Materials Characterization of High-Temperature Epoxy 

Resins: SC-79 and SC-15/SC-79 Blend 

by Michael L. Wang, Ian M. McAninch, and John J. La Scala 

ARL-TR-5484 March 2011 

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Army Research Laboratory 

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ARL-TR-5484 March 2011 

Materials Characterization of High-Temperature Epoxy 

Resins: SC-79 and SC-15/SC-79 Blend 

Michael L. Wang and Ian M. McAninch 

Oak Ridge Institute for Science and Education 

John J. La Scala 

Weapons and Materials Research Directorate, ARL 

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Materials Characterization of High-Temperature Epoxy Resins: SC-79 and 

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14. ABSTRACT 

The relatively low glass transition temperature (Tg) of the Army’s SC-15 epoxy resin system necessitates study into suitable 

alternative resins capable of better low- and high-temperature performance. This work investigates two of those alternative 

resins, SC-79 and CCMFCS2, a blend of SC-15 and SC-79, both manufactured by Applied Poleramic Inc. (Benicia, CA). The 

viscosities and gel times of these resins are similar to SC-15’s, thus substitution of the SC-15 with SC-79 or CCMFCS2 would 

cause no processing issues. Several different curing cycles were tested for each resin in an effort to find the best process for 

U.S. Army applications. Three slow cure cycles showed no meaningful advantages over faster, elevated temperature cures. 

Under all tested cure conditions, both SC-79 and CCMFCS2 are able to achieve higher Tg’s and similar or greater flexural 

properties than SC-15; however, SC-15’s fracture and impact properties were superior. 

15. SUBJECT TERMS

epoxy, resin, composite 

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Ian M. McAninch 

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Contents 

List of Figures iv

List of Tables v

Acknowledgments vi

1. Introduction/Background 1

2. Experiment 2

2.1 Materials and Resin Formulation ....................................................................................2

2.2 Resin Characterization ....................................................................................................3

2.2.1 Rheology .............................................................................................................3

2.2.2 Differential Scanning Calorimetry ......................................................................3

2.2.3 Dynamic Mechanical Analysis (DMA) ...............................................................4

2.2.4 Flexural Testing ...................................................................................................4

2.2.5 Fracture Toughness .............................................................................................5

2.2.6 Izod Impact Testing .............................................................................................5

2.2.7 SEM Characterization .........................................................................................5

3. Results 6

3.1 Rheology Analysis ..........................................................................................................6

3.2 Differential Scanning Calorimetry Analysis ...................................................................6

3.3 DMA Analysis .................................................................................................................7

3.4 Flexural Results Analysis ..............................................................................................12

3.5 SEM Characterization ...................................................................................................13

3.6 Fracture Toughness Analysis ........................................................................................16

3.7 Izod Impact Testing .......................................................................................................18

4. Discussion 20

5. Summary and Conclusions 21

6. References 23

Distribution List 25
iv 

List of Figures 

Figure 1. Storage and loss moduli of SC-79 post-cured at 121 °C (heavy line) and 177 °C 

(light line)...................................................................................................................................9

Figure 2. SC-79 cycle 1 after water immersion (heavy line) compared to SC-79 cycle 1 dry 

(light line)...................................................................................................................................9

Figure 3. Storage and loss moduli of CCMFCS2: cycle 1 (heavy line) and cycle 6 (light 

line). .........................................................................................................................................11

Figure 4. Storage and loss moduli curves for SC-15. ...................................................................11

Figure 5. SEM image of SC-15 with the second toughened phase present at (A) 5000× and 

(B) 10,000× magnification. ......................................................................................................13

Figure 6. SEM images of SC-79 cycle 1 (A and B) and cycle 2 (C and D) at 5000× and 

10,000× magnification. ............................................................................................................14

Figure 7. SEM of CCMFCS2 cycle 1 (A and B), cycle 2 (C and D), and cycle 3 (E and F) at 

5000× and 10,000× magnification. ..........................................................................................15

Figure 8. SEM images of CCMFCS2 cycle 4 (A and B), cycle 5 (C and D), and cycle 6 (E 

and F) at 5000× and 10,000× magnification. ...........................................................................16

Figure 9. Impact resistance of notched samples. ..........................................................................18

Figure 10. Impact resistance of unnotched samples. ....................................................................19

Figure 11. Tg vs. fracture toughness (K1c); increasing symbol size corresponds to increasing 

cycle number. ...........................................................................................................................20

Figure 12. Strength vs. flexural modulus; increasing symbol size corresponds to increasing 

cycle number. ...........................................................................................................................21
v 

List of Tables 

Table 1. SC-79 cure cycles. ............................................................................................................2

Table 2. CCMFCS2 cure cycles. .....................................................................................................3

Table 3. Initial viscosities and time to reach 5000 cP at processing temperatures. ........................6

Table 4. Extent of cure by DSC. .....................................................................................................7

Table 5. DMA results summary. ...................................................................................................10

Table 6. Flexural properties of SC-79 and CCMFCS2. ................................................................12

Table 7. Fracture property summary. ............................................................................................17
vi 

Acknowledgments 

This research was supported in part by an appointment to the Postgraduate Research 

Participation Program at the U.S. Army Research Laboratory (ARL) administered by the Oak 

Ridge Institute for Science and Education through an interagency agreement between the U.S. 

Department of Energy and ARL. 
1 

1. Introduction/Background 

Composite materials are of high importance to the U.S. Army because they can be made lighter 

and stronger than their metallic counterparts. These materials are finding their way into 

everything from personal body armor and vehicle frames for ballistic protection to panels for 

structural support. Lighter loads mean more fuel economy, greater mobility, and less fatigue on 

the troops in the field. But it is also important that these materials be strong enough to satisfy 

their primary mission, be it a structural or ballistic resistance application. 

SC-15 is a high-performance resin being considered for a number of Army composite 

applications. SC-15 is a toughened commercial vacuum-assisted resin transfer molding 

(VARTM) resin produced by Applied Poleramic Inc. (API) (Benicia, CA). It is a low-viscosity, 

two-phase toughened epoxy cured with a cycloaliphatic amine. This resin system was designed 

to work very well in VARTM processes and has good damage resistance in structural and 

ballistic applications. However, the relatively low glass transition temperature (Tg) of ~95 °C 

(1) has limited its use in many U.S. Army applications. Yet, other properties of this resin are 

excellent, including high resin and composite modulus, strength, toughness, and interlaminar 

shear strength (2). Therefore, the Army has been looking into using higher Tg resin systems that 

otherwise are similar to that of SC-15. Two candidate resin systems include SC-79 and 

CCMFCS2, both supplied by API. 

