Soydan Ozcan

Improved mechanical properties of polylactide nanocomposites-reinforced with cellulose nanofibrils through interfacial engineering via amine-functionalization

One of the main factors responsible for the mechanical and physical properties of nanocomposites is the effectiveness of the interfacial region to transfer loads and mechanical vibrations between the nano-reinforcements and the matrix. Surface functionalization has been the preferred approach to engineer the interfaces in polymer nanocomposites in order to maximize their potential in structural and functional applications. In this study, amine-functionalized cellulose nanofibrils (mCNF-G1) were synthesized via silylation of the hydroxyl groups on the CNF surface using 3-aminopropyltrimethoxysilane (APTMS). To further increase the amine density (mCNF-G2), dendritic polyamidoamine (PAMAM) was grafted onto mCNF-G1 by the Michael addition of methacrylate onto mCNF-G1, followed by the transamidation of the ester groups of methacrylate using ethylenediamine. Compared to native CNF-reinforced, poly(l-lactide) (PLLA) nanocomposites, amine-functionalized CNF exhibited significantly improved dispersion and interfacial properties within the PLLA matrix due to the grafting of PLLA chains via aminolysis. It is also a more effective nucleating agent, with 15% mCNF-G1 leading to a crystallinity of 32.5%, compared to 0.1 and 8.7% for neat PLLA and native CNF-reinforced composites. We have demonstrated that APTMS-functionalized CNF (mCNF-G1) significantly improved the tensile strength compared to native CNF, with 10% mCNF-G1 being the most effective (i.e., >100% increase in tensile strength). However, we also found that excessive amines on the CNF surface (i.e., mCNF-G2) resulted in decreased tensile strength and modulus due to PLLA degradation via aminolysis. These results demonstrate the potential of optimized amine-functionalized CNF for future renewable material applications.

A cellulose nanocrystal-based composite electrolyte with superior dimensional stability for alkaline fuel cell membranes

Cellulose nanocrystal (CNC)-based composite films were prepared as a solid electrolyte for alkaline fuel cells. Poly(vinyl alcohol) (PVA) and silica gel hybrid were used to bind the CNCs to form a robust composite film. The mass ratio (i.e., 1 : 1, 1 : 2) of PVA and silica gel was tuned to control the hydrophobicity of the resulting films. Composite films with a range of CNC contents (i.e., 20–60%) were prepared to demonstrate the impact of CNCs on the performance of these materials as a solid electrolyte for alkaline fuel cells. Different from previously reported cross-linked polymer films, CNC-based composite films with 40% hydrophobic binder (i.e., PVA : silica gel = 1 : 2) exhibited simultaneous low water swelling (e.g., ∼5%) and high water uptake (e.g., ∼80%) due to the hydrophilicity and extraordinary dimensional stability of CNCs. It also showed a conductivity of 0.044 and 0.065 S cm−1 at 20 and 60 °C, respectively. To the best of our knowledge, the film with 60% CNC and 40% binder is characterized by the lowest hydroxide conductivity-normalized swelling ratio. Decreased CNC contents (i.e., 40 and 20%) resulted in comparable hydroxide conductivity but a greater swelling ratio. These results demonstrate the advantage of CNCs as a key component for a solid electrolyte for alkaline fuel cells over conventional polymers, suggesting the great potential of CNCs in improving the dimensional stability while maintaining the conductivity of existing anion exchange membranes.

Tunable morphologies of indium tin oxide nanostructures using nanocellulose templates

Metal oxide nanostructures have emerged as an important family of materials for various device applications. The performance is highly dependent on the morphology of the metal oxide nanostructures. Here we report a completely green approach to prepare indium tin oxide (ITO) nanoparticles using only water and cellulose nanofibril (CNF) in addition to the ITO precursor. Surface hydroxyl groups of the CNFs allow for efficient conjugation of ITO precursors (e.g., metal ions) in aqueous solution. The resulting CNF film allows for controllable spatial arrangement of metal oxide precursors, which results in tunable particle morphology (e.g., nanowires, nanospheres, and octahedral nanoparticles). These ITO nanoparticles can also form conductive and transparent ITO films. This work opens a new perspective on developing metal oxide nanostructures.