Evaluation of Durability Conferred by an Oleothermic Treatment on Chestnut and <i>Douglas fir</i> through Laboratory and in Field Tests

doi:10.4236/ojf.2013.32011

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Open Journal of Forestry

2013. Vol.3, No.2, 66-69

Published Online April 2013 in SciRes (http://www.scirp.org/journal/ojf) http://dx.doi.org/10.4236/ojf.2013.32011

Evaluation of Durability Conferred by an Oleothermic

Treatment on Chestnut and Douglas fir through

Laboratory and in Field Tests

Sabrina Palanti

CNR IVALSA, Consiglio Nazionale delle Ricerche Istituto per la Valorizzazione del Legno e delle Specie

Arboree, Sesto Fiorentino, Italy

Email: [email protected]

Received December 11th, 2012; revised February 11th, 2013; accepted February 27th, 2013

bution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the

original work is properly cited.

The research evaluated two wood species, chestnut and Douglas fir, that are widespread in Tuscany,

treated with an oleothermicprocess. Efficacy of this treatment against fungal decay was assessed through

laboratory and field tests. The aim of this research was to investigate if an oleothermic process could add

value to these natural resources when utilized in Use Class 4 (EN 335) for agricultural purposes such as

vineyard poles. The treatment was effective on sapwood of both wood species in laboratory test, giving a

protection similar to the untreated heartwood but in case of chestnut, it was easily washed away. In field

test the leaching during the outdoor exposure reduced the resistance to fungal decay in both species.

Keywords: Conferred Durability; Chestnut; Douglas fir; Oleothermic Treatment

Introduction

The conventional wood protection for Use Classes 3 and 4

according to EN 335 (2006) is actually based on broad spectrum

biocide formulations such as copper/organic biocides, copper-

organometallics, metal free preservatives (Hughes 2004), and

alkyl ammonium compounds (Pernak et al. 2004).

In the last decade, there has been a great interest within Eu-

rope in oils and water repellents for wood preservation prince-

pally focusing on screening of natural and synthetic oils (Sailer

and Rapp 2001; Van Eckeveld et al. 2001; Palanti et al. 2004),

and on the processes for development of wood preservation

technology (Thevenon 2001; Treu et al. 2001). Chestnut and

Douglas fir are widely planted in Tuscany. Tuscany forest con-

tains 862 hectares with 21% of chestnut and 4% conifers prin-

cipally pine, Douglas fir and silver fir (Sanchez et al. 2005).

Promoting the use of these species for agricultural purpose

could add value to this natural resource.

Oleothermic treatment was explored for improving the natu-

ral durability of these species (Grenier et al. 2003). This process

has been known as eco-friendly, biocide-free, cheaper, capable

of being applied without drying the wood.

Oleothermic treatment also prevented the tannin leaching

from chestnut which could maintain natural durability for a

longer period (Grenier et al. 2003). While these results are pro-

mising, there is few data on the long-term performance of oleo-

thermic treated chestnut and Douglas fir heartwood and sap-

wood. In order to evaluate these materials the following test

were performed:

1) Laboratory tests of chestnut and Douglas fir sapwood,

treated with oleothermic treatment, in according to EN 113 and

EN 84.

2) Natural durability test in according to EN 252 (in field) of

Chestnut and Douglas fir.

3) Resistance test in according to EN 252 of treated Chestnut

and Douglas fir.

Materials and Methods

Wood Species

The tested wood species were chestnut (Castanea sativa Mill.)

and Douglas fir (Pseudotsugamenziesii Mirb. Franco) of Tus-

can origin, from Casentino, a valley near Arezzo. The reference

controls were Scots pine (Pinus sylvestris L.) and European

beech (Fagus sylvatica L.), sapwood, in accordance with Euro-

pean norms EN 350-1:1996 and EN 113:1996 and EN 252:

1989.

Treatment

The oleothermic treatment was performed at CIRAD in

Montpellier, France using a two-step process (Grenier et al.

2003).

Chestnut and Douglas fir planks were conditioned at 20˚C

and 65% RH, cut in samples and sent to the plant for oleother-

mic treatment.

The treated samples were then conditioned to constant

weight at 20˚C and 65% RH.

Laboratory Test

Wood blocks (50 ± 0.5) × (25 ± 0.5) × (15 ± 0.5) mm3, were

S. PALANTI

cut from the boards.

