Technical Sheet 08

Sustainable FRPs – naturally derived resins and fibres

In 1998, over 20 million tonnes of construction and demolition waste went to landfill. This represents around 30-40% of the total volume of construction and demolition waste. Many construction materials such as concrete use large amounts of energy in their production while materials made from crops actually sequester CO2 from the atmosphere as well as having inherently lower embodied energy.

Some agricultural crops are already used in construction. Recent UK developments include: • use of natural fibres for reinforcing concrete and polymer composites • , and used in insulation materials • straw-bale houses • hemp-shive concretions with a lime binder used for wall construction • linseed oil in natural paints and resins.

These materials are predominantly used as a replacement for conventional synthetic petroleum based systems. Three main categories of natural fibre composite can be defined: composites where the natural fibre serves as a filler in commodity thermoplastics; composites where longer fibres enhanced with compatibilisers and other additives attain additional strength and toughness in thermoplastics; and composites where natural fibres are used with thermosetting resins as designed elements within engineered components. In parallel to these developments there have been many advances in biodegradable polymers, both thermoplastic and thermosetting in nature. Composites using natural fibres and bio-based resins are poised to see explosive development in the next ten years.

Flax fibre Hemp fibre matting Natural fibres

Buildings are a major source of CO2 emissions, most of which arise during use of the building. Crop- derived materials have performance attributes that can improve the “in-use” energy profile of buildings as well as inherently low embodied energy. Many construction materials, such as concrete or fired bricks and blocks, use large amounts of energy in their production and transport. (This is known as the “embodied energy” of the material). It has been suggested that 66 per cent of total UK energy consumption is accounted for by construction and use of buildings (Woolley et al, 2002). Most of this energy is produced by the burning of fossil fuels, which increases the amount of carbon dioxide (CO2) in the atmosphere, causing the temperature of the earth to rise which is linked to climate change.

NGCC Technical Sheet 08: Sustainable FRPs – naturally derived resins and fibres e-mail: [email protected] Web: www.ngcc.org.uk

The widespread use of agricultural crops would greatly reduce the impact of construction material use. In addition, any waste from agricultural crops can normally be disposed of safely and easily, with little or no environmental damage. These factors combine to provide a substantial environmental benefit to the use of crop-based materials.

Natural Fibres Natural fibres are good candidate s to substitute as reinforcement for composite products in place of the customary synthetic fibres such as E glass. It is estimated that there are some 2.3million tonnes of glass fibres devoted to various applications around the globe so there are a number of opportunities for natural fibres to be used in place of existing glass fibres. Natural fibres have several advantages over glass fibre: low density, low cost, high toughness, acceptable specific strength properties, good thermal properties, low embodied energy, reduced tool wear, reduced irritation to the skin and respiratory system, and they also have a low energy requirement for processing. In addition they are biodegradable or recyclable depending on the selected matrix.

Natural fibres, often referred to as vegetable fibres, are extracted from plants and are classified into three categories, depending on the part of the plant they are extracted from. • Fruit fibres are extracted from the fruits of the plant, they are light and hairy, and allow the wind to carry the seeds. • Bast fibres are found in the stems of the plant providing the plant its strength. In the case of some tropical plant fibres, such as , or ramie, it is possible to exploit the fact that the fibre bundles making the outer stem structure are continuous for the height of the stem in the manufacture of long fibre composites. • Fibres extracted from the leaves are rough and sturdy and form part of the plant's transportation system, they are called leaf fibres. When determining the properties of natural fibres, one has to keep in mind that one is dealing with natural products with properties that are strongly influenced by their growing environment. Temperature, humidity, the composition of the and the air all affect the height of the plant, strength of its fibres, density, etc. The way the plants are harvested and processed can result in a variation of properties

Fruit fibres In comparison with other natural fibres, Cotton is rather weak. It can absorb moist up to 20% of its dry weight, without feeling wet and is also a good heat conductor. Cotton is applied for the manufacturing of clothes, carpets, blankets, mobs and medical cotton wool. Cotton uses a great amount of water when growing and requires intensive fertilisation. These attributes can have an adverse environmental impact, for example: the evaporation of the Aral Sea. Coir (Coconut fibre) Coconut fibre is obtained from the husk of the fruit of the coconut palm. The fruits are dehusked with on a spike and after retting, the fibres are subtracted from the husk with beating and washing. The fibres are strong, light and easily withstand heat and salt water. After nine months of growth, the nuts are still green and contain white fibre, which can be used for the production of yarn, rope and fishing nets. After twelve months of growth, the fibres are brown and can be used for brushes and mattresses.

