1 

, J 

Strength and Durability of Glass 

Fiber Composites Treated With 

Multicomponent Sizing 

Formulations 

by Robert E. Jensen, Steven H. M&night, 

and Matthew J. Quesenberry 

ARL-TR-2655 January 2002 

Approved for public release; distribution is unlimited. 
. 

The findings in this report are not to be construed as an 

official Department of the Army position unless so 

designated by other authorized documents. 

Citation of manufacturer’s or trade names does not 

constitute an official endorsement or approval of the use 

thereof. 

Destroy this report when it is no longer needed. Do not 

return it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-2655 January 2002 

Strength and Durability of Glass 

Fiber Composites Treated With 

Multicomponent Sizing 

Formulations 

Robert E. Jensen and Steven H. M&night 

Weapons and Materials Research Directorate, ARL 

Matthew J. Quesenberry 

University of Delaware 

Anmoved for Dublic release; distribution is unlimited. 
Abstract 

Commercial fiber-sizing packages have been developed to enhance the 

strength and moisture resistance of composite materials, which typically 

decreases ballistic performance. Potential sizing packages developed for Future 

Combat Systems will need to enhance ballistic response while maintaining the 

levels of durability currently benchmarked by existing commercial systems. For 

this research, pultruded vinyl ester/E-glass composites were manufactured in 

which the silane, film former resin, and surfactant reactivity were varied to 

mimic the complete spectrum of commercially available fiber-sizing packages. 

The interlaminar shear strengths of dry and moisture-saturated composites were 

then measured via 3-point bend testing. These strength and durability results 

will be used as the standards of comparison for future development of ballistic 

sizing packages for composite armor applications. 

ii 
Acknowledgments 

This research was supported in part by an appointment to the 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. The authors wish 

to thank the ARL Composite Materials Research (CMR) Materials Center of 

Excellence Contract DAALOl-96-2-0048 to the University of Delaware Center for 

Composite Materials (UD-CCM) for additional support of this project. The 

authors would also like to thank Owens Corning for supplying the epoxy fiIrn 

former emulsion used in the model silane formulation. The authors also wish to 

acknowledge the technical assistance provided by Dr. R. L. Gorowara at UDCCM. 

. . . 

111 
. 

iv 
Contents 

Acknowledgments 

. . . 

111 

List of Figures vii 

List of Tables ix 

1. 

2. 

3. 

4. 

5. 

Introduction 

Experimental 

2.1 

2.2 

2.3 

2.4 

2.5 

2.6 

2.7 

2.8 

2.9 

1 

2 

Fiber Tow Preparation ................................................................................... 2 

Matrix Resin .................................................................................................... 3 

Cylindrical Pultruded Composite Rod Fabrication Equipment.. ........... .4 

Cylindrical Pultruded Composite Rod Fabrication Procedure.. ............. .6 

Composite Rod Test Sample Preparation.. ................................................ .7 

Density Measurements ................................................................................. .7 

Short Beam Shear Testing .............................................................................. 8 

Void Content Testing ..................................................................................... 9 

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

Results 10 

Conclusions 16 

References 17 

Distribution List 19 

Report Documentation Page 25 

V 
iNTENTIONALLY LEFT BLANK. 

vi 
List of Figures 

Figure 1. Molecular structures of (a) MI’S, (b) APS, and (c) GE’!? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

Figure 2. Film former resins used in the fiber-sizing packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Figure 3. BASF Pluronic F-108 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Figure 4. Vinyl ester matrix and styrene reactive diluent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Figure 5. Pultruded composite rod fabrication setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Figure 6. Specific gravity measurement apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Figure 7. ASTM short beam shear test fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Figure 8. DMA of the vinyl ester matrix showing a glass transition 

temperature of approximately 125 “C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Figure 9. ILSS (dry = left bar, wet = right bar, for given fihn former), 

equilibrium moisture uptake percentage at 50 “C (percent uptake 

= up triangles), and durability (ratio of wet ILSS to dry ILSS = down 

triangles) for pultruded rod composites with MPS coupling agent and 

varying film former reactivity towards the matrix vinyl ester resin. . . . . . . . . . . . . . . . 11 

Figure 10. IL!% (dry = left bar, wet = right bar, for given film former), 

equilibrium moisture uptake percentage at 50 “C (percent uptake 

= up triangles), and durability (ratio of wet ILSS to dry ILSS = down 

triangles) for pultruded rod composites with APS coupling agent and 

varying film former reactivity towards the matrix vinyl ester resin. . . . . . . . . . . . . . . . 12 

Figure 11. ILSS (dry = left bar, wet = right bar, for given film former), 

equilibrium moisture uptake percentage at 50 “C (percent uptake 

= up triangles), and durability (ratio of wet IL!% to dry IISS = down 

triangles) for pultruded rod composites with GPS coupling agent and 

varying film former reactivity towards the matrix vinyl ester resin. . . . . . . . . . . . . . . . 12 

