Initial Development of Composite Repair Resins With 

Low Hazardous Air Pollutant Contents 

by John J. La Scala, Scott Bingham, Kevin S. Andrews, James M. Sands, and 

Giuseppe R. Palmese 

ARL-TR-4667 December 2008 

Approved for public release; distribution is unlimited. 
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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-4667 December 2008 

Initial Development of Composite Repair Resins With 

Low Hazardous Air Pollutant Contents 

John J. La Scala, Scott Bingham, Kevin S. Andrews, James M. Sands, and 

Giuseppe R. Palmese 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
ii

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Initial Development of Composite Repair Resins With Low Hazardous Air 

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14. ABSTRACT 

Unsaturated polyester-based repair resins, such as Bondo, are widely used for automotive repair, marine repair, sporting 

equipment repair, and household repair of metal, composites, plastics, and wood. Commercial repair resins usually contain 

10 to 40 weight-percent styrene, which is a hazardous air pollutant (HAP). Reducing HAPs in Army materials has become a 

high priority because of Environmental Protection Agency regulations, including the Defense Land Systems for Miscellaneous 

Equipment National Emissions Standard for Hazardous Air Pollutants (NESHAP) and the Reinforced Plastic Composites 

NESHAP. Fortunately, nonvolatile fatty acid monomers can be used to replace the styrene in these repair resins. Fatty acid 

monomers were formulated with vinyl ester or unsaturated polyester monomers to match the glass transition temperature of 

commercial repair resins. Various inorganic fillers were incorporated to match the rheological and mechanical properties of 

commercial repair resins. These resins have zero to low HAP contents and therefore are well within emissions regulations and 

reduce toxicity effects on workers. 

15. SUBJECT TERMS

styrene emissions, repair resins, fatty acid monomers, vinyl ester resins, unsaturated polyester resins 

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32 

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John J. La Scala 

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iii

Contents 

List of Figures iv

List of Tables v

Acknowledgments vi

1. Introduction 1

2. Experimental Methods 4

2.1 Repair Resin Formulation ...............................................................................................4 

2.2 Rheology and Viscosity Characterization .......................................................................6 

2.3 Repair Resin Cure ...........................................................................................................6 

2.4 Thermogravimetric Analysis ...........................................................................................6 

2.5 Dynamic Mechanical Analysis ........................................................................................6 

2.6 Flexural Testing ...............................................................................................................7 

3. Results/Discussion 7

3.1 Rheology and Viscosity Characterization .......................................................................7 

3.2 Repair Resin Cure .........................................................................................................10 

3.3 Thermogravimetric Analysis .........................................................................................10 

3.4 Dynamic Mechanical Analysis ......................................................................................10 

3.5 Flexural Properties ........................................................................................................17 

3.6 Repair Using HAP-Free Repair Resin...........................................................................17 

4. Conclusions 18

5. References 19

List of Symbols, Abbreviations, and Acronyms 21

Distribution List 22 
iv

List of Figures 

Figure 1. Basic formulation of environmentally friendly repair resin is a blend of UPE or VE 

monomers with FAMs derived from plant oils to replace styrene in commercial repair 

resins and inorganic fillers to make the resin into a viscous paste and reinforce the final 

polymer. .....................................................................................................................................3 

Figure 2. Viscosity as a function of shear rate for Bondo autobody filler and a HAP-free 

repair resin with the following composition: 19.25 weight-percent VE monomer, 35.75 

weight-percent MLau (VE/MLau 35/65), 25 weight-percent talc, 15 weight-percent 

MgCO3, and 5 weight-percent glass microspheres. ...................................................................8 

Figure 3. Viscosity at various shear rates for HAP-free and low-HAP repair resin 

formulations according to table 1 relative to Bondo autobody filler. ........................................8 

Figure 4. Viscosity at various shear rates for HAP-free and low-HAP repair resin 

formulations containing FG relative to that of Bondo glass resin. ............................................9 

Figure 5. The viscosity of VE/MLau 35/65 measured at 1 1/s as a function of talc content. .........9 

Figure 6. TGA plots showing percent mass remaining vs. temperature for Bondo glass and a 

HAP-free resin containing 15.75 weight-percent VE monomer, 29.25 weight-percent 

MLau, 30 weight-percent talc, 10 weight-percent FG, and 15 weight-percent MgCO3. .........11 

Figure 7. Loss modulus DMA results for commercial repair resins and HAP-free repair 

resins with 22 weight-percent talc, 15 weight-percent MgCO3, and 8 weight-percent 

NaBO2. .....................................................................................................................................11 

Figure 8. Storage modulus DMA results for commercial repair resins and HAP-free repair 

resins with 22 weight-percent talc, 15 weight-percent MgCO3, and 8 weight-percent 

NaBO2. .....................................................................................................................................12 

Figure 9. Storage modulus for VE/MLau 40/60 repair resins containing 50 weight-percent 

binder for different fillers.........................................................................................................13 

Figure 10. Tg for VE/MLau 40/60 repair resins containing 50 weight-percent binder. ................13 

Figure 11. The glassy modulus and Tg of repair resin formulations as a function of filler 

content (talc) in the formulation for VE/MLau 35/65. ............................................................14 

Figure 12. Tg for various HAP-free formulations relative to Bondo autobody filler according 

to the peak of the loss modulus. ...............................................................................................15 

Figure 13. Moduli for various HAP-free formulations relative to Bondo autobody filler. ..........15 

