Sustainable Building Material Products from

Bio-fibre Raw Materials

Bengt Svennerstedt

Associate Professor, Bio Fibre Technology Research Group, Department of Agricultural

Biosystems and Technology, Swedish University of Agricultural Sciences (SLU), P.O. Box,

86, 230 53 Alnarp, Sweden. Phone: +46 40 41 54 78. Fax: +46 40 41 54 75.

E-mail: Bengt.Svennerstedt@jbt.slu.se

1. INTRODUCTION

In 1999 CIB (International Council for Building and Construction) in cooperation with some

other organisations published the document “Agenda 21 on Sustainable Construction”. In this

document it is stated that “The construction industry and the built environment must be

counted as two of the key areas if we are to attain a sustainable development in our societies.”

The construction sector has a great impact on the environment because buildings are

responsible for more than 40 % of the total energy consumption and almost 40 % of all

carbon dioxide is produced in buildings. Besides the construction sector is estimated to

generate approximately 40 % of all man-made wastes.

Thus the world community is facing a challenge in having to decrease pollution levels, while

at the same time significantly increasing industrial output. Such predictions have led to

support for enhanced industrial use of renewable resources at the expense of non-renewable

resources. Bio-fibres may therefore face a renaissance, not only for old industrial products but

also for the manufacture of new types of materials and products.

Industrial use of bio-fibres as wood fibres for the manufacture of pulp, paper, fibreboards and

particleboards are well established in the world. The renewed interest in industrial use of bio-

fibre based materials within the automotive, building, furniture and packaging industries has

led to development and production of many new bio-fibre based products.

Several companies in the building material industry worldwide are interested to produce

products based on bio-fibre raw materials. It can be products for outdoor decking as roof

plates, wall boards, windows and door panels. Most of the fibres that are used come from

short wood fibres but some parts come from long jute-, flax- and hemp fibres.

2. BIO-FIBRE RAW MATERIALS

2.1 Bio-fibre production

The annual global production of bio-fibre raw materials are today about 4 billion tons of

which roughly 60 % come from agricultural crops and 40 % from forests. In comparison,

annual world production of steel is currently around 0,7 billion tons and plastic production is

around 0,1 billion tons. As an example the Swedish annual production of bio-fibres is about

50 million tons from forestry and about 0, 1 million tons from agriculture.

Bio-fibres are subdivided based on their origins. They are coming from leafs (abaca, sisal,

henequen), seed-hairs (coir, cotton), basts (flax, hemp, jute, ramie) and wood. Most of the

plant fibres, which have an European interest are coming from flax and industrial hemp.

These varieties are cultivated for both their fibres and their oil. Both flax and indusrial hemp

are annual plants. Flax grows up to 1 m high and produce about 1 ton bast fibres per ha.

Industrial hemp may grow up to 4 m high and produce about 3-4 ton fibres per ha.

In table 1 the worldwide production of plant fibres in 1999 divided into fibres and main

country producer is shown. This plant fibre production amount is focused on the main fibre

plants and does not include straw and wood fibre production.

Table 1 Worldwide production of Plant Fibres in 1999 (Karus, 2000).

Fibre

Main country

producer

Production in

million tons

Production in

% of total

Cotton China, USA, India, Pakistan 18.20 78.5

Jute India, China, Bangladesh 3.37 14.5

Flax EU, China, Eastern Europe 0.63 2.7

Sisal Brazil, China, Mexico, Kenya 0.38 1.6

Cocos Indien, Sri Lanka 0,27 1.2

Ramie/Abaca China, Ecuador, Philippines 0.27 1.2

Hemp EU, China, Eastern Europe 0.07 0.3

Total 23.19 100

Figure 1 Short fibres from oak, wheat and beech in the front and long fibres from coco,

flax and sisal in the back (left to right) (Olesen, 2001).

