Wood Biology

Blue stain fungi

- 50 - 300 species - mainly softwood - only sapwood of hardwood - penetrates cracks of wood rays - feeds from parenchyma cells

Bamboo-based Polymer Composites

- bamboo abundantly available - strength properties crucial over long period

types of rot

- brown rot: only leaves lignin, cubical rot, mainly softwood - white rot: breaks down all three, mostly hardwoods

processing technology WPC

- compounding - extrusion - injection moulding

WPC research results

- effective use of wood - recycled WPC make even better source material for new WPC

why make wood-based composites

- homogenization - production of larger sizes - reduced anisotropy - increasing dimensional stability - use of low value raw materials - cheaper

polylactic acid (PLA)

- made from lactic acid units, either L or D , ratio affects properties - increased DP and crystallinity leads to higher rigidity, less deformation, higher melting temp - used for food additive, textile industry, pharmaceutical industry - produced by bacterial fermentation

red streak fungi

- most common/economically important softwood issue - slow-growing white rot - medium to high moisture, moderate temperature

3 kinds of wood moisture measurements

- ovendry MC - fiber saturation: only the cells walls are completely saturated - maximum moisture content: cell lumina and walls are saturated

climate change mitigation via forests

- planting trees - conserving existing forests - sustainable forest management - managing wood products - soil conservation - using bioenergy fuel instead of fossil fuels - tree species improvement to increase biomass productivity

types of white rot

- red rot: starts in hardwood - white pocket rot: selective lignin degradation, mainly in heartwood - selective white rot: wood is light (initially less cellulose degradation) - simultaneous white rot: all at once, wood gets darker

wood worm beetle damage

- round emergence holes - circular tunnels following year rings - global distribution - most frequent animal wood pest - hard to combat because deep inside timber

form of extrusion

- single screw extruder - double screw counter-rotating extruder - conical screw counter-rotating extruder

termite nutrition (important)

- symbiosis with cellulose-digesting bacteria or others in bowels - only the workers eat the wood - cultivate fungi

Polyhydroxy alkanoates (PHA)

- takes time and money to get from bacteria - but is completely biodegradable and very versatile - easily degraded by acids/bases - PHB formed also in plants

wood density

- very dependent on wood moisture, which affects volume and mass, as well as types of wood, tree age, thickness of annual rings - measured as either ovendry, raw, or standardized conditions

hazard classes

0 - indoors 1 - indoors with <70% moisture 2 - Inside >70 % moisture 3. Outside without contact to earth or water 4. Outside with contact to earth or water 5. Seawater

natural durability again fungi

1 is very durable, 5 is not durable examples: 1 - teak 2 - chestnut 3 - pitch pine 4 - spruce 5 - beech

cell wall density

1,5 tons per m3

steps and machines for making veneers

1. Cutting 2. Drying, with a roller dryer or belt dryer 3. Gluing with a roller coater or a curtain coater 4. Pressing using a multi-daylight press

formaldehyde adhesives steps

1. addition 2. condensation (water exits) 3. polymerization (elimination of water and non-reactive formaldehyde)

Timber preservation

1. avoid cracks, fungi, insects 2. bark attracts insects but stops the other two 3. best is short wet storage time

Phases of wood combustion

1. heating to get rid of moisture 2. at 150C, starts chemical breakdown 3. volatile matter is vaporized, holds 50 - 60% of wood's heat value 4. 700C the vapors burn, temp must be maintained for maximum efficiency 5. After the gases are gone, the remainder is charcoal, which burns at over 1000C

volume of log that is bark

10%

recycled paper

100t of recycled from 130t of recovered paper; cheaper than primary fibers; 74% RP consumption in germany!