Figure 14. Moduli for various HAP-free formulations relative to Bondo glass. ..........................16 

Figure 15. Flexural strength and flexural modulus for Bondo glass, Bondo autobody filler, 

HAP-free FG (20 weight-percent VE monomer, 30 weight-percent MLau, 30 weightpercent talc, 10 weight-percent milled fiberglass, and 10 weight-percent MgCO3), and 

HAP-free resin (20 weight-percent VE monomer, 30 weight-percent MLau, 30 weightpercent talc, 15 weight-percent MgCO3, and 5 weight-percent NaBO2). ................................17 

Figure 16. Photographs of HAP-free repair resin applied to dents in a truck tailgate. .................18 
v

List of Tables 

Table 1. The binder formulations for the repair resins used throughout this work. .......................5 
vi

Acknowledgments 

The authors thank the U.S. Army Environmental Quality Basic Research and Development 

program and the U.S. Army Armament Research, Development, and Engineering Center for 

funding. The authors thank Chief Joanne Wright and the U.S. Army Research, Development, 

and Engineering Command Reserve Officer Training Corps Cadet Research Internship program 

for the financial and logistical support of Scott Bingham. This research was supported in part by 

an appointment of Kevin Andrews 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 

Most U.S. Department of Defense weapons platforms and support equipment are subject to 

extremely taxing conditions and are often damaged during weapons fire and off-road operations. 

For many damage types, small repairs can increase the field life of the platform significantly and 

quickly return the weapon platform to service. Various repair resins, such as Bondo* and 

Belzona, are used in the field-deployed units and in U.S. Army depots (1). Repair resins contain 

~20 weight-percent styrene or other hazardous air pollutants (HAPs), which are up to 50% of the 

resin content (2, 3). These HAP chemicals are used to reduce repair resin viscosity to allow the 

resin to be both easy to blend and easy to apply. Recent work has shown that HAP emissions 

from vehicle and marine repair are one of the largest sources of emissions. Field repair resins are 

always cured in the open, and it is impractical to use enclosures and trapping devices, such as 

scrubbers, to remove and recover these HAP emissions. 

Damage to weapons platforms results from impacts from foreign objects, ballistic impacts, 

moisture intrusion and expansion, corrosion, collision, and various maintenance activities (4, 5). 

Damage levels are categorized as follows: 

• Light: aesthetic repairs and coating repairs. 

• Moderate: delaminations, small patches, and edge repairs. 

• Heavy: full depth, core, and substructure repairs. 

For a typical, moderate field repair, any remaining coating in the repair area is removed by hand 

sanding or portable tools. Composite repair resins, such as Bondo, containing short reinforcing 

fibers can then be applied to the damage zone. The resin cures at room temperature. Light 

repairs will be done using Bondo and similar composite repair resins without much, if any, 

scarfing. For most light repair and some moderate repair, Bondo and similar resins will be used. 

Not only are these repair resins used in composite structures, they are also used to do light and 

moderate repair to nonarmor metal structures, such as body paneling, by filling in holes and 

dents in a manner similar to that used for composite structures (6). 

A recent report to the Army states that there are no environmentally friendly repair resins (7). 

Furthermore, through implementation of the Clean Air Act, the Environmental Protection 

Agency (EPA) has established regulations limiting the amount of HAPs that can be used in 

composite materials, including repair resins (8). This new regulation proposes facility-wide 

emissions limits through National Emissions Standards for Hazardous Air Pollutants (NESHAP), 

which makes compliance through low-emissions materials necessary or requires emissions 

 *

Bondo is a trademark of Bondo Corp. 
2

capture equipment (8), which is impractical for repair operations. One aspect of this law requires 

continuous emissions monitoring of all HAP-containing composite materials. Therefore, this 

legislation will have a significant impact on the use of composite materials in the military, as 

well as commercial applications, unless methods for mitigating HAP emissions during 

processing of composite parts and repairs are developed. Furthermore, the high reactivity of 

commercial repair chemistry results in current technology with a short shelf life (<1 year) (9). 

Thermal and mechanical performance characteristics decrease rapidly after expiration of the 

shelf life (9). Consequently, the military generates thousands of pounds of hazardous waste from 

expired resins annually (6, 9). 

The U.S. Army Research Laboratory (ARL) in conjunction with Drexel University has recently 

shown that fatty acid monomers (FAMs) are ideal candidates to replace styrene in vinyl ester 

(VE) and unsaturated polyester (UPE) resins because they are inexpensive, have low volatilities, 

and promote global sustainability because they are derived from renewable resources: plant oils 

(10–12). Triglycerides are the main component of oils derived from plant and animal sources 

and are composed of three fatty acids connected by a glycerol center (13). Triglycerides are 

simply broken down into fatty acids using industrial processes, such as acidolysis (14). A 

number of synthetic routes have been established by ARL/Drexel for making fatty acid-based 

monomers (10). The methacrylated fatty acid (MFA) monomer (figure 1) has proven to be the 

best FAM for composite production. MFA monomers are produced through a simple addition 

reaction of the carboxylic acid of fatty acids with the epoxide group of glycidyl methacrylate to 

form a single product within a few hours at reaction temperatures ranging from room 

temperature to 80 °C (10). Each MFA contains one terminal polymerizable unsaturation site per 

molecule. In this way, the FAMs act as chain extenders, analogous to styrene in VE/UPE resins. 

