Published Date
Wood Composites 2015, Pages253–310,doi:10.1016/B978-1-78242-454-3.00011-1
Author
M.J. Spear
Abstract
With the widespread use of wood composites in the modern world – from panel products to engineered lumber – there is a need to understand their strengths and weaknesses with respect to weathering and decay. Wood composites have shown very good performance, and substantial service lives when correctly specified for the exposure risks present. Selection of an appropriate product for the job should be accompanied by decisions about the appropriate protection, whether this is by design, by preservative treatment or by wood modification techniques. This chapter reviews many of the environmental hazards encountered by wood composites (moisture, UV degradation, decay, insect attack and fire) and many of the strategies used to counter them.
I. E. Ssemaganda1 , P. Mugabi1 , S. B.Tumwebaze2
ABSTRACT
Termites are one of the major wood destroying agents in the tropics and with the increasing rate
of deforestation, there is a need to protect wood from biodegradation in order to extend its service
life. In this study the incidence and severity of termite attack on Eucalyptus grandis sapwood treated
with CCA, used engine oil and neem extract were investigated. Sixty samples (20 × 20 × 300mm)
were prepared from the sapwood at mid-height of the tree of E. grandis and air seasoned for two
weeks then treated with the preservatives. An area of 20m by 20m in a pine plantation and 15 plots
of 1m by 1m were selected at random. Four samples, one from each treatment, were placed at the
corners of the selected plots.
Inspection and evaluation of stakes was made by visual assessments after every 30 days for
any sign of termite attack for a period of 8 months. The specimens were removed from the ground,
damage assessed and returned to the ground. After 4 weeks all the untreated wood samples had
been attacked, neem extract treated wood samples were attacked after 17 weeks and used engine oil
treated samples after 30 weeks. None of the CCA treated wood samples were attacked by the end
of study period. Chi square analysis showed a high association between treatment and incidence
as well as between treatment and severity. It was recommended that further research be carried out
on neem extract using different concentrations.
Keywords: Eucalyptus grandis, preservatives, termite attack, Uganda INTRODUCTION
Bowyer et al. (2003) indicated that wood products in use throughout the world are subject
to infestation by insects. The same authors further noted that of the insects, termites have by far
the greatest economic importance. Termites destroy wood by feeding on its components, thereby
reducing its structural ability and appearance. Cellulose being the principal food of termites, wood
and wood products such as paper, fabrics and wood structures are avidly consumed, and hence, a
constant effort is directed towards their control (Peralta et al. 2004).
Eucalyptus grandis is one of the widely used construction tree species in Uganda. It is used for
electricity poles, fence posts and roof trusses. However, in a survey carried out in Tororo district
in Uganda, Nyeko and Olubayo (2005) reported that eucalyptus species are highly susceptible
to termites. Some of the strategies to protect wood from termite attack include using naturally
resistant tree species and applying toxic chemicals to wood. The common preservatives used in
Uganda to protect wood against biodegrading agents are creosote, used engine oil and Chromated Copper Arsenate (CCA). Over the past few decades, there has been a substantial global quest to
develop eco-friendly wood preservatives which do not cause any ill effect on the health of mammals
(Venmalar and Nagaveni 2005). The search for effective bio-control methods for wood preservation
is continuing but one that could be useful is the natural insect growth regulator, azadirachtin (AZA).
This botanical compound can be effective yet it is biodegradable and rapidly metabolizes in the
environment (Weathersbee and Tang 2002). AZA can be extracted from the seeds of Azadirachta
indica i.e. the neem tree. According to Venmalar and Nagaveni (2005) neem possesses a number
of toxic constituents exhibiting high toxicity against wood destroying microbes. However, the
effectiveness of chemicals to control biological attack on wood depends upon the wood, the chemical
used and the pests that are present and environmental conditions following treatment (Johnson,
2000). As Walker (1993) noted, the use of a single, universal wood preservative treatment does not
provide optimal economy since the spectrum of hazards to which timber is exposed is wide both
in type and severity. This spectrum of hazards includes attack by fungi, insects and marine borers,
any of which can result in degradation at varying rates depending on the immediate environment.
The objectives of the study were to determine (i) the incidence and (ii) severity of termite attack
on E. grandis sapwood samples treated with CCA, used engine oil and neem extract.