Stem fibres The fibres are extracted from the ribbon of the stem. When harvested the plants are cut near the ground with a sickle shaped knife. The small fibres, 5 mm, are obtained by successively retting in water beating, stripping the fibre from the core and drying. Due to its short fibre length, jute is the weakest stem fibre, although it withstands rotting very easily. It is used as packaging material (bags), carpet backing, ropes, yarns and wall decoration.

NGCC Technical Sheet 08: Sustainable FRPs – naturally derived resins and fibres e-mail: [email protected] Web: www.ngcc.org.uk

Flax Flax is a strong fibre with an increase of strength of 20% in wet conditions and it can absorb 20% moist without feeling wet. The elastic fibre degrades due to sunlight and burns when ignited. Flax has good heat conducting properties, is hard wearing and durable. However, constant creasing in the same place in sharp folds tends to break the fibres. Flax is used for the production of linen and canvas, ropes and sacks. Ramie Ramie is an expensive and durable fibre and can be dyed very easily, and is therefore more often used in decorative fabrics than as construction material. Applications are curtains, wallpaper, sewing thread and furniture covers. Hemp A Hemp yarn is strong and has of all natural fibres the highest resistance against water, but it shouldn't be creased excessively to avoid breakage. The fibre is used for the production of rope, fishing nets, paper, sacks, fire hoses and textile. Kenaf Kenaf is a strong fibre plant grown in tropical regions, now. It is river retted but is capable of continuous cropping. The fibre strands, which are 1.5 - 3 metres long, are used for making rope, cordage, canvas, sacking, carpet backing, nets, table cloths etc.

Leaf fibres Sisal Sisal produces sturdy and strong fibres that are very well resistant against moist and heat. It is mainly used for ropes, mats, carpets and cement reinforcement.

In table 1, properties of the natural fibres are presented and compared to the properties of glass fibre. With respect to the natural fibres one has to keep in mind that large variation in properties exist due to natural circumstances.

Property Glass Flax Hemp Jute Ramie Coir Sisal Cotton Density [g/cm3] 2.55 1.4 1.48 1.46 1.5 1.25 1.33 1.51 Tensile strength 800- 2400 550-900 400-800 500 220 600-700 400 [N/mm2] 1500 Stiffness [kN/mm2] 73 60-80 70 10-30 44 6 38 12 Elongation at break 3 1.2-1.6 1.6 1.8 2 15-25 2-3 3-10 [%] Moist absorption - 7 8 12 12-17 10 11 8-25 [%] Price of raw fibre 1.3 0.5-1.5 0.6-1.8 0.35 1.5-2.5 0.25-0.5 0.6-0.7 1.5-2.2 [$/kg] Table 1: Natural fibre properties compared to glass

Long fibres in thermosetting composites A wide range of long natural fibres (flax, hemp, jute, coir, sisal, kenaf, bagasse, pineapple leaf fibre etc.) have been used in thermosetting matrices such as epoxy, polyester, polyurethane and phenolic resins. Here several different fibre lay ups are possible, with non-woven mats combining low cost and ease of handling. For higher performance and greater precision in aligning fibres in the directions of the principle stresses fibre can be used unidirectionally from tow or in woven textiles. Hand lay up adds to the cost of production, however for high end applications the benefits in terms of performance are greater.

The environmental benefit of using natural fibre in both epoxy resin and thermoplastic resins (polypropylene and ABS) has been reviewed by Life Cycle Assessment and a review of several studies

NGCC Technical Sheet 08: Sustainable FRPs – naturally derived resins and fibres e-mail: [email protected] Web: www.ngcc.org.uk

was made in 2004. It concluded that natural fibre reinforced composites had four principle benefits over glass fibre reinforced systems: • Natural fibre has lower environmental impact in production than glass fibre • NFCs have a higher fibre loading than GFCs thus reducing the proportion on non-renewable resin or polymer required for production • Lighter weight of NFCs means that less energy is used in service, for example, as a vehicle component than would be needed for heavier GFC material • Incineration at the end of life can recover energy • Pyrolysis to produce syn-gas would also be an option

