EXPLOITATION OF THE COMPLEX CHEMISTRY OF HAS 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 future properties of plastics: increase in polymer durability, application extension, reaching new effects. Research provided a lot of information, many of them containing data from commercial tests. Insufficient mechanistic interpretations of the complex effect of environmental factors (harshness of testing, penetration of radiation and oxygen, superposition of temperature, atmospheric impurities) and those of microenvironment (morphology of the polymer matrix, physical relations 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 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) are 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 thermal stabilization effect and improving color retention, assessment of heat stabilization performance of HAS by proper testing, influence of molecular weight of HAS are mentioned together with examples of chemical consumption of HAS in final phases of their lifetime.