Green Composites: Materials & Sustainability

This assignment delves into the fascinating world of green composites, focusing on their use of natural fibers as reinforcements in composite materials. The document examines the mechanical properties, manufacturing processes, and sustainability advantages of these eco-friendly alternatives to traditional synthetic composites. It also explores the challenges and future prospects of green composite development.

GREEN COMPOSITES: LITERATURE REVIEW
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Green Composites: Literature Review 2
Abstract
Green composites are a group of biocomposites comprising of natural fibers as reinforcing
material a matrix (usually bio-based polymer resin). These materials are grouped into different
classes, are environmental friendly and their popularity has increased over the past few decades
following the intensification of global awareness on climate change. They also have a variety of
superior mechanical properties such as Young’s modulus, strain, rupture stress, biodegradability,
low energy consumption, recyclability, abrasiveness, lightweight, non-toxicity, etc.). These
mechanical properties make them suitable for a wide range of applications, including:
transportation and automobile, aerospace, sports, electronics, healthcare, construction, packaging
and energy. There are also different methods of manufacturing green composites, hence the need
to investigate their efficiency and impact on the mechanical properties and final quality of green
composites produced. In this project, a green composite panel will be made then its mechanical
properties and suitable applications determined.
Table of Contents

Green Composites: Literature Review 3
Abstract.......................................................................................................................................................2
1. Introduction.........................................................................................................................................4
2. Interdiction..........................................................................................................................................7
3. Literature Review................................................................................................................................7
3.1. Classification of green composites based on reinforcement....................................................7
3.1.1. Fibrous composites..............................................................................................................8
3.1.2. Continuous fiber composites................................................................................................8
3.1.3. Discontinuous fiber composites...........................................................................................8
3.1.4. Particulate composites.........................................................................................................8
3.1.5. Filler composites..................................................................................................................8
3.1.5. Flake composites..................................................................................................................9
3.1.6. Laminated composites.........................................................................................................9
3.1.7. Hybrid composites...............................................................................................................9
3.2. Attributes and advantages of green composites.......................................................................9
3.2.1. Attributes...................................................................................................................................9
3.2.2. Advantages........................................................................................................................12
3.3. Methods of manufacturing green composites........................................................................15
3.3.1. Open moulding..................................................................................................................15
3.3.2. Closed moulding................................................................................................................16
3.3.3. Autoclave bonding.............................................................................................................18
3.3.4. Rapid prototyping..............................................................................................................19
3.4. Applications of green composites............................................................................................19
3.4.1. Transportation and automobile..........................................................................................19
3.4.2. Aerospace..........................................................................................................................20
3.4.3. Sports.................................................................................................................................20
3.4.4. Electronics.........................................................................................................................20
3.4.5. Healthcare..........................................................................................................................21
3.4.6. Construction.......................................................................................................................21
3.4.7. Packaging...........................................................................................................................21
3.4.8. Energy................................................................................................................................21
3.5. Concerns related to green composites....................................................................................22
4. Methodology.....................................................................................................................................24
5. Conclusion.........................................................................................................................................25

Green Composites: Literature Review 4
References.................................................................................................................................................25
1. Introduction

Green Composites: Literature Review 5
Rising global population, dwindling natural resources and increasing greenhouse gas
emissions are some of the issues that have resulted to more emphasis on use of environmental
friendly and efficient materials and processes1. As a result for this, the need for sustainable
development cannot be overemphasized and it has led to numerous inventions and advances in
engineering field2. The main goal of these developments is to make use of renewable, sustainable
and recyclable materials so as to protect the environment for the benefits of present and future
generations. Green composites are some of the sustainable and environmentally friendly
materials that have been discovered and developed over the recent years and have huge potential
of improving environmental conservation. By definition, green composites are a type of
biocomposites where natural fibers are used to reinforce a biodegradable (bio-based) polymer
resin or matrix. In this context, biocomposite is a composite material comprising of a resin
(matrix) and natural fiber reinforcement. Therefore green composites are materials comprising of
at least two different green materials. Green is used to mean that the materials are environmental
friendly and have high resource efficiency. The structure of green composites usually bears a
resemblance to that of living materials from which they are made of. This is useful in improving
the properties of the green composites, protecting them against mechanical damage and
environmental degradation, and improving their performance.
There are various kinds of natural fibers used in making green composites. Some of the
commonly used natural fibers include: jute, cotton, hemp, flax, sisal, bamboo, banana, ramie,
pineapple, coir (coconut), oil palm, kenaf, saw dust and soft wood, among others3. Each of these
natural fibers have unique physical and mechanical properties, including density, Young’s
1 K.G. Satyanarayana, ‘Recent developments in green composites based on plant fibers-preparation, structure
property studies’, Journal of Bioprocessing & Biotechniques, vol. 5, no. 2, 2015, pp. 1-12.
2 D. Verma, S. Jain, X. Zhang and P.C. Gope, Green approaches to biocomposite materials science and engineering,
Hershey, PA, IGI Global, 2016.
3 V.K. Thakur, Green composites from natural resources, Boca Raton, Florida, CRC Press, 2017.

