Green Fibres and Their Potential in Diversified Applications

Ryszard Kozlowski[31]
Poland

1 INTRODUCTION

Various parts of plants like woody core, bast, leaf, cane, straw from cereals, grass and seed can be used in applications like building materials, particleboards, insulation boards, human food and animal feed, cosmetics, medicine and sources of other bio-polymers and "fine chemicals". They do not damage the ecosystem, they can grow in different climatic zones and they recycle the carbon dioxide for the atmosphere. These plants can contribute to a better agricultural balance in Europe and they will contribute to the growing demand from an expanding population for cellulosic pulp in the next millennium. Some of these green plants like flax and hemp can be used for cleaning soil, polluted by heavy metals, by extracting and removing cadmium, lead, copper and others.

The estimated world-wide production of fibrous raw materials from agricultural crops is provided in Table 1. Other possible sources of straw, which could be used as raw materials for applications such as composites and as energy crops are given in Table 2.

Table 1: Estimated global tonnage of fibrous raw materials from agricultural crops

Crop	Plant component	Availability
		'000 tonnes
Cereals	straw:
barley	straw	218.5
oats	straw	50.8
rice	straw	465.2
rye	straw	41.9
wheat	straw	739.7
corn	stalks	727.3
cottons	lint,	18.0
	linters	2.3
	stalks	35.9
	mote	900
Bast fibrous plants*/	straw	25.0*/
Seed grass	straw	2.0
Oil flax	straw	3.0
Sorghum	stalks	104.7
Sugarcane1	Bagasse1	100.2
Total		2535.4

Source: Rowell, Young and Rowell, (1997). */Estimated by INF

^1. Leão, A. (1998)

Annual ryegrass	Lupins	Sunflower
Bamboo	Meadow foxtail	Pseudocereals
Black locust	Miscanthus	Tall fescue
Broom	Rape	Timothy
Cardoon	Root chicory	Topinambur
Common reed	Rosin weed	Willow and poplar
Cordgrass	Safflower	Amaranth
Eucalyptus	Soybean	Quinoa
Giant knotweed	Salicornia	Microalgae
Giant reed		Triticale
Groundnut

2 TEXTILE AND NON-TEXTILE APPLICATIONS

2.1 Textile fibres

Green fibres in textiles provide for healthy, comfortable clothing, which ultimately will be fully biodegradable.

There are two parallel textile fibre technologies:

2.1.1 Typical long staple fibre production and processing.

Though difficult in handling, traditional long flax, ramie and hemp are still produced and processed by slightly modernised methods.[32] Flax and ramie provide yarns of high strength, lustre and low linear mass.

These products include:

• 100 percent linen or ramie knitted apparels. Perfect hygiene and comfort properties make them specially attractive for hot, humid climates;[33]
• 100 percent linen and ramie fabrics - from almost transparent to terry type, boasting high "Wash and Wear" properties when finished with liquid ammonia[34];
• 100 percent linen anti-bedsore bedding, developed at the Institute of Natural Fibres for ill and aged people. Tests conducted in Polish Academic Clinic showed that no bedsores occurred when such bedding was used[35];
• 100 percent linen knitted bedding which, according to the research, provides the deepest sleep and best mood recovery. These tests initiated by Japanese scientists are conducted at the Institute of Natural Fibres, Poznan;
• hemp and jute sport and Friday-wear[36],
• hemp and linen hygienic, comfortable boots and shoes.

2.1.2 New technologies: modern short and long spinning systems.

To profit from immense progress in this spinning machinery green fibres must become cleaner, shorter, thinner, and softer. The finer the fibre, the narrower fineness and staple diagram, the easier the processing, the higher the bast content, the better the quality of yarns and products.[37]

In some technologies the process of fibre modification starts in the field.[38]^,[39] Some combine mechanical and chemical treatments like new US Patent 5 666 696. A new process developed by Rieter-Elitex bast breaking, cleaning and refining machine "RCZ-120-3" combines all the three processes very effectively into one[40]. The new, mainly blended bast fibre yarns differ from traditional ones. They are of lower linear mass, lower tenacity yet of higher elongation and can be spun at higher speeds.

These yarns can be used in a wide range of woven and knitted apparels, underwear, active wear, healthy textile shoes, socks and other textile items. Special treatmenst like enzymatic; liquid ammonia, plasma and corona treatment provides new promising features and properties of fibres and fabrics like "fineness" and crease resistance. In conclusion, green fibres now are better adapted to modern processing techniques, which develop new clothing and home furnishing items, bio-degradable non-wovens and geo-textiles.

2.2 Green fibres for non-textile products

Science and technology continue to make a significant impact on the potential use of green resources.