The resulting monomers have fairly high molecular weight and are nonvolatile, making them 

excellent alternatives to styrene in liquid-molding resins. Furthermore, these monomers promote 

global sustainability because they are made using a renewable resource. Due to the low cost of 

fatty acids and the simple modifications to produce FAMs, these monomers are inexpensive, 

with an estimated cost only slightly above that of styrene. Although plant oils have been used to 

make polymers for years, using FAMs as reactive diluents is a novel concept (10). 

Repair resins are usually two-part formulations composed of a number of different components. 

Part A contains the polymeric binder, including a cross-linking agent (e.g., VE or UPE 

monomers) and a reactive diluent (e.g., styrene), free-radical decomposition promoter, freeradical inhibitors, and various inorganic additives, such as talc, magnesium carbonate (MgCO3), 

chopped glass fiber, sodium metaborate (NaBO2), and fumed silica (2, 3). Part B contains the 

free-radical initiator and surfactants to enable successful mixing of this hardener into a viscous 

part A (15) and is typically added to part A in amounts of 5 weight-percent or less. 

The filler content in commercial repair resins is typically 45–55 weight-percent of the resin, 

while the resin binder makes up the remaining 55–45 weight-percent (2). The organic resin is 
3

Figure 1. Basic formulation of environmentally friendly repair resin is a blend of UPE or VE monomers with 

FAMs derived from plant oils to replace styrene in commercial repair resins and inorganic fillers to 

make the resin into a viscous paste and reinforce the final polymer. 

typically composed of UPE monomers and styrene. The UPE monomers are composed of 

diethylene glycol units combined with phthalic acid units, which impart stiffness, and maleic 

acid or fumaric acid units, which contain the vinyl functionality enabling free-radical 

polymerization (2, 16, 17). The styrene content in Bondo repair resins ranges from 14 to 17 

weight-percent based on the total resin content or 27–31 weight-percent based on the organic 

resin part (2, 3). The inorganic additives typically used in these resins are talc, magnesium 

carbonate, glass microspheres, glass fibers, and sodium metaborate (2, 3). Glass-reinforced 

resins, such as Bondo glass, contain ~5 weight-percent fiberglass (FG) (3), which produces a 
4

strong rigidizing effect relative to other additives. Lower-grade repair resins use ~3–5 weightpercent glass microspheres (2) instead of FG to reduce density and resin viscosity. Sodium 

metaborate is used for a temporal effect on viscosity during processing. The viscosity remains 

low but increases with time after initial processing. As such, small amounts of sodium 

metaborate (~2 weight-percent [2]) are used to allow for low viscosities during processing but 

form higher viscosities during shipment and storage, giving the proper viscosity and consistency 

for repair applications. Benzoyl peroxide is typically used as the initiator in repair resin putties, 

though methyl ethyl ketone peroxide is typically used to cure unfilled resins (2, 3, 16). N,NDimethylaniline is typically added to the base Bondo resin (component A) and acts as a promoter 

to break down the benzoyl peroxide and allow for free radical polymerization at room 

temperature. N,N-Dimethylaniline is used in amounts of ~0.25% by weight of the repair resin. 

This work presents a method to use MFA monomers to partly or completely eliminate styrene in 

repair resins. The FAMs were blended with VE and UPE resins and various filler to create lowHAP and HAP-free repair resin putties with similar properties relative to commercial repair 

resins. A patent application has been filed for these HAP-free and low-HAP repair resin 

formulations (18). 

2. Experimental Methods 

2.1 Repair Resin Formulation 

Commercially available repair resins, Bondo autobody filler and Bondo glass, were used in this 

work as a point of comparison. Both of these resins have similar constituents according the 

literature (2, 3). The one main difference between these resins is that Bondo glass is formulated 

with FG filler particles, whereas Bondo autobody filler does not contain any FG. 

Zero HAP and low-HAP environmentally friendly repair resin binders were formulated by 

blending FAMs with VE and UPE monomers (figure 1). Various compositions of VE/UPE and 

MFA monomers (Applied Poleramics Inc., Benecia, CA) were used to make a variety of repair 

resin formulations (table 1). In particular, methacrylated octanoic acid (MOct) and 

methacrylated lauric acid (MLau) were used to formulate many of the HAP-free repair resins 

because of their good properties in composite resins and their ability to be easily produced at 

large scales. 

VE repair formulations were prepared using a commercial VE, CN-151 (Sartomer, Exton, PA), 

as the cross-linker (19). MLau in quantities ranging from 35–80 weight-percent was added into 

the VE formulation and blended by heating and mechanical mixing. Styrene was used in some 

VE repair resin formulations to make low-HAP, rather than HAP-free, formulations. To a blend 

containing 35 weight-percent CN-151 and 65 weight-percent MLau, styrene was added to the 

resin in the amount of 10 weight-percent by manually stirring at room temperature.
5

Table 1. The binder formulations for the repair resins used throughout this work. 

Monomer Binder Formulation Number 

1 

(Weight-Percent) 

2 

(Weight-Percent)

3 

(Weight-Percent)

4 

(Weight-Percent)

5 

(Weight-Percent) 

6 

(Weight-Percent)

VE (CN-151) 30 35 40 31.5 — — 

UPE (Bondo 

autobody 

resin) 

— — — — 50 — 

UPE (Bondo 

FG resin) 

— — — — — 55 

MLau 70 65 60 58.5 — — 

MOct — — — — 45 35 

Styrene — — — 10 5 10 

UPE monomers from Bondo FG resin (20) were also used in separate formulations as crosslinkers (table 1). MLau was not soluble in the UPE monomers tested. On the other hand, MOct 

was soluble because of its shorter fatty acid chain length and was used in all UPE formulations. 

