SCIENCE JOURNAL
Ubonratchathani University
Sci. J. UBU, Vol. 1, No. 1 (January-June, 2010) 51-57
http://scjubu.sci.ubu.ac.th
Research Article
Paper Coating with Biodegradable Polymer for Food
Packaging
S. Shawaphun1,2*, T. Manangan1,2
1
Department of Industrial Chemistry, Faculty of Applied Science, King Mongkut’s
University of Technology North Bangkok, Bangkok 10800, Thailand.
2
Research Centre of Nano Industries and Bio-plastics, King Mongkut’s University of
Technology North Bangkok, Bangkok 10800, Thailand.
Received 24/12/09; Accepted 17/05/10
Abstract
Commodity plastics are widely used for food packaging. However, their slow degradation and
predicted exhaustion of the world petroleum reserves have become worldwide major environmental
concerns. Therefore, it is necessary to quickly replace them with biodegradable polymers that can
degrade in a short period when exposed to a biologically active environment. The possibility for the
use of biopolymers, such as poly-3-hydroxybutyrate (PHB) and polylactide (PLA), in paper coating
for food packaging has been investigated in this study. Dip coating process has the potential of
providing an easy and economical way to form PHB and PLA coated layers on paper. The effects of
dip coating operating parameters such as initial concentrations of polymer solution, types of solvent,
types of paper and dipping periods have been investigated in this study. The dip-coated PHB and PLA
papers were analyzed by gravimetric analysis and ATR-FTIR spectroscopy. The results showed that
the polymer film weight also increased, as the polymer initial concentration and dipping period
increased, and then reached the equilibrium state at the polymer initial concentration of 4%w/v and
the dipping period of 5 minutes. By varying types of solvent, chloroform and dichloromethane gave
almost the same satisfactory result for PHB dip coating while ethyl acetate provided the optimal result
for PLA. By using different types of paper, the commercial bleached bagasse paper (Beermat®)
showed the most satisfactory results with the maximum adsorbed capacity of 122.9 and 99.3 mg/g for
PHB and PLA coated paper, respectively. Generally, most coated papers showed better barrier
properties against air, water, and oil than the non-coated paper. However, the PHB coated paper
showed higher water resistance but lower oil resistance than PLA coated paper.
Keywords: Biodegradable plastic, PHB, PLA, Food packaging, Paper coating.
*Corresponding author. E-mail address: sarinya73@yahoo.com
Copyright  2010 Faculty of Science, Ubon Ratchathani University. All Rights Reserved.
Paper Coating with Biodegradable Polymer for Food Packaging
52
1. Introduction
Growing public concern about global warming and environmental pollution caused by
accumulation of commodity plastic wastes
has widely stimulated the development and
design of environmental friendly food containers and packages [1]. Pulp and paper are
renewable and versatile materials that also
have been used for food containers and packages [2]. However, critical required characteristics of food contact packaging are their
barrier properties especially against gas,
water and grease [3]. Typically, paper provides low barrier properties against these kinds
of molecules due to its porosity structure.
Therefore, the common approach is to improve its barrier properties by coating a thin
layer of materials [4]. Currently, wax and
polyethylene film are used to give the paper
containers and packages the desired properties, but they also cause undesired properties,
non-recyclable and non-degradable [5-7].
Among starch based and other synthetic
degradable plastics, two commercial biodegradable polyesters, polyhydroxyalkanoate
(PHA) and polylactide (PLA), have gained
ultimate attention in the past 10 years due to
the environmental concerns and sustainable
issues [8-9]. They have many potential uses,
including many applications in the textile
[10], the medical industries [11], as well as in
the packaging industries [12-13] due to their
various superb properties such as biodegradability, biocompatibility, good mechanical properties and proper degradation rate
[14]. In general, paper can be coated for
various decorative and functional purposes
by using water borne, organic solvent borne,
and solvent-free extruded materials. However, coating paper via organic solvent borne
or water borne coating materials is considered to be more economical based on using
less coating materials than solvent-free
extruded materials and easier to apply onto
the paper or paper food containers in Industrial scale production base on they can be
applied onto any surface shape by using dip
coating technique which is one common
techniques used in paper coating industry.
