Two di e en inco po a ion ou es o cellulose nanoc ys als in wa e bo ne
polyu e hane nanocomposi es
(
h p://dx.doi.o g/10.1016/j.eu polymj.2016.01.035)
A an zazu San ama ia-Echa , Lo ena Uga e, Ai o A belaiz, Nago e
Gabilondo, Ma ia Angeles Co cue a, A an xa Eceiza
G oup ‘Ma e ials + Technologies’, Depa men o Chemical and En i onmen al Enginee ing,
Poly echnic School, Uni e si y o he Basque Coun y, Pza Eu opa 1, Donos ia-San Sebas ian 20018,
Spain
ABSTRACT
The enewabili y, a ailabili y and low-cos o eco- iendly cellulose nanoc ys als (CNC), ha e
gaining a en ion o nanocomposi es p epa a ion due o hei unique p ope ies in he
nanoscale and hei wa e dispe sibili y, becoming a sui able ein o cemen in wa e - bo ne
polyu e hane (WBPU) dispe sions. The eby, a WBPU ma ix wi h a high ha d segmen
con en (abou 48 w %) was syn hesized esul ing in a dispe sion o low pa icle size wi h a
na ow dis ibu ion analyzed by means o dynamic ligh sca e ing and isually s able o e
6 mon hs. The CNC ein o cemen isola ed om mic oc ys alline cellulose ia acid
hyd olysis lead o CNC wi h a high leng h/diame e aspec a io o abou 31, de e mined by
a omic o ce mic oscopy. In he nanocomposi es p epa a ion, wo inco po a ion ou es
we e designed o analyzing he in luence o CNC disposi ion in he nanocomposi es ilms:
he classical mixing by sonica ion o in-si u adding CNC in wa e du ing pa icles o ma ion
s ep. The in luence o CNC addi ion ou e and hei disposi ion in he inal p ope - ies o
nanocomposi es we e analyzed by Fou ie ans o m in a ed spec oscopy, di e en ial
scanning calo ime y, he mog a ime ic analysis, dynamic mechanical analysis, a omic
o ce mic oscopy and dynamic wa e con ac angle, obse ing conside able a ia ions by
adding 1 and 3 w % o CNC. The ein o cemen addi ion ou e in luenced he WBPU-CNC
in e ac ions, which esul ed mo e e ec i e by he al e na i e in-si u inco po a ion me hod.
The CNC inco po a ion es ic ed he c ys alliza ion o so domains, in a highe ex end in
nanocomposi es p epa ed by in-si u ou e, and imp o ed he he momechanical s abili y.
The s udied CNC inco po a ion ou es lead o di e en disposi ions o CNC in he ma ix,
esul ing in di e en mechanical pe o mance, p o iding a sui able s ess ans e in he
nanocomposi e and di e se hyd ophilic beha io , compa ing wi h he WBPU ma ix.
1. In oduc ion
Segmen ed polyu e hanes a e block copolyme s wi h al e na ing ha d and so segmen s
ha sepa a e in mic ophases due o he incompa ibili y be ween bo h segmen s [1]. The
ha d segmen (HS) p o ides usually he igidi y and s eng h o he polyme whe eas he
so segmen (SS) con e s lexibili y. The eby, conside ing he a ie y in he chemical
cons i uen s and composi ion, i is possible o syn hesize speci ic polyu e hanes wi h
pa icula p ope ies [2], opening a wide ange o applica ion ields. Con en ional
polyu e hanes a e sol en bo ne sys ems, bu he en i onmen al awa eness has p omo ed
he de elopmen o wa e bo ne polyu e hane (WBPU) sys ems by he addi ion o in e nal
emulsi ie s [3], a oiding he use o o ganic sol en s and ob aining s able wa e dispe sions
o e mon hs. Wi h he pu pose o syn hesizing new en i onmen ally iendly ma e ials,
WBPU has been employed in he p epa a ion o nanocomposi es. The chance o dispe se
hyd ophilic ein o cemen in WBPU, has ocused a en ion in wa e dispe sible en i ies,
such as cellulose de i a i es. Cellulose is he mos abundan enewable biopolyme which
has a ac ed g ea a en ion due o he a ailabili y, low cos , non- oxici y, biocompa ibili y
This is he Accep ed Manusc ip e sion o a Published Wo k ha appea ed in inal o m in Eu opean Polyme Jou nal 76 : 99-109
(2016) To access he inal edi ed and published wo k see h ps://doi.o g/10.1016/j.eu polymj.2016.01.035. © 2016. This