2.2.1 Green fibres/bast fibrous plants for pulp

In the cellulose industry interest is growing in production of pulp and paper from agro-based lignocellulosic raw materials such as bagasse, bamboo, reeds, esparto, hemp, flax, abaca, sisal, grass, etc. The amount of pulp made of non-wood resources is still growing. In 1995 the capacity of non-wood pulp production was 6.8 percent in total, and in 1998 was about 11 percent. The contribution of cellulose of agro-plant origin to the world production of pulp and paper is growing. Further increases in the contribution of agro-plant cellulose is foreseen and it should reach about 15 percent in 2010 (when the total production is estimated to be about 480 million tons). In addition to cellulose, the main components of lignocellulosics are lignin, hemicelluloses, and pentosans.

An example of the use of jute for pulp (for fibres, but also suitable for non-textile applications) is given by the South India Viscose Company[41] [42]. In the U. S. when the Department of Agriculture was searching for an agricultural source of fibre for paper industries, kenaf was chosen as a prime candidate to prolong the life of North America forests.[43]

Similar developments are in progress through the entire tropical zone[44], and involve jute, kenaf, sisal, abaca, as well as crops like bamboo, reeds, esparto, grass and badges.[45]

The Institute of Natural Fibres developed an environmentally safe technology for producing bleached pulp from hemp grown on land polluted by metallurgic industry.

The productivity of hemp biomass is very high: 2 to 2.5 times higher than can be produced from the same area of forest. The concentration of alpha-cellulose in the raw fibre (bast), reaches the level of 90 percent while the concentration of cellulose in softwood and hardwood ranges from 50 to 54 percent.

Promising solvent methods for the pulping of annual plants include:

• Acetosolve (Germany) - using solution of 93 - 85 percent acetic acid and addition of 0.1 percent HCL, and MILOX (Finland) - using formic acid;
• Alcell method, employing ethyl alcohol;
• Steam explosion pulping (SEP) (Canada) - using chemical impregnated raw material cooked with saturated steam;
• Ethanol pulping (Egypt) - using ethanol/water, ethanol/water/NAOH solutions;
• Peroxy-compounds-using peroxymonosulphate anion (HSO₅)
• The Alcell® process developed by Repap Enterprises Inc., Canada. Trials using organic solvents to dissolve and separate wood components was first documented in early 1990's. The new method consisting in the treatment with ethanol at 195°C under the pressure of 29 bars appeared in 1990.

2.2.2 Green fibres/bast fibrous plants for biocomposites, based on lignocellulosics

Biocomposites include a wide range of products for different applications ranging from construction or insulation panels made of wood pieces, particles and fibres, through special textiles (geo-textiles and non-woven textiles), to plastic products based on polymers filled with lignocellulosic particles. Fibre plants are seen as promising lignocellulosic raw materials for different applications.

These lignocellulosics are biodegradable, recyclable, and, when combined with natural resin, they are as strong as steel yet of lower density. Such composites may be used in motor vehicles, building materials, furniture, machine construction, insulating materials, gardening and agricultural equipment, and other applications. Examples of applications of composite materials containing lignocellulosic components include glue-lam wood, plywood, particleboard, fibreboard, Medium Density Fibre (MDF), Oriented Strandboard (OSB), lignocellulosic-mineral particleboards and composites, special functional (water, fire, and bio resistant), thermosetting polymer composites, thermoplastic polymer composites, natural polymer composites (based on starch, polyhydroxy butyric and polylactic acid), non-woven, geo-textiles, absorption chemotextiles (bentonite, carbon active, silica, hydrogel, linoleum, etc.).

2.2.3 Utilisation of bast fibres in nonwovens.

Nonwovens appeared in the 1940s, and were later developed with different dynamics in various countries. Nonwovens technology was further improved and developed, particularly concerning bonded nonwovens based on valuable chemical fibres and synthetic binding agents facilitating manufacture of better and more useful products for technical usage, clothing and household use.

Nonwovens have a very wide range of applications from furniture to the geo- and chemotextiles.

An example of nonwovens is geotextiles for reinforcement of earth structures like landfills, slopes and embankments like grass mats.

2.2.4 Prospective applications of composites.

Composite materials find uses in car, aircraft, railway and truck industries. Polymers have displaced steel and ferric alloys in car construction from 80 percent used in 1965 to 60 percent in 1995. This field of polymers application was pioneered by Henry Ford, who designed the car body entirely in polymer, a car "made of soybean" in 1941. In 1953 a Chevrolet Corvette had many parts made of polyester resins reinforced with different fibres allowing the weight of the car to be decreased by about 85 kg.

