MATEC Web of Conferences 30, 0 3 01 0 (2015)

DOI: 10.1051/ m atec conf/ 201 5 3 0 0 3 0 1 0


C Owned by the authors, published by EDP Sciences, 2015

Combination of Tung oil and Natural Rubber Latex in PVA as Water Based
Coatings for Paperboard Application
1,a 2 3
Apichaya Jianprasert , Pathavuth Monvisade and Masayuki Yamaguchi
1
College of Nanotechnology, King Mongkut’s Institute of Technology Ladkrabang, Thailand
2
Polymer Synthesis and Functional Materials Research Unit, Department of Chemistry, Faculty of Science,
King Mongkut’s Institute of Technology Ladkrabang, Thailand
3
School of Materials Science, Japan Advanced Institute of Science and Technology, Japan

Abstract. This research is focused on the preparation of the PVA/TO/NRL coatings for paperboard by using
poly(vinyl alcohol) (PVA) as substance and blending with Tung oil (TO) and/or natural rubber latex (NRL) in order
to enhance water resistance and dynamic mechanical properties. The effects of TO: NRL ratios on the structures
were investigated by water resistance property and dynamic mechanical thermal analysis (DMA). The results showed
that the water resistance property was improved by crosslinking of TO and film forming of NRL. The PVA/TO/NRL
coating containing both TO and NRL gave better thermal behavior than those with only TO or NRL. For paperboard
application, the PVA/TO/NRL coatings were applied on the paperboard to study water affinity and absorption rate on
the coated surface. The rate of contact angle change of water on coated paperboards decreased depending on the
ratios of TO and NRL.

1 Introduction PVA/TO/NRL coatings was also investigated. Finally,

the PVA/TO/NRL coatings were applied on paperboard
Coating & Laminate technologies are the regular in order to study water affinity and absorption rate by
stage for protection of the surface of wood and contact angle measurement of water tests.
paperboard products[1]. Among various coating
polymers, PVA is an important water-soluble synthetic
polymer, which has been widely used as coating agents 2 Experimental
[2,3]. However, it has poor resistance to water. To
improve the water resistance property, PVA blends with 2.1 Preparation and characterization of
other hydrophobic polymer have been focused. Natural PVA/TO/NRL coatings
rubber latex (NRL), a natural high elasticity material, is
widely used in the manufacture of thin film products [4]. The PVA solution (15 wt%) in PVA/TO/NRL coatings
Although the NRL provides better water resistance, it was fixed at 85 % by weight. Natural rubber latex (NRL)
must be vulcanized by sulphur or peroxide system with and/or Tung oil (TO) was added to the PVA solution with
high temperature (>100 qC). Tung oil (TO), a drying oil, the weight ratios of (NRL:TO) 15:0 (R15T0), 10:5
is alternatively used as environment-friendly coating for (R10T5), 5:10 (R5T10) and 0:15 (R0T15) under
decades because it can crosslink to a solid film rapidly continuous mixing to obtain a homogeneous mixture.
after exposure to air at even room temperature[5,6]. Redox catalyst (potassium persulfate and sodium
Although TO can crosslink at lower curing temperature, thiosulfate) was then filled into the mixture and stirred
it is relatively expensive and its crosslinked form is more vigorously for 15 min. The PVA/TO/NRL coatings were
brittle than that of NRL. Combination of NRL and TO is later cast into the Petri dish and dried at 50 qC in an oven.
an easy way to improve water resistance of PVA The thickness of the PVA/TO/NRL coating sheets
including the reduction in curing temperature. Therefore measured at five different points using a micrometer was
this work aims to create a water-based coatings based on approximately 300±50 Pm. After that PVA/TO/NRL
PVA. TO and/or NRL at various NRL:TO ratios were coatings were characterized by FTIR and DMA.
applied in the coatings. Moreover, redox catalytic system,
a couple of potassium persulfate (KPS) and sodium
2.2 Water resistance of PVA/TO/NRL coatings
thiosulfate[7,8], was also used to lowering curing
temperature for crosslinking reaction. The effects of The PVA/TO/NRL coating sheets were cut into a
NRL:TO ratios in PVA/TO/NRL coatings were studied rectangular shape (1.5x2 cm). Each of the specimens was
by FTIR and DMA. The water resistance property of
a
Corresponding author: kjapitch@gmail.com

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Article available at http://www.matec-conferences.org or http://dx.doi.org/10.1051/matecconf/20153003010

 MATEC Web of Conferences

Figure 1. FTIR spectra of PVA/TO/NRL coatings using various NRL:TO ratios

Figure 2. Solid remain (%) of PVA/TO/NRL coatings using various NRL:TO ratios after immersion in water at 25 qC for 24 h.

