effectiveness of copper-chrome-boron as wood … · non-durable timbers of kempas (koompassia...

Journal of Tropical Forest Science 6(2): 98 -115 98

EFFECTIVENESS OF COPPER-CHROME-BORON AS WOODPRESERVATIVE

Salamah Selamat, Zaitun Said & Fauzidah Ahmad

Forest Research Institute Malaysia, Kepong, 52109 Kuala Lumpur, Malaysia.

Received March 1992___________________________________________________

SALAMAH SELAMAT, ZAITUN SAID & FAUZIDAH AHMAD. 1993. Effectivenessof copper-chrome-boron as wood preservative. Kempas (Koompassia malaccensis) andmeranti tembaga (Shorea leprosula) samples of two different sizes were treated withCCB and exposed at two test sites. CCA (6%) was used as a reference preservative.A visual on-site assessment of decay on every test stake was made every three months fortwo years and every six months for each of the following years. The amount ofpreservative retained in the treated wood was determined by chemical analysis after6 and 12 months exposure at the test site. The relationships between type ofpreservative, preservative concentration, test site and wood species were statisticallydetermined. CCB preservative at the recommended concentration gave about thesame degree of protection as CCA in ground contact.

Key words: CCB and CCA preservatives-full cell- kempas-meranti tembaga-durability

SALAMAH SELAMAT, ZAITUN SAID & FAUZIDAH AHMAD. 1993. Keberkesanankuprum-kromium-arsenik sebagai bahan awit. Kempas (Koompassia malaccensis) danmeranti tembaga (Shorea leprosula) yang mempunyai dua saiz yang berlainan telahdiawit dengan CCB dan didedahkan di tapak ujian. CCA (6%) digunakan sebagaibahan awit rujukan. Penilaian secara penglihatan mata kasar terhadap kadar pereputpada setiap batang kayu dilakukan setiap tiga bulan selama dua tahun dan setiap enambulan pada tahun berikutnya. Kandungan bahan awit dalam kayu dipastikan dengananalisa kimia selepas 6 dan 12 bulan didedahkan ditapak ujian. Hubungkait diantarajenis bahan awit, kepekatan, tapak ujian dan jenis kayu telah dikenalpasti secarastatistik. Bahan awit CCB pada kepekatan yang dianjurkan telah dapat memberi kadarperlindungan yang sama dengan CCA.

Introduction

Copper-chrome-arsenic (CCA) preservatives are the most popular chemicalsused for effective treatment of wood in ground contact applications. Thesechemicals are effective against termites. Copper in the form of copper sulphate isvery effective against fungus especially soft rot. The chemical interaction, withchromium as a fixation agent, between copper, arsenic (Richardson 1978),andwood carbohydrates (Dahlgreen & Hartford 1972, Pizzi 1990a) and wood lignin(Pizzi 1979, 1981; Kubel & Pizzi 1982) makes these preservatives water insolubleforming stable complexes/esters. For this reason, leaching of the wood cannotredissolve or remove the preservatives. The combination of copper, chromium andarsenic gives high protection against the broad spectrum of biodegrading agents.In Malaysia, CCA is the most important type of waterborne preservative used for


pressure treated timber. The CCA treated timbers have been extensively put toindoor and outdoor uses since the 1960's (Daljeet 1982). However, due to thehigh toxicity of arsenic to human life, there is a need to find an alternative waterborne preservative, especially for indoor applications. There are various attemptsto overcome this problem, the best known being the replacement of arsenic withboron.

Some reports based on microbiological examination and marine borer assess-ments have indicated little difference between the performance of CCA and CCBtreated timber (Cookson & Barnade 1984, Anonymous 1985, Eaton 1987).

In this study, boron was used to replace arsenic in combination with copperand chromium since boron is also good as an insecticide. The objective of this studywas to determine the effectiveness of a CCB preservative with reference to 6% CCAis two different types of timber in contact with the ground.

Non-durable timbers of kempas (Koompassia malaccensis) and meranti tembaga(Shorea leprosula) were used in this study. Kempas is classified in strength groupA which is widely used in heavy construction and as structural component and iseasily treated with wood preservative. Meranti tembaga is widely used in lightconstruction, difficult to treat and classified in strength group C (Wong 1982).

