Effect of some parameters on the synthesis and the physico-chemical properties of new amphiphilic starch-g-copolymers

Article abstract of DOI:10.1016/j.carbpol.2015.05.016

The detailed studies on the graft copolymerization of phenyl methacrylate onto gelatinized potato starch in water using potassium persulfate as radical initiator were presented. The different reaction parameters such as effect of initiator concentration, starch to monomer ratio, reaction temperature and reaction time were studied in terms of grafting efficiency, grafting percent and percent homopolymer formation. It was found that grafting process of aromatic methacrylate monomer onto potato starch backbone allowed obtaining new amphiphilic copolymers with different physicochemical properties as compared to non-modified starch. The influence of the copolymer structure on the swelling behavior in polar and non-polar solvents, moisture absorbance, gelatinization properties, acid and base resistance, surface morphology and thermal properties was discussed.

Full text of DOI:10.1016/j.carbpol.2015.05.016

Carbohydrate Polymers 130 (2015) 344–352
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Effect of some parameters on the synthesis and the physico-chemical
properties of new amphiphilic starch-g-copolymers
∗
Marta Worzakowska , Marta Grochowicz
Maria Curie-Skłodowska University, Faculty of Chemistry, Department of Polymer Chemistry, Gliniana 33 Street, 20-614 Lublin, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The detailed studies on the graft copolymerization of phenyl methacrylate onto gelatinized potato starch
in water using potassium persulfate as radical initiator were presented. The different reaction parameters
such as effect of initiator concentration, starch to monomer ratio, reaction temperature and reaction time
were studied in terms of grafting efficiency, grafting percent and percent homopolymer formation. It was
found that grafting process of aromatic methacrylate monomer onto potato starch backbone allowed
obtaining new amphiphilic copolymers with different physicochemical properties as compared to non-
modified starch. The influence of the copolymer structure on the swelling behavior in polar and non-polar
solvents, moisture absorbance, gelatinization properties, acid and base resistance, surface morphology
and thermal properties was discussed.
Received 6 January 2015
Received in revised form 4 May 2015
Accepted 5 May 2015
Available online 18 May 2015
Keywords:
Potato starch
Phenyl methacrylate
Graft copolymerization
Potassium persulfate
Physico-chemical properties
© 2015 Elsevier Ltd. All rights reserved.
1
. Introduction
Starch is a high-molecular-mass, natural, biodegradable car-
to the presence of hydroxyl groups on the starch backbone, it is
a suitable and widely studied material for the chemical modifi-
cation which can extend their utility for various environmental
and industrial applications. The chemical modification of starch
includes many methods like hydrolysis, oxidation, esterification,
etherification, crosslinking and grafting in order to introduce new
functional groups into starch molecule. It causes to enhance or
repress the inert properties of starch or to impact new physico-
chemical properties (Bhosale & Singhal, 2006; Borsacchi, Calucci,
Geppi, La Terra, Pinzino, & Bertoldo, 2014; Casas, Ferrero, &
Jimenez-Castellanos, 2010; Cova, Sandoval, Balsamo, & Müller,
2010; Parovouri, Hamunen, Fossel, Autio, & Poutanen, 1995; Salimi,
Yilmaz, Rzayev, & Piskin, 2014; Xu, Kennedy, & Liu, 2008; Zhang,
Chen, Du, Xue, Chen, & Yang, 2015).
One of the intensively studied in recent years, techniques of
chemical modification of carbohydrate polymers is the graft copo-
lymerization. The chemical modification of starch through the
graft copolymerization with hydrophobic vinyl monomers, e.g.
methyl methacrylate (Aravindakshan & Kumar, 2002; Castellano,
Gurruchaga, & Goni, 1997; Fakhru’l-Razi, Qudsieh, Yunus, Ahmad,
& Rahman, 2001; Kumar, Ganure, Subudhi, & Shukla, 2014), ethyl
methacrylate (Marinich, Ferero, & Jimenez-Castellanos, 2009),
styrene (Cho & Lee, 2002; Kaewtatip & Tanrattanakul, 2008),
methyl acrylate (Lutfor, Sidik, Haron, Rahman, & Ahmad, 2003),
leads to the preparation of novel materials with better properties
like higher rheological behavior and stability in acidic environ-
ment, higher moisture resistance, lower swelling, higher adhesion
to hydrophobic polymers as compared to unmodified starches.
bohydrate polymer which is mainly composed of two glucan
components with different characteristic, such as linear amy-
lose and highly branched amylopectin. This natural polymer is
a major constituent of many plants such as potatoes, rice, corn,
wheat, cassava, topioca, peas, beans or cereal grains, etc. (Debnath,
Gayathri, & Babu, 2013; MacGregor, 2001). In recent years, polysac-
charides have gained more importance and starch found wide
practical applications due to its low-cost, biodegradable, availabil-
ity and renewable. Starch is utilized in many branches of industry
such as cosmetics, plastics, adhesives, paper, food, pharmaceu-
tical, etc. (Bhosale & Singhal, 2006; Cova, Sandoval, Balsamo, &
Müller, 2010; Kuakpetoon & Wang, 2001; Meshram, Patil, Mhaske,
&
Thorat, 2009; Namazi & Dadkhah, 2010; Parovouri, Hamunen,
Fossel, Autio, & Poutanen, 1995; Pohja, Suihko, Vidgren, Paronen,
Ketolainen, 2004; Simi & Emilia, 2007; Whistler, BeMiller, &
&
Paschall, 1984). However, starch has some drawbacks like highly
hydrophilic nature causing their enormous swelling, brittleness,
low stability in acidic environment, low moisture resistance, poor
processability or incompatibility with some hydrophobic polymers.
