Development of Commercial Wood Preservatives Efficacy

Chapter 11

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Molds and Moldicide Formulations for Exterior Paints and Coatings K . Hansen Wood Business Unit, Troy Corporation, 8 Vreeland Road, P.O. Box 955, Florham Park, N J 07932-0955

Various fungicides are used to control mold in wood products. However, bioactive compounds are facing increasing restrictions worldwide, and this trend will continue. Further, many differences are seen in molds that colonize woody materials around the world. The impact of these differences on moldicide or coating formulation strategies is discussed, along with the water borne and solvent borne biocide combinations currently used to control molds. Other themes discussed include: Molds that have been identified at different sites around the U S A and world, and the microclimate effect on mold growth; construction factors to minimize mold growth; data from treated wood panels that were monitored monthly throughout the year for mold growth. In addition, the issue of mold growth correlated to the amount of active ingredient still present in the treatment and the inherent variation in the test results typically observed which together make it difficult to predict treatment service life is discussed. Future moldicide development is also discussed.

198

© 2008 American Chemical Society In Development of Commercial Wood Preservatives; Schultz, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.

199


Molds, Staining Fungi and Black Yeasts in the Environment on Wood and Coated Exterior Surfaces. Molds are a term used to describe a large group of different fungi having a well-marked mycelium or spore mass (7). Some molds belong to the Class Zygomycetes, such as Mucor and Rhizopus, and cause spoilage of bread and other types of food. Other molds belong to the Ascomycetes, and are mostly seen in their imperfect stages. Molds are able to grow on most carbon containing materials such as wood, leather, plastics, food, paints and many other substrates. On wood and wood treated with paint or wood protection products, staining fimgi and black yeasts may appear. Though they taxonomically belong to the Ascomycetes, as many of the molds do, they are often regarded as belonging to separate groups because of distinct differences in their growth pattern. The staining fungi have a high concentration of dark to black hypha growing among the wooden cells, and the wood will appear dark blue to black stained. The black yeasts can grow and look like mold fungi but will often have stages where conidia multiply with buds in yeast like way.

Figure 7. Black mold on a gable in New Jersey. The portion to the right has been cleaned.

Wood is only rarely destroyed by mold growth. For aesthetic reasons, however, many people invest a lot of effort trying to remove and renovate attacked surfaces. One simple strategy could be to apply a black stain or paint In Development of Commercial Wood Preservatives; Schultz, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.


200 on the substrate's surface, and by this way camouflage growth of fungi with dark or black mycelium. However, when lighter colors are desired, more is needed than just trying to camouflage molds growing on the surface. Any paint or penetrating coating applied to the surface needs to possess an inborn resistance against mold growth, which can be achieved by adding a suitable fungicide, or mixture of fungicides, to the formulations. The particular biocide(s) employed are dependent on the location, and the molds that are typically observed in that location. Other factors include the microclimate, the particular application and the additives used in the formulation. For example, hydrophilic products such as cellulose thickeners, surfactants and some pigments increase the amount of fungicide needed. The physical structure of a film itself can result in more water attachment to the surface, which increases the risk for mold attacks. This is especially true for films with a rough surface or many pinholes.

Molds in the USA and Around the World on Exterior Coated Surfaces If a hydrocarbon-containing product is not sterilized, sealed, frozen or dried, mold fungi by chance will find their way to it sooner or later. This is understandable, due to the huge number of spores and conidia a fungus can produce. A Petri dish containing solidified malt agar and inoculated with the mold fungus Aspergillus niger can easily produce 100 million conidia in less than a week. Many other species of fimgi are producing similar vast numbers of conidia that easily are carried long distances through the air, even over oceans (2). Conidia from Cladosporium herbarum e.g. are found in air samples throughout the world (J, 4). Therefore i f the right conditions are available a mold will invade a space that is not already taken. Aspergillus fumigatus is another cosmopolitic mold with hygroscopic conidia that distributes well in the air masses. This mold had even found its way to a penguin rookery in Antarctica (5). Many different mold species are therefore available in the form of conidia in the air at any time. Which species that actually will have success colonizing a newly exposed surface is dependant partly on the substrate and the nutrients provided and partly on the microclimate. The microclimates can vary considerably over short distances or among racks within a test site, and even from panel to panel. For example, the amount of solar irradiation absorbed by a surface depends primarily on its color, which results in a temperature variation between different colors. At one location in Canada the average temperature difference over a year was found to be about 10°F between horizontal placed white and black panels (6). This means that water will evaporate slower from a white panel than a black panel and fimgi will have water available for a longer

In Development of Commercial Wood Preservatives; Schultz, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.

