In e na ional Jou nal o Biological Mac omolecules 247 (2023) 125855
A ailable online 17 July 2023
0141-8130/© 2023 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/).
Valo isa ion o c ude glyce ol in he p oduc ion o lique ied lignin
bio-polyols o polyu e hane o mula ions
Fabio He n´
andez-Ramos
a
,
*
, Ma ía Gonz´
alez Al iols
a
, M. Mi a i An xus egi
b
, Jalel Labidi
a
,
Xabie E docia
c
a
Bio e ine y P ocesses Resea ch G oup (BioRP), 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 ian, Spain
b
Bio e ine y P ocesses Resea ch G oup (BioRP), Chemical and En i onmen al Enginee ing Depa men , Uni e si y o he Basque Coun y (UPV/EHU), A da. O aola 29,
20600 Eiba , Spain
c
Bio e ine y P ocesses Resea ch G oup (BioRP), Depa men o Applied Ma hema ics, Uni e si y o he Basque Coun y (UPV/EHU), Ra ael Mo eno “Pichichi” 3, Bilbao
48013, Spain
ARTICLE INFO
Keywo ds:
Bio-polyol
O ganosol lignin
C ude glyce ol
Lique ac ion
ABSTRACT
Bio-polyols, p oduced by lique ying lignin wi h polyhyd ic alcohols, o e a p omising al e na i e o con en ional
polyols o polyu e hane p oduc ion. To enhance he sus ainabili y on he p oduc ion o hese bio-polyols, his
s udy p oposes he use o c ude glyce ol and mic owa e-assis ed lique ac ion as subs i u es o con en ional
me hods and comme cial glyce ol. This app oach educes he ene gy equi emen s o he eac ion while also
adding alue o his by-p oduc . The syn hesis o bio-polyols wi h sui able p ope ies o p oduce elas ic and igid
polyu e hane was ca ied ou using p e iously op imised eac ion condi ions. O ganosol lignins ob ained om
Eucalyp us globulus and Pinus adia a we e employed, using polye hylene glycol and c ude glyce ol as sol en s and
sulphu ic acid as a ca alys . Se e al pa ame e s o he bio-polyols we e analysed, including hyd oxyl numbe
(I
OH
), acid numbe (A
n
), and unc ionali y ( ), sugges ing ha he bio-polyols we e sui able o polyu e hane
syn hesis. Bio-polyols o mula ed o p oduce igid polyu e hanes exhibi ed I
OH
alues o 554 and 383 (mg KOH/
g), A
n
alues o 1.91 and 4.21 (mg KOH/g), and unc ionali ies o 4.16 and 3.14 o Eucalyp us globulus and Pinus
adia a lignin. In he case o bio-polyols o elas ic polyu e hanes, he alues we e 228 and 173 (mg KOH/g)
(I
OH
), 20.94 and 25.09 (mg KOH/g) (A
n
), and unc ionali ies o 3.51 and 2.08.
1. In oduc ion
The impac o human ac i i y has become so ele an ha he Nobel
P ize winne , Paul J. C u zen, p oposed a new e m o place i in a
geological con ex [1]. This new e m, he An h opocene, e en hough i
has no been o icially es ablished by academia, is now in ogue.
Howe e , he me e ac ha he scien i ic communi y has acqui ed and
main ained i so a , makes i clea how impo an he human oo p in
on he en i onmen is. The use o pe oleum, no only as uel bu also as
a eeds ock o he manu ac u e o di e en ma e ials, ep esen s one o
he main causes o he deg ada ion o he en i onmen . Fo his eason,
he scien i ic communi y is looking o new sou ces o aw ma e ials ha
could o ally o pa ially subs i u e he use o pe oleum.
Among pe oleum de i ed ma e ials, PUs, i s syn hesised by D .
O o Baye in 1937, ha e become one o he mos e sa ile man-made
syn he ic ma e ials [2]. Such e sa ili y lies in hei excellen mechan-
ical, chemical, and physical p ope ies, such as ab asion esis ance,
elas ici y, biocompa ibili y, du abili y, o oughness [3]. PUs can be
used o he manu ac u e o a a ie y o p oduc s, such as oams, elas-
ome s, pain s, coa ings, adhesi es o medical applica ions [4]. PUs a e
c oss-linked ma e ials o med by a poly-addi ion eac ion be ween iso-
cyana es (wi h mo e han one isocyana e g oup pe molecule) and
molecules wi h wo o mo e OH eac i e g oups called polyols [5]. In
2019, he polyol ma ke gene a ed a ound USD 26.2 billion and i is
expec ed o each USD 34.4 billion by 2024 [6]. Al hough he polyols
employed nowadays o syn hesise PUs a e gene ally pe oleum-de i ed
compounds, i is possible o subs i u e hem wi h lignocellulosic
biomass-de i ed ma e ials o p oduce mo e eco- iendly PUs ha sa is y
he equi emen s o new and mo e igo ous legisla ion [7].
Lignocellulosic biomass is o med mainly by cellulose,
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (F. He n´
andez-Ramos).
Con en s lis s a ailable a ScienceDi ec
In e na ional Jou nal o Biological Mac omolecules
jou nal homepage: www.else ie .com/loca e/ijbiomac
h ps://doi.o g/10.1016/j.ijbiomac.2023.125855
Recei ed 24 Ap il 2023; Recei ed in e ised o m 26 June 2023; Accep ed 14 July 2023
In e na ional Jou nal o Biological Mac omolecules 247 (2023) 125855
2
hemicellulose, and lignin o ming a composi e ma ix [8], and i is
conside ed a sus ainable aw ma e ial sou ce o p oduce high alued-
added commodi ies [9]. Cellulose, he ea h’s mos abundan enew-
able biopolyme , can be used in di e en indus ial ields. P obably i s
mos well-known applica ion, apa om pulp p oduc ion, is he con-
e sion o bioe hanol o be used as bio uel. Ne e heless, i s ema kable
p ope ies, such as high ab asion esis ance, biocompa ibili y, biode-
g adabili y and chemical s abili y, make i sui able o be used o he
manu ac u e o composi es [10], in medical applica ions, ood pack-
aging and pho oelec ic ma e ials, among o he s [11]. Meanwhile,
hemicelluloses can be used o p oduce xylooligosaccha ides and u u al
[12]. Finally, lignin, which is conside ed as he mos abundan enew-
able phenolic polyme [13], is usually bu ned o supply ene gy o pape
mills whe e i is gene a ed as was e [14]. Howe e , due o i s phenolic
na u e, high a ailabili y, low cos , and he p esence o alipha ic and
phenolic OH g oups, lignin can be used o c ea e high alue-added bio-
based p oduc s, including bio-based polyols [15]. Ne e heless, despi e
he la ge numbe o OH g oup p esen in he lignin molecule, chemical
modi ica ions o i s s uc u e a e usually necessa y, as many o hese
g oups a e no accessible because o being s e ically hinde ed, which
signi ican ly dec eases he eac i i y o his molecule [16]. In his wo k,
di e en lignin modi ica ion s a egies ha e been es ed o ob ain hese
polyols, o which, oxyalkyla ion and lique ac ion wi h polyhyd ic al-
cohols a e he mos ele an ones [17].
