Foto: Wood Plastic

"Green Biorefinery - Utilitsation of Grass Fibres"

Basic properties of grass fibres from a green biorefinery will be investigated in order to have a sound base for comparison of grass fibres with other renewable fibres. Selected prototype-products with these grass fibres as main raw material source (e.g. insulation materials, gardening material, animal nutrition) will be developed, tested and evaluated whether they are technologically as well as economically feasible.

Short Description

Currently, the structure of agriculture in Austria is strongly changing, characterised by a decrease of grassland utilisation for production of cattle feed (milk production), thus, resulting in a steady increase of excess grassland areas. In order to keep these areas cultivated - which is essential for the highly desirable preservation of cultural landscape of Austria - new innovative utilisation pathways for green biomass are required. One new promising utilisation pathway for green biomass is offered by the technology concept of GREEN BIOREFINERIES.

Today, petroleum refineries generate efficiently a multitude of products from crude-oil at a very large scale. Similarly, GREEN BIOREFINERIES process and convert the raw material "green biomass" (e.g. grass, clover, lucern) into a range of individual marketable products (multi-product-system) based on deployment of sustainable zero-waste technologies. An essential process unit in a GREEN BIOREFINERY installation is the mechanical fractionation of the primary raw material "green biomass" into a liquid phase (press juice) and a solid phase (press cake). The press juice contains water soluble compounds like lactic acid and amino acids, the press cake contains fibres of different length and diameter.

Considering the fact, that the fibre fraction (press cake) is the largest material stream encountered in a GREEN BIOREFINERY, the overall economic efficiency of a GREEN BIOREFINERY is strongly determined by the economic efficiency of converting this fibre fraction into marketable value added fibre products. Therefore, this project has the following general objectives:

  1. Identification of possible fibre products based on grass fibres from a GREEN BIOREFINERY as raw material.
  2. Development of a method for characterisation of grass fibres and determination of characteristic properties of grass fibres.
  3. Basic experiments aimed at testing, whether grass fibres are in principle suited as raw material for the production of insulation material, materials used in horticulture and speciality feed for animal pets.
  4. Development of fundamentals for design, construction and operation of a GREEN BIOREFINERY installation on pilot / production scale.
  5. Assessment of the economic efficiency of a GREEN BIOREFINERY under the specific Austrian conditions.

The project consists of the following 6 work-packages:

  • WP1: Identification of possible fibre products based on grass fibres from a GREEN BIOREFINERY.
  • WP2: Determination of characteristic properties of grass fibres.
  • WP3: Insulation material from grass fibres.
  • WP4: Material used in horticulture based on grass fibres.
  • WP5: Speciality feed for animal pets (guinea pigs an chinchillas).
  • WP6: Market survey and economic analysis.

For experiments the following grass and legume species were used:

  1. Pure Dactylis glomerata (100%),
  2. Hybrid ryegrass (100% Lolium hybridum GUMPENSTEIN),
  3. Wheat grass (100% Triticum aestivum L.),
  4. Lucerne (100% Medicago sativa L.),
  5. Mix of different grass and clover species from an intensively cultivated meadow,
  6. Mix of different grass and herb species from an extensively cultivated meadow.

The experiments with respect to preparing grass silage from green grass as well as with respect to mechanical fractionation of the grass silage consists of the following process units, each of which realised in a proper machinery and/or device: Mowing of green grass => adding of fermentation bacteria facilitating the ensiling process => pressing of grass bales (baling press) => ensiling process (solid state fermentation) => transport of grass silage bales => crushing of grass silage bales (reduction of fibre length) => mechanical fractionation of grass silage into a liquid phase (press juice) and a solid phase (press cake) by means of an extruder press => filtration, cooling and storing of press juice + drying ad storing of press cake.