Green Composites: Literature Review 6
modulus, tensile strength, elongation or strain, rupture stress, fracture toughness, water
absorption, etc., which make them suitable for different applications4. As a result of this, it is
important for designers and engineers to determine the precise properties of green composites
before establishing their appropriate applications5. This requires them to perform relevant tests
on the materials so as to determine their properties6. These natural fibers also have ecological and
techno-economic advantages over most of the synthetic fibers such as glass and carbon fiber7.
Their advantages over conventional synthetic fibers have led to emergence of numerous
applications in different industries8. As environmental issues continue to be of great concern
across the world, development and application of green composites is expected to expand9.
The physical, mechanical and chemical properties of green composites have made them
rapidly accepted by aerospace, automotive and transportation, construction, energy, military,
healthcare and packaging industries, among others. These materials are being produced and used
all over the world. In 2015, the global market for natural fiber was more than US$3.5 billion.
Currently, the biggest market for green composites is Asia Pacific followed by North America
and Europe. Many governments are also promoting use of green composites as a strategy to
reduce carbon emissions. Thus as global awareness about environmental concerns intensifies,
production and use of green composites are also expected to continue increasing over the coming
4 E. Zini and M. Scandola, ‘Green composites: An overview’, Polymer Composites, vol. 32, no. 12, 2011, pp. 1905-
1915.
5 M.P.M. Dicker et al., ‘Green composites: A review of material attributes and complementary applications’,
Composites Part A: Applied Science and Manufacturing, vol. 56, 2014, pp. 280-289.
6 J.M. Chard et al., ‘Green composites: sustainability and mechanical performance’, Jeju Island, Korea, 18th
International conference on Composite Materials, 2011.
7 Z.B. Kamble, ‘An overview of green composites’, http://textilelearner.blogspot.co.ke/2013/08/green-composite-
manufacturing-process.html, 2013, (accessed 23 September 2017).
8 H. Wang, et al., ‘Green composite materials’, Advances in Materials Science and Engineering, vol. 2015, 2015, pp.
1
9 F.P.L. Mantia and M. Morreale, ‘Green composites: A brief review’, Composites Part A: Applied Science and
Manufacturing, vol. 42, no. 6, 2011, pp. 579-588.

Green Composites: Literature Review 7
years10. Therefore any study conducted to gather information about green composites is
worthwhile.
2. Interdiction
This report will discuss different aspects of green composites, including: classification of
green composites, properties and advantages of green composites, manufacturing processes of
green composites, applications of green composites and challenges and/or issues of green
composites. This will be done by using experimental methodology where a green composite
panel will be made using different manufacturing methods and its mechanical properties
(including Young’s modulus, strain, rupture stress, etc.) determined. Once these properties are
determined, it will be easier to establish the impact of manufacturing method on mechanical
properties and quality of the green composite panel and its suitable applications.
3. Literature Review
3.1. Classification of green composites based on reinforcement
Green composites are usually classified based on the type of reinforcement from which
they are made. Brief descriptions of various classes of green composites are provided below
3.1.1. Fibrous composites
These are green composites that comprise of a matrix or resin and natural fibers
(reinforcement). The fibers are embedded in a matrix to achieve the desired physical, mechanical
and chemical properties for the intended application of the green composite11.
10 B. Baek et al., ‘Development and application of green composites: using coffee ground and bamboo flour’,
Journal of Polymers and the Environment, vol. 21, no. 3, 2013, pp. 702-709.
11 Z. Lei et al., ‘Interfacial micromechanics in fibrous composites: design, evaluation, and modes’, The Scientific
World Journal, vol. 2014, 2014, pp. 1-9