Hectares of forest in Germany

11.5 million (33%)

Annual wood growth

122 million cubic meters of wood

forest density worldwide

130 m3/ha (over 300 in Germany!)

methods for making veneers

3 - sliced veneers, rotary cut veneer, sawn veneer

Wooden stock (germany)

3.7 billion cubic meters of wood

ideal contact angle for adhesives

30 degrees

breakdown of annual wood use

35 sawn industry, 26 fuel wood, 9 wood-based panel, 6 pulp and paper

plastic use

40% for packing, 20% for construction, 7% for automobiles

Chemical composition of wood

49% C 44% O 6% H slight amount N 0,2 to 1% ash minerals

equilibrium moisture content (EMC)

5 to 10% indoors, 15 - 30% outdoors (always 1/5 of relative humidity)

plant cellulose

50 times cheaper than bacterial cellulose, but also tougher and rougher

fuel wood

50% of harvested wood is for fuel

how much wood is there

530 billion m3 of wood worlwide

Abundance hardwood vs softwood

55 softwood and 45 hardwood

paper and cardboard

60 - 95% fibers, fillers, pigments, additives, water

basics natural tropical forest

60 mill. years without human, quick nutrient cycling and low storage, high productivity

Percentage of forest that is mixed

75%

reasons to use wood for energy

CO2 neutral, local source, saves more limited resources, wood is available and can be recycled with fuel as the last use, easy storable

Carbonation equations

CaO + H2O <-> Ca(OH)2 CO2 + H2O <-> H2CO3 Ca(OH)2 + H2CO3 <-> CACO3 + 2H2O

Wood with 20+% moisture

Can be attacked by fungi

National Forest Inventory

Germany, every 10 years, count trees

solvent systems for cellulose

Ionic liquids, Schweizer's reagant

Trees with durable heartwood

Larch (softwood), Oak, Sweet Chestnut, Black Locust

factors affecting strength of pulp products

OH groups at surface, fiber length, flexibility, individual fiber strength

binders for particleboards and OSB production

PB is urea formeldehyde resin OSB is isocyanates bc water stability

difference in particle boards and MDF production

PB: - dry then glue - woodchips are flaked into particles - multiple layers - drum or jet dryer MDF: - glue then dry - woodchips are turned into fibers - one layer - flash tube dryer

Polypropylene

PP-homopolymer, isotactic! no abrasion/corrosion, stiffer than HD-PE, low water uptake

Wood use

Varies based on timber diameter and wood quality

Examples of wood use

Veneer (high large), furniture (high large/medium), framework/construction timber (large low), particle board (small low)

wood

a fibrous and porous structural tissue found in stems and roots of trees

adhesive

a non-metallic substance joining parts through adhesion with cohesion

injection moulding

a process for forming objects where it is injected into a mold in liquid form - unlimited design variations - batch process - for very dry material

necessary condition for adhesives

ability of adhesive to wet the surfaces

world forest cover

about 4 billion hectars

Annual wood use

about 76 million cubic meters

Collagen

adhesive, esp on leather

Biotic growth factors

aging, cell formation, hormones and enzymes, gene expression

chemical pulping

aims to detach lignin and keep the cellulose, digest wood with chemicals

Wood characteristics

are things that can lower the class of the wood

countries with most forest area and wood

area: Russia, brazil, canada growing stock: brazil, russia, canada densest forests: new zealand, germany, cameroon

inorganic fibers

asbestos and gypsum

drywood insects

attack airdry sawn wood, highly relevant technically and economically because they attack obstructed wood , precautions are vital

why are there different techniques for veneers?

because they produce different quality veneers, standard is rotary cut, high quality is sawn

thermal modification

better dimensional stability/durability and lower moisture content, but more brittle

chemical modification

better stability because "freezes" cell in swollen state/prevents additional swelling

bio-based polymer

better term than bioplastic; not necessarily good for environment

longhorn beetle damage and occurance

bore beneath the surface, bore dust remains in the tunnels, tunnels are not used again, minimum moisture 12%, developing period 4 to 18 years

pits

breaks in the lumen for horizontal transport

frame saw

bunch of parallel blades med quality, med-large diameters

wood absorbs water

by capillary transport, is bound by cell walls

Heat value (kWh)

by volume higher in hardwood (best is black locust), by kg higher in softwood (best is spruce)

bioplastics

can either refer to bio-based plastics or biodegradable plastic

Asian longhorn beetle occurence

carried around the world inside wood products/packages/bonsai, eats healthy trees which later die!!

