Irradiated polypropylene

On the basis of the above findings, grafting of vinyl monomers onto irradiated polypropylene has been attempted successfully by the mutual method. Upon irradiation hydroperoxide groups are introduced, which provide sites for grafting. During mutual irradiation in the presence of the monomer in aqueous medium, these hydroperoxide groups and water undergo decomposi-... 

There is still some doubt as to the validity of the assignments of the ESR spectra for high energy-irradiated polypropylene. It is difficult for us to evaluate the probability of the different interpretations, even though these problems have been treated previously in this laboratory (50). 

It is obvious from this review that there is still a great deal of uncertainty in interpreting the ESR spectra of irradiated polypropylene. We believe that applying ultraviolet absorption measurements to polypropylene—a method which Dole et al. (9, 10, II, 12) have used for irradiated polyethylene—could determine whether allylic radicals (IX) are present or not, which is one of the basic questions. 

The ESR spectra of polyisobutylene after irradiation with ultraviolet light (6) are different from those obtained after irradiation with ionizing radiation. The spectra consists mainly of two components one, a sharp quartet which has a half life of 1% hours at liquid nitrogen temperature, has been attributed to free methyl radicals (XI), in analogy with ultraviolet-irradiated polypropylene (51). The broad component is composed of many superimposed lines and was interpreted as caused by three different radicals, all stable at liquid nitrogen temperature. One of these radicals (XV) is the counterpart to the methyl radical (XI) while the others are the two radicals (XIII and XVI) which can both be formed by hydrogen abstraction. 

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. 

Comparison of Chemiluminescence with Impact Strength for Monitoring Degradation of Irradiated Polypropylene... 

The thioether ester (DLTDP) shows a very strong synergistic effect with the phenolic stabilizer at room temperature, and is active alone at 60°C for protection from loss of impact strength of the irradiated polypropylene. 

L. Woo, S.Y. Ding, A Khare, and M.T.K. Ling. Failure progression and mechanisms of irradiated polypropylenes and other medical polymers. In G. Wypych (Ed.), Weathering of Plastics. Testing to Mirror Real Life Performance, Plastic Design Library, 1999. 

When irradiated polypropylene syringe flanges are subjected to the bending test, their curves appear as shown in Figure 8. The main consequence of irradiation is the reduction of the angle at which the sample can be deflected before breakage occurs. As the sample is irradiated... 

The severe degradation of polypropylene following sterilizing doses of irradiation can be characterized mechanically by its failure to undergo the necessary work in practice. Embrittlement increases with time for an irradiated polypropylene, thus rendering an acceptable formulation totally unacceptable a few months after irradiation. Naturally, the decay of radicals can be accelerated by thermal annealing, limited by the geometrical distortion temperature. 

Irradiated Polypropylene. Part II. Electron Spin Resonance Studies, Adv. Chem. Ser. (1978) 169,151. 

In 7-Irradiated Polypropylene Fibers Around the Glassy Transition Temperature... 

Equation (7) gives a satisfactorily description of the anomaly observed by us in gaimna irradiated polypropylene, for various types of irradiation. Analogous behaviour for active centers has been experiioentally reported... 

Exposure of polyolefins to UV radiation in the presence of air leads to autoxidative reactions with the incorporation of oxygenated groups into the polymer. The increase in UV absorbance (measured at 310 mn) of irradiated polypropylene is reported to be too low to measure for wavelengths of irradiation in the range of 260-600 nm. Even at 260 nm, only a minimal increase was observed [121], For polypropylene containing flame retardants, either DBDE (decabromodiphenyl oxide) or TBA (tetrabromobisphenol A) at a 2% level, the maximum efficiency of chain scission was observed at X. = 280 and 260 nm, respectively. 

Meligi, G., Yoshii, F., Sasaki. T., Makuuchi, K., Rabie, A. M. and Nishimoto, S-L, 1995. Comparison of the degradability of irradiated polypropylene and poly(propylene-co-ethylene) in the natural environment. Polymer Degradation and Stability, Vol. 49, No. 2, (No information 1995), pp 323-327, ISSN 0141-3910. 

Figure 2a Dynamic viscosity vs frequency for irradiated Polypropylene, Temperature 180...

DSC curves of irradiated polypropylene subsequent heating at a rate of 10 C/min after isothermal crystallization at 110 C, dose as parameter. 

PETAN-39, Gamma-Irradiated Polypropylene Studies Using DSC. 

Table 9 Oxidation induction times for modified and irradiated polypropylene (7 Cs source dose rate 0.4 kGy.h ). The data were taken from [06Z1]. ...

The percentage elongation at break values showed a decreasing trend with the irradiation dose and with the filler content. Perlite addition to nonirradiated polypropylene caused a sharp drop in elongation at break, from nearly 8% elongation for unfilled polypropylene to 2.5% at 50% perlite addition. However, in irradiated polypropylene, the dose of irradiation for a given perlite content was not very large, especially at the 50% perlite level. 

The effect of gamma radiation dose on melting temperature TJ for polypropylene containing between 0% and 50% perlite was studied. The melting temperature of the unfilled polypropylene decreases with dose of radiation. This decrease becomes even higher by the addition of perlite into gamma-irradiated polypropylene compared to the unfilled polypropylene with nonirradiated polypropylene, where the addition of perlite increased melting temperatures from 165°C to 172°C. 

In conclusion, it was found by Akin-Okten et al. [21] that the ultimate strength of perlite-filled polypropylene after a 25 kGy gamma radiation dose was better than that of unfilled irradiated polypropylene. 

Thus, the addition of mineral filler perlite apparently improves the mechanical properties of gamma-irradiated polypropylene. Even at a high dose of irradiation, perlite addition resulted in snbstantially acceptable mechanical strengths, indicating better interfacial interaction than the variation of the mechanical properties in nonirradiated polypropylene composites and the unfilled polypropylene. 

This approach has also been extended to some protiated polymers, hi y-irradiated polypropylene (PP), the more mobile peroxy radicals, where the main motion was a rotation about the polymer axis, were also more reactive and short lived, compared to peroxy radicals that were rigid on the time scale of the ESR experiment (10 -10" s) and involved only in limited local motions. ... 

When the spectrum of the specimen is recorded after it is heated to +25 °C, this maximum disappears, leaving only a shoulder on the strong band at 6.08 pm. The extinction coefficient [65] of the hand at 6.00 pm is less than that of the 6.08 pm band by a factor of 6.7. Supplementary evidence of the formation of internal double bonds in irradiated polypropylene is provided by the presence in the spectrum of bands in the 12.27-11.69 region. In this region lie bands due to deformation vibration of CH at double bonds in groups, existing in various conformations [43]. The appearance of bands at 12.27 pm and 11.69 pm in the spectrum of irradiated polypropylene can be regarded as an indication of the formation of internal double bonds in the polymer ... 

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