Figure 12. ILSS (dry = left bar, wet = right bar, for given film former), 

equilibrium moisture uptake percentage at 50 “C (percent uptake 

= up triangles), and durability (ratio of wet IL!% to dry ILSS = down 

triangles) for pultruded rod composites with MPS coupling agent and 

varying film former molecular weights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

Figure 13. IL!% (dry = left bar, wet = right bar, for given film former), 

equilibrium moisture uptake percentage at 50 “C (percent uptake 

= up triangles), and durability (ratio of wet ILSS to dry IISS = down 

triangles) for pultruded rod composites with AI’S coupling agent and 

varying film former molecular weights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

vii 
Figure 14. ILSS (dry = left bar, wet = right bar, for given film former), 

equilibrium moisture uptake percentage at 50 “C (percent uptake 

= up triangles), and durability (ratio of wet II.33 to dry ILSS = down 

triangles) for pultruded rod composites with GPS coupling agent and 

varying film former molecular weights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

. . . 

Vlll 
List of Tables 

. Table 1. Complete summary of results for vinyl ester pultruded glass rod 

composites with MPS as the coupling agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Table 2. Complete summary of results for vinyl ester pultruded glass rod 

composites with Al’% as the coupling agent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

Table 3. Complete summary of results for vinyl ester pultruded glass rod 

composites with GE’S as the coupling agent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

ix 
X 
1. Introduction 

The fatigue life, vibration response, structural loading, moisture resistance, and 

most importantly, the ballistic resistance of the structural composite layer found 

in composite integral armor (CIA) will be dependent upon the chemical and 

physical properties of the fiber-matrix interphase [l]. The interphase is the small 

region of material surrounding the fiber that has properties that differ from the 

fiber and the bulk matrix [2]. The response of the fiber-matrix interphase, which 

may only compose as little as 1% of the total volume of material, can control the 

overall mechanical performance (strength, durability, fatigue Iife) as well as 

micromechanical energy absorbing mechanisms of glass fiber-reinforced 

composite materials [3-61. During a ballistic event, a significant portion of the 

incident energy during dynamic loading of the polymeric composites may be 

absorbed through micromechanical mechanisms such as fiber-matrix debonding 

and fiber pull-out, which are directly related to the properties of the interphase 

[7]. Understanding the individual contribution of each mechanism is key to 

tailoring the interphase to achieve maximum energy absorption. 

The driving force for the formation of an interphase in glass fiber-reinforced 

composites is the use of waterborne silane-based sizing packages, The sizing 

package increases the handling ease of the glass fibers while lending protection 

against damage and corrosion [8, 91. The sizing package is applied from an 

aqueous emulsion with the solids content mainly composed of polymeric film 

former (70% by weight). Other minor components of the sizing package include 

surfactant, thickeners, antifoam agents, antistatic agents, stabilizers, and a 

s&me-based coupling agent. Although the silane coupling agent makes up a 

relatively low percentage of the initial sizing package, it serves the critical 

purpose of providing a chemical covalent link between the matrix phase and 

fiber. The silane coupling agent is first hydrolyzed in the aqueous sizing 

emulsion. Upon drying on the fiber surface, the hydrolyzed silanes condense 

and react with silanol groups found on the fiber surface to form a loosely 

crosslinked siloxane network. Once contact has been made between the fibers 

and the matrix resin, the relative proportions of the sizing components on the 

fiber surface change dramatically as diffusion between the matrix resin and fiber 

sizing occurs. At equilibrium, the matrix resin dissolves most of the film former 

and surfactant, leaving a high concentration of crosslinked siloxane at the glass 

surface (80% by weight) [7]. Th e matrix resin then diffuses into and swells the 

loosely crosslinked siloxane network, which remains chemically bonded to the 

glass surface. Chemical bonding occurs during cure between the matrix resin 

and matrix-resin-compatible functional groups of the pre-existing siloxane 

network to form a highly crosslinked and coupled interpenetrating polymer 

1 
network (IPN) structure. This IPN structure has properties that differ from the 

fiber and bulk matrix phase, hence the term “interphase.” 

The Future Combat Systems (FCS) will require unique materials solutions to 

meet the weight, speed, and performance requirements envisioned for the 

objective force. Integrated multimaterial assemblies that incorporate 

fiber-reinforced composite materials are candidates to meet both structural and 

ballistic requirements for envisioned lightweight Army ground vehicle 

applications. The anticipated material property requirements for FCS will 

require substantial increases in composite materials performance for these 

unprecedented applications. Unfortunately, while many commercial fiber-sizing 

packages offer excellent durability properties, the ballistic impact resistance of 

such composites is less than ideal. A great challenge will be the simultaneous 

improvement in both composite ballistic response and structural load bearing, 

since these performance attributes are generally diametrically opposed. Potential 

sizing packages developed for FCS will need to enhance ballistic response while 

maintaining the levels of durability currently benchmarked by existing 

commercial systems. For this research, pultruded vinyl ester/E-glass composites 

were manufactured in which the silane, film former resin, and surfactant 

reactivity were varied to mimic the complete spectrum of commercially available 

fiber-sizing packages. The interlaminar shear strengths of dry and 

moisture-saturated composites were then measured via 3-point bend testing. 

