Article Dispersion of Micro Fibrillated Cellulose (MFC) in Poly(lactic acid) (PLA) from Lab-Scale to Semi-Industrial Processing Using Biobased Plasticizers as Dispersing Aids Giovanna Molinari 1 , Vito Gigante 1,2 , Stefano Fiori 3 , Laura Aliotta 1,2, * and Andrea Lazzeri 1,2, *   Citation: Molinari, G.; Gigante, V.; Fiori, S.; Aliotta, L.; Lazzeri, A. Dispersion of Micro Fibrillated Cellulose (MFC) in Poly(lactic acid) (PLA) from Lab-Scale to Semi-Industrial Processing Using Biobased Plasticizers as Dispersing Aids. Chemistry 2021, 3, 896–915. https://doi.org/10.3390/ chemistry3030066 Academic Editor: Pietro Russo Received: 22 July 2021 Accepted: 21 August 2021 Published: 25 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Civil and Industrial Engineering, University of Pisa, 56122 Pisa, Italy; giovanna.molinari@phd.unipi.it (G.M.); vito.gigante@dici.unipi.it (V.G.) 2 Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), 50121 Florence, Italy 3 Condensia Quimica, C/Junqueras 11-A, 08003 Barcelona, Spain; s.fiori@condensia.com * Correspondence: laura.aliotta@dici.unipi.it (L.A.); andrea.lazzeri@unipi.it (A.L.) Abstract: In the present study, two commercial typologies of microfibrillated cellulose (MFC) (Exilva and Celish) with 2% wt % were firstly melt-compounded at the laboratory scale into polylactic acid (PLA) by a microcompounder. To reach an MFC proper dispersion and avoid the well-known aglomeration problems, the use of two kinds of biobased plasticisers (poly(ethylene glycol) (PEG) and lactic acid oligomer (OLA)) were investigated. The plasticizers had the dual effect of dispersing the MFC, and at the same time, they counterbalanced the excessive stiffness caused by the addition of MFC to the PLA matrix. Several preliminaries dilution tests, with different aqueous cellulose suspension/plasticizer weight ratios were carried out. These tests were accompanied by SEM observations and IR and mechanical tests on compression-molded films in order to select the best plasticizer content. The best formulation was then scaled up in a semi-industrial twin-screw extruder, feeding the solution by a peristaltic pump, to optimize the industrial-scale production of commercial MFC-based composites with a solvent-free method. From this study, it can be seen that the use of plasticisers as dispersing aids is a biobased and green solution that can be easily used in conventional extrusion techniques. Keywords: polymer composites; biodegradable polymers; processing technologies 1. Introduction In the 21st century, the need of finding new substitute materials, to minimize envi- ronmental footprint, is ever more pressing due to many ecological issues [1,2]. Nowadays, there is growing interest in biobased materials, especially for food packaging applications, to substitute the currently used petrochemical-based polymers. Among them, polylactic acid (PLA) has gained interest, because it can be synthesized from natural resources [3]. PLA can be used for single-use items that are used at room temperature, e.g., plastic uten- sils, cold-drink cups, thermoformed lunch boxes which are not reusable plasticware, plastic films, or, and rubber toughened for frozen applications [4,5]. Nevertheless, its poor flexibil- ity, impact resistance, thermal stability during processing, and crystallization rates limit its applications [6]. A common sustainable technique to improve the final performances of PLA is related to different strategies, such as the development of natural-fiber-reinforced biocomposites [7–11]. Biocomposites show an improvement of both mechanical properties and thermal stability with respect to neat biopolymers. In particular, cellulose is known to improve the barrier and mechanical properties of thermoplastic biopolymer films [12]. Actually, special interest has been paid to mi- crofibrillated cellulose (MFC). MFC is a stereoregular linear polysaccharide of ringed glucose molecules with flat ribbon-like conformation. It is characterized by repeated D- glucopyranose units linked by 1,4-β glycoside bonds with particles sizes ranging from Chemistry 2021, 3, 896–915. https://doi.org/10.3390/chemistry3030066 https://www.mdpi.com/journal/chemistry