polyme s
A icle
Colo Fixa ion S a egies on Sus ainable Poly-Bu ylene
Succina e Using Biobased I aconic Acid
Lidia G. Quiles 1,*, Julio Vidal 2, F ancesca Luzi 3, F anco Dominici 3,Ángel Fe nández Cuello 4and
Pe e Cas ell 2,*


Ci a ion: G. Quiles, L.; Vidal, J.; Luzi,
F.; Dominici, F.; Fe nández Cuello, Á.;
Cas ell, P. Colo Fixa ion S a egies on
Sus ainable Poly-Bu ylene Succina e
Using Biobased I aconic Acid.
Polyme s 2021,13, 79.
h ps://doi.o g/10.3390/
polym13010079
Recei ed: 26 No embe 2020
Accep ed: 23 Decembe 2020
Published: 28 Decembe 2020
Publishe ’s No e: MDPI s ays neu-
al wi h ega d o ju isdic ional claims
in published maps and ins i u ional
a ilia ions.
Copy igh : © 2020 by he au ho s. Li-
censeeMDPI, Basel, Swi ze land. This
a icleisanopenaccessa icledis ibu ed
unde he e ms and condi ions o he
C ea i eCommonsA ibu ion(CCBY)
license(h ps://c ea i ecommons.o g/
licenses/by/4.0/).
1Tecnopackaging, Polígono Indus ial Emp esa ium C/Rome o Nº, 12, 50720 Za agoza, Spain
2Fundación Ai iip, Polígono Indus ial Emp esa ium C/Rome o Nº, 12, 50720 Za agoza, Spain;
[email p o ec ed]
3Depa men o Ci il and En i onmen al Enginee ing, Uni e si y o Pe ugia, 05100 Te ni, I aly;
[email p o ec ed] (F.L.); [email p o ec ed] (F.D.)
4Escuela de Ingenie ía y A qui ec u a, Uni e si y o Za agoza, A . Ma ía de Luna, 3, 50018 Za agoza, Spain;
a e nan@uniza .es
*Co espondence: [email p o ec ed] (L.G.Q.); [email p o ec ed] (P.C.);
Tel.: +34-976-46-45-44 (P.C.)
Abs ac :
Biopo-lybu ylene succina e (bioPBS) is gaining a en ion in he biodeg adable polyme
ma ke due o i s p omising p ope ies, such as high biodeg adabili y and p ocessing e sa ili y,
ep esen ing a po en ial sus ainable eplacemen o ossil-based commodi ies. Howe e , he e is s ill
a need o enhance i s p ope ies o ce ain applica ions, wi h aes he ical and mechanical p ope ies
being a challenge. The aim o he p esen wo k is o imp o e hese p ope ies by adding selec ed
addi i es ha will con e bioPBS wi h compa able p ope ies o ha o cu en coun e pa s such
as polyp opylene (PP) o speci ic applica ions in he au omo i e and household appliances sec o s.
A o al o hi een ma e ials ha e been s udied and compa ed, being wel e biocomposi es con aining
combina ions o h ee di e en addi i es: a comme cial ed colo an , i aconic acid (IA) o enhance
colo ixa ion and zi conia (Z O
2
) nanopa icles o main ain a leas na i e PBS mechanical p ope ies.
The esul s show ha he combina ion o IA and he colo ing agen ends o sligh ly yellowish he
blend due o he abso bance spec a o IA and also o modi y he gloss due o he o ma ion o
IA nanoc ys als ha a ec s ligh sca e ing. In addi ion, o low amoun s o IA (4 w %), Young’s
Modulus seems o be kep while elonga ion a b eak is e en aised. Unexpec edly, a s ong aging a ec
was ound a e ou weeks. IA inc eases he hyd ophilic beha io o he samples and hus seems
o accele a e he hyd oliza ion o he ma ix, which is accompanied by an accused disagg ega ion
o phases and an o e all so ening and igidiza ion e ec . The addi ion o low amoun s o Z O
2
(2 w %) seems o p o ide he desi ed e ec o ha dening he su ace while almos no a ec ing he
o he p ope ies; howe e , highe amoun s ends o o m agg ega es sa u a ing he compounds. As a
conclusion, IA migh be a good candida e o colo ixing in biobased polyme s.
Keywo ds:
biopolyme s; biocomposi es; polybu ylene succina e; i aconic acid; zi conium oxide;
colo an ; ha dness; colo ixing; gloss; aging e ec
1. In oduc ion
Technical biopolyme s a e becoming inc easingly a ac i e as sus ainable and good-
pe o ming polyme ic ma e ials [
1
]. One o he mos p omising biopolyme s is biopo-
lybu ylene succina e (bioPBS). BioPBS is an alipha ic polyes e syn hesized om he poly-
me iza ion o wo biobased building blocks: succinic acid (o dime hyl succina e) and 1,4-
bu anediol [
2
,
3
], all coming om enewable sou ces. The ma e ials and p oduc s de i ed
om bioPBS a e so , lexible and ha e become a p omising eplacemen o commodi-
ies [
4
] such as polye hylene e eph hala e (PET), polyp opylene (PP) and polye hylene (PE)
as hey exhibi nea ly compa able mechanical p ope ies [
5
] o hese syn he ic plas ics o
Polyme s 2021,13, 79. h ps://doi.o g/10.3390/polym13010079 h ps://www.mdpi.com/jou nal/polyme s
Polyme s 2021,13, 79 2 o 14
se e al applica ions such as packaging, cons uc ion applica ions, housewa e, u ni u e o
ag icul u e [
6
]. In addi ion, bioPBS unde goes biodeg ada ion du ing disposal in compos ,
mois soil, esh wa e and seawa e [
7
], which educes i s po en ial en i onmen al impac
and makes i a p omising candida e o enhance he sus ainabili y o plas ic p oduc s—as
cu en ly demanded by he ma ke s and consume s.
