Biomedical Engineering Reference
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Glucan chain aggregate
(6-8 chains)
Microfibril
(3-4 nm wide)
Cellulose ribbon
(40-60 nm wide)
Acetobacter Xylinum
(a)
(b)
b
a
Cellulose 1
β
Cellulose 1
α
OH
CH 2 OH
OH
OH
CH 2 OH
CH 2 OH
O
HO
O
O
HO
O
O
HO
(c)
O
O
O
O
HO
O
HO
O
HO
CH 2 OH
CH 2 OH
HO
CH 2 OH
HO
Figure 9.1 Biosynthesis (a), crystalline structure (b) and chemical structure (c) of cellulose
producedbyAcetobacterXylinum(Partiallyreproduced,withpermissionofTaylor&Francis
Informa UK, Ltd-Journals, from: The biosynthesis of cellulose. Brown, R.M.J., Journal of
Macromolecular Science - Pure and Applied Chemistry A33(10),1996;permissionconveyed
throughCopyrightClearanceCenter,Inc.)(1).
under various conditions of pressure (49 to 1960 Mpa) and temperature (120, 150,
200 C) for 5 min revealed that tensile strength and elongation were sensitive to the
hotpressing conditions whereas Young modulus was little affected (7). Young modulus
was rather constant, in the 16-18 GPa range, while the tensile strength and elongation
varied from the 102-260 MPa range and the 0.8-2.1% range, respectively. Interestingly
air-dried BC sheets were found to perform as well as hotpressed sheets since their tensile
modulus, strength and elongation reached 16.9 GPa, 256 MPa and 1.7% respectively,
falling within the range of those measured for the hotpressed samples. The tensile
strength and elongation decrease with higher pressure was ascribed to the introduction
of defects (9). Addition of disintegrated BC to cotton lint pulp also improved the Young
modulus and tensile strength of paper sheets while elongation was little affected by BC
addition (7). The linear increase of Young modulus and tensile strength with BC con-
tent was ascribed to the finer BC fibers that were able to H-bond and give much better
strength (9).
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