It significantly limits its use in practical applications. However, due
∗ Corresponding author. Tel.: +48 81 524 22 51; fax: +48 81 524 22 51.
E-mail addresses: marta.worzakowska@poczta.umcs.lublin.pl
(M. Worzakowska), mgrochowicz@poczta.umcs.lublin.pl (M. Grochowicz).
http://dx.doi.org/10.1016/j.carbpol.2015.05.016
144-8617/© 2015 Elsevier Ltd. All rights reserved.
0

M. Worzakowska, M. Grochowicz / Carbohydrate Polymers 130 (2015) 344–352
345
Hence, hydrophobic graft modification of starch allows obtain-
2.4. Synthesis of aromatic methacrylate monomer
ing new copolymers with potential wide practical applications,
e.g. as stabilizers, rheology modifiers, surface modifiers, com-
patibilizers, fillers, in coatings, as matrices and excipients for
specific drug-delivery systems or as new polymeric materials, etc.
Phenyl methacrylate monomer was prepared in our laboratory
according to Grochowicz and Gawdzik (2013). In a typical pro-
cedure, 0.1 mol of phenol and 0.12 mol of triethyloamine were
dissolved in 150 mL of chloroform in a three-necked glass flask. The
(Aravindakshan & Kumar, 2002; Castellano, Gurruchaga, & Goni,
◦
1
997; Cho & Lee, 2002; Fakhru’l-Razi, Qudsieh, Yunus, Ahmad, &
flack was cooled down to 5 C and then 0.12 mol of methacryloyl
Rahman, 2001; Kaewtatip & Tanrattanakul, 2008; Kumar, Ganure,
Subudhi, & Shukla, 2014; Lutfor, Sidik, Haron, Rahman, & Ahmad,
chloride was slowly dropped to the stirred mixture. The flask was
continuously cooled in order to maintain the reaction temperature
◦
2
003; Marinich, Ferero, & Jimenez-Castellanos, 2009).
in the range of 5–7 C. After the dropping of the whole amount of
◦
The objective of the present work is to study the influ-
methacryloyl chloride, the reaction mixture was stirred at 5 C for
ence of initiator concentration, starch to monomer ratio, reaction
temperature and reaction time on the course of the grafting copo-
lymerization between phenyl methacrylate monomer and potato
starch and the evaluation of the physico-chemical properties of
obtained amphiphilic starch-g-copolymers. To our best knowledge,
the formation of poly(phenyl methacrylate) chains onto gelatinized
potato starch is a novel idea. We believe that the prepared materi-
als due to their properties can find their place as low cost and more
environmentally friendly stabilizers, fillers, modifiers, plastics or
matrices for specific drug-delivery systems.
1 h, and then at room temperature for the next 1 h. The residue
formed during the reaction of methacryloyl chloride with phenol
(triethyloamine hydrochloride) was separated from the solution by
filtrating. The residual liquid was washed with 10% solution of HCl
3
3
(100 cm ), distilled water (50 cm ) and 1% solution of sodium car-
3
3
bonate (100 cm ) and finally with distilled water (100 cm ). The
organic layer was dried over magnesium sulfate. Then, the solvent
(chloroform) was distilled under reduced pressure.
2.5. Graft copolymerization
The graft copolymerization between potato starch and phenyl
methacrylate was performed in glass flask equipped with a ther-
mometer, mechanical stirrer, reflux condenser and a nitrogen gas
inlet. In a typical procedure 2.5 g of purified, dried potato starch and
2
. Experimental
2.1. Materials
5
0 cm3 of distilled water were stirred (300 rpm) and heated using
◦
thermostated water bath up to temperature of 80 C for 30 min in
order to starch gelation. Then, the glass was purred with nitrogen,
and the suitable amount of potassium persulfate (0.5–2 wt%) was
Potato flour containing 12 wt% of water was obtained from
Melvit S.A. (Poland). Methacryloyl chloride (97%) and triethy-
loamine (99%) were acquired from Sigma-Aldrich. Phenol (99%)
was from Loba Chemie (Austria). Potassium persulfate was from
Merck (Germany). Methanol and tetrahydrofuran were obtained
from POCh (Gliwice, Poland).
◦
added and mixed for next 30 min at 80 C under nitrogen in order
to form radical on the surface of starch. After 30 min, the tempera-
ture was adjusted to graft copolymerization temperature. The graft
copolymerization process was performed at different temperatures
◦
(
50–90 C). The aromatic monomer was added and the reaction was
continued for the next 0.5–3 h under purging the nitrogen gas in
the reactor. The starch-to-monomer ratio by weight was 1:0.25,
2.2. Isolation of starch from potato flour
1
:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5 and 1:2. At the end of the reaction,
Starch was isolated from potato flour according to the method
the flask contents were added to methanol (100 mL) to precipi-
tate. The precipitate after 24 h was filtered and dried in an oven
at 60 C to a constant weight. The homopolymer was separated
by Soxhlet extraction using tetrahydrofuran for 48 h. The purified
starch graft copolymer was washed with methanol and dried to a
constant weight at 60 C.
described in Ref. (Lim, Lee, Shin, & Lim, 1999). In a typical proce-
dure, 50 g of potato flour and 150 mL of 0.5% solution of NaOH were
placed in a glass flask equipped with mechanical stirrer and stirred
◦
(
300 rpm) for 5 h at room temperature. Then, the obtained mixture
was placed in refrigerator for 24 h, decanted and washed several
times with distilled water to neutrality. The isolated starch was
◦
The percent homopolymer formation (%H), grafting efficiency
◦
dried to a constant weight at 60 C. Based on this procedure, it was
(%GE) and grafting percent (%G) were calculated using the following
found that the content of starch in potato flour was 85%.
