The role of hindered piperidine (HALS) compounds for the stabilization of polypropylene against oxidation reactions caused by ozone and oxidative products formed during photolysis of ozone

Abstract

SynopsisThe role of hindered piperidine (HALS) photostabilizers for the photostabilization of polypropylene films against oxidative reactions caused by ozone and oxidative species formed during photolysis of ozone under UV irradiation (i.e., atomic oxygen and singlet oxygen) has been investigated and discussed. It has been found that ozonization and/or photoozonization of 2,2,6,6-tetramethyl-piperidine (I) and piperidinoxy radical (2,2,6,6-tetramethylpiperidino-l-oxy) (11) gives a high yield (91-988) 2,6-dimethyl-2-hydroxy-6-nitro-heptane. Ozonization and/or photoozonization of HAIS probably occur by a similar mechanism as reported for (I) and (11). HALS photostabilizer reacts with ozone and/or photolysis products of ozone (atomic oxygen and/or singlet oxygen) and loses its function in the photostabilization process. For that reason protection of polypropylene against photooxidative degradation and photoozonization is of great commercial importance.

Oxidation of polypropylene in a solution of monochlorobenzene

“…6 -8 Salts, more particularly salts of transition metals, act as catalysts in the auto oxidation of atactic PP. 9 -16 The oxidation of atactic PP may also be conducted in solvents such as monochlorobenzene or dichlorobenzene 12 at 70 -125°C, in the presence of ozone, 13,14 ditertiary butyl peroxalate, 15 or an aqueous solution 16 of K 2 Cr 2 O 7 /H 2 SO 4 . The oxidized PP (OPP) may be used as a compatibilizer in polymer blends; it may also be used as a lubricant or processing aid in certain alloys and composite systems.…”

A novel approach to ozone ‐ water mass transfer using hollow ‐ fiber reactors

“…This was not observed in the time frame of these experiments. Studies of the oxidation of polypropylene by ozone [17] indicated reaction times in the order hours are required for significant carbonyl and hydroxyl group formations. CONCLUSION It appears that the hollow fiber membrane reactor shows promise for transferring ozone.…”

“…The slope (B) for the counter-current case is 1.5 times larger than for the co-current case. From the slope of each line, a mass transfer coefficient, ¿¿, can be derived by using equation (14) or (17). The calculated values for ki in the co-current and counter-current cases are 0.034 cm • min" 1 and 0.044 cm • min" 1 , respectively.…”

Kinetic study of hindered amine light stabilizer photografting in low density polyethylene films under natural weathering conditions

“…It is well established that hindered amine light stabilizers (HALSs) are the most efficient photostabilizers for polyolefins1–4 because of their multifunctional activities in the photostabilization mechanisms. These are summarized by Allen and Edge5 as follows: chain‐breaking donor/acceptor redox mechanism through the nitroxyl/substituted‐hydroxylamine intermediates, decomposition of hydroperoxides by the amine during processing, inhibition of the photoreaction of α,β‐unsaturated carbonyl groups in polyolefins, reduction in the quantum yield of hydroperoxide photolysis, singlet‐oxygen quenching (only in polydienes), complexation with hydroperoxides/oxygen, complexation with transition‐metal ions, and excited‐state quenching by the nitroxyl radical. …”