MATERIALS AND METHODS
Timber
One Eucalyptus grandis tree of DBH 25cm was felled from a wood lot in Masaka district, central
Uganda. The tree was crosscut into three portions of 4m each representing the butt, middle and
top parts. The middle portion was further cross cut into two billets of 2m each which were used to
produce eight 20×50×2000mm boards from the sapwood. Each board was then ripped into two 20×
20× 2000mm scantlings (Fig. 1). Sixty samples of 20× 20 × 300mm were then prepared from the
scantlings (Fig. 1) and air seasoned for two weeks to approximately 20% moisture content and
then treated with the preservatives.
For further details log on website :
http://www.scielo.cl/pdf/maderas/v13n2/art01.pdf
Historically most residential wood preservatives were aqueous soluble metal formulations, but recently metals ground to submicron size and dispersed in water to give particulate formulations have gained importance. In this study, the specific role nano-zinc oxide (ZnO) particle size and leach resistance plays in termite mortality resulting from exposure to particulate ZnO-treated wood was investigated. Southern yellow pine (SYP) sapwood impregnated with three concentrations of two particle sizes (30 and 70 nm) of ZnO were compared to wood treated with soluble zinc sulphate (ZnSO4) preservative for leach resistance and termite resistance. Less than four percent leached from the particulate nano-ZnO-treated specimens, while 13 to 25% of the zinc sulphate leached from the soluble treated wood. Nano-ZnO was essentially non-leachable from wood treated with 5% formulation for the 30-nm particle size. In a no-choice laboratory test, eastern subterranean termites (Reticulitermes flavipes) consumed less than 10% of the leached nano-ZnO-treated wood with 93 to 100% mortality in all treatment concentrations. In contrast, termites consumed 10 to 12% of the leached ZnSO4-treated wood, but with lower mortality: 29% in the 1% treatment group and less than 10% (5 and 8%, respectively) in the group of wood blocks treated with 2.5 and 5.0% ZnSO4. We conclude that termites were repelled from consuming wood treated with nano-ZnO, but when consumed it was more toxic to eastern subterranean termites than wood treated with the soluble metal oxide formulation. There were no differences in leaching or termite mortality between the two particle sizes of nano-ZnO.
Introduction
Zinc oxide (ZnO) has a long history of use in numerous applications in forest products and related industries, including UV stabilization in wood coatings, as an antifouling agent in marine paints, pigment and mold inhibitor in latex paints and in coatings for paper. Eco-toxicity tests from the PAN Pesticide Database state that ZnO is moderately toxic to amphibians and fish, and highly toxic to certain types of zooplankton [1]. ZnO occurs naturally as the mineral zincite and is available commercially as either micron or submicron-sized milled powders or as pyrolyzed nano-sphere dispersions. Zinc is a key component of the wood preservative ammoniacal copper zinc arsenate (ACZA), and many wood-plastic composites are treated with zinc borate [2, 3].
Nano-materials often exhibit novel physiochemical properties that differ significantly from larger particles of the same material, such as their interaction with prokaryotic and eukaryotic systems [4, 5, 6]. Indeed, there have been reports of marked antibacterial activity demonstrated by nano-particles of ZnO [5, 7, 8]. Reddy et al. [5] report selective toxicity of nano-materials, including metal oxides, to prokaryotes and eukaryotes. Studies on eukaryotes, primarily involving mammalian cells, indicate that nano-particles of ZnO cause higher levels of oxidative stress resulting in inflammation and cytotoxicity. In prokaryotes, oxidative stress can induce cell death due to interactions between reactive oxygen species and proteins, DNA or the cell membrane [9, 10]. In a previous study, our observations showed that unleached wood impregnated with particulate 30 nm ZnO caused moderate termite mortality in laboratory no-choice bioassays compared to no mortality for termites exposed to wood treated with soluble zinc sulphate (ZnSO4) solution [11, 12].
Another possible mode of action is physical. Alexander et al. [13] showed that the mode of action for inert dust insecticides was independent of chemical reactivity. We have previously shown that concrobium dust causes mortality in Reticulitermes flavipes[14]. Also, inert dusts induced death in grain weevils by desiccation since respiration and ingestion did not seem to harm the insects. While ZnO is not inert, it is entirely possible that termite mortality demonstrated by Kartal et al. [12] and Clausen et al. [11, 15] is the result of a physical reaction alone, or in addition to a physiochemical reaction since a film of nano-particles remained on the surface of the unleached wood blocks. Furthermore, antibacterial activity has been reported to increase with reduction in particle size [8]. In our previous study, wood blocks were treated with a single particle size (30 nm) of ZnO and the effect of particle size could not be ascertained.
The objectives of this study were twofold: to evaluate the affect of leaching on termite resistance in southern pine treated with nano-ZnO and soluble ZnSO4 and to evaluate the affect of particle size on termite mortality.
