Natural active molecule chemical grafting on the surface of microfibrillated cellulose for fabrication of contact active antimicrobial surfaces

In this work, a naturally occurring phenyl isothiocyanate (PITC) molecule was covalently bonded to the surface of microfibrillated cellulose (MFC) to prepare contact active antimicrobial surfaces based on presently used materials. A preliminary comparative study was carried out on the reactivity of the hydroxyl group of cellulose and lignin compounds with phenyl isothiocyanate. Classical second order reaction kinetics was established between the hydroxyl containing model alcohol compounds and phenyl isothiocyanate with the conversion up to 80% in 20 min. X-ray diffraction and scanning electron microscopy (SEM) were utilized to monitor the change in crystallinity and morphology of the surface after grafting. Further, the successful immobilization of isothiocyanate was confirmed after grafting with contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and presence of sulfur by elemental analysis. Antibacterial activity was investigated against gram positive bacteria, Staphylococcus aureus and Bacillus subtilis, in dynamic and static experimental conditions. The PITC grafted MFC did not exhibit a bactericidal activity in dynamic condition, however, a very strong activity (complete killing) was revealed under static condition with 3.5 log initial CFU. These findings may help in the establishment of new and safe strategy for the preparation of antimicrobial contact surfaces for packaging applications.