Lignin lique ac ion eac ion is ypically ca ied ou unde a mo-
sphe ic p essu e and acidic condi ions (H
2
SO
4
) employing mild em-
pe a u es(150–170 ◦C), a eac ion ime a ound 90 min, and using PEG
and CG as sol en s [18]. Hence, as con en ional lignin lique ac ion
me hods en ail high ene gy expenses a ibu ed o leng hy esidence
imes and ele a ed empe a u es, i becomes impe a i e o in es iga e
al e na i e app oaches ha a e mo e eco- iendly. The aim is o
diminish ope a ional cos s and op imise he a o emen ioned ac o s o
enhance he indus ial easibili y o he p ocess. In his ega d,
mic owa e-assis ed i adia ion p esen s i sel as a compelling subs i u e
o adi ional lignin lique ac ion echniques. By enabling apid and
uni o m hea ing, i educes eac ion ime and subsequen ly lowe s en-
e gy consump ion [19]. Gene ally, echnical g ade pe oleum de i ed-
glyce ol is used o he lique ac ion p ocess. The e is, howe e , a la ge
amoun o glyce ol ha is gene a ed as a by-p oduc in he biodiesel
indus y. In ac , o e e y 10 o gene a ed biodiesel, 1 o c ude
glyce ol is p oduced. Once pu i ied, his glyce ol can be used in he ood,
pha maceu ical and cosme ic indus ies [20]. Ne e heless, due o he
la ge su plus o CG caused mainly by he booming o biodiesel indus y,
he p ice o he e ined p oduc dec eased in ecen yea s [21], hus
making i unp o i able o small plan s [22]. I is he e o e necessa y o
ind an indus ial use o his was e, such as eac an i in he lique ac-
ion o lignin o p oduce polyols. Di e en s udies ha e been ca ied ou
in his ield, whe e CG was success ully employed o syn hesise bio-
polyols om lignocellulosic biomass [18,23,24] o lignin [25–29].
Hence, he combina ion o using he applica ion o bo h mic owa e-
assis ed eac ion and he u ilisa ion o c ude glyce ol in he lignin
lique ac ion p ocess can be a signi ican s ep o wa d in inco po a ing
lignin in o he polyu e hane indus y. Howe e , unlike con en ional
me hods whe e empe a u es, imes, and eac an concen a ions a e
well es ablished, i is necessa y o con inue esea ch in o de o es ablish
sui able eac ion condi ions. Fo his eason, in he p esen s udy,
Eucalyp us globulus and Pinus adia a o ganosol lignin samples we e
lique ied employing PEG and CG h ough mic owa e i adia ion ech-
nology. The op imised eac ion condi ions we e ob ained om a p e i-
ous wo k [30]. The p oduced bio-polyols we e cha ac e ised o e alua e
ele an pa ame e s o hei use as polyu e hane p ecu so s. Thus,
hyd oxyl numbe index (I
OH
), acid numbe (A
n
), molecula weigh (M
w
),
polydispe si y index (PI), unc ionali y ( ) as well as lique ac ion yield
and heological beha iou we e de e mined.
2. Ma e ials and me hods
2.1. Ma e ials
Eucalyp us globulus and Pinus adia a we e kindly supplied by Pape-
le a Guipuzcoana Ziku˜
naga S.A. and Ebaki XXI S.A. The ege able oil
employed o ob ain he CG was sun lowe oil used o cooking and
collec ed om he can een o he Gipuzkoa Enginee ing School in Eiba ,
Uni e si y o he Basque Coun y, UPV/EHU. Sulphu ic acid (96 %),
KOH (85 %) and PEG400 we e pu chased om Pan eac. E hanol and
me hanol we e ob ained om Scha lab S.L. The es o echnical e-
agen s we e supplied by Fishe Scien i ic, i.e., sodium sulpha e anhy-
d ous (≥99 %), dime hyl- o mamide (DMF, o HPLC ≥%99.9), e hyl
ace a e (HPLC g ade), li hium b omide, 1,4-dioxane, py idine (analy -
ical g ade) and ph halic anhyd ide (%98).
2.2. Lignin ob en ion p ocedu e
Lignin samples om Eucalyp us globulus and Pinus adia a sawdus
we e ob ained h ough an o ganosol deligni ica ion ea men
employing a 1.5 L s ainless s eel 5500 Pa eac o equipped wi h a 4848
Pa con olle . A e he deligni ica ion p ocess, he esul ing black li-
quo s we e ea ed by an ul asonica ion p ocess using a HD 3100
Sonoplus ul asonic homogenize . Finally, he black liquo s we e acid-
i ied o p ecipi a e he lignin, ob aining an aqueous phase and a solid
phase (lignin) which we e sepa a ed by memb ane il a ion in a 2 L
s ainless s eel holde employing a 0.22
μ
m po e diame e nylon il e .
The eac ion condi ions o he o ganosol and ul asonica ion p ocesses
we e de ined in a p e ious s udy [31]. The molecula weigh dis ibu-
ion o he esul ing ul asonica ed o ganosol lignin samples om
Eucalyp us globulus and Pinus adia a (EUL and PUL espec i ely) a e
lis ed in Table 1 and we e de e mined by gel pe mea ion ch oma og-
aphy (de ails desc ibed in Sec ion 2.4.2).
2.3. Syn hesis o bio-polyols h ough mic owa e assis ed lique ac ion
Table 2 summa ises he eac ion condi ions used o syn hesise he
bio-polyols. These eac ion se ings we e es ablished as op imal in a
p e ious wo k [30].
The eac ion was ca ied ou employing a CEM Mic owa e Disco e
Sys em Model wi h a empe a u e con ol ins umen and an in e nal
empe a u e senso . The eac ions we e pe o med as ollows: he solid
liquid a io was 1:6 in all cases and he eac ion ime was 5 min, unde
cons an s i ing. P e iously es ablished quan i ies o eagen s we e
weighed in o a qua z essel and (4 g in o al) in oduced in o he
eac o . As soon as he eac ion was comple ed, he essel was cooled
down o a sa e empe a u e o handling. Ace one was employed o
dilu e he ob ained p oduc o acili a e il a ion o sepa a e he bio-
polyol om he solids. Finally, a o a y e apo a o was used o
emo e he ace one om he bio-polyol.
