Hybrid nanocomposites by nano-coating fragmentation

Polymer nanocomposite materials (PNCs) with metal nanoparticles are of great interest for several fields, as polymer matrix properties can be improved while maintaining their light weight and ductile nature. However, currently PNCs use is limited by technological issues as difficulties in controlling particle size, shape and aggregation during their synthesis. Moreover, the separation of nanoparticle aggregates should occur during manufacturing process by mixing with the polymer base, but this process is also troublesome. In the present study, a new two-steps process to fabricate polymer matrix nanocomposites, called “Nano-Coating Fragmentation” (NCF) is presented: in the first step, metal nano-films are deposited on polymeric substrates by thin film deposition technique; in the second, coated polymer substrates are mixed with high shear forces at high temperature. As a result, it is the fragmentation of the nanocoating during mixing to produce the nanoparticles directly within the polymer matrix. Silver nanocomposites were firstly produced by using lab-scale equipment to obtain a material having antibacterial properties. Ag nano-films were deposited by PVD sputtering on polypropylene (PP) pellets. The fragmentation was carried out by means of a lab-scale polymer mixer. Then, a massive production of silver nanocomposites was performed with a semi-industrial equipment comprised of a special PVD sputtering system to deposit a large amount of polymeric pellets at a time and an injection molding machine to produce the nanocomposite. Furthermore, silver nanocomposites were produced by coating ABS and PLA filaments by PVD sputtering. Coated filaments were used in 3D printing FDM. Microscopic observations of nanocomposites revealed silver particles homogenously distributed. Thermal and mechanical properties of the nanocomposites were measured as well. The presence of dispersed nanofiller was confirmed by DSC analysis of the molded samples. Their antibacterial activity was verified in accordance to ISO 22196 and ASTM E2149 on Escherichia Coli and Staphylococcus Aureus. A further applications of the new process was carried out by using other coating materials as Al to obtain improved oxygen barrier properties in PET sheets.