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Principles of Textile Manufacturing | Energy in Textile Production

Tuesday, 5 November 2013

Textile Manufacturing:
Textile manufacturing or production is a very complex process. The range of textile manufacturing is so long. It starts from fiber to finished products. It is based on the conversion of three types of fibre into yarn, then fabric, then textiles. These are then fabricated into clothes or other artifacts. Cotton remains the most important natural fiber, so is treated in depth. There are many variable processes available at the spinning and fabric-forming stages coupled with the complexities of the finishing and coloration processes to the production of a wide ranges of products. There remains a large industry that uses hand techniques to achieve the same results.

Principles of Textile Manufacturing:
The machinery needed to produce textiles cannot be simple. Few portable pieces of textile production equipment exist today, with the exception of hand production equipment such as knitting needles, embroidery frames, looms and drop spinning equipment still used by craft workers or indigenous people. As a direct consequence of this, in the vast majority of cases textile production equipment is massive, complex, expensive and difficult to use effectively in its aim of manipulating millions of tiny particles of flexible units at a speed high enough to satisfy the demand for its products. From the ecological perspective, this has two major consequences. First, textile production uses vast amounts of energy. The high demand and the large size of machinery forces the use of a lot of power in all parts of the world to keep the flow of materials going. Second, because of its complexity, the actual production of the machinery is environmentally very costly. The steel for stable framing, supports, protective covers, shafts, bearings and so on, has to be mined and refined. So too do the various non-ferrous metals used in reducing weight, improving electrical or corrosion resistance properties or providing more durable gears in the equipment. Plastic products used to enhance electrical, thermal or acoustic insulation have to be derived from oil, once it has been extracted from great depths below the surface of the ground or sea, by complex chemical reactions. All of these processes use energy, consume raw materials and produce waste matter as pollution discarded to the air, water or land once the intermediate product of the particular stage has been made.
Production in spinning mill
Energy in Textile Production:
As a result of this high environmental cost (and, even more of a spur, the cost of wasted energy), there have been many attempts to produce energy in less costly ways. The use of coal, oil, gas and electricity has been tried, in turn, over the 200 years or so that have elapsed since the Industrial Revolution first introduced the use of power in textile production.
Energy Categories of pollution production
Coal
Coal, the fuel that drove the Industrial Revolution, is rapidly disappearing from use for electricity generation in the developed nations. It creates too many problems, from those encountered during its extraction to those produced by its combustion. Miners working in risky underground locations are constantly in danger of mine collapse, fire, poisonous gases or lung problems and it is not unusual to read of major disasters in those places where coal faces are still worked. The residual piles of waste make a hideous mess of unsightly scars on the face of the Earth. Burning coal gives rise to smog or other atmospheric pollutants (* V-3, A-2, A-3) (see Table 1.1 for explanation of codes) and to health problems induced by breathing the toxic by-products resulting from the combustion of impurities in the coal. However, there are still coal-powered energy generation plants in operation in many parts of the world, to the detriment of our environment and the health of people living on the planet.

Oil
The combustion of oil is currently a popular form of energy production. Oil itself is cleaner-burning than coal, but can cause major problems for the environment in its production. The oil wells that proliferate in those parts of the world where ‘black gold’ is extracted fill the air with fumes (* A-2) from the burning oil that appears at the top of each well. The scars on the land left after sinking a well are as ugly (* V-1) as those left by coal mining, and the pipes must often be sunk to a greater depth than these mines in order to reach the oil site. Drilling operations also produce ecological disturbances, from the displacement of wildlife and the arrival of unsightly equipment to the burning of the fuel used to power the rigs. When the oil is moved, too, the spills (* W-3) that are so common in our modern world can each kill or maim literally thousands of living creatures.