2.4. T anses e i ica ion o ege able oil o ob ain c ude glyce ol
CG was ob ained by he anses e i ica ion eac ion o used ege able
oil (sun lowe oil o cooking) wi h me hanol in a mola a io o 6:1
(me hanol:oil). The eac ion was ca alysed by KOH (1 % w . o oil). Oleic
acid wi h a molecula weigh o 884 g/mol was assumed as he p e-
dominan iglyce ide o he calcula ions. The eac ion was pe o med
as ollows: i s ly, he oil was il e ed o emo e he impu i ies; hen i
Table 1
Molecula weigh dis ibu ion o lignin samples.
Sample M
w
(g/mol) M
n
(g/mol) PI
EUL 2837 888 3.196
PUL 2924 911 3.209
F. He n´
andez-Ramos e al.
In e na ional Jou nal o Biological Mac omolecules 247 (2023) 125855
3
was hea ed o 60 ◦C in a olume ic lask employing a hea ing pla e wi h
magne ic s i ing (600 pm). Once he empe a u e o 60 ◦C was
eached, a p e iously p epa ed me hanol/KOH mix u e was added. The
eac ion was kep o 120 min unde e lux o maximise he con e sion.
The eac ion was conside ed inished as soon as a good phase sepa a ion
o he mix u e was obse ed, and i was le o 24 h in a sepa a ion
unnel o sepa a e he biodiesel and glyce ol.
2.4.1. Cha ac e isa ion o c ude glyce ol
Physical p ope ies o CG, such as densi y, pH and iscosi y we e
de e mined. The densi y was calcula ed by measu ing he weigh o a
known olume o c ude glyce ol a oom empe a u e. The pH o he CG
was de e mined a oom empe a u e employing a pH me e C ison basic
20 by dissol ing 1.00 ±0.1 g o CG in 50 mL o deionised wa e . Ash
con en was analysed ollowing he ISO 2098-1972 S anda d me hod,
which consis in bu ning a 750 ◦C o 3 h 1 g o CG in a mu le u nace.
The elemen al analysis was ca ied ou using a Leco T uSpec HCNS
mic o elemen al analyse a 1050 ◦C. Bo h ca ie gas (pu e Helium 3×)
and es gas (ex a pu e Oxygen 4×) we e supplied by Nippon Gases. The
calib a ion was pe o med using Leco Sul ame hazine (C =51.78 %; H
=5.07 %; N =20.1 %; O =11.5 %; S =11.5 %). T iplica e assays we e
pe o med using 2 mg samples. Oxygen was calcula ed by di e ence.
The chemical composi ion o CG was de e mined h ough GC–MS
analysis. 0.2 g o CG we e dissol ed in o 25 mL o me hanol (HPLC
g ade), and he solu ion was injec ed in a GC (7890)-MS (5975C ine
MSD wi h T iple-Axis De ec o ) Agilen equipped wi h a HP-5MS ((5
%-Phenyl)-me hylpolysiloxane, 30 m ×0.25 mm) capilla y column wi h
Helium as ca ie gas. The empe a u e p og am is as ollows: he p o-
g am s a ed a 50 ◦C; hen, i was aised o 120 ◦C a an 8 ◦C/min hea
a e; his empe a u e was kep o 5 min; hen, i was inc eased o
280 ◦C a 8 ◦C/min and held o 8 min; inally, he empe a u e was
aised o 300 ◦C a 10 ◦C/min and held o 2 min.
FTIR analysis was pe o med o analyse and compa e he chemical
s uc u e be ween CG and comme cial glyce ol. A Pe kinElme Spec-
um Two FT-IR Spec ome e equipped wi h a Uni e sal A enua ed
To al Re lec ance accesso y p o ided wi h an in e nal e lec ion dia-
mond c ys al lens was employed. 20 scans in ansmission mode we e
collec ed wi h a esolu ion o 4 cm
−1
in he ange o 4000–400 cm
−1
.
2.4.2. Cha ac e isa ion o he ob ained bio-polyols
Bio-polyols ha we e ob ained h ough he lique ac ion o lignin
employing PEG400 and CG we e cha ac e ised o de e mine impo an
pa ame e s, such as molecula weigh dis ibu ion (M
w
, M
n
and PI), I
OH
,
A
n
, and .
A gel pe mea ion ch oma og aphy (GPC) analysis was used o
de e mine he molecula weigh dis ibu ion o he bio-polyols. To his
end, a JASCO ins umen equipped wi h an LC.Ne ll/ADC in e ace, wo
columns in se ies (Pola Gel-M 300 mm ×7.5 mm) and a RI-2031Plus
e ac i e index de ec o was used. N,N-dime hyl o mamide wi h 1 %
li hium b omide was employed as mobile phase wi h a low a e o 700
mm
3
/min and a empe a u e o 40 ◦C was used. The calib a ion cu e
was made employing polys y ene s anda ds wi h molecula weigh om
266 o 70,000 g/mol (Sigma-Ald ich).
I
OH
(mg KOH/g) was calcula ed ollowing he ASTM D4274 s an-
da d, as ollows: 0.5–1 g o bio-polyol was dissol ed in o 25 mL o he
ph ala ion eagen consis ing o 115 g o ph halic anhyd ide dissol ed in
700 mL o py idine. The eac ion was ca ied ou a 115 ◦C o 1 h unde
cons an s i ing. A e wa ds, 50 mL o pu e py idine was added h ough
he condense . The esul ing solu ion was back i a ed employing a
NaOH solu ion (O.5 M). The acid numbe (A
n
) was de e mined ac-
co ding o ASTM D974 s anda d by dissol ing 0.4 g o bio-polyol in 50
mL o a 4:1 ( / ) solu ion o 1,4-dioxane in wa e . Due o he da k colou
o he esul ing solu ion, i was no possible o pe o m a i a ion using
phenolph halein as indica o . The e o e, a po en iome ic i a ion was
done using an au oma ic i a o (888 Ti ando Me ohm) h ough
Tiamo 2.5 so wa e.
The he mal deg ada ion o bio-polyols was s udied h ough a he -
mog a ime ic analysis (TGA). 5 mg o bio-polyol we e hea ed unde
ine a mosphe e (N
2
10mL⋅min
−1
) om 25 ◦C o 800 ◦C. The hea a e
was 10 ◦C⋅min
−1
. The equipmen employed was a TGA/SDTA RSI ana-
lyse (Me le Toledo).
