Evaluation and Sustainability of Natural-Fiber Reinforced Polymer Composites in the Automotive Industry

Evaluation and Sustainability of Natural-Fiber Reinforced Polymer Composites in the Automotive
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School of Mechanical and Manufacturing Engineering
Faculty of Engineering
The University of New South Wales
MECH 9420: Composite Materials and Mechanics
Evaluation and Sustainability of Natural-Fiber Reinforced
Polymer Composites in the Automotive Industry
FOR Codes:
0912 – Materials Engineering
0902 – Automotive Engineering
By
Asif Akram
z5086426

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1.0 Introduction:
Composite materials are complex systems which consist of matrix components and reinforced
materials. A definition of composite materials can be: It is a multi-phased combination of two
or more materials with different properties, and it not only retains the characteristics of the
original components but also new properties which were not present in the constituent
components [1]. All composite materials are mainly consisting of three distinct structures, the
matrix phase which is continuous, the reinforced phase which acts around the matrix structure
providing adhesive properties and to impart toughness, and the interphase which is an
agreement between the matrix and reinforced phases. This paper is focused on the study of
natural-fiber polymer matrix composites and their application in motor vehicles.
Polymer matrix composites have been prevalently used in various industries, including
aerospace, automotive, marine, and military [2] because of their high tensile strength and
stiffness which stem from the properties of the fibers and the matrix resins. They are mainly
composed of an organic matrix which bound together continuous fibers.
In the automotive industry, polymer matrix composites have a widespread range of uses with
projected increasing rates of production. In cars, they are seen in the form of dashboards, engine
covers, car covers, floors and seats. Over the past decade more car manufacturers and suppliers
from Europe have embraced the usage of natural-fiber composites with thermoplastic and
thermoset matrices and manufacturing methods [3]. The composition of these neutral-fiber
composites and their properties are desired due to their reductions in weight, their low CO2
emission, and their low cost of manufacture. The manufacture of these thermosets and
thermoplastic matrices are discussed in this study, as well as their application in high
temperatures. Further discussed is the study of newer methods of manufacture of the fiber
materials and their possible use to reinforce them with the polymer composites.
The main focus of this study is on the usage of these natural-fiber composites such as hemp in
the automotive industry as opposed to glass fiber reinforced polymer composites. Hemp is
chosen as the alternative as it showcases similar desirable properties as those of glass fiber,
which will be discussed later in the literature review of this study. The mechanical properties,
methods of manufacture, and performance of hemp and glass fibers are discussed, and a
comparison is made with regards to showing that hemp can be a suitable more sustainable
alternative for the manufacture of car parts.
Finally, a conclusion is drawn from the major points of literature reviewed to provide insight
to the readers.

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2.0 Literature Review:
The following literature review provides the readers the understanding of the parameters
considered when comparing the usage of natural fiber-based polymer composites over glass
for sustainability in the automotive industry. The review is based on literature obtained from
various sources that focus on the application of polymer composites in engineering, as well as
their performances in extreme conditions.
2.1 Natural-fiber reinforced polymer composite materials and properties:
The most prevalent natural fibers in use are “Blast”, which are obtained from plant cellulose,
and fibers that are derived from seeds (such as cotton). Hemp is a classification of blast fiber,
whose world production amounts to about 2.1 × 10'
tonnes per year, as compared to the most
prominent natural fiber (wood), whose world annual production is 1.75 × 10*
tonnes [3].
It can be harvested two or three times every year and can be easily grown in most climates.
Table 1 shows the chemical composition of hemp.
Table 1: Chemical composition of Hemp [3]
Material Percentage Composition
Cellulose 77.5%
Hemi-cellulose 10.0%
Lignin 6.8%
Pectin 2.9%
Fat and Wax 0.9%
Water soluble materials 1.8%
It can be seen that hemp is predominantly a cellulose structure. Over the last couple of decades,
research on implementing natural-fiber composites over synthetic fibers have sped up due to
the negative environmental impacts resulting from increased use of synthetic fibers. The
depletion of fossil fuels and petroleum reserves coupled with coordinated efforts from world
powers to increase environmental regulations have resulted in an increased effort of finding
recyclable materials that agree with the environment and are independent of fossil fuels [4].
Natural-fiber reinforced composites are thus seen as a solution in this study.