Natural durability and the durability conferred by oil treat-

ment of chestnut and Douglas fir were assessed in accordance

with European standards EN 113 and EN 350. A comparison of

resistance against fungi before and after leaching in accordance

with EN 84 was carried out.

The fungi utilized for chestnut and Douglas fir were two

brown rots, Coniophora puteana (Schumacher ex Fries) Kar-

sten, strain BAM Ebw. 15 and Gloeophyllum trabeum (Persoon

ex Fries) Murril, strain BAM Ebw. 19. The white rot fungus,

Coriolus versicolor (Linnaeus) Quélet, strain CTB 863 A was

only utilized for chestnut. The brown rot fungus Poria placenta

(Fries Cooke) sensu J. Eriksson, strain FPRL280 was utilized

for Douglas fir. These fungire present the certificated ones util-

ized in the European normative.

The wood samples were exposed to fungal attack for 16

weeks in a conditioning room (22˚C ± 2˚C, 70% ± 5% RH). For

each set, a treated sample was placed with a reference untreated

sample in a Kolle flask containing one of the test fungi growing

on 20 ml of 4% malt and 2.5% agar medium. Another set of

five untreated wood specimens was used to check for strain

virulence for each tested fungus.

The resistance against fungi was evaluated using mass loss of

wood, which was calculated for each individual block as the

difference between the dry mass before and after the fungal

exposure. The minimum of mass loss on reference wood blocks

were 30% for C. puteana and 20% for P. placenta, G. trabeum

and T. versicolor.

The natural durability class was calculated according to

CEN/TS 15083, expressed as durability class, against wood

destroying basidiomycetes fungi based on the higher median

mass loss determined for all test specimens exposed to each of

the three test fungi. Using the following scale: 1- very durable

(mass loss ≤ 5%), 2- durable (mass loss >5% to ≤10%), 3-

moderately durable (mass loss >10% to ≤15%) 4- slightly du-

rable (mass loss >15% to ≤30%), 5- not durable (mass loss >

30%).

Leaching in Accordance with EN 84

Wood samples, see Table 1, were subjected to leaching ac-

cording to EN 84: 1996. The cycle consisted of an initial 4 kPa

vacuum - atmospheric pressure cycle with deionized water EN

ISO 3696 (1996). The wood specimens were maintained in

water (ratio of water to wood 5:1) for 14 days with 9 water

changes, and then conditioned to constant mass before being

exposed to one of the test fungus.

Table 1.

Median mass losses % of non-treated Chestnut heartwood or sapwood

that was oleotheric treated. Samples were exposed to 3 fungi of EN

113 (H: heartwood, S: sapwood, T: Treated, L: leached, Y: yes, N:not,

D class: durability class ).

Median mass loss %

(n = 5)

S T

Y/N L

Y/N C.

puteana C.

versicolor G.

trabeum

class

S Y N 1.24 1.49 - 1

S Y Y 12.91 12.50 12.92 3

H N N 1.33 1.17 0.92 1

H N Y 3.41 3.39 3.10 1

In Field Test

In ground performance tests were performed in accordance

with EN 252: 1989 over a 70 months period (July 2005 to April

2011). The test site was on an agricultural soil situated in Tus-

cany, Cesa, Val di Chiana Arezzo.

Fifteen stakes for wood species, dimensions (500 ± 1) × (50

± 3) × (25 ± 0.3) mm3, derived from heartwood chestnut, heart-

wood and sapwood Douglas fir were conditioned and cut be-

fore being sent to the plant for oleothermic treatment.

The treated stakes were placed vertically in the soil leaving

half of length exposed.

Untreated stakes of Scots pine and beech were also buried up

to half their length in the soil test site as reference controls.

Fungal decay was annually evaluated in the area around the

ground contact. Inspections were carried out by giving a light

blow to the upper part of each stake to determine if the stake

was close to failure, followed by removal from the ground.

Surface examination was probed with an awl to detect weak-

ness due to fungal rot. Fungal decay was evaluated on the basis

of the depth of fungal softening and damaged area according to

a specific rating system: 0 sound, 1 slight attack, 2 moderate

attack, 3 severe attack and 4 failure (stake breaks in the ground

after blowing). The evaluation was performed in accordance

with guideline for EN 252 of the Nordic Wood Preservation

Council (Borsholt and Henriksen, 1992).