Howe e , a gene al d awback o biopolyme s, among hem bioPBS, is ha hey
p esen poo aes he ic appea ance compa ed o oil-based coun e pa s. E e y he moplas ic
ma e ial has i s own inna e colo . A he moplas ic ma e ial in i s inna e colo s a e is e e ed
o as na u al. The na u al colo o biopolyme s usually a y om yellowish, b ownish
o c ude whi ish, ha many imes is no he p e e ence o he consume . Thus, he use o
pigmen s o addi i es o ailo he appea ance o biopolyme s is equi ed. In e ms o colo ,
bioPBS has a whi ish b igh ma ix. The need o in oduce hese ma e ials in he ma ke
equi es he imp o emen o such p ope ies, allowing cus omiza ion o he inal colo .
The e m “colo an o colo ing agen ” deno es a se ies o colo ed subs ances ha a ec
a ma e ial’s appea ance. The e o e, he in oduc ion o a colo ing agen would inc ease
he a ac i eness o he bioplas ic and he po en ial accep ance o he ma e ial in mo e
applica ions. Ne e heless, how he ma e ial esponds o he colo an is a c i ical aspec o
he o e all appea ance ha also in ol es gloss and ex u e. Gloss is used o desc ibe he
manne in which a su ace e lec s ligh : specula e lec ion (shiny), di use e lec ion o i
can abso b he ligh (dull). Rega ding ex u e, smoo h su aces e lec ligh in he specula
di ec ion, whe eas di use e lec ion domina es in he case o ough su aces.
Two kinds o colo ing agen s a e usually used o colo plas ics: pigmen s and dyes.
Pigmen s may be ei he o ganic o ino ganic in s uc u e and a e insoluble bo h du ing
p ocessing o he plas ics and in he end p oduc [
8
,
9
]. Dyes, on he o he hand, a e o ganic
molecules ha dissol e in o he subs a e o which hey a e applied. Azo colo an s a e
he mos impo an class o syn he ic dyes and pigmen s, ep esen ing 60–80% o all
o ganic colo an s [
10
]. These colo an s con ain one o mo e ni ogen–ni ogen double
bonds (
–N = N–
) in hei chemical s uc u e and may possess o he unc ional g oups [
11
].
They ha e excellen colo ing p ope ies, mainly in he yellow o ed ange, as well as good
ligh as ness. Azo colo an s a e used widely in subs a es such as ex ile ibe s, lea he ,
plas ics, pape s, hai , mine al oils, waxes, oods u s, ubbe s and pain s.
The colo an no only needs o ma ch he desi ed colo bu i should also sa is y o he
cons ain s such as o be chemically compa ible wi h he base polyme ma ix and o be
chemically s able. In o de o be able o p o ide a wide pale e o colo s, i is impo an o
each a good colo ixa ion and gloss, making i long-las ing (du able), and ha i also does
no a ec o he unc ional key p ope ies such as ha dness o mechanical pe o mance.
O he ac o s in luencing colo s eng h a e pa icle size and dispe sion in he plas ic ma ix.
Ideally, when a biobased ma e ial is concei ed, he colo an s and addi i es used in
he o mula ion should come om a bio-based o igin [
12
,
13
]. Na u al pigmen s and dyes
p esen poo colo as ness and yield compa ed o syn he ic ones [
14
]. Fo his eason,
i is necessa y o in oduce a linking agen ha enhances compa ibili y wi h he polyme ic
ma ix. Mos o he na u al dyes p esen hyd oxylic g oups (–OH) in hei s uc u e and
o example can be es e i ied wi h polyca boxylic acids such as ci ic acid o i aconic acid
(IA) [
15
]. These, and o he s such as amino g oups, a e conside ed colo helpe s. They a e
known as auxoch omes [
16
], which a e able o al e bo h he in ensi y and he wa eleng h
o abso bed ligh in luencing he physical-chemical p ope ies o he ma e ial while hey
do no p oduce colo by hemsel es. These a e o en used as colo ixa ion chemicals
enhancing he o e all s abili y o he colo ed pa .
Among he di e en linking agen s used in polyme science, IA has demons a ed
good pe o mance in oil-based polyme s [
17
]. Today, IA is exclusi ely p oduced by e men-
a ion wi h ca bohyd a es by ilamen ous ungi, mainly Aspe gillus e eus [
18
]. Thus, i has
he po en ial o be p oduced exclusi ely om biomass. IA is a ully sus ainable indus ial
building block, an ionic hyd ophilic co-monome , wi h a my iad o chemical applica ions
due o i s s uc u al simila i y o ac ylic and me hac ylic acids [
17
]. In ac , i p esen s a
Polyme s 2021,13, 79 3 o 14
iable solu ion o eplace ac ylic acid in biodeg adable polyme s. Fo example, i is used in
he p oduc ion o lub ican s, ac i e agen s, dyes, plas ics, chemical ibe s, e c. [
19
]. O he
p omising uses a e unsa u a ed polyes e esins, phospha e- ee de e gen s, and in he ood
indus y [
20
]. I is s able a acidic, neu al and middle basic condi ions a mode a e empe -
a u es, so i was conside ed a good candida e o he ex usion-compounding p ocess in
which high empe a u es and shea o ces a e achie ed.
