Abstract
Bacterial nanocellulose (BNC) is becoming an important substrate for engineering multifunctional nanomaterials with singular and tunable properties for application in several domains. Here, antimicrobial conductive nanocomposites composed of poly(sulfobetaine methacrylate) (PSBMA) and BNC were fabricated as freestanding films for application in food packaging. The nanocomposite films were prepared through the one-pot polymerization of sulfobetaine methacrylate (SBMA) inside the BNC nanofibrous network and in the presence of poly(ethylene glycol) diacrylate as cross-linking agent. The ensuing films are macroscopically homogeneous, more transparent than pristine BNC, and present thermal stability up to 265 °C in a nitrogen atmosphere. Furthermore, the films have good mechanical performance (Young’s modulus ≥ 3.1 GPa), high water-uptake capacity (450–559%) and UV-blocking properties. The zwitterion film with 62 wt.% cross-linked PSBMA showed bactericidal activity against Staphylococcus aureus (4.3–log CFU mL−1 reduction) and Escherichia coli (1.1–log CFU mL−1 reduction), and proton conductivity ranging between 1.5 × 10−4 mS cm−1 (40 °C, 60% relative humidity (RH)) and 1.5 mS cm−1 (94 °C, 98% RH). Considering the current set of properties, PSBMA/BNC nanocomposites disclose potential as films for active food packaging, due to their UV-barrier properties, moisture scavenging ability, and antimicrobial activity towards pathogenic microorganisms responsible for food spoilage and foodborne illness; and also for intelligent food packaging, due to the proton motion relevant for protonic-conduction humidity sensors that monitor food humidity levels.
Highlights
The pervasive cellulose biopolymer is one of the most studied natural materials due to its renewability, unique set of properties and potential use in the most varied fields of application [1]
The domains of research are even broader when considering the nanoscale forms of cellulose, such as cellulose nanofibrils (CNFs), cellulose nanocrystals (CNCs) and bacterial nanocellulose (BNC) [2], with applications in catalysis [3], printed electronics [4], supercapacitors [5,6], sensing and biosensing [7], photonics, films, foams, nanocomposites and medical devices [8,9,10], and packaging materials [11,12], among many other examples [2,13]
BNC, a nanocellulose biosynthesized in nature [14], is an exopolysaccharide with the ability to lodge all kinds of molecules and macromolecules within its ultrafine nanofibrous network with the goal of preparing materials with distinct features and different application fields [15,16,17]
Summary
The pervasive cellulose biopolymer is one of the most studied natural materials due to its renewability, unique set of properties and potential use in the most varied fields of application [1]. To the best of our knowledge, the use of BNC in tandem with a zwitterionic polymer has not yet been investigated for engineering nanocomposite films with bioactivity and smart features, and with the ability for application in active and intelligent food packaging. The films were fabricated via the one-pot polymerization of sulfobetaine methacrylate (SBMA) inside the BNC nanofibrous network with poly(ethylene glycol) diacrylate as cross-linking agent, and characterized in terms of structure, morphology, thermal stability, mechanical performance, optical properties, antimicrobial activity against S. aureus and E. coli, moisture- and water-uptake capacity, and protonic conductivity
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