Studies on nanocellulose - Functional microparticles, threads, and aerogels of cellulose nanofibrils

Henrikki Mertaniemi

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Nanocellulose is a general term referring to a promising new family of cellulose-based materials with attractive properties, including high mechanical strength in the dry state and the capability of forming stiff, strongly shear-thinning gels in water. Since cellulose-rich biomass is sustainably available in very large quantities, nanocellulose could potentially, e.g., replace oil-based polymers in many applications. In most current applications, nanocellulose is used as an addidive or a minor component. This thesis aims to broaden the application spectrum of nanofibrillated cellulose (NFC) to functional materials where NFC is the major constituent. This thesis consists of three publications. In Publication I, the NFC is surface modified to pre-pare non-wetting coatings comprising hydrophobized microparticles of NFC. It is observed that at many length scales, the morphology of such surfaces with the microparticles remarkably resembles that of a lotus leaf, which is famous of its superhydrophobicity and self-cleaning properties. The prepared surfaces were superhydrophobic, and water drops easily slid off when the surface was tilted slightly. In Publication II, the NFC is crosslinked to improve the mechanical strength of NFC threads in wet conditions and enable the use of NFC as a stem cell culture substrate in biomedical applications. The wetstate mechanical performance of NFC is greatly improved by crosslinking with glutaraldehyde. The crosslinked NFC threads (NFC-X) soaked in water retain up to 40% of the dry-state tensile strength of NFC. Whereas non-modified NFC is too weak to be handled after 7 days under cell culture conditions, the cross-linked NFC-X is much stronger, and can be pulled through skin and manipulated in the surgical hands-on tests performed. Furthermore, NFC-X threads are able to support stem cell growth without altering the characteristics of the cells or inducing toxicity to them. In Publication III, the rheological properties of highly concentrated NFC hydrogels are utilized to control the size of ice crystals when preparing aerogels. The stiffness of nanocellulose hydrogels can be tuned over several orders of magnitude by changing the solid contents of the gel, up to a shear modulus larger than 600 kPa. The mechanical properties of the hydrogel, in turn, enable the control over the micropore size when preparing aerogels by freeze-drying. The increase in density results in a porous material with a very high surface area to volume ratio up to 3 m2/cm and pore size down to a few micrometers. In conclusion, the results of this thesis demonstrate potential solutions to challenges in employing nanocellulose in applications outside the laboratory. The results suggest that nanocellulose may in future be employed in coatings, biomedical applications, or as functional microporous supports with a very high active surface area.
Translated title of the contributionNanoselluloosa-tutkimuksia: toiminnallisia mikrohiukkasia, lankoja ja aerogeelejä selluloosa-nanofibrilleistä
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Ikkala, Olli, Supervising Professor
Publisher
Print ISBNs978-952-60-7247-0
Electronic ISBNs978-952-60-7246-3
Publication statusPublished - 2017
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • nanocellulose
  • microfibrillated cellulose
  • superhydrophobic
  • stem cell
  • aerogel

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