Exploitation of the Complex Chemistry of Hindered Amine Stabilizers in Effective Plastics Stabilization

摘要

Hindered amine stabilizers (HAS) remain a prominent class of stabilizers having a fortunate development with continuous interest in shaping the future properties of plastics:increase in polymer durability,application extension,reaching new effects.Commercial tests provided much information.Insufficient mechanistic interpretations of the complex effects of environmental factors (harshness of testing,penetration of radiation and oxygen,superposition of temperature,atmospheric impurities) and those of the microenvironment (morphology of the polymer matrix,physical relations of HAS-polymer,interference between HAS and other additives) are a drawback.Model experiments complement commercial studies and explain some phenomena.A careful transfer of information from model experiments must be done to avoid misinterpretation of mechanisms,particularly of the HAS regenerative cycle.A critical analysis of primary steps of the HAS activity mechanism in the polymer matrix based on HAS-related primary nitroxides,formation of their stationary concentration and concentration gradients influenced by polymer morphology,spatial competition between autoreactions,and oxidation of polymer-developed alkyl radicals and their scavenging by nitroxides (the key process of HAS efficiency) is outlined.Cyclic regeneration of nitroxides affected by the structure of the amino moiety in the HAS molecule,influence of acid environment,atmospheric ozone or singlet oxygen,cooperative mixtures of HAS with UV absorbers,combinations with additives increasing the thermal stabilization effect and improving color retention,assessment of the heat stabilization performance of HAS by proper testing,and influence of the molecular weight of HAS are mentioned together with examples of the chemical consumption of HAS in the final phases of their lifetime.