equations (Athawale & Rathi, 1997; Fakhru’l-Razi, Qudsieh, Yunus,
Ahmad, & Rahman, 2001; Fares, El-faqeeh, & Osman, 2003):
weight of homopolymer
weight of monomer charged
2
.3. Determination of amylopectin/amylose content in potato
%
H =
× 100
(1)
starch
The determination of amylopectin/amylose content in potato
weight of grafted polymer
weight of grafted polymer + weight of homopolymer
%
GE =
×100
starch was carried out according to the method described in
Krishnaswamy & Sreenivasan (1948). Five grams of isolated, dried
starch and 300 mL of distilled water were placed in a glass flask
containing a thermometer and mechanical stirrer. The suspen-
(2)
◦
sion was intensely stirred at 60 C for 4 h. Then it was centrifuged
weight of polymer grafted
weight of starch
%
G =
× 100
(3)
at 6000 rpm in order to separate water-insoluble amylopectin
from water-soluble amylose. The obtained solid (amylopectin) was
◦
placed in air-dryer at 60 C and dried to a constant weight. However,
2
.6. Characterization of starch-g- poly(phenyl methacrylate)
to the obtained clear water solution of amylose, 200 mL of methanol
copolymers
was added to precipitate. Then, precipitate was centrifuged at
◦
6
000 rpm, separated from water and dried at 60 C to a constant
2
.6.1. Fourier transformed infrared (FTIR) spectra were recorded
with FT-IR spectrometer Tensor 27, Brucker (Germany) using
the KBr disc technique. Sixty-four scans were collected for each
weight. Based on this procedure, the amylopectin/amylose content
was found to be 83/17 in used potato starch.

3
46
M. Worzakowska, M. Grochowicz / Carbohydrate Polymers 130 (2015) 344–352
−
1
Table 1
sample (un-grafted and grafted) at a resolution of 4 cm over the
−
1
Effect of initiator concentration on grafting parameters.
wavenumber region 600–4000 cm
.
2
.6.2. The surface morphology of the copolymers was investi-
Initator (wt%)
.5
1.0
1.5
H (%)
GE (%)
G (%)
gated using scanning electron microscopy (SEM). Microphotografts
0
29.5 ± 0.5
15.9 ± 0.1
31.2 ± 0.5
35.5 ± 0.7
59.7 ± 1.1
76.0 ± 0.8
53.3 ± 0.9
42.9 ± 0.8
39.5 ± 0.6
43.2 ± 0.4
32.6 ± 0.5
28.7 ± 0.6
were obtained at 3000× and 8000× magnification.
2
.6.3. The swelling studies of prepared copolymers were studied
2.0
in various solvents differ in polarity such as water, ethanol, butanol,
toluene, CCl4 and hexane at 25 C. The swellability coefficients (B)
were determined by equilibrium swelling of copolymers, using the
centrifugation method and expressed as
◦
H, percent homopolymer formation; GE, grafting efficiency; G, grafting percent;
starch to monomer ratio, 1:1.5; temperature, 80 C; 300 rpm, 2 h.
◦
Table 2
Effect of the starch to monomer ratio on the grafting parameters.
Vs − V
d
B =
× 100
(4)
Starch:monomer
H (%)
GE (%)
G (%)
V
d
1
1
:0.25
:0.5
36.0 ± 0.2
24.0 ± 0.3
22.1 ± 0.4
21.2 ± 0.2
20.8 ± 0.1
15.9 ± 0.1
25.4 ± 0.4
64.0 ± 0.6
68.5 ± 0.8
70.2 ± 1.0
73.4 ± 0.6
74.1 ± 0.3
76.0 ± 0.8
54.3 ± 0.6
13.8 ± 0.2
27.5 ± 0.3
39.0 ± 0.5
41.9 ± 0.2
42.5 ± 0.2
43.2 ± 0.4
37.5 ± 0.5
where Vs is the volume of the copolymer after swelling and Vd is
the volume of the dry copolymer (Tuncel, Ecevit, & Kesenci, Piskin,
1:0.75
1:1
1
1
1
:1.25
:1.5
:2
1
996).
.6.4. Moisture absorbance study was carried out for dried sam-
2
ples (100 mg) which were placed in an exsiccator and exposed to
the water vapor at 25 C for 24 h. Before the experiment, the air was
◦
H, percent homopolymer formation; GE, grafting efficiency; G, grafting percent;
◦
1
wt% of potassium persulfate, temperature 80 C, 300 rpm, 2 h.
evacuated from an exsiccator due to which we can assume that the
equilibrium practically saturated water vapor were present over
the samples. Percent moisture absorbance was calculated from the
following equation:
3. Results and discussion
3.1. Effect of initiator concentration
We − W
i
%
M =
× 100
(5)
The effect of the potassium persulfate concentration on the
W
i
grafting parameters is presented in Table 1. It is clearly visible that
firstly as the concentration of initiator increases from 0.5 to 1 wt%,
the grafting parameters such as grafting efficiency (%GE) and graft-
ing percent (%G) increase but the percent homopolymer formation
(%H) decreases. The higher amounts of initiator (above 1 wt%) cause
the decreasing of %GE and %G but result in increasing the %H values.
It is generally known that the potassium persulfate under tempera-
where We is the final weight of the sample and W is the initial
weight of the sample (Pathania & Sharma, 2012).
i
2
.6.5. Gelatinization properties of grafted copolymers and
potato starch were studied using differential scanning calorime-
try (DSC Phoenix 204, Netzsch, Germany). Three milligrams of dry
starch and grafted copolymers were weighted into aluminum pans
and 6 mg of distilled water was then added. The pans were sealed
and put away for 24 h at room temperature to equilibrate. After
−
.
ture decomposes to radicals such as sulfate radical (SO4 ) and other
.