manusc ip e sion is made a ailable unde he CC-BY-NC-ND 4.0 license h ps://c ea i ecommons.o g/licenses/by-nc-nd/4.0/
and biodeg adabili y. Cellulose is p oduced p incipally in na u e by plan s like co on, ju e
o lax, di e en ma ine animals as unica es, and in in e eb a es, ungi, algae, bac e ia,
and amoeba (p o ozoa) in lowe quan i ies [4,5]. Cellulose can be used in di e en
dimensions, om mac oscopic o nanoscale, and di e se assemblies such as ibe s o
c ys als [6]. Among hese, i is wo h no ing he ele ance o cellulose nanoc ys als (CNC)
which a e gaining impo ance in di e se applica ion ields [4,7]. The isola ion o he
c ys alline o de ed egions o cellulose lead o ob aining hose highly c ys alline
nanoen i ies, possessing unique p ope ies in he nanoscale dimension, modula ed by
isola ion hyd olysis p ocess [8] and o igin o cellulose [5]. The high leng h/diame e aspec
a io and high speci ic mechanical p ope ies a e ocusing he a en ion o CNC in
nanocomposi es ield [9]. Se e al s a egies ha e been used in o de o p epa e cellulose
well dispe sed nanocomposi es, such as mel blending o sol en cas ing. In he o me case,
i is di icul o ob ain he adequa e cellulose dispe sion in he ma ix and high empe a u es
could deg ade nanocellulose nanoc ys als [10]. By sol en - cas ing, he slow e apo a ion o
he sol en p omo es he o ma ion o hyd ogen bonds and igid ne wo ks, esul ing in high
he momechanical s abili y and mechanical ein o cemen in he nanocomposi es. Di e se
ypes o polyme s ha e been used o nanocellulose nanocomposi es p epa a ion [11]. The
use o nonpola polyme s equi es an app op ia e o ganic dispe sion medium o he use o
su ac an o su ace chemical modi ica ion o nanocellulose in o de o ob ain a sui able
polyme ma ix dispe sion. Ins ead, he use o aqueous polyme dispe sions ensu es he
compa ibili y be ween he polyme and nanocellulose in wa e , acili a ing he good
dispe sion o homogeneous nanocomposi es p epa a ion wi hou equi ing chemical
modi ica ions o su ac an s [10]. The chance o dispe se hyd ophilic CNC in WBPU, has
ocused hei a en ion in WBPU–CNC nanocomposi es. The e a e di e en wo ks analyzing
he inal p ope ies o CNC ein o ced WBPU [12], bu ew wo ks conside CNC addi ion
s a egy and i s e ec in he inal disposi ion o CNC in he ma ix. The eby, in his wo k he
syn hesis o WBPU dispe sion and he isola ion o CNC ha e been ca ied ou o he
p epa a ion o nanocomposi es conside ing CNC addi ion p o ocol. The e o e, wo CNC
inco po a ion ou es we e designed o he analysis o CNC a angemen in he WBPU
ma ix: he classical mixing by sonica ion a e WBPU syn hesis and he al e na i e in-si u
du ing he WBPU syn hesis p ocess. The e ec o CNC addi ion as well as he inco po a ion
p ocedu e has been analyzed in he inal p ope ies o he nanocomposi es.
2. Expe imen al
2.1. Ma e ials
CNC we e isola ed om mic oc ys alline cellulose (MCC) powde supplied om Ald ich and
sul u ic acid (H
2
SO
4
) (96%) was p o ided om Pan eac. Fo WBPU syn hesis, poly(e-
cap olac one) diol (PCL) (𝑀
= 2000 g mol
-1
), pu chased om BASF was chosen as so
segmen and 1,4 bu anediol (BD), supplied om Ald ich as chain ex ende , being d ied in a
o a y e apo a o a 50 °C o 4 h. Isopho one diisocyana e (IPDI) was kindly supplied om
Baye , and dibu yl in dilau a e (DBTDL) was pu chased om Ald ich. 2,2-
Bis(hyd oxyme hyl)p opionic acid (DMPA) pu chased om Ald ich and used as in e nal
emulsi ie , was d ied a 55 °C o 4 h unde acuum. Hyd anal-molecula Sie e 0.3 nm
(wa e adso p ion capaci y o 15%), supplied by Fluka, and p e iously d ied a 55 °C unde
acuum o 1 day was employed o dehyd a ion o ie hylamine (TEA), bo h p o ided om
Ald ich. N,N-dime hyl o mamide (DMF) and e ahyd o u an (THF), we e also p o ided by
Ald ich.
