Sus ainable Ma e ials and Technologies 33 (2022) e00474
A ailable online 5 Augus 2022
2214-9937/© 2022 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-
nc-nd/4.0/).
In luence o lignin modi ica ions on physically c osslinked lignin hyd ogels
o d ug deli e y applica ions
Amaia Mo ales
a
, Jalel Labidi
a
,
*
, Pa icia Gull´
on
b
a
Chemical and En i onmen al Enginee ing Depa men , Uni e si y o he Basque Coun y UPV/EHU, Plaza Eu opa 1, 20018, San Sebas i´
an, Spain
b
C.A.C.T.I. Labo a o y, Technology Pa k o Galicia- Tecnopole, CTC Building, San Cib ao das Vi˜
nas, 32901 Ou ense, Spain
ARTICLE INFO
Keywo ds:
Modi ied lignin
Pe oxida ion
Hyd oxyme hyla ion
Hyd ogels
D ug deli e y
ABSTRACT
So a , he possibili y o syn hesizing hyd ogels based on mul iple biopolyme s has been in es iga ed, and among
hem lignin has p o en o be one o he po en ials o his pu pose due o he mul iple ad an ages i o e s.
Howe e , because o i s high molecula weigh , s e ic hind ance and ew eac i e si es on i s s uc u e, i is
some imes necessa y o imp o e i s eac i i y hough chemical modi ica ions. On he basis o p e ious esul s,
wo chemical modi ica ions we e selec ed in o de o enhance almond, walnu and comme cial alkaline and
o ganosol lignins' eac i i y: a pe oxida ion eac ion o alkaline ones and a hyd oxyme hyla ion o o ganosol
ones. Bo h eac ions we e con i med by mul iple echniques (i.e. FTIR, GPC and TGA). Hyd ogels we e syn-
hesized om hese lignins acco ding o p e ious wo ks. The high lignin was e o he syn hesized hyd ogels
sugges ed ha despi e he modi ica ion o he lignins, jus he highes molecula weigh ac ions eac ed wi h
he ma ix polyme . Mo eo e , he swelling capaci y o modi ied alkaline lignin-based hyd ogels was nega i ely
a ec ed, whe eas he one o o ganosol lignin-based samples imp o ed. The SEM mic og aphs explained he
a o emen ioned, and he esul s om he DSC and comp ession es s we e in acco dance wi h hem. Sel -
ex ac ed que ce in loading and elease s udies sugges ed ha hese samples could be used o con olled d ug
deli e y.
1. In oduc ion
The insa iable demand o ene gy and ossil esou ces has d i en he
cu en socie y o many global en i onmen al and social conce ns. In
his con ex , lignocellulosic biomass has opened an al e na i e doo o
he p oduc ion o chemicals, ma e ials and uels [1]. This biomass is
cons i u ed by lignin, hemicelluloses and cellulose. Al hough bio-
e ine ies, he sus ainable combina ion o p ocesses able o ans o m
biomass in o a g ea a ie y o comme cial p oduc s [2], ha e mos ly
been ocused on cellulose and hemicelluloses o he p oduc ion o pape
and bioe hanol [3], o ins ance, he con e sion o lignin in o alue-
added compounds is i al o he cos -compe i i eness o bio e ine ies
[4]. In ac , lignin can cons i u e up o 40% o woody biomass and 15%
o he bal one [5] and i has demons a ed o possess in e es ing p op-
e ies no jus in ene ge ic e ms bu also o he syn hesis o new bio-
based ma e ials [6].
Lignins' s uc u e is an in ica e and andom combina ion o phe-
nylp opanoid uni s (i.e. coni e yl, couma il and sinapyl alcohols), which
a ies acco ding o he sou ce and kind o plan , i s cul u e condi ions
and he used lignin isola ion me hod [7]. In addi ion, he lignin s uc u e
is highly b anched and has mul iple unc ional g oups including
ca bonyl (C=O), hyd oxyl (-OH), ca boxyl (-COOH) and me hoxy
(-CH
3
O) g oups [5], which ha e a di ec e ec on i s eac i i y [8].
Mo eo e , he eac i i y o his biopolyme is usually no high enough
owing o i s high molecula weigh , s e ic hind ance and ew eac i e
si es [2,9]. The e o e, in o de o o e come his d awback i is some-
imes necessa y o pe o m a chemical modi ica ion o i s s uc u e [10].
Fo his aim, he e a e ou main ways: he i s one in ol es i s depo-
lyme isa ion o agmen a ion, he second one ocuses on he c ea ion o
chemically ac i e si es, he hi d one is ela ed o he modi ica ion o he
hyd oxyl g oups in i s s uc u e; and he las one would be h ough he
p oduc ion o g a copolyme s [11].
Acco ding o a ious s udies, lignin can con e in e es ing p ope ies
o lignin-based composi e ma e ials such as an ioxidan o an ibac e ial
capaci y [12]. This ac makes lignin a ac i e o he o mula ion o
ma e ials o be used in he biomedical ield. A clea example o his is he
ising end o lignin addi ion in o hyd ogels [13], which a e e y use ul
ma e ials o d ug deli e y [14], wound d essing [15] and issue
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (J. Labidi).
Con en s lis s a ailable a ScienceDi ec
Sus ainable Ma e ials and Technologies
jou nal homepage: www.else ie .com/loca e/susma
h ps://doi.o g/10.1016/j.susma .2022.e00474
Recei ed 13 Ma ch 2022; Recei ed in e ised o m 29 July 2022; Accep ed 2 Augus 2022
Sus ainable Ma e ials and Technologies 33 (2022) e00474
2
enginee ing and egene a i e medicine [16], o ins ance.
Recen ly, modi ied lignins ha e been used o he o mula ion o
hyd ogels in o de o o e come some d awbacks such as agglome a ion
o wa e insolubili y [12], al hough many o hem ha e been applied o
pollu an adso p ion [10,17]. Mo eo e , lignin modi ica ions can be
c ucial o a oid he use o chemical c osslinking agen s, p omo ing he
syn hesis o physically-c osslinked hyd ogels, which a e usually mo e
en i onmen ally iendly and economical [18].
P e iously, he in luence o he sou ce and cha ac e is ics o alkaline
and o ganosol nu -shell (almond and walnu ) lignins was s udied [19]
as well as he impac o comme cial ones [20] on he cha ac e is ics o
he hyd ogels. Ne e heless, a signi ican lignin was e was gene ally
obse ed in all he sys ems as well as a lowe swelling deg ee in o ga-
nosol lignin-con aining hyd ogels. Thus, he objec i e o his wo k was
o o e come he a o emen ioned weaknesses by syn hesizing physical
hyd ogels wi h lowe lignin was es and highe swelling capaci y o
o ganosol lignin-based ones modi ying p e iously employed lignins
[19,20]. Fo his aim, alkaline lignins we e agmen ed ia an oxida ion
eac ion and he o ganosol ones we e hyd oxyme hyla ed so as o
in oduce new eac i e si es in o hem. The modi ied lignins we e
cha ac e ised and he modi ica ions we e con i med ia a ious ech-
niques (FTIR, GPC and
31
P NMR). Then, hyd ogels we e syn hesized
om modi ied lignins and hei lignin was es, swelling capaci ies,
mo phology, glass ansi ion empe a u es and mechanical p ope ies
we e s udied. In addi ion, he possibili y o using hese hyd ogels as d ug
deli e e s was s udied by analysing hei elease kine ics o sel -
ex ac ed que ce in.
2. Ma e ials and me hods
2.1. Ma e ials
O ganosol lignin (powde ) was pu chased om Chemical Poin .
