Introduction to Developing Wood Preservative Systems and Molds in

Chapter 1

Introduction to Developing Wood Preservative Systems and Molds in Homes

Downloaded by 37.9.40.157 on September 29, 2016 | http://pubs.acs.org Publication Date: April 2, 2008 | doi: 10.1021/bk-2008-0982.ch001

Tor P. Schultz and Darrel D. Nicholas Forest Products Laboratory/FWRC, Box 9820, Mississippi State University, Mississippi State, MS 39762-9820

Treating wood with biocides greatly lengthens its service life, saving consumers billions of dollars annually and extending the world's forests. Despite these positive attributes the public has a negative perception of treated wood. Recent health and environmental concerns with the older 1 -generation preservative systems has led to rapid and profound changes on a worldwide basis as we moved to the 2 -generation copperrich preservatives. This rapid change is continuing, with some countries now requiring 3 -generation totally organic systems. Furthermore, 4 -generation processes that protect wood by non-biocidal means are already commercially used in Europe (heat-treated lumber) or will shortly be (acetylated lumber). Recently, molds in homes and other structures have also had much negative publicity - and resulting litigation. The purpose of this book is to describe, chapter-by-chapter, the many steps involved in developing a new wood preservative system. Also included are overview chapters that cover molds in homes, review different aspects of wood deterioration, and discuss the current and expected future status of wood preservation in Europe, North America, and Asia/Oceania. st

nd

rd

th

2

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

3


The Past Wood has long been employed for mankind's benefit. However, wood used to build homes, bridges, fences, ships and many other structures is degraded by decay fungi, insects/termites, bacteria, and marine borers. Non-wood degrading organisms, such as molds and stains, can also colonize wood. Finally, wood is also damaged by abiotic sunlight and weathering/rain mechanisms. This can be a curse. For example, wood deterioration is estimated to cost U.S. homeowners over $5 billion annually, and about 10% of the annual production of forests is required to merely replace degraded products. Wood degradation is also a blessing, as it is nature's way to recycle dead trees and limbs and decay fungi and their enzymes benefit man in many different ways. Historically, some treatments have long been known to protect wood such as heating wood in an anoxic environment or applying copper salts or cedar oil. In addition physical barriers, such as copper plating the bottom of ships for protection against marine borers, were also employed. However, these historical wood protection treatments were only practiced on a small scale and man mainly relied on forests to provide new lumber to replace deteriorated wood. In the process, however, civilizations cut down many trees. About 200 years ago the first major wood preservative, creosote, was developed. Pressure treating wood with creosote greatly increased the service life of ships and other wooden structures. Creosote is a viscous black coal-tar by-product composed of a complex mixture of polyaromatic hydrocarbons (PAHs), polynuclear aromatics (PNAs), and other organic compounds. In 2000 in North America, creosote was used primarily to treat railroad ties, utility poles and marine pilings, accounting for about 10% by volume of all treated wood. In the 1930's chlorinated phenolics were evaluated as wood preservatives and by the early 1950's oilborne pentachlorophenol, or penta, was first employed to treat utility poles and crossarms. Despite some initial resistance by creosote providers penta sales increased, and by 2000 in North America penta was used in about 10% of all treated wood. These two organic systems, creosote and penta, were the main wood preservatives up to the early 1960's, with industrial applications being the major market. A metallic system, based on metallic salts/oxides of arsenic, chromium and copper, was also developed in the 1930's. Known first as Erdalith and later as chromated copper arsenate, or C C A , it was initially promoted by Bell Laboratories as being friendlier to their linemen. Being waterborne, C C A treated wood also had no unpleasant odor, unlike creosote or penta. With the suburban building boom of the I960's homeowners desired decks and patios to enjoy their backyard, and fences to block the neighbor's view, CCA-treated lumber experienced a rapidly increasing market. In 2000 in North America, CCA-treated wood accounted for about 80% by volume of all treated wood. While C C A had some industrial uses, the major application for CCA-treated

