Cellulose Nanocrystal: Order from The Destruction of Disorder
A Rod, Not a Fiber: What CNC Is and How It’s Made
Cellulose nanocrystal (CNC) is a specific form derived from cellulose, distinct from cellulose nanofiber (CNF). Generally, CNC is shorter in length than CNF, making it more like a rod than a fiber.
CNF is typically produced by mechanical and/or chemical modification of cellulose. In particular, mechanical shearing plays a key role in disintegrating bundles of macro-scale cellulose fibers. In contrast, CNC is mainly produced through chemical processes, with acid hydrolysis used to decompose the amorphous regions of cellulose.
The term “amorphous” comes from the Greek “a- (not)” and “morphe (form),” meaning a lack of specific structure. Its opposite is “crystalline,” indicating a well-defined, ordered structure.
What makes cellulose unique is that it naturally contains both amorphous and crystalline regions. This duality raises a fundamental question: What parts of cellulose do we choose to keep, and what do we choose to discard?
Why CNC Is More Prominent in Global Research Than CNF
The distinct features of CNC become more noticeable when compared with CNF. CNF retains the original fibrous form of natural cellulose, while CNC undergoes further refinement. In this sense, CNC can be seen as more tuned for industrial applications.
One of CNC’s key advantages is its uniformity, achieved by selectively removing the amorphous regions. This structural consistency positions CNC alongside other industrial materials that rely on high reproducibility — for example, naphtha, which is systematically separated into well-defined fractions based on differences in boiling point.
This structurally consistent material is generally easier to mix with various plastics than CNF, thanks to its uniformity. A wide range of surface modifications — such as oxidation, cationization, and esterification — are available. These treatments enhance the function of CNC as a plastic modifier, primarily by reducing its hydrophilicity and improving its compatibility with hydrophobic polymer matrices.
Order and Disorder: What We Choose to Keep
As discussed above, CNC is a specific form of cellulose created by the deliberate destruction of its amorphous regions. This destruction inevitably requires both mechanical energy and chemical intervention. Through this process, cellulose becomes increasingly artificial — the more we manipulate it, the further it moves away from its natural state.
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While crystalline regions are relatively resistant to degradation, one may still ask: Is there a reason why amorphous regions exist at all?
Glass is perhaps the most familiar inorganic amorphous material. A representative organic example is an elastomer such as rubber, which is often largely amorphous. Although these materials appear fundamentally different, they share a common thermal characteristic: neither exhibits a sharp melting point. Instead, they soften gradually upon heating.
The challenge with amorphous regions in cellulose lies in the fact that they cannot be cleanly separated from crystalline regions, unlike glass or rubber. This “half-baked” structural nature complicates the use of cellulose as a purely chemical material. At the same time, this duality may reflect the biological need for flexibility and diversity within plant structures.
If our goal is to use cellulose in a truly sustainable way, then perhaps one option is not to refine it further — but instead to reconsider how intact cellulose itself can be used.
Engaging with the Duality of Cellulose
Papermaking is a way to utilize cellulose almost entirely, without excessive destruction of its structure. However, papermaking does not explicitly focus on — or consciously engage with — the duality of cellulose. In most cases, this duality does not appear to directly determine paper quality.
The perspective I am considering is more chemical and more deliberate. Ideally, I would like crystalline and amorphous regions of cellulose to play distinct roles, each contributing different functions.
Modified crystalline regions could be designed to improve compatibility with various materials, including plastics and other resins. In contrast, amorphous regions may interact uniquely with softer materials. I see the amorphous regions of cellulose as playing a role similar to rubber — connecting harder components while remaining structurally flexible. Such a fixed, rubber-like domain could selectively capture certain substances while excluding others.
Like attracts like. Polysaccharides are widely found in bacteria, for example as exopolysaccharides (EPS) or lipopolysaccharides (LPS). Cellulose amorphous regions may have the potential to interact with such biomolecules. Alternatively, grafted polymers built on CNC scaffolds may offer a more effective strategy in some cases. Which approach is optimal depends on the situation.
What matters most, however, is to approach cellulose from multiple angles — rather than treating it simply as a representative “green material.”
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