SAMPE Journal - March/April 2023 - 32

FEATURE / THERMOSET RESINS AND PERFORMANCE
Glass transition temperatures were determined
by dynamic mechanical analysis. The samples
were measured with the TA instruments DHR-2
Rheometer along with the three-point bending
test fixtures. The oven was purged with nitrogen
during the analyses. Tg
determination: the sample
was scanned in dynamic temperature ramp mode,
from 25°C to 200°C at a heating rate of 2°C/minute
and using a dynamic oscillation frequency of one
hertz. The shore D hardness was conducted with a
Shore D durometer. The boiling water absorption
test was conducted by immersing the samples in
boiling water and measuring the weight gain after
24 hours.
RESULTS AND DISCUSSION
Resin Properties and Reactivity
Four DTO vinyl ester resins of GM-175, GM-200,
GM-225 and GM-250 were successfully developed
and characterized. These novel DTO vinyl ester
resins are considered " green " materials: styrenefree,
monomer-free, 100% solids, zero VOC's,
and high bio-contents. The viscosity of the DTO
derived vinyl resins were measured by a Brookfield
viscometer model LV, Spindle #2 @ 20 RPM at 25°C
and the volatile contents were measured at 125°C
oven for 15 minutes. As shown in Table 1, they are
liquid at room temperature, bio-content ranged
from 54% to 66%, and viscosity was in the range of
360 - 4530 cps.
Four formulated DTO vinyl ester resins of
1250, 1260, 1270, and 1280 were prepared. The
room temperature gel time (RTG), cure time
(RTC) and peak exothermic temperature (RTP)
were determined at 25°C using 1.25% MEKP
Table 1. Basic properties of DTO vinyl ester resins.
Sample ID
GM-175
GM-200
GM-225
GM-250
Bio-content
(%)
56
54
64
66
Acid Number
(mg KOH/g)
7
7
12
11
NV (%) Viscosity @ 25°C
(cps)
100
100
100
100
Table 2. Basic properties of formulate DTO vinyl ester resins.
Sample ID
1250
1260
1270
1280
Bio-content
(%)
28
27
32
33
Styrene
(%)
7.5
7.5
7.5
7.5
Viscosity
(cps)
1410
3680
1410
3780
RTG
(min)
4.0
4.5
5.0
9.5
RTC
(min)
9.0
9.5
4.0
3.5
RTP
(o
C)
111
81
116
122
360
2090
410
4530
initiator and 0.15% Cobalt (15%) and 0.15%
N, N-dimethylaniline (DMA) as promoters. As
shown in Table 2, the formulated DTO vinyl ester
resins of 1250, 1260, 1270 and 1280 have a biocontent
of 27% - 33%, very low styrene content of
7.5%, reasonable viscosity and good reactivity at
room temperature that are suitable for reinforced
composite processes and applications.
Figures 1 & 2 list SPI gel time (SPIG), cure time
(SPIC) and peak exothermic temperature (SPIP)
for the formulated DTO vinyl ester resins of 1250,
1260, 1270 and 1280. The SPI gel time (SPIG), cure
time (SPIC) and the peak exothermic temperature
(SPIP) were determined at 82.2°C using 1.0%
Benzyl Peroxide (BPO) as initiator. As seen from
these Figures, the DTO vinyl ester resins have fast
cure at elevated temperature.
Figure 1. SPI gel time and cure time of DTO vinyl
ester resins.
32 | SAMPE JOURNAL | MARCH APRIL 2023
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SAMPE Journal - March/April 2023

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