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


4 wood was the residential market, where C C A accounted for over 95% of all treated wood. The large residential market, about 70% of the total volume of treated wood in 2000 in North America, was a total change from 40 years earlier when industrial uses represented the major market for treated wood products. Some minor wood preservative systems were also utilized during this time, and lumber from naturally durable heartwood, such as redwood and cypress, was employed in relatively small amounts. In addition, some early research on wood modification, principally acetylation and heating wood in a reducing environment, was conducted. However, the primary purpose of the wood modification research was not to develop an environmentally-benign process to protect wood but to improve the dimensional stability of lumber. The above three l -generation preservatives, creosote, penta and C C A , were the major systems due to their long term effectiveness, low cost, and robust formulations that were easy to use in a treating facility. They also had a long and proven track record. Thus, the early 1970's were good years for the wood preservation industry. Starting in the late 1970's, however, health and environmental concerns with C C A , penta and creosote arose in Europe, Asia, and North America. At this time the U.S. Environmental Protection Agency conducted the Rebutable Presumption Against Re-registration study, R P A R , on the l -generation systems. This stimulated research to reexamine some minor systems, such as copper naphthenate and oxine copper, and to identify new wood preservatives from commercial organic agrochemicals used in non-wood applications. Much of the initial research was conducted by various wood preservative companies and the New Zealand Forest Research Institute and Michigan Technological University. R P A R only resulted in minor restrictions in the U.S., but concerns over possible restrictions on the l -generation systems in other countries accelerated the development of non-arsenical waterborne systems for residential applications and penta and creosote alternatives for industrial uses. st

st

st

The Present Overnight, it seems, the wood preservation industry underwent rapid and dramatic changes. Basically, wood preservatives were no longer selected based on economics and efficacy but on governmental regulations and environmental, health and disposal issues. Public perceptions, whether based on facts or misconceptions, also became important. In addition, due to rising energy costs homes were built "tighter" which increased the potential for water to become trapped within walls. This greatly increased the likelihood for mold growth and, with some negative but unsupported publicity, molds quickly became an important public health issue. In the U.S., penta and creosote have had some additional but relatively minor use restrictions imposed in the past few years. The big change was with


5 C C A , due to public concerns on health and disposal issues with lumber that contained arsenic and chromium. Starting in 2004, C C A was no longer labeled [permitted to be used] for almost all residential applications. This reduced C C A usage by about 68%. The 2 -generation preservatives that replaced C C A for residential applications were copper-rich waterborne systems with an organic co-biocide to control copper-tolerant fungi. These new systems required a bit more attention in the treating plants than C C A , and the absence of chromium led to increased metal corrosion problems. Also, wet lumber treated with these systems often had obvious mold growth on the surface which resulted in consumer concerns. [CCA-treated lumber can also have surface mold, but it is usually mistaken for dirt. Consequently, mold growth on CCA-treated lumber was not a serious public issue.] The new systems also leach more copper than CCA-treated wood which can negatively impact aquatic systems, and disposal of metallic-treated lumber from residential structures - including CCA-treated lumber - is a growing concern.


nd

As mentioned earlier, creosote and penta have so far faced only relatively minor restrictions in the U.S., but concern over possible restrictions has led to increased research and the development of new systems. Some of these systems were perhaps rushed into service without being fully tested and/or adequate education and technical support for users, with the result that some wood products treated with a few new systems failed. These failures and the resulting negative publicity, along with public concern with perceived health issues, has led to an increasing market share for non-wood construction alternatives such as plastic lumber and steel studs. Further increasing the public demand for nonwood alternatives is the desire by many homeowners for premium products that require little maintenance. The poor dimensional stability of wood planks, which results in lumber warping, bowing, and checking, increased the market share for dimensionally-stable plastic lumber in the large decking market. Health issues, and the public misconception that naturally-durable lumber is safe, have led to increased demand for redwood and other durable lumber. However, restrictions on harvesting trees with naturally durable heartwood have limited the availability of this lumber. The use of wood composites is increasing due to their good dimensional stability and other desirable properties. However, wood composites that are exposed to the weather will degrade and/or have mold growth. In applications where this may occur, the composite must be protected with a biocide. Zinc borate, which has low water teachability, is used to protect many wood composites. Waterborne borates are low-cost and safe, and have long been used in residential construction in New Zealand to protect lumber against insects. Borates are increasingly used in the U.S. for non-exposed structural lumber and other wood products in regions with drywood or Formosan termites, such as the


6 Gulf Coast or Hawaii. However, borates are quickly leached from wood exposed to moisture and, despite much research and some claims, no borate preservative system has yet been shown effective in long-term outdoor exposure tests. The rapid changes in the past few years in North America occurred a decade earlier in Europe and Japan, where C C A , penta and creosote have been greatly restricted or banned outright. Copper-rich waterborne systems have been commercially available in these countries for over a decade. However, disposal and copper leaching concerns with these 2 -generation systems recently caused three European countries to require totally-organic systems, and other countries may also shortly mandate 3 -generation preservatives. Regulatory pressures and public demand in Europe have brought increased attention to the ^-generation systems, the non-biocidal modification of wood to prevent biodeterioration. Lumber protected by various heat-treatment processes has been commercially available for several years in Europe, and an European plant to produce acetylated lumber is being constructed. In North America it is expected that 3 -generation systems may be required for residential applications in the near future, perhaps as early as 2010. Furthermore, at least one company is considering commercial acetylation of lumber. nd


