Natural fiber
[5][6] Natural fibers can be used for high-tech applications, such as composite parts for automobiles and medical supplies.
[citation needed] Animal fibers generally comprise proteins such as collagen, keratin and fibroin; examples include silk, sinew, wool, catgut, angora, mohair and alpaca.
These fibrils can bundle to make larger fibers that contribute to the hierarchical structure of many biological materials.
[12] These fibrils can form randomly oriented networks that provide the mechanical strength of the organic layer in different biological materials.
It makes up the cell walls of fungi and yeast, the shells of mollusks, the exoskeletons of insects and arthropods.
Chitosan is easier to process that chitin, but it is less stable because it is more hydrophilic and has pH sensitivity.
Collagen has a hierarchical structure, forming triple helices, fibrils, and fibers.
In human hair the filaments of alpha keratin are highly aligned, giving a tensile strength of approximately 200MPa.
[10] The presence of water plays a crucial role in the mechanical behavior of natural fibers.
Water plays the role of a plasticizer, a small molecule easing passage of polymer chains and in doing so increasing ductility and toughness.
When using natural fibers in applications outside of their native use, the original level of hydration must be taken into account.
For example when hydrated, the Young's Modulus of collagen decreases from 3.26 to 0.6 GPa and becomes both more ductile and tougher.
[1] Usage includes applications where energy absorption is important, such as insulation, noise absorbing panels, or collapsable areas in automobiles.
These small, crystalline cellulose fibrils are at this points reclassified as a whisker and can be 2 to 20 nm in diameter with shapes ranging from spherical to cylindrical.
The matrix of these composites are commonly hydrophobic synthetic polymers such as polyethylene, and polyvinyl chloride and copolymers of polystyrene and polyacrylate.
[20][19] Traditionally in composite science a strong interface between the matrix and filler is required to achieve favorable mechanical properties.
If this is not the case, the phases tend to separate along the weak interface and makes for very poor mechanical properties.
Because of the high surface area to volume ratio the fibers have a tendency to aggregate, more so than in micro-scale composites.
Additionally secondary processing of collagen sources to obtain sufficient purity collagen micro fibrils adds a degree of cost and challenge to creating a load bearing cellulose or other filler based nanocomposite.
It has been incorporated as a bone filling material for tissue regeneration, a drug carrier and excipient, and as an antitumor agent.
"Type III collagen (COL3A1): Gene and protein structure, tissue distribution, and associated diseases."