Howe e , as i is a componen usually used in he o mula ion o gums/elas ome s
and la ex, one o he d awbacks o using IA in di e en he moplas ics is he so ening
e ec , which migh be accen ua ed by he o ganic na u e o he diazo pigmen . The use o
ino ganic ille s has been demons a ed o be a good s a egy in composi es o enhancing
mechanical p ope ies [
21
–
25
]. Among hese ille s, nanopa icles such as Z O
2
ha e been
used in se e al applica ions [
26
,
27
]. I s na u al whi ish colo , and i s excellen dimensional
s abili y, mechanical and chemical p ope ies, has made zi conia a highly a ac i e ce amic
ma e ial in medical applica ions such as hip head eplacemen ins ead o i anium o
alumina p os heses and in pa icula o p os hodon ics [
28
,
29
]. Zi conia has also been
used o p oduce ha d coa ings o plas ic su aces wi h an i ogging, an i-we ing and
an is a ic p ope ies [
30
]. Due o his eason, i was decided o add zi conium dioxide o
ha den bioPBS su ace as well as p e en i om losing mechanical p ope ies.
The objec i e o his s udy is o de elop an enhanced biobased ma e ial showing
good aes he ical p ope ies in e ms o colo ixing while keeping a leas he mechanical
p ope ies o he o iginal ma ix polyme (bioPBS) in o de o make i a ac i e o a
ple ho a o applica ions in he ma ke such as au omo i e, householding o u ni u e.
In his esea ch, IA has been selec ed as unc ional colo helpe o be e ix and inc ease he
ligh as ness o an o ganic ed diazo pigmen s in bioPBS ma ix. To enhance he esul ing
ma e ial mechanical p ope ies Z O2was as a ein o cing agen . A comple e and de ailed
cha ac e iza ion has been conduc ed using mic o and mac oscopical echniques such as
SEM, we abili y, colo change, ha dness, and mechanical analysis. Addi ionally, an aging
e ec was e alua ed du ing he ealiza ion o he expe imen al wo k and hei e ec s we e
cha ac e ized and compa ed.
2. Ma e ials and Me hods
2.1. Ma e ials
The polyme ma ix used was a biobased polybu ylene succina e BioPBS FZ71 PD
which was pu chased om Japan Pulp and Pape GmbH (Düsseldo , Ge many).
The IA 99% pu e, was pu chased om Sigma Ald ich (Da ms ad , Ge many). I is a
whi e c ys alline powde , unsa u a ed dica boxylic acid (C
5
H
6
O
4
), in which one ca boxyl
g oup is conjuga ed o he me hylene g oup [
31
]. I p esen s a hyg oscopic p ope y, and i
is odo - ee [32,33]. I s mel ing poin is 167–168 ◦C and he boiling poin is 268 ◦C [34].
The colo ing agen was pu chased om UNNOX GROUPS (Esqui oz, Spain) which is
an o ganic ed diazo pigmen wi h he comme cial code: PR57:1, MDN-1153.
Finally, he Zi conia nanopa icles we e kindly p o ided by he TORRECID g oup
(L’Alco a, Spain). Zi conia is a c ys alline dioxide o zi conium. I s mechanical p ope ies
a e e y simila o hose o me als (i has been called ‘ce amic s eel’ [
35
]). Zi conia c ys als
can be o ganized in h ee di e en pa e ns: monoclinic ( ound a oom empe a u e, unde
ambien p essu e and upon hea ing up o 1170
◦
C), e agonal (be ween 1170 and 2370
◦
C),
and cubic (abo e 2370 ◦C and up o he mel ing poin ) [36].
2.2. Nano-Bio-Composi es P epa a ion
Twel e di e en o mula ions we e p epa ed by ex usion-compounding wi h a 26-
mm win-sc ew Cope ion ZSK 26 compounde machine (S u ga , Ge many). Fi s ly, bina y
blends we e ex uded: F2 and F3; F4 and F5 and F6. The h ee addi i es we e in oduced in
a powde o ma om a seconda y eede di e en om he bioPBS main hoppe . IA was
in oduced a he beginning o he ba el while he Z O
2
and he colo ing agen a he
middle o he ba el. The mel ed polyme and powde s we e mixed a a sc ew speed o
Polyme s 2021,13, 79 4 o 14
200 pm; empe a u e was in-c eased om 160
◦
C in he eeding zone up o 180
◦
C a he
nozzle. The compounding was ex uded h ough a 2 mm diame e die o a cons an ou pu
o 15 kg/h. The ex uda e was quenched in a wa e ba h a oom empe a u e, d ied and
cu in o pelle s. A o al o 3 kg o pe blend we e p oduced. Te na y and qua e na y
o mula ions we e p oduced by e-ex uding in a second s ep using he condi ions abo e.