The heological beha iou o he biopolyols we e analysed h ough
bo h oscilla o y and o a ional es s. The o me was ca ied ou o
de e mine he s o age modulus (G
′
), while he la e was used o s udy
he iscosi y and shea s ess as a unc ion o he shea a e. A Haake
Visco es e IQ (The mo Fishe Scien i ic) heome e was employed using
a coaxial cylinde s geome y (CC 25 DIN/Ti adap e ) wi h a pis on
adius o 12.54 mm and a ing gap o 1.00 mm. The equency sweep o
he oscilla o y es was om 0.1 o 100 ad⋅s
−1
a a ixed s ain o 10 %,
while o he o a ional es a shea a e sweep om 0.02 o 120 s
−1
was
used. The measu emen s we e collec ed a oom empe a u e.
3. Resul s and discussion
3.1. C ude glyce ol cha ac e isa ion
This sec ion con ains he physical p ope ies and composi ion o CG.
The pH o he ob ained c ude glyce ol was 10.55 ±0.02, which in-
dica es he p esence o esidual KOH ca alys and po assium sal s o med
du ing he anses e i ica ion eac ion. This alue is in ag eemen wi h
hose ob ained by o he au ho s who cha ac e ised c ude glyce ol om
he anses e i ica ion eac ion o ege able oils wi h NaOH o KOH as
ca alys [32–34]. As i was expec ed, he densi y o CG (1.03 ±0.07 g/
cm
3
) esul ed lowe han ha o pu e glyce ol (1.259 g/cm
3
) due o he
p esence o ligh e impu i ies such as a y acids, a y acids me hyl es-
e s (FAMEs), wa e and me hanol aces [33]. The wa e con en in CG
signi ican ly a ies depending on he manu ac u ing indus y, om a
3.6 % in he case o he soap indus y o a 55.3 % in CGs om S ea in
p oduc ion. CGs ob ained om anses e i ica ion eac ion p esen
wa e con en s om 8.16 % o 43.2 % [35], al hough a maximum o 12
% is ecommended o educe pu i ica ion cos s [36]. The e o e, he
wa e con en o he CG ob ained in his wo k (11.64 ±1.61 %) is wi hin
he speci ica ions o a c ude glyce ol ob ained h ough ans-
es e i ica ion eac ion. Such wa e , can hyd olyse he iglyce ides o
o m ee a y acids (FFA) which esul s in soaps dec easing he eac ion
yield [35].
The elemen al analysis o CG showed ha he 46.00 ±1.29 % o he
o ganic ma e co esponded o Ca bon (C). This high alue can be
explained by he high p esence o impu i ies, such as, soaps, FAMEs and
glyce ides, which ha e highe C con en han glyce ol. Hu e al. [33]
epo ed simila C alues o CG ob ained om di e en soy and ege-
able oil was es. In addi ion, he ob ained ni ogen (0.15 ±0.01 %),
hyd ogen (8.17 ±0.33 %) and oxygen (35.6 ±1.58 %) pe cen ages
we e in acco dance wi h he alues epo ed o di e en CG ob ained
om di e en ege able oils [20,33,37]. Ne e heless, he measu ed
sulphu concen a ion (1.33 ±0.04) was highe han he alues ob-
ained in he men ioned s udies, anging om ppms o a maximum o
0.078 %. The chemical composi ion o CG was de e mined h ough
GC–MS. In addi ion o glyce ol (41.84 ±0.17 %), CG was ound o be
ich in o he compounds which include a y acids (11.46 ±6.01 %) and
FAMEs (26.31 ±7.68 %), among o he s (Fig. 1).
The chemical s uc u e o he CG was de e mined h ough FTIR
analysis and i was compa ed wi h a comme cial glyce ol sample
Table 2
Lique ac ion eac ion condi ions (da a pending publica ion).
Bio-polyol Rigid bio-polyol Elas ic bio-polyol
EPR
CG
PPR
CG
EPE
CG
PPE
CG
Ca (% w .) 0 0 5 3.86
Tempe a u e (◦C) 161 159 180 160
PEG/CG (% w .) 3/1 3/1 7.57/1 7.34/1
F. He n´
andez-Ramos e al.
In e na ional Jou nal o Biological Mac omolecules 247 (2023) 125855
4
(Fig. 2). CG showed he main unc ional g oups o comme cial g ade
glyce ol: O
–
H s e ching and bending (3300 cm
−1
and 920 cm
−1
espec i ely), C
–
H asymme ic and symme ic s e ching (2920 cm
−1
and 2851 cm
−1
espec i ely), C
–
O s e ching o p ima y alcohol (1456
cm
−1
) and seconda y alcohol (1110 cm
−1
) as well as H
2
O blending
(1650 cm
−1
) [32,38]. Mo eo e , cha ac e is ic peaks o CG we e also
obse ed. The i s one, a small peak associa ed o C
–
–
C s e ching
(3015 cm
−1
) ela ed o unsa u a ed compounds [32]; he second one,
associa ed wi h he p esence o ca bonyl g oups (C
–
–
O) o es e s o
ca boxylic acids o a y acids (1745 cm
−1
) [39]. Finally, a signal ela ed
o he p esence o ca boxyla e ions COO
−
was obse ed (1560 cm
−1
),
indica ing he p esence o soap in he CG sample [32,39].
3.2. Cha ac e isa ion o he bio-polyols
Table 3 summa ises he da a ob ained om he cha ac e isa ion o
he bio-polyols. An adequa e M
w
o polyols is essen ial o ob ain PUs
wi h he desi ed so segmen p ope ies. Depending on he inal appli-
ca ion, he PUs’ molecula weigh should be be ween 300 and 1000 (g/
mol) o igid PU, and be ween 2000 and 10,000 (g/mol) o elas ic PU
[40].
As expec ed, he highe he acid concen a ion, he highe he M
w
.
Thus, bio-polyols o igid PU (EPR
CG
, PPR
CG
) whe e no ca alys was
used, showed lowe M
w
han he bio-polyols o elas ic PU (EPE
CG
,
PPE
CG
) (Fig. 3). This inc ease in he M
w
is a consequence o he epo-
lyme isa ion eac ions which a e a ou ed in he p esence o an acid
ca alys [41]. In addi ion, EPE
CG
bio-polyol showed a signi ican ly
highe M
w
han PPE
CG
since, as he ca alys concen a ion inc eased
abo e 3 %, he epolyme isa ion eac ions also inc ease [18]. On he
o he hand, i has been documen ed ha he polyme isa ion eac ions
be ween glyce ol, FFA and FAMEs o CG can also inc ease he M
w
o bio-
polyols [42]. Howe e , since he bio-polyols wi h highe CG con en bu
wi hou ca alys showed he lowes molecula weigh , i could be
concluded ha hese eac ions we e o lesse impo ance han he
epolyme isa ion eac ions caused by he acid ca alys . The poly-
dispe si y index is also c ucial o he inal applica ion o he PU, as i is
ela ed o he chain leng h a ia ion and, depending on he chain leng h
o he polyme , he PU could show an undesi ed beha iou [43]. I was
obse ed ha he polydispe si y index was also a ec ed by epolyme -
isa ion eac ions caused by an inc ease in ca alys concen a ion. Thus,
he bio-polyol wi h he highes ca alys concen a ion (EPE
CG
) exhibi ed
he highes M
w
and polydispe si y index, ollowed by PPE
CG
. As s a ed
abo e, EPE
CG
and PPE
CG
bio-polyols’ M
w
alues i ed in he ange o
he manu ac u e o elas ic PUs. On he o he hand, al hough he mo-
lecula weigh s o EPR
CG
and PPR
CG
bio-polyols we e sligh ly highe
han he equi ed o he manu ac u e o igid PUs, hey could be
conside ed sui able o he manu ac u e o his kind o PUs.