2.2. Isola ion o cellulose nanoc ys als
CNC we e isola ed om mic oc ys alline cellulose ia sul u ic acid hyd olysis emo ing he
amo phous egions o cellulose. The isola ion was ca ied ou ollowing p e iously epo ed
me hod [13]. B ie ly desc ibed, MCC we e mixed wi h H2SO4 (64 w %) a 45 °C o 30 min.
The suspension was dilu ed wi h deionized wa e and a e washed by cen i uga ion, he
suspension was subjec ed o a dialysis p ocess agains deionized wa e un il pH emained
cons an a ound 5–6. Thus, CNC dispe sion wi h abou 0.5 w % concen a ion was ob ained.
2.3. Syn hesis o wa e bo ne polyu e hane
WBPU wi h a HS con en o abou 48 w % was syn hesized by wo s ep polyme iza ion
p ocess wi h he PCL:IPDI:DMPA: BD mola composi ion o 0.5:3.15:0.5:2 conside ing PCL
as SS and IPDI, DMPA and BD as HS. Acco ding o p e iously published p o ocol [14], he
eac ion was ca ied ou in a 250 mL ou -necked lask placed in a he mos a ized ba h and
equipped wi h a mechanical s i e , he mome e , condense and ni ogen inle . The
p og ess o each eac ion s ep was de e mined by dibu ylamine back i a ion acco ding o
ASTM D 2572-97. In he i s s ep PCL and IPDI we e eac ed wi h 0.1 w % o DBTDL a 90
°C. Then, DMPA was added and allowed o eac un il he heo e ical NCO con en was
eached. In he second s ep BD was added o he chain ex ension. The ea e , he
necessa y amoun o TEA was added in o de o neu alize DMPA ca boxylic g oups and he
polyme was cooled o oom empe a u e while he iscosi y was adjus ed wi h THF. Finally,
deionized wa e was added d opwise unde igo ous s i ing and THF was emo ed using a
o a y e apo a o , ob aining a dispe sion wi h a solid con en o abou 25 w %.
2.4. Nanocomposi es p epa a ion
Polyu e hane nanocomposi es ein o ced wi h 1 and 3 w % CNC we e p epa ed by wo CNC
inco po a ion ou es; mixing WBPU and CNC by sonica ion and in-si u du ing WBPU
syn hesis. In he i s case, CNC dispe sion was sonica ed o 1 h and a e he addi ion o
he WBPU dispe sion, he mix u e was sonica ed o ano he 1 h. In he second case,
p e iously sonica ed CNC dispe sion was inco po a ed o he polyu e hane in he wa e
addi ion s ep o he syn hesis. Bo h dispe sions we e cas in Te lon molds allowing o d y in
a clima ic chambe a 25 °C and 50% o ela i e humidi y du ing 7 days and inally in a
acuum o en. Fu he mo e, nea polyu e hane dispe sion ma ix was cas ollowing he
condi ions used o nanocomposi es ilms p epa a ion. Designa ion o ob ained ilms is
exp essed as WBPU in he case o he ma ix and WBPU-Xson and WBPU-Xsyn o he
nanocomposi es p epa ed mixing by sonica ion and in-si u espec i ely, whe e X deno es
CNC weigh con en in he nanocomposi e. The WBPU and nanocomposi es we e s o ed in
a desicca o o 1 week be o e hei cha ac e iza ion.
2.5. Cha ac e iza ion
2.5.1. Dynamic ligh sca e ing
WBPU and in-si u syn hesized nanocomposi es dispe sion pa icle size and dis ibu ion was
de e mined by dynamic ligh sca e ing (DLS) using a BI-200SM goniome e om
B ookha en. The in ensi y o dispe sed ligh was measu ed a 90° using a luminous sou ce
o He-Ne lase (Mini L-30, wa eleng h k = 637 nm, 400 mW) and a de ec o (BI-APD) placed
on a o a y a m. Samples p epa ed by mixing a small amoun o aqueous dispe sion wi h
ul apu e wa e we e analyzed a 25 °C by iplica e.
