Green Composites: Types, Properties and Manufacturing Process
Zunjarrao B. Kamble
Dept. of Textile Engineering
D.K.T.E. Textile & Engineering Institute,
Ichalkaranji, Maharashtra, India.
Ecological concerns have resulted in renewed interest in natural materials. Development of natural fibers reinforced composites is highly attractive research lines. A natural fiber 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 techno economical 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 fibers with natural resins to create natural composite materials. Biomaterial composites are made from hemp, kenaf, sisal, soybean, etc. Natural fibers are emerging as low cost, lightweight and apparently environmentally superior alternative to synthetic fibers.
Why do We Need Green Composites?
The resins and fibers 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:
- Biodegradable resin
- Natural fibres
Types and Properties of Green Composites:
Environment-friendly green composites were fabricated from a starch-based, dispersion-type biodegradable resin and cellulose fibers. The mixture of the dispersion-type biodegradable resin and cellulose fibers 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 fibers. The tensile strength of green composites is strongly dependent on fiber 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 an E glass fiber substitute in the automotive industry. The advantages of natural fiber 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 fiber 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.
1. Filament Winding:
Filament winding is a process is which continuous fiber (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.
2. 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.
3. Resin Transfer Bonding:
In this method, dry reinforcement fiber 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.
4. 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.
5. 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 particle boards 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 colored 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 fiber. This technique is the most suitable for processing such hard fibers. The steam-exploded fiber is agitated using home-use mixer and flocculent fiber 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 fibers such as banana fiber and bagasse and so on. But depending upon the fiber 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.
Advantages of Green Composites over Traditional Composites:
- Less expensive.
- Reduced weight.
- Increased flexibility.
- Renewable resource.
- Sound insulation.
- Thermal recycling is possible where glass poses problems.
- Friendly processing and no skin irritation.
Disadvantages of Green Composites:
- Lower strength properties (especially impact strength).
- Good moisture absorption causing swelling of fibers.
- Lower durability.
- Poor fire resistance and irregular fiber lengths are the disadvantages. However, recent fiber 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 fiber 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
- Boxes for agriculture purposes
Other Miscellaneous Applications:
- Mobile panels
- Ships and so on.
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 fibers 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 fiber composites with thermoplastic or thermo set matrix, challenging the glass fiber reinforced composites.
With natural fiber composites, car weight reduction up to 35% is possible. This can be translated into lower fuel consumption and the lower environmental impact. Natural fiber 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 fiber based technologies looks more attractive.
In 2000, more than 23,000 tonnes of natural fibers have been used in the automotive sector alone. Natural fibers 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.
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.
Green Composites are used for indoor structural applications in housing. The composite used for the interior decorations is banana fiber 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.
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 fiber (natural/bio fiber) 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.
- Green composites: manufacturing technology and application; O L Snanmugasundaram; ITJ, octo.2009; pg. 63-69.
- Biocomposite textile; B. basu; textile review, sept. 2011; pg. 19-32.
- Environment friendly ‘green’ composites; Katerina Blazek; Cornell Center for Materials Research
- Research Program for Undergraduates
- ‘Green’ Composites: Where we are and where we are headed; Anil N. Netravali Fiber Science Program Cornell University.
- “Green” Composites from Cellulose Fabrics & Soy Protein Resin; National Textile Center Annual Report: November 2003
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.