The I
OH
equi ed o he syn hesis o igid PUs anges be ween 200
and 1000 mg KOH/g, while o elas ic PUs i is be ween 28 and 160 mg
KOH/g [44]. I is also well known ha an ele a ed A
n
can dec ease he
e iciency o he eac ion, so a low A
n
alue is desi ed [45]. These wo
Fig. 1. GC–MS ch oma og am o c ude glyce ol.
Fig. 2. FTIR spec a o comme cial glyce ol and c ude glyce ol.
Table 3
Molecula weigh dis ibu ion, I
OH
, A
n
, unc ionali y ( ), equi alen weigh (EW) and yield o bio-polyols.
Sample M
n
(g/mol)
M
w
(g/mol)
PDI I
OH
(mg KOH/g)
A
n
(mg KOH/g)
EW Yield
(%)
EPR
CG
442 ±34 1742 ±275 4.25 ±0.55 554 ±4 1.91 ±0.06 4.16 ±0.10 101.20 ±0.66 93.55 ±3.00
EPE
CG
941 ±30 8818 ±127 9.38 ±0.16 228 ±36 20.94 ±2.75 3.51 ±0.68 248.98 ±38.77 70.75 ±0.47
PPR
CG
453 ±24 1431 ±362 3.14 ±0.63 383 ±8 4.21 ±0.90 3.14 ±0.16 146.68 ±3.23 90.60 ±0.56
PPE
CG
780 ±20 5530 ±131 7.10 ±0.31 173 ±16 25.09 ±2.59 2.08 ±0.27 325.36 ±30.16 79.35 ±0.83
Fig. 3. Molecula weigh dis ibu ion o he lique ied bio-polyols.
F. He n´
andez-Ramos e al.
In e na ional Jou nal o Biological Mac omolecules 247 (2023) 125855
5
pa ame e s a e closely ela ed, since an inc ease o he acid numbe
dec eases he hyd oxyl numbe o he polyol [46]. This co ela ion is
obse ed o he ob ained bio-polyols, whe e hose wi h he highes I
OH
index (EPR
CG
and PPR
CG
) p esen ed he lowes A
n
alue. The highe A
n
index obse ed in EPE
CG
and PPE
CG
compa ed o EPR
CG
and PPR
CG
esul ed om he use o sulphu ic acid as eac ion ca alys . The highes
I
OH
alues o EPR
CG
and PPR
CG
compa ed o EPE
CG
and PPE
CG
can be
explained, i s ly, by he absence o ca alys in he eac ion, which
dec eased he I
OH
index [47]. On he o he hand, he highe amoun o
glyce ol used in he o mula ion o EPR
CG
and PPR
CG
bio-polyols
con ibu ed o he inc ease o he I
OH
index [48].
The syn hesis o PUs equi es di e en unc ionali ies depending on
he inal applica ion, as shown in Scheme 1. Thus, o he syn hesis o
igid PUs, high unc ionali ies be ween 3 and 8 a e p e e ed o p oduce
c osslinks ha ein o ce he s uc u e, while o elas ic PUs, such as
lexible oams, elas ome s o adhesi es, among o he s, he desi ed
unc ionali ies a e be ween 2 and 3. Such low unc ionali ies esul in
ma e ials wi h low c osslink densi y ha allow he mobili y o he
polyme chains [40].
Consequen ly, he bio-polyols syn hesised o igid PU applica ions
showed app op ia e unc ionali ies o 4.16 in he case o EPR
CG
and 3.14
o PPR
CG
. In he case o he bio-polyols o elas ic PU applica ions,
while PPE
CG
had an adequa e unc ionali y o 2.08, EPE
CG
was sligh ly
abo e 3. Howe e , conside ing i s I
OH
and M
w
alues, i could be
conside ed sui able o he manu ac u e o elas ic PUs. The chain
de i ed om a hyd oxyl g oup, o he equi alen weigh o he polyol, is
also a ele an pa ame e o be conside ed (Eq. (1)). A sho chain im-
plies a highe densi y o u e hane bonds and he e o e mo e cohesion
be ween hem, mainly h ough seconda y hyd ogen bonds. This,
oge he wi h he high unc ionali y, esul s in a igid s uc u e. On he
o he hand, a long chain dec eases he concen a ion o u e hane bonds,
dec easing he cohesion be ween hem, and oge he wi h a low unc-
ionali y and high mobili y o he main polyol chain, esul ing is an
elas ic PU [49].
EW =56.1⋅100
Co ec ed IOH
(1)
As expec ed, acco ding o he da a summa ised in Table 3, he bio-
polyols EPR
CG
and PPR
CG
, showed a low EW, which is adequa e o
he syn hesis o igid PUs, while bio-polyols wi h lowe I
OH
alue, EPE
CG
and PPE
CG
, p esen ed a highe EW mo e sui able o polyu e hanes wi h
a mo e lexible s uc u e.
While all he s udied p ope ies a e ele an o ob ain bio-polyols
wi h he app op ia e cha ac e is ics o PU p oduc ion, he yield con-
s i u es ano he key ac o and is equally impo an o make he p ocess
indus ially easible. In he lignin lique ac ion p ocess, he ca alys has a
signi ican impac on he eac ion yield, since in he p esence o an acid
ca alys he lignin epolyme isa ion eac ions a e inc eased, gene a ing
a highe amoun o solid esidue, and he e o e educing he yield [18].