Material and methods

Test sites

Two different localities were choosen from the FRIM grave yard plots forthis study. One plot was at a lower ground situated at 215 m above sea levelwith soil pH 4.84 and water holding capacity 63% in Jalan Jelutong and the upperground situated at 279 m above sea level with soil pH 4.52 and water holdingcapacity 62.5% in Jalan Bukit Watson area. The total yearly rainfall was 2176,2675 , 2998, 2415 and 2219 mm for the years 1986, 1987, 1988, 1989 and 1990respectively.

Test stakes

Two sizes of 0.75 X 0.75 X 24m and 1.5 X 0.25 X 24 in were used in thisstudy to determine the best size of the wood samples which would give thefastest decay result. Forty wood samples of each species, size, preservative(chemical), preservative (chemical) concentration and location combination atthe moisture content of 20% were prepared according to Table 1. The weightof each stake was determined immediately before commencement of the full celltreatment.


Table 1. Conditions of wood samples*

Species

Kempas

Merantitembaga

Size(in)

1.5x 0.25 x 240.75 x 0.75 x 24

1.5x0.25x240.75 x 0.75 x 24

Preservative

CCB

CCA

CCB

CCA

PreservativeConcentration

% m/v

5,6,8

6

5,6,8

6

Location oftest site

Lower ground & Upper ground




' 40 replicates for each sample size, type of preservative,preservative concentration and test site.

Wood preservative

The compositions of the preservatives were as follows :

Preservative

CCA type 2

CCB paste

Active ingredientCuSO4.5H2OK,Cr,07As2Os.2H20

CuS04.5H2OK,Cr,07

Composition (% m/m)32.341.519.7

32.345.020.0

Three concentrations were selected for CCB at 5,6 (recommended concentra-tion) and 8% m/v. CCA at 6% m/v was used as a reference preservative. The 6%concentration of CCA was selected because it was found effective to protectkempas of size 2 X 2 X 24 in (Daljeet & Dahlan 1991) at the same test plots.

Method of treatment

The wood preservatives were impregnated into the samples by full-celltreatment using the schedule below:

Initial vacuumInitial vacuum periodFlooding timePressurePressure periodDrainFinal vacuumFinal vacuum period

720 mHg45 in15 in14.06 Kgm2.5 h10 min

720 mmHg10 min

Journal of Tropical Forest Science 6(2): 98-115 101

Each wood sample was weighed immediately after treatment. The holdingperiod between time of treatment and time of installation was eight weeks to allowfixation of the preservatives under shade. Immediately after this period, six piecesof wood samples from each set were ground for chemical content determinationat zero month exposure.

Sample handling after treatment

The 34 wood samples from each set of factor combination were exposed at thesites in April 1986. Handling of test stakes after the treatment including installationin test plots and inspection of specimens and the grading system were based on theStandard Method of Evaluating Wood Preservatives by Field Tests With Stakes,ASTM D1758-74 (Anonymous 1974). Inspection was made every three months forthe first two years and every six months following the installation. In this reportdata at 3, 9, 15, 21, 30, 42 and 60 months are presented.

Chemical analysis of treated timber

Three replicates from each set of wood samples were collected after 6 and 12months exposure from the test plots for chemical content determination.

After these periods, only the destroyed samples were taken for fungal or insect(if assessible) identifications followed by chemical content determination.

The amounts of copper, chromium and arsenic in sample were determinedusing Malaysian Standard 821 (Anonymous 1983). The Japanese Standard(Anonymous 1986) was used for boron determination. The atomic absorptionspectrophotometer model Shimadzu AA-670 was used for chemical content de-termination.

Results and discussion

The amounts of preservatives absorbed by the wood samples after full celltreatment are shown in Table 2. The statistical analysis of the data using Anovashows that there are significant interaction effects at 5% level of significancebetween all factors (wood species, sample size, type of chemical and chemicalconcentration) tested, except for one of the six two - factor interactions, namelySI X C as shown in Table 3.

The results indicate that the effects of wood species, sample size and type ofpreservative used in the experiment varied among the concentrations of thepreservatives. It was also found that the effect of preservatives and concentrationvaried among the sample size.

