Ultrasonic Hemp Fibre Processing

• Ultrasonic retting of fibrous materials such as hemp and flax fibers allows for a fast and efficient fiber modification.
• Ultrasonically processed bast fibers are fibrillated and show a significantly higher specific surface, increased tensile strength and flexibility.
• Ultrasonic fiber processing is a fast and easy-to-use processing technology for industrial production.

Ultrasonic Retting

Ultrasonic retting is a fast, efficient and green alternative to traditional wet- or dew-retting. Acoustic cavitation, generated by high-intensity, low-frequency ultrasound, breaks up cellular structures of bio-materials such as non-wood, vegetable fibres which include bast fibre such as flax, hemp, nettle, wheat straw, rice straw, jute,as well as leaf-derived fibres (e.g., sisal, manilla hemp, abacá) and fruit-derived fibre like coir from coconut shells.
Ultrasonic disentangling transforms microfibers (approx. 3-5µm) into nanofibers (≥100nm). Furthermore, ultrasonic processing induced degradation of pure xyloglucan and xylan in solution, demonstrating the ultrasounds ability to degrade hemicellulose.
Although ultrasonic retting is mainly used in an aqueous solution, it is possible – depending on the raw material and the targeted outcome – to combine the ultrasonic process with an alkali treatment. Solutions of NaOH, H₂O₂ and H₂SO₄ can be used for alkalization to obtain cellulose nanofibers in a short processing time. By ultrasonic treatment, a fibrillation of cellulose microfibers can be easily achieved. The ultrasonically produced fibers show a specific morphology in which the nanofibers (≥ 100nm) are distributed across the entire surface of the microfibers (3-5µm).

Scanning electronic microscopy analysis on flax, hemp and coir fibers with or without ultrasonic processing.
source: Renouard et al. 2014

Ultrasonic Hemp Fiber Processing

With the growing market for hemp seeds and phyto-cannabinoids comes an increasing production of hemp straw. As a by-product, hemp straw and its fibers are mainly used for the production of paper or geo-textiles, the reinforcement in composite materials as well as building material.
Dried and cut bast straw can be used as raw material for ultrasonic treatment, however for superior ultrasonic process output the use of (partially) decorticated shives is recommended. The bast material is wetted in water (aqueous solution) so that a pumpable slurry is obtained, which can pass the ultrasonic flow-through cell. The sonication process takes only a short period of time (approx. 30-60 sec.). Scientific research has shown that ultrasonication improves the extraction of hemicellulose and lignin from lignocellulosic materials. Additionally, sonication degrades cellulose and pectin. Ultrasonic processing of hemp and flax also improves the flexibility and tensile strength of the fibers, which are valuable characteristics for textile and composite manufacturing.

Ultrasonic-alkali treatment of hemp fiber (Ferreira et al. 2019)

Ultrasonically Modified Hemp Fiber

Ultrasonically fibrillated bast fiber (e.g., hemp, flax) is particularly suitable as a reinforcement for polymeric resins, thermoplastic, and thermoset composites.
Hemp bast fibers are a valuable source from which cellulose nanocrystals (CNCs) can be extracted. Cellulose nanocrystals are characterised by their high surface area and their extraordinary stiffness and tensile strength. CNCs’ tensile strength excels the strength of glass or aluminum. Cellulose nanocrystals are a quite cheap and are thereby a competitive nano-additive, when it comes to price, availability, toxicity as well as sustainability.
Sonication is an easy-to-use, fast and green technique, which allows to produce high-quality cellulose nanocrystals.

High Performance Ultrasonicators for Fiber Processing

Hielscher Ultrasonics manufactures high-performance ultrasonic equipment for heavy-duty applications. Our ultrasonic systems can by used for batch or continuous inline processing. All Hielscher industrial ultrasonic processors can deliver very high amplitudes. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available. However, the capability of very high amplitudes alone is not enough to run a successful ultrasonic fiber process, such as retting or fibrillation. Depending on the raw material and on the targeted outcome, the process parameters – namely, amplitude, pressure, temperature, and time – must be exactly controllable and adjustable.
Hielscher’s digital ultrasonic processors record automatically all process data on an integrated SD-card, so that process results are reproducible. Amplitude and processing intensity can be precisely adjusted and controlled from very mild to highly intense sonication conditions. This gives you the opportunity to process various materials to optimum output.
The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.
La tabella seguente fornisce un'indicazione della capacità di lavorazione approssimativa dei nostri ultrasonori: