Development of microbeads from unmodified biomass with tunable size and competitive mechanical properties

Abstract

Despite national and international regulations, plastic microbeads are still widely used in personal care and consumer products (PCCPs) as exfoliants and rheological modifiers, causing significant microplastic pollution following use. As a sustainable alternative, microbeads were produced by extrusion of biomass solutions and precipitation into anti-solvent. Despite using novel blends of biodegradable, non-derivatized biomass including cellulose and Kraft lignin, resulting microbeads are within the shape, size, and stiffness range of commercial plastic microbeads, even without crosslinking. Solution processability and resulting bead shape and Young's modulus can be tuned via biomass source, concentration, and degree of polymerization; biomass concentration, extrusion geometry, and precipitation and extraction conditions control the bead size. Lignin incorporation reduces the solution viscosity, which improves processability but also produces flatter beads with higher moduli than cellulose-only microbeads. While some lignin leaches from the beads when stored in water, adding surfactants like sodium dodecyl sulfate suppresses this effect, resulting in good mechanical stability over two months with no noticeable structural degradation. The stability of these mixed-source biomass Development of microbeads from unmodified biomass with tunable size and competitive mech microbeads -despite the absence of chemical crosslinking or derivatizationmakes this route a promising, robust approach for obtaining environmentallybenign microbeads of tunable size and stiffness for use in PCCPs.

A Scalable and Surfactant-Free Emulsion Method for Producing Microbeads from Varied Biomass Feedstocks

“…Beads were synthesized via an emulsion-precipitation method, in which 4 wt % % biomass solutions in ionic liquid (IL) were stirred with an immiscible oil phase to disperse droplets; antisolvent was subsequently added to precipitate these droplets and form microbeads. Based on previous work screening antisolvents for a dripping-precipitation method, 42 ethanol was selected as the antisolvent, which is immiscible with all oils examined (SI.2). Unlike other emulsionprecipitation systems�for example, aqueous alginate solutions 38 �here, the composition of the continuous oil phase cannot be changed gradually to cause precipitation.…”

“…40,41 Our recent work addressed a number of these challenges by using a dripping and precipitation method to produce biomass microbeads from nonderivatized cellulose and Kraft lignin feedstocks. 42 This process produced spherical microbeads with mechanical properties suitable for PCCPs without requiring covalent cross-linking. These larger beads (>800 μm diameter) were easy to characterize and provided information on how compositional and processing parameters influence bead size, shape, and modulus; however, beads of <800 μm diameter were not accessible and the process had limited scalability.…”

“…These larger beads (>800 μm diameter) were easy to characterize and provided information on how compositional and processing parameters influence bead size, shape, and modulus; however, beads of <800 μm diameter were not accessible and the process had limited scalability. 42 Using emulsion processes�which are widely used in industry to produce polymeric particles 43 �could address both the bead size and limited scalability of the dripping process. Previously, Jo, Park, and co-workers produced magnetic cellulose hydrogel beads using an emulsion method with oil, an ionic liquid (IL) solvent, and surfactant.…”

“…Here for the first time, we demonstrate a scalable emulsion and precipitation process for producing microbeads from mixed feedstocks of purely native, nonderivatized biomass using oil and IL both with and without surfactant. Applying insights from our prior work, 42 the process was first refined to minimize bead aggregation upon purification and improve the yield of beads of the appropriate size and mechanical properties for PCCPs. Kraft lignin was then added as a lowcost filler, successfully producing beads with minimal aggregation up to a lignin fraction of 20%.…”

Synthesis and structural design of microspheres comprising cellulose nanofibers and artificial lignin polymer by enzyme-mediated Pickering emulsion templating

“…7,8 Cellulose, which is the major skeletal component of plants and trees, and is the most abundant biomacromolecule in nature, is particularly attractive for various applications, including drug delivery, personal care products, and cosmetics. 9,10 In addition to terrestrial fungi and bacteria, a salttolerant enzyme with glucosidase activity has been found in marine bacteria such as Croceicoccus marinus, suggesting that they may be responsible for the degradation of cellulose in the marine environment. 11 Lignin, another major component of plants and trees, is also abundant in nature, and biodegrades on land and in water, where marine lignin-degrading bacteria have recently been discovered.…”