106
Bacterial Cellulose
specific.heterogeneous.conditions,.when.not.all.hydroxyl.groups.are.accessible.for.reaction.or.if.the.reaction.is.stopped.at.an.early.stage,.modifications.
may. occur. mainly. at. the. fiber. surface. or. in. more. accessible. regions. of. the.
inner.layers.(Freire.et.al..2006).
A. more. hydrophobic. BNC. was. first. developed. by. Cunha. et. al.. (2007).
through. pentafluorobenzoylation.. This. is. a. common. derivatization. procedure. used. for. the. chromatographic. analysis. of. amines. and. alcohols,. since.
it.provides.high.rates.and.yields,.in.addition.to.the.stability.of.the.ensuing.
products..In.that.work,.BNC.membranes.were.mixed.with.pentafluorobenzoyl.chloride.in.the.presence.of.dry.toluene.(a.nonswelling.medium,.chosen.
to.limit.the.modification.to.the.fibers’.surface).and.pyridine..This.procedure.
resulted. in. esterified. membranes. more. resistant. to. hydrolysis.. Moreover,.
the. possibility. to. easily. remove. the. perfluorinated. moieties. in. an. aqueous.
alkaline. medium. constituted. an. additional. advantage,. since. it. ensured. the.
straightforward.reaggregation.of.the.BNC.fibers..In.a.later.work,.Tomé.et.al..
(2010).produced.and.characterized.BNC.membranes.esterified.with.hexanoyl.
chloride. using. the. same. cellulose/fatty. acyl. chloride/pyridine. system.. The.
controlled.h . eterogeneous.modification.of.BNC.resulted.in.more.hydrophobic.
membranes.with.preserved.bulk.structure,.although.with.decreased.thermal. .
stability.. A significant. decrease. in. water. and. gas. (namely. carbon. dioxide.
[CO 2 ],.oxygen.[O 2 ],.and.nitrogen.[N 2 ]).permeation,.indicative.of.the.improvement.of.BNC.barrier.properties,.was.also.observed.
In.another.work,.the.effect.of.surface.functionalization.of.BC.nanofibrils.to.
be.used.in.the.reinforcement.of.polylactide.(PLLA).nanocomposites.for.the.
improvement.of.compatibility.(interfacial.adhesion).between.BNC.and.PLLA.
was.investigated.by.Lee.et.al..(2009)..These.researchers.functionalized.BNC.
with.different.organic.acids.(acetic,.hexanoic,.and.dodecanoic.acid).via.esterification..It.was.concluded.that.the.degree.of.hydrophobicity.could.be.. tailored.
by. the. length. of. the. organic. acid. (C 2 –C 12 ). used.. In. addition,. as. expected,.
incorporation. of. the. functionalized. BNC. into. PLLA. resulted. in. reinforced.
composites.showing.improved.tensile.modulus.and.tensile.strength.
Thus.surface.modification.of.BNC.via.esterification.reactions.is.a.useful.
approach. to. produce. more. hydrophobic. membranes,. with. improved. surface.and.barrier.properties,.and.with.promising.applications,.namely.in.the.
packaging.industry.
Precipitation of Metal Ions
tion.of.metals.into.thin,.flexible,.thermally.stable.membranes..In.fact,.in.contrast.to.plant.cellulose,.BNC.is.capable.of.catalyzing.the.deposition.of.metals.
within.its.structure.to.generate.a.finely.divided.homogeneous.catalyst.layer..
Bacterial Cellulose
specific.heterogeneous.conditions,.when.not.all.hydroxyl.groups.are.accessible.for.reaction.or.if.the.reaction.is.stopped.at.an.early.stage,.modifications.
may. occur. mainly. at. the. fiber. surface. or. in. more. accessible. regions. of. the.
inner.layers.(Freire.et.al..2006).
A. more. hydrophobic. BNC. was. first. developed. by. Cunha. et. al.. (2007).
through. pentafluorobenzoylation.. This. is. a. common. derivatization. procedure. used. for. the. chromatographic. analysis. of. amines. and. alcohols,. since.
it.provides.high.rates.and.yields,.in.addition.to.the.stability.of.the.ensuing.
products..In.that.work,.BNC.membranes.were.mixed.with.pentafluorobenzoyl.chloride.in.the.presence.of.dry.toluene.(a.nonswelling.medium,.chosen.
to.limit.the.modification.to.the.fibers’.surface).and.pyridine..This.procedure.
resulted. in. esterified. membranes. more. resistant. to. hydrolysis.. Moreover,.
the. possibility. to. easily. remove. the. perfluorinated. moieties. in. an. aqueous.
alkaline. medium. constituted. an. additional. advantage,. since. it. ensured. the.
straightforward.reaggregation.of.the.BNC.fibers..In.a.later.work,.Tomé.et.al..
(2010).produced.and.characterized.BNC.membranes.esterified.with.hexanoyl.
chloride. using. the. same. cellulose/fatty. acyl. chloride/pyridine. system.. The.
controlled.h . eterogeneous.modification.of.BNC.resulted.in.more.hydrophobic.
membranes.with.preserved.bulk.structure,.although.with.decreased.thermal. .
stability.. A significant. decrease. in. water. and. gas. (namely. carbon. dioxide.
[CO 2 ],.oxygen.[O 2 ],.and.nitrogen.[N 2 ]).permeation,.indicative.of.the.improvement.of.BNC.barrier.properties,.was.also.observed.
In.another.work,.the.effect.of.surface.functionalization.of.BC.nanofibrils.to.
be.used.in.the.reinforcement.of.polylactide.(PLLA).nanocomposites.for.the.
improvement.of.compatibility.(interfacial.adhesion).between.BNC.and.PLLA.
was.investigated.by.Lee.et.al..(2009)..These.researchers.functionalized.BNC.
with.different.organic.acids.(acetic,.hexanoic,.and.dodecanoic.acid).via.esterification..It.was.concluded.that.the.degree.of.hydrophobicity.could.be.. tailored.
by. the. length. of. the. organic. acid. (C 2 –C 12 ). used.. In. addition,. as. expected,.
incorporation. of. the. functionalized. BNC. into. PLLA. resulted. in. reinforced.
composites.showing.improved.tensile.modulus.and.tensile.strength.
Thus.surface.modification.of.BNC.via.esterification.reactions.is.a.useful.
approach. to. produce. more. hydrophobic. membranes,. with. improved. surface.and.barrier.properties,.and.with.promising.applications,.namely.in.the.
packaging.industry.
Precipitation of Metal Ions
tion.of.metals.into.thin,.flexible,.thermally.stable.membranes..In.fact,.in.contrast.to.plant.cellulose,.BNC.is.capable.of.catalyzing.the.deposition.of.metals.
within.its.structure.to.generate.a.finely.divided.homogeneous.catalyst.layer..