Green Composites: Literature Review 8
3.1.2. Continuous fiber composites
These are a class of single layered fibrous composites comprising of long fiber
reinforcement. Orientation of the long fibers can be in one direction, forming uni-directional
green composites, or the long fibers can also be woven to form bi-directional green composites.
3.1.3. Discontinuous fiber composites
These are a class of single layered fibrous composites comprising of short fiber
reinforcement. The orientation of the short fibers can either be random or preferred.
3.1.4. Particulate composites
These are composites whose reinforcement is in form of particles. The particle reinforcement
in the matrix can have a preferred or random orientation.
3.1.5. Filler composites
These are composites that are filled with a supplementary material in addition to the main
fiber reinforcement. In filler composites, the percentage of main reinforcement is always greater
than that of filler material. The type of filler materials that are commonly used for improving
properties and performance of matrix materials are particle fillers.
3.1.5. Flake composites
These are composites comprising of fiber reinforcement that is in form of chips or flakes.
The geometry of the flakes is usually two dimensional (2D) and they mainly have a sizeable
thickness.

Green Composites: Literature Review 9
3.1.6. Laminated composites
These are a class of multi layered fibrous composites comprising of fiber reinforcement in
form of mat embedded within the matrix. Orientation of the fiber reinforcing mat can be random,
unidirectional or woven (bi-directional).
3.1.7. Hybrid composites
These are a class of multi layered fibrous composites comprising of at least two types of fiber
reinforcements that are embedded within the matrix. Orientation of reinforcing materials in
hybrid composites can be random, unidirectional or woven (bi-directional). Hybrid composites
are created for the purpose of manipulating characteristics of resulting composite based on the
specific application requirement.
3.2. Attributes and advantages of green composites
3.2.1. Attributes
The mechanical, physical and chemical properties of green composites depend on various
factors such as type of materials (matrix and reinforcement) that are used to make the green
composite, proportion of these materials, compatibility between the matrix and fibre and the
processing or manufacturing method that is used to create the green composites12. This makes it
possible to manipulate these properties so as to achieve the most desirable properties for the
intended application. For instance, properties of green composites made from modified soy flour
resin and ramie fibers13 will be different from those made from virgin cotton and garneted fiber
yarn. For this reason, exact properties of green composites, such as density, tensile strength,
elongation or strain, Young’s modulus, rupture stress, toughness and water absorption, can only
12 G. Pamuk, ‘Natural fibres reinforced green composites’, Tekstilec, vol. 59, no. 3, 2016, pp. 237-243.
13 J.T. Kim and A.N. Netravali, ‘Mechanical, thermal, and interfacial properties of green composites with ramie fiber
and soy resins’, Journal of Agricultural and Food Chemistry, vol. 58, no. 9, 2010, pp. 5400-5407.

Green Composites: Literature Review 10
be determined after the composites have been manufactured and subjected to relevant tests for
analysis. This is because each natural fiber and matrix material has its own strengths and
weaknesses in terms of properties14. The properties determined helps in establishing the most
appropriate application of the green composites and their behavior when exposed to different
conditions15. As stated before, the green composites can be modified to improve their mechanical
properties, processability and machinability, thermal properties and moisture resistance thus
making them suitable for use in industries such as aerospace and automotive16.
3.2.1.1. Natural fibers
Natural fibers have some drawbacks and limitations when used as reinforcement materials in
green composites. Some of these drawbacks and limitations include: they are hydrophilic; cannot
withstand temperatures above 200°C, hydrophilic fibers have very low compatibility with
hydrophobic matrices; they are short; and some of their properties are affected by external
factors such as method of harvesting and climate17. The natural fibers consist of polar groups
such as hydroxyl. When they are combined with nom-polar groups, such as those of matrices that
are hydrophilic in nature, the natural fibers end up absorbing water resulting to poor wettability
of matrices and incompatibility18. This results to poor bonding, making failure of the green
composite inevitable. Therefore natural fibers usually have to be modified before they can be
used to make green composites.
14 M. Zampaloni et al., ‘Kenaf natural fiber reinforced polypropylene composites: a discussion on manufacturing
problems and solutions’, Composites Part A: Applied Science and Manufacturing, vol. 38, no. 6, 2007, pp. 1569-
1580.
15 R. Mishra, B. Behera and J. Militky, ‘Recycling of textile waste into green composites: Performance
characterization’, Polymer Composites, vol. 35, no. 10, 2014, pp. 1960-1967.
16 M. Jawaid, M.S. Salit and O.Y. Alothman, Green biocomposites: design and applications, New York City, Springer,
2016.
17 J. Summerscales et al., ‘A review of bast fibres and their composites. Part 1 – fibres as reinforcements’,
Composites: Part A, vol. 41, 2010, pp. 1329-1335.
18 S. Mukhopadhyay and R. Fangueiro, ‘Physical modification of natural fibers and thermoplastic films for
composites – a review’, Journal of Thermoplastic Composite Materials, vol. 22, no. 2, 2009, pp. 135-162.

