A Pilot study on the Flexural properties of vinyl ester composites filled
with glass powder
H Ku
1, a
, M Trada
1,b
and R Huq
1,c
1
Faculty of Engineering and Surveying, University of Southern Queensland, West Street, 4350,
Australia
a
ku@usq.edu.au
b
Tradam@usq.edu.aumail,
c
rezwanul.huq@gmail com
Keywords: Flexural strength, flexural strain, flexural modulus, vinyl resin and glass powder.
Abstract.
Vinyl ester resin was filled with of glass powder with a view to increasing the flexural strength of the
composites for civil and structural applications by a research Centre on composites, University of
Southern Queensland (USQ). In order to reduce costs, the Centre wishes to fill as much glass powder
as possible to the resin subject to maintaining sufficient strength of the composites in civil and
structural applications. This project varies the percentage by weight of the glass powder in the
composites, which are then subjected to flexural tests. The flexural strength and strain of the glass
powder filled vinyl ester composites decreased with increasing filler content but the flexural modulus
was highest at 20 w/t % of glass powder. Scanning Electron Microscope (SEM) was used to analyze
the fractured samples and it was found that the fractured surfaces examined were correlated with the
flexural properties.
Introduction
The most common thermosets used as composite matrices are unsaturated polyesters, epoxies and
vinylesters. Unsaturated polyesters dominate the market, whereas epoxies are preferred in
high-performance applications. Unsaturated polyester offers an attractive combination of low price,
reasonably good properties, and simple processing. However, basic unsaturated polyester
formulations have drawbacks in terms of poor temperature and ultra-violet tolerance. Additives may
significantly reduce these disadvantages to suit most applications. Where mechanical properties and
temperature tolerance of unsaturated polyesters no longer suffice, epoxies are often used due to their
significant superiority in these respects. Of course, these improved properties come at a higher price
and epoxies are used most commonly in areas where cost tolerance is highest [1].
Epoxy vinyl ester
range of resins (vinyl ester resins) was developed in the 1960s [2]. Vinyl esters (VE), as they are
usually called, are closely related chemically to both unsaturated polyesters and epoxies and in most
respects represent a compromise between the two. They were developed in an attempt to combine the
fast and simple crosslinking of unsaturated polyesters with the mechanical and thermal properties of
epoxies [1]. This research project is to investigate the flexural strength, maximum flexural strain and
flexural modulus of vinyl ester composites reinforced with varying percentage by weights of three
types of glass powder with a view to finding out the most effective amount of glass powder in
strengthening the composites.
Vinyl ester resins and their crosslinking
The polymerization product between methacrylic acid and bishphenol A is vinyl ester, which can be a
highly viscous liquid at room temperature or a low melting point solid, depending on the bishphenol
A used. For further processing, the polymer is dissolved in a low molecular monomer, or reactive
dilutent, usually styrene, the result is a low viscosity liquid referred to as resin. With the addition of a
small amount of initiator to the resin the crosslinking reaction, or curing, is initiated. The initiator
used is an organic peroxide, e.g. methyl ethy ketone peroxide (MEKP). The added amount is usually
1 to 2 percent by volume. The peroxide decomposes after it is added to the resin and the reaction is
exothermic. The initiator is a molecule that producers free radicals. The free radical attacks one of
the double bonds on the ends of the polymer and bonds to one of the carbon atoms, thus producing a
new free radical at the other carbon atom, which illustrates the whole crosslinking process. This
newly created free radical is then free to react with another double bond. Since the small monomer
molecules, the styrene molecules, move much more freely within the resin than the high molecular
weight polymer molecules, this double bond very likely belongs to a styrene molecule. The bridging
step creates a new free radical on the styrene, which is then free to react with another double bond and
so on. Health concerns with vinyl esters are considered synonymous with the most common
crosslinking agent, the styrene, and not with the resins themselves. Styrene is volatile and evaporates
easily and becomes an inhalation hazard. The reported levels that cause a specific acute reaction vary
widely, partly because tolerance is individual and depends on build up, and partly because reactions
are subjective. At concentrations in the range of 20-100 parts per million (ppm), styrene is a mild,
temporary irritant to eyes and respiratory tract. Above 200 ppm styrene is a definite irritant causing
central nervous system depression, and above 500 ppm it is a severe irritant.
