Figure 4.2
d s + d h
E =
E s ,.
(1)
d s
76
Bacterial Cellulose
4.0
Gelatin
BNCgelatin
BNC
3.0
3.5
2.5
3.0
Gelatin
BNCgelatin
BNC
Stress [MPa]
2.5
2.0
1.5
Stress [MPa]
2.0
1.5
1.0
1.0
0.5
0.5
0.0
0.0
0.0
0.2
0.4
0.6
0.8
1.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Strain [mm/mm]
Strain [mm/mm]
(a)
(b)
Figure 4.2
Compressive.(a).and.elongational.(b).stress–strain.curves.of.BNC-gelatin.DN,.gelatin,.and.BNC.
gels..The.compression.and.elongation.were.performed.perpendicular.to.and.parallel.to.the.stratified.direction.of.the.BNC.and.BNC-gelatin.DN.gels,.respectively..Concentration.of.gelatin.in.feed:.
30.wt%..EDC.concentration:.1.M..(Reproduced.with.permission.of.Nakayama.et.al..2004.)
compressive.elastic.modulus.of.1.7.MPa.in.a.direction.perpendicular.to.the.
stratified.structure,.which.is.more.than.240.times.greater.than.that.of.BNC.
(0.007.MPa).and.11.times.that.of.gelatin.gel.(0.16.MPa).(Table 4.1)..The.fracture.strength.of.BNC-gelatin.DN.gel.against.compression.reaches.3.7.MPa,.
which.is.about.31.times.greater.than.that.of.gelatin.gel.(0.12.MPa).(Table 4.1)..
The.tensile.stress–strain.curves.of.gels.along.the.direction.of.the.stratified.
layer.are.demonstrated.in.Figure 4.2b..BNC-gelatin.DN.gel.can.sustain.nearly.
3 MPa.and.has.an.elastic.modulus.of.23.MPa,.which.is.112.times.greater.than.
that.of.gelatin.gel..From.the.cyclic.compressive.test,.it.can.be.seen.that.BNC.
does. not. show. its. original. stress–strain. profile,. while. the. BNC-gelatin. DN.
gel.recovers.well.from.compressive.deformation.after.second.testing.under.a.
repeated.compressive.stress.of.up.to.30%.strain..Thus.the.DN.structure.led.to.
a.substantial.improvement.of.the.mechanical.properties.in.tensile.strength.
as.well..Similar.improvement.in.the.mechanical.strength.was.also.observed.
for.the.combination.with.polysaccharides,.such.as.sodium.alginate,.gellan.
gum,.and.ι-carrageenan.(Nakayama.et.al..2004).
For.a.material.composed.of.a.layered.structure.with.two.layers.of.. elastic.
modulus. E s . and. E h (E s . <<. E h )′,. the. macroscopic. modulus. E. of. the. material.
perpendicular. to. the. stratified. direction. depends. only. on. the. modulus.
of. the. soft. component. E s ′,. not. on. the. hard. component. E h . (Okumura. and.
de Gennes.2001):
.
d s + d h
E =
E s ,.
(1)
d s
76
Bacterial Cellulose
4.0
Gelatin
BNCgelatin
BNC
3.0
3.5
2.5
3.0
Gelatin
BNCgelatin
BNC
Stress [MPa]
2.5
2.0
1.5
Stress [MPa]
2.0
1.5
1.0
1.0
0.5
0.5
0.0
0.0
0.0
0.2
0.4
0.6
0.8
1.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Strain [mm/mm]
Strain [mm/mm]
(a)
(b)
Figure 4.2
Compressive.(a).and.elongational.(b).stress–strain.curves.of.BNC-gelatin.DN,.gelatin,.and.BNC.
gels..The.compression.and.elongation.were.performed.perpendicular.to.and.parallel.to.the.stratified.direction.of.the.BNC.and.BNC-gelatin.DN.gels,.respectively..Concentration.of.gelatin.in.feed:.
30.wt%..EDC.concentration:.1.M..(Reproduced.with.permission.of.Nakayama.et.al..2004.)
compressive.elastic.modulus.of.1.7.MPa.in.a.direction.perpendicular.to.the.
stratified.structure,.which.is.more.than.240.times.greater.than.that.of.BNC.
(0.007.MPa).and.11.times.that.of.gelatin.gel.(0.16.MPa).(Table 4.1)..The.fracture.strength.of.BNC-gelatin.DN.gel.against.compression.reaches.3.7.MPa,.
which.is.about.31.times.greater.than.that.of.gelatin.gel.(0.12.MPa).(Table 4.1)..
The.tensile.stress–strain.curves.of.gels.along.the.direction.of.the.stratified.
layer.are.demonstrated.in.Figure 4.2b..BNC-gelatin.DN.gel.can.sustain.nearly.
3 MPa.and.has.an.elastic.modulus.of.23.MPa,.which.is.112.times.greater.than.
that.of.gelatin.gel..From.the.cyclic.compressive.test,.it.can.be.seen.that.BNC.
does. not. show. its. original. stress–strain. profile,. while. the. BNC-gelatin. DN.
gel.recovers.well.from.compressive.deformation.after.second.testing.under.a.
repeated.compressive.stress.of.up.to.30%.strain..Thus.the.DN.structure.led.to.
a.substantial.improvement.of.the.mechanical.properties.in.tensile.strength.
as.well..Similar.improvement.in.the.mechanical.strength.was.also.observed.
for.the.combination.with.polysaccharides,.such.as.sodium.alginate,.gellan.
gum,.and.ι-carrageenan.(Nakayama.et.al..2004).
For.a.material.composed.of.a.layered.structure.with.two.layers.of.. elastic.
modulus. E s . and. E h (E s . <<. E h )′,. the. macroscopic. modulus. E. of. the. material.
perpendicular. to. the. stratified. direction. depends. only. on. the. modulus.
of. the. soft. component. E s ′,. not. on. the. hard. component. E h . (Okumura. and.
de Gennes.2001):
.