Thermal Stability of Gamma Irradiated Low Density Polyethylene Films Containing Hindered Amine Stabilizers

Abstract

Summary: The thermal stability of gamma irradiated low density polyethylene (LDPE) films in presence of various structures of hindered amine stabilizers (HAS) was investigated by the oxygen uptake method under constant temperature of 180 °C and normal pressure conditions. The thermo‐oxidation was run using air environment. The sigmoidal dependency of oxygen uptake allows the calculation of the main kinetic parameters: oxidation induction time and oxidation rate on the propagation step. The various steps involved in the thermal degradation process were detected by the derivative procedure applied to the dependencies of oxygen uptake on time. It was found that the kinetic parameters of the thermal degradation process, determined by oxygen uptake, revealed the antioxidant role of HAS in γ‐irradiated LDPE films by providing better stability, when compared with the unstabilized samples. Moreover, the results indicated that the dependencies of oxygen uptake on thermal degradation time involved two degradation stages: the former occurring in the ungrafted moiety and the latter taking place after the antioxidant depletion is achieved. The stabilization efficiency of these oxidation inhibitors provides satisfactory thermal resistance to LDPE films, especially those based on an alkoxyamine structure.Dependencies of oxygen uptake on time at the thermal degradation of LDPE irradiated at 812 kGy. (‐□‐) free of additive; (‐○‐) Tinuvin 123; (‐▵‐) Sanduvor PR 31; (‐⋄‐) Uvasil 299.magnified imageDependencies of oxygen uptake on time at the thermal degradation of LDPE irradiated at 812 kGy. (‐□‐) free of additive; (‐○‐) Tinuvin 123; (‐▵‐) Sanduvor PR 31; (‐⋄‐) Uvasil 299.

Chemiluminescence of isotactic polypropylene induced by photo‐oxidative degradation and natural weathering

“…In our case, we can clearly observe that Sanduvor PR 31 induces higher values of activation energy of thermal oxidation as compared to unstabilized samples. This effect can be related to an antioxidative effect of the HALS which can occur even at elevated temperatures, as previously reported in the literature19, 20 in the case of polyethylene. In fact, the occurrence of this effect allows us to apply CL in characterization of the HALS effectiveness and in evaluation of the extent of degradation effects.…”

“…Chemiluminescence measurement has been used as a tool for the investigation of the oxidation of various polymers or polymer materials at elevated temperatures,4–11 solar or UV light,12–15 cold helium plasma,16 electrical stress,17 electron beam18 and γ‐ray irradiation 19, 20. Many attempts have been made to use chemiluminescence for estimation the efficiency of stabilizers 21–28…”

Grafting of Hindered Amine Stabilizer in Poly(propylene) Films under γ‐Irradiation

“…Photo‐induced grafting of Sanduvor PR 31 molecules has been already observed and reported in our previous works 17,18. Thermal grafting of this HALS seems to occur also, as it has been reported in a recent paper 4. Taking into account the above‐mentioned grafting phenomena, the objective of this paper has been, therefore, to study a possible radiation‐induced grafting of Sanduvor PR 31 molecules on PP chains.…”

“…While the formation of radicals depends on the polymer structure, the oxidation reactions can be retarded efficiently by the addition of stabilizers 1. Antioxidants like hindered phenols or hindered amines are used customarily to improve the radiation stability of polymers, especially polyolefins 2–4. These additives, which present convenient stability on high‐energy irradiation, act as radical scavengers 5.…”

Synthesis of A Star‐Shaped Macromolecular Antioxidant Based on β‐Cyclodextrin and its Antioxidative Properties in Natural Rubber

“…Thermal oxidation aging is one of the most serious problems in rubber industry because it can deteriorate their physical and mechanical properties, and thus shorten their service life . Protection from thermal oxidation aging is usually realized by the addition of hindered phenol antioxidants, which are displacing aromatic amine antioxidants owing to the toxicity and discoloration . However, due to the poor thermal stability and low extraction resistance, conventional antioxidants with low molecular weight tend to migrate to the surroundings, leading to the loss of protective function .…”