Copper nanoparticles embedded in polypropylene made using beetroot extract show greater antimicrobial activity than comparable silver-based materials or chemically synthesized copper systems, according to a new study published in Materials.
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The research highlights how the method used to make nanoparticles, not just the metal itself, can determine how well antimicrobial polymer composites perform in real-world materials.
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Polymer nanocomposites are widely used across industry because small additions of nanoparticles can dramatically improve mechanical, electrical, and biological properties.
Copper and silver nanoparticles, in particular, are valued for their antimicrobial effects and are increasingly explored for applications ranging from packaging to textiles.
However, most studies focus on nanoparticle composition rather than how synthesis routes affect nanoparticle behavior once embedded in polymers.
While “green” synthesis methods using plant extracts are gaining attention, systematic comparisons with conventional chemical approaches remain limited - especially for less commonly studied extracts such as beetroot.
This study addresses that gap by directly comparing silver and copper nanoparticles produced either through chemical reduction or via a beetroot-based green chemistry route, then testing how those particles behave once incorporated into polypropylene.
From Nanoparticles to Polymer Films
The researchers synthesized four nanoparticle systems: chemically reduced silver (C-AgNPs), green-synthesized silver (G-AgNPs), chemically reduced copper (C-CuNPs), and green-synthesized copper (G-CuNPs).
The green synthesis used beetroot extract as both a reducing and stabilizing agent.
Nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible spectroscopy, and dynamic light scattering (DLS). All four nanoparticle types were then embedded into polypropylene by melt processing to form thin composite films.
Scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed that the nanoparticles were successfully incorporated and distributed throughout the polymer matrix.
Size, Shape, and Dispersion
TEM analysis revealed clear differences associated with the synthesis method. Green-synthesized silver nanoparticles averaged 14 ± 2 nm in size, compared with 18 ± 3 nm for chemically synthesized silver. For copper, green-synthesized particles were smaller (13 ± 4 nm) than their chemically reduced counterparts (20 ± 3 nm).
Morphology also differed. Chemically synthesized copper nanoparticles were relatively uniform, while green-synthesized copper formed irregular, leaf-like particles with rough, polycrystalline structures.
Once embedded in polypropylene, silver nanoparticles (regardless of synthesis route) showed a stronger tendency to agglomerate. Copper nanoparticles were generally better dispersed, particularly those produced via green synthesis, making them more accessible at the polymer-microbe interface.
DLS measurements revealed larger hydrodynamic sizes for green-synthesized nanoparticles, reflecting organic surface layers derived from beetroot phytochemicals rather than larger inorganic cores.
Testing Antimicrobial Performance
The antimicrobial activity of the composite films was evaluated using disk diffusion assays against Gram-positive bacteria (Staphylococcus aureus and Bacillus cereus), Gram-negative bacteria (Escherichia coli), and the fungus Candida krusei.
Pure polypropylene showed no antimicrobial activity. Composites containing chemically synthesized copper nanoparticles also failed to inhibit microbial growth. Silver-based composites showed limited inhibition beneath the test discs.
By contrast, composites containing green-synthesized copper nanoparticles displayed the strongest bactericidal and fungicidal effects across all tested organisms.
The authors attribute this enhanced performance to a combination of smaller crystallite size, reduced agglomeration, and beetroot-derived phytochemicals that promote reactive oxygen species generation and metal-ion release - even after the nanoparticles are locked into solid polymer films.
The antimicrobial effects were assessed qualitatively through inhibition zones rather than minimum inhibitory concentration measurements.
What this Means for Antimicrobial Nanosynthesis
The findings show that the antimicrobial performance of polymer nanocomposites depends strongly on how nanoparticles are synthesized and how they behave within real materials, not just on their chemical identity.
Beetroot-based green synthesis offers a low-cost, environmentally friendly route to producing copper nanoparticles that retain high antimicrobial activity when embedded in polypropylene. This makes them promising candidates for applications such as agro-textiles, packaging materials, and antimicrobial surface coatings.
However, assessing the sustainability of these particles should take into consideration the use of polypropylene and its recyclability, as well as longevity.
The authors note that further work is needed to evaluate long-term stability, nanoparticle release, and performance under application-relevant conditions before such materials can be deployed outside the laboratory.
Journal Reference
Wasilewska A., et al. (2026). Antimicrobial Properties of Polymer-Based Nanocomposites Modified by Nanoparticles Produced by Green Chemistry. Materials 19(2):251. DOI: 10.3390/ma19020251