This technique is performed by dipping a
substrate into a reservoir of polymer
solution for some period of time, and then
with-drawing the substrate form the solution
bath [15]. Based on this technique, the
effective coating will be much dependent on
the ad-sorption process of polymer from
solution during dipping period. Thus, some
condition parameters, types of coating
materials and types of paper have to be
maximized to get the highest adsorption of
polymer onto the paper. Although, there are
some attempts to coat PLA or PHA onto
paper via using organic solvent borne or
water borne to improve the barrier properties of paper while making paper biodegradable and recyclable [16]. However,
there are still some limited data on the
adsorption study of these bio-polyesters
from solution or suspension onto the cellulose paper. Thus, the aim of this work was
to study some parameters that can affect the
coating performance of these biodegradable
polymers onto paper as well as the properties of paper before and after coating. These
findings give insight into the way to improve coating ability of PHB and PLA onto
the paper while improving the barrier properties of paper for using in food packaging.
2. Theory
Polymer adsorption is the process by which
the polymer molecules diffuse from the bulk
of the solution towards the solid/liquid
inter-face and attaches to it. Once attached
to the surface, polymer molecules undergo a
sub-sequent conformational rearrangement
(i.e. spreading process). They change their
coiled shapes to find the set of conformations at the interface which minimizes their
free energy [17]. It is well known that the
adsorption performance of polymer in
liquid-phase adsorption depends on the following factors: nature of the polymer (e.g.
chemical structure, MW, MWD, flexibility),
quality of the adsorbent (e.g. surface functional groups, surface porosity), process
variables (contact time, initial concentrate-
Copyright  2010 Faculty of Science, Ubon Ratchathani University. All Rights Reserved.
S. Shawaphun et al., Sci. J. UBU, Vol. 1, No. 1 (January-June, 2010) 51-57
53
ion), and the quality of the solvent (e.g. Adsorption Isotherm. The commercial bleapolarity, functional group) [18].
ched bagasse papers were cut into the
rectangular shape with the size of 1 cm x 6
cm. Then it was immersed into the PHB or
3. Materials and Methods
PLA solution at specified polymer concentration (0, 2, 4, 6, 8, 10%w/v) in chloroMaterials. A commercial grade of poly-3hydroxy butyrate (PHB) was obtained from form. After 20 minutes of dipping period,
Tianan Biological Material Co. Ltd. (Ningbo, the paper was then withdrawn from the
solution bath at a withdrawal velocity of
Chaina) and poly-L-lactide (PLA) was
obtained from Natureworks LLC (America). 1.95 mm/s. After taken out from the
then it was dried in the oven at 80
Some physical properties of PHB and PLA solution,

C
for
at
least
2 hours or until all the solvent
used in this study were shown in Table 1.
was
completely
evaporated. The coated
Chloroform (analytical grade), dichlorometpaper
was
then
quantified
the amount of
hane (analytical grade), ethylacetate (analypolymer
adsorbed
by
using
gravimetric
tical grade) were purchased from Sigma
analysis
or
ATR-FTIR
technique.
Aldrich. Commercial bleached bagasse paper
with the brand name Beermat® (700 gram or
g/m2) and drawing paper (270 gram or g/m2)
were purchased from the local bookstore.
Homemade bleached bagasse paper (490
gram or g/m2) was kindly provided from the
Department of Science Service, Thailand.
Table
PLA.
Type
PHB
PLA
Solvent Quality Effect. The commercial
bleached bagasse paper cut into the
rectangular shape with the size of 1 cm x 6
cm was immersed into PHB and PLA
solutions (8%w/v) in various solvents:
chloroform, dichloromethane or ethyl acet1. Physical properties of PHB and ate. After 20 minutes of dipping period, the
paper was then withdrawn from the solution
bath at a withdrawal speed of 1.95 mm/s.
After dried in the oven at 80 C for at least 2
Mv
[] in
Tm (C)
hours or until all the solvent was completely
CHCl3
evaporated, the coated paper was then quan1.4967
286,000
164.15
tified the amount of polymer adsorbed by
2.1828
86,000
140.08
using gravimetric analysis.
Adsorption Study.
Adsorption Kinetic. The commercial bleached bagasse paper was cut into the rectangular
shape with the size of 1 cm x 6 cm. Then it
was immersed into the PHB or PLA solution
at 4% w/v concentration in chloroform and
kept an uncoated area on the top. After
required contact time (0, 5, 10, 15, 20, 25
minutes), the paper was then withdrawn from
the solution bath at a withdrawal speed of
1.95 mm/s. After taken out from the solution,
then it was dried in the oven at 80 C for at
least 2 hours or until all the solvent was
completely evaporated. The coated paper was
then quantified the amount of polymer adsorbed by using gravimetric analysis.