SC-79 is a low-viscosity, two-phase toughened, cycloaliphatic amine–cured commercial 

VARTM resin system designed to be easy to handle and have a long processing window for 

large part assembly. According to the technical specification sheet, this resin has a Tg of 

~145–165 °C for the low-temperature cure cycle and 170–194 °C for the high-temperature cure 

cycle (3). 

CCMFCS2 is a blend of SC-15 and SC-79. As expected, this blend is a toughened low-viscosity 

epoxy resin, capable of VARTM composite manufacture. The technical specification sheet 

states a Tg of 130 °C (4). 

While both SC-79 and CCMFCS2 are stated to have higher Tg’s than SC-15, there are potential 

issues with the use of these resins. First, the technical data sheet for SC-79 list two potential cure 

schedules. To select the ideal cure schedule for U.S. Army applications, the effects of the cure 

schedule on morphology and thermal and mechanical properties must be determined. Second, 

the CCMFCS2 resin is recommended to be cured for 16–32 h at room temperature (RT) prior to 

a post-cure at an elevated temperature (4). This cure time is exceedingly long and can lead to 

processing problems including air leaks and high void fractions, as well as low production rates. 

Also, the RT cure schedule is unusual considering that the two resins it is composed of have 

recommended cures at 60 °C. However, modifying the cure schedule can have a deleterious 
2 

effect on the properties of resins, especially phase-separating toughened systems. Thus we 

evaluated the various cure schedules and characterized the mechanical properties of the resulting 

resins by characterizing the resins’ rheological, calorimetric, dynamic mechanical, flexural, 

fracture, impact, and morphological properties and comparing the results to those of SC-15. 

2. Experiment

2.1 Materials and Resin Formulation 

According to SC-15’s technical specification sheet (5), the resin is to be mixed thoroughly in a 

100:30 resin-to-hardener (R:H) ratio by weight and then cured at 60 °C for 2 h before an 

additional post-cure of 4 h at 93.3 °C. For ease of processing and the purpose of this study, the 

post-cure cycle was changed to 100 °C for 3 h. 

According to the specification sheet (3), SC-79 is mixed at a 100:40 R:H ratio by weight, cured 

at 60 °C for 4 h, and then post-cured at either 121 °C or 177 °C for 1 h (table 1), depending on 

the desired properties. The 121 °C cure was designed to meet Boeing Material Specification 

8–79, 8168, 219, and to have better mechanical performance, especially “after hot-wet 

conditioning” with only slightly lower fracture toughness than the qualified pre-preg. In this 

study we investigated both cure cycles to evaluate their mechanical properties after each cycle. 

Table 1. SC-79 cure cycles. 

Cure 

Schedule Cure Post-Cure 

Cycle 1 Ramp 10 °C/min to 60 °C, hold for 4 h Ramp 10 °C/min to 121 °C, hold for 1 h 

Cycle 2 Ramp 10 °C/min to 60 °C, hold for 4 h Ramp 10 °C/min to 177 °C, hold for 1 h 

The blend of SC-15/SC-79 VARTM resins, CCMFCS2, is recommended to be mixed in a 

100:37.5 R:H ratio by weight (4). The suggested cure is 16–32 h at RT, with a post-cure 

consisting of a ramp of 1 °C/min to 121 °C. For the purpose of this study, the cure was 

standardized to a 24-h cure before a post-cure ramp of 1oC/min to 121 oC. Because the 24-h RT 

cure is not an ideal production cure schedule, an alternate cure cycle of 60 °C for 4 h was also 

tested. In addition to the recommended post-cure cycle, two additional post-cure cycles were 

tested; a 1 °C/min ramp to 145 °C followed by 2 h at 145 °C and a 1 °C/min to 

177 °C followed by 1 h at 177 °C. Samples were made in all combinations of cure and postcure cycles (table 2). 
3 

Table 2. CCMFCS2 cure cycles. 

Cure 

Schedule Cure Post-Cure 

Cycle 1 Hold for 24 h at RT Ramp 1 °C/min to 121 °C, hold for 4 h 

Cycle 2 Hold for 24 h at RT Ramp 1 °C/min to 145 °C, hold for 2 h 

Cycle 3 Hold for 24 h at RT Ramp 1 °C/min to 177 °C, hold for 1 h 

Cycle 4 Ramp 10 °C/min to 60 °C, hold for 4 h Ramp 1 °C/min to 121 °C, hold for 4 h 

Cycle 5 Ramp 10 °C/min to 60 °C, hold for 4 h Ramp 1 °C/min to 145 °C, hold for 2 h 

Cycle 6 Ramp 10 °C/min to 60 °C, hold for 4 h Ramp 1 °C/min to 177 °C, hold for 1 h 

2.2 Resin Characterization 

2.2.1 Rheology 

Viscosity and gel times of the curing resins were measured on a TA Instruments AR-2000 

Rheometer at 25 °C and 60 °C with the temperature controlled by a Peltier plate. A parallel plate 

geometry with a 40-mm plate and a gap distance of 1000 m was used for all the samples. 

Immediately prior to measurement, each resin was blended in the proper ratios and thoroughly 

mixed. Viscosity was then measured as a function of time at a shear rate of 1 s–1 and the shear 

stress was measured every 2 s. The viscosity was measured until the sample viscosity exceeded 

5000 cP or until 300 min had past. A repeat run was performed for all the samples. The reported 

viscosity is an average of the first plateau region, generally the first 5 min of data or less if a 

noticeable viscosity change occurred. 

2.2.2 Differential Scanning Calorimetry 

A TA Instruments Q1000 differential scanning calorimeter (DSC) was used to measure the heat 

of reaction during the various cure cycles and determine the extent of cure. Approximately 

10 mg of freshly mixed resin was sealed in aluminum hermetic DSC pans. Each heating ramp 

tested corresponds to an experimental cure cycle, as mentioned before, with additional steps to 

measure any residual cure. The general DSC procedure is as follows: 

1. A heat ramp of 10 °C/min from 25 °C to the cure temperature followed by an isothermal 

hold at the cure temperature for its respective curing time. 

2. A heat ramp of 1 °C/min from the cure temperature to its post-curing temperature, 

followed by an isothermal hold for the length of the post-cure cycle. 

3. Heat at a rate of 10 °C/min to 200 °C and hold for 30 min to measure any residual cure 

before cooling down to RT again. 