—
2.5.2. Sul a e g oups concen a ion ancho ed o CNC
The concen a ion o sul a e g oups ancho ed o he sul u ic acid hyd olyzed cellulose
nanoc ys als was de e mined by conduc ome ic i a ion a 25 °C wi h a C ison EC-Me e
GLP 31 conduc ome e calib a ed wi h 147 μS cm
-1
, 1413 μS cm
-1
and 12.88 mS cm
-1
s anda ds. Fo he i a ion, NaOH and HCl 10 mM we e used. Sul a e g oups concen a ion
was also de e mined by elemen al analysis in a Eu o EA3000 Elemen al Analyze o
Eu o ec o .
2.5.3. Fou ie ans o m in a ed spec oscopy
WBPU, CNC and nanocomposi es cha ac e is ic unc ional g oups we e analyzed by Fou ie
ans o m in a ed spec oscopy (FTIR) using a Nicole Nexus spec ome e p o ided wi h a
MKII Golden Ga e accesso y (Specac) wi h diamond c ys al a a nominal incidence angle o
45° and ZnSe lens. Measu emen s we e un a e aging 64 scans wi h a esolu ion o 8 cm
-1
in he ange be ween 4000 and 650 cm
-1
.
2.5.4. Di e en ial scanning calo ime y
The he mal p ope ies o WBPU and nanocomposi es we e de e mined by di e en ial
scanning calo ime y (DSC) in a Me le Toledo 822e equipmen p o ided wi h a obo ic a m
and an elec ic in acoole as e ige a o uni . Be ween 5 and 10 mg o samples we e
encapsula ed in aluminum pans and hea ed om 75 o 180 °C a a scanning a e o 20 °C
min
-1
in ni ogen a mosphe e. The glass ansi ion empe a u e was ixed as he in lec ion
poin o he hea capaci y change. The maximum o endo he mic peak was se led as he
mel ing empe a u e conside ing he a ea unde he peak as mel ing en halpy.
2.5.5. The mog a ime ic analysis
The he mal s abili y o CNC and WBPU and nanocomposi es ilms was de e mined by
he mog a ime ic analysis (TGA) using a TGA/SDTA 851 Me le Toledo. Be ween 5 and 10
mg o samples we e subjec ed o a dynamic un om 25 o 700 °C a a hea ing a e o 10 °C
min
-1
in ni ogen a mosphe e. The ini ial deg ada ion empe a u e was e e ed o he loss
o 5 w % o he o al sample decomposi ion whe eas he maximum deg ada ion
empe a u e was se led as he minimum o he deg ada ion peak in he de i a i e
he mog a ime ic (DTG) cu es.
2.5.6. Mechanical es ing
Mechanical beha io o ilms we e de e mined a oom empe a u e using a MTS Insigh 10
es ing machine p o ided wi h a 250 N load cell and pneuma ic g ips o hold samples. Films
ensile modulus, yield s ess, s ess a b eak and s ain a b eak we e de e mined om
s ess–s ain cu es pe o med a a c osshead speed o 50 mm min
-1
. Fi e specimens o
8 mm in leng h, 2.5 mm in wid h and 0.4 mm in hickness we e analyzed o each sys em.
2.5.7 Dynamic mechanical analysis
The he momechanical s abili y o he ilms was de e mined by dynamic mechanical
analysis (DMA) using an Eplexo 100 N analyse Gabo equipmen . The measu emen s
ca ied ou in ensile mode we e pe o med om 100 o 150 °C a a scanning a e o
2 °C min
-1
. The ini ial s ain was es ablished as 0.05% and he ope a ing equency was ixed
a 1 Hz.
2.5.8 A omic o ce mic oscopy
The mo phology o CNC and WBPU and hei nanocomposi es was de e mined by a omic
o ce mic oscopy (AFM). The images we e ob ained a oom empe a u e in apping mode,
using a Nanoscope IIIa scanning p obe mic oscope (Mul imodeTM Digi al ins umen s) wi h
an in eg a ed o ce gene a ed by can ile e /silicon p obes, applying a esonance equency
o abou 180 kHz. The can ile e had a ip adius o 5–10 nm and was 125 μm long. Samples
we e p epa ed ia spin-coa ing (Spincoa e P6700) a 200 pm o 130 s. WBPU and
nanocomposi es samples we e p epa ed by spin-coa ing a d ople o he dispe sion on glass
suppo s whe eas a d ople o CNC dilu ed dispe sion was spin-coa ed on a mica lake.