201 time period on the white panel. Therefore, other issues being equal, molds may grow better on a white panel than on an adjacent black panel. As part of this work, the frequency of fungi, algae, cyanobacteria and lichens on painted/coated surfaces were compared at three test sites in the U S A , the east coast (Sparta, NJ), the west coast (Corvallis, OR) and in the south (Miami, FL). Samples of growth were taken from 234 exposed panels. Samples were taken with wetted cotton swabs, or, when possible, pieces of the mold containing film were removed. The swabs were brought to the lab in a transportation medium and the films were transported in sealed plastic bags. Samples were collected from areas with significant growth (more than one cm ). A species was only counted once on each panel. Identifications ,were carried out on material taken directly from the collected sample, using a compound light microscope and with reference to relevant literature (7-18). The frequency of appearance was listed in Table I.


2

The most prevalent molds that grew on the coated panels belonged to the genera Aureobasidium and Cladosporium, followed by Nigrospora, Alternaria, Curvularia, and Pénicillium. However, major differences were observed in species between test sites. A t the Sparta, N J site Aureobasidium pullulons had absolute dominance, occurring in about 90 of the isolates, while the Miami, F L and Corvallis, O R sites had more differentiated growth with two Cladosporium species as the most frequently identified molds. Curvularia lunatus and Nigrospora sp. were only isolated in Oregon. Together with climatic variations between the sites, the structure and the type of ground located under the test racks also had an impact on the microclimate of the panels. The Miami test racks were placed on a huge lawn where mowed grass was not removed. The Sparta site was on gravel and the Corvallis site in shade over bare soil where some soiling was seen on the test panels. Based on the molds identified, biocide producers or paint formulators should choose among the following fungi for their lab evaluations: Aureobasidium pullulans, Cladosporium herbarum, C cladosporioides, Nigrospora sphaerica and Alternaria alternata. A t least Aureobasidium, Cladosporium and Alternaria are commonly used in laboratory testing all over the world. Trichoderma is used in some testing especially for applications or locations with high humidity. Aspergillus niger is usually not seen on outdoor test panels but appears frequently as an indoor fungus. The fungus is one of the favorites in lab testing not because it is especially relevant, but probably because it is very easy to work with. Laboratory research to develop a biocide formulation to control all possible worldwide molds will result in extensive work and often lead to confusion as well; e.g., shall a promising biocide be dropped i f it fails in laboratory tests against a relatively uncommon organism? One strategy could be to concentrate work around five to eight species that appear with high frequency throughout the world, but keeping a door open for local troublemakers as well.


202

Table I. Identified organisms and their frequency at three sites in the U S A


Mold, algae, lichens, bacteria Molds Alternaria alternata Aureobasidium pullulons Chaetomium globosum Cladosporium cladosporioides Cladosporium herbarum Curvularia lunata Drechslera biseptata Drechslera sp. Nigrospora sp. Nigrospora sphaerica Pénicillium sp. Phoma sp. Phyrenochaeta sp. Scytalidium lignicola Sporidesmium vagum Stemphyllium sp. Sterile white mycelium Trichoderma viride Basidiomycetes Schizophyllum commune Green Algae Actinochloris terrestris Neospongiococcum sp. Stichococcus sp. Cyanobacteria Gloeocapsa sp. Scytonema sp. Lichens Evernia prunastri Hypogymnia physodes Usnea subfloridana

Frequency in pet. of identified Corvallis Sparta Miami Oregon New Jersey Florida 4.4 84.5 0.9 15.7 10.5 2.6 0.9 0.9 0.9 6.1 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9