In one set of samples, Bondo UPE from Bondo autobody filler was purified from the fillers by 

dissolving about 18 g of repair resin in about 25 g of acetone in 50-mL centrifuge tubes. The 

organic phase readily dissolved in the acetone, while the inorganic fillers settled to the bottom of 

the tube. The organic components dissolved in the acetone were recovered and allowed to 

evaporate in the ambient environment for 1 week. The resin was then placed in an oven at 50 °C 

for 1 week to remove the acetone and styrene. After evaporation, ~4–5 weight-percent styrene 

and <1 weight-percent acetone remained. A blend of 55 weight-percent of this UPE (containing 

~5 weight-percent styrene and acetone) and 45 weight-percent MOct was then prepared. In 

another set of samples, 57.51 g of Bondo FG resin containing 28 weight-percent styrene was 

blended with 15.93 g of MOct. The resin was allowed to evaporate for 2 weeks at room 

temperature until 12.33 g of styrene evaporated from the resin. Then 2.6 g of styrene was added 

back to the resin to produce a resin with 55 weight-percent UPE monomer, 35 weight-percent 

MOct, and 10 weight-percent styrene. 

N,N-dimethylaniline (Sigma-Aldrich) was added to the part A formulation because this chemical 

promotes free radical cure of benzoyl peroxide initiators, which are typically used in the 

hardener component. N,N-dimethylaniline content in the amount of 0.1–0.5 weight-percent 

worked best for adequately curing the repair resin and allowing sufficient working time. 

Inorganic components, including talcum (Fisher Scientific, laboratory grade), milled glass fibers 

(Jamestown Distributors), magnesium carbonate penta-hydrate (MgCO3

.

5H2O, Fisher Scientific), 

sodium metaborate hydrate (NaBO2, MP Biomedical), aluminum oxide (Alodur), sand, silica 

thickener (Jamestown Distributors), glass microspheres (3M Scotchbrite K37), and phenolic 

microballoons (Jamestown Distributors) were thoroughly mixed into the resin formulations using 

high shear mixers. Silica thickener, sand, phenolic microballoons, aluminum oxide, and carbon 

black were only tested qualitatively in this manner because they are not commonly used in repair 

resins (2, 3). Various inorganic components and contents with various particle sizes were used. 
6

Overall, all of these fillers acted similarly in increasing the viscosity of the uncured resin and 

increasing the stiffness of the cured polymer. The following abbreviations are used for talc (T), 

magnesium carbonate (M), sodium metaborate (N), glass microspheres (MS), and milled FG. 

2.2 Rheology and Viscosity Characterization 

The viscosities of the uncured resin samples were measured using a TA Instruments (New 

Castle, DE) AR2000 rheometer in steady shear flow experiments using parallel plate geometry 

(40-mm plates). The shear rate was increased from 0.001 to 10 s–1 and then decreased back to 

0.001 s–1, and 10 measurements were taken per decade. At a given shear rate, the shear stress 

was measured every 2 s. The shear rate and viscosity were recorded when the shear rate 

stabilized to within 5% tolerance for three consecutive intervals. 

2.3 Repair Resin Cure 

The repair resin was cured using the Bondo red cream hardener. The hardener in the amount of 

1% by weight was thoroughly mixed into the resin, until the resin was a uniform pink color. The 

resins were then added to silicon rubber molds using a spatula. The resins were allowed to cure 

overnight. The cured polymer samples were removed from the mold and then cut into the 

appropriate sizes for testing. All samples were sanded to remove any surface defects and to 

ensure the surfaces were flat. 

2.4 Thermogravimetric Analysis 

Thermogravimetric analysis (TGA) was run on the samples using a TA Instruments hi-res TGA 

2950. A 10-mg sample was placed on a platinum sample holder. The samples were run in air up 

to 800 °C at 10 °C/min. The instrument measures the sample mass as a function of temperature 

throughout the experiment. Liquid component A and liquid red cream hardener (component B) 

were run. In addition, cured samples were also run. 

2.5 Dynamic Mechanical Analysis 

The thermomechanical properties of the repair resins were measured using dynamic mechanical 

analysis (DMA). Rectangular samples with approximate dimensions of 25  9  3 mm were 

tested using a TA Instruments 2980 DMA in single cantilever geometry. The samples were 

tested at 1 Hz with a deflection of 15 m while ramping the temperature from –50 to 150 oC at a 

rate of 2 °C/min. Two temperature ramp experiments were run for each sample. The two ramps 

were nearly identical, indicating almost complete cure after the first run and indicating that 

additional DMA ramps were unnecessary. 

The temperature at which the peak in the loss modulus occurred in the fully post-cured polymer 

was considered the glass transition temperature of the material (21). The experimental error in 

Tg (glass transition temperature) was ±1.5 °C. Tan() can also be used as a measure of the glass 

transition temperature, but it is known that the maximum in tan() is 10–20 °C above the loss 
7

modulus maximum. The loss modulus peak represents the midpoint of the Tg, while tan() 

represents the end of the glass transition region and subsequent beginning of the rubbery region. 