4. A final ramp of 10 °C/min to 200 °C to verify complete reaction. 
4 

We chose this method to examine the heat of cure during the cure cycle and determine whether 

there is further curing in the resin after being subjected to temperatures above its post-curing 

temperature. The extent of cure, α, can be determined using equation 1 (6): 

tot

resid

Q

Q   1 , (1) 

where Qresid is the residual heat generated during step 3, and Qtot is the total heat of reaction. 

Qtot is difficult to measure because of a shifting baseline from the multiple steps; instead, Qtot

was determined by taking ~10 mg of freshly mixed, uncured sample and measuring the total heat 

during a 5 °C/min ramp from RT to 250 °C. Complete reaction was assumed and an average of 

four runs was used. 

2.2.3 Dynamic Mechanical Analysis (DMA) 

A TA Instruments Q800 dynamic mechanical analyzer with a 35-mm dual cantilever clamp was 

used to characterize the resins’ storage modulus (E’), loss modulus (E’’) peak, and tan δ

maximum temperature. DMA applies an oscillatory strain to the sample and measures its 

material response to that force. Samples had rectangular dimensions of ~60 × 12 × 3 mm. 

Temperature ramps from 25 °C to 200 °C at a rate of 2 °C/min with an oscillation frequency of 

1 Hz and a displacement of 7.5 μm were used for the SC-79. Similarly the CCMFCS2 samples 

were measured at the same frequency and displacement from 25 °C to at least 180 °C while 

SC-15 was tested up to 160 °C. The upper temperature limits were chosen to characterize the 

materials up to and through their Tg’s but not necessarily well beyond. The resins were 

compared on the basis of storage modulus, loss modulus peak(s), and the temperature where the 

maximum occurred in tan δ. The Tg of the material was taken as the temperature where the peak 

of the loss modulus, E”, curve occurred. In the case that multiple peaks exist, as in a phaseseparated system, the higher temperature, or second peak, was taken as the Tg. 

In addition to the dry specimens, wet DMA samples were tested to ascertain the susceptibility of 

these resins to water absorption and characterize how water absorption affects material 

properties. These samples were submersed in 90 °C water for 24 h, after which the samples were 

removed from the water, blotted dry, and then immediately tested using the appropriate DMA 

procedure as described previously. 

2.2.4 Flexural Testing 

Three-point bend resin characterization was performed using an Instron 5500R equipped with a 

5-kN load cell. Both the supports and loading nose had cylindrical surfaces. Testing was done 

according to ASTM standard D 790-03 (7). Samples were cut from cast sheets for flatwise 

testing, with the sample span being 16× (tolerance ±1) the depth of the beam. Specimen depth 

was taken to be the depth at the center of the beam. Nominal sample dimensions were ~75 × 12 

× 4 mm. The rate of crosshead motion was calculated by equation 2. 
5 

d

ZL R

6

2

 , (2) 

where: 

R = rate of crosshead motion (mm/min). 

L = support span (mm). 

d = depth of beam (mm). 

Z = rate of straining of the outer fiber (mm/mm/min). 

For our calculations, procedure B (7) with Z = 0.1 was used. The nominal crosshead speed was 

23.4 mm/min. 

2.2.5 Fracture Toughness 

Fracture testing was performed according to ASTM standard D 5045-93 (8) using the singleedge-notch bending geometry. The resin was cured in a 76- × 89- × 12.7-mm open mold, and a 

notch equal to half the thickness was machined through the entire block with one cut. Individual 

test specimens with nominal dimensions of 89 × 6.4 × 12.7 mm were cut from the block. A fresh 

crack was initiated in the samples immediately before testing by drawing a sharp razor blade 

through the machined notch. Each razor blade was used no more than three times. Samples 

were tested on an Instron testing machine with a crosshead speed of 1.27 mm/min and a span of 

50.8 mm. An unnotched sample was tested according to the standard to account for system 

compliance, loading pin penetration, and sample compression. The fracture surfaces were 

examined for signs of plastic deformation, and any sample with noticeable deformation was not 

included in the results. 

2.2.6 Izod Impact Testing 

Notched Izod impact testing was performed according to ASTM standard D 256-05 (9). 

Samples were made using a mold that contains the notch made to the specified dimensions; this 

prevents microcracking or other damage from occurring if one were to machine the notch. The 

samples were ~63.5 × 12.7 × 12.7 mm, excluding the notch. Unnotched Izod impact testing was 

also performed according to ASTM D 4812-99 (10). Rectangular samples with dimensions of 

~63.5 × 12.7 × 3.17 mm were cut from cast sheets. Both types of samples were tested on an 

Instron POE 2000 using Impulse data acquisition software. 

2.2.7 SEM Characterization 

A JEOL JSM 6460LV scanning electron microscope (SEM) was used to characterize the 

morphology of the resins to compare similarities and differences among curing cycles. These 

morphologies were compared to SC-15. DMA samples were fractured to expose internal 

surfaces. The surfaces were then sputtered with a thin layer of gold using a Denton Desk IV 

sputter coater (Moorestown, NJ). 
6 

3. Results 

Note that all samples, regardless of the cure schedule, were white in color and opaque. Opacity 

is a visible sign of phase separation, where the secondary phase forms domains large enough to 

scatter light, whereas nontoughened resins tend to be transparent (11). 

3.1 Rheology Analysis 

The time to reach 5000 cP was measured and considered to be the gel time, as after that point 

VARTM processing is no longer feasible. Materials with gel times ranging from 45 min to 2 h 

are ideal for Army applications. 

Previous U.S. Army Research Laboratory (ARL) work has verified that SC-15 processes easily; 

the viscosities of SC-15, SC-79, and CCMFCS2 are shown in table 3. All three have similar 

viscosities at 25 °C as well at as 60 °C. The viscosities reported here are slightly higher than 

those reported on the data sheets (3–5), but the differences can be attributed to aging that 

occurred after receipt of the resins. 

Table 3. Initial viscosities and time to reach 5000 cP at processing temperatures. 

Resins 

Initial Viscosity 

at 25 °C 

(cP) 

Time to 5000 cP 

at 25 °C 

(min) 

Initial Viscosity 

at 60 °C 

(cP) 

Time to 5000 cP 

at 60 °C 

(min) 

SC-15 (1) 508 ± 60 301 47 ± 8 73 

SC-79 437 ± 42 300+ 44 ± 8 75 ± 7 

CCMFCS2 449 ± 47 300+ 47 ± 8 66 ± 5 

This work finds that all three resin systems have suitable working viscosities in which VARTM 

processing is practical for Army applications; however, the very slow viscosity increases at RT 

can give rise to problems, such as vacuum leaks during the long RT cure. The cures at 60 °C 

offer a much more useful cure schedule, providing gel times well within the acceptable range. 