These strength and durability results will be used as the standards of comparison 

for future development of ballistic sizing packages for composite integral armor 

applications. 

2. Experimental 

2.1 Fiber Tow Preparation 

E-glass fiber tow, prepared by Gorowara et al. [lo] at the Owens Corning Science 

and Technology Center pilot plant facility in GranviIle, OH, was used to 

construct cylindrical pultruded rod composite samples. The silane-based 

fiber-sizing packages were applied from a waterborne emulsion (5.0 wt% solids) 

to the E-glass fibers immediately after drawing the glass fibers from the melt. 

The aqueous fiber-sizing package is composed of 0.6 wt% percent silane coupling 

agent and 4.4 wt% emulsified film former. Fiber-sizing packages were prepared 

with a variety of silane coupling agents including methacrylpropyltrimethoxysilane 

(MI’S), aminopropyltriethoxysilane (AIS), and glycidoxypropyltrimethoxysilane 

(GPS). The MI’S, APS, and GPS were obtained from Witco 05 (A-1100, A-174, 

and A-187, respectively). The chemical structures of the silane coupling agents are 

portrayed in Figure 1. The film former resins chosen included diglycidyl ether of 

2 
bisphenol A (DGEBA) epoxies of varying epoxy equivalent weight (Shell EPON 

828,834, and lOOlF), unsaturated bisphenol A vinyl ester (Sartomer CN-151), and 

polyesters (Reichold Atlac 387 and DSM Neoxil 954D). The film former resins 

used are illustrated in Figure 2. The hydrophobic film former resins were 

stabilized in an emulsified form using a nonionic polyethylene oxidepolypropylene oxide-polyethylene oxide triblock copolymer surfactant (BASF 

Pluronic F-108). The chemical structure of the surfactant used to emulsify the 

sizing packages is illustrated in Figure 3. The fibers were dried for a period of 10 

hr at a temperature of 130 “C prior to shipping to the U.S. Army Research 

Laboratory (ARL). The tows had an average 1150 mg/m tex, 2052 filaments/ tow, 

and an average 16.9~urn filament diameter. 

f 

P 

H2N-y -O-T 

APS 0 

(4 I (b) 

-o-,9-/-o4 

I GPS 

0 

I 

(4 

Figure 1. Molecular structures of (a) ME, (b) Al?3, and (c) GPS 

2.2 Matrix Resin 

For a single pultruded rod composite, -200 g of vinyl ester resin was prepared. 

In circumstances where fiber wetting was difficult, specifically for the cases of 

noncompatible fiber-sizing packages, 250-300 g of resin were used. The 

formulation was composed of Derakane 411-C-50 vinyl ester resin (Dow) and 

1.7 wt% Trigonox 239A peroxide initiator. Because the rods are cured at room 

temperature (20-25 “C), 0.10 wt% cobalt napthenate was added as a room 

temperature catalyst. Cure and crosslinking occur via a free radical mechanism. 

The matrix vinyl ester resin and styrene reactive diluent are illustrated in Figure 

4. 

3 
EPON 834 DGEBA Epoxy 

CN-151 DGEBA Epoxy Methacrylate 

NEOXIL 954-D DGEBA Unsaturated Polyester, MW - 5500 

Figure 2. Film former resins used in the fiber-sizing packages. 

CH3 

I 

HO+CH,CH,O ) x*~+CH,CHO) y +CH,CH,O),H 

Figure 3. BASF Phonic F-108. 

vinyl ester resin derived from bisphenol A 

styrene 

Figure 4. Vinyl ester matrix and styrene reactive diluent. 

2.3 Cylindrical Pultruded Composite Rod Fabrication Equipment 

The basic apparatus for pultruded rod synthesis consisted of three main 

components: (1) an area for wetting the fiber tows (fiber trough), (2) 

polytetrafluoroethylene (F’TFE)-lined copper pipe molds, and (3) a frame for the 

suspension of the resin-filled rod molds during room temperature curing. 

Figure 5 shows the schematic diagram of the mold assembly used to fabricate the 

pultruded composite rods. 

, 

4 
Brass 

Fitting 

copper 

Pipe 

Teflon 

Tube 

Containing 

Rod 

Copper 

Wire 

Weight 

Figure 5. Pultruded composite rod fabrication setup. 