2.5.9 Dynamic wa e con ac angle
The hyd ophilici y o WBPU and nanocomposi es ilms was de e mined by dynamic wa e
con ac angle (DWCA) using a Da aphysics OCA20 equipmen a oom empe a u e. Fou
measu emen s o each sample we e pe o med by sessile d op me hod. Deionized wa e
3 μL d op was deposi ed in he su ace o he ilm by a sy inge ip. The needle was emained
inside he d op, main aining he smalles po ion as possible du ing all expe imen , in o de
o p e en al e a ions in he es s. The ad ancing con ac angle alues we e measu ed by
inc easing he d op olume adding deionized wa e a a cons an low o 0.5 μL, while
eceding con ac angles we e de e mined educing he d op olume.
3. Resul s and discussion
3.1. Cellulose nanoc ys als cha ac e iza ion
AFM images obse ed in Fig. 1 co obo a e he isola ion o CNC nanoen i ies ia acid
hyd olysis showing a od-like mo phology. In o de o de e mine he leng h/diame e (L/D)
aspec a io, a ound 100 CNCs we e measu ed and a e aged. The leng h o CNCs was
de e mined in he heigh image, Fig. 1a, whe eas he diame e s we e measu ed in he AFM
heigh p o iles, Fig. 1c, assuming hei cylind ical shape [15]. The eby, CNCs wi h an a e age
diame e o 5.4 ± 1.5 nm and leng h abou 167 ± 31 nm we e ob ained, co esponding o
an L/D aspec a io o abou 31.
The CNC isola ion by sul u ic acid hyd olysis p ocess in oduces sul a e g oups in he CNCs
su ace p o iding s abili y in aqueous suspension due o elec os a ic epulsion in e ac ions
[8,16]. In his case, he CNCs exhibi a sul u con en o 1.22% measu ed by conduc ome ic
i a ion [8,17]. Elemen al analysis was also pe o med ob aining a simila sul u con en o
1.28%. This alues suppo he modi ica ion o nega i ely cha ged CNCs su ace as a esul
o he hyd olysis.
3.2. Nanocomposi es cha ac e iza ion
Pa icle size and polydispe si y o WBPU ma ix and in-si u syn hesized WBPU-1
syn
nanocomposi e dispe sions a e summa ized in Table 1. I can be obse ed ha small
pa icles wi h a na ow dis ibu ion we e ob ained, leading o isually s able dispe sions
o e 6 mon hs. Mo eo e , he addi ion o 1 w % o CNC in-si u du ing he wa e addi ion
p ocess, does no a ec he o ma ion o he pa icles. Despi e he highe leng h o CNC,
simila pa icle size and polydispe si y we e measu ed in bo h cases. Ins ead, in he case o
WBPU-3
syn
, i was no possible o de e mine he pa icle size since he highe CNC con en
in e e es in i s de e mina ion.
Fig. 1. AFM heigh (a) and phase (b) images o cellulose nanoc ys als. (c) Heigh p o ile o cellulose nanoc ys al
indica ed in heigh image.
Table 1. Pa icle size and polydispe si y o dispe sions
Sample
Diame e (nm)
Polydispe si y
WBPU
52.3 ± 0.5
0.08 ± 0.05
WBPU
-
1
syn
52.6 ± 0.2
0.06 ± 0.02
The WBPU and 1 w % CNC ein o ced nanocomposi es ilms p epa ed om he dispe sions
by means o he wo di e en CNC inco po a ion ou es a e shown in Fig. 2. Al hough only
WBPU and nanocomposi es con aining 1 w % a e shown in Fig. 2, nanocomposi es
con aining 3 w % o CNC esul ed also anspa en . In addi ion, all samples we e comple ely
soluble in THF and DMF.
Fig. 2. (a) WBPU ma ix, (b) WBPU-1
son
and (c) WBPU-1
syn
nanocomposi es ilms p epa ed by cas ing.