Because both of these can be independently affected by the formulation, both of these values 

were recorded for each formulation. 

2.6 Flexural Testing 

Flexural tests, in accordance with ASTM D 790-92 (22), were performed to determine the 

modulus of elasticity and flexural strength. The samples had approximate dimensions of 

10  80  64 mm and actual dimensions were measured prior to testing. The samples were 

tested flatwise on a support span, resulting in a support-to-depth ratio of 16. All tests were 

performed at ambient conditions, which were ~22 °C and 40% relative humidity. The samples 

were tested using an Instron at a crosshead speed of 10 mm/min. The flexural modulus, 

elongation at failure, and flexural strength were calculated according to the ASTM standard. 

3. Results/Discussion 

3.1 Rheology and Viscosity Characterization 

Repair resins must have sufficient viscosities so that they stick to the repair area and do not 

spread too thin. In many cases, repair resins must stick to an upside-down surface. On the other 

hand, the resin must have a low enough viscosity that it can be removed from the container at 

room temperature and be hand mixed with the hardener component. Therefore, an attempt was 

made to match the viscosity of HAP-free FAM binders with those of commercial binders. 

However, this was difficult because the viscosity of styrene (1 cP) is much lower than the 

viscosity of MLau (~60–70 cP). Furthermore, commercial resins shear thin and, as such, have 

viscosities that vary according to the shear rate applied (figure 2). Yet, it was possible to match 

the rheology of the HAP-free formulations to that of commercial repair resins (figure 2). Not 

only do the Newtonian viscosities match (i.e., the region where viscosity is not a function of 

shear rate), but both resins shear thin at similar shear rates and have similar power-law 

relationships in the non-Newtonian regime. In general, repair resins were prepared with a variety 

of viscosities, ranging from lower to higher viscosities relative to their commercial counterparts 

(figures 3 and 4). Note that the resins containing FG (figure 4) had higher viscosities relative to 

resins without FG (figure 3). Overall, resin viscosity was dominated by resin/filler ratio; the 

larger the filler content, the higher the viscosity (figure 5). Furthermore, as the styrene and 

MLau content increased, the resin viscosity decreased. Therefore, repair resins can be created 

with the necessary rheological properties for typical repair scenarios. 
8

100

1000

10000

1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00

Shear rate (1/s)

Viscosity (Pa*s)

Bondo Autobody

HAP-Free Resin

Figure 2. Viscosity as a function of shear rate for Bondo autobody filler and a HAP-free repair resin with the 

following composition: 19.25 weight-percent VE monomer, 35.75 weight-percent MLau (VE/MLau 

35/65), 25 weight-percent talc, 15 weight-percent MgCO3, and 5 weight-percent glass microspheres. 

1

10

100

1000

10000

Bondo

Autobody

Filler

1- 55R

22T 15M

8N

2- 55R

22T 15M

8N

3- 50R

25T 17M

8N

3 - 50R

30T 15M

5N

4- 55R

25T 15M

5N

5- 70R

15T 9M

6MS

6- 70R

15T 7M

3N 5MS

Viscosity (Pa*s)

0.01 1/s

0.1 1/s

1 1/s

Figure 3. Viscosity at various shear rates for HAP-free and low-HAP repair resin formulations according to 

table 1 relative to Bondo autobody filler.
9

1

10

100

1000

10000

100000

Bondo Glass 1 - 45R 30T

10FG 15M

2 - 45R 30T

10FG 15M

3 - 45R 30T

10FG 15M

3 - 50R 30T

10FG 10M

Viscosity (Pa*s)

0.01 1/s

0.1 1/s

1 1/s

Figure 4. Viscosity at various shear rates for HAP-free and low-HAP repair resin formulations containing FG 

relative to that of Bondo glass resin. 

1

10

100

1000

0 10 20 30 40 50 60

Talc Content (wt%)

Viscosity (Pa*s)

Figure 5. The viscosity of VE/MLau 35/65 measured at 1 1/s as a function of talc 

content.
10

3.2 Repair Resin Cure 

Bondo resins and fatty acid-based repair resins cured similarly. If short working times are 

desired, adding 5 weight-percent Bondo red cream hardener caused curing to occur within 5 min, 

while 1 weight-percent red cream hardener caused curing within 30 min, allowing for longer 

working times. 

To avoid using commercially formulated hardeners, benzoyl peroxide was mixed with other oils 

and surfactants. One hardener for the repair resin was formulated by blending benzoyl peroxide 

(30 weight-percent) with Gojo Multi Green hand cleaner (70 weight-percent). Another hardener 

was formulated by blending benzoyl peroxide (30 weight-percent), Gojo Multi Green hand 

cleaner (50 weight-percent), and canola oil (20 weight-percent) together. These formulated 

hardeners were mixed thoroughly with the resin. The high-surfactant contents of the hardener 

allowed for easy blending with the viscous repair resin. The resulting resin gelled in a few 

minutes and cured into a hard but flexible solid. This shows that simple hardeners can be easily 

prepared. These formulated hardeners were used for proof of concept purposes and not used to 

formulate any samples for testing (DMA, Instron, etc.) in this work. 

3.3 Thermogravimetric Analysis 

TGA was run on commercial and zero-HAP formulated repair resins (figure 6). For the HAPfree resins, less mass loss occurred at lower temperatures due to the nonvolatile nature of the 

FAMs vs. the highly volatile styrene in Bondo. Overall, the commercial and zero-HAP resins 

lose approximately the same amount of mass as resins with similar binder contents. For resins 

with greater filler contents, the final char weight was higher. 