Poly ( inyl alcohol) (beads) (M
w
=83,000–124,000 g/mol, 99+% hy-
d olyzed), alkaline lignin (powde ) and phospha e bu e saline (PBS)
able s we e supplied by Sigma Ald ich. Sodium hyd oxide (NaOH,
analysis g ade, ≥98%, pelle s), hyd ogen pe oxide (30% w/ , o
analysis), o maldehyde (37–38% w/w, s abilized wi h me hanol, o
analysis) and hyd ochlo ic acid (37%, o analysis) we e pu chased om
PanReac Química SLU. All eagen s we e employed as supplied.
Almond (AS) and walnu shell (WNS) alkaline and o ganosol lignins
(powde ) ex ac ed in a p e ious wo k ia subsequen au ohyd olysis
and deligni ica ion p ocesses we e used in his wo k [19].
2.2. Lignin modi ica ion
Alkaline lignins om AS and WNS as well as he comme cial one
we e subjec ed o a mic owa e assis ed pe oxida ion eac ion wi h
hyd ogen pe oxide as desc ibed by In an e e al. (2007) [21]. B ie ly,
lignin and hyd ogen pe oxide we e in oduced in o a high-p essu e
essel keeping a LSR o 10:1 (mL:g). A e sealing he essel, i was
subjec ed o h ee i adia ion cycles o 10 s a 1100 W wi h a 30 s sus-
pension pe iod be ween hem. A e wa ds, he essel was cleaned wi h
dis illed wa e and he collec ed mix u e was le o d y o e an o en.
O ganosol lignins ( om AS, WNS and he comme cial one) we e
exposed o a hyd oxyme hyla ion eac ion wi h o maldehyde ollowing
he p ocedu e epo ed by Chen e al. (2020) [9] wi h sligh modi ica-
ions. Concisely, 0.6 g o lignin we e dissol ed in an aqueous NaOH
solu ion (140 mL). Then, 0.495 mL o o maldehyde we e added and he
solu ion was hea ed up o 80 ◦C unde magne ic s i ing and e ige a-
ion. The eac ion was le o 3.5 h. A e wa ds, he modi ied lignin was
p ecipi a ed wi h 2% hyd ochlo ic acid, il e ed, neu alized and d ied.
2.3. Lignin cha ac e isa ion
All he lignins we e cha ac e ised employing he me hods desc ibed
in p e ious wo ks. Thei pu i y and composi ion [22], a e age molec-
ula weigh s and o al phenolic con en s [23], he mal deg ada ion,
c ys allini y and chemical s uc u e [20] we e de e mined. In addi ion,
in o de o con i m he chemical modi ica ion o o ganosol lignins,
31
P
NMR was employed ollowing he p o ocol desc ibed by Meng e al.
(2019) [8].
2.4. Hyd ogel syn hesis
The syn hesis o he hyd ogels was pe o med based on a p e iously
de ailed me hod [19,20]. In b ie , 60 mL o a 2% (w/w) NaOH aqueous
solu ion con aining 9.87 w. % PVA was p epa ed and hea ed up o 90 ◦C
un il comple e dissolu ion o PVA. Then, 9.12 w. % o lignin was added.
A e he lignin was dissol ed, he blends we e pou ed in o silicon
moulds, elimina ing he emaining in e nal bubbles ia ul asound and
he supe icial ai bubbles manually.
Fi e eeze- hawing cycles we e hen pe o med: i s ly, he blends
we e comple ely ozen (2.5 h) a −20 ◦C and, hen, hey we e hawed a
28 ◦C (1.5 h). Du ing he second and las cycles, he samples we e le a
he eeze o e nigh . Finally, he hyd ogels we e washed in o dis illed
wa e and d ied a oom empe a u e.
2.5. Hyd ogel cha ac e isa ion
The cha ac e isa ion o he hyd ogels was also done based on p e-
ious wo ks [19,20,24]. Thei lignin was e, swelling capaci y,
mo phology, he mal beha iou s and comp ession modules we e
s udied.
2.6. D ug ex ac ion and loading- elease es s
Que ce in was ex ac ed as a d ug combining he me hods epo ed
by Geo ge e al. (2019) and Jin e al. (2011) [25,26]. Fi s ly, onion peels
we e cleaned and d ied a 50 ◦C be o e being powde ed. Que ce in,
oge he wi h o he compounds, was hen ex ac ed by mic owa e
assis ed ex ac ion (MAE), which was based on p e ious expe imen s
(da a no shown) modi ying he mic owa e powe epo ed by Jin e al.
(2011) [26]. The ex ac ion was done wi h a 70% e hanol/wa e ( / )
solu ion, keeping a LSR o 40:1 ( /w). Since he used equipmen was no
a comme cial mic owa e o en, he employed powe o in e mi en 10
s i adia ions was ixed a 375 W. The o al eac ion ime was 2 min,
lea ing a 20 s in e al be ween he i adia ions. A e he eac ion, he
solid was il e ed and he liquid phase was o a y e apo a ed o he
comple e elimina ion o e hanol. The emaining aqueous solu ion was
conside ed as que ce in ex ac (QE).
The concen a ion o he que ce in ex ac was de e mined by UV
spec opho ome y. Fo his pu pose, a calib a ion cu e was con-
s uc ed using some solu ions o ce ain concen a ions o comme cial
que ce in (CQE) and measu ing hei abso bances a 375 nm [26]. The
o al phenolic and la onoid con en s (TPC and TFC, espec i ely) o QE
we e es ima ed as desc ibed by Sille o e al. (2019) [27], al hough in he
case o TFC he s anda d was done wi h CQE. QE was eeze-d ied and
analyzed by FTIR and compa ed wi h he spec um o CQE.
The loading es s we e pe o med by in oducing d y hyd ogel
samples in o dilu ed QE (1 mL QE in o 250 mL dis illed wa e ) solu ions
o 24 h. The abso bed QE amoun was calcula ed by he di e ence on
he concen a ions o he ini ial and inal solu ions [25]. A e he loaded
hyd ogels we e d ied, hey we e weigh ed and again imme sed in o PBS
a 37 ◦C, simula ing in i o condi ions, o 24 h. The elease kine ics was
pe o med by measu ing he concen a ion o QE in PBS a ce ain imes.
All elease es s we e done in iplica es. The ob ained esul s we e
in oduced in o a ious kine ic models including ze o o de , i s o de ,
Ko smeye –Peppas and Higuchi (see Eqs. 1–4) so as o unde s and he
elease mechanism o QE [25,28,29].
F=k0 (1)
A. Mo ales e al.
Sus ainable Ma e ials and Technologies 33 (2022) e00474
3
ln(1−F) = − k1 (2)
M
M∞
=kkp n(3)
F=kh 1/2(4)
Being F he pe cen age o que ce in eleased a ime , n he di usion
exponen and k
0
, k
1
, k
kp
and k
h
he a e cons an s o ze o o de , i s
o de , Ko smeye -Peppas and Higuchi kine ic models, subsequen ly.
3. Resul s and discussion
3.1. Lignin cha ac e isa ion
As shown in Table 1 he pu i y o he lignins was al e ed a e he
modi ica ion eac ion, especially in sel -ex ac ed lignins. This migh be
due o he employed eagen s. As o hei molecula weigh , hei
weigh a e age molecula weigh s augmen ed in all cases, especially in
alkaline lignins. Thei numbe a e age molecula weigh s go dec eased
o modi ied sel -ex ac ed alkaline lignins and o comme cial o gano-
sol lignin, leading o a mo e meaning ul ise in hei polidispe si y
index. Su p isingly, comme cial o ganosol lignin (COL) and i s modi-
ied e sion (MCOL) we e he mos he e ogeneous lignins, whe eas he
sel -ex ac ed na i e and modi ied o ganosol lignins (AAOL, AWOL,
MAAOL and MAWOL) we e he mos homogeneous ones.