.
free radical species (HO and HO2 ) in aqueous solution. As the con-
centration of an initiator is increased, more radicals are formed. It
grows larger the chance of hydrogen abstraction from starch and
causes the creation of more active sites (macroradicals) onto starch
backbone which are capable to graft copolymerization (Wanyunus
& Md, 1999; Athawale, & Rathi, 1999). On the contrary, as the
concentration of potassium persulfate is higher than the optimum
value, the formation of more radicals which are able to recombi-
nation process and thus leading to fast termination reaction with
starch macroradicals is more prefer. Due to the non-availability of
active sites onto starch backbone, the homopolymerization process
is more favored (Lanthong, Nuisin, & Kiatkamjornwog, 2006).
◦
that, the samples were heated from 20 to 100 C with a heating
◦
rate of 10 C/min.
2
.6.6. Thermal properties of obtained grafted copolymers were
studied with the use of DSC. Ten milligrams of dry sample was
put in an aluminum crucible with a pierced lid and heated from
◦
◦
2
0 to 500 C with a heating rate of 10 C/min under inert (argon,
purge flow 40 mL/min) conditions. The characteristic temperatures
Tmax) for DSC signals and the enthalpy of decomposition (ꢀH) were
determined based on obtained curves.
.6.7. The chemical resistance analysis of obtained copolymers
(
2
was carried out with 1 M HCl and 1 M NaOH and was expressed as
a function of percentage weight loss (%WL) determined using the
following equation (Kaith, Singha, & Grupa, 2003):
3.2. Effect of the starch to monomer ratio
The effect of the starch to phenyl methacrylate monomer ratio
is presented in Table 2. It was observed that the grafting param-
eters (%GE, %G) continuously increase as the quality of starch to
phenyl methacrylate monomer increases from 1:0.25 up to 1:1.5.
In addition, the percent homopolymer formation (%H) decreases as
the quality of starch to phenyl methacrylate monomer increases
from 1:0.25 up to 1:1.5. However, when the quality of starch to
phenyl methacrylate is 1:2, the slight decreasing of the %GE and
%G are indicated. In addition, it is worth noting that as the starch to
monomer ratio is 1:2, the homopolymer formation is grown up. The
increase in grafting parameters as a quality of starch to monomer
content increases may be a result of higher monomer concentration
close to the vicinity of the starch backbone. It causes higher avail-
ability and diffusion of monomer molecules to starch backbone and
results in greater possibility of collision of reactants (Gupta, Sahoo,
W − W
1
2
%
WL =
× 100
(6)
w
1
where W1 is the initial weight of the sample and W2 is the final
weight of the sample.
The initial weighted samples were treated with hydrochloric
acid or sodium hydroxide and the weight of the samples was
noted down at 24 h intervals until a constant weight of the sam-
ple was reached. The samples were washed with distilled water
◦
to neutrality and dried at 60 C to a constant weight. The obtained
samples were analyzed using FTIR spectroscopy in order to evalu-
ate the degradation path of grafted copolymers in acid and alkaline
solutions.

M. Worzakowska, M. Grochowicz / Carbohydrate Polymers 130 (2015) 344–352
347
Table 3
Table 4
Effect of temperature on grafting parameters.
Effect of reaction time on grafting parameters.
◦
Temperature ( C)
H (%)
GE (%)
G (%)
Reaction time (min)
H (%)
GE (%)
G (%)
5
6
7
8
9
0
0
0
0
0
32.6 ± 0.4
23.7 ± 0.3
18.8 ± 0.3
15.9 ± 0.1
24.5 ± 0.5
44.4 ± 0.5
57.1 ± 0.8
66.2 ± 1.2
76.0 ± 0.8
61.5 ± 1.2
28.3 ± 0.3
31.7 ± 0.4
35.2 ± 0.6
43.2 ± 0.4
37.9 ± 0.8
30
60
90
120
150
24.9 ± 0.2
20.2 ± 0.3
16.5 ± 0.2
15.9 ± 0.1
17.3 ± 0.3
20.7 ± 0.5
53.0 ± 0.4
65.1 ± 0.9
72.9 ± 1.0
76.0 ± 0.8
72.3 ± 1.4
62.5 ± 1.6
29.5 ± 0.3
35.8 ± 0.5
40.6 ± 0.5
43.2 ± 0.4
40.5 ± 0.7
32.8 ± 0.8
180
H, percent homopolymer formation; GE, grafting efficiency; G, grafting percent;
starch to monomer ratio, 1:1.5; 1 wt% of potassium persulfate, 300 rpm, 2 h.
H, percent homopolymer formation; GE, grafting efficiency; G, grafting percent;
starch to monomer ratio, 1:1.5; 1 wt% of potassium persulfate, 300 rpm.
&
Khandekar, 2002; Rahman, Silong, Zin, Ab Rahman, Ahmad, &
Haron, 2000). In addition, as it is visible from Table 2 that for
small amounts of phenyl methacrylate used (0.25), the formation
of poly(phenyl methacrylate) is predominant (H = 36 ± 0.2%) over
grafting process (G = 13.8 ± 0.2%). In this case, rather homopoly-
merization than graft copolymerization process is favored due to
small monomer concentration and thus lower possibility of colli-
sions of starch and monomer reactants. However, further increase
in the starch to monomer ratio above optimum level (1:1.5) results
in the formation of more homopolymer and thus the viscosity
of reaction medium is risen. Due to this, the movement of free
radicals is limited and the rate of the grafting process is drop
down (Gupta, Sahoo, & Khandekar, 2002; Rahman, Silong, Zin, Ab
Rahman, Ahmad, & Haron, 2000; Shah, Patel, & Terivedi, 1995).
