Materials Sciences and Applicatio ns, 2011, 2, 692-699
doi:10.4236/msa.2011.26095 Published Online June 2011 (
Copyright © 2011 SciRes. MSA
Evaluation of Lignin-Calcium Complex as
Thermal Stabilizer for Poly Vinyl Chloride
Hussein Ali Shnawa
Polymer Research Center, University of Basrah, Basrah, Iraq.
Received December 27th, 2010; revised March 18th, 2011; accepted May 19th, 2011.
Chemical modification of lignin was carried out by reacted it with HI acid, then the modified lignin treated with cal-
cium hydroxide to prepare calcium-lignin chelating complex, this derivative was examined as thermal stabilizer for
PVC, thermal degradation of PVC neat as blank and containing three weight percents (1, 2, and 4) into polymer was
accelerated by heat treatment at 190˚C for 2 h then PVC films were casting from THF solvent with thickn ess 0.03 mm.
Thermal stabilization activity of this derivative was investigated by using infrared spectroscopy, according to the re-
sults obtained Calcium-lign in complex have suitable activity to in creased PVC stability at lo w concentration depending
on its ability to reaction with HCl as well as the chemical stru cture of lignin that contain phenolic properties.
Keywords: Lignin, Modification of Lignin, Poly (Vinyl Chloride), Thermal Degradation, IR Study
1. Introduction
Lignin has a highly branched chemical structure consist-
ing of phenol propane unites which are connected mainly
together by ether or C–C linkages [1,2]. Because of vari-
ety functional groups in lignin that provide many poten-
tial reactive sites for chemical modifications and applica-
tions, one of these modification method that used to in-
crease lignin activity were by reacted it with formalde-
hyde in alkaline solution to form methylol groups into
lignin matrix [3,4], or by synthesized polymer from lig-
nin on the basic of some functional groups such as
phenylene, hydroxyl and methoxyl [5].
There are other studies show that the modification lig-
nin by oxidation reaction (obtained through several
sources and methods) can be used as chelating agent for
some type of metal ions [6,7]. German C. Quintana and
his co-worker study the capacity for removal of heavy
metals from liquid streams by formation of complexes
with lignin’s oxidized by acid treatment and their con-
clusions refer to lignin capable of adsorbing Cadmium
ions from aqueous solution and a slight increase in ad-
sorption capacity when lignin was oxidized [8]. Another
study show the used of native lignin as will as modifica-
tion lignin as additive for low density polyethylene
which can act as antioxidant and UV-stabilizers [9].
On the other hand, Poly (vinyl chloride), PVC, is one
of the leading thermoplastic materials. It stands second in
the world after polyethylene so far as production is con-
cerned. However, PVC shows low thermal stability [10].
It is generally accepted that poly(vinyl chloride), PVC, is
an unstable polymer when exposed to high temperatures
during it’s moldings and applications. Therefore, the
poor thermal stability of PVC still remains one of its
main problems [11]. The purpose of this work was to
study the chemical modification of lignin by chelated it
with Ca ion then evaluated its effect on thermal stability
of poly (vinyl chloride).
2. Experimental
2.1. Modification of Lignin
15 g Lignin (Kraft lignin) from paper industries—Basrah
was modified by refluxed it with 60 ml of 30% solution
of HI acid (May & Baker Ltd.) for 3 h at the end or the
reaction period the solution was allowed to cool before
filtrated. Modified lignin washed with distillation water
several times and finally dried under reduced pressure for
24 h.
2.2. Preparation of Calcium-Lignin Chelating
Modified lignin 10 g was dissolved in 250 ml water and
added periodically 10% of Ca(OH)2 as clear and fil-
Evaluation of Lignin-Calcium Complex as Thermal Stab ilizer for Poly Vinyl Chloride693
trated solution with hand stirring. the addition was con-
tious to precipitate all lignin in the mixture as brown dark
powder which was filtered and washed to removal the
non reacted Ca(OH)2, finally the product was oven dry-
ing for 24 h at 50˚C .