Al hough he pe oxida ion eac ion was supposed o ac iona e
lignin, a high pe cen age o he chains seemed o unde go e-
condensa ion eac ions, which made he o al weigh a e age molecu-
la weigh s inc ease. Howe e , no ce ain e idence o his has been
ound in li e a u e. The change on he o al phenolic con en sugges ed
he deg ada ion o a oma ic ings in lignin [21,30]. Howe e , CAL
p esen ed he opposi e end, which could be ela ed o he di e ences
on he pH o he solu ions. Acco ding o he esul s epo ed by Xinping
e al. [30], he eac ion migh ha e yielded mo e deg ada ion
compounds unde alkaline condi ions [11], bu as In an e e al. (2007)
had demons a ed ha his could also be achie ed wi h he non p esence
o a ca alyse , he p esen wo k was done acco ding o he la e [21]. In
addi ion, he di e ences on he ange 1600–1730 cm
−1
on hei FTIR
spec a con i med he eac ion (see Fig. 1a). In ac , he band a ound
1710 cm
−1
mo ed o highe wa enumbe s in all cases, which was
a ibu ed o he –OH oxida ion o side chains, oge he wi h he
weakening o he peak a 1599 cm
−1
co esponding o a oma ic C
–
–
C
s e ching ib a ion. In addi ion, as epo ed by In an e e al., he
appea ance o he band a ound 1640 cm
−1
was also ep esen a i e o he
deg ada ion o a oma ic ings [21].
As o he hyd oxyme hyla ed lignins, i is known ha o maldehyde
may eac wi h lignin in alkaline medium in wo ways: he i s one, by
subs i u ing he ee o ho posi ions in he a oma ic ings, and he sec-
ond one, by eac ing wi h he side chains con aining ca bonyl g oups
[9,31,32]. Ne e heless, i eac i i y o he lignin is wan ed o inc ease,
he la e eac ion should be a oided [32]. Mo eo e , hyd oxyme hyl
g oups can also eac a ee posi ions o o he lignin uni s o ming
me hylene bonds and leading o he condensa ion o he s uc u e
[31,32]. The a ia ion on he dis ibu ions and a e age molecula
weigh s sugges ed ha he modi ica ion occu ed [32]. Despi e de ac
ha he change on he polydispe si y o he lignins was no ep esen-
a i e o ha ing ob ained mo e homogeneous modi ied lignins, hei
molecula weigh dis ibu ions (Supplemen a y da a) e oked a end o
homogeniza ion o he highes molecula weigh ac ions owa ds he
ones wi h lowe molecula weigh s. This beha iou was also obse ed by
o he au ho s [33]. Mo eo e , he inc ease on he numbe and weigh
a e age molecula weigh s was obse ed o MAAOL and MAWOL
samples, which was also epo ed by Cap a u e al. (2012) o g ass
lignins.
The FTIR spec a o na i e and modi ied o ganosol lignins also
indica ed he success o he eac ion (Fig. 1b) [33]. In ac , he in ensi-
ica ion o he –OH band (a 3400 cm
−1
), he one co esponding o C
–
H
(a ound 2930 cm
−1
), he one a ibu ed o me hoxyl and hyd oxyme hyl
g oups (a ound 2850 cm
−1
) and he one ela ed o he C
–
O s e ching
ib a ion o alipha ic C–OH and hyd oxyme hyl C–OH (a ound 1030
cm
−1
) we e a clea e idence o he in oduc ion o hyd oxyme hyl
g oups ia he modi ica ion eac ion [9,32]. The appea ance o a
shoulde a 3660 cm
−1
sugges ed he p esence o ee –OH g oups wi hin
he modi ied lignin s uc u es [34]. These esul s we e in ag eemen
wi h hose ob ained om
31
P NMR analyses, in which an inc ease on he
alipha ic hyd oxyl signal be ween 150 and 145.4 ppm was obse ed o
all he samples a e he hyd oxyme hyla ion eac ion [8] (Supplemen-
a y da a).
The he mal s abili y o all he samples was al e ed h ough he
modi ica ion eac ions. In ac , he maximum deg ada ion s ep was
shi ed o highe empe a u es in all cases. Howe e , in he case o
alkaline lignins, ano he deg ada ion s ep appea ed be ween he s age
co esponding o mois u e e apo a ion (<100 ◦C) and he maximum
deg ada ion s age. This peak was de ec ed a ound 300 ◦C, and was
a ibu ed o he lowe molecula weigh ac ions o lignin gene a ed
du ing he modi ica ion s ep [22,35]. I was also obse ed ha o ga-
nosol lignins we e mo e he mally s able and s a ed o lose weigh a
highe empe a u es han alkaline lignins, al hough hei maximum
deg ada ion empe a u es we e sligh ly lowe . This ac was a ibu ed
o hei molecula weigh dis ibu ions and polydispe si y indexes, since
alkaline samples we e mo e he e ogeneous and, as a o emen ioned, he
lowes molecula weigh ac ions could ha e s a ed o deg ade i s ly.
Compa ed o na i e lignins, modi ied o ganosol lignins p esen ed
highe he mal s abili y and inal esidue, which was also obse ed by
Chen e al. (2020) [9]. This was ela ed o he inc ease on hei molec-
ula weigh s. In addi ion, despi e all he le esidues being o a ound he
40% o he ini ial sample weigh , modi ied o ganosol lignins le highe
esidues han alkaline ones, con e sely o wha happened o na i e
lignins, which may be a ibu ed o he modi ica ion and lignin p ecip-
i a ion s ages.
Table 1
Summa y o he pu i y, GPC, TPC and TGA esul s o he modi ied lignins.
Lignin
Sample
Pu i y
(%)
M
wa
(g/
mol)
M
nb
(g/
mol)
M
w
/
M
nc
TPC
(%
GAE
d
)
T
maxe
(◦C)
AAAL 88.2 ±
0.6 12,793 1528 8.4 33.1 ±
1.1 355
AAOL 95.2 ±
2.2 9020 1520 5.9 26.2 ±
0.1 357
AWAL 95.7 ±
1.9 16,670 1604 10.4 33.8 ±
0.4 354
AWOL 95.2 ±
0.8 7644 1359 5.6 27.2 ±
0.1 365
CAL 91.5 ±
1.2 9333 1365 6.8 20.3 ±
0.1 379
COL 92.5 ±
2.9 32,933 1123 29.3 19.3 ±
0.3 343
MAAAL 85.2 ±
1.1 17,675 1348 13.1 25.3 ±
0.1 384
MAAOL 92.3 ±
0.6 9557 1636 5.8 20.4 ±
0.1 383
MAWAL 84.0 ±
1.9 19,939 1369 14.6 27.6 ±
0.4 384
MAWOL 83.6 ±
2.9 8187 1420 5.8 23.6 ±
0.5 383
MCAL 91.9 ±
1.7 12,141 1718 7.1 25.8 ±
0.9 396
MCOL 96.5 ±
0.5 32,997 968 34.07 21.5 ±
0.4 390
a
M
w
: weigh a e age molecula weigh .
b
M
n
: numbe a e age molecula weigh ;.
c
M
w
/M
n
: polydispe si y index.
d
% GAE: pe cen age o gallic acid equi alen s.
e
T
max
: maximum deg ada ion empe a u e om TG/DTGA cu es.
