Identification and review of the downstream options for the recovery of value from fibre-producing plants: Hemp, Kenaf, Bamboo

JL Broadhurst, T Chimbganda, G Hangone

Fibre-rich plant

?

Post-mining industrial development from fibre-rich plants

?

Conversion

Lead product

Cultivation HarvestPre-

treatmentProductrecovery

Conversion

Plant

biomass

Fibrous-Part

By-products

SeedWater

Non-Fibrous-part(twigs, leaves, seeds etc)

Fibrous-Part

Additional product(s )

Conversion

Processing Manufacturing

Manufacturing

Biorefinery

Biorefinery

High-end

by-products

Key Processing Stages

Bast fibre plants Hemp Kenaf

Bast fibre plants

Bast fibre

Woody core or hurd

Epidermis or bark

Bast fibre plant Bast fibre plant cross section

Different bast plants have a different ratio of bast to woody core

Bast fibre plant properties

Properties Hemp Kenaf

Bast fibre (% in stalk/stem) 25-30 35-40

Fibre fineness (um) 25 to 40 20 to 35

Fibre length (mm) – long fibre 16 to 40 8 to 18

Cellulose (wt%) 70 – 74 45 - 57

Hemicellulose (wt%) 18 -22 21- 23

Lignin (wt%) 4-6 8-13

Tensile Strength (MPa) 550-1000 195-700

STEM

ENTIRE PLANT SEEDS

LEAVES

Example: Hemp

Example - Bioethanol

Energy

Fibre + Woody tissue Leaves or Medicine

Seeds Oilor

Bast fibre crop-to-product profile

Woody tissue

Shives

Construction materials

Short Fibre

Cordage

Paper Pulp

Long Fibre

Bio-compositesBast Fibre

Hurd

&

&

Bast fibre stem cross-section

Conventional textilesIntermediates End-products

70-90%

10-30%

25-40%

60-75%

Bast fibre plant e.g. hemp

Seeds

Stem

Whole plant

Stem

Seeds

Energy (e.g. bioethanol, biogas)

Bast Fibre

Woody tissue/core fibre

Whole seed

Chemicalextracts

Shives (animal bedding etc)

Insulation boards

Oil

ProteinFood

Long fibre

Short fibre

Paper pulp

Leaves

Edible oil (e.g. hemp seed oil)Personal productsPaint/varnishAnimal Fodder

Conventional textiles

Construction composites

CordagePaper pulp

Biocomposite textilesBioplastics

Bioethanol/biobutanol

Human food

or

&

&

or

&

Part of plant Intermediates End-products

&

Medicine

Bast fibre plant multi-product profile

• Hemp and kenaf fabrics are breathable, warm, moisture-wicking,antibacterial and biodegradable.

• Bast fibres can be easily blended with other fibres such as cotton to makelightweight softer fabrics.

Hemp fabric Blended fabrics

Conventional textiles

• Fibre composites are made by embedding plant fibres in synthetic orbiodegradable resins.

• PFRCs are being incorporated into thermoplastic matrix composites and aregaining traction in the automotive and aerospace industries.

Plant Fibre re-inforced composites

• Hemp and kenaf construction products range from insulating panels, non-woven felts for acoustic damping or levelling from woody tissue/hurds tofibre reinforced polymers for façade panels and concrete.

• The most commonly applied product in the building and constructionsector is hempcrete.

Insulation mats

Insulation matting Fibre boards Concrete (hempcrete)

Construction materials

• Paper pulp can be made either from short bast fibre or woody tissue.• Paper made from kenaf bast fibre is reported to be comparable to paper

from some softwoods and most hardwoods• Paper from core fibre or woody tissue (hurd) is not as strong, but is easier to

manufacture as well as softer, adsorbent and more suitable for hygienicproducts.

Paper products

• Hemp and kenaf seeds can either be used as a whole or crushed andpressed to produce oil and a residual seed cake.

• Hemp seeds contain 30% oil by weight, whereas kenaf seeds contain 20%oil.

• Hemp flowers or leaves can be used to make cannabidiols which have lowTHC levels and are used for medicinal purposes.

Hemp seed oil Kenaf seed oil

Pharmaceuticals

• Stems are pre-treated to soften them through retting or degumming, whichcan be chemical, mechanical or high-pressure/temperature processes.

• Bast fibre is separated from woody tissue, into long & short fibre through aprocess known as decortication.

