Description:
(Meth)acrylate functional monomers can be used to address the
growing concerns over the use of styrene monomer in unsaturated
polyester (UPR) and vinyl ester (VE) gel coats and fiberglass
reinforced polymer (FRP) resins for composite applications.
Government environmental regulations and worker health concerns
continue to drive the styrene content of gel coats and FRP resin
systems down in open mold spray-up and hand lay-up processes.
Styrene emissions
can be reduced through resin modification or by the use of wax
suppressants, but both methods typically result in inferior
performance properties. A more positive approach to reduced
styrene emissions is by replacement of styrene with higher molecular
weight specialty (meth)acrylate monomers. Table 1 describes
the monomers studied.
Table 2 below shows
a standard industry isophthalic UPR gel coat formulation cured
with a metal drier promoter and a peroxide initiator. The above
variety of (meth)acrylate functional monomers were evaluated
as partial replacements for styrene monomer to reduce emissions,
while maintaining hardness and physical properties.
Figure 1 plots the
volatile emissions measured by Southern California Air Quality
Management District (SCAQMD) Rule 1162 test method and the gel
time measured by SPI method, respectively, for the (meth)acrylate
monomer-modified and conventional high styrene gel coat formulations.
The (meth)acrylate monomer-modified gel coats exhibit a reduction
in volatile emissions of 6% (using SR239), up to as much as
43% (using SR350). All of the (meth)acrylate monomer-modified
gel coats exhibit gel times within 15-35 minutes. The gel coat
formulated with SR239 exhibits a slightly higher gel time, and
the gel coat formulated with SR206 exhibits a significant reduction
in gel time.
Figure 2 plots the
60° gloss retention and the yellowness index increase after
2000 hrs Q-U-V exposure. Gloss retention was measured using
a Byk Gardner Glossmeter and yellowness index was measured by
a Byk-Gardner Color Sphere using the ASTM E313 test method.
Table 3 below compares
an industry standard DCPD/styrene-based UPR laminating/casting
resin and a (meth)acrylate-modified, styrene-free DCPD-based
UPR laminating/casting resin for use in FRP composite fabrication.
The (meth)acrylate-modified, styrene-free resin exhibits a slightly
higher viscosity and slightly longer gel time, but it is still
sprayable and still gels within the desired 25 – 35 minute range.
In terms of physical properties, the (meth)acrylate-modified,
styrene-free resin exhibits similar hardness and tensile properties
and a significant increase in flexural strength (15,100 psi
versus 8,900 psi).