Green Composites: Literature Review 11
There are two main categories of methods used to modify natural fibers. The main objective
of these modifications is to eliminate surface contamination on the natural fibers and improve
contact or compatibility between them and matrices. The modification methods are categorized
into physical modification and chemical modification. Physical modification involves changing
the surface and structural properties of natural fibers. Examples of physical modification
methods are: surface fibrillation, corona, plasma and barrier techniques, among others. Chemical
modification usually entails developing a compatible hydrophobic coating on the filler’s surface
before the natural fiber is mixed with the matrix. In most cases, coupling agents are used to
enhance transfer of stress between the matrix and natural fiber. These coupling agents perform
two functions: to react with hydroxyl groups present in natural fibers’ cellulose and react with
the matrix’s functional groups. Examples of coupling agents commonly used are reactive
chemistries (also called functional modifiers) and surface-active agents.
3.2.1.2. Matrix materials
There are two main categories of matrix materials: thermoplastics and thermosets. The
chemical crosslinking of thermosets makes it impossible to melt them once they are cured.
However, mechanical properties of thermoplastics are generally good. The transition temperature
of most thermoplastics is usually low resulting to low stiffness and high brittleness. The
thermoplastics do not have chemical crosslinking making them easy to re-melt, reshape and
manufacture. Examples of thermoset polymers that are commonly used include polyester,
vinylester and epoxies while commonly used thermoplastics include polypropylene, polystyrene
and polyethylene.

Green Composites: Literature Review 12
3.2.2. Advantages
The popularity of green composites is rapidly increasing across various sectors mainly
because of the exceptional properties and potential benefits of these materials19. Some of the
advantages of green composites are as follows:
Wide-ranging properties and applications: there are various kinds of natural fibers and matrix
materials, each with unique properties. Natural fibers are acquired from varied natural sources.
The properties of these materials are influenced by factors like climate, plant location, crop
variety, soil quality, seed density, fertilization, harvest timing and location of fiber on the plant,
among others20. Matrix materials also have different properties. When these materials are
combined, they create green composites with wide-ranging mechanical, physical and chemical
properties that are suitable for a variety of applications such as in construction, automotive,
aerospace, military, healthcare, electronics and energy sectors.
Non-toxicity: natural fibers used in making green composites are typically non-toxic21, which
reduces their environmental impacts throughout their lifecycle. Several studies have shown that
natural fibers have far less heavy metals, carcinogenic substances and human toxins than
synthetic fibers such as glass fiber. Therefore green composites have near zero toxicity hence
harmless to humans and ecosystems.
Low cost: natural fibers’ cost is generally lower than that of synthetic fibers22. However,
most biopolymers and matrix materials cost more than synthetic fibers. One of the techniques
19 A.A. Singh, S. Afrin and Z. Karim, ‘Green composites: versatile material for future’, in Green biocomposites (green
energy and technology), New York City, Springer, 2017, pp. 29-44.
20 D.B. Dittenberg and H.V.S. GangaRao, ‘Critical review of recent publications on use of natural composites in
infrastructure’, Composites Part A: Applied Science and Manufacturing, vol. 43, 2012, pp. 1905-1915.
21 E. Zini and M. Scandola, ‘Green composites: an overview’, Polymer Composites, vol. 32, 2011, pp. 1905-1915.
22 S.K. Ramamoorthya et al., ‘A review of natural fibers used in biocomposites: plant, animal and regenerated
cellulose fibers’, Polymer Reviews, vol. 55, pp. 107-162.

Green Composites: Literature Review 13
that manufacturers are using to lower the overall production cost of green composites is
increasing the ratio of natural fibers to matrix materials. It is also worth noting that processing
and treatment techniques needed to improve properties of green composites add extra production
cost. Thus one way that manufacturers of these products are applying to lower production costs
is by developing more efficient production, processing and treatment technologies and processes.
Renewability: green composites comprise of natural materials (matrix materials and
reinforcement) that are mainly obtained from plants, which are renewable and sustainable
resources. These plants are planted annually and therefore availability of raw materials for green
composites is unlimited.
Low energy consumption and carbon dioxide emissions: environmental impacts of materials
are very essential nowadays mainly because of the global change concern. Materials with less
embodied energy and carbon dioxide emissions are always the best choice for any application.
Generally, treatment and processing of natural fibers and production of green composites
consume less energy and generate a smaller amount of carbon emissions than synthetic
composites. This makes green composites environmental friendly alternatives to synthetic
composites.
Biodegradability: biodegradable materials are those that degrade completely by being acted
upon by living organisms. All natural fibers are biodegradable meaning that they degrade and
turn into useful organic matter or compost that can be used for agricultural activities. Some
matrix materials are biodegradable while other are non-biodegradable. If a green composite has a
biodegradable matrix, it can be disposed of through composting hence helping in minimizing
waste disposal problems. But if the green composite is made of non-biodegradable matrix, it can
only be disposed of through landfilling or incineration. Therefore in countries where

