Biomedical Engineering Reference
In-Depth Information
industry. Thus, improving machining accuracy and the depth of natural fiber
products, enhancing product quality, and adding value are inevitable. Meanwhile,
environmental protection, low energy consumption, and utilization of resources
by recycling have become the main themes of the development of the modern
economy. The innovation of the textile industry, focusing on the principal line of
ecology protection, energy saving, and resource-optimized utilization, has become
inevitable for its future development. In this process, the importance of cellulose
biotechnology has caused widespread concern [
1
,
2
].
9.1.1
Structure and Performance of Cotton Fiber
Cotton fiber is a natural fiber with a high fiber content. It contains 94 % cellulose,
1.3 % protein, 0.9 % pectin, 1.2 % ash, 0.6 % wax, and 0.8 % organic acids.
Cellulose is a straight-chain macromolecule composed of thousands of glucose
molecules linked by the
-1,4-glycosidic bonds. The molecular weight of the natural
cellulose is 600-1,500 kDa. The cotton fiber is composed of long chains of fiber
molecules, not arranged in parallel in a certain direction, but arranged in two or
three layers with different degrees of crystallinity and polymerization. The long
chain of 40 cellulose molecules constitutes the basic unit, a fiber bundle, with an
average diameter of 3.5 nm. Several fiber bundles cross with each other to form the
network structure.
The section of cotton fiber from outside to inside includes the cuticle, primary
cell wall, secondary cell wall, and cell lumen. The cuticle is a thin layer with cotton
wax and pectin that has filamentous wrinkles on the surface. When the primary cell
wall is prolonged to some extent, the cell wall gradually precipitates from outside
to inside to form the secondary cell wall, which is almost entirely composed of
celluloses. Cellulose is precipitated to form the slender bundles (microfilaments);
many microfilaments are connected to form microfibril bundles. They tend to
form the spiral structure with the fiber uranium, which presents spiral wrinkles
on the fiber surface. Crystallization regions and amorphous regions are in each of
the microfilaments. The X-ray diffraction spectrum shows that a series of holes,
submicroscopic capillary tubes, run through the primary cell wall and secondary
cell wall. Capillary tubes in cotton fibers include two categories. One is the coarse
capillary tube, such as the cell lumen and pits; the other is the cell wall capillary
tube, such as the gap between microfilaments and the gap between molecular chains
in amorphous regions (there are a thousand more superficial areas of this kind than
of coarse capillary tubes).
The supramolecular structure of the cotton fibers is also called a microstructure,
referring to cellulose in the cell wall. The common structure theory is a model
of two-phase structure, which states that the natural cellulose is a defectively
complete crystalline material. The crystallization region is composed of some high-
ordered parts with complete crystalline grains; the amorphous region consists of
some defective, low-ordered parts with incomplete crystalline grains. In addition,
“