constituents of wood (pas important)

cellulose 40%, lignin 20-30%, extractives 2-10%, hemicellulose 20-30%

why not use bark in particle board

color, strength, damages tools

hydrophobic contact angle

contact angle (droplet to surface) is more than 90 degrees

protection

contruction, paint, impregnantion, medication, heat treatment, biocides

some sources of polymers for WPC

corn, whey, sugar beet (what?)

additives for WPC

coupling agent (MAH), biocides, UV-stabilizers, pigments, flame-retardant, and more

Types of cuts

cross-section, radial cut (pith to bark), tangential (parallel to year rings)

Yew

densest European softwood

Common Horn Beach

densest European wood

heat value per weight unit

depends on moisture content, negative correlation

Histogenesis

differentiation at root/shoot apical meristems

chipping/flaking

disk or drum hacker or knife ring flaker

making particle boards

drying, gluing, pressing

what is wood modification

durable, biocide-free alteration of wood using heat or chemicals

things that degrade wood

earth contact! fungi, insects, water, temperature, sunlight, wind

signs indicating termite presence (important)

earthen packing, excavation of wood (just a paint-thin outside layer), presence of flying insects (colonizing time), collapsed timber (support beams, windowsills, door hinges that come out)

final steps at the sawmill

edging, trimming, sorting

stress-strain diagram

elasticity up to a certain point, then plasticity

sources of wood-based fuels

energy forest plantation, forest biomass (primary and secondary residues as well as whole trees), recycled wood

mechanisms of wood modification

filling the lumen, filling the cell walls, reaction or cross-linking with hydroxl groups, altering cell wall structure

applications of fiber boards

flooring, furniture, building

why are the veneers oriented in different directions sometimes in plywood?

for strength; but it's difficult/expensive so only done if necessary

Casein

form of protein found in milk, used for glue, paint, cheese, bioplastics - company QMILK makes bioplastics from milk

freshwood insects

freshly felled stems with bark, reduces wood quality example: wood wasps

types of wood-destroying insects (important)

freshwood insects, drywood insects, mould insects

examples of wood modification

furfurylation, acetylation, DMDHEU

applications of plywood

furniture and boat constructive

applications of particle boards

furniture, buildings, flooring

forest trends

global forest area declining, 20k ha per day; increase in plantations, 7% of forest is plantations (teak, palmoil, rubber)

epoxy adhesives

good because can bind to other substances besides wood, but expensive

Oak

good for barrels bc of tyloses (not red oak!)

types of paper

graphic paper, cardboards for packaging, household/sanitary papers, special technique paper

harvesting cotton

hand picking, "pickers", or "strippers" , the latter are very efficient

European beech

has little black lines

Fir

has no resin cells

Early wood

has thinner cell walls than late wood

veneer plywood

high dimensional stability; need to be uniformly dry (10-15%) before gluing

mold fungi

high moisture and temp, slightly acidic pH

soft rot

high moisture, soil contact, 1-10% of all building infestations, degrades cellulose, similar appearance to brown rot

wood ash properties

high pH (>13), lots of K, P, Mg, heavy metals, basic reaction, different composition, enrichment factor 100

band saw

high speed and quality for med-large diameters but required great skill and cost

Consider lumber recovery factor (conversion efficiency)

higher for high diameter logs

wood lasts centuries

if completely wet (bc no oxygen) or completely dry

positive aspects of termites

important for recycling wood, tunnels create soil porosity, help reclaim damaged soils, are food for other animals, only cause problems when attack structural lumber

tension wood

in hardwood trees; pulls away from the force (opposite side), due to more cellulose (elastic) in hardwoods

compression wood

in softwood trees; pushes against force (same side), due to more lignin in softwoods

Resin cells purpose

in xylem to protect (from beetles)

Pruning

increases timber quality by removing branches from younger stem to get knotless wood

dampwood termites (important)

infest damp and decaying timber, need high moisture content, no worker castes or soil dwelling

reaction wood

is a response to gravity

Sapwood

is never durable (the outer rings of the tree), purpose is transport not support

modern circular saw

is two smaller saws

chemical adhesives

isocyanate and urea-formeldehyde resin (undergo a reaction)

4 kinds of termites (important)

isoptera, 2500 species globally, four groups: - dampwood termites (limited) - drywood termites - subterranean termites (95% of damage in the US) - mound building termites

things to make out of yarn

knotted net, knitted good, fabric

Forest definition germany

land area covered with trees at least 5 meters tall and a crown cover of >30%; short rotation energy plantation accepted

clearcutting

leads to erosion (forbidden in Germany)