Green Composites: Literature Review 14
manufacturers are held responsible for the products they make throughout their lifecycle, green
composites with biodegradable matrix are largely used as a strategy for mitigating environmental
impacts related to waste disposal.
Abundance: natural fibers, which are a major component of green composites, are natural
resources whose available is unlimited. These resources can be found anywhere making them
applicable worldwide. Infinite availability also reduces the cost of natural fibers and hence green
composites.
Lightweight: the density of natural fibers is relatively low compared with that of synthetic
fibers23. This makes green composites more suitable for use in automotive, transportation, sports,
electronics and aerospace industries that require lightweight components for greater performance
and efficiency.
Abrasiveness: green composites are less abrasive than synthetic composites24. This reduces
wear and tear of tools and equipment used in production and repair of products made from green
composites25. It also makes them easy to process.
Recyclability: green composites can also be recycled at the end of their lifespan and be put
into other uses. Recycling and reusability of these composites helps in reducing environmental
impacts in addition to other economic and social benefits.
23 O. Faruk et al. ‘Progress report on natural fiber reinforced composites’, Macromolecular Materials and
Engineering, vol. 299, no. 1, 2014, pp. 9-26.
24 M.R.N. Fazita et al., ‘Green composites made of bamboo fabric and poly (lactic) acid for packaging applications –
A review’, Materials (Basel), vol. 9, no. 6, 2016, pp. 435.
25 K.L. Pickering, M.G.A. Efendy and T.M. Le, ‘A review of recent developments in natural fibre composites and their
mechanical performance’, Composites Part A: Applied Science and Manufacturing, vol. 83, 2016, pp. 98-112.

Green Composites: Literature Review 15
3.3. Methods of manufacturing green composites
Green composites can be manufactured using a variety of techniques. These techniques have
varied requirements, advantages, limitations and drawbacks. Some of the manufacturing methods
of green composites include:
3.3.1. Open moulding
In this technique, raw materials (i.e. fiber reinforcements and matrices/resins) are combined
in an open mould and remain exposed to air when they are curing or hardening26. There are three
main processes of open moulding: spray-up, filament winding and hand lay-up.
Hand lay-up: this is the simplest, least expensive and commonest type of open moulding
methods. In this method, a spray gun is used to apply a gel coat on the mould followed by
placing fiber reinforcements into the mould by hand. A paint roller, spray or brush is then used to
apply laminating resins or matrix material on the fiber reinforcements. Successive layers of fiber
reinforcements are then added by hand to create the desired laminate thickness.
Spray-up: this process is also known as chopping. The process starts by using a spray gun to
apply a gel coat on the mould. A chopper gun is them used to inject fiber reinforcements on the
mould that are then laminated by matrix using another chopper gun. This is followed by adding
extra coatings of chop laminate until attaining the desired thickness. The process is suitable for
making transportation components, tanks, boats, shower units and bathtubs of different sizes and
shapes.
Filament winding: this is an automated process of open moulding. The mould used in this
process is rotating mandrel. The process starts by using a resin bath to feed continuous
26 Composites Lab, ‘Open molding’, http://compositeslab.com/composites-manufacturing-processes/open-
molding/, 2016 (accessed 24 September 2017).

