145
5
v Answer
During World War II, flax fibre-reinforced phenolic resin was
used to manufacture fuselages of fighter aircraft. Natural
fibres were first used by Henry Ford in automobiles when he
used hemp fibre-reinforced composites in 1942. Presently,
most German cars use natural fibre-reinforced composites
for boot linings, back door panels, back seat fittings, dash
boards, etc. Natural fibre composites are mostly used in the
automotive industry. Presently, BMW cars use 8–13 Kg
natural fibre-reinforced composites per vehicle, and Ford
cars use 5–13 Kg natural fibre-reinforced composites per
vehicle.
The use of biodegradable fillers (such as starch, wood flour, etc.)
in conventional thermoplastic or thermosetting matrices
increases the scope of biodegradable matrices. It is to be noted
that the bulk of natural fibres is quite high, and this makes their
weight percentage in the composite quite low. The processability
of thermosetting green composites is governed by the following
factors:
5 Interphase in the Composite—The hydrophilic nature of natural
fibres restricts their wetting by hydrophobic polymeric
matrices. This may limit the bond strength, resulting in poor
composite properties. In order to make natural fibres processable with polymeric matrices, it is essential that they are chemically treated in order to attach chemical groups on the fibre
surface as potential sites for bonding with the polymeric
matrix. Generally, natural fibres are treated with weak acids –
(—COOH, —CO, —CHO, etc.) to make attachments onto
their surface.
5 Hygroscopic Nature of Natural Fibres—The hygroscopic
nature of natural fibres may lead to imperfections of the
morphology after moulding or to dimensional inaccuracies
of the composite being developed. Adequate drying of the
natural fibres is needed before processing their composites.
The ingress of moisture in the composite also will reduce its
properties.
5 Low Strength—Low strength of natural fibres restricts their
processability using either filament winding, tape layup, or
pultrusion methods.
5 Use of High-Temperature Matrices—Due to the low thermal
stability of natural fibres, their processability as reinforcement
in high-temperature matrices (such as PEI, PEEK, polyimides,
etc.) is not feasible.
5 Service Environments—Service environments having high
temperatures or a high moisture content are not suitable for
natural fibre-reinforced polymeric composites.
5 Safety—The processability of these composites does not
cause any health hazard because the natural fibres are not
toxic.
5.5 · Processability of Thermosetting ‘Green Composites’
5
v Answer
During World War II, flax fibre-reinforced phenolic resin was
used to manufacture fuselages of fighter aircraft. Natural
fibres were first used by Henry Ford in automobiles when he
used hemp fibre-reinforced composites in 1942. Presently,
most German cars use natural fibre-reinforced composites
for boot linings, back door panels, back seat fittings, dash
boards, etc. Natural fibre composites are mostly used in the
automotive industry. Presently, BMW cars use 8–13 Kg
natural fibre-reinforced composites per vehicle, and Ford
cars use 5–13 Kg natural fibre-reinforced composites per
vehicle.
The use of biodegradable fillers (such as starch, wood flour, etc.)
in conventional thermoplastic or thermosetting matrices
increases the scope of biodegradable matrices. It is to be noted
that the bulk of natural fibres is quite high, and this makes their
weight percentage in the composite quite low. The processability
of thermosetting green composites is governed by the following
factors:
5 Interphase in the Composite—The hydrophilic nature of natural
fibres restricts their wetting by hydrophobic polymeric
matrices. This may limit the bond strength, resulting in poor
composite properties. In order to make natural fibres processable with polymeric matrices, it is essential that they are chemically treated in order to attach chemical groups on the fibre
surface as potential sites for bonding with the polymeric
matrix. Generally, natural fibres are treated with weak acids –
(—COOH, —CO, —CHO, etc.) to make attachments onto
their surface.
5 Hygroscopic Nature of Natural Fibres—The hygroscopic
nature of natural fibres may lead to imperfections of the
morphology after moulding or to dimensional inaccuracies
of the composite being developed. Adequate drying of the
natural fibres is needed before processing their composites.
The ingress of moisture in the composite also will reduce its
properties.
5 Low Strength—Low strength of natural fibres restricts their
processability using either filament winding, tape layup, or
pultrusion methods.
5 Use of High-Temperature Matrices—Due to the low thermal
stability of natural fibres, their processability as reinforcement
in high-temperature matrices (such as PEI, PEEK, polyimides,
etc.) is not feasible.
5 Service Environments—Service environments having high
temperatures or a high moisture content are not suitable for
natural fibre-reinforced polymeric composites.
5 Safety—The processability of these composites does not
cause any health hazard because the natural fibres are not
toxic.
5.5 · Processability of Thermosetting ‘Green Composites’