Chap.3: Identification of possible fibre products based on grass fibres from a GREEN BIOREFINERY (WP1)
In principle, grass fibres from a GREEN BIOREFINERY may be used as raw material for the following products:

  1. Insulation material,
  2. fibre boards,
  3. products used in horticulture, erosion control etc.
  4. biocomposites,
  5. packaging material,
  6. additives for building material,
  7. gypsum boards,
  8. pulp and paper,
  9. bioenergy and
  10. speciality feed for animals.

Chap.4: Mechanical fractionation of primary raw materials "grass" and "grass silage", respectively (WP2)

Primary raw materials "grass (green)" and "grass silage (brown)" could be successfully separated by means of an extruder press into press juice and press cake:

  1. In case of "grass (green)" about 40-65% of the total available water goes into the press juice. In case of "grass silage (brown)" 30-60%.
  2. Lactic acid yield in the press juice is quite satisfactory: 25-60 kg/ ton dry matter (dm), which represents about 50% of the total available amounts of lactic acid.
  3. However, protein yield in the press juice is not satisfactory: Only 30-40 kg/ ton dry matter can be found there which represents only about 25% of the total available amount of proteins.
  4. Residue sugar in press cake and press juice is quite high. Methods should be investigated by means of which these residue sugars could be converted into additional lactic acid.
  5. Fibre yield in press cake is about 300 kg / ton dry matter, which represents 95% of total available fibres.

Chap.5: Fibre characterisation - Properties of grass fibres (WP2)

A method for determining characteristic properties of grass fibres could be developed and tested. Results: Fibre content of stems and leaves: 20,2 - 39,5 % (stems) > 6.9 -10,1% (leaves). Fibre length: 800-3200 µm. Fibre diameter 15-18 µm. The mechanical properties of grass fibres like tenacity and elongation are of a similar size than the corresponding properties of bast fibres like jute, hemp: Tenacity: 7,5-21 cN/tex (grass fibres) ≈ 23-31 cN/tex (jute). However, grass fibres do have no bending strength. Conclusion: Technical grass fibres are not suited for textile applications. Thus, in further work products that utilise the whole stem of grasses and/or legumes should be focused (e.g. non-wovens, insulation material).

Chap.6: Miiling of grass - Properties of grass fibre powder (WP2)

Two different types of mills were tested (granulator, impact mill) regarding their suitability for homogenisation and fibrillation of the grass fibres. The resulting grass fibre powders were analysed with respect to fibre length and diameter distribution. It turned out that only the impact mill is suited for the task.

Chaps.7-10: Prototype products from grass fibre (WPs 3-5)

  1. Some properties of insulation boards from grass fibres (e.g. density, heat conductivity, compression stress, and sound absorption) are of the same size or even better than corresponding properties of insulation boards manufactured from wood-wool. However, at the moment grass fibre boards do not exhibit satisfactory properties regarding bending strength, stability against water and smell emissions.
  2. Prototype plastics reinforced by grass fibres showed, that some minor improvements of the mechanical properties can be reached. However, different reinforcement materials exhibit a much bigger increase of these properties.
  3. Prototype pots and mulch boards, each of which manufactured from grass fibres showed, that grass fibres are suited for these types of products
  4. Extensive feeding experiments with guinea pigs and chinchillas showed, the grass pellets manufactured from the press cake of a GREEN BIOREFINERY is very well suited for that purpose.

Chaps.11-12: Market survey and economic analysis (WP6)

According to market survey amino acids, lactic acid and fibres in speciality feed for animal pets turned out to be promising products of a GREEN BIOREFINERY. An economic analysis shows the strong sensibility of the economic efficiency of a GREEN BIOREFINERY installation from important parameters like raw material costs, investment costs, net sales of the products, financing models etc.

Project Partners


DI Dr. Bruno Wachter
Institut für Nachhaltige Techniken und Systeme (JOINTS)
A-8010 Graz, Elisabethstrasse 16-18
Tel.: +43.(0)316/876 2950, Fax: +43.(0)316/876 2955

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