Further analysis using Duncan's Multiple Range Test (DMRT) indicates thatkempas samples gave better preservative loading than meranti tembaga samplesafter full cell process regardless of the other three factors (at alpha 0.05). Samplestreated with CGA preservative differred significantly from those treated with CCBwhen using thin sample size. Samples treated with 8% m/v gave significantly

Journal of Tropical Forest Science 6(2): 98 - 1 1 5 102

Table 2. The amount of preservative solution absorbed by the woodsamples after full cell process

Preservative loading (kg m-1

based on

Species Size

Kempas B

Kempas A

Meranti Btembaga

Meran t i Atembaga

%m/v

5080

5086

5080

5686

Preservative

CCA

CCA

CCB

CCA

CCA

solutionabsorbed

289.4289.1336.7329.4

297.3334.3336.5315.8

207.2307.8324.1311.4

274.7317.3325.6312.6

a.i*

14.517.426.919.6

14.920.120.918.9

13.418.525.918.7

13.719.126.118.8

Note: A = 0.75 x 0.75 x 24 inB = 1.5 x 0.25 x 24 in* = concentration of active ingredient.

Table 3. Statistical analysis of variance of chemical loading and chemicalretention after full cell process (significance at 5% probability )

Chemical Loading Chemical Retention

Source

SPSICONcSP*SISP*CONSP*CSI*CONSI*CCON*CSP*SI*CONSP*SI*CSP*CON*CSI*CON*CSP*SI*CON*CERRORCORRECTED TOTAL

DF

1

2I12121221222

4871

Mean Square

5559.8538.57

13295.9513.20

1128.921898.05447.5078.0515.77

1350.81437.05

1578.28334.32247.97

1228.042.01

F Value

405.95*3.23ns

1114.32*1.11 ns

94.^1*159.12*37.50*0.45*1.32ns

113.21*36.68*

132.27*28.02*

• 20.78*102.97*

Mean Square

15.890.16

F Value

291.66*3.02ns

882.60 16202.24*0.043.454.502.040.300.056.561.635.591.640.814.46

0.71 ns03.30*83.60*48.44*5.50*0.87ns

20.39*29.85*

102.54*30.11*14.91*81.80*

Note: SP = species; SI = sample size; CON = preservative concentrationC = type of preservative; ns = not significant; * - significant

Journal of Tropical Forest Science, 6(2): 98 -115 103

better preservative loading than when treated with 6% m/v and 5% m/v at allfactor levels tested.

The grade indices for the wood samples after exposure to the ground atdifferent periods are shown in Figures 1 to 8. All meranti tembaga samples(Figures 1 to 4) and untreated kempas samples (Figures 5 to 8) were totallydestroyed after 60 months exposure. These figures show that not only the typeof preservative but also the wood species has a significant effect on the durabilityof the wood as supported by the statistical analysis.

Figure 1. The grade index assessment for meranti tembaga (shorea leprosula)of 1.5 X 0.25 X 24 in size at lower ground after exposure for 60 months

The statistical analysis of variance of these data at different levels ofpreservative concentration is shown in Table 4. The results of this analysis showthat three of the two - factor interactions are non-significant (SPC X LOC, LOC XSIZE, SIZE X CHEM). Further more, there are highly significant effects betweenthe three- and four- factor interactions (except for SPC X SIZE X CHEM). Theinteraction of all factors tested is not significant at all different preservativeconcentrations.


The Duncan's Multiple Range Test result shows that kempas was significantlyresistant (based on the grade index) against fungus and insect compared tomeranti tembaga. Meranti tembaga was found to be attacked after exposure on theground by soft rot and termites.

This test also shows that samples exposed at the lower ground were destroyedsignificantly faster than samples exposed at the upper ground. The total amountsof CCA and CCB in the treated wood (Figures 9-12) as dry salt retention showthat both types of preservative were leached out faster at the lower ground at anylevel of chemical concentration, wood species or sample size. The solubility of As,Cu and Cr is pH dependent (Bergholm 1990). Less sunlight passed through thelower ground than through the upper ground due to the tree crown above theplot. This condition might be more conducive to termite and fungal attack(Gunther 1976).