Paper Quality Effect. Commercial bleached
bagasse paper (Beermat®), homemade bleached bagasse paper and drawing paper were
cut into the rectangular shape with the size
of 1 cm x 6 cm. Then they were individually
dip- coated with the PHB and PLA solutions
(6%w/v) in chloroform same as above. The
coated papers were then quantified the
amount of polymer adsorbed by using gravimetric analysis.
Characterization Methods.
Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR).
ATR-FTIR spectrometer (Perkin Elmer
spectrum 2000) was used to examine the ad-
Copyright  2010 Faculty of Science, Ubon Ratchathani University. All Rights Reserved.
54
Paper Coating with Biodegradable Polymer for Food Packaging
sorption of PHB and PLA onto the paper.
The peak of C=O stretching at the wave
number of 1645-1670 cm-1 which belongs to
polyester was expected. Then, the peak area
of this peak was integrated to quantified
amount of polyester adsorbed on the paper in
comparison with the non-coated paper.
Gravimetric Analysis. The adsorbed amount
of coated polymer film on paper was determined by weighing the paper before and after
coating and then calculated the film weight
by using the following formula
Film weight (g) = W2 – W1
(1)
Where, W1 and W2 represent the weights (g)
of paper before and after coating, respectively.
4. Results and Discussion
Adsorption Kinetic. Contact time is an important parameter in adsorption process.
Generally, the adsorption of polymer by adsorbent becomes higher on prolonging the
contact time. However, in practice, it is
necessary to optimize the contact time,
considering the efficiency of coating process. From the results in Figure 1, the kinetic adsorption curve was initially very fast
then slowly reached equilibrium after 5
minutes, where no additional polymer
molecule was adsorbed onto paper. During
this process, the paper surface is progressively blocked by the polymer molecules,
until the surface is completely covered by
polymer molecule.
Liquid Absorptiveness Test (Cobb Method).
Cobb method is used to determine the
absorptiveness of papers to some liquids (e.g.
water and oil) base on measuring the amount
of liquid penetration into a sheet of paper.
The definition of Cobb value for the sizing
degree is the calculated mass of water absorbed in a specified time by m2 of material
under specified conditions. Cobb tests performed in this work were based on ISO535.
Air Resistance Test (Gurley Method). Gurley
method is used to determine the air resistance
of approximately 6.4 cm2 (1 inch2) circular
area of paper using a pressure differential of
approximately 3 kPa. Gurley method performed in this work was based on ISO/CD56365.
Smoothness Test (Bekk Method). Bekk method is used to determine the smoothness of
individual surfaces of paper by measuring air
leakage under a clamping pressure of 100
kN/m2 and using an anvil with an effective
area of 10.00 ± 0.05 cm2. Bekk method
performed in this work was based on ISO5627.
Figure 1. The adsorbed amount of PHB and
PLA films adsorbed on the paper plotted
with dipping period.
Adsorption Isotherm. As shown in Figures 2
and 3, the amount of the polymer adsorbed
onto paper increased with the increase of
initial concentration of polymer solutions.
This is due to the increase in the driving
force of the concentration gradient with the
higher initial polymer concentration. The
shapes of adsorption isotherms in both
figures look very similar and they were
composed of 2 stages; the first stage showed
a steep increase in the adsorbed polymer
(indicating a great affinity of the adsorbent
for the polymer), followed by the second
stage (reaching equilibrium state) which
represented a gradually increase of adsorbed
Copyright  2010 Faculty of Science, Ubon Ratchathani University. All Rights Reserved.
S. Shawaphun et al., Sci. J. UBU, Vol. 1, No. 1 (January-June, 2010) 51-57
polymer. The gradually increase during the
second stage might be due to surface heterogeneous (porosity) on cellulose paper and the
interaction between the adsorbed polymer
molecules. Thus, this result was indicated
multilayer coverage of polymer adsorption
onto paper at the equilibrium state.
55
the adsorbed amount of PHB onto the paper.
However, by changing of solvent from chloroform to ethyl acetate caused significant
effect on the adsorbed amount of PLA onto
the paper. Since, chloroform is a better
solvent for PLA than ethyl acetate, thus the
interaction force between PLA and chloroform is stronger than the interaction force
between PLA and ethyl acetate. Consequently, PLA in chloroform is more difficult
to adsorb onto the paper than PLA in ethyl
acetate.