Application of natural fibres in the automotive industry may include different types of fillings, reinforcing fibre and in some cases replacement of glass fibre, one of the components of hybrid composites, degradable composite of natural fibres and natural polymers. The great advantage of composites reinforced with fibres is that when the fibres are arranged parallel to the direction of applied forces (unidirectional laminates), the possibility of utilisation of anisotropic properties of material for structure arises (crushed fibres, embroided and 3-D weaved structures). The properties of this new material can be compared with regular glass fibre or reinforced polymers in normal conditions, for instance in the automotive industry, road construction, irrigation systems, landfills, furniture industry and also in sport. New nanobinders have been proposed for jute, hemp composites by the Institute for New Materials, Saarbrücken, Germany resulting in flame resistant construction elements with a compressive strength of 3.5 MPa by a specific weight of only 0.13 g/cm².[46]

2.2.5 Particleboards.

Composition boards, including particle board (extruded and plate-pressed), and fibre boards, especially medium-density fibre (MDF) board, are quite common in construction, furniture and interior panelling. The most common raw material used is wood, but many countries successfully use other agriculturally based residues like flax and hemp shives, jute stalks, bagasse, reed stalks, cotton stalks, grass-like Miscanthus, vetiver roots, rape straw, oil flax straw, small grain straw, peanut husks, rice husks, grapevine stalks and palm stalks. These cheap raw materials can be valuable in lignocellulose board production from wood particles.[47] [48]

Medium Density Fibre (MDF) Boards consist 82 percent of fibres from wood or annual plants, 9 percent gluing amino resin, 1 percent parafin and 8 percent water[49]. There is growing interest in using annual plants to make boards because annual plants are renewed each year, and produce three times more cellulose per year than ring-growth in trees. Residues of annual plants such as rape or canola straw, oil flax straw, small grain straw, reed and reed wastes are useful for production of insulating boards for building industry, important for houses in earth-globe areas. Hemp also makes excellent insulating boards[50]. Bast fibrous plants as a source of food, fodder, pharmaceutical products and cosmetics.

Flax and hemp seeds are perfect raw materials for agriculturally based industries such as the production and processing of food, of natural pharmaceuticals and cosmetics, or of paint varnishes.

The Institute of Natural Fibres has developed food additives based on linseed oils, which are high in lignan and unsaturated fatty acids (mainly linolenic and linolic acids)[51]. Brain, spinal cord and its branches are made up of essential fatty acids, particularly linolenic acid. We literally think with these acids - they are the brains! Linseed-based food additives also contain lignans, which seem to be capable of slowing the cell division of some tumours. Lignans also improve urinary function, helping prevent inflammation of the kidneys. Linseed proteins and mucilages are used in food products such as ice cream, powdered sauces and soups to improve smoothness and viscosity[52].

There is a similar market potential for pharmaceutical and cosmetic products based on linseed and hemp seed, especially in the area of "natural products", which has become a key term in marketing success. Hemp seed's nutritional values are already well documented: it is an excellent source of balanced essential fatty acids, particularly omega-3, which is responsible for the proper growth and functioning of the body. Leaves and unripe seeds can be used to produce a fodder that is rich in protein and vitamins. The amino acid and carotenoid content of hemp fodder is similar to that of traditional fodder like Lucerne and clover green meal, but with lower levels of cellulose.

2.2.6 Bast fibrous plants for fine chemicals.

Recent discoveries have shown that some of these fibrous plants are rich sources of not only phytoestrogens (lignans) mentioned above, but promising natural medicine cyclopeptides. In addition to cellulose, the main components of lignocellulosics are lignin, hemicellulose and pentosans. The uses of isolated lignin in the chemical industry grow continually. It is used as a substitute for phenol-formaldehyde resins in composites and as a natural polymer that has applications for agrochemicals, packaging, laminates, moisture barriers, stiffening agents (boxboard), friction materials (brakes, pads), wood adhesives (plywood, waferboard, particle board, fibre board), plastic moulding (automotive), foundry mould binders and antioxidants.

3 CONCLUSIONS REGARDING DIVERSIFIED USES OF GREEN FIBRES

Global trends towards sustainable development have brought to light natural, renewable, biodegradable raw materials, among them bast fibres. Science and technology continue in extending their use in textile and other industries.

Recent achievements and new applications of green fibres and associated products bast fibrous plants can provide, form the background for following conclusions:

• Fast growing population, eco- and health awareness creates large space for future expansion of other than cottons natural cellulosic fibres.
• Present achievements in breading/production/processing extended the use of bast fibres in textiles. To make the way for these, difficult in processing fibres, into textile products being beyond their reach for centuries, it was necessary to develop: new, refined bast fibre types, adapted to modern spinning systems; new, softer, finer 100 percent bast or bast blended yarns, amongst them knitting yarns; new crease resistant finishing treatments; new products, which could meet the needs of demanding apparel sector.
• All the textile goods made on the basis of green fibres can boast high comfort/health properties and are ecological items. They can be labelled as "NATURAL" which is the key to market success.
• Green fibres/bast fibrous plants are used, thanks to research and development, in growing amounts for nonwood pulps.
• Green fibres/bast fibrous plants will also be used in growing amounts in a wide spectrum of biocomposites materials. Being lignocellulosic they can be combined with man-made or natural polymers to provide a wide range of useful composites in textiles (including geotextiles and non-woven).

Green fibrous plants provide valuable by-products like seeds, waxes, fragrances, and pigments. These may be used for food, fodder, pharmaceuticals, cosmetics, and body-care items.

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