Further analysis using DMRT shows that kempas samples treated with CCAwere not significantly different from kempas sample treated with CCB up to 21months exposure . It was only up to three months for meranti tembaga. Afterthese periods samples treated with CCA were significantly more durable thanthose with CCB.


Figure 3. The grade index assessment for meranti tembaga (Shorea leprosula) of0.75 X 0.75 X 24 in size at lower ground after exposure for 60 months

Figure 4. The grade index assessment for meranti tembaga (Shorea leprosula) of0.75 X 0.75 X 24 in size at lower ground after exposure for 60 months


Figure 5. The grade index assessment for kempas (Kompassia malaccensis) of1.5 X 0.25 X 24 in size at lower ground after exposure for 60 months

Figure 6. The grade index assessment for kempas (Koompassia malaccensis) of1.5 X 0.25 X 24 in size at upper ground after exposure for 60 months

Journal of 7ropical Forest Science 6(2): 98 -115 107

Figure 7. The grade index assessment for kempas (Koompassia malaccensis) of0.75 X 0.75 X 24 in size at lower ground after exposure for 60 months

Figure 8. The grade index assessment for kempas (koompassia malaceccensis ) of0.75 X 0.75 X 24 in size at upper ground after exposure for 60 months


Table 4. Statistical analysis of variance (ANOVA) based on the performance of woodspecies (SPC), location (LOG), type of wood preservative (CHEM) and exposure

time (MON) in terms of the grade index (significance at 5% probability)at different preservative concentrations

Preservative concentration ('

Source

SPCLOGSIZECHEMMONSPC*LOCSPC*SIZESPC*CHEMSPC*MONLOC*SIZELOC*CHEMLOC*MONSIZE*CHEMSIZE* MONCHEM*MONSPC*LOC*SIZESPC*LOC*CHEMSPC*LOC*MONSPC*SIZE*CHEMSPC*SIZE*MONSPC*CHEM*MONLOC*SIZE*CHEMLOC*SIZE*MONLOC*CHEM*MONSIZE*CHEM*MONSPC*SIZE*CHEMSPC*I.OC*SIZE*MONSPC*SIZE*CHEM*MONLOC*SIZE*CHEM*MONSPC*LOC*CHEM*MONSPC*LOC*SIZE*CHEM*MONERRORCORRECTED TOTAL

- DF

1119

6I]2612626

1212626

1226

121226

12121212

504671

MeanSquare

1142.4512.5425.85

1465.79529.56

0.274.18

22.0739 3S0.375.605.860.236.08

56.693.185.495.130.114.59

57.055.500.735.883.215.200.863.730.792.040.270.219

F Value

5217.90*57.28*

118.06*6694.68*2418.64*

1.22ns19.09*

100.81*179.65*

1. 70ns25.58*26.76*

1. 06ns27.77*

258.91*14.51*25.08*23.43*0.51ns

20.98*260.56*25.11*3.34*

26.84*14.65*23.74*3.92*

17.05*3.63*9.31*1.22ws

MeanSquare

1053.5013.7732.33

1539.16519.61

0.1913.7721.0351.120.224.864.340.278.40

54.007.939.247.590.395.83

62.277.222.264.472.18

10.261.721.912.332.340.300.216

F Value

4870.80*63.67*

149.48*7116.22*2402.38*

0.90ns63.67*97.22*

236.34*1.03ns

22.45*20.04*

1.24ns38.85*

249.66*36.66*42.73*35.09*

1.82ns26.93*

287.88*33.36*10.46*20.64*10.09*47.45*

7.94*8.83*

10.79*10.81*

1 .39ns

MeanSquare

978.7526.0121.79

1582.38514.94

0.100.75

23.0650.65

0.200.922.600.297.27

56.733.574.113.720.083.36

60.601.852.263.961.845.632.272.820.751.700.330.219

F Value

5001.43*132.90* .1 1 1 .33*

8085.98*2631.32*

0.5 Ins54.94*

117.85*258.83*

0.93ns4.72*

1 3.30*1.47ns

37.16*289.88*

18.26*20.99*19.00*

0.38ns17.19*

309.67*9.46*

11.72*20.22*9.39*

38.75*1 1 .60*14.44*3.81*8.69*1 ,68ns

Note: SPC = species; LOG = location; CHEM = type of preservative; CON = preservative concentrationMON = months; ns= not significant; * = significant

