Bacterial Nanocellulose as a Structured Platform for Conductive Biopolymers 253
and.amine.groups.of.PAni..Hu.et.al..(2011).and.Marins.et al..(2011).also.evidenced.a.shift.on.the.BNC-OH.absorption.band.following.PAni.deposition..
The.emergence.of.a.new.band.at.2100/cm.(Marins.et al..2011).on.PAni·DBSA.
composites.was.proposed.to.be.an.indication.of.the.formation.of.new.chemical.bonds,.probably.originated.from.grafting.. reactions.of.PAni·DBSA.on.the.
BC. chains.. Also,. the. X-ray. diffraction. pattern. of. BNC/PAni·DBSA. blends.
showed.the.characteristic.peaks.related.for.both.undiluted.components,.but.
one.peak.at.2θ.=.14.5°.was.shifted.for.higher.2θ values,.suggesting.the.presence.of.new.crystals.forms,.probably.due.to.the.interactions.of.components.
(Marins. et. al.. 2011).. These. observations. suggest. that. BNC. is. activated. by.
acids.and.the.intermolecular.hydrogen.bands.are.broken.during.the.in.situ.
polymerization.of.Ani..As.more.OH.groups.become.accessible,.more.PAni.
can.be.deposited.in.the.nanofibrous.membrane.
The. thermal. behavior. of. BNC,. PAni. and. BNC/PAni·HCl. was. studied.
using.thermogravimetric.analysis.(TGA).and.differential.scanning.calorimetry. (DSC). (Izasa,. S.A.,. Portugal). (Figure 12.10).. Acquisition. of. the. results.
was.done.using.TA-50WS.software.(version.1.14)..For.the.assays,.5 mg.were.
weighted.(the.exact.masses.were.recorded).into.aluminum.pans.(Izasa,.S.A.,.
Portugal)..Open.pans.were.used.for.the.assays..Samples.were.heated.over.the.
temperature.range.25°C–500°C.at.a.scanning.rate.of.5°C/min..All.. samples.
showed.a.small.amount.of.adsorbed.water.(5%–8%.w/w,.on.average).that.
was.removed.at.up.to.125°C..This.occurred.mostly.as.a.two-stage.process,.
where. a. weakly. adsorbed. water. fraction. (“free. water”). was. lost. at. up. to.
100°C,.while.a.more.strongly.adsorbed.(“freezing.bound.water”).was.lost.at.
up.to.125°C..This.two-step.stage.was.followed.by.a.third.step.in.weight.loss..
For. BNC,. this. occurred. at. 200°C,. while. for. PAni. and. 1:10. BNC/PAni·HCl.
this.was.at.260°C.and.represents.the.oxidative.degradation.of.the.polymers.
(BNC. and. PAni).. These. results. also. show. that. the. polymerization. of. Ani.
onto.BNC.improves.its.thermal.properties,.as.observed.by.a.shift.to.higher.
temperatures.on.the.profile.of.weight.loss..The.water.desorption.registered.
in. the. TGA. profile. coincides. with. a. small. endothermic. peak. at. 50°C. in.
the. DSC. assays.. Degradation. of. BNC. begins. at. 200°C,. producing. a. . single.
and. broad. exothermic. peak. at. 273°C.. A. similar. profile. can. be. observed.
for.1:10 BNC/PAni·HCl,.only.shifted.to.300°C,.in.agreement.with.the.shift.
observed.for.the.weight.loss.from.TGA.results..Finally,.the.chemical.process.
associated.with.PAni’s.exothermic.peak.(at.285°C).was.proposed.to.be.due.to.
cross-linking.. reactions.(Scherr.et.al..1991)..This.reaction.resulted.from.a.coupling.of.two.neighboring.–N–Q–N–.groups.(where Q.stands.for.the.quinoid.
ring).to.yield.two.–NH–B–NH–.groups.(where.B.stands.for.the.benzenoid.
ring).through.a.link.of.the.N.with.its.neighboring.quinoid.ring..Interestingly,.
in.a.second.run,.the.DSC.thermogram.of.the.emeraldine.base.of.PAni.powder. indicated. no. significant. endothermic. or. exothermic. peaks,. given. the.
removal.of.moisture.and.destruction.of.PAni.intermolecular cross-links.