Designing High Performance All-Cellulose Composites by Dissolution/Swelling of Macro- and Nano-scale Cellulose Fibers

Feng Chen

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

All-cellulose composites (ACCs) is a new generation of biocomposites with both the matrix and reinforcing fibers being based on cellulose. This thesis explores various designs of ACCs using either macro- or nano-scale cellulose fibers as raw materials and ionic liquids (ILs) as cellulose solvents. Prior to ACCs fabrication, the swelling and dissolution kinetics of different cellulose fibers (natural fiber flax, viscose-type Cordenka and two Ioncell fibers with one containing lignin and hemicelluloses) in solvent power tuned ILs (1-ethyl-3-methylimidazolium acetate, [EMIM][OAc] and N-methyl-1,5-diazabicyclo[4.3.0]non-5-enium dimethyl phosphate, [mDBN][DMP]) was studied. High performance unidirectional flax-based ACCs, isotropic filter paper-based ACCs and nanopaper were then produced involving controlled dissolution and/or swelling of cellulose fibers. The fundamental investigation on fibers swelling and dissolution kinetics revealed that the rate of fiber dissolution in [EMIM][OAc] depended on fiber accessibility and solvent viscosity. The fastest dissolution (in [EMIM][OAc] and [EMIM][OAc]-5% water) or swelling (in [EMIM][OAc]-15% water) was recorded for Ioncell fibers and the slowest for Cordenka. An anomalous two-step dissolution-swelling behavior of flax was observed in [mDBN][DMP] and [mDBN][DMP]-water. ACCs from either unidirectional flax or isotropic filter paper were produced via selective dissolution strategy. For flax-based ACCs, it was shown that the mechanical properties were controlled by the sufficient amount of matrix and the non-dissolution of the inner, mechanically strong cell walls in the fiber. The interface between the matrix and the fibers was further artfully re-modelled by utilizing two-step dissolution-swelling phenomenon in [mDBN][DMP], resulting in increased tensile strength in both transverse direction and fiber direction. For isotropic paper-based ACCs, a digital image correlation technique was explored for accuracy enhanced analysis of mechanical properties. A 30-60 min impregnation allowed increasing tensile strength, Young's modulus and toughness of a filter paper in almost 10 times, 5 times and 25 times, respectively. Isotropic ACC constructed from highly disordered and entangled cellulose nanofibrils (CNFs) through their self-binding exhibited an exceptional ductility (up to 35%) while combining high strength (up to 260 MPa) and toughness (up to 51 MJ/m3). This was realized by swelling of hemicelluloses in-between the nanofibrils in [EMIM][OAc]–water below the dissolution limit of cellulose and hemicellulose, thus allowing delamination of thick CNF bundles into thinner ones without influencing the length. The results obtained demonstrate that a fundamental understanding of cellulose swelling and dissolution promotes various possibilities to design ACCs with engineered performance. The findings bring new perspectives to the design of macroscale and nanoscale cellulosic materials.
Translated title of the contributionDesigning High Performance All-Cellulose Composites by Dissolution/Swelling of Macro- and Nano-scale Cellulose Fibers
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Budtova, Tatiana, Supervising Professor
  • Budtova, Tatiana, Thesis Advisor
  • Sixta, Herbert, Thesis Advisor
  • Hummel, Michael, Thesis Advisor
Publisher
Print ISBNs978-952-64-0235-2
Electronic ISBNs978-952-64-0236-9
Publication statusPublished - 2021
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • cellulose
  • nanocellulose
  • ionic liquid
  • all-cellulose composite
  • mechanical properties

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