However, the samples treated with CCA or CCB were significantly protectedfrom termite and soft rot as compared to untreated samples. The difference inperformance of CCA and CCB preservatives between kempas and meranti might bedue to the reaction of CCA and CCB with the carbohydrates (Pizzi 1990a), woodlignin (Pizzi 1990b) and the salt distribution in the respective wood (Salamah &Zaitun 1991). The amount of lignin and carbohydrates in the respective wood mayaffect the amount of stable insoluble complexes formed by Cr with lignin (Pizzi


Exposure: period (months)

Figure 9. The amount of ary salt retention in CCB and CCA treated kempasat two different test sites for sample size of 0.75 X 0.75 X 24 in

Exposure period (months)

Figure 10. The amount of dry salt retention in CCB and CCA treated kempasat two different test sites for sample size of 0.75 X 0.75 X 24 in


Exposure period ( m o n t h s

Figure 11. The amount of dry salt retention in CCB and CCA treated merantitembaga at two different test sites for sample size of 0.75 X 0.75 X 24 in

Figure 12. The amount of dry salt retention in CCB and CCA treated merantitembaga at two different test sites for sample size of 0.75 X 0.75 X 24 in


1979, 1982; Hon & Chang 1985). Statistical analysis based on various CCB preser-vative concentrations shows no significant difference in treatment at concentra-tions of 8, 6 and 5% m/v up to 21 months exposure for kempas and up to 3 monthsexposure for meranti tembaga against wood destroying agents. The effect ofpreservative concentration was detected to be highly significant only after 21months exposure for kempas and 3 months for meranti. Samples treated withconcentration 8% m/v show no significant difference to samples with concentra-tion 6% m/v. However, samples treated with concentrations 8 and 6% m/v weresignificantly better protected that those treated with concentration 5% m/v.

The result from this study shows that the sample size at 0.75 X 0.75 X 24 inwas not significantly different from that at 1.5 X 0.25 X 24 in based on the gradeindex. However, the latter sample size caused easy mechanical damage to thesamples during the test, especially for meranti tembaga.

Assessment at various months after exposure at the test plots shows that thegrade index of samples significantly decreased as the number of months increased.It means that the samples were more susceptible toward termite or/with funguswhen the samples were left longer in the ground. One reason might be due to theleachability of the respective salt in the treated wood (Tables 5 and 6). Three typesof subterranean termites were found as the major destroying agents at the plotsduring the 60 months exposure period, i.e. Macrotermes maccensis, Coptotermescurvignathus and Odontotermes sp.. Only one type of decay fungus was found onthe wood during that period, that is soft rot. However, the type of soft rotattacking the wood was not identified. Both termites and soft rot were found in allsamples. Nearly 80% of the wood deterioration was due to termite attack and20% from soft rot.

There are many types of complexes that can be formed between any individualsalt or salts in CCA and CCB with the wood components or extractives. Thesereactions are still under study by many scientists interested in wood preservation.The individual salt of copper, chromium, arsenic and boron in the treated woodhas a tendency to leach out after exposure of the wood to water or rain for a certainperiod. However, the rate of leaching for boron from the treated wood is muchhigher than that of the other three chemicals as shown in Tables 5 and 6.

Conclusion

CCA and CCB preservatives gave almost the same degree of protection at 6%of solution strength. The similarity in performance of the two preservatives isinteresting, particularly in view of the more severe loss of boron from the CCBtreated timber than arsenic from the CCA treated timber.

In this study the most important factors influencing the severity of attack werethe site conditions and type of timber. There are many factors which contribute tothe performance of treated woods in ground contact such as timber permeabilityand the distribution of preservative within the wood structure. Further study isrecommended for preservative distribution in the wood structure after treatmentand the effect of extractives on the preservative fixation.