2.2 Bio-fibre structure and properties

All plant species are made of cells. When a cell is very long in relation to its width it is called

a fibre. The fibre is like a microscopic tube and it consists of cellulose, hemicelluloses and

lignin. Cellulose is the basic structural component of all plant fibres. The cellulose molecules

consist of glucose units linked together in long chains. Hemicelluloses are also found in all

plants. Hemicelluloses are polysaccharides bonded together in branching chains. Lignin is the

compound, which gives rigidity to the plant. Lignin is a three-dimensional polymer with an

amorphous structure (Olesen & Plackett, 1999). Pectin is the glue, that holds the fibre bundles

together. In table 2 the chemical composition of some selected agricultural and wood fibres is

shown.

Table 2 Chemical composition of some selected agricultural and wood fibres

(weight-%) (Olesen & Plackett, 1999).

Fibre Cellulose Hemi-

Cellulose

Lignin Pectin

Jute 70-75 12-15 10-15 1

Flax, hemp 68-85 10-17 3-5 5-10

Seed hair, cotton 89-99 3-6 - -

Wood 38-45 24-39 22-34 0.5

The good specific mechanical properties are due to their relative high strength and low

density. In table 3 mechanical properties of plant fibres are compared with conventional

reinforcing fibres.

Table 3 Mechanical properties of plant fibres as compared to conventional reinforcing

fibres (Biedzki & Gassan, 1999).

Fibre Density

(g/cm3)

Elongation

(%)

Tensile strength

(MPa)

Young´s modulus

(GPa)

Jute 1.4 1.5-1.8 200-450 20-55

Flax 1.5 2.7-3.2 500-900 50-70

Hemp 1.5 1.6-3.5 310-750 30-60

Sisal 1.5 2.0-2.5 80-840 9-22

E-glass 2.5 2.5 2500-3500 70-73

Aramid 1.4 3.3-3.7 3500-4000 85-135

Carbon 1.4 1.4-1.8 2500-6000 220-700

The combined effect of the three main constituents results in properties, which are unique for

plant fibres. The most important properties are:

* High tensile strength and low density. In relation to its weight the best bast fibre attain

strength properties similar to that of fibre-glass.

* High heat, sound and electrical insulating ability

* Biodegradability

3. BUILDING MATERIAL PRODUCTS

3.1 Mats

A number of bio based products are made from mats, which are made of bio-fibres or a

mixture of bio-fibres, plastic fibres and resins in varying amounts. Mats may be used in a

number of products, e.g. filters for air and water, growth media for production of vegetables,

flowers and grass mats. Bio-fibre geo textiles are already available on the market. Bio-fibre

mats also have a promising future as insulation material within the building industry. The

market potential for partial replacement of mineral wool mats for insulation is huge.

Insulation materials made of flax and hemp fibres show advantages, which make these

products excellent construction materials. They are clean to process and produce very little

dust. They can be tolerated very well by the skin, it does not cause any itching.

”Thermo-Hemp” is a German example of a hemp fibre insulation product, which is composed

of 85% hemp fibres and 15% polyester carrier fibres. Soda is added as fire - proofing.

“Thermo-hemp“ is the world’s first hemp insulation, which has been approved for use in

construction. That was issued by the German Institute for Constructional Engineering in

Berlin. Hemp felts have the property to absorb moisture

from the surrounding air and to emit this moisture again as soon as the air has dried.

The result is a better indoor climate. “Thermo-hemp“ has good thermal insulation properties

and is delivered in the form of mats. It is suitable for insulation in roofs, walls or floors. It

makes no difference whether it is used for new or old buildings.

Figure 2 “Thermo-hemp“ is suitable for insulation in roofs, walls or floors

(Hock homepage, www.thermo-hanf.de)

Another example of a bio-fibre insulation product is “Zapp”, which is a new Swedish product.

The product contains 80% cellulose fibres and an inorganic binder based on stable silicate

compounds. The insulation mat is biodegradable and can be recovered to new products. When

the product is deposited it will moulder to organic material. “Zapp“ has good insulation

properties and is delivered in the form of mats. It is suitable for insulation in roofs and walls.

3.2 Composite Products

Composites for structural and non-structural purposes are manufactured by hot pressing of

mats. Fibre/polymer composites can also be manufactured through extrusion or injection

moulding. New fibre/cement composites can be designed to have the required stiffness and

strength. The importance of the role of final product design can not be overstated.

