United States Department of Agriculture

Forest

Service

Forest Products

Laboratory

Research Note

FPL–RN–0339

September

2016

Effects of Cedar Oil and Silica Gel 

Treatment on Dimensional Stability 

and Mechanical Properties of 

Southern Yellow Pine Boards

Xiping Wang 

Christopher A. Senalik 

Robert Ross

Neal Bennett

Deborah Conner
Abstract

A laboratory study was conducted to investigate the effects 

of cedar oil and silica gel treatment on dimensional stability 

and mechanical performance of southern yellow pine (SYP) 

boards. Two hundred pieces of SYP and 100 pieces of red 

oak boards with a nominal dimension of 1 by 6 by 48 in. 

(25 by 152 by 1,219 mm) were selected for this study. The 

red oak boards were included as a standard ammunition 

pallet stock for comparison. The experimental procedure 

involved stress wave E-rating, grouping, defect mapping, 

preservative treatment, high-temperature kiln exposure 

(simulating hot and dry service condition), and flatwise 

static bending test. Cedar oil and silica gel treatment had a 

positive effect on dimensional stability of the No. 2 SYP 

boards, as indicated by reduced visible end-splits and board 

warp. Our results also indicated that cedar oil and silica gel 

treatment had a detrimental effect on stiffness and strength 

of the No. 2 SYP boards. Both modulus of elasticity and 

modulus of rupture decreased significantly in treated SYP 

compared with those of untreated SYP.

Keywords: End split, pallet deck boards, stiffness, strength, 

warp, work to maximum load

September 2016

Wang, X.; Senalik, C.A.; Ross, R.; Bennett, N.; Conner, D. 2016. Effects 

of cedar oil and silica gel treatment on dimensional stability and 

mechanical properties of southern yellow pine boards. FPL-RN-0339. 

Madison, WI: U.S. Department of Agriculture, Forest Service, Forest 

Products Laboratory. 5 p.

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive, 

Madison, WI 53726-2398. This publication is also available online at 

www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries 

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The Forest Products Laboratory is maintained in cooperation with the 

University of Wisconsin.

The use of trade or firm names in this publication is for reader information 

and does not imply endorsement by the United States Department of 

Agriculture (USDA) of any product or service.

Contents

Introduction..........................................................................1

Materials and Methods.........................................................1

Results and Discussions.......................................................2

Conclusions..........................................................................4

Literature Cited ....................................................................5

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Introduction

Use of wood in the manufacture of shipping containers, specifically pallets, is well documented and based on a strong 

theoretical and experimental research base. Wood pallets are 

now in use worldwide to ship a wide range of products, 

from agricultural food stuffs to ammunition used in military 

operations. The USDA Forest Products Laboratory (FPL) 

was recently contacted by technical representatives from the 

U.S. Department of Defense (DoD) and asked to provide assistance in evaluating the performance of a new wood preservative treatment that is being considered for potential use 

in the manufacture of wood pallets used to transport smallarms ammunition. The hypothesis tested in this project was 

if cedar oil and silica gel, a commercially available and environmentally friendly preservative product, can cause softwood four-way entry ammo pallets to perform as well as 

hardwood pallets yet without experiencing dimensional stability problems.

The foundation for the preservative treatment utilizes natural wood oils extracted from Juniperus species. Research 

has been conducted to determine the termiticidal and fungal 

activities of heartwood, bark/sapwood, and leaves from 

dominant juniper species in the United States as part of an 

evaluation of the commercial potential of plants that are 

now considered to be a noxious tree species in rangelands 

(Adams and others 1988; Adams 1991; Clark and 

McChesney 1990). Based on results from these studies, a 

commercial cedar oil and silica gel product was developed 

and is now manufactured and marketed as an environmentally friendly wood preservative.

The goal of this project was to investigate the effects of the 

cedar oil and silica gel treatment on the dimensional stability and mechanical performance of southern yellow pine 

(SYP) boards. Red oak boards were included as a standard 

ammunition pallet stock for comparison. The project involved stress wave E-rating, grouping, defect mapping, preservative treatment, high-temperature kiln exposure (simulating hot and dry service condition), and flatwise static 

bending. Specific objectives were to (1) develop technical 

data on the effect of high-temperature kiln exposure on end 

splits and warp in preservative-treated and untreated deck 

boards; (2) determine the effect of cedar oil and silica gel 

treatment on dimensional stability of SYP boards; and 

(3) determine the effect of cedar oil and silica gel treatment 

on mechanical properties of SYP boards.