Biobased resins The rapidly developing bioderived polymer market has led to wide ranging research on natural fibres in many matrices. Some of the main thermoplastics are starch and starch caprolactone blends; polyesters such as polyalkenesuccinates, polyesteramides; polyhydroxy alkanoates such as polyvinyl butyrate and polyvinylvalerate; and poly α-hydroxy acids such as polylactic acid and polyglycolic acid. Of these only some are biodegradable, including the starch polymers, polyhydroxyalkanoates and polyesteramides. The use of these polymers with natural fibre reinforcement could lead to a new generation of biodegradable products suited to packaging and disposable applications. The provision of increased compositing facilities is anticipated in many urban areas over the coming decade as many countries seek to reduce the quantity of material going to landfill.

Of these matrices, poly-L-lactic acid has received much attention, this biodegradable polymer is widely available and has a relatively high melting point (160°C) allowing processing conditions similar to those employed for polypropylene. PLLA also has relatively high mechanical properties. In tests with 70% kenaf fibre in PLLA the strength at failure was three times higher than in PLLA. This showed a strong anisotropic effect, however further tests using a laminate with fibre oriented in four principal directions (0°, 45°, 90° and 135°) showed a great improvement.

Starch Starch is a complex polymer comprising a mixture of amylose and amylo-pectin polysaccharides; the exact structure is as yet uncharacterized. The properties of starch will vary according to the amylose/ amylo-pectin ratio and hence according to the plant source. A major source of starch is corn but it can also be extracted from potato, wheat and rice. The polymer is crystalline due to the presence of the amylo-pectin component. The two main disadvantages of starch are its water-solubility and poor mechanical properties. Hence, this polymer is suited to applications where long term durability is not needed and where rapid degradation is advantageous. It is often processed as foam where it provides an alternative to polystyrene for use in the manufacture in food trays, moulded shaped parts or as loose packing filler.

Polyesters This group includes polyhydroxyalkanoates and poly(alkylene dicarboxylates) and are produced synthetically by condensation reactions between dicarboxylic acids and diols. Poly(alpha-hydroxy acid) examples include PGA (polyglycolic acid) and PLA (polylactic acid). PLA in particular shows potential as a structural material since it can be polymerized to a high molecular weight and is hydrophobic, yet vapour permeable. The latter properties render the polymer sufficient lifetime to maintain mechanical competence without rapid hydrolysis, whilst maintaining good composting capability, provided always that industrial, not domestic, composting techniques are employed. Current uses for this polymer group centre on medical applications such as implants, sutures, drug delivery systems and grafts.

Cellulose acetate Cellulose acetate is a modified polysaccharide which can be prepared from a reaction between acid anhydride and cellulosic products derived from cotton linters, pulp, recycled paper or sugar cane. Biodegradation occurs through microbial attack. The manufacturing process for cellulose acetate was

NGCC Technical Sheet 08: Sustainable FRPs – naturally derived resins and fibres e-mail: [email protected] Web: www.ngcc.org.uk

first patented at the end of the nineteenth century and the polymer found use in filaments, films and lacquers since that time. This biodegradable polymer exhibits good toughness and a high degree of transparency.

Polyurethanes Polyurethanes as a generic polymer type are not generally biodegradable unless chemically modified. Such modified biodegradable polyurethanes are now being synthesised for use in regenerative medicine.

Furfural alcohol and furan resins The pre-cursor to furfural alcohol and furan-based resins is furfural, a compound which is extracted from naturally occurring agricultural residues. Residues may derive from sugar cane bargasse as well as corn cobs, wood products or cereal by-products.

Biobased thermosetting resins A large number of biobased thermosetting resins can be formed from vegetable oils – by grafting hydroxyl, acrylate and maleate moieties or combinations of these onto the fatty acid triglyceride. Vegetable oils can also be epoxidised to form a reactive component for bio-based epoxy resins, the epoxidised oil can also be further reacted to produce polyols and used with diisocyanates in polyurethane resin formulations. Thermosetting polyester resins can be produced using many combinations of diols and diacids to form the polyester resin base, the base then cross links on addition of carboxylic acid curing agents.