To his end, he colo an and he zi conia we e added in o bioPBS/IA ex uded ma ices,
by in oducing hem a he middle o he ba el as o he i s ex usion-compounding s ep.
No modi ica ions we e equi ed ega ding he pa ame e s and condi ions o he ex usion
p ocess. Table 1summa izes he composi ion o all e e ences.
Table 1. Summa y o ma e ial o mula ions based on bioPBS FZ71PD ma ix.
Re e ence bioPBS Ma ix IA Colo an Z O2
F1 100% - - -
F2 96% 4% - -
F3 90% 10% - -
F4 96% - 4% -
F5 98% - - 2%
F6 96% - - 4%
F7 94% - 4% 2%
F8 92% 4% 4% -
F9 86% 10% 4% -
F10 94% 4% - 2%
F11 88% 10% - 2%
F12 90% 4% 4% 2%
F13 84% 10% 4% 2%
Samples we e analyzed a week 0 (W0), jus a e hei p epa a ion and a e aging in
ambien condi ions a week 4 (W4).
2.3. Gene al Cha ac e isa ion Me hods
2.3.1. Two Types o Specimens We e De eloped o Ma e ial Cha ac e iza ion
•
Injec ed specimens o mechanical ( ensile o dog-bone ollowing ISO 178 s anda d)
and ha dness (pa allelepiped specimens o 80
×
100
×
4 mm) es ing we e ob ained
by injec ion molding wi h a JSW 85 EL II elec ic injec ion machine.
The empe a u e p o ile was inc eased om 150
◦
C a he hoppe up o 180
◦
C a he
nozzle wi h 40 pm. The dosage and illing p essu e we e a ied o each o mula ion
injec ed. A packing p essu e o 35% (55 ba du ing 20 s) was applied. When injec ing
samples con aining IA, empe a u es we e dec eased om 140
◦
C a he hoppe up o
160
◦
C a he nozzle and cooling ime inc eased by 10 s so ha i was cooled enough o be
expelled om he mold.
•
Ci cula specimens o 50 mm diame e and 2 mm hick om all he o mula ions
we e p oduced o measu ing we abili y and colo change. The same p ocessing
pa ame e s we e conside ed. The ma e ials we e mixed o 120 s a 90 pm in a
co- o a ing win-sc ew ex ude Mic ocompounde a 5 and 15 cc, DSM (Si a d,
The Ne he lands), using a empe a u e p o ile o 120–125–130
◦
C. Due o he low
iscosi y o he o mula ions con aining IA, a p essu e- ime injec ion molding p o ile
o 1.0–5; 1.1–15; 1.1–15 in ba -seconds was used. The mold and injec ion empe a u es
we e se a 30 and 150 ◦C, espec i ely.
2.3.2. Measu emen s
Mechanical es s we e conduc ed unde ambien condi ions using a Zwick Roell Z 2.5
(Ulm, Ge many). A leas i e specimens pe ma e ial we e es ed, acco ding o ISO 178
and ISO 527 Me hodology
Polyme s 2021,13, 79 5 o 14
S uc u al p ope ies we e e alua ed by scanning elec on mic oscopy (SEM) wi h
a Hi- achi S3400N (Tokyo, Japan) equipmen in o de o de e mine he mo phology and
dispe sion. B oken samples coming om he mechanical es s we e used.
Ha dness was measu ed using a po able ha dness es e , he METALTEST es e
model T500 (Ba celona, Spain), o e i y ma e ial ha dness wi h load-cell echnology o
Vicke s, B inell and Rockwell es ing. The Rockwell B scale was used o his s udy.
The su ace p ope ies o p oduced ma e ials we e e alua ed by s a ic con ac angle
measu emen s (FTA1000 Analyze (Newa k, NJ, USA)). The we abili y o he su aces was
s udied by using he sessile d op me hod, in ai , in con ac wi h HPLC g ade wa e . When
a su ace is hyd ophilic, he d op ex ends o e he ma e ial a an angle be ween 0
◦
and
30
◦
. I he su ace o he solid is hyd ophobic, he con ac angle will be g ea e han 90
◦
.
On su aces ha a e e y hyd ophobic, he angle can be g ea e han 150
◦
and e en close
o 180◦.
Colo change and gloss o samples was in es iga ed by means o a spec opho ome e
(CM-2300d Konica Minol a, Japan). Da a we e acqui ed by using he SCI 10/D65 me hod,
CIELAB colo a iables, as de ined by he Commission In e na ionale de 1
0
Éclai age (CIE
1995), we e used.
Samples we e placed on a whi e s anda d pla e and L*, a*, and b* pa ame e s we e
de- e mined. L* alue anges om 0 (black) o 100 (whi e); a* alue anges om
−
80
(g een) o 100 ( ed); and b* alue anges om
−
80 (blue) o 70 (yellow). Fo each sample,
3 measu emen s we e aken a andom loca ion. The o al colo di e ence o dis ance
be ween colo s (Euclidean dis ance)
∆
E* be ween whi e and he samples was calcula ed as
indica ed in Equa ion (1) [37]: colo -di e ence o mula:
∆E∗=q(∆L∗)2+(∆a∗)2+(∆b∗)2(1)
3. Resul s and Discussion
3.1. Mechanical Tes s
The mechanical p ope ies o biocomposi e ma e ials a e always a comp omise be-
ween s i ness and oughness which a e gene ally mu ually exclusi e. The elas ic modulus
(E) and elonga ion a b eak (
εB
) a e use ul pa ame e s o desc ibe he mechanical be-
ha io o he de eloped ma e ials and a e closely ela ed o he in e nal mic os uc u e.
