7.3.1 Cottonisation

Cottonisation is a process that gives the relatively long fibre bundles of hemp the texture and consistency of short staple fibres, such as cotton, so that they can be spun, woven and knitted on cotton-specific systems. The physical properties that can be changed by cottonisation are length, fineness, and diameter.
Hemp fibres contain less cellulose than cotton fibres, so they do not have the same softness as cotton fibres. This makes hemp fibre a less popular fibre in the textile industry. Cottonising can (partially) overcome this disadvantage, making hemp fibres more similar to cotton fibre.

The raw material for cottonisation is the whole bast fibres intended for technical applications (§6.1), and/or the short fibres released from the scutching and hackling line (§7.1.1, 7.1.3). During cottonisation, the pectin and lignin bonds between the plant cells in the bast fibre bundle are weakened such that these plant cells can be isolated as fibres, with dimensions similar to cotton or wool.

During cottonisation, it is important not only to make the hemp fibres finer, but also to maintain their strength. If pretreatment is too harsh, the fibres can lose their quality and become less useful for spinning. Cottonised fibres are usually blended with cotton or Tencel to facilitate spinning and achieve better yarn strength. Cottonised hemp fibres can also be used to compensate for the decreased strength of recycled fibres in a 'new yarn'. Conversion yield of cottonisation is about 80 – 85%.

There is no single set procedure to cottonised hemp. Companies have their own approaches to deliver best possible fibre products.

Methods of making cottonised hemp fibres include:

• Mechanical, after alkali pretreatment

• Steam explosion

• Electroshock treatment

Methods under development:

• Oxidation with ozone

• Acoustic cavitation using ultrasound

• Microwaves