Other naturally derived resins can be formed from cashew nut shell liquid (CNSL) which is extracted from the shell of cashew nuts as a by product of the nut industry. The CNSL is rich in anarcardic acid, which is converted to cardanol during the heated extraction process. Cardanol can be polymerised by free radical polymerisation, and condensation polymerisation between phenolic units can occur in the presence of aldehydes.

These two component resin systems are suited to the same resin transfer moulding, vacuum bagging, sheet moulding and bulk moulding systems used in traditional thermoset composite manufacture.

Bio-derived composite applications in the Construction Industry Various attempts have been made at developing new sustainable construction materials. For example, sisal fibre reinforced CNSL (cashew nut shell liquid) resin composites have been tested and had a mean strength of 24.5 MPa and Young’s modulus of 8.8 GPa. Bending tests confirmed that these composites have adequate strength to be used in roofing applications. Other researchers working with vegetable oil resin systems have demonstrated that roofing panels can be made using foam cores wrapped in natural fibre reinforcement impregnated with AESO (acrylated epoxidised soybean oil) and co-polymerised with styrene. Demonstration sized sections of roof have been formed and tested.

One exciting example of non-food crop use in the sustainable construction sector has been in the construction of a 8000m 2 distribution centre built for Adnams Brewers in Suffolk, UK. The architects were given a strict brief to minimise the environmental impact whilst at the same time producing a building which met Adnams requirements for years to come. The resulting design featured a living grass roof, which incorporated diaphragm walls built with blocks made from hemp-lime and quarry waste. The walls, constructed from Hemcrete, gave a high thermal performance and excellent strength.

Natural Insulation A critical component of eco-efficient building is insulation. This is because such a large proportion of a building’s energy requirement is expended “in-use”, the vast majority for heating (or cooling) the living space.

NGCC Technical Sheet 08: Sustainable FRPs – naturally derived resins and fibres e-mail: [email protected] Web: www.ngcc.org.uk

Crop-derived insulation materials are usually based on fibres: products made from hemp, flax and wool are on the market in addition to those derived from wood such as recycled newsprint, wood fibre and wood wool boards. Natural insulation materials offer genuine performance advantages over non- renewable alternatives such as stone wool, glass wool and polymer foam. For instance the thermal conductivity of based material is severely compromised by moisture whilst natural material continues to provide effective insulation even after absorption of up to 30% of its own weight in water. In fact this ability to absorb and desorb water vapour prevents accumulation of moisture at sites where it may cause damage.

Renewable products can also store around twice as much heat as mineral alternatives for an equivalent thickness and density offering thermal buffering against swings in the external temperature. In addition, the flexibility of natural fibres makes them effective acoustic insulation agents.

In terms of their ecological profile, natural insulation materials have lower embodied energy. They are also safer for operatives to handle than mineral products and, finally, they can be composted or burnt for energy recovery at end of life.

Most crop-based insulation materials are imported, with a few notable exceptions such as Thermafleece. However development of domestic markets through procurement policies or fiscal support for ecologically desirable products could change this. For instance, in Germany, renewable insulation materials attract government support of 40 per cubic metre and have a significantly larger share of the market than in the UK.

Plant Fibre Technology (a spinout company from the BioComposites Centre) has produced a range of natural based construction products. One of which is the Isonat® insulation fibre, made from hemp grown on UK farms and from waste cotton fibres. Isonat® contains 15% polyester fibres to give loft and stability. These fibres are completely inert and harmless. Hemp is grown without the use of herbicides and pesticides and the fibres are extracted in a waste free and chemical free mechanical process. Agricultural fibres such as hemp lock up CO 2 during growth and therefore Isonat® has an extremely positive roll to play in combating global warming. Isonat® can be harmlessly disposed of by composting or incineration. The ability of Isonat® to absorb and release humidity actively assists the control of moisture in buildings without any loss in thermal performance, and without affecting on the durability of the insulation. This function is particularly important in modern timber frame construction. Isonat® natural fibre insulation is suitable for use in external walls in timber and steel frame buildings, as well as for all internal applications including walls, suspended floors, lofts and roofs. Isonat® is suitable for both new build and renovation.

Floor coverings Natural materials such as wood and wool have a long history of use as floor coverings, in fact some of the UK wool industry’s problems arise from collapse in the demand for wool by the carpet market. In addition to these traditional materials, crop-based feedstocks are used in manufactured floor coverings. For instance, linoleum is derived almost entirely from renewable materials - mainly oxidised linseed oil and tall oil mixed with rosin and wood flour pressed on to a jute backing. Interestingly life cycle assessment of linoleum floor coverings has shown that they have a very small environmental foot-print - comparable to wood derived from sustainably managed forests.