A. Mo ales e al.
Sus ainable Ma e ials and Technologies 33 (2022) e00474
4
The c ys allini y o he samples was almos unal e ed by he modi-
ica ion eac ions (Supplemen a y da a). All he samples p esen ed a
wide peak a ound 22◦, which is ela ed o he amo phous s uc u e o
lignin [36,37].
3.2. Hyd ogel cha ac e isa ion
3.2.1. Lignin was e
As in p e ious wo ks, he lignin was e o he syn hesized hyd ogels
was de e mined h ough UV spec oscopy (Table 2) [19,20,24]. I was
expec ed o ha e lowe lignin was es han in he p e ious wo ks due o
he highe eac i i y o he modi ied lignins. Ne e heless, he esul s
p o ed ha he hypo hesis was inco ec , since he lignin was e de e -
mined o all he samples esul ed o be highe han hose epo ed
p e iously. This change was signi ican ly g ea e o he samples con-
aining MCAL and MCOL, which p esen ed a loss o almos 89 and 97%
o hei ini ial amoun o lignin, espec i ely. The samples con aining
MAWA did also show a huge inc ease. The es o he samples exhibi ed
lowe lignin was e aises, anging om 12 o 14%.
As he obse ed lignin was es we e so unexpec ed and so as o s udy
he eusabili y o lignins in he washing solu ions, i was decided o
p ecipi a e hese lignins and s udy hei molecula weigh s. These esul s
a e shown in Table 3. I was obse ed ha in all cases he los lignins had
a lowe weigh a e age molecula weigh han he na i e ones, and hey
we e also mo e homogeneous, since hei polydispe si y indexes we e
lowe . These esul s sugges ed ha he polyme ic ma ix could ha e
eac ed wi h he highes molecula weigh ac ions, leading o a big
elimina ion o he lowes molecula weigh ac ions.
3.2.2. Swelling capaci y
In o de o de e mine he e ec ha he lignin modi ica ions had on
he p ope ies o he syn hesized hyd ogels, hei swelling capaci y was
s udied. The esul s a e depic ed in Fig. 2.
Compa ing o p e ious esul s [19], i was obse ed ha in he case
o he alkaline lignin-con aining samples, he swelling capaci y go
signi ican ly educed when modi ied lignins we e employed o hei
syn hesis. These esul s sugges ha he pe oxida ion o lignin pe -
o med in he p esen wo k was no an app op ia e modi ica ion o
ob ain hyd ogels wi h a high swelling capaci y. On he o he hand, when
modi ied o ganosol lignins we e used, hei swelling capaci y was
enhanced, especially in he case o he samples wi h MCOL (450%),
which had also p esen ed he highes lignin was e. Mo eo e , MAAO
Fig. 1. FTIR spec a o modi ied and na i e alkaline (a) and o ganosol (b) lignins.
Table 2
Lignin was e (%) o na i e and modi ied lignin-con aining hyd ogels.
Sample Na i e (%) Modi ied (%)
AAA 59.6 ±2.8 73.5 ±0.5
AAO 71.1 ±3.0 83.4 ±4.6
AWA 44.2 ±1.6 71.6 ±0.5
AWO 59.9 ±4.0 74.0 ±4.8
CA 67.8 ±2.0 88.7 ±3.4
CO 77.4 ±1.7 96.5 ±0.3
Table 3
A e age molecula weigh s and polydispe si y indexes o he lignins eco e ed
om he washing solu ions.
Lignin Sample M
wa
(g/mol) M
nb
(g/mol) M
w
/M
nc
MAAAL 10,134 1317 7.7
MAAOL 7250 1592 4.5
MAWAL 10,350 1643 6.3
MAWOL 6804 1569 4.5
MCAL 9710 1985 4.9
MCOL 3685 636 5.8
a
M
w
: weigh a e age molecula weigh .
b
M
n
: numbe a e age molecula weigh .
c
M
w
/M
n
: polydispe si y index.
Fig. 2. Swelling pe o mance o modi ied lignin-based hyd ogels du ing he
i s 48 h.
A. Mo ales e al.
Sus ainable Ma e ials and Technologies 33 (2022) e00474
5
samples we e he second ones wi h imp o ed swelling capaci y (410%),
which also coincided wi h he second highes lignin was e. Simila ly,
MAWO samples exhibi ed he ligh es enhancemen on hei swelling
deg ee and had displayed he lowes lignin was e among he samples
con aining modi ied o ganosol lignins. Thus, i could be concluded ha
hyd oxyme hyla ion could be a good me hod o enhance he swelling
abili y o o ganosol lignin-based hyd ogels. As epo ed p e iously, he
molecula weigh and he phenolic/alipha ic hyd oxyl g oup con en in
lignin a e impo an ac o s when syn hesizing hyd ogels [19,38].
Looking a he esul s in Tables 1 and 3, i was concluded ha he highes
molecula weigh ac ions we e a ached o he ma ix. In he case o
alkaline samples, as he molecula weigh s and TPC con en s we e
highe , hese ac ions migh ha e p omo ed he in e ac ions wi h PVA.
The e o e, a compac s uc u e wi h es e ic hind ance could ha e been
ob ained, leading o a lowe swelling capaci y and a lowe lignin was e.
On he con a y, o o ganosol lignins he molecula weigh s we e
much lowe and mo e homogeneous, leading o a dec ease on hei in-
e ac ions wi h he ma ix and enabling highe swelling capaci ies
[39,40].
Looking a he p esen esul s and compa ing hem wi h p e ious
ones, i should be men ioned ha al hough hyd oxyme hyla ion
demons a ed o be e ec i e o imp o ing he swelling capaci y o
lignin-hyd ogels, o he a ia ions du ing he syn hesis p ocess (leng h-
ening he las hawing s ep, o ins ance) leaded o highe imp o emen s
on his p ope y, wi hou needing o modi y he na i e lignins.
3.2.3. Mo phology
Scanning Elec on Mic oscopy (SEM) pe mi ed s udying he
mo phology o he samples. The ob ained mic og aphs a 500×and
1500×magni ica ions a e shown in Fig. 3.
The images, in gene al, did no e eal highly po ous s uc u es;
indeed hey showed qui e dense and con inuous mo phologies wi h
sca cely de ec able oids. This ac was mo e e iden in he samples
con aining alkaline lignins, which may be a ibu ed o a g ea e
c osslinking densi y, which would also cla i y he decline on hei
swelling abili y. Fo he samples con aining o ganosol lignins, espe-
cially o MAAO samples, he c ea ed oids we e mo e ob ious, which
we e p obably esponsible o he augmen on hei wa e abso p ion
capaci y. Howe e , as he swelling s udy was pe o med a he same
condi ions as p e iously, he ob ained mic os uc u es migh ha e jus
hinde ed he wa e di usion h ough he ma ix, and a e lea ing hem
longe imes imme sed, hey may p esen highe swelling capaci ies.
Fig. 3. SEM mic og aphs o modi ied lignin-based hyd ogels a 500×and 1500×magni ica ions.
A. Mo ales e al.
Sus ainable Ma e ials and Technologies 33 (2022) e00474
6
Hence, i is clea ha he lignin modi ica ions had di ec impac on he
mic os uc u es o he syn hesized hyd ogels, which also clea ly a ec ed
hei swelling capaci y.
3.2.4. The mal beha iou
Fo some applica ions, he glass ansi ion (T
g
) and mel ing em-
pe a u es (T
m
) o polyme ic ma e ials a e de e mining ea u es. Hence,
hese pa ame e s oge he wi h he mel ing en halpy (ΔH
m
) and he
c ys allini y indexes (
χ
c
) o each sample we e de ined by Di e en ial
Scanning Calo ime y (DSC) and he esul s a e displayed in Table 4. The
T
g
was ound on he in lec ion poin o he speci ic hea inc emen
du ing he second hea ing scan, a e emo ing he he mal memo y o
he samples, bu he es o he pa ame e s we e iden i ied om he i s
hea ing scan.