The s uc u e and hyd ogen bonding in e ac ions be ween CNC and WBPU we e s udied by
FTIR. Fig. 3 shows spec a o nanocomposi es and nea componen s. Two ypical egions
ha e been analyzed. In he in e al om 3600 o 3100 cm
-1
nea WBPU shows he s e ching
ib a ion ela ed o N-H o u e hane g oups and CNC shows a b oad band ela ed wi h OH
s e ching ib a ion [18]. Sligh di e ences can be obse ed be ween he nanocomposi es
and nea WBPU. The peak obse ed abou 3340 cm
-1
is ela ed wi h he N-H ib a ion o
u e hane g oups associa ed by hyd ogen bonding in e ac ions. In WBPU-1
son
and WBPU-3
son
samples, an ex ended shoulde a ound 3530 cm
-1
, simila o he obse ed in CNC spec um
can be app ecia ed whe eas in WBPU-1
syn
and WBPU-3
syn
is ba ely no iceable. I could be
ela ed wi h he CNC disposi ion in he nanocomposi e. In he case o mixing componen s
by sonica ion, CNC a e homogeneously dispe sed in WBPU and OH g oups o CNC a e also
app eciable by b oadening he peak in ha egion o highe wa enumbe s, simila o he
peak obse ed in CNC spec um. Howe e , in-si u inco po a ion ou e a o s he
in e cala ion o CNC in WBPU pa icles du ing dispe sion o ma ion, and conside ing
ATR-FTIR as su ace physicochemical analysis, i is hough ha CNC could esul embedded
in he ma ix du ing ilm o ma ion, hinde ing he isualiza ion o CNC hyd oxyl g oups, bu
a o ing in e ac ions be ween hem. Rega ding o he ca bonyl egion, an ampli ica ion o
he spec a has been included in Fig. 3b. The b oadening and inc ease o he ela i e
in ensi y o he peak ela ed wi h he hyd ogen bonded C=O a ound 1700 cm
-1
espec o
he ee C=O g oups abou 1720 cm
-1
, sugges s he exis ence o WBPU–CNC in e ac ions in
he nanocomposi es, which inc eases wi h CNC con en .
Fig. 3. (a) FTIR spec a o he ma ix and he nanocomposi es and (b) an ampli ica ion o he ca bonyl s e ching
egion.
The mal beha io o he ilms was s udied by DSC. The he mog ams a e displayed in Fig. 4.
The he mal ansi ion alues co esponding o he so domain glass ansi ion
empe a u e (Tg
SS
), mel ing empe a u e (Tm
SS
) and en halpy (ΔHm
SS
) ob ained om he
cu es a e summa ized in Table 2. Analyzing so domain mel ing endo he mic peak, i has
been obse ed ha he addi ion o CNC dec eases he mel ing en halpy o he
nanocomposi es. The WBPU-CNC in e ac ions p esumably es ic so segmen chains o
a ange in c ys alline domains [19], p o iding highe mobili y o so segmen chains
[20,21] and hence, obse ing a sligh dec ease in Tg
SS
alues. Fu he mo e, he lowe Tm
SS
and ΔHm
SS
alues in WBPU-1
syn
compa ing wi h WBPU-1
son
, sugges s he g ea e WBPU-CNC
in e ac ions, which would hinde in a g ea e ex en c ys als g ow h. Indeed, a highe CNC
con en , o WBPU-3
syn
, so domain c ys alliza ion is o ally hinde ed. In his case,
WBPU-CNC in e ac ions lead o a clea e b oad ansi ion a ound 85 °C ela ed wi h he
sho ange o de o ha d segmen [22], which es ic s so segmen chains mobili y and
inc eases sligh ly Tg
SS
.