The PTFE tube was utilized within the copper pipe to reduce adhesion of the 

matrix vinyl ester resin to the inner surface of the copper pipe upon completion 

of cure. A brass fitting was then attached to the pipe with a set of Swagelok 

fittings. After the wetted fibers are pulled through the PTFE tube-copper pipe 

setup, a plastic “zip-tie” was used to firmly secure the fibers in the brass fitting. 

Another function of the brass fitting was to serve as a “resin reservoir,” which 

facilitated further wetting of the fibers using excess resin poured into the fitting. 

Finally, the PTFE tube-copper pipe setup was suspended from a frame via the 

Swagelok fitting, and a weight of approximately 5 kg was firmly secured to the 

copper wire that protruded from the bottom of the mold. The weight 

effectively placed enough tensile force on the fibers to ensure unidirectional 

alignment in the final composite specimens. 

5 
2.4 Cylindrical Pultruded Composite Rod Fabrication Procedure 

The complete process of creating the composite rods begins with the careful 

spinning of the fibers into a bundle of 38 tows. The exact number of tows (J) 

needed to produce a composite rod with a fiber volume fraction of 4s, = 0.50 can 

be calculated using the following equation: 

J= @ -‘ef xl@ 

2N.df2 ’ (1) 

where 

N = the number of filaments per tow, 

Dt = the M’FE inner-tube diameter in millimeters, and 

dj = the fiber diameter in microns. 

The fiber spinning was completed using a plastic loop frame. Care was taken to 

ensure that the fiber tows were reasonably aligned and taut during this step. The 

diameter of the loop also had to be slightly longer than twice the mold length. A 

wetting trough was then used in collaboration with a laminate hand roller and 

the resin to effectively wet out the fibers inside a fume hood. The wetting trough 

needed to be as long as the diameter of the bundle loop and also needed be lined 

with a release sheet to facilitate clean-up. Careful rolling was required to ensure 

that the fibers did not fray or that the resin did not gel or begin to cure. This 

process typically spanned lo-15 mm. A copper wire was looped around the 

middle of the fiber bundle, and the copper pipe was flipped upside-down so that 

the brass fitting was directly above the wetted fiber bundle. A second individual 

was needed to pull the fiber bundle through the copper pipe. One person pulled 

the copper wire with the fibers through the tube, while the second person 

secured the copper tube and PTFE tube combination. When approximately 1 in 

of fibers was left protruding from the brass fitting, a zip-tie was used to secure 

the fibers in the brass fitting. The copper pipe-PTFE tube combination was again 

flipped over and hung on the support frame. A small amount of resin, -20 g, 

was deposited into the top of the brass fitting, and the 5-kg weight was secured 

to the copper wire as shown in Figure 5. Finally, the composite rod was allowed 

to cure at room temperature for -2 hr in an enclosed fume hood. Once the 

composite rods had completely cured inside the fume hood, the 5-kg weight was 

removed, and the complete copper pipe-composite rod combination was placed 

in an oven at 110 “C for 1 hr. The oven was then shut off and the composite rods 

were allowed to slow cool to minimize internal residual stresses. 

6 
2.5 Composite Rod Test Sample Preparation 

The composite rod was carefully removed from the F’TFE tube and copper pipe. 

A hacksaw was then used to detach the rod from the brass fitting and copper 

wire. Upon removal, the rod was inspected for defects and placed in a desiccator 

to ensure dryness. Before testing, the rod was carefully sawed into pieces 2.375 in 

long. (A diamond saw or other precise cutting instrument is strongly 

recommended to complete this task.) The ends of the cut rods were lightly 

sanded with 400-grit sandpaper and replaced in the desiccator in labeled sample 

bags until further testing. All rods were dried in a vacuum oven at 50 “C and 

-25~in mercury (Hg) overnight before any testing was begun. 

2.6 Density Measurements 

Density measurements were made using a balance from which a pan was 

submerged into a beaker filled with distilled water. Figure 6 displays a schematic 

of the instrument used to measure the density of the composite rods. 

I-&/- Suspended Pan 

Figure 6. Specific gravity measurement apparatus. 

The distilled water was allowed to equilibrate overnight to room temperature. 

The procedure required three measurements, including the dry mass of each rod, 

the mass of the pan submerged in the water, and the mass of the rod resting on 

the pan submerged in water. The following formula was used to calculated the 

specific gravity of each rod (S&d): 

SG,, = A 

A+W-B ’ 

where 

7 
A = the dry mass of the rod, 

B = the mass of the submerged rod and pan, and 

W = the mass of the submerged pan only. 

Density (D,) is th en calculated from equation (3): 

DC = SG,, m x PH,O mr 

where 

(3) 

T = the test temperature and 

pHzO (T) = the density of water at the tested temperature. 