Gas
For reasons of cleanliness and economy, many textile factories have adopted gas as the source of at least a part of their energy. Coal gas, the original fuel in this category, merely transferred the pollution from the point of use to the point of production, since it was manufactured by burning coal. It was also notorious for its toxic (* A-2) nature. More recently, coal gas has been replaced by natural gas, extracted from the ground along with oil, which is cleaner burning and not toxic. Unfortunately, gas of any kind cannot be carried around easily, so pipe lines or pressurised containers are needed to be able to make use of this fuel. It also has to be refined to some extent to keep it clean and has an odour that can be objectionable to some people. More to the point, even if it is completely pure, it still produces considerable amounts of carbon dioxide when it burns, adding a significant contribution to the global warming problem.

Electricity
All of this brings us to consider the most common source of energy in textile plants, electricity. At first glance, it is the ideal fuel. It is clean, convenient, versatile and has all those other attributes that we seek to make our lives easier. Examine the situation more closely, though, and a different perspective begins to emerge. All those benefits, it is true, are experienced by the user, but the way in which electricity is actually produced is far from ideal. It may be the result of burning coal or oil, with the drawbacks already mentioned. It can also be generated by burning all kinds of waste material, much of which is domestic pollution, with the consequent release into the atmosphere of carbon dioxide (* A-1) and even more undesirable substances created as by-products of the chemical combustion process (* A-2). In an attempt to give electricity generation a better image, modern production has relied heavily on hydroelectric generation techniques. These involve allowing a large quantity of water to flow from a higher to a lower level through a pipe in which turbines are caused to rotate by the rushing motion of the water. Apart from the need to produce the equipment, potentially an environmentally costly process in itself, there is often a need to create artificial height differentials so that the water has somewhere to flow from and to. This can mean diverting rivers or streams, building dams, flooding valleys and excavating tracts of land, ecologically expensive ways of providing a flow of water.

Nuclear Power
The proliferation of nuclear power plants over many parts of the world is an indication of how much promise this technique was once believed to have as an alternative means of producing energy. The unfortunate truth, of course, is that there are drawbacks to nuclear energy that were either not foreseen or were mistakenly assumed to be trivial.  
 
The first of these to surface was the difficulty in disposing of spent fuel. Nuclear fuel rods contain highly concentrated radioactive elements. Their activity cannot just be turned off once the fuel is spent. At the end of its useful life in terms of an energy source, there is still a dangerously high level of radiation left in the atoms of the radioactive element. This is not enough to make it possible to take advantage by generating electricity, but certainly enough to kill off a few thousand people by radiation sickness if it were to be left lying about (* L-2).

The solutions adopted to overcome this drawback include reprocessing and storage, but these, especially the latter, remain problematic in view of the costs involved and the risk of leakage over the enormous storage time needed. Even if the material is encased in concrete or stainless steel containers and buried in deep water, cracking or corrosion can occur, so that the nuclear waste (* W-3) can spill out into the sea. From there, fish and other aquatic life can become contaminated, or air currents, water flow and earth tremors can distribute the harmful material around the surface of the planet. Sadly, the radioactivity is likely to last for a much longer time than the encasing materials, so the results of our careless discarding of radiation are being bequeathed for future generations to inherit.

A second side-effect has been brought to our attention in a dramatic way. Sellafield, Pickering and Chernobyl are names that conjure up images of nuclear power plants that went wrong. The latter, especially, taught us that one careless act at a nuclear plant can bring about a disaster capable of destroying the livelihood, and lives in many cases, of thousands or millions of people. The margin of error between nuclear fuel that reacts fast enough to create energy at a reasonable pace, and that reacting fast enough to blow its container apart, spreading devastation over the face of the earth, is not all that great.

Even when the fuel cells are controlled properly, there are still undesirable consequences of the process. Electricity generation takes place because the nuclear energy heats water to steam, which is then used to drive turbines. The spent water is hot and has to be discarded somewhere, often into the nearest river or lake water. Although it has cooled down sufficiently to avoid boiling any nearby fish in the water, it is still warm enough to make the area uninhabitable for them (* W-1). Other species, both fish and plant, can take over and change the balance of nature in the region downstream of the plant discharge site. The consequences for the environment and for the people living in the area are not yet understood, but the changes already occurring as a result of this nuclear warming give us cause to reflect that our energy comes at a tremendous cost to our planet’s natural health.