3.4 Dynamic Mechanical Analysis 

Figure 7 shows the loss moduli and figure 8 shows the storage moduli for various formulations 

as a function of temperature. Bondo autobody filler, Bondo glass, and Bondo all-purpose putty 

all had glass transition temperatures of 20–25 °C. VE/MLau ratios of 20/80 matched the Tg and 

glassy modulus of commercial repair resins (figures 7 and 8). Resins with VE/Lau ratios of 

35/65 had higher Tg’s than that of commercial resins but had similar room temperature moduli 

(figure 7). However, the glass transition was significantly broader for the fatty acid-based repair 

resin (figure 7). This broader Tg prevents the HAP-free repair resins from having identical DMA 

properties as a function of temperature. On the other hand, the broader Tg allows the resin more 

flexibility so it is less fragile in cold weather. UPE/MOct/Sty 50/45/5 also produced similar 

DMA properties relative to commercial repair resins. 
11

0

10

20

30

40

50

60

70

80

90

100

0 200 400 600 800 1000

Temperature (oC)

Percent Mass Remaining

Bondo

HAP-Free

Figure 6. TGA plots showing percent mass remaining vs. temperature for Bondo glass and a HAP-free resin 

containing 15.75 weight-percent VE monomer, 29.25 weight-percent MLau, 30 weight-percent talc, 

10 weight-percent FG, and 15 weight-percent MgCO3. 

0

100

200

300

400

500

600

700

-50 0 50 100 150

Temperature (oC)

Loss Modulus, E' (MPa)

Bondo Autobody Filler

VE/MLau 20/80

VE/MLau 35/65

UPE/MOct/Sty 50/45/5

Figure 7. Loss modulus DMA results for commercial repair resins and HAP-free repair resins with 22 weightpercent talc, 15 weight-percent MgCO3, and 8 weight-percent NaBO2.
12

0

1000

2000

3000

4000

5000

6000

-50 0 50 100 150

Temperature (oC)

Storage Modulus, E' (MPa)

Bondo Autobody Filler

VE/MLau 20/80

VE/MLau 35/65

UPE/MOct/Sty 50/45/5

Figure 8. Storage modulus DMA results for commercial repair resins and HAP-free repair resins with 22 weightpercent talc, 15 weight-percent MgCO3, and 8 weight-percent NaBO2. 

Figure 9 shows the glassy and room-temperature moduli, and figure 10 shows the Tg for the 

same binder formulation (VE/MLau 40/60) and the same binder content (50 weight-percent) but 

with varying amounts of talc, magnesium carbonate, and sodium metaborate. The results clearly 

show that at this binder content, the particular fillers used have little effect on modulus and Tg. 

Note that none of the resins in figure 10 used FG as filler. Similarly, figure 11 shows that 

increasing the resin binder content has no significant effect on Tg for the polymer in the range of 

45–75 weight-percent binder. From 90 weight-percent to 100 weight-percent binder content, the 

Tg decreased by as much as 5 °C as a result of reduced stiffening. Note that the loss modulus 

trends and tan() trends do not match exactly. Because the loss modulus represents the midpoint 

of the glass transition, while tan() represents a maximum in viscous to elastic response, the loss 

modulus maximum is more typically used to represent Tg and is used as such throughout the rest 

of this work. On the other hand, the glassy modulus increased as the filler content increased 

(figure 11). This is expected because the fillers should be capable of carrying a load across the 

sample once percolation of the filler particles occurs. Load-bearing capacity and stiffness should 

increase as the concentration of particles increases above the percolation threshold (23). These 

results show that filler content alone affects the modulus, and the individual fillers used are of 

little importance.
13

0

1000

2000

3000

4000

5000

6000

3- 50R 30T 15M 5N 3- 50R 30T 10M 10N 3- 50R 25T 17M 8N

Storage Modulus, E' (MPa)

E' at –40 °C

E' at 25 °C

Figure 9. Storage modulus for VE/MLau 40/60 repair resins containing 50 weight-percent binder for different 

fillers. 

0

10

20

30

40

50

60

70

80

3- 50R 30T 15M 5N 3- 50R 30T 10M 10N 3- 50R 25T 17M 8N

Glass Transition Temperature, Tg (oC)

E"

tan delta

Figure 10. Tg for VE/MLau 40/60 repair resins containing 50 weight-percent binder.
14

2000

2500

3000

3500

4000

4500

5000

5500

6000

0 10 20 30 40 50 60

Talc Content (wt%)

Modulus, E' (MPa)

0

10

20

30

40

50

60

70

80

Tg(E") (°C)

E' at –50 °C

Tg

Figure 11. The glassy modulus and Tg of repair resin formulations as a function of filler content (talc) in the 

formulation for VE/MLau 35/65. 