Hardwood

leafy trees; tracheids, vessels (diffused poroud vs ring porous), parenchyma (wood rays), longer fibers

aspect ratio

length/diameter (fibers have a high aspect ratio)

mechanical pulp production

lignin stays inside; either chipping and milling or sawing and grinding; later washing and bleaching

physical adhesives

lignin, protein glues, tannin (do not require further reactions)

root end reduction

logs must have a uniform diameter for smooth flow through the mill

paper machine

long sieve (flexible but low speed) and moving screen, press section (dewater and compress paper web to at most 55% moisture), dryer section (contact drying with heated cylinders)

types of drywood insects

longhorn beetle, wood worm beetle, sapwood beetle, termites

Resin cells appearance

look like tiny white dots in the wood

advantages of pellets

low emissions, pure wood, high energy density, low ash content, low dust

circular saw

low-medium quality, low-medium diameters lots of waste

lightweight boards

lower the density, by using lightweight core materials for ex.

Polyvinylchloride

mainly unplasticized, has corrosion, processing not possible without additives, amorphous, polar, good chemical resistance and durability properties

flax, or linseed

makes fibers (stem) and oil (seeds)

materials for papermaking

mechanical pulp, chemical pulp, chemical additives, fillers

retting (flax)

microbial degradation of plant parts to loosen and separate bast fiber bundles from non-fiber fractions method: dew retting

main factors for viscoelastic behavior

moisture content, temperature, structure

why debark in a mill?

more accurate measurements, less damage to blades

sulphate pulping

more common, basic pH, higher yield, higher strength

characteristics of fibers

morphology (length, diameter, structure), surface, chemistry (composition, stability, therm.), mechanical properties (ductility, strength, stiffness)

cellulose as polymer

most abundant biopolymer; tensile strength like steel, lots of H bonds; occurs in plants and bacteria

continuous press

most important european press type, feed rate up to 2m/s

Spruce

most used construction wood

Pine

most used for wood panels and furniture

oriented strand boards applications

mostly used for building, then packaging

timber sources

natural forests, managed natural forests, plantations, parks, savannas, and more

the three T's for combustion

need this plus O for combustion; Time, Temperature high enough for fuel gases to ignite , Turbulence to mix gases with O

Softwood

needle trees; tracheids and parenchyma; more distinct year rings (more stripey), 95% tracheids

Polyethylene

no pre-drying necessary, low water no abrasion or corrosion, mostly HD-PE used, low water uptake, wide range of mechanical properties

wood staining fungi

no rot or strength loss but decreases wood value: staining/hygiene

drywood termites

no soil contact, sapwood, hard to recognize

suitable wood species for chemical? modification

not hardwoods generally; poplar, willow, alder, some pines

relaxation

observed decrease in stress in response under constant strain

swelling and shrinkage

occurs when moisture content changes and is below fiber saturation point and can distort the wood (because of differences between annual rings)

Timber certification

of sustainable forest management and product certification (chain of custody)

polyurethanes

one of most important, ubiquitous, lignin is significant

plantation features

one target (production of timber), largely private ownership, need fertilizer, harvest by clearcutting

complete combustion process

only CO2 and H2O; no harmful emissions, no visible smoke, no significant sulfur and heavy metals

honeycomb sandwich boards

outside is wood composites, inside is paper/plastics/aluminum, used for furniture mostly

monomers of lignin

paracoumaryl alcohol coniferyl alcohol sinapyl alcohol

researching WPC

particle size and geometry, processing techniques, mechanical techniques, structural analysis

differences between particles and strands?

particles are either fine or coarse, (PB has 3 layers, outside are fine inside is coarse) Strands have coarse on outside and fine on inside

Why bioplastics?