Furthermore, all resins had similar gel times at 60 °C, and thus substitution of the SC-15 with 

SC-79 or CCMFCS2 would cause no processing issues. 

3.2 Differential Scanning Calorimetry Analysis 

The total heats of reaction for SC-79 and CCMFCS2 were measured to be 434 ± 17 J/g and 

416 ± 8 J/g, respectively. Using these data and the measured ∆Hresid, we calculated the extents of 

cure for each resin cycle and summarized the results in table 4. 
7 

Table 4. Extent of cure by DSC. 

Cure Schedule ΔHresid 

(J/g) 

Extent of Cure (Cure + PC) 

(%) 

SC-79

Cycle 1 40 90.86 ± 0.35 

Cycle 2 21 95.11 ± 0.19 

CCMFCS2

Cycle 1 13 96.90 ± 0.06 

Cycle 2 4 99.03 ± 0.02 

Cycle 3 6 98.67 ± 0.03 

Cycle 4 10 97.71 ± 0.04 

Cycle 5 3 99.32 ± 0.01 

Cycle 6 2 99.50 ± 0.01 

For cycle 1 of SC-79, the extent of cure is somewhat low at 91%; this is not surprising given that 

the post-cure temperature of 121 °C is well below the maximum Tg of 170 °C reached with the 

177 °C post-cure (3). For SC-79 cycle 2, the 95% extent of cure is more surprising, given that 

the post-cure exceeds the ultimate Tg. Since the resin is toughened, diffusion limitations could 

have trapped the unreacted monomer in its nonpreferred phase, limiting the reaction potential. 

For CCMFCS2 cured at RT (cycles 1–3), raising the post-cure from 121 °C to 145 °C increased 

the extent of cure, while a further increase in post-cure temperature to 177 °C had no significant 

effect. The same trend was seen when the cure temperature was raised to 60 °C (cycles 4–6). 

Thus it can be concluded that 145 °C and higher post-cure temperatures allow for maximum 

mobility of the polymer reactive groups, while 121 °C post-cure is not completely above the 

vitrification temperature of the resin. The extent of cure was slightly higher when cured at 

60 °C, again because of higher mobility of the reactive groups during cure. 

3.3 DMA Analysis 

The SC-15 material properties, as reported on the material specification sheet provided by API, 

lists a Tg of 104 °C and Tg (wet) of 81 °C (5). However, previous ARL work (1) finds that the 

Tg is 95 ± 1.5 °C with a Tg (wet) of 80 °C and a corresponding storage modulus (E’) of 2.5 ± 

0.1 GPa at 30 °C. Our experiments measured a Tg of 95.0 ± 0.7 °C, when the Tg is taken as the 

peak of the E’’ curve and supports ARL’s previous work. The maximum in the tan  was found 

to be 108.3 ± 3.0 °C, which is very similar to the Tg reported by API. The E’ we obtained was 

2.2 ± 0.3 GPa, which is not significantly different from the previous study. 

For the two SC-79 cure cycles, the materials specification sheet from API claims a Tg of 

145–165 °C for the 121 °C cycle and 170–194 °C for the 177 °C cycle (3). It also reports Tg 

(wet) of 110 °C for the 121 °C cycle and 135–160 °C for the 177 °C cycle. Our results for the 

121 °C cycle were 115.1 ± 1.5 °C and 2.6 ± 0.2 GPa for the Tg and 30 °C modulus, respectively. 

A second DMA run of the same samples raised the Tg to 141.7 ± 0.9 °C and the E’ to 2.8 ± 

0.3 GPa. This jump in Tg is the result of additional curing of the sample during the first run. 
8 

This agrees with the DSC results, showing incomplete reaction for the 121 °C cure. For the 

177 oC cycle, the Tg was 152.2 ± 2.5 oC and the storage modulus 2.6 ± 0.1 GPa. A second run 

raised these values to 155.4 ± 5.8 oC and 2.8 ± 0.1 GPa for the Tg and E’, respectively. Here, the 

changes between the first and second DMA runs were minor, reflecting the more complete cure. 

As for the SC-15, the Tg’s specified by API more closely match the temperature of the tan 

maximum. 

In the DMA results for both cure cycles for SC-79, all E’’ curves had a second peak, which 

indicates phase separation of the system, as shown in figure 1. The intensity of the peak varied, 

appearing as only a shoulder in the 121 °C cured samples and as a distinct peak in the 177 °C 

cured samples. The location of the peaks was similar: 69 ± 1 °C for the 121 °C cured samples 

vs. 74 ± 3 °C for the 177 °C cured samples. This secondary peak corresponds to a toughenerrich phase while the main higher-temperature peak corresponds to an epoxy-rich phase. 

Unfortunately, the data sheet does not give details on the nature of the toughener. 

The higher-temperature post-cure allows the resin to more completely phase separate, yet it also 

significantly increases the higher-temperature loss modulus peak by 25 °C. Despite the higher 

Tg of the SC-79 resin post-cured at 177 °C up to ~90 °C, the resin post-cured at 121 °C has a 

similar modulus. For the wet cycle 1 samples, when comparing the dry DMA data to the wet 

DMA data (figure 2), the storage modulus is depressed and there are changes in the loss modulus 

curve. For the wet sample, the lower-temperature loss peak is much more intense than before 

and it occurs 20 °C lower, while the higher-temperature loss modulus peak has increased 10 °C. 

Two mechanisms could explain this behavior. First, the toughening phase could have a higher 

affinity for water than the epoxy phase; however, another study using carboxyl-terminated 

butadiene-acrylonitrile (CTBN)-toughened epoxy showed lower water absorption for toughened 

systems (12). Again, the lack of knowledge of the toughening phase limits insight. Second, the 

24 h at 90 °C in water could give unreacted toughening monomers additional time to phase 

separate from the epoxy phase, or unreacted monomers could leach out from the polymer. 

Similar behavior was seen in a nontoughened epoxy: after 32 h in 80 °C the Tg increased ~5 °C, 

and after longer immersion times, the Tg increased ~15 °C (13). The wet cycle 2 samples had a 

depression of ~10 °C for both loss modulus peaks, and the modulus was lower for all 

temperatures relative to cycle 1. Wet and dry DMA data are summarized in table 5. 
9 

Figure 1. Storage and loss moduli of SC-79 post-cured at 121 °C (heavy line) and 177 °C (light 

line). 

Figure 2. SC-79 cycle 1 after water immersion (heavy line) compared to SC-79 cycle 1 dry 

(light line).