The p esence o wa e in he eac ion can p omo e he agmen a ion o
lignin in o smalle and mo e eac i e molecules h ough hyd olysis
inc easing he eac ion yield [25]. This wa e can be o med as a by-
p oduc o he condensa ion o glyce ol in o polyglyce ol du ing he
lique ac ion eac ion, he e o e, he mo e glyce ol in he medium, he
mo e wa e and he highe he yield [50]. Acco ding o he esul s ob-
ained and summa ised in Table 3, EPR
CG
and PPR
CG
bio-polyols wi h a
highe amoun o c ude glyce ol and wi hou ca alys showed highe
yield han EPE
CG
and PPE
CG
bio-polyols whe e ca alys and lowe con-
cen a ion o glyce ol we e used. The use o CG in lique ac ion eac ions
can educe he yield o such eac ions. This is due o he p esence o
impu i ies such as FA and FAMEs and a lowe amoun o glyce ol in he
eac ion medium [45]. Howe e , he p esence o acid ca alys in he
medium showed mo e in luence on he educ ion o he lique ac ion
yield. Thus, EPE
CG
and PPE
CG
wi h a lesse CG con en showed a sub-
s an ially lowe yield han EPR
CG
and PPR
CG
, which can only be
explained by he g ea e in luence o he acid ca alys . Fu he mo e, i
was also obse ed ha wi h a e y simila PEG/CG a io, bu wi h a
highe ca alys concen a ion, EPE
CG
showed lowe yield han PPE
CG
.
The mog a ime ic analysis o he esul ing bio-polyols was pe -
o med o de e mine he ela ionship be ween chemical s uc u e and
deg ada ion. The TGA he mog ams and hei co esponding de i a i e
he mog a ime ic cu es (DTG) a e shown in Fig. 4. Based on he DTG
cu es, i was concluded ha EPE
CG
and PPE
CG
bio-polyols showed ou
deg ada ion zones, while only h ee deg ada ion zones we e obse ed in
EPR
CG
and PPR
CG
bio-polyols. In addi ion, EPE
CG
, PPE
CG
and PPR
CG
showed an uniden i ied deg ada ion zone which was no obse ed in
EPR
CG
sample. This deg ada ion s ages a e summa ised in Table 4.
The i s one, be ween 30 and 110 ◦C, is associa ed wi h mois u e o
he p esence o sol en in he sample. I could be obse ed a weigh loss
in all cases in his deg ada ion zone. Howe e , i was clea ly isible a
highe weigh loss in PPR
CG
and PPE
CG
samples, which could be due o
he p esence o he ace one employed in he p ocess. The second
deg ada ion egion (115–270 ◦C) co esponds o he deg ada ion o
glyce ol [51]. The hi d deg ada ion egion akes place be ween 275 and
Scheme 1. Hypo he ical c osslinking in lignin-based igid and elas ic polyu e hanes.
F. He n´
andez-Ramos e al.
In e na ional Jou nal o Biological Mac omolecules 247 (2023) 125855
6
335 ◦C o EPE
CG
and PPE
CG
and i is ela ed o he deg ada ion o PEG
[51]. I should be no ed ha he deg ada ion o he β
–
O
–
4 and C
–
C
bonds o lignin occu s be ween 250 and 400 ◦C. Ne e heless, depending
on he M
w
and he epolyme isa ion deg ee o he lignin molecule, his
deg ada ion could happen a di e en empe a u es [52]. Thus, in he
case o EPE
CG
and PPE
CG
, wi h highe M
w
, lignin deg ada ion (4 h
deg ada ion a ea) was obse ed be ween 315 and 440 ◦C, whe eas in
bio-polyols wi h lowe M
w
(EPR
CG
and PPR
CG
), his deg ada ion akes
place a lowe empe a u es. This can be caused because, in he la e ,
he deg ada ion zone o PEG and lignin o e lap, showing a single
deg ada ion zone, i.e. he hi d deg ada ion egion o hese bio-polyols.
Finally, be ween 690 and 775 ◦C, a small weigh loss was obse ed,
possibly due o he p esence o ino ganic impu i ies in he samples.
Howe e , he o igin o his peak could no be clea ly de e mined.
Finally, o de e mine he iscoelas ic p ope ies and he luid
beha iou o he bio-polyols, a heological s udy o he samples was
pe o med. To s udy he iscoelas ic beha iou , an oscilla o y es was
ca ied ou compa ing he s o age module (G
′
) wi h he loss module (G
″
).
Based on he analysis o his es , illus a ed in Fig. 5, i was concluded
ha he bio-polyols exhibi ed a liquid beha iou , since in all cases he G
″
was highe han he G
′
o e he whole equency ange. Fu he mo e, as
expec ed, he alue o he modules inc eased wi h inc easing molecula
weigh s, EPE
CG
and PPE
CG
showed highe modules han EPR
CG
and
PPR
CG
[53]
.
The luid beha iou o bio-polyols, as well as hei iscosi y, was
s udied h ough a o a ional es analysing he ela ion be ween he
iscosi y (
η
), shea s ess (
τ
) and shea a e (˙γ). These pa ame e s we e
i ed o he Os wald-de Waele powe -law equa ion (Eq. (2)), whe e he
i ing pa ame e s (n and k) a e dependen on he na u e o he luid and
he measu emen condi ions.
τ
=k⋅˙γn(2)
Thus, he luid can be New onian, pseudo plas ic o dila an when he
low index pa ame e (n) is n =1, n <1 and n >1, espec i ely. The
alue o he pa ame e k, known as he consis ency index, which is
associa ed wi h he appa en iscosi y o he luid a a shea a e o 1 s
−1
,
inc eases wi h inc easing iscosi y. A summa y o he da a p o ided by
he so wa e is p esen ed in Table 5, and he ob ained low cu es a e
shown in Fig. 6a and b.
R
2
alues >0.99 we e ob ained in all cases, indica ing ha he
heog ams we e well adjus ed, and, he e o e, he selec ed model o
e alua e he heological beha iou was adequa e. In all cases, since he
low index (n) alues we e equal o e y close o uni y, i was concluded
ha he bio-polyols we e New onian- ype. This beha iou was obse ed
in Fig. 6a, whe e he iscosi y emained cons an ega dless he applied
shea a e (˙γ) and was con i med by s udying he beha iou be ween he
shea s ess (
τ
) and shea a e (˙γ) (Fig. 6b). I was obse ed ha , in all
cases, he g aphical ep esen a ion o hese pa ame e s esul ed in a
s aigh line which passed h ough he o igin and whose slopes we e
equal o he k alue o each bio-polyol. Fu he mo e, as expec ed, he
iscosi y o he bio-polyols wi h highe M
w
we e highe han hose wi h
lowe molecula weigh s [54]. Thus, he iscosi y o each bio-polyol was
in conco dance o i s consis ency index (k) alue [55], being 1.4299 Pa⋅s
o EPE
CG
, 0.7290 Pa⋅s o EPR
CG
, and 0.9352 Pa⋅s and 0.7927 Pa⋅s o
PPE
CG
and PPR
CG
. The e o e, as hese alues we e lowe han 300 Pa⋅s,
he bio-polyols we e sui able o PU p oduc ion.
Fig. 4. TGA he mog ams and DTG cu es o lique ied bio-polyols.
