Research and development of new products and processes: reclamation of a manufacturing waste

The aim of the research was the development of new products and processes from a manufacturing waste. The manufacturing waste were produced by a metallurgic Italian company which produced thin silver metallic films. These films were used as coating and food decoration. Thin films were produced by an hammering process. The starting material, silver laminate, had a thickness of 10 μm. During the hammering process films with various thickness were obtained. The final produced silver films had a thickness of about 300 nm which can be considered a submicrometric dimension, near to the nanometric range (≤100 nm). At the end the submicrometric films were cut, giving a square shape (10 cm x 10 cm) and inserted into boxes. The residues, produced during this step, named untreated flakes (UF), were used in the research. Mainly we studied the possible use of UF as a catalyst in antimicrobial applications in aqueous medium. After a thorough bibliographic research considering the various aspects of the use of silver as antimicrobial agent (chapter 2), the research was divided in various stages: to investigate the use of flakes as antimicrobial agent, at first we verified if they possessed antimicrobial capability. We conducted some antimicrobial tests using Escherichia coli (E. coli JM109) as Gram-negative microorganism model. We showed that the flakes (UF) didn’t present antimicrobial capability up to 24 h (chapter 3). On the basis of these results we treated the UF with three activation processes: 1)Thermal activation in reducing atmosphere; 2)Thermal activation in air; 3)Chemical activation with H2O2. Then we tested the antimicrobial activity of the new obtained products. We showed that the activation processes gave the flakes antimicrobial capability (chapter 3). The antimicrobial agents are classified as bacteriostatic or bactericidal. Bacteriostatic agents cause only the growth inhibition of microorganisms while bactericidal agents cause the cells death. E. coli were observed at a fluorescence microscope and at a scanning electron microscope (SEM), after specific treatment processes. In this way we determined that activated flakes were bactericidal agents (chapter 4). In the next two stages we investigated the possible mechanism of action of the flakes: On the basis of literature knowledge we studied the relationship between the capability of flakes to release silver in aqueous medium and their antimicrobial activity. We showed that the presence of flakes was necessary to have E. coli decrease over time (chapter 5); we characterised the morphology and chemical composition of the flakes surface by SEM and XPS to verify if the antimicrobial activity acquired by activated flakes could be affected by some morphological or chemical change. We concluded that the antimicrobial property was due to the presence of dissolved oxygen (chapter 6). In the final stage we performed some experiments which simulated possible applications of activated silver flakes (chapter 7).