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Figure 1: Cellulose structure
Figure 1 shows the chemical structure of cellulose and the organic bonds that occur in them.
2.1.1 Manufacturing of natural-fiber (hemp) reinforced composites:
The manufacturing process of obtaining natural-fiber reinforced polymer composites involves
the use of a thermoset or thermoplastic polymer matrix system [5]. Thermoplastic materials are
plastic polymers that can be molded into a desired shape at high temperature and solidified
upon cooling. For non-structural components of vehicles, the adequate system currently used
is thermoplastic polypropylene. Polypropylene is chosen due to its low density, desirable
mechanical and electrical properties, good dimensional stability and impact strength [3]. The
process of developing thermoplastic natural-fiber composites involves the use of a mould. This
involves using thin reinforced sheets of the thermoplastic material and allowing them to soften
[5]. Once they are softened, they are then transferred to the corresponding molded tool, where
they are simultaneously shaped and cooled. This process is a lot less time consuming as
opposed to preheating the thermoplastic sheet in a separated heating unit. This process is called
compression moulding.
Compression moulding is used for manufacturing low to medium range automotive parts such
as body panels and doors. It is advantageous due to its short cycle times and low fiber attrition.
As mentioned above, the temperature range of the process is a predominant feature in
determining the properties of the product. The temperature limit before degradation occurs is
concluded through experiments to be 150° C for long duration processes, while for short term
exposure it is found to be 220° C. Long term exposure to high temperatures results in
discoloration, poor adhesion between fiber and polymer, and release of volatiles. Thus, it is
desirable to ensure as fast a reaction rate as possible to avoid degradation [5].
For commercial production of natural-fiber composites, particularly where complex shapes are
required such as in the automotive industry, injection moulding is the preferred method. It is a
desirable process due to its excellent dimensional tolerance and low cycle time [3]. However,
there are drawbacks to this process. The mechanical action of the screws involved in the

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process may damage the fibers. Furthermore, since the intricate shapes of the product arise
from the interaction between the fibers, the polymer, and the machine, any disagreement or
mishap may lead to the constituent particles remaining in the composites.
2.1.2 Compatibilization and Coupling
The physical properties of the composites depend largely on the adhesion between the natural
fiber and polymer matrix [3]. And thus, to ensure suitable adhesion and increase efficiency, the
blend is compatibilized or coupled.
Compatibilization involves any kind of operation that ensures there is suitable moisture levels
in the blend. Natural fibers absorb moisture from the surroundings depending on the current
relative humidity. Absorption of excess moisture or having very low moisture may result in
changes of the desired properties of the composite.
Coupling is a process in which polymers and fillers that are not similar are made into alloys by
the help of external agents. One such suitable external agent is Vinylester resin, which is
obtained from reaction between epoxy resin and an unsaturated carboxylic acid [5]. This
external agent offers good chemical and mechanical properties, and low cost and ease of
manufacture. The Vinylester allows for absorption of energy by the polyester chain, resulting
in a tougher material.
Choosing a suitable method of manufacturing natural-fiber reinforced composite materials
depends on the type of application of the material, the specific properties of material, and the
cost of manufacture.
2.2 Glass-fiber polymer reinforced polymer composite materials and properties:
As a comparison to the natural fiber procured from hemp introduced in a previous section, E-
glass fiber is chosen as the benchmark synthetic fiber whose properties the hemp natural-fiber
must at least match. Glass fiber is light in weight, extremely durable, and robust [6]. Properties
such as high tensile strength, high specific Young’s modulus, heat resistance and relatively low
density as opposed to metals mean that E-glass is the most common synthetic fiber used in
industries. Table 2 shows the chemical composition of E-glass by weight percentage.