0

500

1000

1500

2000

2500

3000

20 40 60 80 100 120 140 160 180 200

Temperature (°C)

Storage Modulus (MPa)

0

20

40

60

80

100

120

140

160

180

Loss Modulus (MPa)

Cycle 1

Cycle 2

0

500

1000

1500

2000

2500

3000

20 40 60 80 100 120 140 160 180 200

Temperature (°C)

Storage Modulus (MPa)

0

20

40

60

80

100

120

140

160

180

Loss Modulus (MPa)

Wet

Dry
10 

Table 5. DMA results summary. 

Cure Schedule Tg 

Loss Modulus 

Peaks (LM1/LM2)

(°C) 

Max tan δ

(°C) 

Wet Tg 

(LM1/LM2) 

(°C) 

E’ at 30 °C 

(MPa) 

SC-15 (1) 

Single cycle 95.4 ± 1.5 – /95.4 ± 1.5 110.7 ± 1.0 – / 80 2.5 ± 0.1 

SC-79

Cycle 1 115.1 ± 2.0 67.8 ± 1/ 

115.1 ± 2 138.6 ± 1.8 49.3 ± 2.8/ 

125.3 ± 0.4 2.6 ± 0.2 

Cycle 2 152.2 ± 3.0 74.2 ± 3/ 

152.2 ± 3 175.2 ± 4.2 57.0/143.4 2.6 ± 0.1 

CCMFCS2

Cycle 1 119.3 ± 5.4 – /119.3 ± 5.4 137.8 ± 3.0 45.5 ± 4.3/ 

107.0 ± 0.7 2.5 ± 0.1 

Cycle 2 122.3 ± 1.0 – /122.3 ± 1.0 140.6 ± 0.8 56.4 ± 1.4/ 

112.9 ± 0.8 2.3 ± 0.1 

Cycle 3 130.0 ± 0.8 72.1 ± 2.7/ 

130.0 ± 0.8 145.7 ± 0.5 58.3/120.3 2.2 ± 0.2 

Cycle 4 121.4 ± 6.3 68.4 ± 3/ 

121.4 ± 6.3 140.9 ± 3.0 52.8 ± 0.5/ 115.4 ± 1.1 2.1 ± 0.2 

Cycle 5 128.2 ± 1.6 73.7 ± 5.8/ 

128.2 ± 1.6 145.3 ± 0.5 54.7 ± 1.7/ 114.4 ± 5.8 2.5 ± 0.1 

Cycle 6 131.9 ± 3.3 74.7 ± 3.2/ 

131.9 ± 3.3 148.0 ± 2.0 57.9 ± 0.4/ 

122.0 ± 3.6 2.2 ± 0.1 

The datasheet of the blend, CCMFCS2, reported a Tg of 130 °C and a wet Tg of 118 °C for 

cycle 1. This cure cycle resulted in a Tg of 119.3 ± 5.4 °C, a storage modulus of 2.5 ± 0.1 GPa 

at 30 °C, and a maximum in tan δ at 137.8 ± 3.0 °C, again suggesting that the reported Tg is the 

peak of the tan δ curve rather than the loss modulus. Cycles 2 and 3 yielded Tg’s of 

122.3 ± 1.0 °C and 130.0 ± 0.8 °C with storage moduli of 2.3 ± 0.1 GPa and 2.2 ± 0.2 GPa, 

respectively. For the cycles cured using an accelerated time and elevated temperature schedule, 

cycle 4 resulted in a Tg of 121.4 ± 6.3 °C and a E’ of 2.1 ± 0.2 GPa, while cycle 5 had a Tg of 

128.2 ± 1.6 °C and E’ of 2.5 ± 0.1 GPa, and cycle 6 had a Tg of 131.9 ± 3.3 and E’ of 

2.2 ± 0.1 GPa. 

In most of the samples, there is evidence of a second peak similar to SC-79’s phase separation 

(figure 3, light line). This secondary peak occurs around the same temperatures as the secondary 

peak in SC-79, 65–75 °C. In cycles 1 and 2, the secondary peak is only visible as a small 

shoulder on the main peak (figure 3, heavy line). SC-15 does not show a secondary loss peak in 

this temperature range, as illustrated in figure 4, so it is possible that the secondary loss peak in 

the CCMFCS2 is caused by the SC-79 toughener rather than SC-15’s. Yet, SC-15’s lower Tg 

would more likely result in a single, broader glass transition, whereas the larger difference 

between the loss modulus peaks of SC-79 and CCMFCS2 would likely be more visible as 

distinct transitions. 
11 

Figure 3. Storage and loss moduli of CCMFCS2: cycle 1 (heavy line) and cycle 6 (light line). 

Figure 4. Storage and loss moduli curves for SC-15. 

0

500

1000

1500

2000

2500

20 40 60 80 100 120 140 160 180 200

Temperature (°C)

Storage Modulus (MPa)

0

20

40

60

80

100

120

140

160

Loss Modulus (MPa)

Cycle 1

Cycle 6

0

500

1000

1500

2000

2500

3000

30 50 70 90 110 130 150

Temperature (°C)

Storage Modulus (MPa)

0

50

100

150

200

250

Loss Modulus (MPa)
12 

The DMA results show that Tg increases as the post-cure temperature increases. For cycles 1–3, 

the room-temperature-cured samples, there is a small increase in Tg comparing the 121 °C to the 

145 °C post-cured samples; a larger increase occurs between post-cures of 145 and 177 °C. For 

cycles 4–6, the 60 °C cured samples, the largest change occurs between 121 and 145 °C postcured samples, with 177 °C post-cured samples having a similar Tg as the 145 °C post-cured 

samples. These results agree with the DSC results. From table 4, cycles 1 and 4 had the lowest 

extents of cure, which corresponds to the lowest Tg’s. The other four cycles have very similar 

extents of cures, but for small residual heats, the Tg changes can be a more accurate indicator of 

additional cure (14). Overall, the Tg trends agree with the extents of cure from DSC. Table 5 

provides a summary of DMA results for SC-15, SC-79, and CCMFCS2. 

All cycles show similar behavior after immersion in 90 °C water. The Tg was depressed by 

6–14 °C with no trend between the cycles. The secondary loss peak also shifted to lower 

temperatures by 15–20 °C for all cycles. Wet Tg data are also summarized in table 5. 

