Food-grade hydroxypropyl methylcellulose-based formulations for electrohydrodynamic processing: Part I – Role of solution parameters on fibre and particle production

Abstract

Electrohydrodynamic (EHD) processing allows the production of micro and nano structures with high surfacearea-to-volume ratio from biopolymers and environmentally friendly solvents. Such structures hold a very significant potential for application in the food area. The aim of this work was to assess the role of solution parameters in the formation of hydroxypropyl methylcellulose (HPMC)-based micro and nanostructures through EHD processing, establishing a relationship between variables such as viscosity and concentration, and processing zones (i.e., combinations of processing conditions that move the system towards electrospinningfibres are formedor electrosprayingparticles are formed).Micro and nano structures were produced through electrospinning and electrospraying using HPMC with low (HPMC LMW) and high (HPMC HMW) molecular weight. Solutions were characterized regarding surface tension, conductivity, viscosity, zero-shear rate and specific viscosity. Plotting specific viscosity versus concentration allowed determining the electrospraying and electrospinning zones, which were confirmed through scanning electron microscopy analysis. HPMC LMW led to the formation of particles. For concentrations between 1 and 2% (w/v) rod like particles were formed, and round particles were obtained for concentrations ranging from 3 to 6% (w/v). The mean particle diameter varied between 833 and 1188 nm, while the aspect ratio ranged from 1.3 to 3.7. Nanofibres were generated using HPMC HMW, being beaded fibres produced at a concentration of 1% (w/v) and smooth fibres produced for concentrations between 1.5 and 2.25% (w/v). The developed nanofibres displayed a mean diameter ranging between 79 and 161 nm.Electrospraying and electrospinning zones were successfully determined for HPMC LMW and HMW. Nevertheless, near transition zones variability regarding the obtained morphology was observed once other processing parameters (e.g., flow rate) can influence the morphology of fibers and particles.

Management of Operational Parameters and Novel Spinneret Configurations for the Electrohydrodynamic Processing of Functional Polymers

“…At higher concentrations of polymer ( c > c* ), chain entanglements can stabilize the electrospinning jet and, thus, allow for solvent evaporation and fiber formation. [ 26,38 ] By establishing a relationship between particle or fiber formation and the value of ( n e ) soln , the spinnability of a given solution can be determined. For instance, Shenoy et al.…”

“…[17] In general terms, EHDP is a facile top-down method to produce micro-and nanostructures. [25,26] It can be operated in two basic methods: electrospinning, which allows produc- ing micro-and nanofibers, and electrospraying that produces micro-and nanoparticles. Operation methods and equipment may vary according to the intended structures and use, but the basic setup is equal for both electrospinning and electrospraying techniques.…”

“…Operation methods and equipment may vary according to the intended structures and use, but the basic setup is equal for both electrospinning and electrospraying techniques. [12,[25][26][27][28][29] A schematic illustration of the basic setup of EHDP, both for electrospinning and electrospraying, can be seen in Figure 2. A basic setup requires just four components, namely a syringe equipped with a metal capillary (usually a needle-shaped spinneret), a feed pump to feed the polymer solution through the spinneret, a high-voltage power supply (usually applied at the tip of the spinneret), and a grounded collector (of variable morphology) to collect the produced structures.…”

“…A basic setup requires just four components, namely a syringe equipped with a metal capillary (usually a needle-shaped spinneret), a feed pump to feed the polymer solution through the spinneret, a high-voltage power supply (usually applied at the tip of the spinneret), and a grounded collector (of variable morphology) to collect the produced structures. [12,[25][26][27][28][29] The voltage difference between the spinneret and the grounded collector creates an electrical field that, when the droplet's surface tension is exceeded, draws the polymer solution from the spinneret tip to the grounded collector, either in the shape of fibers (electrospinning) or particles (electrospraying). This causes rapid evaporation of the solvent and results in the production of dry micro-and nanofibers or micro-and nanoparticles, respectively, that are deposited on the collector.…”

“…[ 38 ] The solution entanglement number [( n e ) soln ] can be determined using Equation (), which is essential to determine whether fibers or particles will be obtained during EHDP. [ 38 ] It is defined as the ratio between polymer's M W to its solution entanglement molecular weight [( M e ) soln ], where M e is the entanglement molecular weight of the undiluted polymers: [ 26,38 ] $$\begin{equation}{\rm{\;}}{\left( {ne} \right)_{s{\rm{oln}}}} = \frac{{{M_{{\rm{W\;}}}}}}{{{{\left( {{M_{\rm{e}}}} \right)}_{{\rm{soln}}}}}}{\rm{\;}} = \frac{{\left( {\phi_P}{M_{\rm{W}}} \right)}}{{{M_{\rm{e}}}}}\end{equation}$$…”