Table 4
Deg ada ion s ages on o he TGA-DTG cu es o he analysed bio-polyols.
Sample 1s 2nd 3 d 4 h 5 h
Tin Tm Tin Tm Tin Tm Tin Tm Tin Tm
EPE
CG
30–100 72 115–270 233 270–315 283 315–440 391 705–775 758
EPR
CG
30–110 70 125–255 214 214–513 360 – – – –
PPE
CG
30–110 70 120–270 235 270–335 291 335–450 403 705–775 758
PPR
CG
30–110 56 120–250 205 250–512 361 – – 690–770 740
Tin : Tempe a u e in e al; Tm: Maximum deg ada ion empe a u e.
Fig. 5. S o age module (G
′
) and loss module (G
″
) (Pa) as unc ion o
ω
( ad/s) o
bio-polyols.
Table 5
Powe -Law linea unc ions based on he heological da a ob ained om he
s udied bio-polyols.
Sample Func ion k (Pa⋅s
n
) n R
2
EPE
CG
τ
=1.4299⋅˙γ1.0176 1.4299 1.0176 0.9985
EPR
CG
τ
=0.7290⋅˙γ0.9911 0.7290 0.9911 0.9995
PPE
CG
τ
=0.9352⋅˙γ0.9978 0.9352 0.9978 0.9988
PPR
CG
τ
=0.7927⋅˙γ1.0011 0.7927 1.0011 0.9939
F. He n´
andez-Ramos e al.
In e na ional Jou nal o Biological Mac omolecules 247 (2023) 125855
7
3.3. E ec o c ude glyce ol in bio-polyols pa ame e s
The esul s ob ained by o he au ho s by lique ying lignocellulosic
biomass employing, among o he s, glyce ol and CG as sol en s a e
summa ised in Table 6. None heless, since he eac ion condi ions
employed in his s udy we e he op imal condi ions es ablished in ou
p e ious wo k, he esul s ob ained in his wo k (Table 3) we e i s
compa ed wi h he esul s ob ained in ou p e ious wo k (Table 6) [30].
The eac ion yields employing CG and echnical g ade glyce ol we e
e y simila , howe e a dec ease was obse ed when CG was used due o
he p esence o impu i ies and lowe glyce ol con en , which dec eased
he eac ion e iciency [45]. In addi ion, he lowe amoun o glyce ol
molecules in c ude glyce ol and he consump ion o hyd oxyl g oups due
o compe i i e eac ions caused by impu i ies a e esponsible o he
dec ease o he I
OH
index in bio-polyols compa ing o hose ob ained
when comme cial glyce ol was employed [23]. The A
n
exhibi ed he
same beha iou as ha obse ed in ou p e ious s udy, i.e., he highe
he ca alys concen a ion, he highe he numbe o acids. None heless,
using c ude glyce ol as sol en , he A
n
alues we e sligh ly lowe since
o ganic impu i ies in he c ude glyce ol could lead o he consump ion o
acidic compounds [23]. Compa ing he molecula weigh ob ained in
his wo k wi h hose ob ained in ou p e ious wo k, whe e a echnical
Fig. 6. (a) Viscosi y (
η
) as a unc ion o shea a e (˙γ); (b) shea s ess (
τ
) as a unc ion o shea a e (˙γ).
Table 6
Di e en s udies o lignocellulosic biomass and lignin lique ac ion employing comme cial o c ude glyce ol.
Raw ma e ial Sol en Yield (%) I
OH
A
n
Mw PI Ca alys H
2
SO
4
USE Re .
Eucalyp us globulus
o ganosol lignin
PEG +G 98.63 ±
0.71
595.15 ±
33.92
2.74 ±
0.00
1394 ±12 3.69 ±
0.08
4.03 ±
0.15
– Rigid PU [30]
71.98 ±
1.41
253.84 ±
60.59
33.01 ±
0.00
4895 ±
325
9.37 ±
1.12
2.36 ±
0.44
5 % Elas ic PU
Pinus adia a o ganosol
lignin
98.93 ±
0.14
514.28 ±
42.70
5.63 ±
0.23
1383 ±43 3.58 ±
0.08
3.55 ±
0.26
– Rigid PU
87.56 ±
3.30
209.67 ±
3.70
30.56 ±
0.15
5408 ±
765
6.95 ±
0.91
2.91 ±
0.08
3.86 % Elas ic PU
Eucalyp us globulus K a
lignin
PEG +G 95.27 537.95 – 1775 3.51 – 3 % – [54]
Oli e ee p uning
o ganosol lignin
PEG +G 99.07 811.8 – – – – 1 % – [57]
Eucalyp us globulus k a
lignin
PEG +G >86 100–660.08 0.8–10.70 1459–1990 – – 3, 6, 9 (o ganic acids) – [58]
Enzyma ic hyd olysis lignin
o co ns alk
PEG +G >90 191–409 – – – – 15 % – [47]
Alkaline co ncob lignin PEG +G 97.47 484.03 – 525 1.13 – 1.5 % PU oam [59]
K a lignin (so wood) CG >0.61 (g/g
CG)
412 5088 2.2 – – PU oam [27]
O ganosol lignin
(suga cane bagasse)
224 7867 4.9 –
Lignosulphona e
(ha dwood)
592 7384 3.3 –
Ace one soluble lignin CG +1,4-
BDO
72.64 ≈1100 ≈4 – – – – PU oam [29]
K a pine lignin CG +1,4-
BDO
93 670 – – – – – PU oam [25]
Rapeseed cake PEG +G 84 586 – – – – 80:20:3 (PEG: G:
H
2
SO
4
)
– [51]
Da a seeds 96 395 – – – –
Oli e s one 92 496 – – – –
Co ncob 91 504 – – – –
Apple pomace 97 428 – – – –
Whea s aw – 350 28 1270 1.22 – PU oam [48]
Taiwan acacia PEG +G 95.2 310 25.6 – – – 3:1:0.09 (sol en :
biomass: H
2
SO
4
)
Adhesi es [60]
China i 98.4 287 38.0 – – –
No way sp uce EG 99.7 825–623 48.2–47.8 – – – 4.5 g Adhesi es [61]
1,4-Bu anediol (1,4-BDO), glyce ol (G), c ude glyce ol (CG), e hylene glycol (EG).
F. He n´
andez-Ramos e al.