The mechanical p ope ies de e mined om uniaxial ensile es s a e summa ized in
Table 2
and hei com-pa ison among he di e en o mula ions and aged samples a e shown in
Figu e 1.
Table 2.
Mechanical p ope ies unde ensile o ce: Young’s modulus and elonga ion a b eak o all cha ac e ized ma e ials;
su ace ha dness and con ac angles measu emen (we abili y). Measu emen s done a week 0 (W0) and a e 4 weeks
aging (W4).
Ma e ial Young0s Modulus
(MPa) W0
Young0s Modulus
(MPa) W4
Elonga ion a
B eak (%) W0
Elonga ion a
B eak (%) W4
Ha dness
(HRB) W0
Ha dness
(HRB) W4
WCA
(◦) W0
WCA
(◦) W4
F1 590 ±30 685 ±20 268 ±27 262 ±9 6.2 ±1.3 5.1 ±0.9 76 ±1 69 ±3
F2 473 ±37 866 ±33 289 ±119 1.5 ±0.8 20.6 ±2.6 B eak 54 ±3 54 ±0
F3 528 ±49 953 ±63 317 ±75 0.67 ±0.05 5.1 ±0.4 B eak 66 ±3 47 ±3
F4 645 ±24 740 ±14 258 ±16 60 ±4 2.6 ±1.4 2 ±1.3 68 ±3 70 ±3
F5 625 ±13 740 ±60 258 ±7 173 ±18 6.6 ±1.1 1.6 ±0.5 75 ±3 66 ±1
F6 726 ±31 960 ±351 205 ±68 192 ±18 4.3 ±1.3 1.1 ±0.6 76 ±3 71 ±2
F7 631 ±31 739 ±23 249 ±16 225 ±32 1.1 ±0.8 1.1 ±0.8 70 ±3 66 ±3
F8 634 ±59 966 ±32 75 ±65 0.88 ±0.2 10.4 ±1.5 B eak 63 ±4 56 ±3
F9 626 ±52 946 ±39 259 ±133 0.27 ±0.01 6.4 ±0.7 B eak 65 ±3 58 ±4
F10 659 ±52 1052 ±67 247 ±42 0.97 ±0,4 17.4 ±0.3 B eak 59 ±2 44 ±3
F11 587 ±34 937 ±24 279 ±45 0.56 ±0.28 5.0 ±1.2 B eak 67 ±2 61 ±3
F12 610 ±52 1027 ±66 57 ±7 0.88 ±0.2 10.2 ±1.6 B eak 60 ±3 61 ±3
F13 585 ±103 979 ±53 145 ±108 0.3 ±0.05 5.6 ±0.6 B eak 60 ±4 59 ±3

Polyme s 2021,13, 79 6 o 14
Polyme s 2021, 12, x FOR PEER REVIEW 7 o 15
Figu e 1. Young’s moduli (a) and elonga ion a b eak alues (b) o all specimens e alua ed a W0 and W4.
3.1.1. Compa a i e esul s among o mula ions a W0 (compa isons among pink col-
umns—Young′s modulus; and among g een columns—elonga ion a b eak)
When IA is added o nea PBS a educ ion in he Young’s modulus by 11% o F2 and
by 26% o F3 is obse ed, while an inc ease in he elonga ion a b eak by 8% o F2 and
by 18% o F3 is ound. Thus, IA seems o induce a plas icizing e ec , which is in cohe ence
wi h Ki imu a e al. [34] who explained he use o his componen in ubbe -like polyme s
due o i s excellen s eng h and lexibili y, making he PBS oughe . This esul is also
aligned wi h K ishnan e al. [38], who used IA o design an alipha ic copolyes e elas ome
ha was used as PLA oughene .
The addi ion o he colo an (F4) as well as low amoun s o Z O2 (F5) sligh ly in-
c eases he Young’s modulus, while he ma e ial s i ness is conside able aised by 23%
when a 4 w % o Z O2 is inco po a ed (F6). On he one hand, Zi conia a ec s in he elon-
ga ion a b eak and an o e all all can be obse ed (F6 dec eases a 24%). Ne e heless, he
da a dispe sion is b oad, ha indica es he appea ance o agglome a es p oducing a s ess
concen a ing e ec a o ing a p ema u e up u e [39]. All in all, his dec ease is no icea-
bly ound o 4 w % o Z O2, which is a qui e posi i e esul o such a high con en o
zi conium i compa ed wi h o he simila s udies using i as ein o cemen agen in poly-
me s. Fo example, Mish a T.K. e al. [40] ound he same dec ease in he elonga ion a
b eak o PEEK/Z O2 compounds wi h jus a 1 w %. On he o he hand, when he colo an
is inco po a ed o PBS (F4) elonga ion a b eak alues emain almos unchanged. Conse-
quen ly, he colo an appea s o be be e dispe sed and in eg a ed han he Z O2 p obably
due o i s o ganic na u e which is mo e compa ible wi h he blend.
