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

Production stages

Conversion

Lead product

Cultivation HarvestPre-

treatmentProduct

recovery

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

Bast fibre plants Hemp Kenaf

Bark (epidermis)

Bast fibre

Hurd (woody core)

Hollow core

Bast fibre plants

• The “bast” produces long fibres (70-90% of the bast) and short fibres (10-30% of the bast).

• The hurd or woody core is the inner woody tissue which accounts forabout 60-75% of the stem.

• Different bast plants have a different ratio of bast to woody core - Kenafbast fibre is about 35% of the stem and hemp bast fibre is about 30%.

Bast fibre plant e.g. hemp

Seeds

Stem

Bast plant productsWhole plant

Stem

Seeds

Energy (e.g. bioethanol, biogas)

Bast Fibre

Woody tissue/core fibre

Whole seed

Chemicalextracts

Shives (animal bedding etc)

Insulation boards

Oil

Protein

Food

Long fibre

Short fibre

Paper pulp

Leaves

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

Animal Fodder

Conventional textiles

Construction composites

CordagePaper pulp

Biocomposite textiles/ concreteBioplastics

Bioethanol/biobutanol

Human food

or

&

&

or

&

Part of plant Intermediates End-products

&

Medicine

Main process stagesConventional textiles

• 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

Main process stagesPlant fibre reinforced composites

• 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.

Main process stagesConstruction materials

• 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)

Main process stagesPaper products

• 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 paperfrom some softwoods and most hardwoods

• Paper from core fibre or woody tissue (hurd) is not as strong, but is easier tomanufacture as well as softer, adsorbent and more suitable for hygienicproducts.

Main process stagesSeed oils

• 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.

• The residual seed cake has been proven to be a protein-rich feed forlivestock.

Hemp seed oil Kenaf seed oil

Main process stagesBast fibre processing

• 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

Woody

productsConversion

FibreStem

Main process stagesBast fibre processing

• Different retting pre-treatments result in different fibre length, colour,quality and strength. Water or dew retting are commonly used.

• Bast fibre processing is fairly standard via decortication – though there areslight variations depending on desired end-products (high-end vs low-endproducts).

• Various products can be produced at different stages of processing topotentially form a multi-product flow sheet.

Breaking Scutching HacklingFibre

Long & short

fibre

Fibre

Woody tissue

Woody tissue (or

shives)

WasteShort fibre

Woody

Products

Long-fibre

products

Short fibre

Shives

Short fibreShives

Short-

fibre

products

Short fibre

Cultivation Harvest Retting

Soil Water

Drying

MillingScutching

Shives

Long & short

Fibre

Dust

Extraction

Short fibre

Short-

fibre

products

Long-fibre

products Woody

products

StemPlant

Water

Water

Fibre

Woody tissue

Dust from process

Dust

Seeds

LeavesSeeds

Leaves

By-

products

By-

products

Seed

Waste (leaves, seeds, dust)

Fibre

*high tech

Bast fibre multi-product process flow sheet

Bamboo

Bamboo products

Whole plant

Culm

Leaves

Energy; biofuels

Strips

Poles

Food

Pulp

Chemical extracts

Fodder (Manure)

Branches Sticks

Medicine

Textiles

Construction materials

Flooring

Furniture/decor

Shoots

Part of plantRaw products End-products

Polymer composites

Whole leaves

or

&

&

&

and/or

or

Paper & cardboard

Rayon fibres

Natural fibres

HandicraftsWoven products

Engineered “wood-based” composites

and/or

Sporting equipment

Mats, blinds, chopsticks

Intermediate products

Culm

Node

Internode

Rhizome

Shoot

Twigs

Leaves

Roots

Bamboo plant

Uses of the parts of a bamboo plant

Main process stagesWood-based products

• 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

Main process stagesFibre-based products - textiles

• 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

Main process stagesFibre reinforced composites

• 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.

Main process stagesEnergy based products

• 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.

Main process stagesBamboo processing

• Each product type requires a separate treatment or processes.

• Bamboo processing is more intensive and extensive than bast fibreprocessing

Harvest Splitting Fibre recoveryPlantCulm

By-products

Leaves

Shoots

Branches

Strips

ConversionWood-based

products

Strips

Treatment Poles

Conversion

Energy-based products

Whole

plant

Conversion

Fibre-based products

Pulping/

ConversionPaper products

Conversion

Bamboo multi-product flowsheet scenarios

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

Potential metal recovery

Potential integrated metal recovery process options

ConversionWaste

Leadproducts

Cultivation HarvestPre-

treatmentFibre-

recovery

Ashing

Plant Fibrous-

Part

Bio-ore

SoilWater

Non-Fibrous-part

(twigs, leaves, roots etc)

Metals

FibreFibrous-

Part

Additional

products

Conversion

Metals

Leachate

(metals)

Hydrometallurgical

/pyrometallurgical

extraction Metals

(metals)

**Alternatively use hyperaccumulators to recover metals/remove contaminants prior to growing fibres

Plant-

synthesised

nano-

catalysts

Main process stagesSummary

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

• The selection of product recovery and treatment processes is highlydependent on desired product types and output of low-end vs high-endproducts.

• Therefore the exploitation of fibre-based plants will depend on the following;

❖ The considered selection of lead and additional products and by-products

❖ The relationship between the biomass properties, processing methods and desiredquality of the intermediate and final products

❖ Socio-economic drivers and environmental impacts

• Currently few holistic and systemic studies to inform decision-making on theselection of fibre-producing plants, products and processing methods

Minerals to Metals project team

Acknowledgements