3.3. Effect of temperature
The effect of temperature on grafting parameters was studied by
Fig. 1. FTIR spectra of phenyl methacrylatemonomer(a), poly(phenylmethacrylate)
(b), potato starch (c), starch-g-copolymer (G = 43.2 ± 0.4%) (d).
◦
varying the reaction temperature from 50 up to 90 C. The results
are presented in Table 3. The grafting parameters increase by raising
◦
the polymerization temperature from 50 to 80 C. However, when
indicated. The increasing of grafting parameters values (%GE and
%G) as the reaction time increases may be connected with higher
extent of initiation and propagation of the graft copolymerization
with time which resulting in the addition of the great number of
phenyl methacrylate units to the hydroxyl group of starch (Kumar,
Ganure, Subudhi, & Shukla, 2014). However, as the reaction time
is growing, the loss in grafting may be due to the various reasons
such as the reduction of monomer and initiator concentration as the
reaction proceed, the decreasing of the number of available active
sites for grafting process or the retardation of diffusion of reactants
due to the formation of long grafted chains (Ojah & Dolui, 2006)
(Table 4).
◦
temperature is above 80 C, the drop of grafting efficiency and graft-
ing percent and the growth of percent homopolymer formation
are observed. The potassium persulfate is thermally dissociating
◦
initiator which rapidly decomposes at temperatures of 60–80 C
Branrup & Immergut, 1989). Due to this, at temperatures lower
(
than temperature at which decomposition of radical initiator is
optimum, slow formation of radicals is expected. As a result, lower
concentration of radicals influences on lower rate of the abstrac-
tion of hydrogen from starch backbone and thus slow formation of
starch macroradicals. Due to this rather homopolymerization than
grafting process is preferred at lower temperatures. However, as
◦
the reaction temperature is raised from 50 to 80 C, the rate of
the production of primary radical species increases and thus the
number of grafting sites onto the polymer backbone is expected
to increase. In addition, higher reaction temperature influences
on the decreasing of the viscosity of the reaction medium. As a
result, the rate of diffusion of phenylmethacrylate molecules to
the starch macroradicals grows larger. Thus, the rate of grafting
process is increased. The drop of grafting parameters as the tem-
3.5. Characterization of copolymers by FTIR
The structure of phenyl methacrylate monomer, phenyl
methacrylate homopolymer, starch and starch-g-poly(phenyl
methacrylate) copolymers was confirmed by FTIR analysis (Fig. 1).
All the characteristic absorption bands for aromatic monomer were
−
1
clearly observed. The small signals at 3021–3064 cm , two sig-
◦
−1
perature raised above 80 C can be explained by the higher rate of
nals at 1490 and 1590 cm
690–743 cm
and the strong intensity bands at
−
1
termination of growing graft chains due to the excess of free rad-
ical formation and chain transfer reactions causing the increase of
the amount of homopolymer formation (Bartlett & Cotman, 1949;
Hebeish & Guthrie, 1981).
are the result of stretching vibrations of CAr–H
groups, stretching vibrations of C C at the phenyl ring and out-of-
plane ring deformation vibrations (CAr–H), respectively. The bands
range between 2930–2980 and 1377–1493 cm
−
1
are due to the
stretching vibrations of CH3 groups and the deformation vibra-
3.4. Effect of reaction time
tion of C H at CH groups. The formation of ester type compound
3
during the catalyzed reaction of methacryoyl chloride with phenol
was confirmed by the presence of the absorption bands charac-
teristic for ester compounds. The presence of the intensive band
The effect of reaction time on grafting parameters was stud-
ied in the presence of optimum initiator concentration (1 wt%) and
◦
−1
optimum temperature (80 C) during when the highest grafting
at 1742 cm (the stretching vibrations of C O group) and at 1120,
−
1
parameters were obtained. The results are placed in Table 4. As it
is seen, the grafting parameters (%GE and %G) are increased as the
reaction time increased from 30 to 120 min and then as the reaction
time was longer than 120 min the decreasing in their values was
1160 and 1195 cm (stretching vibrations of C
formation of ester. In addition the small band responsible for the
O C) confirms the
−
1
stretching vibrations of C C at 1636 cm and the bands ranges
from 805 to 945 cm
−
1
(out-of-plane deformation vibrations of

3
48
M. Worzakowska, M. Grochowicz / Carbohydrate Polymers 130 (2015) 344–352
Fig. 2. SEM imagines of potato starch (a), starch-g-copolymer with %G: 13.8 ± 0.2% (b), 27.5 ± 0.3% (c), 39.0 ± 0.5% (d), 43.2 ± 0.4% (e) at 3000× and starch-g-copolymer with
%
G: 13.8 ± 0.2% (f) and 43.2 ± 0.4% (g) at 8000×.
−
−
1
C
H) were indicated on FTIR spectra of vinyl monomer (Sokrates,
001).
On the contrary, the FTIR spectra of potato starch shows the
characteristic bands which are present as a broad OH-stretching
(2840–2930 cm ), the stretching vibrations of CAr H groups
1
2
(3021–3064 cm ) and the stretching vibrations of C C at the
−
1
phenyl ring visible (1490 and 1590 cm ) is indicated. Also,
the two bands at 690–743 cm
H) are observed. In addition, the presence of bands
(stretching vibration of C O) and wide band with
two non-well pointed maxima at 998 and 1016 cm
−
1
(out-of-plane ring deformation
−
1
−1
vibration in the region of 3200–3550 cm , at 2878–2910 cm due
to the stretching vibrations of C-H and at 1330–1435 cm respon-
sible for the deformation vibration of C H. The bands at 921, 997,
076 and 1148 cm indicated on the stretching vibrations of C
in starch (Lanthong, Nuisin, & Kiatkamjornwong, 2006; Sokrates,
001). For homopolymer formed during graft copolymerization,
the disappearance of the characteristic absorption bands for the
stretching vibrations of C C bonds and the shift of the stretching
vibrations of C
monomer were indicated.
