Electrospinning of Ethyl Cellulose - Poly(ethylene oxide) and Cellulose Acetate - Poly(ethylene oxide) Nonwovens for the Encapsulation and Release of Thymol and Carvacrol
Thymol and carvacrol are naturally-occurring antimicrobial agents in herb essential oils. This study investigated the encapsulation of thymol and carvacrol using electrospun ethyl cellulose-poly(ethylene oxide) (EC-PEO) and cellulose acetate-poly(ethylene oxide) (CA-PEO) nonwovens, respectively. EC-PEO nonwovens were electrospun from dopes prepared in 80% (v/v) aqueous ethanol solution, and CA-PEO nonwovens were electrospun from acetic acid:acetone blend solvents (1:0, 3:1, and 1:1 weight ratios), respectively. The solution properties of the spin dopes were evaluated, including surface tension, electrical conductivity, viscosity, as well as solvent vapor pressure and dielectric constant. Moreover, polymer-polymer, polymer-solvent, polymer-antimicrobial and solvent-antimicrobial compatibilities were explained using Hansen solubility parameters. Antimicrobial-incorporated electrospun nonwovens were further analyzed using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy to elucidate how thymol and carvacrol interact with the polymers. The encapsulation efficiency (EE) of antimicrobial agents decreased as their loading in the spin dope increased. On the other hand, increasing PEO molecular weight increased the EE values. For the encapsulation of carvacrol in CA-PEO nonwovens, increasing acetic acid ratio in the binary solvent resulted in an increase in carvacol EE. Both EC-PEO and CA-PEO electrospun nonwovens exhibited humidity-dependent release behavior; as the relative humidity increased from 33 to 93%, the release rates and equilibrium concentrations for thymol and carvacrol increased considerably. The thymol-loaded EC-PEO and cavacrol-loaded CA-PEO nonwovens potentially can be useful as substrates for antimicrobial applications, such as in active packaging for the extension of food shelf life.