Cellulose dissolution: insights on the contributions of solvent-induced decrystallization and chain disentanglement

Abstract

The dissolution of cellulose is a critical step for the efficient utilization of this renewable resource as a starting material for the synthesis of high value-added functional polymers and chemicals and also for biofuel production. The recalcitrance of semicrystalline cellulose microfibrils presents a major barrier to cellulose dissolution. Despite research efforts, important aspects of cellulose dissolution such as solvent-induced decrystallization and chain disentanglement are not well-understood. Here we address these fundamental issues with the practical goal of gaining insights into the swelling and dissolution of cellulose that cannot be obtained from macroscopic experimental data. To this end, we have used a newly-developed phenomenological model that captures the phenomena governing the dissolution of semicrystalline polymers as well as the thermodynamics and kinetics of dissolution. This model fits well experimental data for swelling and dissolution of cotton fibers in the ionic liquid [bmim]Cl, and allows the quantification of two important aspects, i.e., solvent effectiveness in cellulose (1) decrystallization and (2) chain disentanglement, the balance of which controls the mechanism and kinetics of cellulose dissolution. The activation parameters of cellulose decrystallization, estimated using the obtained decrystallization constant values, reveal that the decrystallization of cellulose in [bmim]Cl is associated with positive enthalpy and entropy and it is also very sensitive to temperature. When the solvent effectiveness in the disruption of cellulose crystals is relatively lower than its ability to disentangle the chains, the kinetics of dissolution are controlled by decrystallization. Furthermore, conditions that facilitate cellulose chain disentanglement, in addition to increasing the rate of dissolution, can result in faster decrystallization. The solvent effectiveness in chain disentanglement is the only factor that determines the decrease of the cellulose fiber radius. In cases where the fiber dissolution rate is lower than the decrystallization rate, the dissolution of cellulose is mostly controlled by the solvent ability to disentangle the chains. The insights obtained from this study improve the understanding of cellulose-solvent interactions underlying decrystallization and disentanglement and their contributions in controlling the kinetics of cellulose swelling and dissolution.

The influence of the cation type of ionic liquid on the production of nanocrystalline cellulose and mechanical properties of chitosan-based biocomposites

“…Nowadays, ionic liquids are used mainly to dissolve or modify biomass and cellulose (Brandt et al 2013;Ghasemi et al 2017;Borysiak et al 2018), but there is also a growing interest in the use of ionic liquids for the direct production of nanometric cellulose. Swatloski et al (2002) proved that cellulose can be dissolved, without any previous activation of pretreatment, in e.g.…”

Micellization Thermodynamics of Pluronic P123 (EO20PO70EO20) Amphiphilic Block Copolymer in Aqueous Ethylammonium Nitrate (EAN) Solutions

“…Ionic liquids (ILs), low-melting salts with combinatorially high chemical diversity, are being considered for applications in various fields [ 23 ], such as biomass processing [ 24 , 25 ], pharmaceuticals [ 26 , 27 ], separations and extraction [ 28 , 29 ], catalysis and batteries [ 23 , 30 ] due to their unique properties and intermolecular interactions [ 23 , 31 ]. Some amphiphiles can self-assemble in neat ionic liquids and in ionic liquid aqueous solutions into ordered structures including micelles and lyotropic liquid crystals [ 31 , 32 , 33 , 34 ].…”

Cellulose dissolution in aqueous NaOH–ZnO: cellulose reactivity and the role of ZnO

“…If the cellulose-solvent interactions are stronger than the intra-and intermolecular interactions between cellulose chains, the crystalline network of cellulose is gradually destroyed increasing the possibility of conformational chain movement of individual chains (Rabideau et al 2013). The weakening interactions between cellulose molecules and the increasing chain movement result in the transformation of solid cellulose fibers to swollen gel-like medium (Ghasemi et al 2017a;Lu et al 2011). With increasing swelling, the individual cellulose chains start to disintegrate from each other and diffuse into the bulk solution (Ghasemi et al 2017a).…”