Polypropylene oxidative stability

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

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)... 

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. 

A variety of methods for evaluating antioxidants in polypropylene has been developed during the past several years. Polymer producers, end-use manufacturers, additive suppliers, academicians, and others have developed widely disparate test methods, all of which presumably yield the same results—i.e., the test methods rate the antioxidants and antioxidant systems in the same relative order of effectiveness. Many of these test methods are useful tools in distinguishing unstabilized polymer, moderately stabilized polymer, and highly stabilized polymer systems. Today, all of the polypropylene producers offer highly stabilized polymers. Effective antioxidants are available from several additive suppliers. How does one select the best antioxidant or polymer formulation for a particular end use This paper compares the results obtained by various test methods used to evaluate the two basic types of oxidative stability, processing stability and end-use or environmental stability. The correlation or lack... 

Metal oxide semiconductor chemical sensors in combination with MDA have been shown to be useful to estimate the oxidative stability of polypropylene during processing instead of traditional melt flow index analysis (50). An array of sensors was used to receive a detailed analysis of volatiles. At quality measurements of different poly(butylene adipate)s the use of indicator products has been proven better than analyses of the decrease in molecular weight or mass loss for early degradation detection. Adipic acid, quantified using gas chromatography, was then used as the indicator product [51]. 

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. 

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". 

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

A comparison of the thermal stability of polyethylene oxide, polypropylene oxide, polyethylene and polypropylene has been presented by Madorsky and Straus [230]. More recently, studies on the thermal degradation of polytetramethylene oxide (I), polyhexamethylene oxide (II) and polydioxolane (III)... 

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

Precision of time-to-failure measurements in controlled conditions, when the said test procedure is closely followed, is rather fair. ASTM D 3012-00 lists an example with three polypropylene samples, apparently, of different origin, tested in seven different laboratories (a ronnd robin test). They showed oxidative stability of the samples (time to failnre) at 150°C as 14.0 0.8,35 3, and 63 5 days, respectively, for within-laboratory standard deviations of the average, that is, within 6-9% of the average, and 14 + 3, 35 + 7, and 63 + 19 days, respectively, for between-laboratory standard deviations of the average, that is, within 20-30% of the average. 

The solution oxidation technique allows the study of polyolefin autoxi-dation under conditions where the temperature, concentration of reactants, and rates of radical initiation can be controlled. The results should be considered as a useful prelude to any fundamental understanding of the autoxidation processes which occur in neat polymers where the effects of very high viscosity, partial crystallinity, and oxygen diffusion rates are included. The objective of our work was to determine the kinetics and stoichiometry of the inhibited autoxidation of polypropylene in solution. A relatively detailed study of the oxidation of polypropylene inhibited by 2,6-di-terf-butyl-4-methylphenol [butylated hydroxytoluene (BHT)] has been made for comparison with data obtained in polypropylene oxidations inhibited by a variety of other stabilizers which include commercial polyfunctional antioxidants. Singly hindered phenols appeared to be superior in the inhibited-solution oxidation of polypropylene, and the application of this finding to stabilization technology was investigated briefly. 

Upon heating, sulfonyl azide compounds containing a hindered phenolic antioxidant moiety graft to the polymer matrix. This technique is applicable to saturated and unsaturated hydrocarbon polymers, copolymers, and terpoly-mers such as NBR, NR, EPDM, polyethylene, and polypropylene. Even after extraction with an organic solvent, the oxidative stability of the polymers is much greater than that of the polymers containing conventional antioxidants. The preparation of the sulfonyl azide antioxidants and the chemistry and application of the nitrene insertion mechanism are described. 

The photo-oxidative degradation of polypropylene and stabilization by hindered amines has been reviewed. A study has appeared of the effect of P-carotene on the photoreactivity of anthracene in hexane solution and a kinetic scheme has been proposed to account for the photochemical and photophysical processes that occur on irradiation at 365 nm. Quenching rate constants have been determined between /S-carotene and singlet oxygen. Some characteristics have been communicated of the sensitized photo-oxidation of abietic acid contained in a vinyl butyl ether-butyl methacrylate-methacrylic acid copolymer. At 400 nm... 

ISO 4577 [198] covers the thermal oxidative stability of polypropylene. Test pieces are mounted on a rotating drum located in a forced air circulating oven set to the preferred temperature value of 150 C, although where the effect of temperature on the stability is required, temperatures down to 100°C may be used (Fig. 34). The failure time in this standard is taken as the time in days for the test pieces to show localized crazing, crumbling. and or discoloration. 

Stable double emulsions, based on various block copolymers of polyethylene oxides and polypropylene oxides known as Pluronies, have been used. In a recent example. Cole and Whateley (84) have used complexes of Pluronic F127 PAA (polyaerylie aeid) in the internal aqueous phase. In the oil phase, Span 80 and Pluronie LlOl (5 wt %) were used. The outer interfaee was stabilized by xanthan gum (0.25 wt %) and Tween 80 (1 wt %). Theophylline and I-insulin (iodinated insulin) were ineorporated in the internal aqueous phase of the stabilized multiple emulsion, and the release rates were studied. The release rates were found to be related to the droplet sizes of the emulsion whieh were dependent on the partiele size of the pluronie F127 PAA eomplex in the internal aqueous phase and the type of the lipophilie surfaetant in the oil phase. The authors have used the eomplex between the poloxamer surfactant and PAA that occurred at pH 2 and at low molar ratio as a barrier for the release of active matter from the inner to the outer phase. 

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