Wood Composites

Presentation on Wood Composites

Course Teacher

By

Dr.I.Sekar

A.Maheshwaran

Associate Professor

BSF-04-012

Wood Plastic Composites

Wood plastic • • •

Plastic ranging from polypropylene to PVC Binders/Fillers – Wood flour to Wax Wood – saw dust & scrap wood products

Benefits • • • • • • • •

True hybrid materials & combine best features of wood & plastics Use low cost & plentiful raw materials Competitively priced Easily produced & easily fabricated Available in broad range of finishes & appearance Easily recycled after use No further processing is needed Weather, water, & mould resistant

Properties

Properties • • • • • •

High resistance to moisture (0.7% compared to 17.2% in Pine) Moisture not transmitted across plastic boundaries Good stiffness & impact resistance Dimensional stability Resistance to rot Excellent thermal properties

Environmental Benefits • • • • •

Negligible waste & that produced is reused No volatile organic compound Recycled & reused after their service life Disposed using standard methods Increase efficiency up to 40% compared to traditional wood

Processing

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• • •

Mix of wood & plastic - modified with process & additives - to improve processing / final properties of WPC Compatibiliser/coupling agent – Improve blending Basic wood product – fine saw dust(40-60mesh range) Simple die can be used even for most complex profile

Wood filler     

Wood putty or Plastic wood wood dust combined with a binder that dries and a diluent and a pigment fill imperfections, nail holes or pores in wood Wood putty or plastic wood - thicker version Wood filler - thinner version

Plastic wood 

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The base product -100% recycled High-Density Polyethylene (HDPE) shampoo and detergent bottles, to milk jugs Some, entirely of HDPE recycled HDPE + with wood fibers, rubber, fiberglass, or other plastics

Like Natural wood, Plastic lumber is 

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expand & contract with heat (Magnitude varies) cut and shaped with traditional wood working tools

Plastic wood will not:     

Rot (seawalls, docks) crack warp splinter degrade

Plastic wood is:         

denser than wood virtually maintenance free long lasting stain resistant waterproof UV resistant aesthetically pleasing impervious to insects not affected by exposure to most substances

Plastic wood also:   

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works with any deck fastener requires no painting or sealing used in composite extruded panel plastic wood for flooring Provides a good shock-absorbing surface for pedestrian traffic, such as runners and hikers.

Plastic lumber and Wood-plastic composites - difference 

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fiber plastic lumber can have less than 50% wood fiber. balloted in ASTM by Committee D20 Standard Test Method for Shear Properties of Plastic Lumber and Plastic Lumber Shapes.

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Wood-plastic composites have at least 50% or more wood balloted in ASTM by committee D07 Standard Test Methods for Evaluating the Mechanical and Physical Properties of Wood-Plastic Composite Products

New technology in plastic composite lumber 

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post-consumer plastics such as high density polyethylene (HDPE) mixed environmental wastes and plastic material into extruded composite lumber 65% recycled Cellulostics materials and 30% recycled plastic materials.

CATEGORIES 1. 2. 3. 4. 5. 6.

Material Preparation Extruder Design Screw Design Cooling Technology Die technology Fillers

Wood cement

Wood cement  

wood wool cement boards (WWCB) cement bonded particleboard (CBPB)

General Properties 

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durable and resistant to frost/thaw, fire, moisture, rot, vermin, fungus and termites easy workability

MANUFACTURING PROCESSES  Manufacture

of Wood Wool Cement Board

 Manufacture

of Cement Bonded Particle Boards

 Manufacture

of Cement Bonded Fibre Boards

Manufacture of WWCB  

Long wood + cement wool strands (or excelsior) - cut from debarked logs  

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400-500mm length prior to cutting the wood wool treated to prevent blue-staining

The logs stored on racks a month to reduce the moisture & sugar content

Manufacture of WWCB 

wood is shredded

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salt (CaCl2) solution + Portland cement (2:1 ratio)

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spread onto plywood moulds & stacked

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The mats pressed at room temperature under 10 psi.

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stack is clamped under pressure for another 24 hours then removed from the moulds & cured for 2-3 weeks.

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They are subsequently trimmed and finished.

Workers collecting sawn logs for shredding

Logs being shredded into wood wool

The wood wool is then soaked in a salt solution

Eltomation Rotating Wood Wool Machine Boards

The pressed and finished boards

Manufacture of CBPC  

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wood is in particle rather than strand form softwood logs debarked & stored to reduce moisture and sugar content Portland cement: wood: water in ratio 3:1:1 Water evaporation is monitored CaCl2 added - cement setting The mixture fed to a conveyor

Manufacture of CBPC  

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mat subsequently cut These stacked & compressed together to 1/3rd of its original height over a 2-3 minute period. The mats are clamped and heated in a chamber at 70-80 degrees Celsius for 6-8 hours. boards dried, trimmed and stored for 12-18 days until the cement cures.

Modern CBPB plant

Manufacture of CBFB 

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wood  pulped cellulose fibre (with an air-dry moisture content of 12-16%) Silica + alumina + water + pulped cellulose Binders added water removed and mixture is rolled onto mats, cut, and sized, or moulded

Properties

Properties of WWCB     

insulation fire retardation water resistance resistance to organism attack mechanical properties

Insulation        

WWCB provides very good insulation, both thermally and acoustically. Acoustic Insulation Resistance of a plastered wall of 5cm Wood Wool Cement Boards 36-40dB Resistance of a plastered double wall with air space between WWCBs 53-57dB Resistance of a permanent shuttered wall with 12cm concrete core 354-56dB Noise Reduction Coefficient for 2.5cm board 0.7 Thermal Insulation (Evans,1996) Thermal resistance (R) for 2.5cm board 5

Fire Resistance  

5cm boards 1 hour resistance 10cm boards 2 hours resistance

Water Resistance Dimensional change after soaking in water for 48 hours:  0.84% thickness swelling  0.21% linear expansion  22% water absorption

Resistance to Organism Attack WWCB is highly resistant to dry rot and other fungal growth as well as to termites.

Mechanical Properties 

Specific Gravity  

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light boards for insulation only 360kg per cubic metre denser boards for roofs and permanent shuttering 450kg per cubic metre

Bending Strength = 20-30kg per cubic centimeter Design load for 2cm board = 50psf Ultimate load for 2cm board = 200psf Allowable span for 2cm board = 122cm Deflection at design load = 0.2cm

Properties of CBPB    

insulation machinability water resistance mechanical properties

Insulation 

Thermal Insulation 

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Electrical Insulation 

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Thermal conductivity (k value) = 0.35W/m.K Linear thermal expansion = 0.01W/m.K

CBPB is resistant to tracking and does not build up static charges, thus be used as backing panelling for electrical appliances.

Acoustic Insulation 

The sound reduction for boards of various thicknesses is as follows:     

6mm - 28dB 10mm - 31dB 20mm - 33dB 30mm - 36.5dB 40mm - 38dB

Machinability 

working - CBPB can be worked using hard tipped tools in a similar manner to timber,plywood or chipboard.

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sawing - can be sawn with handsaws, jigsaws with suitable blades or power saws with tungstentipped blades.

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drilling - use hand drill or high speed power drill

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sanding - manual sanding or mechanical sander preferably applied to both sides of board simultaneously.

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fixing - drilling of pilot holes for nails and screws is recommended for most board thicknesses.

Water Resistance 

Thickness swelling   

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