Heating Typically, heating is responsible for over 80% of the energy that is used in homes. In most of the UK this heat is provided by fossil fuel with only a lucky few enjoying wood burning stoves. However wood

NGCC Technical Sheet 08: Sustainable FRPs – naturally derived resins and fibres e-mail: [email protected] Web: www.ngcc.org.uk

fuel in the form of pellet and wood chip is becoming more widely available for both domestic and large scale central heating systems. Modern wood-fuelled boilers are over 85% efficient, compared with a typical conversion efficiency of <30% for generation of electricity. Heating is therefore an attractive way to use biomass for reducing greenhouse gas emissions.

Simple guides to wood pellet and wood chip heating are available on the web (www.xco2.com , http://www.nnfcc.co.uk/library/publications/index.cfm )

Re-inforcement of blocks and plaster Plant fibres, including straw and hemp, can be used to reinforce building blocks. For non-load-bearing interior walls, lightweight, unfired and blocks reinforced with straw have good acoustic properties and the natural fibre also contributes temperature and humidity buffering.

A more robust with very low embodied energy is hemp/lime mix. Two houses were built using this technology in Haverhill in Suffolk. A thermographic survey showed significantly more heat loss through the walls constructed from conventional masonry compared with the hemp-lime houses. This decrease in heat loss was reflected in lower gas and electricity consumption in the hemp- lime houses.

Surface coatings Crop-derived surface coatings have seen a renaissance over recent years partly driven by environmental regulation and market demand for “natural” materials, but also by their performance characteristics. For instance, many respected modern brands include a significant amount of starch in their emulsion paints to improve their products’ performance; manufacturers do not advertise this, however, because in the past starch has been associated with low value paints.

Linseed oil is widely used for timber treatments because its slow drying time enables the oil to penetrate more deeply than synthetic resins. It also forms a strong but flexible micro-porous skin which will accommodate contraction and expansion of surfaces in response to fluctuations in temperature or humidity as well as limited diffusion of moisture.

Linseed is probably the most widely used crop-derived component of surface coatings, however binders and thinners from soya, sunflower, poppy seed and safflower are also used as well as bio- ethanol and vinegar. Solvents derived from citrus oils such as D-limonene and αpine and lecithins from soya, maize and peanuts are used. Casein-based paint has become increasingly popular because it is completely vaour permeable, emits no Volatile Organic Compounds (VOCs), and it contains no Titanium Dioxide, preservatives or solvents.

Composite boards Many composite boards used in building are based on wood and non-biodegradable resins. However there is increasing interest in the use of compressed straw for construction. A UK-based company Stramit International, owns the worldwide patent on the techniques for compressing straw to make boards without the use of resin. Although the equipment for manufacturing these boards has been exported, UK farmers are interested in better understanding the market for straw board, with a view to adding value to the millions of tonnes of excess straw generated every year in the UK.

Summary The use of natural fibres in composite applications has increased significantly over the last two decades. The possibilities of utilising natural fibres and their associated composites are now being realised and as a result there are now numerous examples where natural composites have found application in a number of diverse industries from Automotive, construction, packaging and leisure products.

NGCC Technical Sheet 08: Sustainable FRPs – naturally derived resins and fibres e-mail: [email protected] Web: www.ngcc.org.uk

The recent surge of activity has been driven by an increase in government legislation setting targets on the amount of material that can go to landfill sites, for example, the end-of-life vehicle directive in the case of the automotive industry. An increase in consumer awareness on the subject of recycling and the impact that materials have on the environment, along with a greater understanding of natural composite materials by researchers are all contributing to a greater interest and uptake in these natural based composite systems by industry.

Further reading European research on natural composites: http://www.biomatnet.org

European research on bio-derived materials: http://www.biocomp.eu.com

UK TSB project NatCom: http://www.ngcc.org.uk

Suddell B. ‘Natural Composites – the solution?’ Composites Innovation, Barcelona, 5-6 Oct. 2007.

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NGCC Technical Sheet 08: Sustainable FRPs – naturally derived resins and fibres e-mail: [email protected] Web: www.ngcc.org.uk