New Energy Sources:
One consequence arising from our realisation of the risks of nuclear mishap is the effort to find new ways to provide energy. Solar, tidal and wind energy have all been proposed as ways in which electrical energy can be produced. The hydrogen cell has been suggested as a means of powering devices in place of intermediate electricity generation. At first sight, again, all these methods of providing supposedly unlimited energy seem impressive. They are natural, reliable (with certain fairly obvious limitations, such as location or time of day) and, more importantly, free. There will almost certainly be unexpected drawbacks, as the lessons of history have shown. Before we find them, however, there are obvious ones that can be predicted even without experiencing them, all resulting from the nature of energy supply.

Energy production is complicated. The natural source has to be collected, harnessed, converted into electricity and distributed to its point of consumption. In all of these steps, equipment is essential. This equipment, like that used to make textiles, is generally large, heavy, complex and made of many different materials, making it environmentally costly to produce. Its manufacture and operation produce pollution, because waste material is generated in the former case and lubricants are needed in the latter, contaminating the air, water or land. It also has a relatively short life, because materials subjected to heat and mechanical action from sun, weathering, water or wind will eventually corrode or suffer fatigue fracture. As a safety precaution if for no other reason, they will have to be replaced by new equipment roughly every 20 to 30 years, thus producing a continual environmental cost that never ends.

More importantly, perhaps, is the mental attitude that will be engendered by the use of these ‘revolutionary’ energy sources. If energy is cheap (free?) and appears to be clean, then we should be able to use it in unrestricted amounts. We can waste it without any qualms of conscience and need not concern ourselves with the consequences of our actions, because neither the environment nor our pockets are being harmed in the process. It is only when we look at the entire cycle, from starting to make the power generation equipment to the end results of using it, that we can begin to realise how wrong our assumptions might be. The actual energy consumed in making or using a product is a minor fraction of its overall environmental impact, because the extraction of materials to manufacture the equipment designed to make the energy or to use it, and the pollution resulting from such extraction, must also be taken into account. Unlimited energy use means unlimited equipment production and hence unlimited ecological degradation.

So the textile industry, like most others, is unlikely to find any sop to its collective conscience with respect to power consumption in the foreseeable future. Unfortunately, this is not the only way in which the environment suffers for the sake of the industry. Every stage of manufacture, from fibre production or harvesting to shipping, inevitably involves damage (considerable in some cases) to the environment. The following chapters will summarise how this damage arises, looking briefly at its consequences and examining the ways in which it can be alleviated. In addition, the way in which textiles can themselves be harmed by the environment in the process of degradation will be considered.

Green Composite | Manufacturing Process of Green Composite | Application of Green Composites

Tuesday, 27 August 2013

AN OVERVIEW OF GREEN COMPOSITES

Zunjarrao B. Kamble
Dept. of Textile Engineering
D.K.T.E. TEXTILE & ENGINEERING INSTITUTE,
Ichalkaranji, Maharashtra, India.
Email: kamblezunjar@gmail.com





Introduction :

Ecological concerns have resulted in renewed interest in natural materials. Development of natural fibers reinforced composites is highly attractive research lines. A natural fibers provides interesting properties for composites, especially capacity of recycling, renewable raw material, which is less abrasive and harmful to mankind.

Issues such as recyclability and environmental safety are becoming increasingly important to the introduction of materials and products. Natural fibers like flax, hemp, banana, sisal, oil palm and jute have a number of technoeconomical and ecological advantages over synthetic fibers like glass fiber. Combination of interesting mechanical and physical properties together with their environmentally friendly character has create interest to numbers of industrial sector, notably the automobile industry.

Definition of Composite: 
A composite is defined as a multiphase material and composition of material differing in composition, which remain bonded together, but retain their identities and properties, without going to any chemical reaction. Composite is engineered to meet specific application, performance and specific needs.