It is possible to calculate the mean life as indicated in stan-

dard EN 350-1 when all stakes fail. The mean life, where not all

stakes have reached the end of their life, can be predicted using

the procedure of Purslow, 1976.

The number of replicates utilized for calculating average de-

cay grade was unequal for wood species and treatments because

some stakes failed as the test site who maintained and it was not

possible to determine whether decay was the sole cause of failure.

Statistical Analyses

Analysis of variance (ANOVA) one-way, ANOVA multiple

factors way and a post-hoc Tukey HSD multiple comparisons

of means were carried out with open source R software.

The statistical analyses were on the following tests:

Laboratory test: chestnut and Douglas fir mass loss % of

blocks exposed to C. puteana.

Field test: chestnut decay rating after six year; Douglas stakes

rating of third (mid-term evaluation) and sixth year.

Results and Discussion

Laboratory Tests

Chestnut

Average uptake of oleothermic treatment on sapwood (n = 39)

was 13% as (m/m) %.

The results obtained by natural and the conferred durability

are reported in Table 1. Results due G. trabeum were omitted

because the beech reference wood blocks had mass losses lower

than minimum required by the standard.

The oleothermic treatment provided a good protection to

sapwood but it was not fixed very well. Durability rating de-

creased from 1 to 3 when the wood was leached in accordance

with ageing procedure EN 84. Durability of non-leached treated

was similar to the inherent durability of non-leached heartwood.

Weight losses of non-treated heartwood samples increasedwith

S. PALANTI

leaching procedure, but the increase did not affect the durability

class.

The one-way analysis of variance (Anova) of mass loss % of

different treatment against C. puteana, indicated that there were

significant differences between samples (F3,16 = 2.2e−16***).

The post hoc Tukey multiple comparisons of means, at a 95%

family-wise confidence level, showed a significant difference in

leached and non-leached treated chestnut underlined that the

oleothermic gave a good durability (Table 2). In leached and

non-leached heartwood the significant difference depended on

leaching procedure that washed away the natural extractives. It

was also interesting observe that only pair with not significant

difference was untreated heartwood and treated sapwood where

it was found a similar grade of effectiveness when exposed to C.

puteana. This fact confirmed that sapwood treated with oleo-

thermic treatment reached the same grade of durability of the

heartwood.

Douglas fir

The average oleothermic uptake (n = 4) in sapwood and

heartwood were 16% and 14% m/m % respectively.

The oleothermic treatment gave a good protection to Douglas

fir sapwood, improving durability to class 2 (Table 3) in both

leached and non-leached blocks.

In the untreated Douglas fir heartwood the leaching proce-

dure determined a decreasing in durability from class 2 to 4.

Probably this low durability was due to the fact that the leach-

ing procedure washed away most part of the extractives.

Table 2.

Post hoc Tukey multiple comparisons of means at a 95% family-wise

confidence level. T: treated, U untreated, L Leached, S sapwood, H

heartwood.

Pair Mean

differ-

ence

Lower

bound Upper

bound

p value at

a 95%

confident

level

TSL-TS 11.692 10.7594919 12.624508 0.0000000

UH-TS 0.116 −0.8165081 1.048508 0.9839834

UHL-TS 2.396 1.463491 3.328508 0.0000089

UH-TSL −11.576 −12.5085081 −10.643492 0.0000000

UHL-TL −9.296 −10.2285081 −8.363492 0.0000000

UHL-UH 2.280 1.3474919 3.212508 0.0000164

Table 3.

Median mass loss % of Douglas fir (H: heartwood, S: sapwood, T:

Treated, L: leached, Y: yes, N:not). In the brackets the number of

samples utilized for the determination of the medians are reported.D

class: Durability class.

Median Mass loss %

S T

Y/N L

Y/N C.

puteana G.

trabeum P.

placenta

class

S Y N 1.37 (2) - 7.67 (2) 2

S Y Y 7.42 (5) 3.62 (3) 5.91 (4) 2

H N N 3.88 (3) 3.79 (2) 9.03 (4) 2

H N Y 12.37 (3) 1.45 (4) 19.67 (2) 4

S N N 11.26 (4) 5.02 (2) 13.89 (4) 3

The set of untreated sapwood gave reaching the durability

class 3 (Table 2).

