Engineering of Hemp — Hemp Processing to Yield Different Products

The varied range of industrial hemp products represents the greatest agricultural opportunity the world has seen in the last five decades. Hemp is a versatile plant offering thousands of applications across a plethora of industries. From nutritional applications to fashion, textiles, fuels, and plastic replacement, the possibilities of the crop are expanding as we learn more about it. Industrial hemp has the potential to disrupt not only the agricultural industry but medical, health care, pharmaceutical, energy, and tech industries as well.

Hemp Varieties

As one might expect from a plant with so many applications, hemp itself has assorted varieties and strains. Different varieties of hemp perform differently under different environmental conditions. While some varieties are more suited for medicinal purposes, others are better suited for creating biomass or textiles.

Traditionally, industrial hemp has been divided into three main categories:

• Fibre
• Grain
• High-Cannabinoid producing

Fibre Hemp Varieties

Fibre varieties of hemp produce long fibres and biomass. These types of hemp are employed in building materials, textiles, composites, pulp/paper, and fuel industries. The hemp fibre cultivars are slender ranging from 10 feet to 18 feet in height. These varieties are cultivated and harvested for bast fibre and hurd — both with a great potential to be used in fabric, construction, and some manufacturing operations. Fibre varieties of hemp call for the development of the processes and infrastructure that can support large scale harvesting, transportation, and processing. This is because hemp bales are voluminous and ideally require processing facilities in proximity to the grows.

Grain Hemp Varieties

These are the varieties of hemp that are used primarily for food and nutritional applications owing to their high fibre, protein, and fatty acid content. Traditionally, these varieties yield lower cannabinoid content. Grain hemp seeds are thin-walled and fragile and thus require careful handling while being processed or transported. With grain crop, it is imperative to conduct proper harvesting, processing, transportation, and storage processes to ensure the optimal value for the harvested grain.

Cannabinoid Hemp Varieties

These are currently the most productive of the varieties. However, they can present regulatory challenges according to the end product that is produced from them. Hemp contains a molecule called Cannabidiol (CBD) which has a varied range of applications as pharmaceutical, nutraceutical, and/or dietary supplement. Because hemp has a tainted reputation, the regulation of CBD varies from region to region. High cannabinoids varieties are generally grown only as female plants because the combination of male and female plants leads to seed production and alleviated cannabinoid yield.

Hemp Cultivation

As we have seen, hemp can be cultivated for seeds and for psychoactive substances. But its main product remains bast fibre. Traditionally bast fibres were used for making ropes, twines, hand-wearing fabrics, and bags. In recent times, the potential applications of the bast fibre have widened. Apart from textile destinations, bast fibres are used in the production of speciality paper. Some studies have evaluated the possibility of using the entire stem to produce paper pulp.

In addition, a promising destination for hemp bast fibres is the production of insulating products and fibre-reinforced composites.

That is not to say that the cultivation of hemp for seeds and psychoactive (and non-psychoactive) substances is not prevalent. Cultivated hemp seeds were most commonly used as animal seeds but in recent times, multiple food and industrial applications are emerging.

Fun Fact: Hemp seeds are healthier than flax and chia seeds and have more nutritional value. A 100 gram serving of hemp seeds can serve as much as 64% of our daily nutritional value.

As for the psychoactive substances present in hemp, the CBD industry has, and continues to grow drastically. The extraction of CBD oil for numerous health benefits is gaining traction. And oil extracted from the seeds is gaining popularity as a cosmetic and skincare supplement.

Hemp Harvesting

The harvesting of the hemp crop has taken different shapes according to the end-use of the crop. Each end-use of the crop calls for different cultivation practices. For instance, the cultivation techniques vary greatly when hemp is grown to obtain long fibre bundles and when it is cultivated for seeds and fibre.

Hemp harvesting, in the present time, has taken two shapes:

1. Longitudinal Hemp Harvesting
2. Disordered Hemp Harvesting

Longitudinal Hemp Harvesting

The main products obtained at the end of the traditional hemp production are parallel fibre bundles also known as long hemp. These can be spun into yarn by the process of wet spinning. For this, harvesters mimic the operation of creating stem hoods that were once carried out by hand. A reaper and binder cuts the stem in a single passage, ties them into bunches, and drops them on the field where manual labour arranges them for efficient drying. After drying, the stems are baled with common flax balers.

Disordered Hemp Harvesting

With the increasing technical applications of bast fibres, it was important to develop techniques that enabled and improved the supply of raw material w.r.t to the quality requirement of the successive processor.

The most common technique to achieve this is based on the principle of one-knife cutting drum. This system is mounted onto tractors with a rear driving system. There is a header and an adapted one-knife cutting drum with mass balancing. The hemp stalks are lengthwise fed into the chopping drum, cut into 600–700 mm long pieces and placed onto the field directly under the drum.

Multiple field experiments have shown that this method enables adequate retting and drying behaviour of the mowed and cut plant.

Further Advancements in Hemp Harvesting

Another important development in hemp harvesting came with the idea to preserve the original array of the hemp plant until it is cut into 600–700 mm long pieces. After it has been cut, eccentric steered conveyor elements snatch up the hemp stalks in a vertical position. The cutting discs, located at fixed positions, then chop the upright stalks multiple times before laying them on the ground. This harvesting system is suitable for all field and weather conditions because the cutting discs can be interchanged.

In addition, the simple cutters that have been used to harvest industrial hemp for decades have been developed into multi-level cutters to cut hemp into shorter pieces.

