Evaluation of Degree of Deterioration of Plastics Surfaces by the Methylene Blue Adsorption Method

Abstract

Plastics have been used widely for food-related household products such as tableware. These products deteriorate with the passage of time owing to the actions of oxygen, light, heat and other chemical or physical factors. Thus, consideration should be given to the undesirable contamination of foods by additives and decomposed products in the plastics.A simple method of measuring the degree of the deterioration of plastics has not previously been reported. However, we found that methylene blue (MB) is not adsorbed on an intact plastic surface, but is adsorbed on a deteriorated one. On the basis of this property, a simple MB method of determining the deterioration of plastics was developed, as follows.The plastic item was dipped in 0.2% MB solution. After five minutes, the solution was discarded and the item was rinsed in tap water. The adsorbed MB was completely recovered from the stained sample by 4% acetic acid extraction for 20 minutes. The optical density (OD) of the eluate was measured with a spectrophotometer at the wavelength of 665nm.The results obtained by the MB method for 76 items of tableware showed that the OD levels of the eluates from the samples were well correlated with the visually estimated degree of deterioration, and indicate that the method is useful for the quantitative evaluation of plastics deterioration.