Revestimentos ativos a base de poli(estireno-co-butadieno) com nanocristais de celulose (CNC) e nanoparticulas de prata biogênica (AgNPs) por aspersão por sopro em solução (SBSp) para aplicação em embalagens de alimentos

Abstract

In this work, antimicrobial coatings containing poly(styrene-co-butadiene) SB latex, cellulose nanocrystals (CNC) and biogenic silver nanoparticles (AgNPs) produced by solution blow spraying (SBSp) on two substrates, glass and paper, were developed and evaluated in order to provide easy-to- apply coating. The biogenic AgNPs were produced by chemical reduction of silver nitrate with oregano extract (Origanum vulgare L). The nanoparticles presented a concentration of 0.000 17 g/mL, an average diameter of 60 nm, determined by dynamic light scattering (DLS), and a minimum inhibitory concentration (MIC) detected for E. coli and S. aureus of 27.8 μg/g. After drying under ambient conditions, the AgNPs acquired the shape of rods and semi-spheres with micrometric size, observed by scanning electron microscopy with field emission coupled to energy dispersive X-ray spectrometry (SEM-FEG/EDS). The coatings were produced by mixing 20% by mass of SB latex with 3% by mass of CNC (SB/CNC) in relation to the dry mass of SB and the SBSp spraying conditions were adjusted for both substrates obtaining uniform SB/CNC and thickness of the order of 0.7 μm and 1.6 μm on the glass and paper substrates, respectively. The SB/CNC/AgNPs, SB/CNC/AgNPs1x and SB/CNC/AgNPs2x coatings were produced using three variations in the SBSp processing and also the form of incorporation of AgNPs was observed (anchoring on the external surface, or incorporation in the dispersion of the polymeric nanocomposite), in addition to the effect of the concentration of AgNPs on the coating surface (SB/CNC/AgNPs1x and SB/CNC/AgNPs2x). In the case of the paper substrate, a maximum coating weight of 17.8 g/m2 and values lower than 30 mg/g for water absorption capacity (WBC) were established as a target, taking as reference the cardboard coated with the SB/CNC/AgNPs nanocomposite by lamination. The SEM-FEG/EDS images revealed silver agglomeration on the surface of the SB/CNC/AgNPs2x. The SB/CNC/AgNPs1x showed antimicrobial activity similar to the SB/CNC/AgNPs coating. Although the inhibition of biofilm growth was lower for S. aureus (63%), all coatings with AgNPs had antimicrobial action against the two strains studied, E. coli and S. aureus, and showed minimal silver migration content, being suitable for use in food packaging.