rd

rd

The Future rd

Likely future North American 3 -generation organic wood preservatives are already commercially available in Europe and Asia. Totally-organic systems have several disadvantages compared to the metallics, however, including the relatively high cost of organic biocides compared to copper(II) and that organic biocides are depleted by various biological and chemical pathways that do not affect metallic biocides. Furthermore, residential wood preservatives will be waterborne, but most organic biocides are not soluble in water. Thus, emulsion formulations, or alternative technologies to the traditional pressure treating processes, need to be developed. Use of wood composites will increase and these products must also be protected with approved preservatives. Development of effective and economical 3rd-generation organic systems for areas with high or severe deterioration hazards, such as exist in the southeastern U.S., will be "interesting". As noted by Alan Preston at CSI, the wood preservation industry will face conflicting issues - durability versus cost versus consumer expectations. Some systems may be commercialized without the lengthy testing previously employed and, as a result, some unanticipated problems may arise. In addition, the desire to minimize costs has resulted in some preservative proposals being submitted to regulatory organizations with recommended biocide levels that many professionals feel are too low. Rushing systems into commercial production without long-term testing or a com-


7 prehensive review, or having systems with too low a biocide level, may result in failures that will further increase consumer demand for non-wood alternatives. In addition, the poor weathering properties of the current 2 -generation treated lumber will increase demand for the relatively expensive plastic decking. Many North American consumers are interested in non-biocidal treatments or naturally-durable lumber. As mentioned earlier, however, governmental restrictions are limiting the harvesting of trees that contain naturally durable heartwood. Also, the heat-treatment process would likely not be effective in outdoor exposure in high or severe deterioration hazard areas such as the southeastern U.S. What may prove successful are chemical-modification nonbiocidal processes, such as acetylation. Lumber treated with non-biocidal silicates, with borates sometimes co-added, is being advertised as suitable for outdoor above-ground or ground-contact applications. However, to the best of our knowledge no long-term outdoor exposure tests with publicly reported results have shown that a silicate and/or borate treatment is effective.


nd

The recent dramatic increase in energy costs will cause structures to be built even more "tightly". Unfortunately, these structures are susceptible to trapping water within walls which will lead to mold growth. While much scientific knowledge has been developed by professionals that could greatly lower the potential for mold growth and reduce wood deterioration, for various reasons this knowledge is not available or utilized by many home builders. Basically, the near future looks pretty grim for the wood preservation industry - ever increasing governmental regulations, a product that the public views negatively, increased competition from non-wood alternative construction materials, a high chance for litigation, and continuing low prices for treated wood. Furthermore, the mature nature of the treated wood industry has resulted in limited R & D funds to develop future products. The long-term future prospects, however - at least to our eyes - looks very bright! How can we be so optimistic? Trees provide an organic material that is easily and with minimal energy converted into a wide variety of useful products, is renewable and can be easily and safely disposed (and, i f burned, provides energy when disposed of), and traps carbon as the raw material is grown. However, the wood preservation profession needs to develop high-value products with desirable and dependable properties, with products that have a profit margin sufficient to encourage companies to undertake the long-term and expensive research necessary to develop additional wood-based products for the future.

Book Objective Our first A C S symposium and subsequent book on wood deterioration emphasized the science of wood biodégradation. For this second symposium



8 and book, we five co-organizers addressed the practical side of wood preservation with presentations by world-recognized experts that covered the many steps involved in developing a commercial wood preservative system. This includes developing new biocides or identifying commercial biocides used in non-wood applications, formulation, testing the new system, registration and approval of all active components by appropriate governmental agencies, submitting the proposed system for standardization [approval to use in clearly specified products and applications] by regulatory organizations, and environmental and disposal issues. Additionally, for readers unfamiliar with wood preservation we have provided overview chapters on different aspects of wood deterioration and that summarize the current and future status of wood preservation in Europe, Asia/Oceania, and North America. In addition to the above, we also organized a mini-symposium on Molds in Structures, with these overview chapters also presented. We hope that this book will prove useful to our profession, and sincerely thank our many colleagues and friends who spent considerable time writing the many chapters and the industries/organizations that provided the necessary financial support. Many chapters cover areas that are extremely complex, but the authors had a limited number of pages. In addition, the subject matter is rapidly changing. Thus, readers should feel free to contact any particular author, or one of the five co-editors, for further information. We five co-editors have enjoyed working with everyone involved and each other. We especially thank the professionals with the American Chemical Society, particularly Dara Moore of the A C S Books Deptartment and our many collègues and friends in the A C S Cellulose Division. One of us, Tor, also thanks Jake, Red, Irv, Tom and Darrel for all that you have taught me.


Introduction to Developing Wood Preservative Systems and Molds in

Recommend Documents