TABLe 4.1
Effect.of.Gelatin.Concentration.in.Feed.on.the.Degree.of.Swelling.and.Mechanical.
Properties.of.BNC-Gelatin.and.Gelatin.Gels..The.EDC.Concentration.was.1.M..
(Reproduced.with.permission.of.Nakayama.et.al..2004.)
Compression
Elongation
Elastic
Fracture
Fracture
Elastic
Fracture Fracture
Degree of Modulus, Stress, σ F Strain, ε F Modulus, Stress, σ F Strain, ε F
Sample Swelling, q E (MPa)
(MPa)
(mm/mm) E (MPa)
(MPa)
(mm/mm)
BNC-Gelatin
15.wt%
11
1.3
2.1
0.41
5.0
1.1
0.22
30.wt%
5.8
1.7
3.7
0.37
23
2.8
0.17
40.wt%
3.6
2.8
5.2
0.36
19
3.7
0.23
50.wt%
3.1
3.9
5.3
0.44
21
3.8
0.28
Gelatin
15.wt%
41
0.047
0.029
0.34
0.040
0.006
0.11
30.wt%
11
0.16
0.12
0.35
0.23
0.025
0.11
40.wt%
5.2
0.93
0.44
0.29
0.78
0.070
0.10
50.wt%
3.8
1.2
1.2
0.37
1.8
0.18
0.10
BNC
120
0.007
—
—
2.9
2.2
0.21
77
Tough Bacterial Nanocellulose Hydrogels Based on the Double-Network
where.d s .and.d h .are.the.thickness.of.the.soft.and.hard.component,.respectively..Therefore,.if.one.assumes.that.the.cellulose-rich.part.behaves.as.a.hard.
layer.and.the.gelatin.part.as.a.soft.layer,.the.overall.macroscopic.modulus.
should. largely. depend. on. the. modulus. of. the. soft. component—gelatin—
since.d s .≈.d h .
Effect of Cross-Linking
The. mechanical. property. of. gelatin. can. be. modulated. by. the. extent. of.
cross-linking.with.EDC..Therefore.the.effect.of.the.degree.of.cross-linking.
on.the.elastic.modulus.was.investigated.by.changing.the.EDC.concentration..
Without.EDC,.gelatin.at.a.concentration.of.30.wt%.cannot.form.a.gel.that.is.
strong.enough.for.mechanical.measurement..In.the.presence.of.EDC,.gelatin.
forms.a.chemically.cross-linked.gel.with.a.compressive.elastic.modulus.of.
about.0.1.MPa,.as.shown.in.Figure 4.3..As.shown.in.Figure 4.3a,.a.substantial.increase.in.the.compressive.elastic.modulus.of.BNC-gelatin.DN.gel.was.
observed.with.an.increase.in.cross-linker,.while.only.a.modest.enhancement.
of.the.elastic.modulus.was.observed.in.gelatin.gel..It.was.also.found.that.the.
compressive.fracture.stress.of.BNC-gelatin.DN.gel.increases.with.an.increase.
in.EDC.concentration,.which.is.similar.to.the.behavior.observed.in.gelatin.
gel.(Figure 4.3b)..Thus.the.mechanical.property.of.DN.gel.is.predominantly.
enhanced.by.the.cross-linkage.of.gelatin.