metal stearates on the thermo-oxidative degradation has been examined in the solid phase and in solution. In the latter case activity decreased in the order Cu, Mn, Fe, Cr, Co, Ni, Ti, Al, Zn, and V. The chemiluminiscence observed during thermo-oxidation has been interpreted as arising from the decomposition of ctketone hydroperoxides followed by oxidation of the polymer chain by secondary peroxy radicals. U.v. and fluorescence microscopy together with energy-dispersive. Y-ray analysis have been used to develop a model for the distribution of partially degraded polymer in isotactic polypropylene. ... 

Several applications of polymers placed in contact with metals require detailed study on the effect of this kind of materials upon the durability of plastics. Ozawa and Tsurumi studied by chemiluminescence the consequence of various transition metal stearates (concentration 0.5 phr) on the thermo-oxidative degradation of polypropylene even at low temperature (105 C). They stated the relative decreasing catalytic order of these compounds as follows [8901] ... 

Related very much to practical considerations are the results of thermooxidation in the melt, or of immersion in boiling water, followed by extrusion, of pyrolysis in a fluidized bed reactor and of thermo-oxidation of an oriented film, whilst under stress. Depending upon the stress applied the rate of oxidation may either be increased, or decreased. A study has also been made of the effects of layer thickness, temperature, oxygen pressure, and antioxidants on the thermo-oxidative degradation of both polypropylene and polyethylene. The degradation mechanisms are discussed in detail. 

Gensler, R., Plummer, C.J.G., Kausch, H.H., Kramer, E., Pauquet, J.R., Zweifel, H., Thermo-oxidative degradation of isotactic polypropylene at high temperatures phenolic antioxidants versus HAS. Polym Degrad Stab 2000 67(2) 195-208. 

Steiner, G., Koppelmann, J. Measurement of thermo-oxidative stability of isotactic polypropylene by isothermal long-term differential thermal analysis. Polymer Degradation and Stability, 19 (1987), p. 307-314... 

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