Figure 2. The adsorbed amount of PHB and
PLA films on the paper quantified by using
film weight plotted with initial concentration
of polymer solution.
Figure 4. The adsorbed amount of PHB and
PLA films on the paper as a function of
solvent used to prepare polymer solution.
Figure 3. The adsorbed amount of PHB and
PLA films on the paper quantified by using
the carbonyl peak area plotted with initial
Figure 5. The adsorbed amount of PHB and
concentration of polymer solution.
PLA film on the paper as a function of types
Solvent Quality Effect. To investigate the of paper used.
effect of solvents on the adsorption performance of PHB and PLA, three different types
of solvent including chloroform, dichloromethane and ethyl acetate have been used in
this study. As shown in Figure 4, the change
of solvent from chloroform to dichloromethane did not cause the significant effect on
Paper Quality Effect. The paper quality effect was performed adsorption experiment by
using three different types of paper including commercial bleached bagasse paper
(bagasse-®), homemade bleached bagasse
Copyright  2010 Faculty of Science, Ubon Ratchathani University. All Rights Reserved.
Paper Coating with Biodegradable Polymer for Food Packaging
56
paper (bagasse) and drawing paper (drawing).
As shown in Figure 5, the commercial bleached bagasse paper (bagasse®) gave the
optimum result for both PHB and PLA dip
coating and provided the maximum adsorption capacity of PHB and PLA at 122.9 and
99.3 mg per g of paper, respectively. This
might be due to the commercial bleached
bagasse paper is smoother and contained less
porosity when comparing with homemade
bleached bagasse paper and drawing paper,
thus it contains more site for polymer to
adsorb. Therefore, the polymer molecule
tends to adsorb more on this type of paper.
Characterization of Coated Paper. According to the results in Table 2, both PLA and
PHB coated paper showed the improvement
in barrier properties against air, water and
grease when compared with the non-coated
(bare) paper. Water and oil absorptiveness
based on Cobb test for PLA and PHB coated
papers are significantly decreased. The Cobb
values of water absorptiveness for coated
paper showed the decrease from 1351.3 g/m2
to 83 g/m2 and 43.7 g/m2 in PHB and PLA
coated paper, respectively. Further-more, the
oil absorptiveness of paper after coating
showed the decrease of Cobb values from
1.5 g/m2 to 0.3 g/m2 and 0.1 g/m2 for PHB
and PLA coated paper, respectively. These
result suggested that PHB and PLA can
improve water and oil resistance to the
paper base on their chemical structures
which are not too hydrophilic or hydrophobic and their large structures which can
enhance their ability to patch up the pores
on the paper. However, PLA coated paper
seemed to absorb more water than PHB
coated paper, but PHB coated paper seemed
to absorb more oil than PLA coated paper,
this might be due to the chemical structure
of PHB that is a little bit more hydrophobic
than that of PLA. In addition, all coated
papers showed the increa-se of air resistance
from 35.5 sec/100 mL to 145.6 sec/100 mL
and 140.6 sec/100 mL for PHB and PLA
coated paper, respectively. Furthermore, the
surface of paper after coating also became
smoother when compared with bare paper
for both PLA and PHB coated papers,
possibly, because the polymers can help to
patch up some pores and heterogeneous
structure on the paper surface after coating.
Table 2. Smoothness and barrier properties of coated and non-coated papers.
Test
Smoothness (sec.bekk)
Air Resistance (sec/100mL)
Water absorptiveness (g/m2)
Oil absorptiveness (g/m2)
Bare paper
3
35.5
1351.3
1.5
5. Conclusions
The adsorption of PHB and PLA solutions in
organic solvent onto the surface of paper has
been studied by using gravimetric analysis
and ATR-FTIR spectroscopy. The adsorption
rate experiments indicated that the adsorption
of both PHB and PLA was very quick and
reached the equilibrium state after 5 minutes
PHB coated paper
4
145.6
83
0.3
PLA coated paper
4
140.5
43.7
0.1
of dipping period. Adsorption isotherms of
PHB and PLA solutions in chloroform
revealed that polymer can adsorb very
strong to the paper, but the adsorbed layers
of these polymers tended to get multilayer
adsorption at very high initial concentraions
based on interaction between polymer molecules. Commercial bleached bagasse paper
(Beermat®) seemed to have the highest
Copyright  2010 Faculty of Science, Ubon Ratchathani University. All Rights Reserved.
