Publication: Development of waterborne epoxyacrylate core-shell emulsion for wood coating
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Date
2024-02-01
Authors
Lee, Eyann
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
With the rise of environmental awareness, the waterborne coating has been
widely developed and researched. Due to the potential of wood furniture in the market,
the coating for wood application is worth to be developed. Thus, in this thesis, the
waterborne epoxy acrylate (WEA) core-shell emulsions have been developed for the
wood coating. The emulsions were successfully synthesized through semi-continuous
emulsion polymerization using the poly (Butyl acrylate (BA)- Methyl methacrylate
(MMA)) as the seed emulsion. To achieve a WEA emulsion with stable stability and
small particle size, the properties of seed emulsion were studied. Due to the limited
knowledge of the effects of surfactant (Tween 80) and monomer (BA and MMA) on
the properties of seed emulsion, the effects of surfactant (1, 2, and 3 g) and monomer
(5, 10, and 15 g) amount were studied. The hydrodynamic diameter (Dh) is reduced
with the monomer amount and increases with the surfactant amount. While the zeta
potential (ζ) reduces with the surfactant amount but is unaffected by the monomer
amount. Then, with the limited studies on the effect of epoxy (EP) in the WEA, the
study on the epoxy (EP) amount (0, 2.5, 5, 7.5, and 10 g) in the core layer of the WEA
was conducted. Surprisingly, the change in EP amounts in the core layer shows
significance to the properties of the shell layer. The glass transition temperature (Tg)
of the shell layer was increased with the EP amounts (up to 69 °C). It is because of the
formation of interlayer crosslinking that provides high crosslinking density (up to 7.01
-4
× 10
-3
mol cm
) with high EP amounts. Therefore, by increasing the EP amount, the
thermal stability and mechanical properties, especially the elastic modulus (E) of the film, were significantly improved (up to 489 MPa). However, a high EP amount will
lead to poor shelf-life and resistance to acid. Lastly, to study the impacts of crosslinkers
on the stability of the WEA emulsion, the crosslinking systems on the WEA were
investigated. It was found that the shelf-life of the WEA emulsion was affected by the
reaction between the oxirane ring of the EP with the water molecules instead of the
crosslinking systems or the crosslinker. Besides, The incorporation of the methacrylic
acid (MAA) could improve the heterogeneity between the two layers, allowing them
to show two Tg. Furthermore, the interlayer crosslinking is achieved by adding the
MAA to the shell layer; in contrast, the intralayer crosslinking happens when MAA is
added at the core layer. The interlayer crosslinking improves the compatibility between
two layers and causes high crosslinking density density (up to 7.01 × 10
-4
-3
mol cm
).
Therefore, the film has a compact structure with high E (489 MPa) and low water
absorption (7.13 %). However, the intralayer crosslinking leads to poor compatibility
between the layers and results in layer separation. Thus, the film has high elongation
at break (213 %) with low E (0.38 MPa). The loose structure also causes the film to
have a high water absorption (51.25 %) and poor water resistance. It is believed that
the findings from this thesis can provide more information for future researchers to
develop an outstanding WEA core-shell emulsion for wood coating.