7.5 15.1 1.9 37.7 0.0 7.5 0.0 1.9 1.9 15.1 3.8 0.0 1.9 1.9 0.0 0.0 1.9 0.0

2.2 88.8 0.0 0.0 6.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0

1.9

0.0

0.0 1.7 0.9

0.0 0.0 0.0

1.1 0.0 0.0

2.6 0.9

0.0 0.0

0.0 0.0

0.9 0.9 0.9

. 0.0 0.0 0.0

0.0 1.1 0.0



203 To cover as many markets as possible, it would be beneficial to identify common denominators among molds growing around the world, and then use these as test organisms. Towards this end, molds were collected and identified from 5 countries representing the temperate, the sub-tropical and the tropical climate zones on 4 continents. The most common molds identified from various areas are shown in Table 2. Based on the above, i f a global set of molds was to be chosen as test fungi, then Alternaria, Cladosporium, Phoma and Aureobasidium would be a reasonable set. For formulations intended for the tropics, Phoma should not be omitted as a test fungus. This mold is frequently seen in temperate climates; however, it probably does not have the same importance as in the tropics. It should be recognized that developing biocides that are effective against specific fungi might well prove an effective strategy to eliminate the growth of those fungi on target substrates. However, if biocidal specificity is too narrow, eliminating one fungus may simply create an environment where a different less common mold species, that is more resistant to the biocide, is created. Caution should therefore be exercised in developing selective biocidal treatments and it is not the intent of this chapter to suggest this strategy.

How to Avoid Mold Growth If free water is kept away from the wood, the moisture content will usually remain below 20% and, consequently, there will be no mold growth. There are various ways to keep water away from construction: Avoid flat roofs, because there is a risk that over the years the roof membrane will become damaged and water will easily find a way into the construction. It is important to be careful with the site grading when gutters and downspouts are installed and later to keep the gutters clean. Flashing around windows, doors and chimneys must also be installed in a way that water traps are avoided. Keeping water from penetrating into the wood through paint or other wood coatings and water repellent film can be difficult, since water vapor and even free water are able to penetrate directly through most films. Wood is hydrophilic and thus will absorb moisture through the film during periods of high humidity while water will evaporate during dry periods. This will result in swelling of the wood in times of high rainfall and humidity, and shrinking of the wood when the humidity is low. Wood will shrink from a few percent to more than 10 percent when the wood goes from saturated to completely dry, depending on the wood species and the direction of measurement relative to the grain orientation. In reviewing water penetration properties of common wood coatings, acrylic films tend to allow more water to penetrate through the film than alkyd-based films. Polyurethane coatings can be totally impermeable; however, i f the film


204 Table 2. Most Important Molds Identified Throughout the World


Molds

Alternaria Aureobasidium Cladosporium Curvularia Fusarium Nigrospora Pénicillium Phoma Stemphyllium Other molds and algae

Miami, Kuala Oregon, Seelze Lumpur (Germany) Sparta, (Malaysia) (USA) 7 24

3 44 25

Mongagua, Kabinburi, Gravatai Rio G. Belem Trang, (Brazil) (Thailand)

8

4 7 11

1 6 6 7 6

18

59

13

52

19

15

5 2 2 65

23

55

cracks due to normal swelling and shrinking, water will have easy access to the wood, where it will accumulate underneath the film, leading to more wood swelling and fungal growth. The film itself can contain readily available carbon food sources to sustain fungal growth, and it is therefore often highly vulnerable to mold growth. A typical film contains compounds such as softeners, emulsifiers, defoamers, thickeners and detergents that provide a nutrient source for mold growth. This is the reason the first attacks on an unprotected film are often observed after only a few weeks of exposure. Then there often follows a period with less vigorous growth, since many of the formulation additives have been leached out and the substrate is depleted of nutrients. When the film starts to crack and fail after two to three years, nutrients from the wood underneath become accessible and a new wave of mold attacks occurs.