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Table 2: Chemical composition of E-glass [6]
Material Percentage
Composition
Silicon dioxide 54%
Aluminum oxide 14%
Calcium Oxide + Magnesium Oxide 22%
Sodium Oxide + Potassium Oxide < 2%
Boron Trioxide 10%
Other impurities < 1%
2.3 Comparison between natural-fiber and glass fiber reinforced composites:
Due to the abundance of natural-fiber sources and their recyclability, they have been suitable
alternatives to synthetic fibers such as glass or carbon [4]. Table 3 shows the mechanical
properties of various natural fibers. These properties are then used to determine the most
appropriate natural fiber alternative to E-glass.
Table 3: Mechanical properties of natural fibres and E-glass [3]
Fiber Density (g/cm3
) Tensile strength
(MPa)
Young’s
Modulus (Gpa)
Specific
tensile
strength
(Mpa/gcm-3)
Specific
Young’s
Modulus
(Gpa/gcm-3
)
Flax 1.5 345-1830 27-80 230-1220 18-53
Hemp 1.5 550-1110 58-70 370-740 39-47
Jute 1.3-1.5 393-800 10-55 300-610 7.1-39
Cotton 1.5.1.6 287-800 5.5-13 190-530 3.7-8.4
E-glass 2.5 2000-3000 70 800-1400 29
The advantage that the natural fibers have over E-glass is that they are all less dense. It can be
seen from the table that E-glass is the most superior in terms of specific tensile strength, with
Flax coming a close second. However, it can be inferred that both Hemp and flax have specific
Young’s Modulus that range higher than that of E-glass, so hemp and flax can be chosen as
suitable natural fibers for automotive applications. Flax has a very broad range of specific
tensile strength and specific Young’s Modulus and so it would be more time consuming and
less cost-effective method to manufacture flax reinforced composites with the correct
mechanical properties [3]. Therefore, hemp is chosen as the best option. The relatively low

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tensile strength opens up the scope of further research of obtaining hybridized composites
which have higher strength properties. This will be discussed later in the study.
2.3.1 Manufacturing comparison of hemp reinforced and E-glass reinforced composite:
As discussed previously, the manufacture of hemp reinforced composites involves either
injection moulding or compression moulding, depending on the application and grade of
product needed. The manufacture of E-glass essentially involves the heating of silica (SiO2)
sand at high temperature, and then rapidly cooling to form crystalized quartz [7]. Glass is then
produced by careful regulation of the heating/cooling processes. The overall process is broken
down into five steps [7]:
• Batching: The process of weighing the exact quantities of raw materials needed.
• Melting: The batched materials are then sent to a gas-powered furnace operating at high
temperatures. The temperature range of the furnace is approximately 1400° C.
• Fiber formation: The formation of glass fibers involves the process of extrusion and
attenuation. In the extrusion process, the molten glass is cooled down by water jets as
they exit the furnace
• Coating: This is where a chemical coating is added to the plates. The coating may
include lubricants or coupling agents, which help with protecting the filaments from
breaking.
• Packaging: The produced filaments are then coupled into large bundles which form a
glass strand consisting of a large number of filaments.
Due to the processing of glass fiber involves a number of intricate steps, the cycle time of
manufacture is higher than that of manufacturing natural fibers [7]. There are also various
drawbacks to this manufacturing method. During the melting process, the melting and moving
of the glass damages the furnace which results in a shorter service life and proper maintenance
[7]. In terms of cost, the glass filament plates are expensive, and their shapes are imperative to
the fiber formation process. The temperature range at which the manufacture of natural fiber
operates is much lower than that of glass fiber manufacture [3] (150°-220° C as opposed to
1400° C). With abundance of materials, lower cost of manufacture, and less maintenance, the
manufacture of natural fibers is more advantageous than that of glass fiber. But in terms of cost
effectiveness, the widespread usage of petroleum-based fiber reinforced composites are still
preferred because obtaining the raw materials for natural-fiber composites are still more
expensive overall than synthetic raw materials. This is because of the low volume of production
rather than the cost of the raw materials themselves [4].