2.3. Preparation of PVC Samples
Commercial polyvinyl chloride (supplied from petro-
chemical industries Basrah) with K-value 66, volume
density 0.45 gm/cm2 and without thermal stabilizer was
mixed thermally by hakee thermal mixer (hakee rheocord
torque rheometer) at 170˚C with 60 rpm with Ca-lignin
chelating complex at three weight percentage (1, 2, and
4)% w/w and 0% as blank, the samples were compres-
sion molded at 170˚C under 5 MPa for 5 min. to get
sheets .
2.4. Thermal Degradation Condition
Accelerated PVC degradation was performed by fixed
the samples in the oven at 190˚C for 2 h under air as at-
2.5. Films Preparation
PVC samples were dissolved in THF then filtrated to
remove Ca-lignin chelating or other compounds from
PVC polymer. PVC was re-precipitated from THF solu-
tion by ethanol and filtrated, fixed concentration from
PVC (0.1/5 ml)in THF were casting on class plate to
prepare polymer film with 0.03 mm thickness (measured
by Starrett micrometer, Jedburgn Scotland), the films
were further dried at 40˚C for 24 h.
2.6. Infrared Analysis
IR-spectrophotometer that used in our study was Shi-
matzu-FTIR-8400S infrared sepectrometer for measure-
ment infrared sepecrometry of lignin, modified lignin,
and Ca-lignin chelating complex after dried, ground and
mixed with KBr and pressed to form pellets. The infrared
spectrometry of PVC samples as films specimens were
placed in the path of IR beam, all spectrums were re-
corded in the range 4000 - 600 cm–1.
3. Results and Discussion
One modification method have been made on the De-
etherfication of methoxyl groups of the guaiacyl propane
and syringyl propane units by reacted lignin with HI acid
this reaction lead to lignin molecule containing more
phenolic hydroxyl gr oups [9].
FTIR spectrum of lignin (Figure 1) and modified lig-
nin (Figure 2) show the same basic absorption peaks of
main chemical groups that contained in lignin.
One of these peaks the broad and strong peak at 3300 -
3400 cm–1 that attributed to hydroxyl groups and the
peaks at 1600 cm–1 and 1520 cm–1 corresponding to the
absorption of double bonds of alkene and aromatic
skeletal vibration. But the main differences in the
chemical structure between lignin and modified lignin
can be represented by that peak of phenolic hydroxyl at
1220 cm–1 which become more intense and the peak at
1120 cm–1 that attributed to the alcoholic hydroxyl and
aliphatic ether which appe ar less intensity.
The chemical reaction of lignin with HI lead to clear
Figure 1. FTIR spectrum of unmodified lignin.
Copyright © 2011 SciRes. MSA
Evaluation of Lignin-Calcium Complex as Thermal Stab ilizer for Poly Vinyl Chloride
increment in the intensity o f these peaks due to increased
the phenolic hydroxyl into modified lignin [9]. It’s ex-
pected that the modification of lignin by above reaction
lead to increased reactivity to some metal ions to form
complex salts or chelating complexes; Figure 3 gives
evidence of the chemical bonding occurring as conse-
quence of the reaction modified lignin with Ca(OH)2 to
formation chelating complex .
The major defferences between the two FTIR spec-
trum obtained from modified lignin and Ca-lignin chelate
showed in Figure 2 and Figure 3, the presence of clear
and broad peak at 1400 cm–1 and the sharp peak at 860
cm–1 that attributed to formed ionic bond (Ca-O) into this
derivative [12]; One the other hand the absence the peak
at 1220 cm–1 due to chelating phenolic groups with Ca2+
ion that refer to formation chelating salt.
Generally, infrared spectroscopy has been proven to be
a highly effective means to qualitatively and quantita-
tively studies in polymer field where are deferent bonds
and functional groups present in polymer which have
Figure 2. FTIR spectrum of modified lignin.
Figure 3. FTIR spectrum of Ca-lignin chelating complex.