The one-way analysis of variance (Anova) of mass loss

showed that there were significant difference among treatments

with fungus C. puteana, gave significant differences between

means ((F6,16 = 0.784800**). The post hoc Tukey multiple

comparisons of means, 95% family-wise confidence level, evi-

denced significance in the mass loss in all combination with the

exclusion of the pairs untreated heartwood-treated and leached

sapwood, untreated heartwood-treated sapwood. The efficacy

of treatment when applied into sapwood, and its fixation is

evidenced by not significance between untreated heartwood-

treated and leached sapwood.

In Field Test

Chestnut

The year-by-year results obtained by in field test of chestnut

are reported in Table 4.

Only a slight difference was observed between treated and

non-treated chestnut stakes. Four of eight treated stakes failed

(decay grade 4) at the end of the test, and the mean life of these

stakes was six years. Five of twelve untreated chestnut failed at

sixth year with a mean life of 6 years, the number of ruptures

was 6 on 12 and the mean life was, as well as treated ones, six

years. The beech control stakes all failed after two years.

The analysis of variance of the decay grade of 68 months

evidenced significant difference between treated and non-

treated samples (F2,27 = 0.03873*). The post hoc Tukey multi-

ple comparisons of means at 95% family-wise confidence level,

indicated that there are significant differences in decay grade

were weather untreated chestnut and beech.

Douglas fir

In the Table 5 are reported the overall results obtained from

Douglas fir stakes.

In the treated heartwood, at the end of the test, six stakes on

eight reached the rupture with a mean life 5.33 years. In the

treated Douglas fir sapwood set at the end of the test 9 on 10

stakes reached the decay grade 4 with a mean life 5.11 years.

The Douglas fir untreated set sapwood reached a mean life 4.60

years. In the untreated heartwood set only two stakes on 10

reached the rupture.

The decay grade of 68 months evidenced significance be-

tween samples (F4,38 = 0.00064***) and the post hoc Tukey

multiple comparisons of means, 95% family-wise confi-

dencelevel, gave as significant the pairs untreated Douglas fir

Table 4.

Decay rating of average annual evaluations of Chestnut in field testing.

Average decay rati ng

Exposition

time (month)Treated

Chestnut,

heartwood

Untreated

Chestnut,

heartwood Beech

13 0.23 0.21 2.1

23 0.25 1.00 3.6

36 1.13 1.57 3.9

47 1.75 2.21 4.0

62 2.25 2.50 Failed

68 3.38 3.29 Failed

S. PALANTI

Table 5.

Decay rating of field average annual evaluations of Douglas fir.

Average decay rati ng

Exposition

time (m on th ) Trea ted Douglas fir

sapwood Treated Douglas fir

heartwood Untreated Douglas fir

sapwood Untreated Douglas fir

heartwood Scot pine sapwood

13 1.09 0.11 1.00 0.30 0.3

23 1.36 0.78 1.29 1.00 1.1

36 1.55 1.44 2.29 1.70 4

47 2.80 2.63 3.14 2.20 4

62 2.90 2.63 3.14 2.40 Failed

68 3.89 3.75 3.71 3.11 Failed

heart wood-treated Douglas fir sapwood, untreated Douglas fir

heartwood-treated Douglas fir heartwood and Scot pine-un-

treated Douglas fir heartwood.

Conclusion

The results showed that oleothermic treatment improved the

durability of chestnut and Douglas fir, both laboratory and

fields exposition. Oleothermic treatment provided a good pro-

tection to chestnut sapwood as evidenced by laboratory ex-

periments, but the treatment it was susceptible to the leaching

during the field test.

With regarding Douglas fir field test is remarkable that the

significant difference observed in the pair heartwood treated

and not treated was due also to the presence of natural extrac-

tives inside the wood, responsible for the conferred durability.

The protection given by oil was susceptible to leach and further

studies are recommended to develop methods for fixing the

treatment.

Acknowledgements

The author thanks the Regional Agency for Agriculture De-

veloping and Innovation (ARSIA) that supported this research,

CIRAD for theoleothermic treatment, and Mrs. Anna Maria

Torniai from CNR Trees and Timber Institute who helped with

fungi cultures.

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