Green composite combines plant fibres with natural resins to creat natural composite materials. Biomaterial composites are made from hemp, kenaf, sisal, soybean, etc. Natural fibres are emerging as low cost, lightweight and apparently environmentally superior alternative to synthetic fibres.

Why do we Need Green Composites?
The resins and fibres used in the green composites are biodegradable, when they dumped, decomposed by the action of microorganisms. They are converted into the form of H2O and CO2. These H2O and CO2 are absorbed into the plant systems.

The two main components of the green composites include:
  1. Biodegradable resin
  2. Natural fibres
Types & Properties of Green Composites:
Environment-friendly green composites were fabricated from a starch-based, dispersion-type biodegradable resin and cellulose fibres. The mixture of the dispersion-type biodegradable resin and cellulose fibres were blended well by using a home-use mixer and a stirrer, and then dried in air or in a vacuum. Composites were prepared by conventional hot pressing at a constant temperature of 140 degree celsius and at pressures of 10 to 50 MPa their flexural strength as well as flexural modulus increased with increasing the moulding pressure. The composites were from a starch based biodegradable polymer and Manila hemp fibres. The tensile strength of green composites is strongly dependent on fibre content. The tensile strength of cross-ply composites increases with the fiber content until nearly 50% by weight.

Fibers used in Green Composites :
It is remarkable that natural fibers such as kenaf, flax, jute, hemp, and sisal have attracted renewed interest, especially as a E glass fibre substitute in the automotive industry. The advantages of natural fibre over synthetic are low cost, low density, acceptable specific strength properties, ease of separation, carbon dioxide sequestration, and biodegradability. Plastics are lighter but they are not fit for load-bearing application because of the lack of strength, stiffness, and dimensional stability. In fibre-reinforced composites, the fibre serve reinforcements by giving strength and stiffness to the composite structure.

Natural / Bio-fibers may be classified in two broad categories:
  • Non-wood fibres
  • Wood fibres
In automotive applications, non-wood fibres such as hemp, kenaf, flax and sisal have attained commercial success in the design of bio-composites.

Methods of Manufacturing Composites
  • Filament winding
  • Lay up methods
  • Resin transfer moulding
  • Injection moulding
  • Vacuum bonding
  • Autoclave bonding.
Filament Winding:
Filament winding is a process is which continuous fibre (either pre-pregnated with resin, or coated during winding) are pulled from a large spool and wound on to a rotating mandrel after sufficient layers have been built up the wound form is curved and the mandrel removed. The parts most commonly made by this method are cylindrical pipes, drive shafts, portables air raft water tanks, spherical pressure tanks and yacht masts.

Lay-up Methods :
Layers of prepreg fabrics are built upon a mould, in unidirectional or multi axial form. They are then subjected to’ a consolidating force and cure them. The process can be done either by hand, or by automated lay-up which decreases the manufacture time significantly. Complicated shapes can be credited in this way.

Resin Transfer Bonding :
In this method, dry reinforcement fibre is held in a closed mould, and then resin is pumped through the mould at high pressure. This is a more time consuming process, as it involves labour intensive preparation and lay-up but it has many advantages, as the mould is closed, harmful emissions are reduced and a void-free laminate and complex parts can be created in this method.
 
Vacuum Bonding :
In vacuum bonding, the composite (usually large sandwich structures) is first placed over a mould then a vacuum bay is placed over the top, the air is removed from the vacuum, which forces the bag down onto the lay-up with a pressure of 1 bar. The whole assembly is then placed inside an oven to cure the resin, and the material is produced in a relatively short time. This method is used in conjunction with either filament winding or lay-up techniques.

Autoclave Bonding :

An autoclave is a pressure vessel, which controls exact pressure temperature and vacuum conditions. The technique is very similar to that of vacuum bonding except that the over is replaced by an autoclave. This means that wring condition can be controlled accurately to give high quality composites for a specific purpose. The process takes much longer than others, and is relatively expensive.
 
Methods of Manufacturing Green Composite Boards :
In general there are various methods existing by which the green composite particleboard can be produced. This chapter mainly includes various methods of manufacturing particleboards with examples of several natural composite boards.
 