Green Composites: Literature Review 16
constituent roving that is then coiled on the mandrel. There is a trolley on which the roving feed
runs. The filament is then placed in preset geometric configuration so as to obtain maximum
strength in the desired orientation. After applying sufficient layers, curing of the laminate on the
rotating mandrel is done followed by stripping the moulded part from the mandrel.
3.3.2. Closed moulding
In this technique, raw materials (i.e. fiber reinforcements and matrices/resins) are combined
inside a vacuum bag or two-sided mould. Closed moulding processes are mostly automated and
are performed by special equipment hence suitable for large scale production of green
composites. Some of the closed moulding techniques are discussed below.
Vacuum bag moulding: in this process, a release film (matrix) is placed over the natural fiber
laminate then on top of it is placed a bleeder layer of a material that is able to absorb excess
matrix from the laminate. Another bleeder layer of the same material is placed on top of the
previous layer then a vacuum bag is secured on top of the whole assembly. Thereafter pressure is
extracted from the vacuum bag allowing atmospheric pressure to be exerted on the bag thus
eliminating excess resin and entrapped air and compacting the laminate. This also increases the
percentage of natural fiber and enhances adhesion between the fiber and matrix.
Vacuum infusion processing: this process starts by placing dry fiber reinforcement in the
mold, including laminate, then placing a pricked release film on top of the dry reinforcement. A
flow media comprising of a fold layer or coarse mesh is positioned then a pricked pipe is put in
place for resin distribution on the laminate. This is followed by placing and sealing the vacuum
bag around the perimeter of the mould. A tube connection between the resin vessel and vacuum
bag is then used to apply a vacuum to combine the laminate and pull the resin into the mould.

Green Composites: Literature Review 17
Resin transfer moulding: the process starts by placing dry reinforcement in a closed mould
followed by pumping the resin at high pressure through the mould. The process is time
consuming and labour intensive but has less emissions and can produce complex components.
Compression moulding: in this process, a mould is fixed in a mechanical or hydraulic
moulding press then it is heated to a predetermined temperature27. Fiber reinforcement and resin
with a balanced charge are put in the open mould followed by closing of the mould’s two halves
then applying pressure. The moulding material is then allowed to cure for a length of time
determined by shape, size and thickness of the composite. After curing, the mould is opened
followed by removing the finished component. This method is suitable for making automobile,
electrical, structural, housing and furniture components.
Continuous lamination: here, resin and fiber reinforcement are combined on a plastic film
drawn through the lamination process followed by applying a second film over the resin and
reinforcement to facilitate proper mixing and air exclusion. The composite is then transferred to
an oven for curing. If panels are the ones being produced, they can be automatically cut and
trimmed to the desired dimensions. Imprinted carrier films can also be used to create special
effects on the components’ surface.
Pultrusion: This technique entails filling fiber reinforcement in a resin basin then using a
strong tractor apparatus to pull it via a steel die. The reinforcement gets consolidated with the
steel die which also adjusts the composite shape and ratio of fiber to resin. The resin is then
cured rapidly by heating the steel die.
27 K.C. Birat, M. Pervaiz, O. Faruk, J. Tjong and M. Sain, Green composite manufacturing via compression molding
and thermoforming, in Manufacturing of Natural Fibre Reinforced Polymer Composites, 2015, Cham (ZG),
Switzerland, Springer International Publishing.

Green Composites: Literature Review 18
Centrifugal casting: in this method, resin and fiber reinforcements are placed in a rotating
mould and held there by centrifugal force until the component is adequately cured. The external
surface of the component gets cured against the mould’s internal surface.
Reinforced reaction injection moulding: in this method, fiber reinforcements are used to
improve resin’s properties. The process starts by metering at least two reactive resins which are
then mixed under extreme pressure to create a thermosetting polymer. The polymer is injected
into a coated and cured mould from the two sides under low pressure then reinforcement is added
for polymerization to take place.
3.3.3. Autoclave bonding
This process uses an autoclave, a pressure vessel that regulates vacuum and pressure
temperature conditions. The green composite of fiber reinforcement and resin is placed on the
mould followed by placing a vacuum bay on top of it. Air is then emptied from the vacuum
forcing the bag to collapse on the composite. The assembly is then moved into the autoclave for
the resin to cure under accurately controlled conditions.
3.3.4. Rapid prototyping
This is the latest method of manufacturing green composites. It is a high-tech technique that
is used for producing complex and high quality components. The method entails use of digital
fabrication to manufacture components quickly and precisely28. Various rapid prototyping
techniques used include: selective laser melting/sintering, laminated object manufacturing,
ultrasonic consolidation, 3D printing, laser engineered net shaping and fused deposition
modelling.
28 P. Nadya, Rapid prototyping of green composites, Master’s Thesis, Massachusetts Institute of Technology, 2011.