Copyright © 2011 SciRes. MSA
Evaluation of Lignin-Calcium Complex as Thermal Stab ilizer for Poly Vinyl Chloride695
different vibration frequencies, and by identifying char-
acteristic frequencies as absorption peaks can be detected
and monitoring many functional groups in polymer
structure and composites [13,14]. The application of in-
frared spectroscopy in polymer are concerned with the
range 650 - 4000 cm–1; many works used IR or FTIR to
study the decomposition and thermal degradation of PVC
as well as evolution the thermal, photo-stabilizer and
antioxidants additives for this polymer [11, 15-19].
Matuana L. M. (2001) classified the characteristic IR
bands of PVC into three regions the first is called the
(C–Cl) stretching region in the range from 600 - 700
cm–1, the second region is attributed to (C–C) stretching
in the region from 900 - 1200 cm–1 and the third region is
at 1250 - 2970 cm–1 assigned to numerous C–H mode.
The IR spectrum of stander PVC without added thermal
stabilizer or heat treatment is presented in Figure 4; ab-
sorption bands of this polymer evidenced at about 2950
cm which attributed to C–H stretching from CH2, 1440
cm–1 wagging of CH2, 1300 cm–1 of CH2 deformation,
1250 cm–1 C–H stretching from CHCl, 1070 cm–1 C–C,
930 cm–1 rocking of CH2, 700 cm–1 and 600 cm–1 stretch-
ing of C–Cl.
After degradation of PVC by heated it for 2 h. at
190˚C main differences occur in the chemical structure
lead to found new chemical groups such as polyene, hy-
droxyl, carbonyl, cyclic compound and other [20,21], this
new chemical structure can be observed and monitored
by IR spectrometry; Figure 5 shows the IR spectra of
PVC after decomposed with out any thermal stabilizer.
This spectrum contain clear and new deference peaks
at several position where are not found in IR spectrum of
stander PVC; (Figure 4) one of these peaks that appear
at 3650 cm–1 which attributed to th e free hydrox yl g roup s
stretching vibration which can formed as a result to
thermal-oxidation process, while in the state of PVC
contain deferent percent from Ca-lignin chelating com-
plex; Figure 6, Figure 7, and Figure 8, where in this
samples the peak became much less intense or not found.
Additionally, clear peak can be detected in Figure 5,
in the region between 320 0 - 3400 cm–1 corresponding to
absorption of hydroxyl with hydrogen bond, but this not
found in the presence on lignin derivative at all %wt. that
mean increased PVC stability to thermal degradation by
this additive where appear that the Ca-lignin chelating
complex can be play a main role in the PVC stabilizing
mechanism by it’s chemical structure which can ab-
sorbed HCl.
The intensified new strong and sharp at 1730 cm–1 in
Figure 5 attributed to formation carbonyl groups as ali-
phatic ketone in PVC after heat treatment and this not
found in PVC contain 1% Figure 6 and became less in-
tense in 2 wt% sample, Figure 7; other significant peak
used to study the thermal degradation of PVC, polyene
40060080010001200140016001800200030004000 1/c m
33 Faise hussen PVCS
Figure 4. IR spectrum of pure PVC (blank).
Copyright © 2011 SciRes. MSA
Evaluation of Lignin-Calcium Complex as Thermal Stab ilizer for Poly Vinyl Chloride
40060080010001200140016001800200030004000 1/cm
34 Faise hussen PVCO
Figure 5. IR spectrum of pure PVC after degradation.
40060080010001200140016001800200030004000 1/cm
32 Faise hussen pvc-1
Figure 6. IR spectrum of PVC contain 1% Ca-lig.chelating complex.
that formed in the first state of degradation process
(Owen 1984) at 1602 - 1640 cm–1 which appear in Fig-
ures 5, 7 and 8 and not found in Figure 6, that mean the
best activity can be achieved at less concentration from
this derivative.
The absorption of the polyene and hydroxyl groups are
used to follow the extend of polymer degradation by
calculation polyene index (IPe) and hydroxyl index (IOH)
and carbonyl index (ICO); as seen from Figure 9, Figure
10 and Figure 11 the presence of lignin derivative lead
Copyright © 2011 SciRes. MSA
Evaluation of Lignin-Calcium Complex as Thermal Stab ilizer for Poly Vinyl Chloride 697
40060080010001200140016001800200030004000 1/cm
33 Faise hussen pvc-2
Figure 7. IR spectrum of PVC contain 2% Ca-lig. chelating complex.