Table 5. The percentage of individual compounds in treated rnerantitembaga slakes at. 0, 6 and 12 months exposed in the test, plots

Location Size Preservative

LG A CCB

CCA

UG A CCB

CCA

I.G B CCB

CCA

UG B CCB

CCA

% m/v

5686

5686

5686

568G

Cu salt

0.770.861.980.72

0.770.861.980.72

0.861.1 11 .240.63

0.861.111.240.63

CONTROL

Cr salt.

1.301.682.331.82

1.301.682.331.82

1.131 .521.891.36

1.131.521.891.36

As/B salt

0.510.491.391.01

0.510.491.391.01

0.320.450.520.97

0.320.450.520.97

On salt

0.610.691.050.5 1

0.710.811.480.57

0.680.721.120.52

0.770.831.170.40

6 MONTHS

Cr salt

0.811.222.471.53

1.241 .442.071.61

0.991.121.451.12

1.011.271.581.23

As/B salt

0.250.370.360.97

0.310.280.901.00

0.190.260.360.78

0.290.170.400.91

On salt

0.570.520.980.38

0.290.490.940.45

0.430.580.940.43

0.540.760.980.26

12 MONTHS

Cr salt

0.680.841.391.23

0.871.151.781.31

0.720.931.140.96

0.830.971.331 .06

As/B salt

0.130.200.200.57

0.090.170.350.96

0.010.140.260.87

0.060.170.130.90

I

'-D00

Note: A = 0.75 x 0.75 x 24 inB= 1 . 5 x 0 . 2 5 x 2 4 inLG = Lower ground

Cu salt = C u 2 s o 4 .Ou salt = K.,Cr./XAs salt = As.,O5.2H,O

Table 6. The percentage of individual compounds in treated merantitembaga stakes at 0, 6 and 12 months exposed in the test plots

Location Size Preservative

LG A GCBCCBGCBCGA

UG A CCBCCBCCBCCA

LG B CCBCCBCCBCCA

UG B CCBCCBCCBCCA

% m/v

5686

5686

5686

5686

Cu salt

0.650.701.140.45

0.650.701.140.45

0.530.770.980.49

0.530.770.980.49

CONTROL

Cr salt

1.041.161.420.72

1.041.161.420.72

0.620.841.180.69

0.620.841.180.69

As/B salt

0.130.100.280.68

0.130.100.280.68

0.210.270.180.57

0.210.270.180.57

Cu salt

0.310.531.950.37

0.590.681.010.47

0.430.690.700.44

0.470.700.810.42

6 MONTHS

Cr salt

0.640.871.120.68

1.080.991.210.68

0.510.731.020.68

0.570.901.040.60

As/B salt

0.100.070.130.49

0.090.070.190.56

0.100.150.120.43

0.190.160.070.22

Cu salt

0.300.410.470.33

0.480.520.630.41

0.200.330.370.33

0.370.440.490.33

12 MONTHS

Cr salt

0.420.571.681.52

0.531.651.981.57

0.370.440.690.56

0.430.710.820.53

As/B salt

0.050.080.110.39

0.070.050.080.48

0.070.080.090.38

0.080.120.070.46

I00

SS

Note: A = 0.75 x 0.75 x 24 inB= 1.5 x 0.25x24mLG = Lower groundUG - Upper ground

Cu salt = Cu,SO,.5H2OCu salt = K^C^O,As salt = As2O5.2H2OBsalt = HaBO,


Based on this study, CCB preservative was found to be effective for woodprotection under Malaysian conditions. However, the treated wood can be usedonly for indoor application which is protected against rain. This is due to the boronin CCB preservative that is largely unfixed in the wood and will leach out when thetimber is exposed to rain and ground contact. The actual concentration of woodpreservative that should be used in the treatment solution would have to bedetermined and approved by the relevant authorities.

Acknowledgement

We are grateful for the assistance received from the Entomology Section ofFRIM and Andrew Wong for termite and fungi identification respectively, andAzizol Abd. Kadir, Khoo Kean Choon and external reviewers for their valuablecomments on a draft of this paper. We also wish to thank the Soil Science Sectionof FRIM for analysing the soil samples and Flassan Buang, Zahari Mohd Nor andMohamad Daud for their technical assistance.

References

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