However, on the FTIR spectra of novel graft copoly-
mers, the presence of the stretching vibrations of OH groups
region 3200–3550 cm ), of C H in CH2 and CH3 groups
vibrations C
Ar
−1
−
1
at 1742 cm
−1
and the
−1
−1
1
O
bands at 1150 and 1190 cm
(stretching vibrations of C O C)
is the confirmation of the grafting process of vinyl monomer
onto starch. It is worth noting that the reduction of intensity of
OH bands in grafted starch copolymers compared to un-grafted
starch is indicated. In addition, the complete disappearance of
the characteristic bands for carbon–carbon double bonds of vinyl
monomer was observed. It directly confirms that the grafting
process of phenyl methacrylate onto starch is through the reaction
of hydroxyl groups of starch and carbon–carbon double bonds of
phenyl methacrylate monomer.
2
−
1
O C to 1090, 1160 and 1184 cm as compared to
−1
(

M. Worzakowska, M. Grochowicz / Carbohydrate Polymers 130 (2015) 344–352
349
Table 5
Table 6
Swelling studies of grafted copolymers.
Moisture absorbance studies.
%
Grafting
Water
Ethanol
Butanol
Toluene
CCl4
Hexane
%grafting
%M
1
2
3
4
3.8 ± 0.2
7.5 ± 0.3
9.0 ± 0.5
3.2 ± 0.4
48 ± 1 39 ± 2
40 ± 2 35 ± 1
33 ± 2 32 ± 1
30 ± 1 25 ± 3
70 ± 3 55 ± 4
30 ± 3
26 ± 2
22 ± 1
20 ± 2
39 ± 2
10 ± 1
15 ± 1
23 ± 1
27 ± 2
5 ± 1
12 ± 1 15 ± 1
18 ± 2 18 ± 1
25 ± 2 25 ± 2
28 ± 3 28 ± 2
13.8 ± 0.2
27.5 ± 0.3
39.0 ± 0.5
43.2 ± 0.4
Potato starch
44.8 ± 0.5
34.5 ± 0.7
26.3 ± 0.3
25.4 ± 0.2
50.3 ± 0.8
Potato starch
8 ± 1
9 ± 1
3.6. Surface morphology of copolymers
a
According to the SEM imagines (Fig. 2a), the potato starch gran-
ules exhibit rather regular shape with smooth surface morphology.
The particles of potato starch are not monolithic. They are varied
in particle sizes. Based on SEM measurements, the particle size of
starch granules ranges from 5 to ca. 30 ␮m. However, the graft-
ing of phenyl methacrylate onto potato starch backbone causes the
destruction of starch granules, the losing of their original granular
structure and significant changes in the morphology of obtained
copolymers (Fig. 2b–e). The starch-g-poly(phenyl methacrylate)
copolymers have irregular morphology with high heterogene-
ity and rough surface. As the grafting percent of copolymers is
increased, the creation of more dense, rigid and compact aggregates
is observed. Copolymer with low grafting percent (13.8 ± 0.2%)
forms aggregates which look like bushes, however copolymer with
high grafting percent creates lobule aggregates. In addition, the
grafting process of phenyl methacrylate onto potato starch allows
the formation of porous network (irregular voids between agglom-
erates). Fig. 2 clearly shows that for copolymers with lower grafting
percent (Fig. 2f), the surface is less stiff and have wide pores struc-
ture. Generally, the pore sizes are in the range of 0.3–2.6 ␮m.
However, copolymer with high grafting percent (43.2 ± 0.4%) has
more stiff structure with less complex and irregular voids which
size is from 0.3 ␮m to almost 3.9 ␮m, with higher participation
of higher pore size (Fig. 2g). The SEM analysis additionally con-
firmed that the grafting process of phenyl methacrylate onto starch
backbone was successful. It allowed obtaining the new amphiphilic
materials with high heterogeneous structure.
69.5°C
b
c
7
3.6°C
86.6°C
d
e
5
5
65
75
85
95
Temperature/°C
Fig. 3. DSC curves of gelatization of potato starch (a) and grafted copolymers with
G: 13.8 ± 0.2% (b), 27.5 ± 0.3% (c), 39.0 ± 0.5% (d) and 43.2 ± 0.4% (d).
%
hydrophobic groups are present on the surface of copolymers.
It caused better solvolysation of copolymers by non-polar sol-
vents and their swelling in toluene, hexane and CCl4 is higher
as compared to potato starch. It is worth noting that due to the
amphiphilic properties of obtained copolymers, the hydrophilic
interactions between copolymer backbone and solvent are stronger
for copolymers with lower grafting percent than the hydropho-
bic interactions of copolymer-solvent. The affinity to polar and
non-polar solvents for copolymer with maximum grafting percent
(
43.2 ± 0.4%) seems to be medial, however still, the highest swelling
in water was indicated.
3.7. Swelling studies of copolymers
3.8. Moisture absorbance study
The prepared novel copolymers are non-soluble in polar and
The results on the moisture absorbance studies were presented
in Table 6. The graft copolymers exhibit highest moisture resistance
as compared to potato starch. However, the extent of moisture
absorbance was found to decrease with increasing of the graft-
ing percent. Starch, due to its hydrophilic nature, absorbs moisture
very well through the formation of hydrophilic interactions with
water molecules, mainly through the formation of hydrogen bond-
ing. However, partial blocking of the hydroxyl groups of starch by
hydrophobic polymer chain caused the decreasing in the sensitivity
of starch copolymers toward moisture as compare to non-modified
potato starch.
non-polar solvents, but it swells. The swelling studies of potato
starch and grafted copolymers were studied in the solvents which
differ in their polarity. As polar solvents, water, ethanol and butanol
were applied. As non-polar solvents, hexane, toluene and CCl were
4
used. The results are presented in Table 5.
