Determination of the Resistance to Light of Polyethylene Shrink Films Used for Pallet Loads

Abstract

The shrink films used to fix t h e loads on pallets are subjected to outdoor exposure and, particularly, t o temperature changes and light. The resistance t o photodegradation of these films must be taken into account in the design o f a quality certificate.The natural degradation o f the films was carried out in the natural environmental testing station in Bandol (south o f France). The climate o f this area represents the conditions encountered around the Mediterranean (moisture, temperature and radiant energy), which are as severe as those in most temperate countries.The accelerated tests were made at 60°C in a Sairem-Cepap 12/24 cabinet comprising four mercury gas-filled arc lamps o f the mean pressure type. The quality o f the light is representative o f natural photoageing. Any radiation o f wavelength lower than 290 nm, which is absent f r o m the solar spectrum, is carefully eliminated. The light sources radiate light rich in photons that have wavelengths between 290 and 450 nm, and provide one of the main factors o f degradation. The intensity o f emission and the spectral composition were constant during 5000 h.Three kinds o f films o f 120pm thickness were tested:(i) four films with 'medium' protection against sunshine (6 months resistance in a(ii) four films with 'high' protection against sunshine (12 months resistance in a very sunny country); (iii) one reference film without any protection.A film was considered acceptable if its mechanical properties (tensile strength and elongation) did not fall more than 50% after exposure t o natural radiations for 6 or 12 months, respectively. Comparative tests have shown that for these particular kinds o f polyethylene films, exposure t o natural radiations at Bandol for 6 or 12 months is equivalent t o an accelerated ageing in a Sairem-Cepap cabinet o f 350 or 500 h, respectively.

Combined Impact of Ultraviolet and Chemical Fluids on High‐density Polyethylene Packaging Material

“…The spread of the oxidation starts at impurities or other imperfections in the material and first spreads over the surface and later into the depth of the material. The degradation means a cumulative decrease in the molecular weight of the polymer, which reduces the mechanical strength …”

“…The degradation means a cumulative decrease in the molecular weight of the polymer, 1 which reduces the mechanical strength. 2,3 Existing concepts to protect against degradation by UV 4 include the following:…”