In e na ional Jou nal o Biological Mac omolecules 247 (2023) 125855
8
g ade glyce ol was used o he lique ac ion p ocess, i is wo h no ing
ha he e was an inc ease on he molecula weigh in all cases, pa ic-
ula ly in EPE
CG
bio-polyol. This can be explained by he polyme isa ion
eac ions be ween glyce ol, FFA and FAMEs [56]. Consequen ly, he
polydispe si y indexes o he CG syn hesised bio-polyols we e highe
han hose ob ained wi h echnical g ade glyce ol. This inc ease in he
M
w
and PI was in ag eemen wi h ha epo ed by Hu e al. [45]. I could
also be concluded ha he unc ionali ies we e also simila in all cases
and app op ia e o he class o PUs o which hey we e syn hesised.
Howe e , in he case o EPE
CG
, he unc ionali y was sligh ly abo e he
limi alue o he syn hesis o elas ic PU. As o he iscosi ies, i should
be no ed ha , as expec ed, wi h he inc ease in he molecula weigh o
he samples ob ained wi h c ude glyce ol, he iscosi ies also inc eased
o emained p ac ically equal, as in he case o PPE
CG
.
EPR
CG
and PPR
CG
bio-polyols yields we e wi hin he ypical alues
ob ained o he lique ac ion o lignocellulosic biomass o lignin, despi e
using CG ins ead o echnical g ade glyce ol (Table 6). Howe e , he
yields ob ained by T an e al. [29] lique ying soluble ace one lignin
using CG and 1,4-BDO in he p esence o sulphu ic acid we e e y
simila o hose ob ained o EPE
CG
and PPE
CG
. I is no ewo hy ha , in
mos o he s udies ha a e summa ised in Table 6, polyols we e used o
he manu ac u e o oams. In such s udies, he I
OH
a ied be ween 100
mg KOH/g and 811.8 mg KOH/g. The e o e, he I
OH
alues ob ained o
EPR
CG
and PPR
CG
bio-polyols, which a e in ended o igid PUs, we e
ound o be in good conco dance wi h he alues o he li e a u e. Few o
he s udies summa ised in Table 6 indica ed he PI o polyols, and hose
ha did so, e e ed o polyols o he syn hesis o PU oams. The PI
ob ained o EPR
CG
and PPR
CG
in his wo k a e in line wi h hose e-
po ed by o he au ho s in such s udies.
Lee e al. [60] lique ied Taiwan acacia and China i employing PEG
and glyce ol wi h sulphu ic acid as ca alys o p oduce polyols. Such
polyols, which showed a I
OH
o 310 and 287 (mg KOH/g), we e used o
syn hesise PU adhesi es. EPE
CG
and PPE
CG
bio-polyols, syn hesised o be
used in he elabo a ion o elas ic PUs, showed a e y simila I
OH
o hose
ob ained in ha s udy. Simila ly, Jiang e al. [61] syn hesised PU ad-
hesi es employing polyols om lique ied lignocellulosic biomass (No -
way sp uce). Howe e , in his case he I
OH
was signi ican ly highe (825
and 623 mg KOH/g). As o PI, un o una ely, o he bes o ou
knowledge, no s udies we e ound indica ing he PI alue o polyols
ob ained h ough he lique ac ion o lignin o PU adhesi e syn hesis.
Likewise, no pape s we e ound indica ing he unc ionali y o polyols
ob ained h ough his p ocess. Finally, he A
n
alue was, in all cases,
wi hin he usual ange (0–40 mg KOH/g) o his ype o p ocess.
4. Conclusions
In his pape , bio-polyols sui able o he manu ac u e o igid and
elas ic PUs we e success ully p epa ed h ough he lique ac ion o
o ganosol lignin om Eucalyp us globulus and Pinus adia a. The
lique ac ion eac ion was ca ied ou employing a mic owa e eac o
using he op imal eac ion condi ions es ablished in a p e ious s udy.
Polye hylene glycol and c ude glyce ol, which was ob ained om used
ege able oil, we e u ilised as sol en s o his p ocess. The e ec o
c ude glyce ol is ob ious when compa ing he esul s ob ained wi h
hose ob ained in ou p e ious wo k. The lique ac ion yields dec eased
in all cases due o he lowe amoun o glyce ol in he mix u e. Thus, he
yields ob ained o bio-polyols p oduced o igid PUs whe e no ca alys
was employed we e highe han 90 %, whe eas o bio-polyols in ended
o elas ic PUs, whe e sulphu ic acid was used as ca alys , he yields
we e signi ican ly lowe , be ween 70 and 80 %. The I
OH
o bio-polyols
we e also a ec ed by he lowe glyce ol con en when c ude glyce ol
was used. The I
OH
alues ob ained in his s udy we e 554 and 383 (mg
KOH/g) o EPR
CG
and PPR
CG
bio-polyols espec i ely and 228 and 173
(mg KOH/g) o EPE
CG
and PPE
CG.
The A
n
alue o he samples was in
he expec ed ange o his ype o polyols. Rega ding he unc ionali ies,
al hough in he case o EPE
CG
he ob ained alue was sligh ly abo e he
desi ed one, i could be said ha he unc ionali ies we e adequa e o
he manu ac u e o he ype o PU o which hey we e in ended. This
assump ion was con i med by aking in o accoun hese esul s oge he
wi h he es o he pa ame e s ha we e s udied. O e all, e en hough
he esul s o some pa ame e s ha e wo sened, i can be said ha c ude
glyce ol eco e ed om used oil is sui able o he manu ac u e o bio-
polyols o p oduce elas ic and igid PUs.
CRediT au ho ship con ibu ion s a emen
Fabio He n´
andez-Ramos: Concep ualiza ion, Me hodology, In es-
iga ion, Fo mal analysis, Da a cu a ion, Valida ion, W i ing – o iginal
d a , W i ing – e iew & edi ing. Ma ía Gonz´
alez Al iols: Supe ision,
Valida ion, Da a cu a ion, Visualiza ion. M. Mi a i An xus egi: Su-
pe ision, Valida ion, Da a cu a ion, Visualiza ion. Jalel Labidi: Vali-
da ion, Fo mal analysis, Resou ces, Supe ision. Xabie E docia:
Me hodology, In es iga ion, Fo mal analysis, Da a cu a ion, Valida ion,
Supe ision, W i ing – o iginal d a , W i ing – e iew & edi ing.
Decla a ion o compe ing in e es
The au ho s decla e he ollowing inancial in e es s/pe sonal e-
la ionships which may be conside ed as po en ial compe ing in e es s:
Fabio He nandez-Ramos epo s inancial suppo was p o ided by
Gipuzkoa P o incial Council.
Acknowledgemen s
The au ho s would like o acknowledge he inancial suppo o he
Uni e si y o he Basque Coun y (p ojec COLAB20/04). F. He n´
andez-
Ramos would like o acknowledge he G an ecei ed om he En i-
onmen al Depa men o he Dipu aci´
on Fo al de Gipuzkoa. The au ho s
hank SGIke (UPV/EHU/ERDF, EU) o hei echnical and human
suppo .
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