Technical products

Composite materials are a mixture of different materials that are combined into one. These materials combine different qualities and properties of multiple materials into one.

Not only can hemp shives be utilised for insulating applications, but the structural properties of hemp fibres also allow them to be processed into mats that resemble traditional insulating materials like mineral wool insulation boards. These boards offer similar insulating properties while lacking harmful characteristics such as skin irritation and respiratory hazards, thus eliminating the need for protective masks and gloves during installation.

Processing

The purified hemp fibres are mixed with jute fibres and a small percentage of petrochemical support fibres that give the insolation mats rigidity and fixate the natural fibres by melting during the heating process.

To increase the fire resistance, the fibres are mixed with sodium carbonate and a bonding resin. The homogenised mass is then put into a compression mould and formed under constant pressure and heat. The formed mats are extracted from the mould, cooled and finally cut to a uniform size.

Traditionally, plastics consisting of-derived polymers that require enhanced physical properties can be reinforced by incorporating fibres into their matrix. Typically, these fibres are composed of fibreglass or carbon fibre. Hemp fibres, however, offer a bio-based alternative to these mineral-based fibres. Their biodegradability, recyclability, low cost, and particularly their excellent mechanical properties make hemp fibres a valuable alternative in the reinforced composite market.

Soilless growing media are traditionally produced from materials like rockwool, coconut coir, and peat moss. However, hemp hurds and bast fibres can be processed into a viable eco-friendly, locally produced alternative. After decortication, the hemp fibres and shives undergo a sterilization step and are then mixed with a starch-based binder. The bast fibres provide sufficient water-holding capacity and act as anchors for the roots, while the hemp hurds contribute to the media's porosity, allowing for good aeration.

Hempcrete is an innovative building material derived from hemp shives. It combines the names "hemp" and "concrete" but is actually suited only for non-structural applications due to its lower compression strength compared to traditional concrete. Its physical properties are more like those of fibreglass insulation.

Hempcrete is celebrated for its environmental friendliness and boasts numerous advantageous properties. It offers excellent insulation and thermal properties, making it an ideal choice for energy-efficient building solutions. While it is suited for non-structural concrete mixtures, its economic attractiveness further enhances its appeal in the construction industry.

One of the standout benefits of hempcrete is its ability to promote local value chains, thereby contributing to regional economic development. It can easily be mixed and processed on the building site without complex machinery. The material's fire resistance, attributed to its lime content, adds an extra layer of safety to buildings. Additionally, hempcrete is known for its robustness and non-toxicity, making it a safer and more durable option compared to traditional insulating materials.

Hempcrete's natural resistance to mould, bacteria, and insects ensures a healthier living environment. Its good noise insulation capabilities and ability to regulate humidity make it an excellent choice for creating comfortable indoor spaces. Furthermore, hempcrete is easily recyclable, aligning with sustainable building practices and reducing overall environmental impact.

Composition

Hempcrete is a bio-composite mixture composed of hemp shives, a lime binder, and water. The shives are chopped into particle sizes ranging from 5 to 25 mm and then mixed with water and a minor portion of cement. The porosity of the resulting hempcrete is influenced by the particle size of the shives, the composition of the other materials, and the degree of compression during application.

In terms of density, hempcrete can vary based on its application method. For wall applications, the density typically ranges from 400 to 500 kg/m³. When utilising the spray method, a variation where the hempcrete mixture is pressurized and applied as a spray on insulator, the density is lower, ranging from 200 to 250 kg/m³. However, with higher amounts of binder, the density can increase significantly, reaching values between 600 and 1000 kg/m³.

The strength of hempcrete improves with greater density and compaction, making it a versatile and robust material for various non-structural construction applications.

Application

Hempcrete is utilised in the construction of walls, floors, and roofs. This versatile material can be applied monolithically, formed into precast bricks, or sprayed directly onto surfaces. Traditionally, hempcrete is filled between timber frames that act as load-bearing components in the construction. For optimal thermal conductivity, the space between the formwork boards should be filled with hempcrete in 20 cm layers and compressed to a density of 400 kg/m³ and then dried before the next 20 cm of insulation are applied.

In roof insulation applications, a lower density is preferred, typically within the range of 200-250 kg/m³. Conversely, for floor insulation applications, a higher density of around 500 kg/m³ is ideal to ensure adequate strength and functionality.

The most critical step in applying hempcrete is mixing the components in the correct ratio. A typical formula for wall insulation involves combining 100 liters of hemp shives, 22 kg of PF70 lime, and 30-35 kg of water (Yadav & Saini, 2022).

By adhering to these guidelines, hempcrete can be effectively used to enhance energy efficiency, durability, and overall environmental friendliness in various building applications.

Hemp paper can be derived from either long fibres or hemp hurds. Paper made from long fibres tends to be coarser and crumblier, whereas paper made from hurds is generally thicker and softer.

What makes hemp paper particularly interesting is its potential to replace wood-derived cellulose. One acre of hemp can produce as much paper as 20 acres of wood, primarily because wood has a lower cellulose content of only 40%, compared to 85% in hemp. This higher purity of cellulose in hemp reduces the need for chemicals and pretreatment processes.

In addition to its ecological advantages, hemp-derived paper boasts superior characteristics, such as greater resistance to yellowing and higher tear strength. Its enhanced recyclability, driven by the greater resilience and elastoplastic behaviour of the fibres, allows for more recycling cycles compared to traditional wood-based paper.

Despite these benefits, hemp paper is mostly used for specialty products like rolling paper, currency, and Bible paper. The lack of infrastructure for hemp paper production compared to traditional paper making limits its ability to compete in the market for writing, printing, and packaging paper.

Paper pulping process

The fibres are subsequently processed by washing and separating the hurds from other plant material. The material is then soaked and delignified, followed by mechanical beating into a pulp slurry. This pulping step cuts and opens the cellulose fibres, enabling hydration, flocculation, and fibrillation. As a result, the fibres become more flexible and can bond more effectively to form a strong, uniform material.

The resulting pulp is then spread thinly, dried, and cut to the desired size.

Particle boards are typically produced from hemp hurds. In certain applications, hemp particle boards made from hemp shives can serve as replacements for traditional wood particle boards. Alternatively, hemp shives can be mixed into wood particle boards to partially substitute the wood-based inputs.

Processing

The particles are generally ground to a specific size, dried, mixed with a resin (often urea or phenol formaldehyde), and then hot-pressed into boards.

Hemp hurds and stalks/ stems can be processed into biomass pellets, charcoal and briquettes for heating. For solid biofuels (pellets, briquettes), it is necessary to dry and grind the stalks and hurds and then compress the grinded biomass into small cylindrical pellets (6-12 mm diameter). For briquettes, the biomass is compressed into larger solid blocks with natural lignin as a binder.

For obtaining biochar, thermal decomposition in low oxygen is done (pyrolysis) after the moisture is reduced to below 10% and the biomass is grinded into small particles of 5-50 mm. Depending on temperature, there could be biochar (slow pyrolysis), bio-oil (fast pyrolysis) or syngas (gasification).