Three-layer particle board :
This type of manufacturing is mainly known for producing three-layer particleboard. More recently, graded density particleboard has also evolved. It contains particles that gradually become smaller as they get closer to the surface such manufacturing can also be produced by this process.

Manufacturing Process of three Layer Particle Board :
Particleboard is manufactured by mixing wood particles or flakes together with a resin and forming the mix into a sheet. The raw material to be used for the particles is fed into a disc chipper between four and sixteen radially arranged blades. The particles are first dried, after which any oversized or undersized particles are screened out.

Resin, in liquid form, is then sprayed through nozzles onto the particles. There are several types of resins that are commonly used. Urea formaldehyde resin is the cheapest and easiest to use. It is used for non-water resistant boards. Melamine formaldehyde resin is significantly more expensive. Phenol formaldehyde is also fairly expensive. It is dark coloured and highly durable. These resins are sometimes mixed with other additives before being applied to the particles, in order to make the final product waterproof, fireproof, insect proof, etc. Once the resin has been mixed with the particles, the liquid mixture is made into a sheet.

A weighing device notes the weight of flakes, and they are distributed into position by rotating rakes. In graded density particleboard, the flakes are spread by an air-jet which throws finer particles than coarse ones. Two such jets, allow the particles to build up from fine to coarse and back to fine. The sheets formed are then cold-compressed to reduce their thickness and make them easier to transport. Later, they are compressed again, under pressures between two or three mega pascals and temperatures between 140°C and 220°C. This process sets and hardens the glue. All aspects of these process must be carefully controlled to ensure the correct size, density and consistency of the board. The boards are then cooled, trimmed and sanded.

Method of Bamboo Composite Board :
This method is adopted for manufacturing of a particleboard with the bamboo fibre. This technique is the most suitable for processing such hard fibres. The steam-exploded fibre is agitated using home-use mixer and flocculent fibre along with PLA resin (dispersion type) is mixed and dried at a temperature of 70 C for about 15 hours. And finally hydraulic pressing is done at a temperature of 180 C for 10 minutes. The sketch of the process is given below:

The similar process is followed with various fibres such as banana fibre and bagasse and so on. But depending upon the fibre used, the time of drying and pressing will vary.

Soy source for Green Composites :
Researchers in the US have developed an environmentally friendly, biodegradable material from soy flour resin and flax yarn. It is made from plant fibres and resins — renewable sources — making the composite material a greener alternative to petroleum-derived materials. This composite has good physical and mechanical properties compared to similar materials made from renewable resources - the yarn reinforces the resin, which is also cross-linked to improve its strength. The resin-yarn material is strong and durable enough for low-load indoor applications. Resin and yarn are expected to degrade easily at the end of the composite material’s life.

Minimizing waste by composting is a considerable benefit of this material over traditional plastics, whose very strength and stability make them difficult to degrade and adds large volumes of waste to landfill sites. Flax yarn’s low density makes it an attractive fiber-reinforcement material for applications where weight is a consideration. However, natural fibres might limit these materials’ widespread use.

Reliable and predictable mechanical performance is also critical to structural applications and the quality of the raw materials needs to be consistent. Natural fibres are not uniform and those from a single species of plant change with the climate and growing season. Processing raw materials with consistent dimensions and properties is probably the main challenge.
Fig. Soy Protein/Flax Fabric ‘Green’ Composite Testing
Advantages of Green Composites over Traditional Composites :
  1. Less expensive.
  2. Reduced weight.
  3. Increased flexibility.
  4. Renewable resource.
  5. Sound insulation.
  6. Thermal recycling is possible where glass poses problems.
  7. Friendly processing and no skin irritation.
Disadvantages of Green Composites:
  1. Lower strength properties (especially impact strength).
  2. Good moisture absorption causing swelling of fibres.
  3. Lower durability.
  4. Poor fire resistance and irregular fibre lengths are the disadvantages. However, recent fibre treatments have improved these properties.
Application and End Uses of Green Composites:
Green composites are applied to various components with moderate and high strength such as cars, mobile phones, etc. Various problems associated with green composites include effects of moisture and humidity, strength reliability, enhancement in fire resistance, etc. Moreover, there are some concerns over natural fibre quality and consistency, fogging and odour emission and processing temperature limits (200 C).