2.7 Short Beam Shear Testing 

The Instron 1331 equipped with a 2000-lb load cell was used in collaboration 

with a set of custom-made American Society for Testing and Materials (ASTM) 

D4475-85 [ll] standard steel fittings. The setup including the fittings is depicted 

in Figure 7. Before testing, the diameter of each specimen was measured to the 

nearest 0.001 in at the midpoint. The rod was placed in the test fixture as shown 

in Figure 7. The specimen was then aligned so that the midpoint was centered 

and the long axis was perpendicular to the loading nose. The bottom fittings 

were then adjusted to a span of 2.45 in. A computer was utilized in collaboration 

with the Instron 1331 to collect load force and displacement data. The load was 

applied to the specimen at a crosshead speed of 1.3 mm/min. Testing was 

declared completed when the specimen exhibited stress fractures indicated by a 

sudden, rather large, decrease in load-force readings on the Instron 1331 

instrument control panel. Four trials of each specimen were made. Interlaminar 

shear strength (KSS) was calculated using equation (4): 

ILSS = 

0.849 x P 

uk$ ’ 

(4) 

where 

P = the maximum measured load and 

Drod = the rod diameter. 

Additionally, samples were also tested after reaching an equilibrium moisture 

uptake percentage (Mm) upon exposure to water at a temperature of 50 “C. 

Composite durability is then defined simply as the ratio of wet ILSS to dry ILSS. 

8 
e Loading Arbor 

-Specimen 

Bottom Fittings 

Figure 7. ASTM short beam shear test fittings. 

2.8 Void Content Testing 

The samples used for short beam shear testing were re-used for void content 

testing after drying in the vacuum overnight at 50 “C and -25-m Hg. All samples 

were weighed completely dry. Then, the crucibles, in which the samples were 

placed, were massed. The samples were heated at 1100 “F for approximately 3 hr 

to burn off the vinyl ester matrix, leaving clean E-glass fibers behind. The 

crucibles and the clean E-glass fibers that they contained were massed. By 

subtracting the weight of the crucible, the actual E-glass fiber mass was 

calculated. From these measurements, the E-glass fiber mass percent (Xj,) and the 

matrix mass percent (X,) were calculated using the following equations: 

x, =~xlOO%, 

and 

x, =100%--X, I 

(5) 

(6) 

where 

F = the E-glass fiber mass and 

M = the sample dry mass. 

From these computations, the void content (6) and the volume fraction of the 

fibers (&) were easily calculated from: 

(b, 400~D,($+gq, 

m J 

(7) 

and 
where 

DC = the specimen density, 

D, = the matrix density (1.130 g/cm’), and 

D/ = the fiber density (2.600 g/cm3). 

2.9 Dynamic Mechanical Analysis 

Dynamic mechanical analysis (DMA) was carried out using a TA Instruments 

2980 DMA in the dual cantilever-bending mode. The neat vinyl ester resin was 

tested using a 20-mm clamp frame and oscillatory displacement amplitude of 

7.5 p. The displacement amplitude was verified to ensure linear viscoelastic 

response by deriving corresponding stress-strain (O-E) curves. Constant heating 

rate experiments were carried out at 2.0 “C/n-tin at a frequency of 1 Hz from 

35” to 200 “C. The glass transition temperature (Tg) was taken as the peak 

maximum of the loss modulus (E”) curve measured at 1 Hz. 

3. Results 

The loss modulus (E”) and storage modulus (E’) DMA results for the neat 

non-fiber-reinforced vinyl ester matrix are shown in Figure 8. The E” curve 

shows a small relaxation peak near 80 “C and a large glass-to-rubber transition 

peak at approximately Tg = 125 “C. The storage modulus also decreases from 

glassy values in excess of 109 rascals (Pa) below temperatures of 110 “C to 

rubbery values of 107 Pa above temperatures of 145 “C. The rubbery plateau at 

temperatures greater than 145 “C is typical for crosslinked thermosets. The small 

relaxation peak near 80 “C could be the result of heterogeneous regions of 

crosslink density within the cured vinyl ester sample [12]. However, the purpose 

of performing DMA was not to investigate the molecular relaxation mechanisms 

of cured and crosslinked vinyl ester resin in detail, but rather to simply verify 

that the curing procedure and conditions resulted in glassy crosslinked 

thermoset for the moisture uptake and mechanical property measurements. 

The ILSS (wet and dry), moisture uptake percentages, and durability results are 

plotted in Figures 9-14. These results are numerically tabulated in Tables 1-3 

along with the specimen weight fraction of fibers, void content 

percentage, and moisture uptake percentage. 

10 
. 

8- 

50 75 100 125 150 175 200 

Temperature (“C) 

Figure 8. DMA of the vinyl ester matrix showing a glass transition temperature of 

approximately 125 “C. 