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2.4 Sustainability of natural-fiber (hemp) reinforced composites:
The abundance of plastics in the environment, the depletion of fossil fuels and petroleum
resources, increased carbon dioxide emission, and growing concerns for the environment all
over the world has led to increased research on finding bio-degradable and sustainable
alternatives to synthetic fiber composites [4]. The most accepted definition of sustainability is:
A sustainable product would meet the needs of the present without compromising the needs of
future generations. Sources of natural fiber materials largely meet the definition of
sustainability as their plant cellulose can be easily replaced by booming agriculture. There are
other factors which determine whether a material is sustainable. These include cost
effectiveness, profitability, life cycle assessment, the energy consumed, and its recyclability
[4].
It should be noted that the research on development of bio-degradable natural composites have
only started since the last two decades, while synthetic composites have been around for
centuries. Therefore, there is lot of scope for developing suitable bio-degradable raw materials
in the future which can provide the same strength properties as that of glass fibers. Currently,
since the natural fibers made from cellulose/starch are bio-degradable, but the common
thermosets and thermoplastics are non-biodegradable, bio-composites are thus classified as
partially bio-degradable.
2.4.1 Application of natural-fiber (hemp) reinforced composites:
The following figure presents the schematics of the interconnection between the development
and application of natural-fiber composite materials.
Figure 2: Schmatics [4]

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It can be seen that in order for natural-fibers to fully replace synthetic fibers, it must
showcase or exceed the structural and functional stability of the synthetic fibers [4], whilst
demonstrating no adverse environmental impact and withstand degradation. It is currently not
possible to compete economically with petroleum-based fibers, hence further refinement and
research is required before natural-fibers are more widely accepted.
2.4.2 Carbon offsetting and environmental impact:
The life-cycle of biodegradable polymer composites can help maintain the CO2 balance in the
environment, thus greatly reducing emissions. Other environmental benefits of bio-degradable
polymer usage include, complete biological degradation, preservation of materials based on
fossil fuels, waste disposal solutions, and recyclability. Furthermore, the rise in oil prices
helped to pique interest in the development of natural resources. Figure 3 shows the cycle of
natural polymers that offsets and maintains the atmospheric composition of Carbon dioxide in
the atmosphere [4].
It can be seen from the figure that using natural resources for composite manufacture can help
maintain CO2 composition. Once the composites or excess materials have been discarded, they
then help produce water and carbon dioxide after degradation for plants to then
photosynthesize. The raw resources are then used for the production of polymers, thus
restarting the cycle.

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2.5 Future prospects for natural-fiber reinforced composites:
The use of polymer composites from natural resources have a lot of criteria to meet if they are
to compete with synthetic fibers. As mentioned in the previous passages of this study, there are
a lot of drawbacks preventing natural-fiber reinforced composites from widespread use in the
automotive industry.
One of the most notable shortcomings is the low impact strength of the fibers. Structural
integrity is an important property of car bodies. But natural composites exhibit non-brittle
properties on impact, allowing for increased safety over glass fiber composites. During the
manufacturing process of natural composites, ensuring adequate moisture is present is also a
complex factor to consider. For them to be considered for high-volume applications, new and
developed biopolymer composites have to be used, with higher structural properties while
maintain current performance of carbon dioxide offsetting and biodegradability. For this
purpose, research has been ongoing for the development of hybridization techniques.
2.6 Hybridized synthetic/natural fiber-reinforced composites:
Hybridization involves the addition of extra fibers to the polymer matrix to increase the
mechanical properties of the composites [8]. This is achieved by two reasons, first, having
multiple fibers of the same length but different diameters allow for uniform transfer of stress
to take place by increasing the effective area of application [8]. And second, fibers with higher
elongation are able to carry the loads in case lower elongation fibers are broken, thus preventing
matrix failure. Hybridized composites thus allow for having composite structures with better
or equal mechanical properties than homogenous natural/synthetic fiber reinforced composites.
One type of fiber reinforced composites has been selected.
2.6.1 Synthetic/natural fiber-reinforced thermoplastic composites:
This hybrid composite is prepared by injection moulding with appropriate fractions of fibers.
It involves the intertwining of glass fibers with polypropylene. Through experiments [8], it has
been found that there has been increase in tensile strength and modulus intensity. The
mechanical properties are shown in the table.

