Chapter 9: Degradation and Protection Lecture 2: Protection

Learning Objectives Identify the factors that are responsible for material durability Understand the unique importance of water in durability and protection Become familiar with the common preservative and protective treatments for bio-based materials

Why is Biomass Durable? Density, extractives, silica, lignin, low nitrogen Cellulose is not starch – Same sugars but chemical bonds not accessible to starch-digesting enzymes Crystalinity prevents attack

The Threats… Abiotic – Fire – Weathering Biotic – Insects – Fungi

Hazard? Location – US Southeast is hot, humid, and home to termites Exposure – Sun, wetting, and ground contact all increase risk Risk if failure occurs – Structural products need more protection than decorative products Scheffer & Morrell, 1998 Decay hazard map

The Durability Pyramid Design is most important – Keeping bio-based materials dry prevents most degradation

Design – Dry Avoid wetting Promote drying Concept applies to materials and buildings (systems) – Careful construction Important to realize the advantages of dry design Problem area! – On-site construction offers poor quality control – New building materials/systems – Fewer professional builders

Durable Materials – Naturally durable wood Used to advantage for a long time – Chemical Preservatives Dominant technology today – Modification treatments Potential for future, not commercial in US

Naturally Durable Wood Heartwood only! Agricultural residues and annual crops are not naturally durable From: Wood Handbook

Wood Preservatives Add a layer of protection A range of possibilities Heavy Duty Borates Fire retardents Mildewcides Solid wood products for outside use are pressure treated with heavy duty preservatives

Wood Preservatives Based on agricultural pesticides Regulated and standardized Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Pesticide registry American Wood Protection Association Standards related to treated products (processes, applications, loadings, analytical methods, etc.)

TREATING METHODS PRESSURE TREATMENT Uses differential pressure to force preservative solutions/emulsions deep into solid wood – Eg. ACQ, CuAzole, Creosote, Pentacholorphenol Standard for decking, utility poles, railroad ties – Some plywood is pressure treated NON-PRESSURE TREATMENT Surface protection – Primarily used in conditions presenting only moderate decay Include: vacuum, brushing, dipping and soaking – Can also incorporate powdered preservative (Zinc Borate) in blending step of composites formation

Preservatives - Borates Broad spectrum Inexpensive, safe Diffusible Will penetrate in wet materials (advantage) Will eventually leach out of materials that stay wet (disadvantage)

Borates for Composites Zn-borate most common preservative for composites – Eg. OSB – Zn lowers borate solubility – reduces leaching

Borates for Composites (cont.) Zn-borate – Added as a fine powder during manufacture (blending) – % by weight as described in AWPA standard N2-05

Preservatives - Mildewcides Mixed with finishes Acronyms! – IPBC - Polyphase – TCMTB – CuNap – Copper-8 – TBTO A surface treatment for a surface problem

Fire Retardants Many proprietary product mixtures Goal is to slow fire, allowing time to escape Borate is often a component Video

Wood Modification May reduce… – hygroscopicity (wettability) – susceptibility to insects and fungi A variety of technologies being developed – Acetylation – Heat treatment – Furfurylation – Etc. More popular in Europe – Not in US – yet. – Cost, effectiveness, and negative impacts on material properties are concerns

Maintenance Keep the building dry – Maintain roof, gutters, drainage – Vent showers, driers & kitchens Regular inspection Can include finishes and refinishing Photos%20-%20JPG/5/5b.jpg Termite tubes in a crawl space. Termites are able to bypass the concrete footing to access the unprotected wood above.

Finishes Liquids applied to product surface Protect – Shed liquid water – Weathering Change/preserve appearance Finishes cannot replace preservatives – Only slow rate of water uptake

Finishes are Short-term Durability is function of – Substrate Swelling/shrinking, UV breakdown – Finish pigment resin preservative water repellent amount of finish carrier UV blocker – Interface Bonding between substrate and finish Affected by substrate, finish, and steps taken during application

Finish Types Protection versus looks – Pigments (colors) offer best protection – Clear finishes show substrate Penetrating (no film) vs. film forming – Penetrating can breath, finish wont peel, can be pretreatment – Film forming (low penetration) but potential for greater protection on surface Paint Solid color stain Varnish Lacquer

Regulation and Environment Concerns – In the treating process Spills, ground water contamination, air emissions, sludge (dirt/chemical mixtures) – In use Leaching – movement of preservative out of treated product into the environment Responses – Regulation Restrictions on old types New chemicals (moving from metals to organics) – In treatment Containment, fixation (reacting the chemicals with the lignocellulosic), training

Review What are the four requirements for decay fungi? – Give examples of how bio-based composites can be protected by limiting each of them Why would a dead fish deteriorate faster than a piece of plywood? How long will a bio-based composite last in service?