Biocides When all constructional precautions have presumably been taken, it is still important to incorporate a coating or finish to exposed wood to inhibit mold growth. Adding fungicide, water repellent and U V protectant to a coating formulation best accomplish the task of protecting exposed wood. The list of available permitted fungicides is, for environmental reasons, being reduced yearly. Table 3 shows the most common current fungicides used to protect wood and paint films against mold fungi:


Table 3. Biocides commonly used for wood preservation or film protection Wood Fungi X X

Film Fungi

X


X X

X

X

X

X X X

X X

X

X X X

X

X

X

X

X

X X

Name of Compound

Algae

X

Boric Acid 2-bromo-2Nitropropane-1 -3diol (Bronopol) a-[2-(4-Chlorophenyl)ethyl]-a-( 1,1dimethylethyl)-1 H-1,2,4-triazole-1 -ethanol (Tebuconazole) Copper naphthenate 4-5-dichloro-2-n-octyl-4-isothiazoline-3-one (DCOIT) 1 -[2-(2.4-dichlorophenyl)4-propyl-1.3-dioxolan 2-ylmethyl]-1 H-1,2,4-triazole (Propiconazole) Di-sodium octaborate tetrahydrate (DOT) Diiodomethyl-p-tolylsulphone 3-iodo-2-propynyl butylcarbamate (IPBC) Methyl benzimidazole-2-ylcarbamate (carbendazim) N-(3,4-dichlorophenyl)-N,N-dimethylurea (Diuron) N-cyclopropyl-N-( 1,1 -dimethylethyl)-6(methyltio)l ,3,5-triazine-2,4-diamine (Irgarol) N-dichlorofluromethyl thio-N,N-dimethyl-Nphenylsulfamide (Dichlofluanid) N-dichlorofluoromethyl thio-N,N-dimethyl-Ntolylsulfamide (Tolylfluanid) N-trichloromethyl thiophthalimide (Folpet) 2-octyl-2H-isothiazol-3-one (OIT) Quaternary ammonium compounds ( B K C , DDAC, TMAC) N -tert-butyl-N -ethyl-6methylthio-1,3,5triazine-2,4-diamine (Terbutryn) Tetrachloroisophthalonitrile (Chlorothalonil) 2-(thiazol-4-yl)benziiiiidazole (Thiabendazole) 2-(thiocyanomethylthio)benzthiazole (TCMBT) 2

X

X

X X

X X X X X

X

Zinc Zinc Zinc Zinc

4

bis (dimethyldithiocarbamate) (Ziram) borate naphthenate oxide


206


Solvent and Water Based Biocide Systems A perfect biocide would be a compound that would be easy to dissolve in a liquid and when deposited at its target substrate, would withstand the sun and leaching by water. Most organic biocides can be easily dissolved completely in a solvent-based formulation. Compromises are sometimes seen, for example, when only 0.5% of a biocide can be dissolved in a formulation that requires 1.1% a.i. to work. If 1.1% is used, the product will contain both dissolved and undissolved biocide. This is often seen when Folpet is the biocide of choice. Some biocides can only be used in solvent based formulations, such as Dichlofluanide and Tolylfluanide that hydrolyze upon contact with water. Practical knowledge about how to utilize a biocide optimally increases with the length of time the compound is commercially employed. For example, certain fungi may build up resistance against a biocide, or it is found that the biocide may be weak against a particular type of molds. As a consequence, more than one biocide is often used in a formulation. However, not all biocides can be mixed with each other. In Tables 4 and 5 the biocides most often are used in mixed formulations are listed.

