Chapter 9: Degradation and Protection Lecture 2: Protection.

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 http://www.awpa.com/• Standards related to treated products (processes,

applications, loadings, analytical methods, etc.)

TREATING METHODS

PRESSURE TREATMENTUses 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 TREATMENTSurface 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)

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Borates for Composites

• Zn-borate most common preservative for composites– Eg. OSB– Zn lowers borate

solubility – reduces leaching

http://www.borax.com/wood/products1b.html

Borates for Composites (cont.)

• Zn-borate – Added as a fine

powder during manufacture (blending)

– 0.75-1.5% by weight as described in AWPA standard N2-05

http://www.borax.com/wood/products1b.html

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

http://www.accoya.com/technology.html

Maintenance

• Keep the building dry– Maintain roof, gutters,

drainage– Vent showers, driers &

kitchens• Regular inspection• Can include finishes

and refinishing

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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 areShort-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

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Finish Types

• Protection versus looks– Pigments (colors) offer best

protection– Clear finishes show

substrate• Penetrating (no film) vs. film forming

– Penetrating can breath, finish won’t 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?