Materials and Methods

Materials

In late November 2014, 150 pieces of red oak and 300

pieces of SYP boards were obtained by the Department of 

Ammunition Center (DAC) and shipped to the wood laboratory in Princeton, West Virginia. All boards were in a nominal dimension of 1 by 6 by 48 in. (25 by 152 by 1,219 mm). 

The red oak group appeared to be clear and high-quality 

wood; all the SYP boards were No. 2 kiln dried and heat 

treated (Fig. 1). Through initial stress wave E-rating procedure, we selected 100 pieces of red oak and 200 pieces of 

SYP boards as test specimens:

• Group 1—100 oak boards, standard pallet materials

• Group 2—100 SYP boards (kiln dried and heat treated), 

no preservative treatment and used as a control group

• Group 3—100 SYP boards (kiln dried and heat treated), 

to be treated with cedar oil and silica gel

In mid-February 2015, Group 3 was shipped to McAlester 

Army Ammunition Plant (MAAP) to receive preservative 

treatment. At MAAP, all boards of Group 3 were treated 

with cedar oil and silica gel through immersion method for 

Effects of Cedar Oil and Silica Gel 

Treatment on Dimensional Stability 

and Mechanical Properties of 

Southern Yellow Pine Boards

Xiping Wang, Research Forest Products Technologist

Christopher A. Senalik, Research General Engineer 

Robert Ross, Project Leader 

Forest Products Laboratory, Madison, Wisconsin

Neal Bennett, General Engineer 

Deborah Conner, Biological Technician

Forest Products Laboratory, Princeton, West Virginia 
Research Note FPL–RN–0339

2

over 12 h. In mid-June 2015, the treated SYP boards 

(Group 3) were shipped back to Princeton, West Virginia, 

for physical measurements.

Testing Procedures

Board samples were measured for basic physical properties 

at the time received, before entering the kiln, and after 30

days of high-temperature exposure in the kiln. A kiln exposure of 160 °F dry-bulb temperature with low relative humidity in a 1,000-board-foot Irvington Moore Dry Kiln 

(Jacksonville, Florida) was used to simulate a hot and dry 

environmental condition that the ammo pallets could experience during service. Figure 2 shows all the sample boards 

wheeled into the dry kiln to be heated for a 30-day hightemperature exposure. The physical measurements on the 

board samples at each stage included the following:

• Measure warp (crook, bow, twist) of each board using 

aluminum wedges and a measurement table

• Mark end splits with a color pen (defect mapping)

• Measure stress wave velocity on each board (E-rating)

• Weigh each board

• Measure moisture content on a subsample of boards

Following the 30-day kiln exposure and final physical measurements in Princeton, boards of all three groups were 

shipped to the Forest Products Laboratory in Madison, Wisconsin, and stickered in a conditioning room of 75 °F and 

65% relative humidity. Upon reaching equilibrium moisture 

content, the boards were subjected to flatwise static bending 

testing with a center point load according to ASTM standard 

D 198 (ASTM 2014). Load-deflection data for each board 

were recorded to determine mechanical properties: modulus 

of elasticity (MOE), modulus of rupture (MOR), and work 

to maximum load (WML). During the static bending test 

process, a subsample of 20 boards were randomly selected 

from each group and a moisture block was cut from each of 

these boards for determination of moisture content (MC) using oven dry method ASTM D 4442-15 (ASTM 2015).

Results and Discussions

Dimensional Stability

As service conditions change during service, wood pallets 

tend to change dimension and develop defects such as 

checks, cracks, and splits. These defects could cause wood 

pallets to be downgraded or rejected if they are not within 

specifications. The quantitative parameters we examined 

concerning the dimensional stability of the pallet boards

were end splits and board warp (bow, crook, and twist). Figure 3 shows the distribution of end splits for three groups of 

pallet deck boards measured before and after the high-temperature kiln exposure. Table 1 summarizes the cumulative 

length of the end splits for each group.

Figure 1—Red oak and southern yellow pine boards as 

received: (top) red oak boards (nominal 1 by 6 by 

48 in.); (bottom) southern yellow pine boards (nominal 

1 by 6 by 48 in.).