Green Composites: Literature Review 19
Other methods manufacturing methods include: extrusion, thermoforming, melt mixing and
solution casting.
3.4. Applications of green composites
Different areas where green composites are applied include:
3.4.1. Transportation and automobile
Automotive market has become very competitive worldwide. Players in the industry are
using green composites because of their lightweight, good mechanical properties, great sound
absorption, good formability and low embodied and carbon dioxide emissions. Green composites
are being used for making different automobile components such as dashboards, headliners,
trunk liners, door panels, rims, package trays and body panels, among others29. Automotive in
this context includes trucks, vans, buses, passenger cars, recreational vehicles and sport utility
vehicles30. Besides automobiles, green composites are also used in ships and trains.
3.4.2. Aerospace
Lightweight, strength, low cost and environmental friendliness are some of the major
attributes of aircraft components. Green composites exhibit these attributes and that is why they
have found wide-ranging applications in aerospace industry. They are used for making different
aircraft components, which help in improving energy efficiency and reducing costs and carbon
emissions31.
29 G. Koronis, A. Silva and M. Fontul, ‘Green composites: A review of adequate materials for automotive
applications’, Composites Part B: Engineering, vol. 44, no. 1, 2013, pp. 120-127.
30 O. Akampumuza et al., ‘A review of the applications of bio composites in the automotive industry’, Polymer
Composites, 2016, pp. 1-46.
31 K. Georgis, A. Silva and S. Furtado, Applications of green composite materials, in Biodegradable Green
Composites, 2016, Hoboken, New Jersey, John Wiley & Sons, Inc.

Green Composites: Literature Review 20
3.4.3. Sports
Most sporting equipment need to be strong, lightweight, resistant to vibration and safe. Green
composites provide these very important properties and that is why they are widely used for
making sporting equipment nowadays. Examples of sporting equipment made from green
composites include: snow boards, tennis rackets, golf clubs, bicycle frames, boat hulls and
archery bows, among others.32.
3.4.4. Electronics
Green composites are used to make a wide range of electronic and electrical equipment and
appliances. These include circuit boards, electrical panels, mobile panels, mobile phones, etc.
3.4.5. Healthcare
Properties of green composites, including bioactivity, biodegradability and biocompatibility
have made them better than synthetic composites in biomedical applications. Some of the
applications of green composites in healthcare industry include: tissue engineering, implants,
medical equipment and devices, etc.
3.4.6. Construction
Green composites have a wide range of applications in construction industry because of their
high strength, corrosion resistance, low maintenance needs and light weight properties. They can
be used for making structural components of buildings such as beams, columns and roofs. They
are also used for decorative purposes (interior decorations), flooring, walls, partition purposes,
insulation purposes, ceilings, doors, windows, panel rails, furniture, bathtubs, countertops,
fireplace surrounds, shower receptors, kitchen products, fencing, decking, plumbing systems, etc.
32 H.J. Kim, H.J. Lee, T.J. Chung, H.J. Kwon, D. Cho and W.T.Y. Tze, Applications and future scope of “green”
composites, in Polymer Composites, 2013, Weinheim Germany, Wiley-VCH Verlag GmbH & Co. KGaA.

Green Composites: Literature Review 21
These uses reduce carbon emissions and costs of the buildings besides improving structural
soundness, thermal comfort and aesthetic value of the building.
3.4.7. Packaging
Green composites are used for making packaging and other short lifespan items such as
plastic cutlery and toys.
3.4.8. Energy
Green composites have also found applications in energy sector especially renewable energy
sources such as wind and solar energy. Because of low weight, low cost, high strength, high
corrosion resistance and high toughness of green composites, these biocomposites are being used
to make structural components of wind turbines and solar panels.
3.5. Concerns related to green composites
Green composites have numerous advantages over synthetic composites. However, there are
some concerns that are hindering use of green composites. If these composites have to become
reliable in use as structural components then the issues need to be resolved. The key concerns
are:
Properties disproportion: green composites are made of two or more different materials,
usually a matrix or resin and natural fiber reinforcing material(s). The natural fiber reinforcing
materials are usually obtained from different sources and therefore they exhibit significant
variations in their characteristics and properties33. These variations can cause compatibility
problems with matrix material thus affecting the properties of resulting green composites
33 Z. Xiaolei et al., ‘Natural fibers for the production of green composites’, in Green approaches to biocomposite
materials science and engineering, Hershey, PA, IGI Global, 2016, pp. 1-23.