Figures 12 and 13 show the properties of each resin formulation (table 1) with selected amounts 

and ratios of fillers. Overall, similar dynamic mechanical properties relative to commercial 

resins were achievable with selected resin formulations. In addition, depending on need, resin 

Tg’s can be selected with similar, higher, or lower values relative to commercial repair resins 

(figure 12). As expected, Tg increased as the VE content in VE/MLau formulations increased 

from 30% (binder formulation 1) to 40% (binder formulation 3). In addition, Tg further 

increased according to the loss modulus for the VE/MLau sample with 10% styrene (binder 

formulation 4) because polystyrene has a higher Tg relative to poly-MLau (11). All the 

VE/MLau formulations shown had Tg values above that of the commercial repair resin. Yet, the 

Tg of the repair resin could be dropped by simply increasing the MLau-to-VE ratio (11). The 

UPE resin formulations had slightly lower Tg’s than the commercial repair resin. This is again a 

result of the low Tg of poly-MOct relative to polystyrene. Increasing the styrene content from 

5 weight-percent (binder formulation 5) to 10 weight-percent (binder formulation 6) increased Tg

significantly. Yet, the purpose is to develop styrene-free repair resins. To do this and prepare 

resins with similar Tg relative to the commercial resins, either a higher Tg UPE monomer must be 

used as a partial or complete replacement for the Bondo UPE or a higher Tg nonvolatile 
15

0

10

20

30

40

50

60

Bondo

Autobody

Filler

1- 55R 22T

15M 8N

2- 55R 22T

15M 8N

3- 50R 25T

17M 8N

4- 55R 25T

15M 5N

5- 70R 15T

9M 6 MS

6- 70R 15T

7M 3N 5MS

Glass Transition Temperature, Tg (°C)

Figure 12. Tg for various HAP-free formulations relative to Bondo autobody filler according to the peak of the loss 

modulus.

10

100

1000

10000

Bondo

Autobody

Filler

1- 55R 22T

15M 8N

2- 55R 22T

15M 8N

3- 50R 25T

17M 8N

4- 55R 25T

15M 5N

5- 70R 15T

9M 6 MS

6- 70R 15T

7M 3N 5MS

Storage Modulus, E' (MPa)

E' at –40 °C

E' at 25 °C

Figure 13. Moduli for various HAP-free formulations relative to Bondo autobody filler. 
16

monomer must be used as a partial or complete replacement for styrene and MOct. Figure 13 

shows that despite these changes in Tg, there is little effect on the mechanical performance of 

these resins, with the exception of the UPE/MLau/Sty 50/45/5 (binder formulation 5). However, 

this repair resin was also formulated with the lowest content of fillers, which is a contributing 

effect for this reduced modulus. Figure 14 shows the mechanical properties of repair resins 

formulated with FG. The glassy modulus is considerably higher for these formulations relative 

to resins without FG (figure 13). Thus high aspect ratio solid fillers like FG do affect mechanical 

properties to a larger degree than particle fillers, like talc and magnesium carbonate. However, 

the room temperature modulus and Tg are not significantly affected by adding FG because Tg is a 

resin-dominated phenomenon and room temperature is very close to Tg so that filler-type effects 

are being masked by drastic changes in resin stiffness. Overall, similar dynamic mechanical 

properties relative to commercial resins were achievable. Also, lower and higher Tg’s and 

moduli were easily formulated by varying the FAM content and filler contents in the resin. 

0

1000

2000

3000

4000

5000

6000

7000

Bondo Glass 1- 45R 30T

10FG 15M

2- 45R 30T

10FG 15M

3- 45R 30T

10FG 15M

6- 72R 13T

8M 7FG

Storage Modulus, E' (MPa)

E' at –40 °C

E' at 25 °C

Figure 14. Moduli for various HAP-free formulations relative to Bondo glass. 
17

3.5 Flexural Properties 

The samples using FG had significantly higher moduli and strengths than the samples without 

FG (figure 15). However, there was no significant difference between the properties of 

commercial resins using FG and HAP-free formulated resins with FG. There was also no 

significant difference in the properties of the Bondo autobody filler and the HAP-free 

formulation using talc, MgCO3, and NaBO2 as fillers. 

0.1

1

10

100

Bondo Glass HAP-free FG Bondo Autobody HAP-Free

Formulation

Flexural Strength (Mpa) or Flex. Modulus (GPa)

Strength

Modulus

Figure 15. Flexural strength and flexural modulus for Bondo glass, Bondo autobody filler, HAP-free FG 

(20 weight-percent VE monomer, 30 weight-percent MLau, 30 weight-percent talc, 10 weight-percent 

milled fiberglass, and 10 weight-percent MgCO3), and HAP-free resin (20 weight-percent VE 

monomer, 30 weight-percent MLau, 30 weight-percent talc, 15 weight-percent MgCO3, and 5 weightpercent NaBO2). 

3.6 Repair Using HAP-Free Repair Resin 

A dented truck tailgate was repaired using a zero-HAP repair resin formulation. This 

formulation had 19.25 weight-percent CN-151, 35.75 weight-percent MLau, 22 weight-percent 

talc, 17 weight-percent MgCO3, and 8 weight-percent NaBO2. The application of the resin and 
18

cure was similar to that of commercial repair resins. The resulting repair was excellent as shown 

in figure 16. The product was able to be sanded down to produce a smooth surface similar to 

that of commercial repair resins. Scraping the edges of the repaired area with a razor blade did 

not result in delamination of the resin. This shows that the repair resin had good adhesion 

properties with the substrate. 

Figure 16. Photographs of HAP-free repair resin applied to dents in a truck tailgate. 