Glass powder
The glass powder used is SPHERICEL® 60P18 which are hollow glass spheres are used for
enhancing performance and reducing viscosity in paints and coatings and as lightweight additives in
plastic parts. They are chemically inert, non-porous, and have very low oil absorption. Hollow
Spheres are now widely used in diverse applications such as industrial explosives and as performance
additives for the refractory and ceramic industries. Typical properties of the spheres are shown in
Table 1 [3].
Table1: Typical properties of hollow glass spheres
Table 2: Flexural strength, maximum flexural strain and
flexural modulus of vinyl ester composites filled with
Sphericel 60P18 glass spheres
* by extrapolation # standard deviation
Results and discussions
Ray et al. filled FB-701 vinyl ester resin of Ruia Chemicals with fly ash particles [5]. It was found
that the addition of fly ash particles decreased the flexural strength of the composites. Due to weak
matrix/filler interaction, the filler did not accommodate the deformation force much. The value was
minimum when the particulate loading was 30% and then increased gradually with more particulate
loading because the smaller particles could now occupy the interstitial spaces, and consequently
increasing the surface area of contact and hence the flexural strength [4]. The flexural strength of
neat resin was 85.02 MPa and dropped to 32.89 MPa when the particulate loading was 30% but
increased steadily to 45.98 MPa and 52.83 MPa for the 40 and 50 w/t % loaded composites
respectively. At 60 % by weight of filler, the flexural strength decreased again. At such a high filler
Mechanical
properties
Percent by
weight of glass
powder
0*
10
20
30
Flexural strength (MPa)
86.22
59.53
(5.55)
39.22
(5.90)
31.02
(3.07)
Maximum flexural strain (%)
2.64
2.00
(0.29)
1.43
(0.24)
0.98
(0.09)
Flexural modulus (GPa)
3.55
2.95
(0.20)
2.76
(0.24)
3.13
(0.27)
Glass powder type
SPHERICEL® 60P18
Shape
Spherical
Colour
White
Composition
Proprietary Glass
Density
0.6 g/cc
Particle Size
18 microns
Hardness
6 (Moh’s Scale)
Chemical Resistance
Low alkali
leach/insoluble in water
Crush Strength
>10,000 psi
Flexural strength of VE/Sphericel 60P18
0
20
40
60
80
0% 10% 20% 30% 40%
Glass powder by weight
Flexural strength (MPa)
Flexural strength
(Sphericel 60P18)
Flexural strength of glass reinforced phenolic composite
15
20
25
30
35
0 5 10 15 20 25 30
Percentage by weight of glass powder
Flexural strength (MPa)
Figure 1: Flexural strength of Sphericel 60P18 filled Figure 2: Flexural strength of varying percentage
vinyl ester composites with varying percentage by by weight of glass powder reinforced phenolic resin
weight of glass powder.
loading, the resins was not enough to encapsulate the fly ash particles completely, leading to the
generation of a large number of voids, which reduced the strength. They not only reduced the stress
bearing areas but also acted as stress raisers, initiating the cracks [4]. Auad et al. found that the
flexural strength of neat divinyl ester resin (DVES) was 88.18 MPa, which was also not far from that
obtained by Ray et al [5]. They modified the flexural properties of divinyl ester resin with carboxyl
terminated poly (butadiene-co-acrylonitrile) (CTBN) and vinyl terminated poly
(butadiene-co-acrylonitrile) (VTBN) respectively. It was found that for both types of rubber, the
flexural strengths increased slightly up to 5 % by weight of modifiers. They then dropped either
moderately for VTBN modified composites or drastically for CBTN modified composites. For
VTBN modified composite, the flexural strength increased again after 7.5 % by weight of reinforcer
[5].