Fig. 4. DSC he mog ams o WBPU ma ix and he nanocomposi es
Table 2. The mal p ope ies o he ilms
Sample
T
gSS
(
°
C)
T
mSS
(
°
C)
ΔHm
SS
(J g-1)
WBPU
-
42.7
49.5
10.8
WBPU
-
1
son
-
45.8
49.1
7.1
WBPU
-
3
son
-
47.5
47.5
4.1
WBPU
-
1
syn
-
47.3
47.2
6.0
WBPU
-
3
syn
-
42.0
-
-
The he mal s abili y o CNC and WBPU and nanocomposi es ilms analyzed by TGA cu es
a e exhibi ed in Fig. 5a and DTG cu es, whe e he a e o weigh loss can be analyzed, a e
displayed in Fig. 5b. In polyu e hanes, a unique deg ada ion s age as well as mul iple
deg ada ion s ages ha e been obse ed, in luenced by he polyu e hane na u e,
composi ion, c ys allini y and mic ophase sepa a ion deg ee o he sys em, among o he s
[23–25]. In his case, he nea WBPU shows a single decomposi ion peak wi h he maximum
deg ada ion empe a u e cen e ed a 331 °C, whe eas in nanocomposi es a shoulde can
also be obse ed. The ini ial deg ada ion empe a u e (T
i
), he maximum deg ada ion
empe a u e (T
m
) and he empe a u e o he shoulde obse ed in nanocomposi es (T
s
) a e
summa ized in Table 3. I has been obse ed an inc ease in he T
i
and T
m
alues in he
nanocomposi es compa ing wi h he ma ix, a ibu able o he s abiliza ion o u e hane
g oups by in e ac ions o WBPU and CNC and he enhancemen o he he mal esis ance
wi h CNC addi ion. Analyzing T
i
and T
m
alues, he CNC addi ion by sonica ion and in-si u
causes a delay o 5–7 °C in he s a o he deg ada ion p ocess and a delay a ound 30 °C in
he T
m
alues. This ema kable imp o emen , could be owed o a sui able dispe sion o he
CNC in he WBPU ma ix [21,26] p o iding in e ac ions. Analyzing CNC deg ada ion cu es,
mul iple decomposi ion s eps can be obse ed ela ed wi h sul a e g oups [27,28], whe e
he maximum deg ada ion empe a u es a e cen e ed a 239 and 325 °C. O he wise, he
shoulde obse ed a ound 315-320 °C in he deg ada ion o he nanocomposi es could be
a ibu ed o he less o de ed domains induced by he in e ac ions be ween WBPU and CNC
in he polyu e hane.
Table 3. Ini ial deg ada ion, maximum deg ada ion and shoulde empe a u es o he WBPU ma ix and
nanocomposi es
.
Sample
T
i
(°C)
T
m
(°C)
T
s
(°C)
WBPU
281
331
–
WBPU
-
1
son
288
359
322
WBPU
-
3
son
287
365
316
WBPU
-
1
syn
286
362
323
WBPU
-
3
syn
288
361
313
Fig. 5. (a) TGA and (b) DTG cu es o CNC, WBPU ma ix and nanocomposi es.
Fig. 6 shows s ess–s ain cu es o he ilms. Modulus, s ess a yield, s ess a b eak and
s ain a b eak alues de e - mined om he cu es a e summa ized in Table 4. I can be
obse ed ha mechanical p ope ies depend on bo h, CNC con en as well as CNC addi ion
ou e. In he case o CNC addi ion by sonica ion, whe e WBPU so segmen s o de in
c ys alline domains, highe modulus and s ess a yield alues and lowe s ain a b eak
alues a e ob ained as CNC con en is inc eased [29]. In he case o in-si u me hod and a 1
w % o CNC, an inc ease in modulus and s ess a yield alues and a dec ease in s ain a
b eak alue a e also obse ed compa ing wi h he ma ix. Howe e , a 3 w % o CNC,
modulus and s ess a yield dec ease, a ibu able o he absence o so o de ed domains,
as obse ed by DSC esul s. In u n, s ess a b eak and s ain a b eak alues inc ease
espec o 1 w % o CNC owing o he addi ional esis ance p o ided by CNC and chain
mobili y. These imp o emen s sugges he e ec i e ein o cemen e ec caused by CNCs
due o new in e ac ions wi h he WBPU, main aining a sui able s ess ans e in he
nanocomposi e besides hei mo phology wi h an ele a ed L/D aspec a io [30]. By his
way, ailo ed mechanical p ope ies can be ob ained a ending o he CNC addi ion me hod
as well as con en . When CNC a e added by sonica ion, he s ain induced c ys alliza ion o
he ma ix is main ained. Ne e heless, when CNCs a e added du ing he syn hesis p ocess,
he sys em esul s in sha pe WBPU-CNC in e ac ions, hinde ing he o ien a ion and
c ys alliza ion o he WBPU unde s ain [13]. O he wise, he possible eac ion o esidual
isocyana e g oups (isocyana e/ hyd oxyl g oups a io o 1.05) wi h hyd oxyl g oups o CNC
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