Preirradiated Polypropylene Research Articles

Grafting onto polypropylene. I. Effect of solvents in gamma radiation‐induced graft copolymerization of poly(acrylonitrile)

AbstractGraft copolymerization of acrylonitrile (AN) onto isotactic polypropylene (PP) fiber has been studied by using gamma rays from a 2100 Ci 60Co source as initiator by preirradiation technique. The preirradiated PP was treated with AN and the mixture was graft copolymerized by heating to 100°C for different time periods. The percentage of grafting is determined as a function of total dose, reaction time, and monomer concentration. The effect of different solvents such as H2O, CH3OH, and dioxane upon percentage of grafting has been studied. The maximum effect was observed in water and the minimum in CH3OH. PP—g—PAN was characterized by IR spectroscopic and thermogravimetric methods. A plausible mechanism of gamma radiation induced grafting of AN onto PP in the absence and in the presence of solvents has been proposed. An attempt has been made to compare the relative abilities of different solvents to influence grafting.

Electron spin resonance studies on graft copolymerization of gaseous styrene onto preirradiated polypropylene. II. Preirradiation under vacuum

AbstractGraft copolymerization of gaseous styrene was carried out at 40°C onto polypropylene preirradiated under vacuum. In order to investigate the origin of graft initiation activity, ESR spectra of irradiated polymers were measured and discussed. Although there are about three times as many radicals trapped in the sample irradiated at −78°C as in the sample irradiated at room temperature, both the samples showed nearly same degree of grafting. This is due to the ineffectiveness of radicals trapped in the amorphous region for grafting. The samples irradiated under vacuum showed more grafting than those irradiated in an oxygen atmosphere. This is compatible with the conclusion in the previous paper that in grafting of polypropylene irradiated in an oxygen atmosphere the carbon radicals produced by hydrogen abstraction by trapped peroxy radicals are the effective active centers.

Electron spin resonance studies on graft copolymerization of gaseous styrene onto preirradiated polypropylene. III. Preirradiation under vacuum followed by exposure to oxygen at −78°C

AbstractGrafting of styrene vapor was carried out onto polypropylene γ‐irradiated under vacuum followed by exposure to oxygen at −78°C. A comparison with the results on polypropylene irradiated in an oxygen atmosphere leads to an interesting result. Two samples were irradiated at room temperature under vacuum and in an oxygen atmosphere, respectively, the former being followed by exposure to oxygen. Although irradiation was carried out at room temperature for either sample and nearly the same amounts of the peroxy radicals are trapped, the former showed more grafting than the latter. The origin of this difference was investigated by means of electron spin resonance. Significant differences were observed in ESR spectra as well as in isothermal decays of the trapped peroxy radicals. In the former sample, the trapped peroxy radicals had a higher mobility, and consequently a significant hydrogen abstraction by the peroxy radicals was observed during storage at 40°C. This result supports the conclusion of the previous paper that the radicals effective in the grafting reaction of polypropylene preirradiated in an oxygen atmosphere are the carbon radicals which are produced by hydrogen abstraction by the peroxy radicals.

Electron spin resonance studies on graft copolymerization of gaseous styrene onto preirradiated polypropylene. I. Preirradiation in the presence of oxygen

AbstractGraft copolymerization of gaseous styrene was carried out onto polypropylene preirradiated in the presence of oxygen at −78°C and at room temperature, respectively. The origin of the graft initiation activities of these polymers was investigated by means of electron spin resonance (ESR) of trapped radicals. More grafting was found for the polymers irradiated at −78°C than for those irradiated at room temperature. The difference of grafting between polymers irradiated at −78°C and those irradiated at room temperature was not explained by the total amounts of trapped radicals, and it was found that all radicals are not effective in the grafting reaction. ESR measurements showed that there exist two kinds of peroxy radicals, one has more effective ability of abstracting hydrogen atoms from the surrounding polymer chains to form carbon radicals, and another is less effective at the temperature of grafting reaction (40°C). Although the samples irradiated at −78°C contain the both types of radicals, those irradiated at room temperature do not contain the former type of radicals. It was shown that the carbon radicals produced by such a hydrogen abstraction reaction are actually the effective centers in the grafting reaction of polymers irradiated in the presence of oxygen.

Graft copolymerizations of gaseous vinyl chloride and vinylidene chloride on preirradiated polypropylene

AbstractThe graft copolymerizations onto the preirradiated polypropylene fibers of gaseous vinyl chloride and also of gaseous vinylidene chloride were carried out. The fibers were preirradiated with γ‐rays from a 60Co source at −78°C. in air to a total dose of 8 X 105 rad, and were thus presumed to contain peroxide radicals which were active in grafting at ordinary temperature. The volume decrease of monomers at constant pressures due to the sorption and the grafting reaction was followed automatically at temperatures ranging from −10 to 80°C. The net monomer consumption through the grafting process was estimated by subtracting the volume change due to the sorption from the total volume change of monomers. In general, the extent of grafting was lower at the higher grafting temperature and the decrease of the grafting activity of fibers was also accelerated. The grafting was found to increase almost linearly with the logarithm of the reaction time and the logarithm of the radiation of the radiation dose to the fibers. The extent of grafting was also proportional to the vapor pressure of monomer at a given reaction temperature and was supposed to be controlled by the amount of the monomer adsorbed. Raising the irradiation temperature higher than 0°C. brought about a marked decrease in the activity of preirradiated polypropylene. The grafting activity was successfully retained by the polymer for at least a fortnight at −78°C.

Heat Treatment of Irradiated Polypropylene

IT has been shown by Lawton1,2 that during the high-energy irradiation of a polymer, the main effect produced is either intermolecular cross-linking or degradation of the molecular chain, and radicals produced during irradiation can be trapped in the crystalline regions. Crystalline ‘Marlex-50’, irradiated at 25° C. and then annealed at 150° C., gave more cross-links than ‘Marlex-50’ irradiated at 25° C. and not annealed, but less than that of the polymer irradiated at 150° C. for the same dose of irradiation. We have been able to demonstrate the delayed cross-linking effect by heat treatment of pre-irradiated isotactic polypropylene. We find that many trapped radicals produced during irradiation, which are stable at room temperature (as detected by electron spin resonance measurements), could contribute to delayed cross-linking on annealing the irradiated polymer after irradiation, and a big increase of gel content was observed. On the other hand, materials irradiated at 180° C. (molten state) gave no gel content for high dosage beyond 80 Mrads, indicating that in the molten state degradation of the molecular chain was predominant. The phenomenon is very different from the effect in polyethylene.