Te na y o mula ions (F5, F6, F8, F9, F10, F11) and qua e na y blends (F12, F14), lead
o a complex mechanical beha io in which he igidi y o he ma e ials is kep o e en
sca cely in-c eased when compa ed o nea PBS. The combina ion o hese addi i es in-
duce a ema kable all in he elonga ion a b eak espec o nea PBS. The mos p ominen
dec ease is ound o F8 by 72% and F12 by 79%, closely ollowed by F13. Bo h o mula-
ions a e complex blends combining a 4% w % o IA and colo an . The high sca e ing o
he da a con i ms a lack o in eg a ion be ween he IA, he ma ix and he addi i es, p ob-
ably o ming egions o high and low IA concen a ion peaks; and he o ma ion o zi co-
nia and colo an agg ega es wi h insu icien dispe sion (a esul ha has been co obo-
a ed wi h SEM mic og aphs).
3.1.2. Compa a i e Resul s o Same Fo mula ions be ween W0 and W4 (Aging E ec )
All plas ic ma e ials su e om aging wi h ime. They end o ec ys allize as he
polyme chains end hei o de ing. The plas ic ge s s i e and in a long- e m becomes
Figu e 1. Young’s moduli (a) and elonga ion a b eak alues (b) o all specimens e alua ed a W0 and W4.
3.1.1. Compa a i e Resul s among Fo mula ions a W0 (Compa isons among Pink
Columns—Young0s Modulus; and among G een Columns—Elonga ion a B eak)
When IA is added o nea PBS a educ ion in he Young’s modulus by 11% o F2 and
by 26% o F3 is obse ed, while an inc ease in he elonga ion a b eak by 8% o F2 and by
18% o F3 is ound. Thus, IA seems o induce a plas icizing e ec , which is in cohe ence
wi h Ki imu a e al. [
34
] who explained he use o his componen in ubbe -like polyme s
due o i s excellen s eng h and lexibili y, making he PBS oughe . This esul is also
aligned wi h K ishnan e al. [
38
], who used IA o design an alipha ic copolyes e elas ome
ha was used as PLA oughene .
The addi ion o he colo an (F4) as well as low amoun s o Z O
2
(F5) sligh ly in-
c eases he Young’s modulus, while he ma e ial s i ness is conside able aised by 23%
when a 4
w %
o Z O
2
is inco po a ed (F6). On he one hand, Zi conia a ec s in he
elonga ion a b eak and an o e all all can be obse ed (F6 dec eases a 24%). Ne e heless,
he da a dispe sion is b oad, ha indica es he appea ance o agglome a es p oducing a
s ess concen a ing e ec a o ing a p ema u e up u e [
39
]. All in all, his dec ease is
no iceably ound o 4 w % o Z O
2
, which is a qui e posi i e esul o such a high con en
o zi conium i compa ed wi h o he simila s udies using i as ein o cemen agen in
polyme s. Fo example, Mish a T.K. e al. [
40
] ound he same dec ease in he elonga ion
a b eak o PEEK/Z O2 compounds wi h jus a 1 w %. On he o he hand, when he
colo an is inco po a ed o PBS (F4) elonga ion a b eak alues emain almos unchanged.
Consequen ly, he colo an appea s o be be e dispe sed and in eg a ed han he Z O
2
p obably due o i s o ganic na u e which is mo e compa ible wi h he blend.
Te na y o mula ions (F5, F6, F8, F9, F10, F11) and qua e na y blends (F12, F14),
lead o a complex mechanical beha io in which he igidi y o he ma e ials is kep o
e en sca cely in-c eased when compa ed o nea PBS. The combina ion o hese addi i es
induce a ema kable all in he elonga ion a b eak espec o nea PBS. The mos p ominen
dec ease is ound o F8 by 72% and F12 by 79%, closely ollowed by F13. Bo h o mula ions
a e complex blends combining a 4% w % o IA and colo an . The high sca e ing o he
da a con i ms a lack o in eg a ion be ween he IA, he ma ix and he addi i es, p obably
o ming egions o high and low IA concen a ion peaks; and he o ma ion o zi conia and
colo an agg ega es wi h insu icien dispe sion (a esul ha has been co obo a ed wi h
SEM mic og aphs).
3.1.2. Compa a i e Resul s o Same Fo mula ions be ween W0 and W4 (Aging E ec )
All plas ic ma e ials su e om aging wi h ime. They end o ec ys allize as he
polyme chains end hei o de ing. The plas ic ge s s i e and in a long- e m becomes
b i le. Kimble e al. [
41
], s udied aging in PLLA/PBS blends including annealing and
Polyme s 2021,13, 79 7 o 14
c eep s udies. As conclusion, blends wi h high con en o PBS end o dec ease i s Mw
wi h ime p oduced by deg ada ion and showing and emb i lemen o samples. Thus,
hei esul s also highligh ed he impo ance o app op ia e s o age condi ions o duc ili y
e en ion. In his s udy, he Young’s modulus o nea PBS inc eased by 16% (F1) a e
4 weeks. The elonga ion a b eak was main ained, ha indica ed he good in eg i y o he
ma e ial and, appa en ly, an absence o deg ada ion.
The e ec o he IA was ema kable. In F2 and F3 samples, he Young’s modulus aised
by 80%, which clea ly indica ed he igidiza ion e ec . The blends los hei oughness and
became e y b i le. A d op in he elonga ion a b eak by mo e han 98% was obse ed in
all he o mula ions con aining IA.
