Polypropylene stability

Polypropylene, stabilized irradiated. Radiation-stabilized grades,... 

Figure 20 An increase of induction time of oxidation of polypropylene stabilized by Irganox 1010 (points 1) due to prior sample annealing at 130°C (points 2) in oxygen. The induction time corresponds to the time of cross-section of the straight line passing the CL inflexion point and time axis. It was determined for an oxygen atmosphere and temperature 150°C.

Four main types of antioxidants are commonly used in polypropylene stabilizer systems although many other types of chemical compounds have been suggested. These types include hindered phenolics, thiodi-propionate esters, aryl phosphites, and ultraviolet absorbers such as the hydroxybenzophenones and benzotriazoles. Other chemicals which have been reported include aromatic amines such as p-phenylenediamine, hydrocarbon borates, aminophenols, Zn and other metal dithiocarbamates, thiophosphates, and thiophosphites, mercaptals, chromium salt complexes, tin-sulfur compounds, triazoles, silicone polymers, carbon black, nickel phenolates, thiurams, oxamides, metal stearates, Cu, Zn, Cd, and Pb salts of benzimidazoles, succinic acid anhydride, and others. The polymeric phenolic phosphites described here are another type. 

Here we discuss a new class of polypropylene stabilizers—the polymeric phenolic phosphites. These compounds exhibit unique, broad-spectrum activity which may allow simplification of polypropylene stabilizer systems. The most active species are synergistic with thiodipro-pionate esters, are effective processing stabilizers when used alone or with other compounds, and contribute to photostability. Compounds of this type appear to function as both free radical scavengers and peroxide decomposers, and through a mechanism not yet completely understood, allow significant reductions in the concentration of ultraviolet absorbers required to achieve high levels of photostability. 

Aromatic amines and some other compounds are also effective hydrogen transfer agents and will give excellent molecular stability in most cases when used in place of the hindered phenolics. However, these compounds are rapidly oxidized to form color bodies in the polymer and may be toxic compared with the phenolics. Hence, aromatic amines are not widely used in polypropylene stabilizer systems. 

Representative compounds of importance in polypropylene stabilization are tris( mixed nonyl phenyl) phosphite and dilauryl thiodipropionate-(DLTDP). The aryl phosphite is used in film grade resins and in other... 

The polymeric phenolic phosphites are excellent heat and processing stabilizers and can contribute significantly to photostability. These broad-spectrum stabilizers offer possibilities for simplifying polypropylene stabilizer systems. They may allow one to use lesser amounts of other additives, and they open up a new area for potential cost savings in formulating polypropylene resins. 

In this study we measured chemiluminescence of polypropylene stabilized with different combinations of antioxidants and irradiated to different extents, and made correlations with conventional impact strength measurements of the same materials. 

Another class of additives for polypropylene stabilizations is compounds containing a 2,2,6,6-tetramethyl piperidyl group (I). These compounds are frequently referred to as... 

Figure 12.10 shows the release of volatiles during thermal degradation of polypropylene. Mica reinforces the polypropylene stability, while halogenated flame retardant reduces it. Both composite polymers are compared with the pure polymer. The thermal stability of low, medium and high-density polyethylenes has its linkage to the number of branches in the main polymer chain. It is of interest that the flammabihty expressed in the amount of oxygen consumed follows the similar tendency (Fig. 12.11). 

Figure 114 Experimental and fitted dependence of the onset of oxidation temperatures, as a function of the heating rate for polypropylene stabilized with different amounts of lignin. (Reproduced by permission of Elsevier. Copyright 2005. Reprinted from Reference [14]).

TABLE 5.3 Polypropylene Stabilization Days in 135°C Oven to Reach Embrittlement... 

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.

Peltzer, M., Jimenez, A. (2009). Determination of oxidation parameters by DSC for polypropylene stabilized with hydroxytyrosol (3,4-dihydroxy-phenylethanol), J. Therm. Anal. Cal, P6(7)j 243-248. 

Polypropylene stabilizers Polypropylene Japan 16,395 1968 Mitsubishi Rayon... 

Table 3.1 Comparison of processing stabilization of polypropylene stabilized with 0.1% of a classic blend system (0.1 % Irganox B 215 (phenol (Irganox 1010) + phosphite (Irgafos 168) 1 2)) and with 0.07% of a lactone-based product (0.07% Irganox HP 2215 (85% phenol/phosphite blend (Irganox B 215)) + 15% lactone (HP 136)) [539]...

Schematic of the loss of mechanical properties of polypropylene stabilized with phenolic antioxidant and sterically hindered amine [543]...

Laermer SF, NaHiolz F. Use of biological antioxidants as polypropylene stabilizers. Plast Rubber Proc Appl 1990 14(4) 235-9. 

E. Richaud, B. Fayolle, J. Verdu. Polypropylene stabilization by hindered phenols - Kinetic aspects. Polymer Degradation and Stability 96(1), 1-11, January (2011). 

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