4. Conclusions 

This work clearly shows that HAP-free repair resins based on VEs, UPEs, and MFAs were 

formulated. These resins contain no styrene, unlike commercial repair resins that contain 14–17 

weight-percent styrene. As a result, these repair resins exceed the Reinforced Plastic Composites 

NESHAP regulations and meet the Defense Land Systems for Miscellaneous Equipment 

NESHAP regulations. These HAP-free resins had similar rheological, thermal, and mechanical 

properties relative to commercially available repair resins, like Bondo. As a result, using these 

HAP-free repair resins should result in high-quality repair and allow environmentally compliant 

repair of vehicles while eliminating worker exposure to harmful emissions. Yet additional work 

needs to be done to optimize the properties of these repair resins for a variety of applications.
19

5. References 

1. Misc. Adhesives and Sealants Technology Thrust Area. Concurrent Technologies 

Corporation, Potential Alternatives Report (CDRL A007) Task No. 0420, December 2005. 

2. Bondo Corporation. Bondo Body Filler Materials Safety Data Sheet, Atlanta, GA, June 

2006. 

3. Bondo Corporation. Bondo Glass Reinforced Filler Materials Safety Data Sheet, Atlanta, 

GA, March 2001. 

4. Mehkam, P. Support of Composite Structures on Naval Aircraft. Presented at Second Joint 

NASA/FAA/DOD Conference on Aging Aircraft, Williamsburg, VA, 1998. 

5. Koon, R. W. Aircraft Skin Repair Procedures and Requirements. Invited presentation at 

U.S. Army Research Laboratory, Aberdeen Proving Ground, MD, 1998. 

6. Fink, B. K.; McKnight, S. H.; Newton, C. H.; Gillespie, J. W.; Palmese, G. R. NonPolluting Composites Repair and Remanufacturing for Military Applications: An 

Environmental and Cost-Savings Analysis; ARL-TR-2139; U.S. Army Research Laboratory: 

Aberdeen Proving Ground, MD, December 1999. 

7. Misc. Adhesives and Sealants Technology Thrust Area. Concurrent Technologies 

Corporation, Gap Analysis Report (CDRL A007) Task No. 0420, February 2006. 

8. Environmental Protection Agency. National Emissions Standards for Hazardous Air 

Pollutants: Reinforced Plastic Composites Production. Federal Register 2003, 68, 19375. 

9. Sands, J. M.; Fink, B. K.; McKnight, S. H.; Newton, C. H.; Gillespie, J. W.; Palmese, G. R. 

Clean Products and Processing 2001, 2, 228–235. 

10. Palmese, G. R.; La Scala, J. J.; Sands, J. M. Fatty Acid Monomers to Reduce Emissions and 

Toughen Polymers. U.S. Patent Appl. 60/569,379, May 2005. 

11. La Scala, J. J.; Sands, J. M.; Orlicki, J. A.; Robinette, E. J.; Palmese, G. R. Fatty Acid-Based 

Monomers as Styrene Replacements for Liquid Molding Resins. Polymer 2004, 45, 

7729–7737. 

12. La Scala, J. J.; Sands, J. M.; Palmese, G. R. Clearing the Air: Army Composites Research 

Reduces Harmful Emissions. The AMPTIAC Quarterly 2004, 8, 118–125. 

13. Litchfield, C. Analysis of Triglycerides; Academic Press: New York, 1972; p 3. 

14. Gunstone, F. D. Fatty Acid and Lipid Chemistry; Blackie Academic and Professional: New 

York, 1996; p 72.
20

15. Bondo Corporation. Bondo Red Cream Hardener Materials Safety Data Sheet, Atlanta, GA, 

June 2006. 

16. Hexion. Hexion 111–1930 Technical Data Sheet, Columbus, OH, May 2005. 

17. Fink, J. K. Reactive Polymers Fundamentals and Applications: A Concise Guide to 

Industrial Polymers; William Andrew Publishing: Norwich, New York, 2005. 

18. La Scala, J. J.; Palmese, G. R.; Sands, J. M. Composite Repair Resins Containing Minimal 

Hazardous Air Pollutants and Volatile Organic Compounds. U.S. Patent Appl. 11/689,191, 

August 2007. 

19. Sartomer. Technical Data Sheet for CN151, Exton, PA, May 1999. 

20. Bondo Corporation. Bondo Fiberglass Resin Materials Safety Data Sheet, Atlanta, GA, 

May 2006. 

21. Nielsen, L. E.; Landel, R. F. Mechanical Properties of Polymers and Composites; Marcel 

Dekker: New York, 1994. 

22. ASTM D 790-92. Annual Book of ASTM Stand. 1987, Vol. 08.01; pp 155–162. 

23. Wool, R. P. Polymer Interfaces, Structure, and Strength; Hanser Publishers: New York, 

1995; pp 102–116. 
21

List of Symbols, Abbreviations, and Acronyms 

ARL U.S. Army Research Laboratory 

DMA dynamic mechanical analysis (polymer thermomechanical analysis) 

E’ storage modulus 

E” loss modulus 

FAM fatty acid monomer 

FG fiberglass 

HAP hazardous air pollutant 

M magnesium carbonate, MgCO3

MFA methacrylate fatty acid 

MLau methacrylate lauric acid 

MOct methacrylate octanoic acid 

MS glass microspheres 

N sodium metaborate, NaBO2

NESHAP National Emissions Standards for Hazardous Air Pollutants 

T talc 

tan() ratio of loss modulus to storage modulus 

Tg glass transition temperature of polymer 

TGA thermogravimetric analysis 

UPE unsaturated polyester 

VE vinyl ester
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