When adding he colo an (F4) and a 2 w % o Z O
2
(F5), he ma e ial became a 15%
s i e in bo h cases, while when inc easing he addi ion o Z O
2
by 4 w % (F6) he Young’s
modulus doubled by eaching a 32% highe alue. S i ness and oughness a e usually
comp omised p ope ies, and we can ind a educ ion in elonga ion a b eak by 6% o F6
and by 33% o F5. These esul s d aw a be e dispe sion o Z O
2
o F6 a he han F5.
The colo an also seems o highly a ec his p ope y, alling by 77% (F4), ha may indica e
a disagg ega ion o he o ganic phases wi h ime ha weakens he in e phase be ween he
colo an and he addi i e.
When e na y and qua e na y blends a e s udied (F8–F13), we can obse e a ise in
he Young’s modulus be ween 60% and 70%, as expec ed, and p ac ically an absence o
elonga ion a b eak e ec induced by he IA.
3.2. Ha dness
3.2.1. Ha dness Resul s a W0
The highes alue on ha dness is ound o F2 (4 w % IA), which mul iplies almos
by ou he ha dness alue o nea PBS, while o F3 (10 w %) i dec eases a 18% down
nea PBS alue. I is likely ha a 10 w % IA has sa u a ed he blend, showing a lack
o miscibili y among he wo phases (polybu ylene succina e (PBS) and IA). The shea
o ces o he modynamics p oduced du ing he compounding p ocess migh no ha e been
enough o dispe se and homogenize he componen s, which seem no o be compa ible
and which end o o m sepa a ed phases inside he blend. Mo eo e , as hese phases a e
dis inc , he IA appa en ly seems o c ys allize in o he su ace o he injec ed specimen.
Using he SEM mic og aphs we can obse e he IA c ys als, and when he inden e inds a
high concen a ion o IA in he su ace i also inds a agile and b i le poin .
When obse ing F4, he PBS phase mainly con ains he colo an , which is a so
pigmen , and he o e all ha dness o he blend dec eases by 58%. On he o he hand. when
cha ac e izing F5 and F6, we can ind a ha dening e ec by 6% o he 2 w % o zi conia.
Howe e , when adding a 4 w % o zi conia, ha dness dec eases by 31%, p obably due o a
sa u a ion o he blend accompanied by he appa i ion o agglome a es. The high su ace
ene gy o nanopa icles is p one o induce he o ma ion o nanopa icles agg ega ion [
42
].
Thus, phase sepa a ion o en akes place owing o he g ea di e ences in he p ope ies o
polyme and ino ganic ma e ials.
When combining he colo an and he Z O
2
(F7), he e is a nega i e syne gis ic e ec ,
dec easing he ha dness alue by 82%, while he combina ion o any o hem wi h he
4 w %
IA induces a posi i e syne gy in which he IA domina es he beha io o he
complex blends (F8 by 68%, F10 by 181% and F12 by 65%). Howe e , wi h a 10 w % IA
added ins ead, i s ill domina es he blend keeping simila alues o hose ound o F3.
3.2.2. Ha dness Resul s a W4
When ha dness was measu ed a W4, he au ho s ound a clea emb i lemen o he
samples. Especially in hose con aining IA (F2, F3 and F8–F13), o which i was no possible
o epea he cha ac e iza ion es . The specimens b oke when he inden e pene a ed he
sample, and some o he expe imen samples e en had a duc ile ac u e jus om being
manipula ed.
Polyme s 2021,13, 79 8 o 14
3.3. S uc u al P ope ies (SEM)
The su ace mo phology o he de eloped o mula ions was s udied by using scanning
elec on mic oscope (SEM). Mic og aphs o ep esen a i e specimens a e shown in
Figu e 2
.
Polyme s 2021, 12, x FOR PEER REVIEW 9 o 15
he sample, and some o he expe imen samples e en had a duc ile ac u e jus om
being manipula ed.
3.3. S uc u al P ope ies (SEM)
The su ace mo phology o he de eloped o mula ions was s udied by using scan-
ning elec on mic oscope (SEM). Mic og aphs o ep esen a i e specimens a e shown in
Figu e 2.
Figu e 2. SEM—W0 (le —(a,c,e,g)—and cen al—(b,d, ,h)—columns) and W4 ( igh column—i,j,k,l). (a): F1; (b): F3; (c):
F9; (d): F13; (e, ): F5; (g,h): F4; (i):F1; (j): F3; (k): F9; (l) F10.
3.3.1. S uc u al Resul s a W0
The mic og aphs con i m he endencies obse ed in he mechanical and ha dness
esul s. IA c ys allizes in he o m o ec angula nanoc ys als. I clea ly mani es s a special
phase mo phology cons i u ed by he dispe se phase o IA. These nanoc ys als a e ound
o g oup hemsel es in a he e ogeneous way showing a lack o compa ibili y be ween he
IA and he PBS (b,c). The IA nanoc ys als a e ound o mig a e o he su ace o he pa .
The au ho s obse ed his phenomena: ei he o e ime ou side o he ex e nal su ace
Figu e 2.