Figure 2—Board samples entered into the dry kiln to 

be heated to 160 °F for a 30-day exposure.
Effects of Cedar Oil and Silica Gel Treatment on Dimensional Stability and Mechanical Properties of Southern Yellow Pine Boards

3

Figure 3—Distribution of end splits measured on red oak and southern yellow pine 

boards (1 in. = 25.4 mm).
Research Note FPL–RN–0339

4

No discernible differences in end splits for both red oak 

(Group 1) and untreated SYP (Group 2) were found before 

and after the kiln exposure. However, overall end splits in 

treated SYP (Group 3) were reduced 11% after kiln exposure. The cedar oil and silica gel treatment may have contributed to relief of drying stress during kiln exposure and 

subsequently yielding very few new short end splits while 

reducing the length of some visible splits based on our visual observation.

Table 2 shows cumulative warp for each board group. Overall, the red oak group had much less warp than the SYP

groups. This is not surprising, because the oak boards we received were high-quality wood with few defects (Fig. 1a). 

The SYP boards, on the other hand, were No. 2 grade and 

had various defects such as big knots, slope of grain, wane, 

and blue stain (Fig. 1b). For SYP boards, cumulative warp 

for the untreated group increased with a magnitude higher 

than that for the treated group. The cedar oil and silica gel 

treatment seemed to help stabilize wood and reduce the tendency of warping in SYP boards.

Mechanical Properties

Table 3 shows basic properties of the pallet boards measured at the time they were received. Both density and dynamic MOE of the oak group were significantly higher than 

those of two SYP groups (p = 0.0000) at a 95% confidence 

level. These measured properties are consistent with property values given in the Wood Handbook (FPL 2010) for the 

species.

For SYP boards, no statistical differences in density (p =

0.2538) and dynamic MOE (p = 0.0682) between Group 2 

(Untreated SYP) and Group 3 (SYP to be treated) were 

found at 95% confidence level, indicating that the SYP 

boards in these two groups can be deemed as having the 

same quality.

Table 4 shows the moisture conditions of the red oak, untreated SYP, and treated SYP boards before and after the 

kiln exposure and at the time of static bending tests. The 

MC dropped to 2.2% for red oak and about 7% for SYP after the 30-day kiln exposure. After conditioning in the environmental room at 75 °F and 65% RH for 2 months, the MC 

was up to 7.9% for red oak, 10.6% for untreated SYP, and 

10.4% for treated SYP.

Table 5 tabulates static bending properties (MOE, MOR, 

and WML) of the pallet boards after the 30-day kiln exposure. All static bending properties of the oak group are significantly higher than those of the two SYP groups at a 95% 

confidence level (p = 0.0000). There are statistical differences in MOE (p = 0.0218) and MOR (p = 0.0263) between 

Group 2 (SYP with no preservative treatment) and Group 3 

(SYP with preservative treatment) at the 95% confidence 

level. Both MOE and MOR decreased significantly in the 

treated SYP group compared to that in untreated SYP group, 

indicating a possible detrimental effect of the preservative 

on mechanical performance. There is no statistical difference in WML (p = 0.1778) between the two SYP groups at 

95% confidence level.

Conclusions

The red oak boards received were high-quality boards with 

very few defects. The 30-day dry kiln time did not have 

much effect on existing end splits and warp of the boards. 

Mechanical properties of the red oak group obtained 

through destructive bending tests were significantly higher 

than those of untreated SYP and preservative-treated SYP.

The cedar oil and silica gel treatment had a positive effect 

on dimensional stability of the No. 2 SYP boards. Cumulative length of the end splits in treated SYP was reduced by 

11% after kiln exposure, compared to that before kiln exposure, whereas cumulative length of end splits in untreated 

SYP remained the same after kiln exposure. The cedar oil 

and silica gel treatment likely contributed to relief of drying 

stress during high-temperature exposure and subsequently 

reduced the length of visible splits, though technically end 

Table 1—Cumulative length of end splits visually 

mapped on the boards at the time received, before kiln 

exposure, and after kiln exposure

Pallet deck board

No. of 

boards

Cumulative length of all end 

splits (in.)a

Received

Before kiln 

exposure

After 

kiln 

exposure

Group 1: Red oak 100 75.6 73.7 73.9

Group 2: Untreated SYP 100 93.7 89.0 89.4

Group 3: Treated SYP 100 71.3 72.3 64.3 a 1 in. = 25.4 mm.