3.4 Flexural Results Analysis 

The flexural strengths of the resins at various cure conditions are shown in table 6. SC-15 has a 

flexural modulus of 2.8 ± 0.1 GPa, a strength of 110 ± 2 MPa, and a strain at failure of 6.4 ± 

0.3% (1). For SC-79 at 121 °C, we measured a flexural modulus of 2.6 ± 0.1 GPa, a strength of 

106 ± 5 MPa, and a strain at failure of 5.8 ± 0.5%. With the 177 oC cycle, we measured a 

modulus of 3.4 ± 0.1 GPa, a strength of 126 ± 2 MPa, and a strain at failure of 4.9% ± 0.5%. Of 

these flexural results, it appears as though cycle 2 (table 6) has superior performance, with higher 

strength (+20 MPa) and modulus (+800 MPa), with only a 1% reduction in strain at failure. 

Table 6. Flexural properties of SC-79 and CCMFCS2. 

Cure 

Schedule Flexural Strength 

(MPa) 

Flexural Modulus 

(GPa) 

Strain at 

Failure 

(%) 

SC-15 (1) 

Single cycle 110 ± 2 2.8 ± 0.1 6.4 ± 0.3 

SC-79

Cycle 1 106.2 ± 4.7 2.6 ± 0.1 5.8 ± 0.8 

Cycle 2 126.2 ± 2.2 3.4 ± 0.1 4.9 ± 0.5 

CCMFCS2

Cycle 1 105.8 ± 2.6 2.4 ± 0.1 7.4 ± 0.8 

Cycle 2 121.9 ± 7.4 3.0 ± 0.0 6.8 ± 1.8 

Cycle 3 119.5 ± 7.8 2.9 ± 0.2 6.1 ± 0.9 

Cycle 4 109.2 ± 6.6 2.6 ± 0.1 5.9 ± 0.9 

Cycle 5 110.9 ± 5.0 2.6 ± 0.1 6.4 ± 0.8 

Cycle 6 120.6 ± 1.7 2.7 ± 0.1 6.6 ± 0.4 
13 

CCMFCS2 cycle 1 resulted in a flexural modulus of 2.4 ± 0.1 GPa, a strength of 106 ± 3 MPa, 

and a strain at failure of 7.3 ± 0.7%, while cycle 2 resulted in a flexural modulus of 3.0 ± 

0.0 GPa, a strength of 122 ± 7 MPa, and a strain at failure of 6.8 ± 1.8%. Cycle 3 resulted in a 

flexural modulus of 2.9 ± 0.2 GPa, a strength of 119 ± 8 MPa, and a strain at failure of 6.1 ± 

0.9%. These results show that cycle 1, in addition to having the lowest Tg, also has the lowest 

flexural modulus and strength due to its lowest extent of cure. Cycle 2 is preferred to cycle 3, as 

both have essentially the same properties consistent with the similar extent of cure and 

thermomechanical properties, but cycle 2 uses a lower post-cure temperature. Cycles 4 and 5 

both had flexural moduli of 2.6 ± 0.1 GPa, while cycle 6 had a flexural modulus of 2.7 ± 

0.1 GPa. Their strengths were 109.2 ± 6.6, 110.9 ± 5.0, and 120.6 ± 1.7 MPa, respectively. 

Their strains at failure were 5.9 ± 0.9%, 6.4 ± 0.8%, and 6.6 ± 0.4%, respectively. In addition to 

having the highest Tg for the CCMFCS2 cycles, cycle 6 also has the highest flexural modulus 

and strength. Table 6 gives a summary of the flexural results for SC-15, SC-79, and CCMFCS2. 

Comparing the data in tables 5 and 6, we see that SC-79 cycle 2 has the highest overall strength, 

modulus, and Tg, but it also has the lowest strain at failure by 1%–2%. CCMFCS2 cycle 6 is the 

second best with similar strength and better strain at failure, but with a lower modulus and a 

substantially lower Tg (20 °C lower than SC-79 cycle 2). 

3.5 SEM Characterization 

The extent and size of phase-separated domains were characterized using SEM. Figure 5 shows 

the phase separation in SC-15 at 5000 and 10,000× magnification. The toughening phase 

appears to be around 0.5–1 μm in size. Figure 6 shows the phase separation of SC-79 for both 

cycles. Again, the second phase is ~1 μm in size, but the concentration appears to be lower than 

in the SC-15. The morphology is not noticeably different between the 121 °C and the 177 °C 

post-cure. 

Figure 5. SEM image of SC-15 with the second toughened phase present at (A) 5000× and (B) 10,000× 

magnification. 
14 

Figure 6. SEM images of SC-79 cycle 1 (A and B) and cycle 2 (C and D) at 5000× and 10,000× 

magnification.

Figure 7 shows the morphology of the CCMFCS2 resin cycles 1–3, those with a 24-h cure time. 

The second phase appears similar in size in all cycles, being ~0.5 μm in diameter with a 

concentration more similar to SC-15 rather than SC-79. 

The morphology of the higher-temperature cured samples, cycles 4–6, is shown in figure 8. 

Again, the post-cure temperature causes little difference between the samples, with particle size 

~1 μm, presumably because the morphology is locked in during the cure rather than the post-cure 

step. The concentration of particles is also more similar to SC-15 than SC-79. 

Comparing figures 7 and 8, it appears that cycles 1–3 have more and smaller particles while 

cycles 4–6 have fewer and larger particles. While smaller particles have been shown to toughen 

epoxies better than larger particles (15), it is not clear that the small size difference is large 

enough to affect the fracture properties significantly (15, 16). 
15 

Figure 7. SEM of CCMFCS2 cycle 1 (A and B), cycle 2 (C and D), and cycle 3 (E and F) at 5000× and 

10,000× magnification.
16 

Figure 8. SEM images of CCMFCS2 cycle 4 (A and B), cycle 5 (C and D), and cycle 6 (E and F) at 5000× 

and 10,000× magnification. 

3.6 Fracture Toughness Analysis 

As the cure cycle can affect the morphology, so can the morphology influence toughness, 

especially in phase-separating systems. The extent of phase separation and size of the phaseseparated domains can significantly affect the fracture toughness. 

According to previous ARL work, SC-15 has a K1c value of 2.08 ± 0.09 MPa·m1/2 and a G1c

value of 1460 ± 120 J/m2

.
17 

SC-79 cycle 1 has a K1c value of 1.61 ± 0.25 MPa·m1/2 and a G1c of 1086 ± 267 J/m2. Cycle 2, 

the higher-temperature post-cured cycle, had a much lower fracture toughness of K1c 

0.79 ± 0.19 MPa·m1/2 and a G1c value of 329 ± 122 J/m2. A trend of increasing extent of cure 

and increasing post-cure temperature with decreasing overall fracture toughness is seen in this 

case. The unreacted monomer in SC-79 cycle 1 can plasticize the resin and improve fracture 

properties (17). With the higher post-cure of cycle 2, the extent of cure is increased, decreasing 

the amount of plasticizing monomers. 