Table 4. Fungicide-combinations for solvent-based systems Copper naphthenate + Dichlofluanide Coper naphthenate + Folpet Copper naphthenate + Tolylfluanide Dichlofluanide + Propiconazole Dichlofluanide + Tebuconazole Folpet+ IPBC IPBC + Propiconazole IPBC + Tebuconazole IPBC + Propiconazole + Tebuconazole Propiconazole + Tebuconazole Propiconazole + Tolylfluanide Tebuconazole + Tolylfluanide

„

Other Organisms That Grow on Wood Surfaces: Cyanobacteria, Green Algae and Lichens In reviewing the growth of mold fungi on garden and other exterior building elements exposed to high moisture, cyanobacteria, green algae and lichens must


207


Table 5. Fungicide-combinations for water-based systems Carbendazim + Chlorothalonil Carbendazim + DCOIT Carbendazim + IPBC Carbendazim + OIT Carbendazim + Quaternary ammonium compounds Carbendazim + Zinc oxide _ _ Carbendazim + Zinc pyrithione Carbendazim + Ziram Chlorothalonil + DCOIT Chlorothalonil + IPBC Chlorothalonil + OIT Chlorothalonil + Propiconazole Chlorothalonil + Zinc oxide DCOIT + OIT DCOIT + OIT + Zinc oxide DCOIT + IPBC IPBC + OIT IPBC + Quaternary amm. Comp. IPBC + Quaternary amm. Comp. + Propiconazole IPBC + Thiabendazole IPBC + Propiconazole IPBC + Propiconazole + Tebuconazole IPBC + Zinc oxide IPBC + Zinc pyrithione IPBC + Ziram OIT + Zinc oxide Propiconazole + Quaternary amm. Comp. Thiabendazole + Ziram ^ Zinc oxide + zinc pyrithione

_

also be discussed. Cyanobacteria and green algae often play a major role in the initial colonization of surfaces that are moist for long periods. Later in the succession process as when surfaces have been exposed for years, lichens also appear. Without the aid of a microscope, it is often impossible to determine i f a growth consists of Cyanobacteria or mold or i f both groups are represented at the same time, since both organisms often appear dark green to black when dry (19). Figure 2 shows part of a bench with growth that looks like it was attacked by mold fiingi. However, examination by microscope showed that the growth was a mixture of both mold and blue green algae.



208

Figure 2. Garden bench with mixed growth of both mold and cyanobacteria

Algaecides are normally added to a formulation together with a fungicide and, for waterborne systems, a bactericide as well. The five algaecides listed in Table 3 can be regarded as herbicides. The formulations, therefore, must be of a quality that will minimize leaching as much as possible to avoid damage to the surrounding vegetation. They are, in general, easy to formulate, although an algaecide such as Terbutryn must be formulated with care to avoid odor problems due to its methyl thio group.

Formulations Because very few actives are available today, only a few combinations are possible. To further improve performance, strategies that involve adding nonbiocidals need to be considered: • • •

Avoiding hydrophilic ingredients in the paint formulation. Reducing/eliminating pinholes by using efficient bubble breakers and reducing the viscosity. Ensuring that enough of the product is applied on the substrate for an adequate film thickness; e.g. 8 0 - 1 0 0 pm.


209 •

• •


•

•

Applying on a clean surface. Wood unprotected for only a few days will be loaded with spores and conidia that may grow later when conditions are right. Keeping the film as dry as possible by incorporating wax, silicones or other water repellents into the formulation. Protecting the biocide by incorporating UV-absorbers in the formulation. Using pigmented systems, and remembering that the color choice may affect the surface temperature, and thus have an influence on which microorganisms may attack the film. Most acrylic films are more difficult to protect than alkyd-based films, due to differences in water permeability.

Testing of Stains and Paints Against Mold Fungi in Outdoor Exposure Tests A common way to compare coatings is to apply paints and wood protection products on wood panels. These are then exposed to outdoor conditions on racks at a test site. The panels are inspected periodically for the paint's physical performance and for the degree of mold growth. For example, a three-foot panel can be divided into four parts. The first portion is coated with paint without biocides, and remaining portions are coated with paint plus 0.1%, 0.3%, and 0.5% of the chosen fungicide. Normally two replicates are used and the panels are inspected periodically over the next two years and rated for fungal growth. In the US, most field test ratings for field performance follow the A S T M standard D3274 Revision 95 with the scale going from 0 to 10, where 0 is completely overgrown and 10 is free of growth. In Europe a reversed scale is used that goes from 0 to 5, where 0 is free of growth and 5 is completely overgrown. There is no "pass" or "fail" criterion with these scales, and most evaluators are uncomfortable with that. It is therefore typical for evaluators to use a "passfail" point, which in the US is typically "7" and in Europe "2". The definition of the "pass-fail" point will vary from company to company, but is often defined as the point where a layman may think it is time to clean or repaint the panel. Using this technique, the "pass-fail" point will soon be the most important point on the scale. The problem, however, has always been to agree on the exact borderline between "pass" and "fail", as the visual rating is subjective and each person has a different standard for when a surface is no longer acceptable. Complicating the issue, inherent test variations are normally large in outdoor exposure tests (20). This is often seen when blank controls are randomly placed on a rack and ratings may vary from "2", almost completely overgrown, to "9",