SEM—W0 (le —(
a
,
c
,
e
,
g
)—and cen al—(
b
,
d
,
,
h
)—columns) and W4 ( igh column—
i
,
j
,
k
,
l
). (
a
): F1; (
b
): F3; (
c
): F9;
(d): F13; (e, ): F5; (g,h): F4; (i):F1; (j): F3; (k): F9; (l) F10.
3.3.1. S uc u al Resul s a W0
The mic og aphs con i m he endencies obse ed in he mechanical and ha dness
esul s. IA c ys allizes in he o m o ec angula nanoc ys als. I clea ly mani es s a special
phase mo phology cons i u ed by he dispe se phase o IA. These nanoc ys als a e ound
o g oup hemsel es in a he e ogeneous way showing a lack o compa ibili y be ween he
IA and he PBS (b,c). The IA nanoc ys als a e ound o mig a e o he su ace o he pa .
The au ho s obse ed his phenomena: ei he o e ime ou side o he ex e nal su ace
(Figu e 2j,k a e aken om he bo de pe ime e ), o wi hin in e nal c ea ed su aces such
as o example in bubbles o de ec s gene a ed du ing he injec ion p ocess o he specimen
Polyme s 2021,13, 79 9 o 14
(Figu e 2d). The e o e, we ind a highly ein o ced ma e ial a he su ace le el, bu as i is
no miscible, i is no well in eg a ed, and a seg ega ion o he phases is obse ed.
Appa en ly, as he pigmen is highly o ganic, i displays a good in e acial bonding
wi h he polyme (Figu e 2g,h). The Z O
2
seems o be well dispe sed, al hough a ew
agg ega es can be ound (Figu e 2e, ). When e na y and qua e na y blends a e s udied,
hose con aining IA nanoc ys als end o su ound he colo an agg ega es. This e ec can
be explained as p obably being due o he combina ion o he pola –apola pe o mance
o bo h ma e ials, ha gene a es a complex in e ace inducing a low adhe ence wi h he
polyme ic ma ix, PBS. The IA is an acid, ha means ha he hyd ogen on he OH g oup
can easily be emo ed, lea ing an anion. Bo h he colo an pigmen as well as Z O
2
, may ac
as a sal o he IA, a o ing he a ac ion be ween hem (Figu e 2d). These agg ega es
ha e a s ess concen a ing e ec which educes he oughness o he ma e ial, a o ing a
p ema u e b eaking, ha explains he mechanical beha io ound.
3.3.2. S uc u al Resul s a W4
Finally, a change in he ype o ac u e can be obse ed be ween W0 and W4. A W0
he ac u e su ace e idenced a duc ile beha io (Figu e 2a), while a W4 a mo e agile
su ace is ound showing a la ac u e su ace o he polyme accompanied by some
s ia ions (Figu e 2i), in which polyme ic chains ha e had he ime o ea ange. So does
he IA, which is uns able in he blend and mig a es o he su ace o he specimen, seeking
he s a e o minimum ene gy (Figu e 2j,k,l). Thus, i can be con i med ha he ma e ials
su e om aging ha induces a igidiza ion mechanism and ha i is clea ly in ensi ied
wi h he addi ion o IA.
3.4. Hyd ophobici y/We abili y
We abili y esul s a e included in Table 2. The ange WCA alues o ou bioPBS
sys ems a y be ween 44◦and 76◦.
3.4.1. S uc u al Resul s a W0
The p esence o IA in bina y sys ems educes WCA when compa ed wi h nea PBS
(F1), his phenomenon is mo e p onounced in F2 han in F3 making he ma e ial mo e
hyd ophilic. I is also ound a sligh educ ion in he WCA when colo an is added (F4)
while he p esence o Z O
2
does no change he WCA alue o e e ence PBS ma ix (F5,
F6). Mizuno e al. [
5
], showed he same endency as wi h IA when in oduced g a ed
Ac ylic Acid in o PBS o s udy and con ol he biodeg adabili y o his alipha ic polyes e .
Thei s udy demons a ed ha a mo e hyd ophilic su ace had a conside able impac in
he biodeg ada ion o he PBS and hus i nega i ely a ec s he mechanical and s uc u al
p ope ies.
In he samples whe e IA was combined wi h Z O
2
(F10, F11 sys ems), he WCA seems
o be in luenced only by he p esence o IA and he con ac angle alues a e simila o he
alues eco ded o PBS/IA bina y sys ems.
The addi ion o Z O
2
(F7) does no change he alues o F4, in luenced by he colo an
pigmen , as al eady no ed in he case o e na y sys ems. The p esence o IA educes he
alues o F4, so he dec ease in we abili y in he p esence o IA is con i med e en in colo ed
samples (F8, F9). Mo eo e , as explained, he colo ed samples su e om clea age o he
labile g oups o he ed pigmen , hus accele a ing e en mo e his deg ada ion p ocess ha
is also ansla ed in a mo e hyd ophilic su ace.
Including he Z O
2
in he F12 and F13 sys ems only sligh ly changes he WCA alues,
when compa ed o e na y sys ems ha ing IA bu wi hou Z O2(F8, F9).
3.4.2. S uc u al Resul s a W4
An o e all dec ease on WCA was obse ed compa ing he alues ob ained o PBS
samples a W0 and a W4, making he ma ix ma e ial mo e hyd ophilic wi h ime as a
esul o ma e ial deg ada ion. Acco ding o Mizuno e al., we abili y oge he wi h he