The CCMFCS2 room-temperature-cured resins, cycles 1–3, resulted in K1c values of 1.28 ± 

0.25 MPa·m1/2, 1.12 ± 0.16 MPa·m1/2, and 1.24 ± 0.14 MPa·m1/2, respectively. Their G1c values 

were 671 ± 225 J/m2, 596 ± 163 J/m2, and 742 ± 193 J/m2, respectively. The elevated 

temperature-cured cycles, 4–6, resulted in K1c values of 1.55 ± 0.13 MPa·m1/2, 1.44 ± 0.22 

MPa·m1/2, and 1.24 ± 0.11 MPa·m1/2, respectively. Their G1c values were 855 ± 147 J/m2, 977 ± 

219 J/m2, and 724 ± 123 J/m2, respectively. Cycle 2 breaks from the trend of increasing postcure temperature, leading to decreased fracture properties, but overall the samples post-cured at 

the lowest temperature have the highest fracture properties. The accelerated cured cycles (4–6) 

have, in general, higher fracture toughness values than the RT-cured cycles (1–3) even though 

they have higher extents of cure. A summary of all fracture values can be seen in table 7. 

Table 7. Fracture property summary. 

Cure 

Schedule

K1c 

(MPa·m1/2) 

G1c 

(J/m2) 

G1c 

(J/m2) from K1c

SC-15 (1) 

Single cycle 2.08 ± 0.09 1460 ± 120 1533 ± 137 

SC-79

Cycle 1 1.61 ± 0.25 1086 ± 267 901 ± 288 

Cycle 2 0.79 ± 0.19 329 ± 122 226 ± 116 

CCMFCS2

Cycle 1 1.28 ± 0.25 671 ± 225 652 ± 273 

Cycle 2 1.12 ± 0.16 596 ± 163 480 ± 145 

Cycle 3 1.24 ± 0.14 742 ± 193 610 ± 137 

Cycle 4 1.55 ± 0.13 855 ± 147 1006 ± 175 

Cycle 5 1.44 ± 0.22 977 ± 219 753 ± 224 

Cycle 6 1.24 ± 0.11 724 ± 123 625 ± 104 

Overall, SC-15 has the highest toughness, SC-79 cycle 1 has the second highest toughness, and 

SC-79 cycle 2 has the lowest toughness. SC-15’s high toughness can partially be explained by 

its lower Tg. With similar toughening agents, the resin with the lowest cross-link density, and 

hence the lowest Tg, has been shown to have the highest fracture toughness (18). Conversely, 

SC-79 cured at 177 °C has the highest Tg and, assuming a similar concentration of toughening 

agent, would have the lowest fracture toughness. The high toughness from SC-79 cycle 1 most 

likely comes from the ~10% unreacted monomer coupled with the rubber toughening; an 

incomplete reaction can plasticize resins, leading to increased toughness (17). The other samples 

only had 0%–5% unreacted monomers. 
18 

3.7 Izod Impact Testing 

Figure 9 shows the notched Izod impact testing data for all cycles of the CCMFCS2, along with 

SC-15 and both cycles for SC-79. Surprisingly, the impact data does not correlate with the 

fracture toughness measurements. Where SC-79 cycle 1 had the highest K1c values, it has the 

second lowest for the impact test. For the CCMFCS2 samples, the impact resistance does not 

vary with the post-cure temperature; all values are very similar considering the error. 

Figure 9. Impact resistance of notched samples. 

For the unnotched samples, cycles 4–6 appear to have a slightly higher impact resistance than 

cycles 1– 3, similar to the results seen in the fracture toughness results (figure 10). Values for 

both SC-79 cycles follow the trend of the notched samples, with cycle 2 having the lowest 

overall value. 

0

5

10

15

20

25

SC-15

SC-79 Cycle 1

SC-79 Cycle 2

CCMFCS2 Cycle 1

CCMFCS2 Cycle 2

CCMFCS2 Cycle 3

CCMFCS2 Cycle 4

CCMFCS2 Cycle 5

CCMFCS2 Cycle 6

Impact Resistance (J/m)
19 

Figure 10. Impact resistance of unnotched samples. 

In both notched and unnotched tests, SC-15 had the highest impact resistance while the SC-79 

cycle 2 samples had the lowest. Again, SC-15’s lower Tg helps the impact resistance and SC-79 

cycle 2’s high Tg hinders it. Unlike the fracture toughness results, SC-79 cycle 1 had the second 

lowest impact resistance. Other work has shown that increased fracture toughness correlates 

with increased impact toughness for toughened epoxies (19); however, if SC-79 cycle 2’s 

fracture toughness was influenced more by the unreacted monomer than the toughening agent, 

that correlation may not apply. One large difference between the fracture and impact tests is the 

loading rate. In the Izod tests, the loading speed was several orders of magnitude higher than in 

the fracture testing, 1.4–2.3 m/s vs. 2 × 10–5 m/s. The impact test’s loading rate is high enough 

to partially restrict the movement of the unreacted monomer, partially preventing its ability to 

absorb and dissipate the energy. 

0

100

200

300

400

500

600

700

800

SC-15

SC-79 Cycle 1

SC-79 Cycle 2

CCMFCS2 Cycle 1

CCMFCS2 Cycle 2

CCMFCS2 Cycle 3

CCMFCS2 Cycle 4

CCMFCS2 Cycle 5

CCMFCS2 Cycle 6

Unnotched Impact Resistance (J/m)
20 

4. Discussion 

Figure 11 clearly illustrates the relationship between Tg and fracture toughness. In general, as 

the Tg increases, the fracture toughness decreases. The CCMFCS2 cycles 4–6 show a more 

consistent trend than cycles 1–3. This is most likely due to the fact that 24 h at RT has the 

potential for more variation than 4 h in a temperature-controlled oven. 

Figure 11. Tg vs. fracture toughness (K1c); increasing symbol size corresponds to increasing cycle number. 

Also, given that all CCMFCS2 cycles are clustered together, the different post-cures have only 

minor effects on the ultimate fracture toughness. A much larger difference is seen between the 

two cycles of SC-79, both in terms of Tg and fracture toughness. 

The flexural strength and flexural moduli are compared in figure 12. A general trend of 

increasing strength with increasing modulus is seen; however, there is not a trend of increased 

post-cure temperature leading to increased strength and modulus. CCMFCS2 cycle 1 has the 

lowest strength and modulus. 

