Polypropylene thermal oxidative

Figure 4 The effect of stabilizer concentration on the induction period of polypropylene thermal oxidative breakdown (temperature 200°C P02 = 300 Tor). 1-polyamineani-line disulfide 2-polydiiminodiphenyloxide disulfide 3-polythiosemicarbazide disulfide 4-Santanox 5-hydroru-beanic polydisulfide 6-thiocarbamidepoly disulfide 7-po-lydisulfide.

Table I. The evaluation of polypropylene thermal oxidative stability by the chemiluminescence and oven aging methods at 150°C...

Figure 3 Thermal oxidative breakdown of polypropylene (temperature 200°C Poj = 350 Tor stabilizer concentration 0.5 mass percent). 1-without stabilizer 2-Santanox 3-polythiosemicarbazide disulfide 4-polyamineaniline disulfide 5-polydi-iminodiphenyloxide disulfide 6-polyaniline disulfide 7-polydiiminodiphenylmethane disulfide 8-hydrorubeanicpoly disulfide 9-thiocarbamide polysulfide 10-polyiminoazobenzene disulfide.

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)-... 

Table 2 Effect of Polyamine Disulfide Concentration on the Polypropylene Flow-Melt Index During Thermal Oxidative Breakdown...

ISO 4577, Plastics - Polypropylene and propylene-copolymers - Determination of thermal oxidative stability in air - Oven method, 1983. 

During processing polypropylene melts under the action of transverse strain there occur strain-chemical conversions which can result in both decrease and increase in their molecular masses the mechanical effect on the rapidity and level of the occurring processes is considerably more prominent than the mere contribution of thermal and thermal-oxidative breakdown. These data necessitate studying the process of polymer destruction. For this purpose it would be most effective to apply the criterion of assessment of the intensity with which destructive processes happen in polymer melts. 

ISO 4577 1983 Plastics - Polypropylene and propylene-copolymers - Determination of thermal oxidative stability in air - Oven method ISO 7279 1984 Polypropylene (PP) fittings for pipes under pressure - Sockets for fusion using heated tools - Metric series - Dimensions of sockets ISO 7671 2003 Plastics piping systems for soil and waste discharge (low and high temperature) inside buildings - Polypropylene (PP)... 

In addition to acting as photostabilizers for polypropylene, nickel complexes also inhibit their direct thermal oxidative degradation by molecular oxygen. The salicylate complex (26), thought to be square planar, was more effective than the analogous cobalt(II) and copper(II) complexes.83 Iron(III) and chromium(II) analogues were almost inactive. Complexes (25) and (27) were roughly... 

Stabilizing Activity of Pyrocatechols in Thermal Oxidation and in y-Irradiation of Polypropylene. It is interesting to compare the relationships found on stabilizing isotactic polypropylene oxidized over the melting temperature with the results of our previous study (22, 23) of the stabilizing properties of some derivatives of pyrocatechol in y-irradiated polypropylene. 

Iring, M. Tudos, F. Thermal oxidation of poly-ethylenes and polypropylene effects of chemical structure and reaction conditions on the oxidation process. Prog. Polym. Sci. 1990, 15 (2), 217-262. 

During oxidative degradation, a concentration gradient always develops at a film surface. Inasmuch as the depth profile depends on permeabilities and reaction rates, the effect is more noticeable in photooxidations than in thermal oxidations. An unusually marked skin effect observed in photooxidized polypropylene has been ascribed (14) to the action of chronophores located at or near the surface. 

Photomicrographs to observe additive compatibility in the oriented film were taken at 400X using a transmission light microscope. Blooming was measured at 70°C using unoriented film samples 7 mil in thickness. Thermal oxidative stability was measured in a circulating air oven at 140°C on polypropylene films 5" x 1" x. 025". 