All he de e mined T
g
alues we e in he ange o 77–103 ◦C. These
alues we e highe han hose epo ed p e iously [19], sugges ing ha
lignin modi ica ions leaded o mo e compac s uc u es in which he
mo emen o he amo phous polyme ic chains was hinde ed, which was
also ela ed o he ob ained SEM mic og aphs. In addi ion, i was
obse ed ha he hyd ogels con aining modi ied o ganosol lignins
p esen ed lowe T
g
alues han he ones con aining alkaline ones.
Mo eo e , hese esul s we e aligned wi h he ones epo ed o he
swelling capaci y o he samples, being he a o emen ioned highe o
he samples wi h lowe T
g
. Despi e all he mel ing empe a u es being
simila (≈235 ◦C), hey we e qui e close o pu e he T
m
o PVA
hyd ogels [20,24], and hei mel ing en halpies we e also high, sug-
ges ing he exis ence o many c ys alline egions [41]. The c ys alliza-
ion indexes we e calcula ed based on a well-known equa ion [20,42],
and he esul s sugges ed ha a g ea pa o he hyd ogels was c ys-
alline. In addi ion, he samples wi h highe ille con en s seemed o
ha e highe c ys allini y deg ees, which would be in acco dance wi h
p e ious esul s [20] and could be due o an enhancemen o in e acial
in e ac ions ia hyd ogen bonding be ween he mul iple hyd oxyl
g oups on he ma ix polyme and lignin [42]. I was also obse ed ha
he samples con aining alkaline lignin p esen ed highe c ys allini y
indexes, which would explain hei lowe swelling abili ies and highe
T
g
alues.
3.2.5. Comp ession es s
The comp ession es s o he samples we e pe o med in o de o
de e mine he impac ha lignin modi ica ion had on hei comp ession
modulus a 80% o s ain. Once again, all he es ed hyd ogels we e able
o keep o al in eg i y and good eco e abili y hanks o hei elas ic
beha iou .
F om he esul s in Fig. 4 i was concluded ha hyd ogels con aining
alkaline lignins had g ea e comp ession modulus han hose con aining
o ganosol lignins. The la e is consis en wi h he esul s ob ained o
hei c ys allini y, since he mo e c ys alline and compac he sample is
he highe i s comp ession modulus should be [43]. Ne e heless, his
imp o emen o he comp ession modulus could also be a ibu ed o he
highe solid con en (m
ille
) on alkaline hyd ogels, as explained by
Quei oz e al. (2021) [44]. Mo eo e , all he modules alues o he
samples wi h alkaline lignin we e in he ange o 10–12 MPa, whe eas
he ones o hyd ogels wi h o ganosol lignin we e be ween 4.5 and 6
MPa. Compa ing o he p e ious wo k [19], an enhancemen o i s
comp ession modulus was especially obse ed o MAWA samples,
al hough MAAO also go sligh ly highe . All hese alues we e aligned
wi h he esul s epo ed o lignin-hyd ogels by some au ho s [45] bu
hey we e also highe han hose ob ained by o he s [44,46,47].
3.2.6. D ug loading and deli e y es s
Que ce in (QE) is a bio la onoid p esen in ui s and ege ables wi h
in e es ing an i-in lamma o y, an ioxidan , an i-ca cinogenic and an i-
obesi y p ope ies [25,26,48]. Due o he a o emen ioned cha ac e is-
ics and he cu en end o p e e ing na u al compounds a he han
syn hesized d ugs, que ce in has ecen ly gained g ea a en ion. This
compound can be ound in onion peels, which a e an abundan was e all
o e he wo ld. Thus, he ob aining o a la onoid- ich ex ac om his
was e would gi e an added- alue o i , con ibu ing o ci cula economy.
Among he ex ac ion s a egies ha ha e been s udied o QE, mi-
c owa e assis ed ex ac ion (MAE) has p o en o be a p omising sus-
ainable and g een p ocess [26]. The e o e, QE was ex ac ed hough
MAE.
3.2.6.1. Cha ac e isa ion o QE ex ac . The solid con en on he ex ac
was de e mined h ough g a ime ic analyses, d ying 1 ml o he ex ac
a 105 ◦C o 24 h. This measu emen e ealed a solid con en o 18.3 ±
0.2 mg o solid/g o liquid ex ac . TPC and TFC analyses showed high
phenolic and la onoid con en s o he ex ac (576.4 ±75.4 mg GAE/g
d y ex ac and 470.1 ±22.5 mg CQE/g d y ex ac ). These alues o
TPC we e highe han hose epo ed by o he au ho s and he ones o
TFC we e simila [25]. In addi ion, he cha ac e is ic peaks o CQE e-
po ed by Geo ge e al. (2019) we e also p esen on he FTIR spec a o
QE, con i ming he exis ence o his compound in he ex ac (see
Fig. 5a) [25].
3.2.6.2. D ug loading es s. The d ug loading es s we e pe o med by
imme sing d y hyd ogels in o dilu ed QE solu ions (68.4 mg que ce in/
L). The objec i e o hese es s was o analyse he capaci y o hese
samples o abso bing and eleasing his d ug, no o op imize he
loading- elease kine ic.
Acco ding o he abso bance di e ence be ween he ini ial and inal
solu ions, all he samples we e capable o apping be ween 26 and 34%
o he d ug in he ini ial solu ion (see Table 5), being his pe cen age
highe o he hyd ogels con aining o ganosol lignins, which had also
p esen ed he highes swelling capaci ies.
Table 4
Summa ized esul s o he analyzed pa ame e s by DSC and calcula ions.
Sample 1s hea ing scan 2nd hea ing scan
T
m
(◦C) ΔH
m
(J/g) m
ille
(%)
χ
c
(%) T
g
(◦C)
MAAA 235 64 25 53 103
MAAO 235 59 15 43 92
MAWA 236 62 27 52 81
MAWO 234 61 25 50 77
MCA 235 60 11 42 91
MCO 234 59 4 38 88
Fig. 4. Comp ession beha iou s o modi ied lignin-based hyd ogels.
A. Mo ales e al.
Sus ainable Ma e ials and Technologies 33 (2022) e00474
7
3.2.6.3. D ug elease es s. A e he loaded hyd ogels had d ied, hey
we e imme sed in PBS a 37 ◦C o d ug elease, simula ing in i o
condi ions. The abso bance o he elease medium was pe o med a
se e al imes du ing he i s 6.5 h. As he hyd ogels con ained lignin,
and his lignin p esen ed an abso bance peak a 330 nm, a high con-
cen a ions his peak sagged he esul s o he peak co esponding o QE
a 375 nm. Thus, he elease kine ics was pe o med du ing he i s 6.5
h, while he eleased lignin was negligible.
F om he elease p o iles shown in Fig. 5b i was concluded ha
al hough all he samples we e able o be loaded wi h simila d ug
amoun s, he elease capaci y was comple ely di e en o each sample.
In ac , wi h espec o he loaded amoun s o d ug, he eleased d ug
pe cen ages anged om 12 o 30%. The samples displaying he highes
elease d ug pe cen age we e MAWA, ollowed by MAAO and MAAA.
The lowes elease was obse ed o MCO samples, sugges ing ha
despi e ha ing highe d ug loading abili ies, he in e ac ions wi h he
d ug made i s elease di icul . Ne e heless, i should be no ed ha
hese p o iles we e jus o he i s 6.5 h, and canno be ex apola ed o
longe imes.