210 almost clean. As a consequence of such a variation among controls, the whole test may not be valid. To overcome the problem with very heterogeneous data sets, it is necessary to randomize samples using procedures such as a Completely Randomized Design (27, 22). Using this method the number of replicates is determined by the variation in results between samples of same treatment. This, of course, cannot be known before the test has been completed and it is therefore necessary to rely on earlier results to estimate the number of replicates needed, which will often be around 5 and never less than 3. To obtain useful data, outdoor exposure can take from as little as one month to more than three years, depending on how severe the conditions are at the test site. Over the test period the degree of differentiation in mold growth between treatments will increase until a maximum is reached (Point of Maximum Differentiation). Later, when the average rating (ASTM) for the set falls to around four, the difference between treatments will decrease again and eventually disappear when the samples become totally overgrown.

Seasonal Variations in Ratings In climates with distinct seasons, panel ratings often appear to improve over the winter months. This is because the fungi stop growing in the cold season and get rinsed off by snow and rain. To see this effect demonstrated, panels can be inspected at short intervals, such as monthly. Following the winter season, the molds will again begin to grow and ratings will start to decrease again shortly after springtime (Fig. 3). Typically in the second season less improvement is seen during the winter months, and the drop in ratings is more dramatic during the summer and the following autumn.

Comparison Between Rating Methods It is often desirable to compare the visual subjective evaluation to a more objective evaluation by relying on a quantitative measurement of the biocide level in the film. High Performance Liquid Chromatography (HPLC) is a common analytical method for organic biocides. Neutron Activation Analysis ( N A A ) requires only a small sample and is precise, but one drawback is that it only measures the elements present rather than the active compound. In some situations, the biocidal compound itself may degrade but the specific compositional element may still be present on the substrate surface. A n alternative method is the use of bioassays, where a fungal response to a sample containing a biocide is measured. The sample, which could be a disc cut out of a board with a plug cutter, is placed on nutrient agar with the painted surface toward the agar and sprayed with fungal conidia. The clear zone of inhibition


211


between the growing mold fungus and the sample disc is measured. The method is well suited for biocides that are not strongly chemically bound to the substrate. Some leaching of the biocide into the agar is needed to obtain a measurable zone of inhibition (23). It is important to use a fungus that is very sensitive to the biocide, in order to differentiate between biocide concentrations. Typically the best results are obtained with fimgi having minimum inhibitory concentration (MIC) values close to 1 ppm.

Figure 3. Polyphast CST is an UV-stabilizedproduct containing 20% IPBC. This bioassay was carried out on a paint film initially containing 0.4% Polycast CST. Relative performance: The ASTM 1 to 10 rating scale was converted to relative performance by multiplying by 10, and the bioiassay was converted by regarding the maximum zone of inhibitaion as 100 and no zone as 0.

In Figure 3, the A S T M rating was compared to a bioassay test carried out with Aspergillus niger on 66.5 mm discs cut from the exposed panels. A. niger was chosen as test fungus because it was easy to work with, and because it was very sensitive to even small concentrations of IPBC with a M I C value between one and two ppm. A concentration dependent response for Polyphase C S T was observed; however, at a level of 0.1% the fungicide did not perform better than the control. Specifically, the bioassay showed no zone of inhibition after 16 months, indicating a low level of biocide in the film. However, 0.2 and 0.4% Polyphase C S T still performed satisfactorily after 16 months. The reason was probably that even very low levels of the biocide were enough to prevent growth in a film where nutrients, such as emulsifiers, water-soluble carbohydrates and detergents had been leached out. 2


212 The bioassay method proved to be an easy and relatively precise method to monitor the biocide level in a film over time. The paint performed well even when the bioassay indicated a low level of biocide in the film. It was easy to find the "Point of Maximum Differentiation". It was easy to determine which months the fiingi thrived as well and when molds were inactive during the winter months.