80

90

100

110

120

130

140

150

160

0 0.5 1 1.5 2 2.5

K1c (MPa m1/2)

Tg (°C)

SC-15

SC-79

Cycles 1-3

Cycles 4-6
21 

Figure 12. Strength vs. flexural modulus; increasing symbol size corresponds to increasing cycle number. 

5. Summary and Conclusions 

Two cure cycles of SC-79 and six cycles of CCMFCS were characterized and compared to 

SC-15. All resins have suitable viscosities for VARTM, though the slow viscosity rise during 

the 24-h cure time for CCMFCS2 cycles 1–3 is less desirable because of the increased potential 

for vacuum leaks, as well as the slower production rates. 

Regardless of the cure cycle followed, the CCMFCS2 resin reached 96+% cure as measured by 

DSC. The lowest extents of cure occurred when the post-cure was only 121 °C. Extents of cure 

of 98.7+% were achieved whenever the post-cure temperature was 145 °C or higher. The SC-79 

reached 91% and 95% cured for post-cures of 121 and 177 °C, respectively. 

Large property differences exist between the two SC-79 cycles, while the differences between 

the six CCMFCS2 cycles are minor. The morphology changes very little between cycles, though 

the secondary phase appears slightly smaller for cycles 4–6 of CCMFCS2. The post-cure 

temperature has a greater influence on fracture toughness rather than the cure temperature. 

Higher fracture toughness can be achieved by sacrificing Tg by using a lower post-cure 

temperature.

100

105

110

115

120

125

130

2000 2200 2400 2600 2800 3000 3200 3400 3600

Flexural Modulus (MPa)

Strength (MPa)

SC-15

SC-79

Cycles 1-3

Cycles 4-6
22 

SC-79 cycle 1 can provide a Tg above 110 °C with good fracture toughness, while cycle 2 

provides a much higher Tg along with higher strength and modulus. The slow CCMFCS2 cycles 

1–3 do not provide meaningful advantages over the much faster cycles 4–6. A decision between 

cycles 4–6 must be made given the desired properties. The highest Tg, modulus, and strength for 

CCMFCS2 can be achieved with a 177 °C post-cure, while the 145 °C post-cure gives only a 

slightly lower Tg, strength, and modulus but increased toughness. The maximum fracture 

toughness occurs with the 121 °C post-cure but also comes with lower modulus, strength, and 

Tg. Regardless of the resin or cycle chosen, the fracture toughness does not exceed that of 

SC-15, whereas all Tg’s exceed that of SC-15.
23 

6. References 

1. McAninch, I. M.; Boyd, S. E.; La Scala, J. J. Matrix Resin Screening for Composite Armor 

Applications; ARL-TR-4825; U.S. Army Research Laboratory: Aberdeen Proving Ground, 

MD, May 2009. 

2. Boyd, S. E.; McAninch, I. M.; Mulkern, T. Evolution of Thermoset Matrix Composite 

Materials for Composite Armor Applications; ARL-TR-4824; U.S. Army Research 

Laboratory: Aberdeen Proving Ground, MD, May 2009. 

3. Applied Poleramic Inc. SC-79: Toughened Dual Temperature Cure VARTM Resin

Technical Datasheet; Benicia, CA, July 2009. 

4. Center for Composite Materials, University of Delaware. CCMFCS2: 250–200 °F Curing 

Epoxy Matrix; Newark, DE, April 2009. 

5. Applied Poleramic Inc. SC-15: Toughened Epoxy Resin System Technical Datasheet; 

Benicia, CA, July 2009. 

6. Lam, P. W. K. Characterization of Thermoset Cure Behavior by Differential Scanning 

Calorimetry. Part 1: Isothermal and Dynamic Study. Polymer Composites December 1987, 

8 (6), 427–436. 

7. ASTM Standard D 790-03. Standard Test Methods for Flexural Properties of Unreinforced 

and Reinforced Plastics and Electrical Insulating Materials. Annu. Book ASTM Stand. 2003. 

8. ASTM Standard D 5045-93. Standard Test Methods for Plane-Strain Fracture Toughness 

and Strain Energy Release Rate of Plastic Materials. Annu. Book ASTM Stand. 1993. 

9. ASTM Standard D 256-05. Standard Test Methods for Determining the Izod Pendulum 

Impact Resistance of Plastics. Annu. Book ASTM Stand. 2005. 

10. ASTM Standard D 4812-99. Standard Test Method for Unnotched Cantilever Beam Impact 

Resistance of Plastics . Annu. Book ASTM Stand. 1999. 

11. Pascault, J. P.; Sautereau, H.; Verdu, J.; Williams, R. J. J. Thermosetting Polymers. Marcel 

Dekker: New York, 2002. 

12. Lin, K. F.; Yeh, R. J. Moisture Absorption Behavior of Rubber-Modified Epoxy Resins. 

Journal of Applied Polymer Science 2002, 86, 3718–3724. 

13. Papanicolaou, G. C.; Kosmidou, T. V.; Vatalis, A. S.; Delides, C. G. Water Absorption 

Mechanism and Some Anomalous Effects on the Mechanical and Viscoelastic Behavior of 

an Epoxy System. Journal of Applied Polymer Science 2006, 99, 1328–1339.
24 

14. Wisanrakkit, G.; Gillham, J. K. The Glass Transition Temperature (Tg) as an Index of 

Chemical Conversion for a High-Tg Amine/Epoxy System: Chemical and DiffusionControlled Reaction Kinetics. Journal of Applied Polymer Science, 1990, 41, 2885–2929. 

15. Peterson, R. A.; Yee, A. F. Influence of Particle Size and Particle Size Distribution on 

Toughening Mechanisms in Rubber-Modified Epoxies. Journal of Materials Science 1991, 

26, 3828–3844. 

16. Yee, A. F.; Peterson, R. A. Toughening Mechanisms in Elastomer-Modified Epoxies: Part 1 

Mechanical Studies. Journal of Materials Science 1986, 21, 2462–2474. 

17. Selby, K.; Miller, L. E. Fracture Toughness and Mechanical Behavior of an Epoxy Resin. 

Journal of Materials Science 1975, 10, 12–24. 

18. Peterson, R. A.; Yee, A. F. Toughening Mechanisms in Elastomer-Modified Epoxies: 

Part 3 The Effect of Cross-Link Density. Journal of Materials Science 1989, 24, 2571–

2580. 

19. Kong, J.; Ning, R.; Tang, Y. Study on Modification of Epoxy Resins With Acrylate Liquid 

Rubber Containing Pendant Epoxy Groups. Journal of Materials Science 2006, 41, 1639–

1641.
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