Some of the other areas in which the Green Composites are used:
  • False ceilings
  • Partition purposes
  • Doors
  • Furniture
  • Boxes for agriculture purposes
Other Miscellaneous Applications:
  • Rims
  • Mobile panels
  • Toys
  • Aircraft
  • Ships and so on .
Fig. green composite panels
Fig.Natural fibre composites in Mercedes E-class fig.NTT Docomo –cell body made of green composite
Automobiles:
The automotive market is becoming increasingly competitive; The latest European legislation limits the emission of CO2 and requires car designers to take into account pedestrian safety in case of impact. These influences are forcing the automotive industry to change the habits and to “Think composites” more and more, although composites will only be employed more extensively if those materials and technologies are competitive.

Composites made from natural fibres are attractive because of ecological concerns and also because they allow a decrease of the weight of parts and have good mechanical properties. Green composites are used in door panels, headliners, package trays, dashboards and trunk liners, based on natural fibre composites with thermoplastic or thermo set matrix, challenging the glass fibre reinforced composites.

With natural fibre composites, car weight reduction up to 35% is possible. This can be translated into lower fuel consumption and the lower environmental impact. Natural fibre based composites also offer good mechanical performance, good formability, high sound absorption and cost savings due to low material costs. Moreover their “Green look” as well as ecological and logistical benefits of the natural fibre based technologies looks more attractive.

In 2000, more than 23,000 tonnes of natural fibres have been used in the automotive sector alone. Natural fibres in automotive should experience a sustainable growth as EU regulations regarding recycling and “End of life vehicle” directives set car recycling targets to 95% by 2015.

Aircrafts and Ships:
The green composites are used in aircrafts and ships as because the weight is less and also it is eco-friendly which is also biodegradable. It is known that the fuel consumption will come down certainly if the weight of the vehicle is decreased. Also these types of green composites are also used in trains for the above reason.

Mobile Phones:
Green composites are used for mobile phone’s body. For example kenaf and PLA composites are applied to mobile phone parts in Japan to reduce the amount of CO2 emissions during fabrications. NTT Docomo is one of the models of mobile phones in Japan in which green composites are used for such purposes.

Decorative Purposes :
Green Composites are used for indoor structural applications in housing. The composite used for the interior decorations is banana fibre and its composites. The board used for flooring can be seen in the image. Also the walls can be covered with the boards, which will be attractive and will decrease the cost of construction.

Conclusion  :
Green composites may be easily composted after their life, completing nature’s carbon cycle. green-composites can supplement and eventually replace petroleum-based composite materials in many applications, offering new agricultural, environmental, manufacturing, and consumer benefits. Eco-friendly green-composites from plant-derived fibre (natural/bio fibre) and crop-derived plastics are novel materials of the twenty-first century and would be of great importance to the materials world, not only as a solution to growing environmental threat but also as a solution to the uncertainty of petroleum supply. Despite of having some disadvantages of green composites, the green composites can be the materials of future.

References:
  1. Green composites : manufacturing technology and application ; O L Snanmugasundaram; ITJ, octo.2009; pg. 63-69.
  2. Biocomposite textile; B. basu; textile review, sept. 2011; pg. 19-32.
  3. Environment friendly ‘green’ composites ; Katerina Blazek; Cornell Center for Materials Research
  4. Research Program for Undergraduates
  5. ‘Green’ Composites: Where we are and where we are headed; Anil N. Netravali Fiber Science Program Cornell University.
  6. “Green” Composites from Cellulose Fabrics & Soy Protein Resin ; National Textile Center Annual Report: November 2003 
  7. www.compositeworld.com
  8. www.technicaltextile.net