Nanocellulose crystals (CNC) are short, stiff, highly crystalline rods; nanofibrils (CNF) are longer, more flexible and entangled. Aligning fibers along the load axis boosts tensile stiffness, but the same alignment opens straighter channels for gas to slip through — a real strength-vs-barrier trade-off.
E_rel ∝ density · alignment^1.4 · (1 − 0.3·strain)
P(gas blocked per step) ∝ density · (1 − 0.6·alignment)
permeability = molecules transmitted / molecules launched
- Fiber type (CNC/CNF) — switches between short rigid crystal rods and long entangled fibrils.
- Fiber density — how many fibers pack the film; denser mats are stiffer and better gas barriers.
- Alignment / crystallinity — how strongly fibers orient along the load axis versus random entanglement.
- Applied tensile strain — stretches the film and reduces effective stiffness as strain rises toward failure.
Real-world relevance: this exact trade-off drives real nanocellulose packaging research — CNF films are prized as oxygen barriers for food packaging, while highly aligned CNC composites are used for lightweight, high-stiffness structural films.