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Table 4: Mechanical properties of hybrid composites [8]
Fibers Matrix Tensile strength Impact strength Manufacturing
method
Glass/hemp Polypropylene 388-390 2.2 Injection moulding
Glass/flax Polypropylene 388-390 2.1 Injection moulding
Carbon/Kevlar Bismalemie 200.5 12.25 Resin transfer
It can be seen that the properties of the hybrid composites have been drastically improved in
terms of the tensile strength natural fibers seen in Table 3.
3.0 Summary:
With increased world efforts and awareness about the adverse environmental impacts of using
fossil fuel based synthetic fibers for the automotive industry, there is massive scope for
research on refining natural based composite materials for application in the automotive
industry. The advantages of natural fibers over synthetic fibers have been discussed, such as
its low cost, high biodegradability, abundance, renewability, and ease of manufacture.
However, there are major disadvantages that are preventing it from widespread use and
replacing synthetic fibers. These disadvantages are far too major to overcome, such as the
relatively low impact strength of natural fiber composites, the maintenance required for
meeting specific conditions for proper manufacture, and the low volume production. To
address these problems, further research has been ongoing for the development of stronger
composites that are sustainable and biodegradable. One such solution discussed is
hybridization, which allows for the incorporation of both synthetic and natural fibers, albeit at
the cost of biodegradability, hence providing further refinement of the method of processing
newer biodegradable materials.
Sustainability played an important role for selecting natural fibers as an alternative to glass in
this study, and it has been shown that using natural based fibers such as hemp is a viable
solution with positive environmental impacts. Biodegradable natural fibers, despite its
shortcomings in strength, makeup for it by being fully sustainable, while maintaining the
carbon dioxide emission in the atmosphere.
With further research into producing viable natural fiber reinforced composites or hybrid
composites, over the next couple of decades natural fiber composites will have fully replaced
synthetic composites in the automotive industry, thus paving the way for a greener world.

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References:
[1] Google Books. (2019). Polymer Matrix Composites and Technology. [online] Available at:
https://books.google.com.au/books/about/Polymer_Matrix_Composites_and_Technology.ht
ml?id=uHhwAgAAQBAJ&printsec=frontcover&source=kp_read_button&redir_esc=y#v=on
epage&q&f=false [Accessed 8 Mar. 2019].
[2] Polymerjournals.com. (2019). [online] Available at:
http://www.polymerjournals.com/pdfdownload/1223113.pdf [Accessed 8 Mar. 2019].
[3] Link.springer.com. (2019). [online] Available at:
https://link.springer.com/content/pdf/10.1007%2Fs11837-006-0234-2.pdf [Accessed 8 Mar.
2019].
[4] Taylorfrancis.com. (2019). [online] Available at:
https://www.taylorfrancis.com/books/9780203508206 [Accessed 8 Mar. 2019].
[5] S. Grove, J. (2019). Manufacturing methods for natural fiber composites. Retrieved from
http://J. SUMMERSCALES
[6] (2019). Retrieved from https://www.cyut.edu.tw/~ijase/2016/14(3)/2_040015.pdf
[7] The making of glass fiber. (2019). Retrieved from
https://www.compositesworld.com/articles/the-making-of-glass-fiber
[8] Mechanical Properties of Hybrid Fibers-Reinforced Polymer Composite: A Review:
Polymer-Plastics Technology and Engineering: Vol 55, No 6. (2019). Retrieved from
https://www.tandfonline.com/doi/pdf/10.1080/03602559.2015.1098694?needAccess=true

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