So as o de e mine he elease kine ics, se e al models we e applied
(i.e. ze o o de , i s o de , Ko smeye –Peppas and Higuchi) [25,28,29].
The es ima ed kine ic pa ame e s o each o hese models a e displayed
in Table 5 and he g aphic ep esen a ions o he ou kine ic models in
he Supplemen a y da a. F om he o iginal elease p o ile, i was in e -
ed ha he elease kine ics would no i co ec ly o a ze o o de model,
which was con i med by he de e mina ion coe icien s (R
2
). Among he
es o he models, Ko smeye –Peppas model was he one i ing he bes ,
excep o MCA sample, whose i ing did no imp o e ei he wi h
Higuchi model.
As indica ed by Saidi e al. (2020) [29], he elease exponen s (n) and
he loga i hms o he a e cons an s (ln k
kp
) we e de e mined om he
slopes and in e cep s o he plo s (ln (QE %) e sus ln ) o he expe i-
men al da a. As shown in Table 5, all he es ima ed alues o n we e
below 0.5. Al hough Fickian di usion is usually conside ed when n =
0.5 [25,28], in his case i could also be said ha he QE elease ollowed
a Fickian di usion [25]. Thus, i could be said ha he syn hesized
hyd ogels could be used as con olled d ug deli e y sys ems.
4. Conclusions
On he basis o he esul s ob ained o he p ope ies o p e iously
syn hesized alkaline and o ganosol lignin-based hyd ogels, wo
chemical modi ica ions we e pe o med o hese lignins in o de o
enhance hei eac i i y. The pe oxida ion o alkaline lignin was
con i med by FTIR, bu he molecula weigh s udies sugges ed ha
condensa ion eac ions had also happened du ing he eac ion, leading
o ac ions wi h highe a e age molecula weigh s. The hyd ox-
yme hyla ion o o ganosol lignin was also con i med by FTIR,
31
P NMR
and GPC. Mo eo e , his eac ion leaded o mo e he mally s able lig-
nins, which suppo ed he success o he eac ion. F om he modi ied
o ganosol lignins, hyd ogels wi h imp o ed swelling capaci ies (up o
450%) we e syn hesized, al hough hei lignin was es we e highe han
he ones epo ed p e iously. On he con a y, modi ied alkaline lignins
leaded o a dec ease on he swelling capaci y o he hyd ogels unde he
employed assay condi ions. These esul s we e explained by he
con inuous and compac s uc u es seen on SEM mic og aphs, being
mo e ob ious o alkaline lignin con aining samples. These samples also
p esen ed highe comp ession moduli han he o ganosol ones, which
would be desi able depending on he applica ion ield, bu hey s ill
p esen ed p omising esul s in d ug loading and elease s udies.
Al hough all he es ed samples allowed a Fickian di usion o QE,
MAWA sample was he one wi h he mos adequa e elease p o ile.
Fig. 5. (a) FTIR spec a o sel -ex ac ed (QE) and comme cial (CQE) que ce in
ex ac and (b) QE elease p o iles o modi ied lignin-based hyd ogels.
Table 5
Kine ic pa ame e s es ima ed om models o QE elease om hyd ogels.
Loading Ze o o de Fi s o de Ko smeye –Peppas Higuchi
Sample (%) R
2
R
2
R
2
n
a
ln k
kpa
R
2
MAAA 29.0 0.8194 0.8438 0.9852 0.37 ±0.13 2.38 ±0.18 0.9764
MAAO 31.8 0.8946 0.9165 0.9947 0.48 ±0.11 2.30 ±0.14 0.9962
MAWA 30.4 0.8134 0.849 0.9809 0.37 ±0.16 2.74 ±0.21 0.9741
MAWO 32.0 0.8781 0.8968 0.9868 0.47 ±0.16 2.20 ±0.22 0.9904
MCA 26.0 0.7248 0.7473 0.9284 0.29 ±0.25 2.53 ±0.33 0.9294
MCO 34.5 0.7725 0.7872 0.9978 0.30 ±0.04 1.96 ±0.06 0.9562
a
Es ima ed in e als a 95% o con idence le el.
A. Mo ales e al.
Sus ainable Ma e ials and Technologies 33 (2022) e00474
8
Howe e , hey could all be employed as po en ial con olled d ug de-
li e y sys ems.
Decla a ion o Compe ing In e es
The au ho s decla e ha hey ha e no known compe ing inancial
in e es s o pe sonal ela ionships ha could ha e appea ed o in luence
he wo k epo ed in his pape .
Acknowledgemen s
The au ho s would like o acknowledge he inancial suppo o he
Depa men o Educa ion o he Basque Go e nmen (IT1498-22). A.
Mo ales would like o hank he Uni e si y o he Basque Coun y
(T aining o Resea che S a , PIF17/207). P. Gull´
on would like o
acknowledge he G an s o he ec ui men o echnical suppo s a
(PTA2019-017850-I) unde he Spanish S a e Plan o Scien i ic and
Technical Resea ch and Inno a ion 2017-2020. The au ho s hank
SGIke (UPV/EHU/ERDF, EU) o hei echnical and human suppo .
Appendix A. Supplemen a y da a
Supplemen a y da a o his a icle can be ound online a h ps://doi.
o g/10.1016/j.susma .2022.e00474.
Re e ences
[1] C.G. Yoo, X. Meng, Y. Pu, A.J. Ragauskas, The c i ical ole o lignin in
lignocellulosic biomass con e sion and ecen p e ea men s a egies: a
comp ehensi e e iew, Bio esou . Technol. 301 (2020), h ps://doi.o g/10.1016/j.
bio ech.2020.122784.
[2] G. D agone, A.A.J. Ke ssemake s, J.L.S.P. D iessen, C.K. Yamakawa, L.P. B umano,
S.I. Mussa o, Inno a ion and s a egic o ien a ions o he de elopmen o
ad anced bio e ine ies, Bio esou . Technol. 302 (2020), 122847, h ps://doi.o g/
10.1016/j.bio ech.2020.122847.
[3] A. Kuma , J. Anush ee, T. Kuma , Bhaska , u iliza ion o lignin: a sus ainable and
eco- iendly app oach, J. Ene gy Ins . 93 (2020) 235–271, h ps://doi.o g/
10.1016/j.joei.2019.03.005.
[4] H. Wang, Y. Pu, A. Ragauskas, B. Yang, F om lignin o aluable
p oduc s–s a egies, challenges, and p ospec s, Bio esou . Technol. 271 (2019)
449–461, h ps://doi.o g/10.1016/j.bio ech.2018.09.072.
[5] A. T ibo , G. Ame , M. Abdou Alio, H. de Baynas , C. Dela e, A. Pons, J.
D. Ma hias, J.M. Callois, C. Vial, P. Michaud, C.G. Dussap, Wood-lignin: supply,
ex ac ion p ocesses and use as bio-based ma e ial, Eu . Polym. J. 112 (2019)
228–240, h ps://doi.o g/10.1016/j.eu polymj.2019.01.007.
[6] S. I a ani, R.S. Va ma, G eene syn hesis o lignin nanopa icles and hei
applica ions, G een Chem. 22 (2020) 612–636, h ps://doi.o g/10.1039/
c9gc02835h.
[7] L.A. Ze allos To es, A. Lo enci Woiciechowski, V.O. de And ade Tanobe, S.
G. Ka p, L.C. Guima ˜
aes Lo enci, C. Faulds, C.R. Soccol, Lignin as a po en ial sou ce
o high-added alue compounds: a e iew, J. Clean. P od. 263 (2020), h ps://doi.
o g/10.1016/j.jclep o.2020.121499.
