The effects of ionizing radiation on the molecular weight of crystalline polypropylene

Abstract

Absolute molecular weight measurements were obtained on samples of crystalline polypropylene before and after irradiation i.wac. Some of the chain fracture was produced directly by the radiation, and some occurred days later by a reaction between trapped free radicals and atmospheric oxygen when the ampoules were opened to remove the polymer. The latter reaction is the cause of the abnormally large decrease in the molecular weight of polypropylene when it is irradiated to low doses i.vac. and subsequently exposed to the atmosphere. This observation raises questions as to the validity of many polymer irradiation studies where care is not taken to destroy the radicals before allowing the irradiated polymer t o contact oxygen.When the trapped free radicals in irradiated polypropylene were destroyed with methyl mercaptan prior t o the admission of air, scission yields became normal and the gelation dose decreased markedly.)The radiochemical yields of chain fractures and crosslinks at 35OC. are G(chain fracture) = 0.62 and G(cross1inks) = 0.50 when oxidation is not permitted. ZUSAMMENFASSUNG:Absolute Messungen des Molekulargewichts von kristallinen Polypropylenproben wurden vor und nach Bestrahlung im Vakuum erzielt. Spaltung von Bindungen in der Hauptkette wurde zu einem gewissen AusmaS direkt durch die Strahlung herbeigefiihrt, wahrend weiterer Abbau einige Tage spater stattfand, und zwar durch Reaktion eingefangener freier Radikale mit atmosphiirischem Sauerstoff, als die Ampullen zwecks Entfernung des Polymerisates geoffnet wurden. Die letztere Reaktion hat eine ungewohnlich groBe Abnahme des Molekulargewichts von Polypropylen zur Folge, wenn das Polymerisat im Vakuum mit niedrigen Dosen bestrahlt und anschlieaend der Atmosphtire ausgesetzt wird. Diese Beobachtung legt die Frage nahe, wie giiltig viele Arbeiten a d dem Gebiet der Polymerbestrahlung eigentlich sein konnen, wenn keinerlei Vorkehrungen getroffen worden sind, um die Radikale vor dem Kontakt zwischen bestrahltem Polymeren und Sauerstoff zu zerstoren.Als eingefangene freie Radikale in bestrahltem Polypropylen mit Methylmerkaptan vor Zulassung von Luft reagierten, wurde die Ausbeute des Abbaus normal und die Geldosis verringerte sich stark. Die 100-eV-Ausbeute des Abbaus und der Vernetzungen bei ciner Temperatur von 35OC sind G(Abbau) = 0,62 und G(Vernetzung) = 0,50, wenn jegliche Oxydation ausgeschlossen wird.

Impact of Swift Heavy Ions and Gamma Radiation upon Optical, Structural, and Chemical Properties of Polypropylene Polymer Films

“…15 The growth of this band signifies that the free radicals created due to gamma exposure have reacted with the atmospheric oxygen giving radiation induced oxidation and got converted to peroxides and hydroperoxides and consequently PP is carbonized. 18 In case of carbon ionsirradiated samples, oxidation occurred by a reaction between trapped free radicals and atmospheric oxygen 38 after the ladder (containing samples) was immediately removed from the vacuum chamber (after ion irradiation). But in case of lithium ions irradiation, the ladder was removed almost 3 h after the irradiation due to the high radiation dose level, so the oxidation in case of lithiumirradiated samples was least probable.…”

Sterilization Induced Changes in Polypropylene-Based Ffp2 Masks

“…However, it is well-known that irradiation induces changes in organic materials at the molecular, macromolecular and microscopic levels. Due to surgical and FFP2 masks being made of different layers of polypropylene, it was essential to ascertain the materials’ resistance to possible sterilization protocols, since PP is actually well known to be quite sensitive to radiolytic degradation [ 9 , 10 ]. Answers to this question arose during each previous pandemic—the last one being the Influenza one in 2009 [ 11 , 12 , 13 ]—but fell into disuse either when the pandemic was disappearing or when the mask production reached a sufficient level.…”