Hemp Processing

The crop is processed in the industrial factories following two main processing routes. Longitudinal hemp for clothing textiles is obtained in processing lines which always keep the fire bundles aligned to avoid tangle. This ensures maximum fibre yield. Old hemp processing lines are still available in parts of Eastern Europe. These scutch entire stems and yield hemp fibre bundles that are as long as the stems. For processing, short hemp crops or to cut hemp stems to an appropriate size, flax scotching lines can be employed.

As for the disordered hemp, since their fibres and fibre bundles have no preferred orientation, multiple processing lines have been developed.

Retting

Irrespective of the processing route that is being used, hemp stems of fibre bundles have to go through the process of retting.

Retting is a process of employing the action of microorganisms and moisture on plants to dissolve or rot away much of the cellular tissues and pectins surrounding bast-fibre bundles.

This process facilitates the separation of the bark from the core and loosens the binds between single fibres. This is done in order to ensure that after the extraction process, cleaner and finer fibre bundles are obtained.

Water Retting

Traditionally, hemp is retted by soaking it in ponds and rivers to produce high-quality fibre bundles. The water penetrates to the central stalk portion, swells the inner cells which burst the outermost layer and increases absorption of both moisture and decay-producing bacteria. In the process of water retting, retting time has to be carefully observed as under-retting makes the separation harder and over-retting results in weakened fibre.

Natural water retting uses stagnant or slow-moving waters (ponds, slow streams, and rivers). Bundles of hemp stalk are weighed down with stones or wood for approximately 8 to 14 days depending upon the temperature and mineral content of the water.

Dew Retting

More modern techniques for retting hemp fibre bundles include dew retting. This method is popular in areas that have limited water resources. In dew retting, the harvested plant stalks are spread evenly in grassy fields where the mutual action of sun, bacteria, air, and dewdrops lead to fermentation which dissolves much of the stem material around the fibre bundles.

The fibres are separated usually within 2 or 3 weeks. Dew-retted fibre is darker in colour and poorer in quality than water-retted fibre.

Extraction of Hemp Products

The hemp crop is used to make a variety of commercial and industrial products. Hemp’s applications spread across food, fibre, building material, jewellery, paper, plastic, hemp concrete, and biofuels. In this section, we’ll take a brief look at how each of these products is derived from the crop.

Hemp Concrete

More commonly known as Hempcrete, hemp concrete is a bio-composite material which uses the inner woody core of the hemp stalk to produce a mineral matrix which forms a non-toxic, carbon-negative, and energy-efficient building material. Hempcrete is one of the most sustainable construction materials available today. Hemp stalks are mixed with lime and water to make concrete-like blocks. The silica-content in the stalks binds with lime and results in a lightweight cementitious insulating material.

Hemp concrete is not used as a structural element but only as insulating infill between the frame members.

The first use of hempcrete was witnessed in 1986 in France when Charles Rasetti renovated the Maison de la Turquie.

Hemp Paper

Hemp Paper contains exclusively or to a large extent, pulp obtained from fibres of industrial hemp. Compared to wood pulp, hemp pulp offers four times longer fibre, a considerably lower lignin fraction, and high tear resistance and tensile strength.

The main products made from hemp paper are speciality papers such as banknotes, cigarette paper, and technical filter paper. Hemp paper is 4–5 times costlier to produce than wood paper. It is one of the main reasons why we do not use hemp paper for mass applications such as printing and packaging paper.

Hemp Cordages

Hemp ropes are among the oldest rope fibres known to man. From the age of classic sail to the present times, hemp has remained a soft, supple, and strong rope versatile for use in decorating, design, marine, sports, and theatrical applications. A typical hemp rope is used through the following process.

The hemp fibres are separated and cut into lengths approximately twice as long as the desired length rope. The cutting is continued until we have a bundle of fibres that are half the size of the desired diameter.

The bundles are folded in half secured by a dowel rod. The fibres of the bundles are smoothed along the length of the cord. The bundles are then divided into two parts. Each bundle is rotated clockwise until the cord begins to kink and loop.

The two cords are then twisted together wrapping one over the other in a counter-clockwise motion. The ends are secured with overhand knots beginning with the end in the maker’s hand. Once the first end is tightly tied, the rope is slipped off the dowel rod and tied.

Hemp Biofuel

Hemp can provide mankind with two types of fuels — hemp biodiesel and hemp ethanol/methanol. The hemp-based biodiesel is obtained by pressing hemp seeds to extract oil.

CBD Extraction

The extraction of the cannabinoid CBD is perhaps currently the widest use of hemp. With more and more research revealing the many benefits of CBD, the extraction of CBD-based products from hemp is gaining traction.

The extraction of CBD rests on the selection of the source plant of optimal quality. Once the source has been selected, CBD is extracted using the following extraction processes:

Whole Plant Extraction

This is the most beneficial and least quality-compromising extraction process where the whole hemp plant is used to obtain a broader spectrum of cannabinoids.

Isolates Extraction

This extraction process focuses on removing all the plant matter and extracting only and only CBD. The CBD obtained through this process is more extensively refined than whole plant extracts.

Alcohol Extraction

This is the most common extraction process for CBD where the alcohol (mostly ethanol or isopropyl) combines with dried plant material. It acts as a solvent and pulls the cannabinoids from the plant after which the extractors further separate the solvent and the extracted components.

CO2 Extraction

This is the most expensive process of extracting CBD from hemp. It employs a series of CO2 chambers to react with the cannabinoids and then separate them.

As technology advances and we further research into Hemp and its potentials, more engineering of hemp to obtain varied uses is hopeful. After its long infamous association with cannabis, hemp is making a comeback into people’s life at its own pace. With the increasing demand for sustainable alternatives to present solutions, hemp appears to be the future of mankind.

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