High-Pressure Microfluidization as a Green Tool for Optimizing the Mechanical Performance of All-Cellulose Composites

Abstract

We herein report the production of environmentally inspired all-cellulose composites in response to the ever-growing concern on the extensive usage of nonbiodegradable materials derived from nonrenewable resources. Hydroxypropyl methylcellulose (HPMC) was used as a film-forming matrix, while microcrystalline cellulose (MCC) was added as a reinforcement filler. Because the efficiency of fillers in transferring mechanical strength to polymer matrixes relies upon the dispersion level of the former within the latter, this contribution set out to improve the homogeneity of the composite films through a green, solvent-free approach. Indeed, as-received MCC actually decreased the tensile strength, Young’s modulus, and elongation at break of HPMC films in ca. 80%, 33%, and 90%, respectively. High-pressure microfluidization was demonstrated to break MCC particles down, not to play a role on cellulose crystallinity, and to expose surface groups and/or create mechanoradicals, as suggested by a combination of spectroscopic, structural, morphological, and rheological techniques, capable of interacting with HPMC and increasing MCC colloidal stability, thus lessening particle aggregation and improving its dispersion within film matrix. A central composite design guided the optimization of the filler–matrix interaction, which presented a quadratic behavior; that is, overprocessing led to impaired mechanical properties. Seven cycles was the most cost-effective processing condition leading to the strongest, stiffest composites. This study sheds light on the effect of high-pressure microfluidization on cellulosic particles and on the impact of these in all-cellulose composites.

Upcycling Microbial Cellulose Scraps into Nanowhiskers with Engineered Performance as Fillers in All-Cellulose Composites

“…While increasing the tensile strength and YM of HPMC-only films to 41 and 80%, respectively, adding 5 wt % of the BCNC through a high-energy mixing process did not affect (p > 0.05) the EB (Figure 4b), although some of the treatments did reduce film extensibility, as reported elsewhere for similar systems. 7,29 The aforementioned treatment also lessened (p < 0.05) the WVP of HPMC-only films in 22.5%, whereas none of the others affected (p > 0.05) the WVP of pristine HPMC films. Because low WVP values are typical of good barriers to moisture, one may conclude that HPMC films may represent a better barrier material when filled with the BCNC, though depending on the filler content and mixing protocol.…”

“…This is a clear outcome of the filler-in-matrix state of dispersion, which must be sufficiently high to prevent particle aggregation that is known to create stress raisers as well as to decrease the specific filler/matrix interfacial area, impairing the load transfer efficiency. 7 Comparably, Salari et al 30 found CNCs to reinforce chitosan films when the particles were homogeneously dispersed within the nanocomposite, favoring filler/ matrix interactions and the effective matrix-to-filler load transfer. A similar effect was observed on the tensile strength of HPMC-only films, which became more resistant (p < 0.05) upon BCNC addition followed by a high-energy procedure, regardless of the BCNC-to-HPMC ratio.…”

“…16 This is beneficial for composites because filler-inmatrix dispersion is a key factor enabling optimum transfer of mechanical stress, while filler aggregation may give rise to stress raisers. 7,17 Using a cellulosic matrix as a binder for BCNCs (i.e., all-cellulose composites) is an interesting approach because of the chemical compatibility among the phases, 18 leading to proper matrix/filler interactions and benefited mechanical and barrier properties, to mention a few. Hydroxypropyl methylcellulose (HPMC) is a cellulose ether that serves as a proper matrix for such materials because of its good film-forming ability and nonionic nature, 7 avoiding matrix/filler repulsion in case both are negatively charged or prompt matrix/filler complexation if these phases are unlikely charged.…”

“…It is highly versatile and can be used either as a continuous matrix or in its colloidal formthe so-called nanocelluloses, that is, cellulose nanofibrils (CNFs) or cellulose nanocrystals (CNCs)to hierarchically assemble sustainable, yet multifunctional materials . In order to parallel traditional materials in terms of performance, all-cellulose (nano)­composites films, − filaments, and beads have been extensively reported lately. Higher plants have been by far the major source of (nano)­celluloses, which can also be bottom-up extruded by some strains of bacteria, termed as bacterial cellulose (BC), microbial cellulose, or biocellulose.…”

“…Depending on the isolation route, charged groups may be introduced on the surface of BCNCs, providing them with improved colloidal stability arising from electrostatic repulsion . This is beneficial for composites because filler-in-matrix dispersion is a key factor enabling optimum transfer of mechanical stress, while filler aggregation may give rise to stress raisers. , Using a cellulosic matrix as a binder for BCNCs ( i.e. , all-cellulose composites) is an interesting approach because of the chemical compatibility among the phases, leading to proper matrix/filler interactions and benefited mechanical and barrier properties, to mention a few.…”