Figure 1 shows the flexural strength of Sphericel 60P18 filled epoxy composites. By extrapolation, it
can be found that the flexural strength of neat resin in this study was 86.22 MPa which was a little bit
higher than that found by Ray et al. but a bit lower than that found by Auad et al. but not much. It can
therefore be argued that it is pretty accurate. The values of the flexural strength then dropped
progressively with increasing particulate loading, up to 30 % by weight of particulate, as those in Ray
et al.‘s case. It can be argued that when the particulate loading was increased to over 30 % by weight,
the flexural strength in this study would climb to a maximum and then dropped back as in Ray et al.’s
study. Moreover, Ku et al. discovered a similar trend when phenolic resin was reinforced with
varying percentage of Sphericel 60P18, glass powder as depicted in Figure 2 [6]. Sen and Nugay
observed similar behaviour for the tensile strength of fly ash filled polyester composites and
concluded that the presence of voids and the formation of air bubbles were responsible for the
lowering of the strength [7]. Table 2 shows the flexural strength, strain and modulus of Sphericel
60P18 glass spheres filled vinyl ester composites with varying particulate loading and standard
deviations. Figure 3 shows the flexural modulus of glass powder filled epoxy composites. The trend
of the values of the flexural modulus was the same with that of this study and that of Ray et al.. The
minimum value of flexural strength occurred at 15 % by weight of particulate loading; it then rose
back to a maximum at 30 w/t % of filler before dropping down with higher particulate loading [8].
Figure 4 is the SEM image of 10% by weight of Sphericel 60P18 filled vinyl ester composite and the
amount of porosity in the specimen was quite low due to the abundance of vinyl ester resin, which in
turn gave it a high flexural strength.References
Conclusions
This study has evaluated the flexural strength, strain and modulus of varying percentages by weight of
glass powder reinforced vinyl ester resin. The flexural strength values of glass spheres decreased with
Flexural modulus of glass powder reinforced
epoxy composites
1000
1750
2500
3250
0 5 10 15 20 25 30 35
Pecentage by weight of glass powder
Flexural modulus
(MPa)
Figure 3: Flexural modulus of glass powder filled Figure 4: SEM image of 10% by weight of
epoxy composites Sphericel 60P18 filled VE composite, 200 X
increasing particulate loading. The values of the flexural strain had the same trend as that of flexural
strengths. On the other hand, the flexural moduli dropped slowly to a low value at 10 to 20 percent by
weight of filler but then rose steeply to a value higher than that of neat resin at around 50 % particulate
loading but then dropped back with further particulate loading. It can be argued that when the fusion
between vinyl resin (matrix) and glass powder (reinforcer) is improved by adding some other filler,
e.g. barium sulfate and other resins to the composites, its flexural strength and modulus will be
improved.
References
[1] Astrom, B T, Manufacturing of polymer composites, Chapman and Hall, UK, 1997:74-83, 432-4.
[2] Pritchard, G (Editor), Reinforced plastics durability, Woodhead publishing Ltd., UK,
1999:282-93.
[3] Potters Industries, undated,
http://www.pottersbeads.com/markets/polySphericel.asp <viewed on 14 August 2009>
[4] Ray, D, Bhattacharya, D, Mohanty, A K, Drzal, L T and Misra, M, Static and dynamic mechanical
properties of vinyl ester resin matrix composites filled with fly ash, Macromolecular Materials and
Engineering, Vol. 291, pp. 784 – 792 (2006).
[5] Auad, M L, Frontini, P M, Borrajo, J and Aranguren, M I, Liquid rubber modified vinyl ester
resins: fracture and mechanical behaviour, Polymer, 2001, Vol. 42, pp. 3723 – 3730.
[6] H Ku, M Trade, R Nixon and P Wong, Flexural properties of phenolic resin reinforced with glass
powder: preliminary results, Journal of Applied Polymer Science, 2009 (accepted for publication).
[7] Sen, S and Nugal, N, Uncured and cured state properties of fly ash filled unsaturated polyester
composites, Journal of Applied Polymer Science, 2000, Vol. 77, Issue 5, pp.1128 – 1136.
[8] Ku H, Wong, P, Huang, J, Fung, H and Trada, M, Flexural Properties of Epoxy Composites filled
with glass powder: Preliminary Results, Journal of Applied Polymer Science, 2009 (submitted for
publication).
Glass powder
Porosity
Vinyl ester resin