Materials and methods
Treatment chemicals
Nano-ZnO (Nanophase Technologies Corporation, Romeoville, IL, USA) was provided as an aqueous dispersion containing 50% ZnO particles (30 or 70 nm) with a proprietary dispersant. Zinc sulphate was obtained from Mallinckrodt Chemicals, St. Louis, MO, USA.
Specimen treatment
Test specimens (25 × 25 × 6 mm), prepared from sapwood portions of defect-free southern yellow pine (SYP) sapwood were vacuum-impregnated with nano-ZnO or soluble ZnSO4 treatments according to American Wood Protection Association (AWPA) E10-08 standard method [16]. Pre-weighed specimens that were conditioned to 20°C and 65% relative humidity (RH) were vacuum-treated (45 min vacuum at 172 kPa) with aqueous solutions of 30 or 70 nm ZnO diluted in deionized (DI) water to 1.0, 2.5 and 5.0% based on the metal oxide (ZnO) of the dispersion (Nanophase Technologies, Inc., Romeoville, IL). Aqueous zinc sulphate solutions were prepared to contain an equivalent amount of Zn for comparison with each concentration of nano-ZnO. Untreated specimens impregnated with DI water served as controls. Treated specimens were weighed, dried at 40°C for 3 days, and re-conditioned for 2 weeks. Some treated specimens were ground to pass through a 30-mesh screen and analyzed for zinc (Zn) with inductively coupled plasma atomic emission spectrometry (ICP-AES) (Ultima ICP-AES instrument, Jobin Yvon, Inc., Edison, NJ) according to the AWPA standard method A21-00 for analysis of wood and wood treating solutions to determine the initial chemical retention in the treated blocks [17] (Table 1).
Table 1
Average chemical retention of pre-leached wood blocks
Treatment
Concentration
Retention (kg/m3)
Std dev.
Untreated
-
26.8
1.8
30 nm ZnO
1.0
45.7
1.9
30 nm ZnO
2.5
59.4
3.0
30 nm ZnO
5.0
109.1
33.7
70 nm ZnO
1.0
43.0
25.4
70 nm ZnO
2.5
67.8
25.9
70 nm ZnO
5.0
64.0
25.2
ZnSO4
1.0
36.9
7.4
ZnSO4
2.5
45.8
6.9
ZnSO4
5.0
74.5
9.3
Chemical leaching
Leaching procedures were a modification of AWPA E11-06 [18]. Five specimens per treatment were placed in a 500-mL beaker and submerged in 100 mL of DI water for 14 days without agitation. The leachate water was changed after 6 h, and 1, 2, 4, 6, 8, 10, 12 and 14 days and leachate samples were collected at each time point. Leachates were analyzed for Zn with ICP-AES and the total quantity of zinc leached over the course of leaching was calculated. Percent leaching was calculated by comparing the average leach rate of five specimens per treatment to the subset of treated unleached specimens that were assayed for zinc based on initial chemical retention (Table 1).
Termite bioassay
A no-choice termite resistance test with Reticulitermes flavipes Kollar (eastern subterranean termites) was performed using five leached test specimens (25 × 25 × 6 mm) for each treatment group. Termites were collected from Janesville, WI, USA. One specimen was placed in the bottom of an acrylic cylindrical container (90 mm diameter and 60 mm height) with 1 g of R. flavipes and moist sand. The containers were maintained at 27°C and 85% RH for 4 weeks based on AWPA E1-09 standard method [19]. Containers were periodically checked for moisture and mortality. At the end of the test, wood specimens were oven-dried, reconditioned at 27°C and 70% RH, and reweighed to calculate mass losses. Each block was visually rated using the following system: 10-sound; 9-slight attack with up to 3% cross-sectional attack; 7-moderate to severe attack with 10 to 30% of the cross-sectional area affected; 4-very severe attack with 50 to 75% cross-sectional area affected; 0-failure. Termite mortality was estimated visually.
Results and discussion
Leach test
Results of the leach test are summarized in Figure 1. Percent of nano-ZnO that leached was relatively low; only 1.8 to 3.9% leached from all nano-ZnO treatment groups regardless of particle size. In contrast, wood treated with a zinc sulphate solution leached to a greater degree at higher treatment concentrations. For example, 2.5 and 5.0% treatments leached 25 and 22% of the metal oxide, respectively.
Figure 1
Percent total Zn leached during 14-day laboratory leach test [18].