Irradiation of polymers with y- or electron beams is an attractive alternative to chemical sterilization because of its speed, ease of control, and the absence of residue. Radiation treatment of polypropylene, however, also initiates chemical changes which lead ultimately to embrittlement. These changes in physical properties may not become apparent until some time after the treatment. The ability of antioxidants to prevent radiation damage does not always follow the trends observed in thermal oxidation, which has stimulated efforts to develop new stabilizers or optimized combinations of existing ones. 

Chemiluminescence has been used by a number of workers to characterize the thermal oxidation of polypropylene ( 1 2). This study allowed an opportunity to use fiber-optics for transmitting chemiluminescence from the heated sample to the detector, which promises to simplify greatly the apparatus required for the technique. 

The thioether alone at room temperature does not protect polypropylene from loss of physical properties after electron-beam treatment, although irradiated samples that are subsequently heated to 150°C are apparently protected from thermal oxidation. 

Gugumus F. Re-examination of the thermal oxidation reactions of polymers 3. Various reactions in polyethylene and polypropylene. Polym Degrad Stab 2002 77(1) 147-55. 

Polymeric hydroperoxides are the major product of low temperature oxidation [Refs. 46, 113,115, 148, 189, 191, 193,195,196, 300]. Yields of hydroperoxides in oxidized polypropylene exceed 40%, and more than half that amount is contained in low molecular weight degradation products. It was shown that isolated hydroperoxide groups in thermally oxidized polypropylene constitute less than 10% of the total hydroperoxide concentration, and the majority of the polypropylene hydroperoxide groups occur in dimers, trimers, or longer sequences [148]. 

The content of aldehyde and ketone groups reaches 42% during the thermal oxidation of polypropylene, and 35—44% in polyethylene [5, 7]. This content depends on the conditions of the oxidation, particularly the temperature. The quantitative distribution of various functional groups formed during the oxidation of polyolefines is shown in Table 2. 

FUNCTIONAL GROUP CONTENT IN THERMALLY OXIDIZED POLYPROPYLENE AND POLYETHYLENE [5, 7]... 

Fig. 12. Molecular weight distribution of unstabilized polypropylene during thermal oxidation at 138°C [5],...

Ostwald and Turi [471] noted that the molecular weight distribution found during thermal oxidation of polypropylene below the melting point was broader than that found for a degradation carried out above the... 

M. Celina and G.A. George, Heterogeneous and homogeneous kinetic analysis of the thermal oxidation of polypropylene, Polym. Degrad. Stab. 1995, 50, 89-99. 

ASTM D 3012 Standard Test Method for Thermal-Oxidative Stability of Polypropylene Using a Specimen Rotator Within an Oven ... 

It has been observed that the intramolecular propagation plays an important role in the oxidations of 2,4-dimethylpentane (32,33), 2,4,6-trimethylheptane (34), and polypropylene (35,36). However, this intramolecular propagation must be unimportant in PVA oxidation since 2,4-pentanediol did not give 2,4-pentanedione under similar conditions (Run 18). Rust (37) also found no 2,4-pentanedione in the thermal oxidation of 2,4-pentanediol. Table III shows that 4-hydroxy-2-pentanone is the major primary product from 2,4-pentanediol. Therefore, the primary products from PVA must be /3-hydroxyketone and hydrogen peroxide. 

The Effect of Transition Metal Compounds on the Thermal Oxidative Degradation of Polypropylene in Solution... 

Effects of a series of transition metal stearates, the concentration of the copper stearate, the solvent, various additives, and other factors on the thermal oxidation of polypropylene were studied in trichlorobenzene solution. The mechanism of copper catalysis is discussed. The order of decreasing catalytic activity of the metal stearates was Cu > Mn > Fe > Cr > Al Ni Co control Ti >> Zn >> V. The addition of propionic acid to the solvent accelerated the oxidation of the polymer. The presence of the copper leveled off oxygen uptake of the polymer after a certain time. The amount of oxygen absorbed decreased with increasing concentration of the copper, and at higher concentration (7.9 X 10 3M) the polymer oxidation was inhibited. 

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