The Future When the number of biocides started to shrink about 25 years ago, it was relatively easy to change to alternative biocides. Since approximately 10 years ago, however, very few new biocides emerged and, at the same time, fungal resistance developed against some of the most common biocidal compounds. This initiated a period of time where formulators began to combine the biocides available to ensure broad fungal efficacy, combat resistance or just to increase the general efficiency of a product. Regulatory trends suggest that there will be even fewer biocides permitted in the future; however, the need for biocides will remain. The consequences of this are that most paints and stains will rely on the same few actives for mold protection. However, this is not the end of development work. Formulators are already trying to enhance the quality of formulations to develop products that will provide long-lasting hygroscopic films with dependable and desirable properties while minimizing use of the remaining approved organic biocides.

References 1.

Ainsworth, G.C. Ainsworth and Bisby's Dictionary of the Fungi; Commonwealth Mycological Institute, Kew, 1960. 2. Pady, S.M.; Kapica, L. Mycologia 1955, 47, 34-50. 3. Hudson, H. J. Trans. Br. Mycol.Soc. 1969, 52, 153-159. 4. Hyde, Η. Α., Williams, D. A. Trans. Br. Mycol. Soc. 1949, 36, 260-266. 5. Wicklow, D. T. Can. J. Microbiol. 1968, 14, 717-719. 6. Stephenson D. G . Can. Building Digest 1963, 47, 1-6. 7. Domsch, Κ. Η. , Gams W. and Anderson T. H . Compendium of Soil Fungi. 1980, Academic Press, London. 8. Wang, C. J. K . and Zabel, R. A . Fungi from Utility Poles. 1990, American Type Culture Collection, Allen Press, Inc., Kansas. 9. larone, D . H . Medically Important Fungi 1995, A S M Press, Washington, D.C. 10. Ellis, M. B . Dematiaceous Hyphomycetes. 1993, C A B Int., Wallingford.



213 11. Ellis, Μ. Β. More Dematiaceous Hyphomycetes. 1993, C A B Int., Wallingford. 12. Barron, L . B . The Genera of Hyphomycetes from Soil 1977, Robert E . Krieger Publishing Co. Inc., New York. 13. Gams, W. Cephalosporium - artige Schimmelpilze. 1971, Gustav Fischer Verlag, Budapest. 14. Hanlin, R. T. Illustrated Genera of Ascomycetes, Vol. I and II. 1992, A P S Press, St. Paul, Minnesota. 15. Arx Von, J. A . The Genera of Fungi Sporulating in Pure Culture. 1974, J. Cramer, Vaduz. 16. Holt G . J. et al. Bergey's Manual of Determinative Bacteriology. 1994, Williams and Wilkins, Baltimore. 17. Hanus, E.; Gärtner Süsswasser Flora von Mitteleuropa. 1988, Gustav Fischer Verlag, Stuttgart. 18. Prescott G . W. Freshwater Algae, 1978, McGrawhill, Boston. 19. Hansen, K . PPCJ, 1997, 187, 21-23. 20. Colon, I., Kuusisto, E.-L.; Hansen, K . ; Location affects performance of biocide - containing paints; 2004, PCI, 11. 21. Steel, R. G . D. and Torrie, J. H . Principles and Procedures of Statistics 1960, McGraw-Hill Book Company, Inc, New York. 22. Snedecor, G . W.; Cochran, W. G . Statistical Methods. 1968, The Iowa State University Press, Iowa. 23. Morrell, J. J. Wood and Fiber Sci. 1987, 19(4), 388-391.


Development of Commercial Wood Preservatives Efficacy

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