Green Composites: Literature Review 22
created. As a result of this, there is need to perform statistical analysis34 on each green composite
created so as to know their exact properties before use35. In general, variability in properties of
natural fibers makes it difficult to rely on green composites in structural uses where component
failure is intolerable.
End-life disposal: all natural fibers are biodegradable hence their end-life disposal is easy.
Most matrix materials are bio-based but not all of them are biodegradable. If green composites
are made of non-biodegradable polymer matrix, they cannot be disposed of through composting
hence causing waste disposal problems. The non-biodegradable materials can only be disposed
via landfilling or incineration, which have negative impacts on the environment.
Water absorption: cellulose is the main substance contained in most natural fibers36. This
substance is highly hydrophilic and causes wettability and compatibility problems when natural
fiber is combined with matrix materials that are hydrophobic. Finished green composites made of
natural fibers experience swelling that causes surface roughening, delamination and loss of
material strength and other mechanical properties. Therefore natural fibers have to be treated37
through chemical modifications38 or physical modifications so as to improve their properties by
reducing water absorption capability.
Poor durability: durability of green composites is generally limited because their largest
percentage of materials are biodegradable. Growth of bacteria and fungi in natural fibers
34 A.S. Virk, W. Hall and J. Summerscales, ‘Modelling tensile properties of jute fibres’, Material Science Technology,
vol. 27, 2011, pp. 458-460.
35 J. Summerscales, A.S. Virk and W. Hall, ‘A review of bast fibres and their composites: Part 3 – Modelling’,
Composites Part A: Applied Science and Manufacturing, vol. 44, 2013, pp. 132-139.
36 R. Masoodi and K.M. Pillai, ‘A study on moisture absorption and swelling in bio-based jute-epoxy composites’,
Journal of Reinforced Plastic Composites, vol. 31, 2012, pp. 285-294.
37 S. Kalia, B.S. Kaith and I. Kaur, ‘Pretreatments of natural fibers and their application as reinforcing material in
polymer composites – a review’, Polymer Engineering Science, vol. 49, 2009, pp. 1253-1272.
38 M.J. John and R.D. Anandjiwala, ‘Recent developments in chemical modification and characterization of natural
fiber-reinforced composites’, Polymer Composites, vol. 29, 2008, pp. 187-207.

Green Composites: Literature Review 23
degrades green composites and this worsens when these composites are exposed to
environmental conditions such as moisture and weathering. Some of the degradations include
resin cracking, colour fading, black spots, fibrillation and bulging. Thus mechanical properties
and durability of green composites reduces significantly as a result of exposure to the
environment39. The composites must be treated appropriately so as to mitigate rapid
deterioration.
Degradation at higher temperatures: natural fibers start degrading when exposed to
temperatures above 200 °C. This significantly limits the range of processing methods and
applications of green composites.
4. Methodology
This research will be completed using both qualitative and quantitative methods. The chosen
methodology to complete this research is experimental method, which is a scientific method that
is appropriate for testing and observing scientific hypothesis. In the context of this research,
making a green composite and determining its mechanical properties is a scientific process,
which makes experimental method suitable for this research. Experimental method allows the
researcher to control the variables of the tests being carried out. In this case, there are different
types of green composites hence the researcher will be able to determine the type of green
composites by selecting their materials (i.e. type of natural fiber and matrix/resins). This
methodology also allows the researcher to make the same green composite panel using different
manufacturing methods. As a result, the researcher can establish the relationship between the
manufacturing method and mechanical properties and quality of green composite panel
39 E. Nadali et al., ‘Natural durability of a bagasse fiber/ polypropylene composite exposed to rainbow fungus
(Coriolus versicolor)’, Journal of Reinforced Plastic Composites, vol. 29, 2009, pp. 1028-1237.

Green Composites: Literature Review 24
produced. Once the manufacturing method is identified, its standardized measures and
procedures will be followed to make the green composite panel. The panel will then be subjected
to relevant tests so as to collect both qualitative and quantitative data. The data will be
systematically analyzed so as to establish the actual mechanical properties of the green
composite panel and match them with their most suitable applications. The following is the
general procedure of the experimental methodology that will be used in this research: identifying
and defining the research problem; reviewing important literature; identifying mechanical
properties to be determined; selecting manufacturing method to be used; constructing appropriate
experimental design; carrying out the experiment; collecting raw data; analyzing collected data
qualitatively and quantitatively; and presenting finding and conclusions.
5. Conclusion
Increased awareness about environmental issues such as global climate change has
significantly contributed to rapid development and use of green composites. This report was
about discussing different aspects of green composites, including: classification, mechanical
properties, advantages, manufacturing processes, applications and challenges and/or issues of
green composites. The report has also discussed the methodology (experimental methodology)
that will be used to complete the research. The data collected from this methodology will be
systematically analyzed so as to determine various mechanical properties of the green composite
panel and establish its most suitable application.
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