Polypropylene, ozonized

Organic light-emitting devices Organic luminescent devices Optical mass spectrometer Oriented polypropylene Ozone-safe... 

In our study we have found that UV-light greatly accelerates the rate of ozone attack at the polypropylene surface. Presented results were undertaken to determine mechanism of the photo-oxidation of polypropylene surface upon UV-irradiation of polymer films in ozone. 

Figure 1. ESR spectra of P00 radicals formed during exposure of polypropylene films to (——) ozone and (—) ozone and UV light (LI).

Figure 2. Kinetic curve of POOH groups formation in polypropylene film after 10 hours exposure to ozone.

Figure 3. Formation of carbonyl group absorption at 1714 cm in polypropylene samples exposed to ozone and UV light (L2).

Figure 4. Kinetics of carbonyl group formation at 1714 cm- in polypropylene samples (0) and ( ) ozone and UV light (L2) (4) and (A) ozone only (0) and ( ) ATR spectra (A) and (A) transmission spectra.

Table 1. Change in the wettability of polypropylene film after exposure to ozone and ozone-UV irradiation...

Figure 6. Fluorescence emission spectra of polypropylene films at 340 nm a. Treated with ozone only b. ozone and UV light (L2) c. UV-irradiated (L2) in oxygen. Excitation wavelength 240 nm.

The ozonization of polyethylene constitutes a case derived from ozoniza-tion of polypropylene since this polymer presents branchings involving tertiary carbons and also double bonds coming from the type of polymer syn-... 

Other authors took advantage of the use of ozone in the object of block copolymerization. Smets et al. ozonized polypropylene and studied the obtained hydroperoxides/peroxides ratios [124, 125] vs ozonization time. They show that hydroperoxide content is favored by long ozonization time (Table 1). 

The modification of the chemical composition of polymer surfaces, and thus their wettability with chemical substances, can be realized in different ways electric discharges more commonly called Corona effect, oxidation by a flame, plasma treatment, UV irradiation and also UV irradiation under ozone atmosphere. Numerous studies have been devoted to the effects of these different treatments. More recently, Strobel et al. [204] compared the effects of these treatments on polypropylene and polyethylene terephthalate using analytical methods such as E.S.C.A., F.T.I.R., and contact angle measurements. They demonstrated that a flame oxidizes polymers only superficially (2-3 nm) whereas treatment realized by plasma effect or Corona effect permits one to work deeply in the polymer (10 nm). The combination of UV irradiation with ozone flux modifies the chemical composition of the polymers to a depth much greater than 10 nm, introducing oxygenated functions into the core of the polymer. 

Kulik et al. [205] focused their studies on the identification of chemical species formed during the treatment of polyolefins such as polyethylene or polypropylene by gaseous ozone or ozone in aqueous medium. Experimental conditions have a great influence on the nature of the obtained species. For example, peroxidic functions, carboxylic acids, and ketones have been identified, aldehydes being absent of the surface of the materials. It must be noted here the instability of the peroxidic species formed during the treatment... 

As a result of its saturated polymer backbone, EPDM is more resistant to oxygen, ozone, UV and heat than the low-cost commodity polydiene rubbers, such as natural rubber (NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR). Therefore, the main use of EPD(M) is in outdoor applications, such as automotive sealing systems, window seals and roof sheeting, and in under-the-hood applications, such as coolant hoses. The main drawback of EPDM is its poor resistance to swelling in apolar fluids such as oil, making it inferior to high-performance elastomers, such as fluoro, acrylate and silicone elastomers in that respect. Over the last decade thermoplastic vulcanisates, produced via dynamic vulcanisation of blends of polypropylene (PP) and EPDM, have been commercialised, combining thermoplastic processability with rubber elasticity [8, 9]. 

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. 

They have all the rubberiness of the ethylene/propylene (EPR) rubber matrix, and the crystalline polypropylene (PP) domains hold them together. As saturated elastomers, they have natural resistance to oxygen and ozone aging. They are the second largest class of thermoplastic elastomers, 25 percent of the total market, used mainly in mechanical rubber parts. 

Many systems of this kind have been described up to the pressent time. An interesting example is the application of ozonized polypropylene as initiator. By this kind of emulsion polymerization, chains of methyl methacrylate, styrene, and of other monomers [157,158] can be grafted on polypropylene, thus modifying its properties. 

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