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)