Plant fibre reinforced thermoplastic composites for the building industry may be products

with climatic protective functions and less load-bearing capacity. The composites are

manufactured by different technologies e.g. extrusion, injection moulding, thermoforming,

vacuum forming and resin transfer moulding. The thermoplastic compounds are usually

environmental friendly e.g. polypropylene, polystyrene, vinyl and high- and low-density

polyethylene.

Product examples for the building industry are window frames, door panels and wall panels.

Window frames made of plant fibre reinforced thermoplastic should be competitive to

corresponding product reinforced with fibre-glass.

Figure 3 Plant fibre reinforced thermoplastic composites (Olesen, 2001).

Roofing is one of the most important and difficult problem in housing. In most developing

countries and in many industrialized countries natural materials are used for roofing in rural

areas. An interesting solution to the roofing problem seems to be thin sheets made of plant

fibre concrete.

When mixing plant fibres in the mortar the fresh concrete may be shaped in a simple manner,

which is one advantage with this material technology. Another advantage is that the fibres

increase the toughness and impact resistance of the hardened concrete. This means that the

material may be used in structural applications. A corrugated roof sheet is probably one of the

most interesting forms even if other forms can be produced. Apart from roofing materials

plant fibre concrete can be used for production of sun screens, thin-walled blocks, small

beams, and other products.

4. DISCUSSION

Today we see a fast development in the industrialized world, primarily in USA and Europe,

towards utilization of bio-fibres as an industrial raw material. This change from synthetic oil

based plastics towards environmental friendly (renewable and recyclable/compostable)

materials, is of great importance in order to eliminate an ecological crisis.

Examples of bio-fibres from Nordic agriculture and forestry are flax and hemp fibres and pine

and spruce fibres. The use of bio-fibres in industrial products is CO2 neutral. The use of bio-

fibres is also very price competitive to synthetic fibres as fibre-glass. The bio-fibre based

products show renewability and biodegradability.

The most beneficial advantage is the high specific strength and stiffness. This advantage

concerns mostly the long fibres from flax and hemp. These fibres show a low density and a

relatively high tensile strength. These properties make together the bio-fibres very

competitive compared to fibre-glass.

There are also disadvantages of bio-fibre utilization. One disadvantage is the variability of the

fibre dimensions. The length and the diameter of the bio-fibres vary very much in production.

This is natural because we deal with biological material but the problem has to be solved in

the production process.

5. CONCLUSIONS

There is an abundance of biological fibres in the world, both from agriculture and forestry and

there are many advantages of bio-fibre utilization. The greatest advantage is the high specific

strength and stiffness. This advantage concerns mostly the long fibres from jute, flax and

hemp.

The goal for the bio-fibre building material product development should be to present for the

market completely “green” products based only on biological raw materials. This is a

challenge for research institutes and industry, which includes solving the main problems.

6. REFERENCES

Bledzki,A.K.& Gassan,J., 1999. ´Composites reinforced with cellulose based fibres´,

Progress in Polymer Science 24 (1999), 221-274.

CIB, 1999. Agenda 21 on Sustainable Construction, CIB Report 237. 1999. Rotterdam.

The Netherlands.

Karus, M. 2000. Naturfasermärkte weltweit (Worldwide markets for natural fibres)´(in

German). Proceedings of the third International Symposium Bio Resource Hemp and other

Fibre Crops. 13-16 september 2000. Wolfsburg. Germany.

Olesen, P.O. 2001. Plant Fibres-A Raw Material with Great Possibilities (in Danish). Proceedings of Industrial Symposium. Januar 16, 2001. Horsens. Denmark. Olesen, P.O. & Plackett, D.V. 1999. ´Perspectives on the Performance of Natural Plant Fibres´. Proceedings of the International Conference Natural Fibres Performance Forum. May 27-28, 1999. Copenhagen, Denmark.

Hock, 2002. Homepage www.thermo-hanf.de. Zapp, 2002. Homepage www.zappab.com