No abstract

The purpose of this study was to determine the root cause of fracture in bottoms of rectangular 18 l cans of water-based acrylic paint used in the building industry and sold in retail. Following a change in the formulation of the inner coating of the cans, fractures developed in the double seams of the can bottoms, which were made of electrolytic chromium/chromium oxide-coated steel internally coated with pigmented varnish (epoxy melamine). Slight differences were detected in the infrared spectra of both the new and altered varnishes produced with the same base resin. The microanalysis of paint samples collected from both damaged and undamaged cans revealed presence of practically the same elements. The evaluation of the varnished surface of can bottoms revealed depressions in the varnish of all cracked bottoms, inclusive in the curved areas and bottom hook of the double seam, which did not get in direct contact with the paint. However, depressions were not detected in undamaged can bottoms. The metallographic analysis did not reveal significant differences between the microstructures of the metal of cracked or uncracked bottoms. The conclusion was that paint elements got in contact with the steel sheet in the defective spots of the varnished surface, thus starting punctual corrosion that evolved to stress corrosion with ensuing rupture. The stressing agent was the weight of the paint itself or else residual metal stress due to the change in its microstructure caused by the metal-forming process.

The aim of this study was to evaluate the quality of some glass bottles used for extra virgin olive oil (EVOO) related to light barrier properties, including clear and coloured glass in different colour intensities, glass with shrink labels, and external ceramic decoration. Some of these glass bottles available on the Brazilian market were also evaluated for closure integrity and barrier to oxygen, headspace gas atmosphere, and the quality of the product according to legislation. An increase in light barrier properties was observed for the darkest glass bottle that depends on the pigment quantity and the wall thickness. A total light barrier was obtained for glass with black shrink labels and external ceramic decoration. Closure systems used for the analysed packaging showed good integrity and low oxygen permeability, and the inertness of headspace atmosphere ensured a lower availability of oxygen for product oxidation. In general, the products met the requirements imposed in the legislation.