Table 2—Cumulative board warp (crook, bow, twist) physically measured 

at time received, before kiln exposure, and after kiln exposure

Cumulative warp (in.)a

Pallet deck board

Received

Before kiln 

exposure

After kiln 

exposure

Crook Bow Twist Crook Bow Twist Crook Bow Twist

Group 1: Red oak 0.00 3.56 0.75 0.00 1.16 0.84 0.19 6.63 0.38

Group 2: Untreated SYP 0.66 5.84 7.31 0.63 3.53 6.59 1.84 11.44 11.75

Group 3: Treated SYP 0.81 4.78 5.19 0.29 4.21 3.25 1.69 7.31 5.41 a 1 in. = 25.4 mm.
Effects of Cedar Oil and Silica Gel Treatment on Dimensional Stability and Mechanical Properties of Southern Yellow Pine Boards

5

Table 3—Basic properties of the pallet deck boards 

measured at the time receiveda

Pallet deck boards

No. of 

boards

Density

(lb/ft3

)

Dynamic 

MOE 

(×106 lb/in2

)

Mean

Standard 

dev. Mean

Standard 

dev.

Group 1: Red oak 100 42.50 3.50 2.01 0.283

Group 2: Untreated SYP 100 32.54 3.53 1.56 0.320

Group 3: SYP to be treated 100 32.10 3.54 1.49 0.310 a 1 lb/ft3 = 16.02 kg/m3

; 1 lb/in2 = 6.895 kPa.

Table 4—Moisture content of pallet deck boards 

during the course of the project

Pallet deck boards

Moisture content (MC) (%)

Before kiln 

exposure

After kiln 

exposure

At time of 

static 

testing

Group 1: Red oak 7.1 2.2 7.9

Group 2: Untreated SYP 9.1 6.8 10.6

Group 3: Treated SYP 13.0 6.7 10.4

splits did not heal and just visually closed. Treated SYP also 

had less warp than the untreated SYP group. The treatment 

seemed to help stabilize the wood and reduce the tendency 

of warping in SYP boards.

The cedar oil and silica gel treatment had a detrimental effect on stiffness and strength of the No. 2 SYP boards. Both 

MOE and MOR decreased significantly in the treated SYP 

group compared to that of untreated SYP group. However, 

the preservative treatment had no significant effect on 

WML.

Literature Cited

Adams, R.P.; McDaniel, C.A.; Carter, F.L. 1988. Termiticidal activities in the heartwood, bark/sapwood and leaves 

of Juniperus species from the United States. Biochemical 

Systematics and Ecology. 16(5): 453-456.

Adams, R.P. 1991. Cedar wood oils—analysis and properties. In: Modern methods of plant analysis. New Series, Volume 12. Essential oils and waxes. Linskens, H.F.; Jackson,

J.F., eds. Berlin: Springer-Verlag. pp. 159-173.

ASTM. 2014. D 198-14. Standard test methods for static 

tests of lumber in structural sizes. West Conshohocken, PA: 

American Society for Testing and Materials.

ASTM. 2015. D 4442-15. Standard test methods for direct 

moisture content measurement of wood and wood-base materials. West Conshohocken, PA: American Society for 

Testing and Materials.

Clark, A.M.; McChesney, J.D. 1990. Antimicrobial properties of heartwood, bark/sapwood and leaves of Juniperus

species. Phytotherapy Research. 4(1): 15-19.

Forest Products Laboratory. 2010. Wood handbook—wood 

as an engineering material. General Technical Report FPLGTR-190. Madison, WI: USDA Forest Service, Forest 

Products Laboratory. 510 p.

Table 5—Static bending properties of pallet boards after 30-day hightemperature exposurea

Pallet deck boards 

No. of 

boards

MOE 

(×106 lb/in2)

b

MOR 

(lb/in2)b

WML

(in-lbf/in3)c

Mean

Standard 

dev. Mean

Standard 

dev. Mean

Standard 

dev.

Group 1: Red oak 100 2.03 0.320 15,021 2,455 10.6 3.60

Group 2: Untreated SYP 100 1.58 0.363 10,191 2,618 5.2 2.51

Group 3: Treated SYP 100 1.47 0.389 9,417 2,990 4.9 2.62 a Average moisture content (MC) of boards was 7.9% for red oak, 10.6% for untreated SYP,

and 10.5% for treated SYP. Wood Handbook property values at 12% MC: northern red oak,

MOE = 1.82 × 106 lb/in2, MOR = 14,300 lb/in2, WML = 14.5 in-lbf in3; loblolly pine,

MOE = 1.34 × 106 lb/in2, MOR = 9,400 lb/in2, WML = 10.4 in-lbf in3. b 1 lb/in2 = 6.895 kPa. c 1 in-lbf/in3 = 6.923 kJ/m3

.