The effect of hindered amine light stabilizers on the photooxidative stability of high‐density polyethylene

Abstract

SynopsisThe photoprotective effectiveness of various polymeric and nonpolymeric hindered amine light stabilizers (HALS) was determined by exposing samples of high-density polyethylene (HDPE) containing these additives to ultraviolet (UV) light and measuring the resultant oxygen uptake characteristics. Values of the initial quantum yield for oxygen uptake calculated for these formulations indicate that the higher molecular weight HALS compounds are less effective photostabilizers than the nonpolymeric HALS, and this is partly attributable to their decreased mobility in the polymer matrix. It was further found that the addition of an ultraviolet absorber ( W A ) to a formulation containing a polymeric HALS compound enhances its photostability, although this phenomenon may be partly due to synergism between the UVA and the antioxidant, the latter having been added as part of the base stabilization. The antagonism which exists between certain sulfur-containing antioxidants and HALS compounds was also investigated and it was found that the lower molecular weight sulfur-containing antioxidants exhibit the greatest degree of antagonism. The results confirm that the mobility in the polymer matrix of the stabilizer system can serve as an explanation of its effectiveness. The article provides evidence that the technique of oxygen uptake monitoring is a sensitive and rapid method of assessment of polymer photostability in the presence of stabilizer systems.It is believedlg that during the uninhibited photooxidation of polyolefins, the chain reaction is normally terminated by the interaction of two propagating radicals, which results in inactive products. It is reasonable to assume that photostabilization can be achieved by scavenging free radical species (such as hydroperoxyl, hydroxyl, and macroalkyl radicals), which are formed during propagation and chain branching. In fact, free radical scavenging is the main mechanism by which phenolic antioxidants protect polymers against thermo-

HALS stabilization of LDPE films used in agricultural applications

“…Bigger and Delatycki 40) reported that the photoprotective mechanism of HALS compounds is based on their ability to prevent Norrish types I and II processes from occurring following photolytic conversion of a,b-unsaturated carbonyl impurities to the b,c-unsaturated species.…”

Modeling of the Kinetic Degradation of Unstabilized and HALS-Stabilized LDPE Films in Natural Aging

“…Moreover, it has been found that a certain amount of piperidinoxyl radicals is covalently attached to the polymer backbone. The effectiveness of Tinuvin 622 is due to the stability of piperidinoxyl and their regenerations [18,19]. These values of half-life time are reported in Fig.…”

Photostabilisation of Polymer Materials

“…Using oxygen uptake experiments Bigger and Delatycki [98] showed the negative influence of BFS-1, S-1 and BFS-2 on the effectiveness of LMW-HALS-1 as UV stabilizer in HDPE (see Fig. However, in many cases this combination behaves antagonistic.…”

“…HALS] (wt%) Initial quantum yield oxygen uptake * The initial quantum yield for oxygen uptake of HDPE as a function of the amount of LMW-HALS-1 for formulation with 0.15%wt/wt BFS-1 (1), S-1 (2), BFS-2 (3), and without a sulfur containing stabilizer (4)[98].…”