weighed and immersed in water for 24 h. Finally, the recording the contact angle change of a water drop with
specimen was dried to constant weight in an oven. The time within 300 s at room temperature.
percentage of solid remains was calculated as follows:
% Solid remain= (W2/W1)×100 (1) 3 Results and Discussion
Where W1 is the dry weight (g) before immersion in
3.1 FTIR characterization
water and W2 is the dry weight (g) after immersion in
water for 24 h. The FTIR spectra of PVA/TO/NRL coatings as a function
of NRL:TO ratios are shown in Fig. 1. The -C=C-H
2.3 Initial contact angle and dynamic change of vibration in the structures of TO and NRL was allowed to
contact angle follow the formation of crosslinking reaction. For R0T15,
the pattern of the characteristic peaks related to -C=C-
The contact angle of water on the surface and dynamic H vibrations of TO (3012 cm-1 for -C=C-H stretching,
contact angle change of coated samples were measured 992 cm-1 for conjugated trans: trans -C=C-H bending
with a contact angle analyzer (model OCA 20, and 965 cm-1 for conjugated cis: trans -C=C-H bending)
Dataphysics instruments) at room temperature. A [9] disappeared. It implies that the crosslinking network
distilled water drop of ca. 30 PL was placed on surfaces in the films would occur via the addition reaction at the
of the uncoated or coated samples using micro-syringe. double bonds of TO. On the contrary, R15T0 still
Dynamic contact angle change was measured by showed characteristic peaks corresponding to

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Figure 3. Temperature dependence of (a) storage modulus (E’), and (b) tan G of PVA/TO/NRL coatings

not crosslink at relatively low curing temperature. The

double bonds of NRL at 3036 cm-1 (-C=C-H stretching) combination of TO and NRL in the coatings displayed a
and 741 cm-1 (-C=C-H bending). It is suggested that the high level of E’ compared to R15T0 and R0T15. This
crosslinking reaction at double bonds of NRL did not phenomenon was due to the crosslinked structures of TO
predominate. In case of R10T5 and R5T10, only the within the PVA/TO/NRL coatings resulting to enhancing
characteristic peaks of TO depleted whereas those of storage modulus. In addition, the intensities of tan G peak
NRL remained, suggesting that the crosslinking reaction of PVA in PVA/TO/NRL coatings with higher TO
of TO was predominant. content exhibited a depression trend compared to that of
the R15T0 coating because of the increase in network
3.2 Water resistance of PVA/TO/NRL coatings chain by the crosslinking reaction.

The water resistance of the coating adhesive was

investigated in terms of the % solid remain as shown in 3.4 Initial contact angle and dynamic change of
Fig.2. Considering to NRL and TO structures, they have contact angle
hydrophobic structures. Thus the addition of NRL and/or The water contact angle of the uncoated paperboard, and
TO could improve the water resistance of PVA. As coated paperboard with PVA/TO/NRL coatings was
observed in Fig.2, the % solid remain values of R15T0 investigated. An uncoated paperboard showed water
were higher than that of neat PVA. In addition, the contact angle of 105.2 ± 8.2q. In case of the coated
presence of TO dramatically increased the % solid remain paperboard, the initial contact angles of water were in the
values compared with those of neat PVA and R15T0.
range of 59.6-104.7q lower than that of the uncoated
This is because TO could crosslink to be the network
paperboard. The lower level in water contact angle by
structures at the conjugated double bonds of TO through
PVA/TO/NRL coatings indicates the higher wetting
free radical mechanism[10]. Therefore, PVA and NRL
ability due to the change in the chemical compositions on
chains were retained within the crosslinked TO structures.
the surface. Moreover, the synergy of TO and NRL in
This caused PVA and NRL in R10T5, R5T10 and R0T15
coating adhesive presented the relatively high in water
to have more difficulty to dissolve in water than R15T0.
contact angle, especially when R5T10 was applied. It is
reasonable because TO and NRL are hydrophobic
3.3 Mechanical thermal property of PVA/TO/NRL structures and the crosslinked TO resisted to water
coatings absorption.
The rate of contact angle change (k) of water on
The tan G and storage modulus (E’) of PVA/TO/NRL paperboards decreased from 0.095 s-1 of the uncoated
coatings in various NRL:TO ratios were investigated by paperboard to the range of 0.045-0.069 s-1 of the coated
DMA, as shown in Fig. 4(a) and (b), respectively. The T g paperboards. A slightly decrease in the k values pointed
of PVA in PVA/TO/NRL coatings increased with at better water barrier of the surface because of chemical
increasing TO content. This is because when TO compositions of PVA/TO/NRL coatings. The results
crosslinked, NRL and PVA chains were retained within demonstrated that all PVA/TO/NRL coatings can modify
the crosslinked TO structures resulting in the restriction the surfaces of paperboards to yield better water affinity
movement of NRL and PVA chains. In case of E’, the with lower absorption rate.
storage modulus of R15T0 showed the lowest value than
that of other PVA/TO/NRL coatings because NRL could

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4 Conclusion References
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This work was financially supported by the Royal Golden Eng. J. 153, 199–205 (2009)
Jubilee Ph.D. Program, Thailand Research Fund and the 9. Y. Wang, Q. Wang, W.E. Artz, G.W. Padua, J. Agr.
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