Various renewable insulation materials for building applications have been developed and are marketed. In many cases these may substitute the mineral wool or glass wool insulation blankets and fossil based polymer based foams (polystyrene / polyurethane). Biobased products on the market for insulation materials include a variety of products ranging from sheep wool blankets, polylactic acid foams, cellulose and expanded cork. Also flax and hemp wool insulation mats have been demonstrated to perform well in building applications.
Insulation of buildings is performed primarily to reduce the energy needed for heating, but also has sound proofing and acoustic damping effects. The technical performance of these biobased insulation products are comparable with established market products (Table 1) and suppliers advertise the positive impact of their product on the humidity control and indoor climate conditions. The insulation value (R) is dependent on the thickness (d) of the material: R = l/d. Other relevant technical aspects are the vapour diffusion coefficient (m), the density (r) and fire safety according the building and construction requirements. Insulation of the outer walls and roofs is promoted to enhance the energy performance of buildings. In new construction and renovation projects biobased insulation products may be promoted as CO2 neutral alternative.
2. Expertise on production technologies
Bast fibres can be processed into non-woven dry laid (needle punched) or resinated mats by conventional technologies. The performance of fibre mats as insulation material in building application is comparable to other commercialized products on the market. The thermal and acoustic insulation are satisfactory, when precautions are taken for fire retardency, moisture absorption, sensitivity towards moulds and insects.
For the production of insulation mats from flax and hemp commonly flax tow (as the by-product of linen yarn production) or cut hemp bast fibre are used to manufacture non-wovens by the air lay process or needle punching. The density of a needle punched non-woven mat commonly is higher (r=120-150 kg/m3) than used for wall insulation and is better suitable in under-floor insulation. The non-woven density is dependent on the fibre fineness (expressed in tex) as well as the needling density. The compressibility of a needle punched non-woven is important for its application in underfloor insulation.
The bonding of the fibres in the light weight open insulation mats (r=25-35 kg/m3) is commonly promoted by the use of a binder (starch, latex or other cross-linking glue) that is sprayed in the fibre mat and cured. Alternatively, the fibres are blended with thermo-bonding (commonly synthetic thermoplastic polymers such as polypropene, polyethene or polyester) fibres. The curing of the binder or the cross-linking with thermo-bonding fibres requires a controlled heating step. The fibre mats are supplied in rolls or cut sheets of different thickness.
The life-cycle impact of bast fibre insulation boards was compared with LCA’s of various competing insulating products such as polyurethane foam, glass wool, kenaf and jute non-woven, mineral wool and paper wool. Highest impacts are assigned to synthetic materials, while mineral wools appear to have the lowest. However, bast fibre based products have the least impact if a complete life cycle scenario is considered, including after functional life the incineration with energy recovery or compostable.
Fire retardants are commonly used (e.g. borax, ammonium sulfate, etc.) to enhance the fire performance of flax and hemp insulation materials. For biobased insulation materials the aspects of performance risk in humid conditions and sensitivity of decay need to be addressed in the application.
The flax or hemp bast fibre insulation materials are not sensitive to decay, when moisture penetration is prevented.
Light weight particle boards manufactured of the woody core or shives / hurts for flax and hemp also possess good insulation properties. These boards commonly do not have constructive and load bearing properties and are mainly used in indoor separation walls and roof elements.
3. Expertise on the use of products
Flax and hemp non-woven insulation mats find application in wall and roof insulation. The mats can be applied in unfinished walls between joists and beams, and in ceilings or floors. The application of insulation mats in prefab sandwich panels or doors as the core material. The use as loose-fill fibres in cavities of existing constructions is not common for the relatively long fibres.
4. Product characteristics – properties
The properties of flax and hemp fibre insulation mats are in the same range and given in table 1 together with a number of other insulation materials.
Table 1. Technical characteristics of insulation materials
5. Product characteristics – Durability
The flax and hemp fibre mats are extremely durable when the mats are not exposed to for longer periods to the influence of light, moisture and extreme heat. The fibre strength will decline when the fibres are exposed to uv irradiation. The fibres will slowly decompose in contact with soil and moulds may grow on untreated and humid mats. The thermal stability of the fibres is good below ca 180 oC. At higher temperatures (above ca 240 oC) the fibres will carbonize or burn. The fire resistance of the fibre mats is influenced by treatment with fire retardants. These retardants are chemicals that have a inhibiting effect on flame propagation. Often these are mineral salts (borates, phosphates, siclicates). Halogen compounds are known to be effective fire retardants, but are banned because of environmental and health concerns.