Harvest Retting Decortication

Conversion

Plant biomass

By-products

Leaves &Seeds

Fibre products

Woody tissue

StemConversion

WoodyproductsConversion

FibreStem

Bast fibre processing

Plant

Textiles

Woody tissue

Stem FibreStemHarvest Pre-

treatmentProduct recovery

Spinning

Conversion

Long

ShortCarding

Pulping

Cordage

Composites

Paper

Sorting

PulpingPaper

Conversion

Shives

Seed oilCleaning

Compression

Construction materials

Leaves Cleaning

Conversion

Whole leaves

Seeds Whole seeds

Fibreproducts

Woodytissueproducts

By-products

By-products

Medicine

Spinning

Conversion

Carding

Pulping

Bast fibre multi-product flowsheet options

Environmental & socio-economic impacts

Energy inputs

Water inputs

Job Creation potential

Skills level requirement

Conventional textiles Low Medium High Low

Fibre-reinforced composites

High Low Low High

Construction materials High High Medium Medium

Paper High High Medium Medium

Implications of the various product options

Bamboo

Bamboo plant structure

Culm

Node

Internode

RhizomeShoot

Twigs

Leaves

Roots

Fibre

Endodermis

Exodermis

STEM/CULM

ENTIRE PLANT BRANCHES

Example - Biochar

SHOOTS

Energy

Wood or Fibre or Pulp

Household wood products

Vegetable

Bamboo crop-to-product profile

Fibre

Natural

Rayon

Pulp

Cardboard

Paper Pulp

Wood

OR

OR

Poles

Wood products

Bamboo culm/stem

Intermediates End-products

Whole plant

Culm

Leaves

Energy; biofuels

Strips

Poles

Food

Pulp

Chemical extracts

Fodder (Manure)

Branches Sticks

Medicine

Textiles

Construction materials

FlooringFurniture/decor

Shoots

Part of plant Raw products End-products

Polymer composites

Whole leaves

or

&

&

&

and/or

or

Paper & cardboardRayon fibres

Natural fibres

HandicraftsWoven products

Engineered “wood-based” composites

and/or

Sporting equipment

Mats, blinds, chopsticks

Intermediate products

Culm

Node

Internode

RhizomeShoot

Twigs

Leaves

Roots

Bamboo plant

Bamboo multi-product options

• Bamboo has many applications in the construction and building industriesdue to its woody nature and similar properties to timber.

• The culm is either used whole as poles or split into strips to make wovenproducts or engineered bamboo wood-composites.

Bamboo poles

Woven bamboo strips

Plybamboo boards Strand woven boards

Particle boardsBamboo mat boards

Wood-based products

• There are two types of bamboo textiles – bamboo linen (also called“natural bamboo fibre”) extracted by mechanical or microbial processes.

• Bamboo rayon made through chemical treatments similar to themanufacturing of rayon viscose.

Natural bamboo fibre Bamboo rayon

Fibre-based textiles

• Similar to bast fibre composites, bamboo fibres can be used to reinforcenatural or synthetic polymer matrices.

• Bamboo-fibre reinforced plastic (BFRP) composites’ tensile strength iscomparative to mild steel and have a lower density, making them ideal forstructural applications.

Fibre reinforced composites

• Bamboo has a number of desirable characteristics as a fuel for combustion,such as a low ash content and alkali index compared to other bioenergyfeedstocks.

• Bamboo culm can be processed into pellet form or other forms of fuels,such as biogas, bioethanol and charcoal.

Energy-based products

• Each product type requires a separate treatment or processes.• Bamboo processing is more intensive and extensive than bast fibre

processing

Harvest Splitting Fibre recoveryPlantCulm

By-products

LeavesShootsBranches

Strips

Conversion Wood-basedproducts

Strips

Treatment Poles

Conversion

Energy-based products

Wholeplant

Conversion

Fibre-based products

Pulping/Conversion Paper products

Conversion

Bamboo processing

HarvestPlant

Plybamboo/

Burning

Pulping

Energy

Board making

Splitting

Option 1a

Low quality stems/wastes from options 1 and 2

Whole plant (100%)

Top of culm

Culm (80%) High-end

products

Strand woven boards

Bamboo mats

Particle board Low-End or bulk

products

Fibre recovery

Weaving

Board-making

High quality stems

Option 1b

Option 2a

Board making

Natural fibre

Option 2bMDF boards/

Poles

Medium quality stemsPre-treatment

Bamboo mat boards

Paper pulp Option 3a

Option 3b

Option 3c

Medium-value

products

Bamboo multi-product processing scenarios

Environmental & socio-economic impacts

Energyinputs

Waterinputs

Job Creation potential

Skills level requirement

Wood-based products Low Medium High Low

Fibre-based textiles High High Medium High

Fibre re-inforced textiles High High Medium Medium

Energy products Medium Medium High Medium

Implications of the various product options

Potential metal recovery

Leadproducts

Cultivation HarvestPre-

treatmentFibre-

recoveryPlant Fibrous-Part

SoilWater

FibreFibrous-Part

Additional products

Manufacturing

Non-fibrous parts Leachate (metals)

(metals)

AshingBio-ore

Hydrometallurgical/pyrometallurgical

extraction Metals

Plant-synthesised nano-catalysts

Manufacturing

Potential integrated metal recovery process

• All the fibre-producing plants can generate multiple products however,the range of products and targeted markets differ for the different planttypes.

• There appear to be few holistic or systemic studies on the selectionof products and processing of fibre-rich plants.

• This review shows that the selection of product recovery and treatmentprocesses is highly dependent on desired product types and output oflow-end vs high-end value products.

Summary

Lead to by-product

ratio

Processing methods

Product qualitySite specific

factors

Socio-economic impacts

Environmental impacts

Multi-product potential

The exploitation of fibre-based plants will depend on….

• Bast fibre plants appear to be the best downstream option for the productionof “green” textiles and high-end niche products such as fibre-reinforcedcomposites.

• Bamboo is more suitable as a replacement for conventional timber in theproduction of functional products such as wooden flooring and constructionmaterials and paper.

• Further studies will be required to investigate the effect of contaminants onproducts and processing options.

Summary

Acknowledgements