[8] X. Meng, C. C es ini, H. Ben, N. Hao, Y. Pu, A.J. Ragauskas, D.S. A gy opoulos,
De e mina ion o hyd oxyl g oups in bio e ine y esou ces ia quan i a i e 31P
NMR spec oscopy, Na . P o oc. 14 (2019) 2627–2647, h ps://doi.o g/10.1038/
s41596-019-0191-1.
[9] Y. Chen, H. Zhang, Z. Zhu, S. Fu, High- alue u iliza ion o hyd oxyme hyla ed
lignin in polyu e hane adhesi es, In . J. Biol. Mac omol. 152 (2020) 775–785,
h ps://doi.o g/10.1016/j.ijbiomac.2020.02.321.
[10] M. Goliszek, D. Kołody´
nska, I.V. Pylypchuk, O. Se as yano a, B. Podko´
scielna,
Syn hesis o lignin-con aining polyme hyd ogels wi h unable p ope ies and hei
applica ion in so p ion o nickel(II) ions, Ind. C op. P od. 164 (2021) 20–31,
h ps://doi.o g/10.1016/j.indc op.2021.113354.
[11] P. Figuei edo, K. Lin inen, J.T. Hi onen, M.A. Kos iainen, H.A. San os, P ope ies
and chemical modi ica ions o lignin: owa ds lignin-based nanoma e ials o
biomedical applica ions, P og. Ma e . Sci. 93 (2018) 233–269, h ps://doi.o g/
10.1016/j.pma sci.2017.12.001.
[12] L. Musilo ´
a, A. M ´
aˇ
cek, A. Ko alcik, P. Smolka, A. Minaˇ
ík, P. Humpolíˇ
cek,
R. Vícha, P. Poníˇ
zil, Hyalu onan hyd ogels modi ied by glycina ed K a lignin:
mo phology, swelling, iscoelas ic p ope ies and biocompa ibili y, Ca bohyd .
Polym. 181 (2018) 394–403, h ps://doi.o g/10.1016/j.ca bpol.2017.10.048.
[13] D. Rico-Ga cía, L. Ruiz-Rubio, L. P´
e ez-´
Al a ez, S.L. He n´
andez-Olmos, G.
L. Gue e o-Ramí ez, J.L. Vilas-Vilela, Lignin-based hyd ogels: syn hesis and
applica ions, Polyme s (Basel). 12 (2020) 1–23.
[14] E. La a˜
ne a, M. Imízcoz, J.X. Toh, N.J. I win, A. Ripolin, A. Pe mino a,
J. Domínguez-Robles, A. Rod íguez, R.F. Donnelly, Syn hesis and cha ac e iza ion
o lignin hyd ogels o po en ial applica ions as d ug elu ing an imic obial coa ings
o medical ma e ials, ACS Sus ain. Chem. Eng. 6 (2018) 9037–9046, h ps://doi.
o g/10.1021/acssuschemeng.8b01371.
[15] Y. Zhang, B. Yuan, Y. Zhang, Q. Cao, C. Yang, Y. Li, J. Zhou, Biomime ic lignin/
poly(ionic liquids) composi e hyd ogel d essing wi h excellen mechanical
s eng h, sel -healing p ope ies, and eusabili y, Chem. Eng. J. 400 (2020),
125984, h ps://doi.o g/10.1016/j.cej.2020.125984.
[16] A. Ba os, S. Qu aishi, M. Ma ins, P. Gu iko , R. Sub ahmanyam, I. Smi no a, A.R.
C. Dua e, R.L. Reis, Hyb id algina e-based c yogels o li e science applica ions,
Chemie-Ingenieu -Technik. 88 (2016) 1770–1778, h ps://doi.o g/10.1002/
ci e.201600096.
[17] Y. Meng, C. Li, X. Liu, J. Lu, Y. Cheng, L.-P. Xiao, H. Wang, P epa a ion o magne ic
hyd ogel mic osphe es o lignin de i a e o applica ion in wa e , Sci. To al
En i on. (2019), h ps://doi.o g/10.1016/j.sci o en .2019.06.278.
[18] A. O yan, A. Kamali, A. Moshi i, H. Baha and, H. Daemi, Chemical c osslinking o
biopolyme ic sca olds: cu en knowledge and u u e di ec ions o c osslinked
enginee ed bone sca olds, In . J. Biol. Mac omol. 107 (2018) 678–688, h ps://
doi.o g/10.1016/j.ijbiomac.2017.08.184.
[19] A. Mo ales, J. Labidi, P. Gull´
on, Impac o he lignin ype and sou ce on he
cha ac e is ics o physical lignin hyd ogels, Sus ain. Ma e . Technol. 31 (2021),
e00369, h ps://doi.o g/10.1016/j.susma .2021.e00369.
[20] A. Mo ales, J. Labidi, P. Gull´
on, E ec o he o mula ion pa ame e s on he
abso p ion capaci y o sma lignin-hyd ogels, Eu . Polym. J. 129 (2020), 109631,
h ps://doi.o g/10.1016/j.eu polymj.2020.109631.
[21] M. In an e, F. Ysambe , M. He n´
andez, B. Ma ínez, N. Delgado, B. B a o,
A. C´
ace es, G. Ch´
a ez, J. Bull´
on, Mic owa e assis ed oxida i e deg ada ion o
lignin wi h hyd ogen pe oxide and i s ensoac i e p ope ies, Re . Tec. La Fac. Ing.
Uni . Del Zulia. 30 (2007) 108–117.
[22] I. D´
a ila, P. Gull´
on, M.A. And ´
es, J. Labidi, Cop oduc ion o lignin and glucose
om ine shoo s by eco- iendly s a egies: owa d he de elopmen o an
in eg a ed bio e ine y, Bio esou . Technol. 244 (2017) 328–337, h ps://doi.o g/
10.1016/j.bio ech.2017.07.104.
[23] A. Mo ales, B. Gull´
on, I. D´
a ila, G. Eibes, J. Labidi, P. Gull´
on, Op imiza ion o
alkaline p e ea men o he co-p oduc ion o biopolyme lignin and bioe hanol
om ches nu shells ollowing a bio e ine y app oach, Ind. C op. P od. 124 (2018),
h ps://doi.o g/10.1016/j.indc op.2018.08.032.
[24] A. Mo ales, J. Labidi, P. Gull´
on, Assessmen o g een app oaches o he syn hesis
o physically c osslinked lignin hyd ogels, J. Ind. Eng. Chem. 81 (2020) 475–487,
h ps://doi.o g/10.1016/j.jiec.2019.09.037.
[25] D. Geo ge, P.U. Maheswa i, K.M.M.S. Begum, Syne gic o mula ion o onion peel
que ce in loaded chi osan-cellulose hyd ogel wi h g een zinc oxide nanopa icles
owa ds con olled elease, biocompa ibili y, an imic obial and an icance ac i i y,
In . J. Biol. Mac omol. 132 (2019) 784–794, h ps://doi.o g/10.1016/j.
ijbiomac.2019.04.008.
[26] E.Y. Jin, S. Lim, S.Oh. Kim, Y.S. Pa k, J.K. Jang, M.S. Chung, H. Pa k, K.S. Shim, Y.
J. Choi, Op imiza ion o a ious ex ac ion me hods o que ce in om onion skin
using esponse su ace me hodology, Food Sci. Bio echnol. 20 (2011) 1727–1733,
h ps://doi.o g/10.1007/s10068-011-0238-8.