80 1.00 

. T 

70 - f f T 

- -2.0 

60 0.75 

Pi 

.Z 

E 

f 

-I 

n 

- 20 0.25 

10 

0 0.00 

d 

0+ 

@ 

9 .\% 

Figure 9. ILSS (dry = left bar, wet = right bar, for given film former), equilibrium 

moisture uptake percentage at 50 “C (percent uptake = up triangles), and 

durability (ratio of wet IL.% to dry IL!% = down triangles) for pultruded rod 

composites with MI3 coupling agent and varying film former reactivity 

towards the matrix vinyl ester resin. 

11 
60 

70 

60 

2 50 

z. 40 

zj 3o 

- 

20 

10 

0 

1 .oo 

0.75 

>r 

.= 

z 

0.50 s 

5 

13 

0.25 

0.00 

Figure 10. ILSS (dry = left bar, wet = right bar, for given film former), equilibrium 

moisture uptake percentage at 50 “C (percent uptake = up triangles), and 

durability (ratio of wet ILSS to dry ILSS = down triangles) for pultruded rod 

composites with AI’S coupling agent and varying film former reactivity 

towards the matrix vinyl ester resin. 

1 .oo 

0.75 

h 

.C 

r= 

0.50 $j 

5 

cl 

0.25 

Figure 11. ILSS (dry = left bar, wet = right bar, for given film former), equilibrium 

moisture uptake percentage at 50 “C (percent uptake = up triangles), and 

durability (ratio of wet ILSS to dry ILSS = down triangles) for pultruded rod 

composites with GPS coupling agent and varying film former reactivity 

towards the matrix vinyl ester resin. 

12 
. 

60 1.00 

70 

60 0.75 

2 h 50 

z 

E 40 0.50 lg 

! 3o 

f 

n 

- 20 0.25 

10 

0 0.00 

Figure 12. ILSS (dry = left bar, wet = right bar, for given film former), equilibrium 

moisture uptake percentage at 50 “C (percent uptake = up triangles), and 

durability (ratio of wet ILSS to dry IL.!% = down triangles) for pultruded rod 

composites with MI’S coupling agent and varying film former molecular 

weights. 

60 1 .oooo 

T T 

70 70 - - * 

- 2.0 

60- x T ,o 75 

Figure 13. ILSS (dry = left bar, wet = right bar, for given film former), equilibrium 

moisture uptake percentage at 50 “C (percent uptake = up triangles), and 

durability (ratio of wet ILSS to dry ILSS = down triangles) for pultruded rod 

composites with AI’S coupling agent and varying film former molecular 

weights. 

13 
Figure 14. ILSS (dry = left bar, wet = right bar, for given film former), equilibrium 

moisture uptake percentage at 50 “C (percent uptake = up triangles), and 

durability (ratio of wet ILSS to dry ILSS = down triangles) for pultruded rod 

composites with GPS coupling agent and varying film former molecular 

weights. 

Table I. Complete summary of results for vinyl ester pultruded glass rod composites 

with MI’S as the coupling agent. 

Film 

Former Xf 

Wet 

ILSS 

(MY 

Durability 

Silane 0.6980 0.9741 1.8184 59.943 0.8039 56.205 0.9376 

Only -+ 0.0106 5 0.0096 + 0.0049 _+1.834 _+ 0.0085 _+ 1.783 5 0.0041 

EPON 834 0.6805 0.9882 1.8150 60.154 0.7791 51.290 0.8527 

z!z 0.0013 3~ 0.0012 + 0.0030 5~4.055 310.0681 k 1.468 5 0.0062 

EPON 1OOlF 0.6671 0.9977 1.8100 56.895 0.7783 50.033 0.8794 

+ 0.0059 kO.0053 f0.0130 k2.036 kO.0975 k1.221 f 0.0038 

CN 151 0.6823 0.9899 1.8211 57.044 0.7781 53.810 0.9434 

zk 0.0033 f 0.0031 ~!10.0117 zk 3.457 kO.0724 2 1.535 310.0069 

Neoxil 0.6853 0.9852 1.8175 57.083 0.7741 49.138 0.8608 

945/D * 0.0003 IL 0.0003 It 0.0020 k 2.849 + 0.0279 + 0.706 ItI 0.0045 

Atlac 387 0.6839 0.9851 1.8148 52.200 0.8801 42.783 0.8196 

?I 0.0004 f 0.0004 + 0.0031 f 2.947 f 0.1117 f 1.800 2~ 0.0058 

No Sizing 0.7034 0.9953 1.8673 56.436 1.0722 18.654 0.3305 

k 0.0058 + 0.0054 f 0.0035 Y!I 3.077 3~ 0.0240 + 1.192 rf: 0.0028 

14 
Table 2. Complete summary of results for vinyl ester pultruded glass rod composites 

with APS as the coupling agent. 