Particle size
Two sizes of nano-ZnO particles were evaluated to ascertain differences in bioactivity based on previous reports that bioactivity increases with decreasing nano-particle size [8]. In this study, no significant differences were seen between the two particle sizes tested for leach resistance, wood consumption by eastern subterranean termites or termite mortality. However, both sizes of nano-particles tested cause higher termite mortality than the soluble ZnSO4.
Termite resistance
Termite resistance results are summarized in Table 2 and Figure 2. Termite consumption of the treated wood blocks was based on visual ratings and mass loss following a standardized termite bioassay and mortality is based on visual inspection. For the nano-ZnO particulate treatments, including all concentrations and both particle sizes, wood consumption was less than 4% which is indicative of treatment non-pallitability or repellency. Despite low consumption, all nano-ZnO treatment concentrations for both particle sizes caused 94 to 99% mortality after 25 to 27 days incubation. In contrast, termites consumed slightly more (10 to 12%) of the blocks treated with ZnSO4, however, termite mortality was considerably lower for all three treatment concentrations. Twenty-nine percent of the termites died following exposure to 1% ZnSO4 but only 5 and 8% of the termites died following exposure to blocks treated with 2.5 and 5.0% ZnSO4, respectively.
Table 2
Average visual rating of damage to wood blocks by subterranean termites and estimated termite mortality
Treatment
Concentration
Ave. visual rating
Ave. mortality (%)
Untreated
-
0
12
30 nm ZnO
1.0
9
95
30 nm ZnO
2.5
9
97
30 nm ZnO
5.0
9
97
70 nm ZnO
1.0
9
94
70 nm ZnO
2.5
9
95
70 nm ZnO
5.0
9
99
ZnSO4
1.0
7
29
ZnSO4
2.5
7
5
ZnSO4
5.0
7
8
Figure 2
Inhibition of eastern subterranean termite feeding by treatment of southern pine with particulate nano-ZnO and soluble ZnSO4[19].
Higher termite mortality in wood treated with particulate nano-ZnO compared to soluble ZnSO4 may be due to differences in bioactivity that results from changes in the chemical structure as has been the case in other studies [20]. The pyrolyzation process alters the surface charge of nanoparticles and essentially increases the effective surface area of the metal in an evenly dispersed layer. If the particle size is smaller than the diameter of the wood window pit (< 10,000 nm) or the opening of the bordered pit (400 to 600 nm), complete penetration and uniform distribution would be expected [21].
Termiticides can generally be characterized as (1) slow-acting, non-repellent stomach poison (e.g. naphthaloylhydroxylamine, sulfuramid) [22], (2) contact or cuticular toxin (e.g. fipronil) or (3) chitin synthetase inhibitor (e.g. hexaflumuron) that mimics insect hormones which regulate a wide array of physiological functions. Some examples include interfering with molting, pupal emergence or body wall formation. Little et al. [23] reported 100% mortality to R. flavipes using the antioxidants butylated hydroxytoluene (BHT), flavanone and propyl-gallate as surrogates for heartwood extractives. Fipronil is known to work by blocking the gamma-aminobutyric acid (GABA)-regulated chloride channel in neurons, thus disrupting the activity of the insect's central nervous system (i.e. neurotoxin) [24, 25]. Our results suggest that nano-ZnO behaves as a slow-acting, non-repellent stomach poison.
Conclusions
Nano-ZnO (30 and 70 nm) was essentially non-leachable from wood impregnated with up to 5% of these treatments. There was no difference in leachability or termite resistance between the two sizes of nano-particles evaluated. Consumption of wood blocks treated with nano-ZnO by eastern subterranean termites was uniformly low (less than 4%) and mortality was uniformly high (greater than 94%) for all treatment concentrations tested.