petroleum is limited, production has potential to be climate neutral, wide range of source materials

why use wood

plentiful renewable resource, creates local jobs, carbon neutral, & more

saw types

primary machines and secondary machines (circular saws can be in both)

juvenile wood

produced first 10 - 15 years at each level, lower strength, less cellulose, thin cell walls

anisotropy

properties vary by direction

regenerated cellulose and cellulose derivatives

pure cellulose and only sulphite pulping; makes rayon, viscose, foils, plastics

speed up drying

rate doubles for every 10 degree increase, sun, air movement, stack loosely for ventilation, only cover top to keep off rain, elevate off ground

amount of pores in wood

reaches 50 - 60%

things fibers can do

reinforcement component, insulation, soundproofing, fluid sealing, upholstery, packaging

define moisture content of wood

related to dry mass; how much water compared to the amount of wood

aims of wood modification

resist fungi/insects, reduce moisture uptake, increase stability or coating adhesion, increase strength

cotton processing

roller gin separates seeds and fibers

parts of a saw mill

roundwood storage, production site, timber storage

raw material wood

saw and veneer logs for timber, industrial wood for composites and pulp, fuelwood for energy

Tyloses

seals vessels (of some hardwood)

cotton properties

seed fibers, 30 million ha of land, 25 million tons, vulnerable to insect damage

Heartwood

sometimes durable, sometimes different color; functionally dead, contains different extractives, sometimes biocides

Sorption isotherm

sorption isotherm is the relationship between equilibrium moisture content (EMC) and relative humidity (RH)

forms of adhesion

specific adhesion: physical attractive forces between molecules (adsorption), chemical bonding between molecules (chemisorption) mechanical adhesion: using surface roughness

sawmill waste

splinter, slabs, chips, bark, saw dust

types of wood fuel

split logs, chips (from logs, branches, recycled), pellets and briquets (from sawdust and shavings), sawdust, gasified, liquified or as hydrogen

role of forests

stabilizing soils and climates, regulating water flow, giving shade and shelter, habitat for pollinators and predators of pests

trees support agriculture

stabilizing soils, stabilizing climate, regulating water, supporting pollinators, shade and shelter

some natural polymers

starch, glycogen, cellulose, lignin, rubber

forms of blue stain fungi

stem wood stain, sawn timber stain, coating stain (when wood coating damaged)

6 steps to avoid termites

suppression of nearby colonies, site management, chemical or sand/stone soil barrier, slab and foundation details, termite resistant timbers, surveillance and remediation (with heat/fumigation)

creep

tendency of viscoelastic material to deform over time under constant stress

hygroscopic

tending to absorb water

thermoplastics vs thermoset plastics

the former can be remelted to a liquid (easy to recycle!) and the second cannot due to irreversible chemical bonds (important for high-heat applications)

microfibril angle

the smaller the angle, the greater the tensile strength of the fibril

additives to adhesives

thinners, fillers, stabilizers, fortifiers (to improve durability under specific conditions)

rheology

time-dependent deformation

carbonation of wood ash

to use as fertilizer it needs to be "carbonized" (longer contact to water vapor in air) to reduce pH to like 8; CaO -> CaCO3

log merchandising

to use each part of the tree in the best and most profitable way

FAO definition of forest

tree cover of more than 10%, minimum area of 0.5 ha, still should be able to reach 5m

finishing the particle board

trimming, sanding, conditioning, coating

fire behavior (pas important)

unlike steel, which fails suddenly, wood can insulate itself by charring only the outer layer

fillers in paper

up to 40%, improves appearance and printing properties and strength; inorganic compounds like silicates and sulphates

types of cotton

upland cotton! extra long staple cotton, short staple cottons: tree cotton and Levant cotton

Resonance wood

usually spruce

sulphite pulping

varying pH, higher purity, lower strength, easier to bleach

isocyanates

very reactive, which makes polymerization efficient and rapid, but causes reactions with water in wood and is more expensive

sources of water in walls (pas important)

water leaks and vapor laden air

turning a polymer solution into fibers

wet spinning

insulation board production wet process vs dry process

wet: fibers more defibrated, less glue, more wastewater, longer pressing time

wood shrinkage due to water loss

when the lumen loses water at about 30% moisture content (at fiber saturation point)

saw mill

where logs are cut into lumber

WPC

wood polymer composites; polymer is matrix and wood is reinforcing (50 - 80% wood by weight)

Animal fibers

wool (sheep), hairs (other animals), and silk (silk worms)