Film Dry Wet 

Former Xf b IL!% Ma ILSS Durability 

(%) (g/?n3) (MPa) (%) (MPa) 

Silane 0.6495 1.0068 1.7978 50.252 0.8237 37.449 0.7452 

MY 310.0024 Ik 0.0022 + 0.0123 f 4.288 It 0.0221 31 2.782 + 0.0084 

EPON 828 0.6748 0.9893 1.8075 45.790 0.7665 43.897 0.9587 

+0.0024 f 0.0021 rtO.0056 + 2.737 zkO.0445 k1.130 kO.0062 

EPON 834 0.6954 1.0005 1.8631 52.871 0.7094 46.162 0.8731 

f0.0083 +0.0077 +0.0049 + 2.477 +0.0468 zk 0.748 zk 0.0043 

EPON 0.6726 0.9959 1.8159 45.738 0.7144 43.845 0.9586 

1OOlF It 0.0044 T!z 0.0040 +0.0049 I? 3.575 f 0.0395 f 1.181 lk 0.0025 

CN 151 0.6704 0.9855 1.7933 57.681 1.3576 29.086 0.5043 

z!Io.o022 f0.0019 f0.0020 rt 3.210 f 0.0755 k 2.902 +0.0056 

Neoxil 0.6748 0.9900 1.8088 53.545 1.0307 30.242 0.5648 

945/D + 0.0028 + 0.0025 +0.0014 rk 2.315 + 0.0858 + 0.662 rf:O.O027 

No Sizing 0.7034 0.9953 1.8673 56.436 1.0722 18.654 0.3305 

f 0.0058 f 0.0054 +0.0035 2 3.077 f 0.0240 k1.192 zkO.0028 

Table 3. Complete summary of results for vinyl ester pultruded glass rod composites 

with GPS as the coupling agent. 

Film Dry Wet 

Former Xf 4v IL!% la ILSS Durability 

(%) (MPa) (%) (MPa) 

Silane 0.6770 0.9822 1.7982 46.159 2.0059 20.435 0.4427 

OdY zkO.0032 +0.0029 +0.0020 f 3.762 + 0.1603 k1.956 f0.0056 

EPON 828 0.6989 0.9926 1.8544 42.231 1.0182 33.534 0.7941 

* 0.0031 f0.0029 zkO.0038 IL 2.722 + 0.1653 + 2.616 f 0.0063 

EPON 834 0.6731 0.9795 1.7869 37.507 1.7511 27.558 0.7347 

f o.ooo9 +O.OOOS +0.0027 If 1.890 + 0.1885 f1.047 zk 0.0050 

EPON 0.6759 0.9795 1.7915 33.818 1.6228 24.474 0.7237 

1OOlF rtO.0009 f0.0008 f0.0034 31 2.476 f 0.2162 k1.574 + 0.0071 

CN151 0.6840 0.9917 1.8271 55.221 1.1471 37.661 0.6820 

k 0.0006 I? 0.0006 +0.0035 + 2.153 zk 0.1707 + 2.398 It 0.0051 

Neoxil 0.6734 0.9881 1.8030 49.182 1.4229 20.097 0.4086 

945/D f 0.0009 f 0.0008 rt 0.0020 It 2.173 f 0.1225 f 0.739 + 0.0023 

No Sizing 0.7034 0.9953 1.8673 56.436 1.0722 18.654 0.3305 

t 0.0058 k 0.0054 + 0.0035 rt 3.077 310.0240 211.192 zi 0.0028 

15 
4. Conclusions 

The results presented in this report show the influence of the silane coupling 

agent reactivity, film former reactivity, and film former molecular weight of 

waterborne glass sizing packages towards the strength and durability of 

composite materials. The most important conclusion to be drawn from these 

results is that the greatest overall strength and durability/moisture resistance is 

obtained when both the silane coupling agent and film former have chemical 

reactivity with the matrix resin. Of these two sizing components, the degree of 

silane coupling agent reactivity with the matrix resin phase is the most critical. 

The order of silane reactivity towards the vinyl ester matrix used in this report is 

Ml?5 > Al?? > GPS. The results shown in this report represent the strength and 

durability benchmarks for ballistic fiber sizing packages to be developed in the 

future. 

. 

16 
5. References 

1. 

. 

7. 

2. 

3. 

4. 

5. 

6. 

8. 

9. 

Fink, B. K., A. M. Monib, and J. W. Gillespie. “Damage Tolerance of 

Thick-Section Composites Subjected to Ballistic Impact.” ARL-TR-2477, U.S. 

Army Research Laboratory, Aberdeen Proving Ground, MD, May 2001. 

CulIer, S. R., H. Ishida, and J. L. Koenig. “FT-1R Characterization of the 

Reaction at the Silane Matrix Resin Interphase of Composite Materials.” 

Journal ofCoZZoid and Inferface Science, vol. 109, pp. l-10,1986. 