40060080010001200140016001800200030004000 1/cm
33 Faise hussen pvc-4
Figure 8. IR spectrum of PVC contain 4% Ca-lig. chelating complex.
to lower growth rate of polyene and hydroxyl indices
respectively, with increased the wt% of this add itive into
PVC samples. Therefore, at 0% from lignin derivative
the indices appear at higher values and decreased with
increased wt% into polymer.
4. Conclusions
1) The chemical reaction of lignin with HI acid lead to in -
Copyright © 2011 SciRes. MSA
Evaluation of Lignin-Calcium Complex as Thermal Stab ilizer for Poly Vinyl Chloride
%wt. of Ca-lig.chelating
polyene Index
Figure 9. Relationship between the polyene indix and wt%
of Ca-lignin chelating complex.
% wt. Ca-lig. chelating
Hydroxyl in d ex
Figure 10. Relationship between the hydroxyl indix and
wt% of Ca-lignin chelating complex.
% wt. Ca- lig.chelating
Carbonyl index
Figure 11. Relationship between the carbonyl indix and
wt% of Ca-lignin chelating complex.
creased it’s contain from hydroxyl group and it’s chemi-
cal reactivity to reaction with Calcium ion to form
Ca-lignin chelating complex.
2) Investigating the influence of this derivative on the
thermal stability of PVC showed increased thermal sta-
bility of PVC by the action of it’s chemical structure to
absorbed HCl from polymer system.
3) Ca-lignin chelating complex have thermal stabilizer
effect with high activity at 1 wt% and less activity at
above percentag e.
5. Acknowledgements
The author is grateful for the suppo rt of said Faise Jumaa
Mohameed a technique in petrochemical industries for
your help in FTIR measurement and said Ibraheem K.
Ibraheem a researcher for his notes for complete my re-
[1] R. F. Gould, “Lignin Structure and Reactions,” Advance
in Chemistry, Series No. 59, Journal of the American
Chemical Society, Washington DC, 1966.
[2] K.V. Sarkanen and C. H. Ludwing, “Lignin Occurance,
Formation, Structure, and Reactions,” Wiley-Interscience
& Son Inc., New York, 1971, pp. 1-65.
[3] R. W. Heningway, A. H. Conner and S. J. Baranham,
“Adhesives from Renewable Resources,” Journal of the
American Chemical Society, 1989, pp. 13-42.
[4] H. A. Shnawa , S. Sh. Al-Laibi and N. Sh. Addai, “Ki-
netic Study of Reaction the Lignin with Phenol Formal-
dehyde Resins,” Iraqi Journal of Polymers, Vol. 7, 2003,
pp. 33-42.
[5] S. Hirose, T. Ha takey a ma a nd H. Hatakeyama, “Synthesis
and Thermal Properties of Epoxy Resins from Es-
ter—Carboxylic Acid Derivative of Alcoholysis Lignin,”
Macromolecular Symposia, Vol. 179, No. 1, 2003, pp.
157-169. doi:10.1002/masy.200350715
[6] A. R. Goncalves and S. M. Luz, “Chelation of Copper (II)
Ions with Kraft Lignin, 10th International Symposium on
Wood and Pulping Chemistry,” Yokohama-Japan, 1999,
Vol. III-Poster Presentations, pp. 410-413.
[7] A. R. Goncalves and S. M. Luz, “Evaluation of the Re-
moval of Heavy Metals by Kraft Lignin Considering Co-
precipitation,” Solubility and Coordination Capacity of
the Ions Tested, 6th Brazilian Symposium on the Chemis-
try of Lignin and Other Wood Components, Guaratin-
gueta-SP, Brazil, 2001, pp. 266-269.
[8] G. C. Quintana, G. J. M. Rocha, A. R. Gonçalves and J. A.