[27] L. Sille o, R. P ado, M.A. And ´
es, J. Labidi, Cha ac e isa ion o ba k o six species
om mixed A lan ic o es , Ind. C op. P od. 137 (2019) 276–284, h ps://doi.o g/
10.1016/j.indc op.2019.05.033.
[28] D. Geo ge, K.M.M.S. Begum, P.U. Maheswa i, Suga cane bagasse (SCB) based
p is ine cellulose hyd ogel o deli e y o g ape Pomace polyphenol d ug, Was e
and Biomass Valo iz. 11 (2020) 851–860, h ps://doi.o g/10.1007/s12649-018-
0487-3.
[29] M. Saidi, A. Dabbaghi, S. Rahmani, Swelling and d ug deli e y kine ics o click-
syn hesized hyd ogels based on a ious combina ions o PEG and s a -shaped PCL:
in luence o ne wo k pa ame e s on swelling and elease beha io , Polym. Bull. 77
(2020) 3989–4010, h ps://doi.o g/10.1007/s00289-019-02948-z.
[30] X. Ouyang, Z. Lin, Y. Deng, D. Yang, X. Qiu, Oxida i e deg ada ion o soda lignin
assis ed by mic owa e i adia ion, Chin. J. Chem. Eng. 18 (2010) 695–702,
h ps://doi.o g/10.1016/S1004-9541(10)60277-7.
[31] N.A.M. Aini, N. O hman, M.H. Hussin, K. Sahaka o, Hyd oxyme hyla ion-modi ied
lignin and i s e ec i eness as a ille in ubbe composi es, P ocesses. 7 (2019) 315,
h ps://doi.o g/10.3390/p 7050315.
[32] I.A. Gilca, R.E. Ghi escu, A.C. Pui el, V.I. Popa, P epa a ion o lignin nanopa icles
by chemical modi ica ion, I an. Polym. J. (Engl. Ed.) 23 (2014) 355–363, h ps://
doi.o g/10.1007/s13726-014-0232-0.
[33] A.M. Cǎp a u, E. Ungu eanu, L.C. T incǎ, T¸ . Mǎlu an, V.I. Popa, Chemical and
spec al cha ac e is ics o annual plan lignins modi ied by hyd oxyme hyla ion
eac ion, Cellul. Chem. Technol. 46 (2012) 589–597.
[34] D. Zang, F. Liu, M. Zhang, Z. Gao, C. Wang, No el supe hyd ophobic and
supe oleophilic sawdus as a selec i e oil so ben o oil spill cleanup, Chem. Eng.
Res. Des. 102 (2015) 34–41, h ps://doi.o g/10.1016/j.che d.2015.06.014.
[35] C. Xu, F. Liu, M.A. Alam, H. Chen, Y. Zhang, C. Liang, H. Xu, S. Huang, J. Xu,
Z. Wang, Compa a i e s udy on he p ope ies o lignin isola ed om di e en
p e ea ed suga cane bagasse and i s inhibi o y e ec s on enzyma ic hyd olysis,
In . J. Biol. Mac omol. 146 (2020) 132–140, h ps://doi.o g/10.1016/j.
ijbiomac.2019.12.270.
[36] D. Ciolacu, G. Cazacu, New g een hyd ogels based on lignin, J. Nanosci.
Nano echnol. 18 (2018) 2811–2822, h ps://doi.o g/10.1166/jnn.2018.14290.
[37] A. Gouda zi, L.-T. Lin, F.K. Ko, X- ay di ac ion analysis o K a Lignins and
lignin-de i ed ca bon nano ibe s, J. Nano echnol. Eng. Med. 5 (2014), 021006,
h ps://doi.o g/10.1115/1.4028300.
[38] L. Wu, S. Huang, J. Zheng, Z. Qiu, X. Lin, Y. Qin, Syn hesis and cha ac e iza ion o
biomass lignin-based PVA supe -abso ben hyd ogel, In . J. Biol. Mac omol. 140
(2019) 538–545, h ps://doi.o g/10.1016/j.ijbiomac.2019.08.142.
A. Mo ales e al.
Sus ainable Ma e ials and Technologies 33 (2022) e00474
9
[39] L.K.S. Gujjala, J. Kim, W. Won, Technical lignin o hyd ogels: an eclec ic e iew on
sui abili y, syn hesis, applica ions, challenges and u u e p ospec s, J. Clean. P od.
363 (2022), 132585, h ps://doi.o g/10.1016/j.jclep o.2022.132585.
[40] S. Yan, L. Chai, W. Li, L.P. Xiao, X. Chen, R.C. Sun, Tunning he p ope ies o pH-
esponsi e lignin-based hyd ogels by egula ing hyd oxyl con en , Coll. Su . A
Physicochem. Eng. Asp. 643 (2022), 128815, h ps://doi.o g/10.1016/j.
colsu a.2022.128815.
[41] W. Yang, E. Fo una i, F. Be oglio, J.S. Owcza ek, G. B uni, M. Kozanecki, J.
M. Kenny, L. To e, L. Visai, D. Puglia, Poly inyl alcohol/chi osan hyd ogels wi h
enhanced an ioxidan and an ibac e ial p ope ies induced by lignin nanopa icles,
Ca bohyd . Polym. 181 (2018) 275–284, h ps://doi.o g/10.1016/j.
ca bpol.2017.10.084.
[42] X. He, F. Luzi, X. Hao, W. Yang, L. To e, Z. Xiao, Y. Xie, D. Puglia, The mal,
an ioxidan and swelling beha iou o anspa en poly inyl (alcohol) ilms in
p esence o hyd ophobic ci ic acid-modi ied lignin nanopa icles, In . J. Biol.
Mac omol. 127 (2019) 665–676, h ps://doi.o g/10.1016/j.ijbiomac.2019.01.202.
[43] J.L. Holloway, A.M. Lowman, G.R. Palmese, The ole o c ys alliza ion and phase
sepa a ion in he o ma ion o physically c oss-linked PVA hyd ogels, So Ma e 9
(2013) 826–833, h ps://doi.o g/10.1039/c2sm26763b.
[44] B.G. Quei oz, H. Ciol, N.M. Inada, E. F ollini, Hyd ogel om all in all
lignocellulosic sisal ibe s mac omolecula componen s, In . J. Biol. Mac omol. 181
(2021) 978–989, h ps://doi.o g/10.1016/j.ijbiomac.2021.04.088.
[45] J. Cai, X. Zhang, W. Liu, J. Huang, X. Qiu, Syn hesis o highly conduc i e hyd ogel
wi h high s eng h and supe oughness, Polyme (Guild ). 202 (2020), 122643,
h ps://doi.o g/10.1016/j.polyme .2020.122643.
[46] Y. Chen, K. Zheng, L. Niu, Y. Zhang, Y. Liu, C. Wang, F. Chu, Highly mechanical
p ope ies nanocomposi e hyd ogels wi h bio enewable lignin nanopa icles, In . J.
Biol. Mac omol. 128 (2019) 414–420, h ps://doi.o g/10.1016/j.
ijbiomac.2019.01.099.
[47] R.M. Kalinoski, J. Shi, Hyd ogels de i ed om lignocellulosic compounds:
e alua ion o he composi ional, s uc u al, mechanical and an imic obial
p ope ies, Ind. C op. P od. 128 (2019) 323–330, h ps://doi.o g/10.1016/j.
indc op.2018.11.002.
[48] S.G. Lee, J.S. Pa ks, H.W. Kang, Que ce in, a unc ional compound o onion peel,
emodels whi e adipocy es o b own-like adipocy es, J. Nu . Biochem. 42 (2017)
62–71, h ps://doi.o g/10.1016/j.jnu bio.2016.12.018.
A. Mo ales e al.