Generally, the swelling properties of starch-g-copolymers are
highly depended on the grafting percent as well as the polarity of
the solvent. The swellability coefficients (B) in water, ethanol and
butanol continuously decrease as the grafting percent increases.
The B values in water, ethanol and butanol are generally lower
for grafted copolymers compared to potato starch. However, in
non-polar solvents (toluene, CCl4 and hexane), the swellabil-
ity coefficients (B) increases as the grafting percent increases.
In addition, their values in non-polar solvents are higher than
those obtained for potato starch. The incorporation of hydropho-
bic phenyl methacrylate chains into starch backbone causes the
decreasing of the quantity of hydrophilic hydroxyl groups in starch
backbone and resulting in higher hydrophobicity of the surface
of chemically modified starches. Due to this, polar solvents have
lower affinity for more hydrophobic surface of the copolymers than
non-polar solvents and thus the swelling of starch-g-copolymers in
water, ethanol and butanol is more restricted than non-modified
potato starch. However, as the grafting percent increases, more
3.9. Gelatinization properties
The gelatinization properties of potato starch and grafted
copolymers were studied by the use of DSC technique. The example
DSC curves were presented in Fig. 3. On DSC curve of potato starch
one, asymmetric, endothermic signal with maximum gelation tem-
◦
perature of 69.5 ± 0.5 C and enthalpy of gelation 4.96 ± 0.08 J/g
was indicated. However, for the grafted copolymers with graft-
ing percentage higher than 14%, no gelation was indicated on
DSC curves. Only, the small endothermic signal with two maxima
for grafted copolymer with 13.8 ± 0.2% grafting which appeared
at higher temperatures and with smaller enthalpy of gelation

3
50
M. Worzakowska, M. Grochowicz / Carbohydrate Polymers 130 (2015) 344–352
Table 7
DSC data.
◦
◦
◦
Sample
Tg ( C)
Tmax1 ( C)
Tmax2 ( C)
ꢀH2 (J/g)
Potato starch
–
280/285/303.5
238.5/253.7
238.7/261.2
246.2/256.6
256.5/267.3
–
–
–
13.8% ± 0.2
27.5% ± 0.3
39.0% ± 0.5
43.2% ± 0.4
125.0 ± 2.5
126.2 ± 1.9
126.6 ± 1.7
129.1 ± 2.3
107.0 ± 2.2
396.2
393.7
396.5
391.5
396.5
36.8 ± 0.4
52.4 ± 0.9
76.5 ± 1.0
91.7 ± 1.9
213.8 ± 3.1
Homopolymer
Fig. 4. DSC curves of potato starch (a), copolymers with %G: 13.8 ± 0.2% (b),
7.5 ± 0.3% (c), 39.0 ± 0.5% (d), 43.2 ± 0.4% (e) and homopolymer (f).
2
(
2.80 ± 0.02 J/g) as compared to that for potato starch was indicated.
According to literature survey, for gelatinization properties of
starches, amylose is responsible (Odenigbo, Ngadi, Ejebe, Nwankpa,
Danbaba, Ndindeng, & Manful, 2013). However, the grafting of the
hydrophobic methacrylate monomer onto starch backbone causes
the changes in the properties of starch. Probably, due to the insignif-
icant levels of non-grafted amylose, and high crosslinking of the
starch-g-copolymers, the gelation of newly obtained materials with
higher than 14% of grafting is highly restricted.
Fig. 5. Effect of grafting on base resistance.
3.11. The chemical resistance
3.10. Thermal properties
The chemical resistance studies of obtained graft copolymers,
potato starch and poly(phenyl methacrylate) were performed in
a fixed volume of hydrochloric acid and sodium hydroxide. The
results are presented in Fig. 5. In alkaline conditions, potato starch
gelatinizes completely (Leach, Schoch, & Chessman, 1961; Maher
Peoria, 1983; Mangels & Bailey, 1933). However, the graft copoly-
mers have higher chemical resistance in base conditions than
potato starch. It is worth noting that the base resistance of graft
copolymers grows up with the increase in grafting percent. After 5
days, the maximum weight loss of starch-g-poly(phenyl methacry-
late) copolymers was observed. Interestingly, no weigh loss of
poly(phenyl methacrylate) in base conditions was visible. It indi-
cated on high base resistance of this methacrylate homopolymer.
The further increase in time of keeping the samples in base solu-
tions (above 5 days) was not resulted in enlargement of their weight
loss. In addition, it was observed, that the percent of the residue
formed after the base resistance studies was similar to the percent
grafting values counted based on Eq. (3).
The thermal properties of potato starch, homopolymer and
starch-g-copolymers with different grafting percent were studied
by DSC. The obtained DSC curves are presented in Fig. 4. On DSC
curve of potato starch, one asymmetrical signal with three maxima
is clearly observed. This peak is attributed to the degradation pro-
cess of starch under elevated temperatures. However on DSC curve
of poly(phenyl methacrylate) only one, endothermic signal at rel-
atively higher temperatures than these observed for potato starch,
connected with the degradation of homopolymer is indicated. In
contrast, DSC curves of starch-g-copolymers show two endother-
mic signals. The first was the result of the degradation process of
starch in copolymers. This signal was shifted to lower tempera-
tures as compared to potato starch. Probably, it was due to the
losing of crystalline structure of starch during gelation and graft-
ing and thus forming amorphous copolymer (Pathania & Sharma,
2
012; Singh, Tiwari, Pandey, & Sigh, 2006). In addition, lower degra-
dation temperature of graft copolymers may also be due to the
partial degradation of starch during grafting process which causes
the formation of starch fragments and thus copolymers with lower
polymerization degree. The second peak was indicated at temper-
atures similar to degradation temperature of homopolymer. As it
To determine the degradation path of starch-g-copolymers in
alkaline conditions, the FTIR spectra of the remaining residue after
chemical resistance studies were performed. The example FTIR
spectra of grafted copolymer before and after chemical resistance
in NaOH are presented in Fig. 6. The obvious differences between
initial and base treated samples for 5 days with NaOH are observed.
