Polyolefin polymers (LLDPE, LDPE, HDPE and PP) are widely used for packaging materials (bags and sacks) and agricultural mulch films. When used and discarded these types of products pose a special problem in that they are not readily susceptible to accelerated degradation in the environment, whether in landfill, sewage sludge or compost systems. They are expected to remain pollutants for many years and in certain instances form permanent refuse or waste.

Like other organic materials polyolefin polymers will however over time undergo very slow oxidative degradation by elemental oxygen on exposure in the environment. The most important accelerating environmental influences apart from oxygen are heat, light, metal ion contamination, ozone and mechanical deformation. The nature of degradation varies in rate and extent depending on the polymer chemical structure, composition, impurity profile and external environmental conditions.

Oxidative degradation of polymers under ambient conditions can be achieved by the peroxidation process involving free radical chain reactions consisting of initiation, propagation and termination steps. Unstable hydroperoxides are formed in each cycle of the peroxidation chain sequence. Their instability is due to the weakness of the peroxide bond which readily undergoes thermolysis and photolysis on exposure to heat and light respectively. This reaction is powerfully catalysed by transition metal ions. The ultimate oxidative products are lower molecular weight carboxylic acids and alcohols.

Antioxidants and stabilisers are normally employed to decompose peroxide into non radical products in order to stabilise polymers against oxidative degradation. However, by manipulation of the antioxidant system environmental oxidative degradation could be induced at will by the use of selective pro-oxidants.

Robinson Brothers Limited have developed and commercialised a pro-oxidant system known as Metone Technology. It is highly effective in the oxidative degradation of polyolefin polymers under conditions of UV and thermal exposure. It can be used in applications where accelerated but controlled degradation of polymer is required after a useful lifetime. Examples include packaging (bags an sacks) , agricultural mulch films, and greenhouse cover. It has no adverse effect on polymer processing, product properties, manufacturing, storage and use. Metone technology controls and catalytically induces oxidative degradation on exposure to environmental conditions particularly heat and light, leading to the total destruction of polymers.

Metone technology consists of a two component system; Metone A and Metone M. Metone A which controls the rate of radical formation and hence peroxidation sequence by hydrogen abstraction in its triplet state. Metone M produces catalytic transition metal ions which catalytically decompose hydroperoxide into radical products. Overall control of the chain reaction depends on the concentration of individual components - Metone A and Metone M.

The products can be supplied either as discreet powders or in a combined masterbatch at 1%-2%-3% in PE.

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