Madhukar, M. S., and L. T. Drzal. “Fiber-Matrix Adhesion and Its Effect on 

Composite Mechanical Properties. 1. Inplane and Interlaminar Shear 

Behavior of Graphite Epoxy Composites.” JoumaI of Composite Materials, 

vol. 25, pp. 932-957,199l. 

Madhukar, M. S., and L. T. Drzal. “Fiber-Matrix Adhesion and Its Effect on 

Composite Mechanical Properties. 2. Longitudinal (O-Degrees) and 

Transverse (90-Degrees) Tensile and Flexural Behavior of Graphite Epoxy 

Composites.” Journal @Composite Materids, vol. 25, pp. 958-991,199l. 

Lesko, J. J., R. E. Swain, J. M. Cartwright, J. W. Chin, K. L. Reifsnider, 

D. A. DiIlard, and J. P. Wightman. “Interphase Developed From Fiber 

Sizings and Their Chemical-Structural Relationship to Composite 

Compressive Performance.” Joumnl ofAdhesion, vol. 45, pp. 43-47,1994. 

Zheng, J. I’., and T. R. Jow. “A New Charge Storage Mechanism for 

Electrochemical Capacitors.” Journal of the Electrochemical SocieQ, vol. 142, 

no. 1, pp. 6-12,1995. 

Tanoglu, M., S. H. M&night, G. R. Palmese, and J. W. Gillespie. “The Effects 

of Glass-Fiber Sizings on the Strength and Energy Absorption of the 

Fiber/Matrix Interphase Under High Loading Rates.” Composites Science and 

Technology, vol. 61, pp. 205-220,200l. 

Reifsnider, K. L. “Modeling of the Interphase in Polymer-Matrix 

Composite-Material Systems.” Composites, vol. 25, pp. 461-469,1994. 

Thomason, J. L. “The Interface Region in Glass-Fiber-Reinforced Epoxy-Resin 

Composites. 3. Characterization of Fiber Surface-Coatings and the 

Interphase.” Conzposifes, vol. 26, pp. 487-498,1995. 

10. Gorowara, R. L., W. E. Kosik, S. H. M&night, and R. L. McCullough. 

“Molecular Characterization of Glass Fiber Surface Coatings for 

Thermosetting Polymer Matrix/Glass Fiber Composites.” Composites: Purf A, 

vol. 32, pp. 323-329,200l. 

17 
11. American Society for Testing and Materials. “Standard Test Method for 

Apparent Horizontal Shear Strength of Pultruded Reinforced Plastic Rods by 

the Short-Beam Method.” D4475-85, West Conshohocken, PA, 1985. 

12. Brill, R. P., and G. R. Palmese. “An Investigation of Vinyl-Ester - Styrene 

Bulk Copolymerization Cure Kinetics Using Fourier Transform Infrared 

Spectroscopy.” Journal @Applied Pohper Science, vol. 76, pp. 1572-1582,200O. 

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a. TITLE AND SUBTITLE 5. FUNDING NUMBERS 

Strength and Durability of Glass Fiber Composites Treated With Multicomponent AH42 

Sizing Formulations 

8. AUTHOR(S) 

Robert E. Jensen, Steven H. M&right, and Matthew J. Quesenberry* 

7. PERFORMING ORGANWTION NAME(S) AND ADDRESS 

U.S. Army Research Laboratory 

ATTN: AMSRL-WM-MA 

Aberdeen Proving Ground, MD 2 10055069 

8. PERFORMING ORGANlZATlON 

REPORT NUMBER 

ARL-TR-2655 

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AGENCY REPORT NUMBER 

11. SUPPLEMENTARY NOTES 

*University of Delaware, Newark, DE 19716. 

12a. DlSTRlBUTlONlAVAllABlLlTY STATEMENT 

Approved for public release; distribution is unlimited. 

12b. DISTRIBUTION CODE 

13. ABSTRACT(hlaximum 200 words) 

Commercial fiber-sizing packages have been developed to enhance the strength and moisture resistance of composite 

naterials, which typically decreases ballistic performance. Potential sizing packages developed for Future Combal 

jysterns will need to enhance ballistic response while maintaining the levels of durability currently benchmarked by 

:xisting commercial systems. For this research, pultruded vinyl ester/E-glass composites were manufactured in which 

he silane, film former resin, and surfactant reactivity were varied to mimic the complete spectrum of commercially 

available fiber-sizing packages. The interlaminar shear strengths of dry and moisture-saturated composites were then 

neasured via 3-point bend testing. These strength and durability results will be used as the standards of comparison fox 

inure development of ballistic sizing packages for composite armor applications. 

14. SUBJECT TERMS 

;ilane, ILSS, film former, vinyl ester, composite, E-glass, durability, moisture uptake 

15. NUMBER OF PAGES 

32 

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