Velsquez, “Evaluation of Heavy Metal Removal by Oxi-
dised Lignnins in Acid Media from Various Sources,”
BioResources, Vol. 3, No. 4, 2008, pp. 1092-1102.
[9] Ali T. Y. AL-Saraefi, “Efficiency Study and Comparison
of Lignin as Thermal and Photo Antioxidant for Low
Density Polyethylene,” Master’s Thesis, University of
Basrah, Basrah, 2005, pp. 32-72.
[10] N. A. Mohamed and W. M. Al-Magribi, “N-(Substituted
phenyl) Itaconimides as Organic Stabilizers for Rigid
Poly(Vinyl Chloride) against Thermal Degradation,”
Polymer Degradation and Stability, Vol. 78, No. 1, 2002,
pp. 149-165. doi:10.1016/S0141-3910(02)00129-5
Copyright © 2011 SciRes. MSA
Evaluation of Lignin-Calcium Complex as Thermal Stab ilizer for Poly Vinyl Chloride
Copyright © 2011 SciRes. MSA
[11] H. F. Alfred and W. H. Raymond, “The Mechanism of
Poly(Vinyl Chloride) Tabilization by Barium, Cadmium,
and Zinc Carboxylates. Infrared Studies,” Journal of Po-
lymer Science, Vol. 40, No. 137, 1959, pp. 419-431.
[12] J. F. Rabek, “Experimental Methods in Poly mer Chemis-
try,” John Wiley & Sons, New York, 1970, pp: 221-253.
[13] E. Yousif, A. Hameed, A. Kamil, Y. Farina, N. Asaad and
A. Graisa, “Synthesis of New Polymers Derived from
Poly (Vinyl Chloride) and Study Their Biological
Evaluation,” Australian Journal of Basic and Applied
Sciences, Vol. 3, 2009, pp. 1786-1794.
[14] H. Mekki and M. Belbachir, “Preparation of Vinyl Chlo-
ride—Vinyl Ether Copolymers via Partial Etherification
from PVC,” EXPRESS Polymer Letters, Vol. 11, 2007, pp.
[15] A. V. Karyakin, G. V. Grishin and B. D. Kurykin, “A
Study of Photodegradation of PolyvinylChloride by In-
frared Spectroscopy,” Polymer Science USSR, Vol. 7, No.
3, 1965, pp. 389-393. doi:10.1016/0032-3950(65)90077-8
[16] H. Kaczmarek, A. Felczak, D. Bajer and D. Bajer,
“Photooxidative Degradation of Carboxylated Poly(Vinyl
Chloride),” Polymer Bulletin, Vol. 62, No. 4, 2009, pp.
503-510. doi:10.1007/s00289-008-0030-y
[17] M. Giurginca and Traian Zaharescu, “Thermo-Oxidative
Degradation of Some Polymer Couples Containing
HNBR,” Polymer Bulletin, Vol. 49, No. 5, 2003, pp. 357-
362. doi:10.1007/s00289-002-0115-y
[18] R. Rasheed, H. Mansoor, E. Yousif, A. Hameed, Y. Fa-
rina and A. Graisa, “Photostabilizing of PVC Films by
2-(Aryl)-5-[4-(Aryloxy)-Phenyl]-1,3,4-Oxadiazole Com-
pounds,” European Journal of Scientific Research, Vol
30, 2009, pp. 464-477.
[19] M. T. Taghizadeh, N. Nalbandi and A. Bahadori, “Stabi-
lizing Effect of Epoxidized Sunflower Oil as a Secondary
Stabilizer for Ca/Hg Stabilized PVC,” EXPRESS Polymer
Letters, Vol. 2, 2008, pp. 65-76.
[20] D. Braun and E. Bezdadea, “Theory of Degradation and
Stabilisation Mechanisms,” In: L. I. Nass and C. A.
Heiberger, Eds., Encyclopedia of PVC, Vol. 1, Mercel
Deckker Inc., New York and Basel, 1986, pp. 397-429 .
[21] E. D. Owen, “Degradation and Stabilisation of PVC,”
Elsevier Applied Science Puplishers Ltd., London & New
York, 1984, pp: 21-252.