S. Shawaphun et al., Sci. J. UBU, Vol. 1, No. 1 (January-June, 2010) 51-57
affinity to both polymers possibly due to less
porosity structure than the homemade
bagasse paper and drawing paper. Replacing
chloroform with ethyl acetate for solvent
showed a significant effect in PLA adsorption. All of coated papers showed satisfactory
improvement of barrier properties towards
air, water and oil. Barrier properties against
air for PHB and PLA coated papers are
almost the same. PHB coated paper showed
better water barrier property than the PLA
57
coated paper. However, the PLA coated
paper showed slightly better oil barrier
property than the PHB coated paper.
Acknowledgements
The author would like to thank the department of Science Service for providing the
homemade bleached bagasse paper used in
this study.
References
[1] Chiellini, E. (2008). Environmentally
compatible food packaging. Cambridge:
Woodhead.
[2] Kirwan, M.J. (2005). Paper and paperboard
packaging technology. Oxford: Blackwell.
[3] Kaplan, D.L. (1998). Biopolymers from
renewable resources. Heidelberg: SpringerVerlag.
[4] Berube, S. (2002). Repulpable Chlorine free
barrier coating for packaging materials. US
6,441,080.
[5] Stark, D. E. (1999). Repulpable moisture
vapor barrier. US 5,897,411.
[6] Daniels, C.L., Bott, R.H., Halat, J.J., Rabaso,
J.J., & Jones, R. B. (2005). Polymer emulsion
coatings for cellulosic substrates with improved barrier properties. US20,050,014,013.
[7] Lee, R.A., Hutchinson, G.A., & Klass, C.P.
(2004). Process for coating paper, paperboard, and molder fiber with a water-dispersible polyester polymer. US20,040,131,871.
[8] Schuman, T., Adolfsson, B., Wickstrom, M.,
& Rigdahl, M. (2005). Surface treatment
and printing properties of dispersion-coated
paperboard. Prog. Org. Coating , 54 , 188-97.
[9] Moggridge, G.D., Lape, N.K., Yang, C., &
Cussler, E.L. (2003). Barrier films using
flakes and reactive additives. Prog. Org.
Coating, 46, 231-40.
[10] Gupta, B., Revagade, N., & Hilborn, J.
(2007). Poly(lactic acid) fiber: an overview.
Prog .Polym. Sci., 32, 455-82.
[11] Zhu, K.J., Xiang zhou, L., & Shilin, Y.
(1990). Preparation, characterization, and
properties of polylactide (PLA)-poly(ethyl-
ene glycol) (PEG) copolymers: a potential
drug carrier. J. Appl Polym. Sci., 39, 1-9.
[12] Bucci, D.Z., Tavares, L.B.B., & Sell, I.
(2005). PHB packaging for the storage of
food products. Polymer Testing, 24, 564-71.
[13] Auras, R., Harte, B., & Selke, S. (2004). An
overview of polylactides as packagaing
materials. Macromol. Biosci., 4, 835-64.
[14] Vink, E.T.H., Rabago, K.R., Glassner, D.A.,
& Gruber, P.R. (2003). Application of life
cycle assessment to natureworks polylactide
(PLA) production. Polym. Degrad. Stab.,
80, 403-19.
[15] Fang, H., Li, K., Su, T., Yang, T.C., Chang,
J., Lin, P., & Chang, W. (2008). Dip coating
assisted polylactic acid deposition on steel
surface: Film thickness affected by drag
force and gravity. Materials Letters, 62,
3739-41.
[16] Erkske, D., Viskere, I., Dzene, A., Tupureina, V., & Savenkova, L. (2006). Biobased
polymer composites for films and coatings.
Proc.Estonian Acad. Sci. Chem., 55, 2, 707.
[17] Fleer, G.J., Stuart, C.M., Scheutjens, J.M.,
Cosgrove, T., & Vincent, B. (1993). Polymers at Interfaces, London: Chapman and
Hall.
[18] Chornaya, V.N., Todosiichuk, T.T., Menzheres, G.Y., Lipatov, S.Y., & Maslak, V.Y.
(2008). Effect of flexibility of polymer
chains on the kinetics of adsorption of polymer mixtures from solutions. Colloids and
Surfaces A: Physicochem. Eng. Aspects,
318, 53-61.
Copyright  2010 Faculty of Science, Ubon Ratchathani University. All Rights Reserved.