American Wood Protection Association Standards: P22–10: Standard for ammoniacal copper zinc arsenate (ACZA). Annual Book of AWPA Standards2010, 130.Google Scholar
American Wood Protection Association Standards: P51–10: Standard for zinc borate (ZB). Annual Book of AWPA Standards 2010, 164.Google Scholar
Clausen CA: Nanotechnology: Implications for the wood preservation industry. International Research Group on Wood Protection 2007, 15. IRG/WP/07–30415 IRG/WP/07-30415Google Scholar
Reddy KM, Feris K, Bell J, Wingett DG, Hanley C, Punnoose A: Selective toxicity of zinc oxide nanoparticles to prokaryotic and eukaryotic systems. Appl Phys Lett2007, 90: 2139021–2139023.Google Scholar
Xia T, Kovochich M, Liong M, Madler L, Gilbert B, Shi H, Yeh JI, Nel AE: Comparison of the mechanism of toxicity of zinc oxide and cerium oxide nanoparticles based on dissolution and oxidative stress properties. ACS Nano2008, 2: 2121–2134. 10.1021/nn800511kView ArticleGoogle Scholar
Chang H, Leung H: Evaluation of antibacterial activities of zinc oxide-titanium dioxide nanocomposites prepared by sol-gel method. Nanotechnology 2008, 1: 811–814.Google Scholar
Nair S, Sasidharan A, Divya Rani VV, Menon D, Manzoor K, Raina S: Role of size scale of ZnO nanoparticles and microparticles on toxicity toward bacteria and osteoblast cancer cells. J Mater Sci Mater Med 2009, 20: S235-S241.View ArticleGoogle Scholar
Aertsen A, Michiels CA: Stress and how bacteria cope with death and survival. Crit Rev Microbiol 2004, 30: 263–273. 10.1080/10408410490884757View ArticleGoogle Scholar
Clausen CA, Yang VW, Arango RA, Green F III: Feasibility of nanozinc oxide as a wood preservative. Proc Am Wood Protect Assoc 2009, 105: 255–260.Google Scholar
Kartal SN, Green F III, Clausen CA: Do the unique properties of nanometals affect leachability or efficacy against fungi and termites? Int Biodeter Biodegrad2009, 63: 490–495. 10.1016/j.ibiod.2009.01.007View ArticleGoogle Scholar
Alexander P, Kitchener JA, Briscoe JVA: Inert dust insecticides. I-III. Ann Appl Biol 1944, 31: 143–149. 10.1111/j.1744-7348.1944.tb06225.xView ArticleGoogle Scholar
Green F III, Arango RA, Esenther GR: Transfer of termiticidal dust compounds and their effects on symbiotic protozoa of Reticulitermes flavipes(Kollar).International Research Group on Wood Protection 2008, 9. IRG/WP/08–10661 IRG/WP/08-10661Google Scholar
Clausen CA, Green F III, Kartal SN: Weatherability and leach resistance of wood impregnated with nano-zinc oxide. Nanoscale Res Lett 2010, 5: 1464–1467. 10.1007/s11671-010-9662-6View ArticleGoogle Scholar
American Wood Protection Association Standards: E10–09: Standard method of testing wood preservatives by laboratory soil-block cultures. Annual Book of AWPA Standards 2010, 383–392.Google Scholar
American Wood Protection Association Standards: A21–08: Standard method for the analysis of wood and wood treating solutions by inductively coupled plasma emission spectrometry. Annual Book of AWPA Standards 2010, 254–257.Google Scholar
American Wood Protection Association Standards: E11–06: Standard method of determining the leachability of wood preservatives. Annual Book of AWPA Standards 2010, 393–395.Google Scholar
American Wood Protection Association Standards: E1–09: Standard method for laboratory evaluation to determine resistance to subterranean termites. Annual Book of AWPA Standards 2010, 351–359.Google Scholar
Sekine N, Ashitani T, Murayama T, Shibutani S, Hattori S, Takahashi K: Bioactivity of latifolin and its derivatives against termites and fungi. J Agric Food Chem 2009, 57: 5707–5712. 10.1021/jf900719pView ArticleGoogle Scholar
Green F III, Lebow S, Yoshimura T: Inhibition of termite damage by N'N-napthaloylhydroxyamine (NHA): Reticulitermes flavipes(Kollar) vs.Coptotermes formosanus Shiraki. International Research Group on Wood Protection 2000, 8. IRG/WP/00–10354 IRG/WP/00-10354Google Scholar
Freeman MH, McIntyre CR: A comprehensive review of copper-based wood preservatives. For Prod J 2008, 58: 6–27.Google Scholar
Little NS, Schultz TP, Nicholas DD: Termite-resistant heartwood. Effect of antioxidants on termite feeding deterrence and mortality. Holzforschung 2010, 64: 395–398. 10.1515/HF.2010.053Google Scholar
El Hassani AK, Dacher M, Gauthier M, Armengaud C: Effects of sublethal doses of fipronil on the behavior of the honeybee ( Apis mellifera).Pharmacol Biochem Behav 2005, 82: 30–39. 10.1016/j.pbb.2005.07.008View ArticleGoogle Scholar
Glenn GJ, Gold RE: Evaluation of commercial termite baiting systems for pest management of the Formosan subterranean termite (Isoptera: Rhinotermitidae). Proceedings of the 4th International Conference on Urban Pests 2002, 325–334.Google Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
For further details log on website :
https://nanoscalereslett.springeropen.com/articles/10.1186/1556-276X-6-427