The disappearance of the characteristic signals responsible for the
is seen, the enthalpy of decomposition (ꢀH ), marked as an area
2
under endothermic peak, increases as grafting percent increases.
It additionally confirmed the preparation of starch-g-copolymers
with different grafting percent. It is worth noting that the glass
transition temperature of copolymers was higher as compared to
glass transition temperature of homopolymer (Table 7). It can be
explained by the formation of modified starches with lower chain
mobility and thus with more stiff structure compared to the struc-
ture of homopolymer due to the covalent bonding of polymeric
chains containing methyl and phenyl groups onto starch backbone.
In addition, the changes in Tg values additionally confirmed that
the grafting process was successful and resulted in obtaining new
polymeric materials.
−1
stretching vibrations of OH groups (3200–3550 cm ) and for the
−1
stretching vibration of C
O
C groups (998–1190 cm ) in graft
copolymer after base resistance studies was observed. However,
all characteristic signals for grafted phenyl methacrylate polymer
were indicated on FTIR spectra. This confirms that the base degra-
dation of graft copolymers happened through the breaking of new
formed
O C bonds during the radical copolymerization process
of starch and phenyl methacrylate molecules, causing the release of
starch and graft polymer molecules. The released starch molecules
are gelatinized completely in base conditions, but graft polymer is
high resisted to base conditions and it is remained as a residue.

M. Worzakowska, M. Grochowicz / Carbohydrate Polymers 130 (2015) 344–352
351
a
a
b
b
6
00
1100
1600
2100
2600
3100
3600
6
00
1100
1600
2100
2600
3100
3600
-
1
Wavenumber/cm
-
1
Wavenumber/cm
Fig. 6. FTIR spectra of starch-g-copolymer (a) G = 43.2 ± 0.4%, and starch-g-
Fig. 8. FTIR spectra of starch-g-copolymer (a) G = 43.2 ± 0.4%, and starch-g-
copolymer after chemical decomposition in NaOH (b).
copolymer after chemical decomposition in HCl (b).
starch backbone was visible (Fig. 8). Those results confirmed that
during the acid resistance studies, the gradual decomposition of
grafted copolymers is happened, but the acid degradation process
of copolymers is slower as compared to acid degradation process
of potato starch.
4. Conclusions
The novel, amphiphilic starch-g-poly(phenyl methacrylate)
copolymers with different grafting percent depending on the
reaction conditions in the form of white powders under graft
copolymerization process of phenyl methacrylate monomer onto
gelatinized potato starch using potassium persulphate as radical
initiator were obtained. The chemical modification of hydrophilic
potato starch backbone by hydrophobic methacrylate monomer
caused preparing the copolymers with completely different prop-
erties than properties of potato starch. The copolymers are
insoluble in polar and non-polar solvents, even in DMSO where
the dissolution of potato starch was observed. However, due to
their amphiphilic surface properties and porous structure, the
copolymers swell in polar and non-polar solvents. As the grafting
percent increased, the swelling properties of starch-g-poly(phenyl
methacrylate) copolymers in polar solvents and the moisture
absorbance decreased but the swelling properties in non-polar
solvents, acid and base resistance of copolymers increased with
increasing the grafting percent as compared to potato starch.
In addition, as a result on the covalent bonding of hydropho-
bic monomer onto starch backbone, the changes in gelatinization
properties, glass transition temperature and thermal stability of
copolymers as compared to non-modified potato starch were
observed. It may be concluded that novel starch-g-poly(phenyl
methacrylate) copolymers due to better properties like higher sta-
bility in acidic and basic environment, higher moisture resistance,
lower swelling in polar solvents and higher swelling in non-polar
solvents compared to potato starch can be valuable materials for
practical applications. They can find their place as stabilizers, fillers,
modifiers, plastics or matrices for specific drug-delivery systems.
Fig. 7. Effect of grafting on acid resistance.
It can be concluded, that this base resistance method could be
successfully used for the determination of grafting percentage of
studied copolymers, since the high agreement of the data obtained
by the use of the equation 3 and this method is confirmed.
The results of acid chemical resistance of potato starch,
poly(phenyl methacrylate) and starch graft copolymers are pre-
sented in Fig. 7. The results show that the obtained graft copolymers
are more acid resist than potato starch. The weight loss of potato
starch in acid was ca. 80%, however the weight loss of graft copoly-
mers was dependent on grafting percent. As the grafting percent
is increased, the weight loss of copolymers in acid conditions is
decreased. The weight loss of graft copolymers was from ca. 40%
for grafting percent 43.2 ± 0.4 to almost ca. 51.2% for grafting per-
cent 13.8 ± 0.2%. The greater resistance of grafted copolymers than
potato starch toward acid can be due to the blocking of hydroxyl
groups on the starch backbone by hydrophobic polymer chains
which resulted in less affinity of grafted copolymers than potato
starch for acid degradation.
The FTIR spectra of starch-g-copolymers before and after acid
resistance show only small reduction in intensities of the sig-
nals characteristic for the stretching vibrations of OH groups
−
1
(
3200–3550 cm ) and for the stretching vibration of C
O
C
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