118
5
The processability of polymeric composites depends upon various
factors ranging from raw materials, coupling agents, additives present, processing method, mould design, processing parameters, surrounding environmental conditions, and post-fabrication handling.
Uniformity in the properties of raw materials is essential for the
desired processability of polymeric composites. It is quite common
in reinforcements that their mechanical properties diminish once
their useful life is expired. In glass fabrics, it is also seen that wet resin
does not stick to its surface, indicating the loss of the coupling agent
on glass fibres, thus making them hydrophilic [1, 2]. The presence of
additives influences the properties of thermosetting composites,
including curing of the matrix, interphase with the reinforcement,
etc. The right selection of the processing method and its parameters
aids in processability. Mould design and tooling too have an influence on the efficiency and quality of thermosetting composites being
manufactured. The surrounding environmental conditions (such as
humidity, dust, and temperature) have an influence on raw materials
and processing conditions. Handling a manufactured part requires
care so that further processing and finishing operations (such as
printing, embossing, metalizing, etc.) can be carried out.
These factors influence the processability of thermosetting composites, and the following sections delve into more details for a better insight on the processability of thermosetting composites.
5.1 Interface and Interphase in Thermosetting
Composites
Interface is the surface of the adherent (i.e. reinforcement or matrix)
that comes in contact with each other. The interphase is the continuous region of dissimilar composition between the reinforcement
and the matrix, thus bonding them. Interfacing is bonding the surface between the reinforcement and the matrix and across where a
discontinuity in some parameter occurs. Due to dissimilarity in the
surface properties of the reinforcement and the matrix, the region
between them forms the third phase in the composites, which is
called the interphase. An interphase is the region through which
material parameters (such as crystal structure, atomic structure,
tensile modulus, density, coefficient of thermal expansion, etc.)
change from one side to the other. The chemical composition of the
interphase is such that one end of interphase binds with the reinforcement and the other end binds with the matrix. One end of the
coupling agent makes a covalent bond with matrix, while the other
end forms a hydrogen bond with the inorganic reinforcement. The
hydrogen bond remains labile and does not break on experiencing
minor strains during a fibre-to-fibre load transfer through shear in
composites. In composites, a fibre-to-fibre load is transferred
through the matrix. Therefore, the matrix experiences shear force
during the load transfer. The classical theory of interphase advocates that the bond between the reinforcement and the matrix is
strong and rigid [3–5]. In such a situation, the interphase bond fails
on the slightest strain and, thus, causes failure of composites during
Chapter 5 · Processability of Thermosetting Composites
5
The processability of polymeric composites depends upon various
factors ranging from raw materials, coupling agents, additives present, processing method, mould design, processing parameters, surrounding environmental conditions, and post-fabrication handling.
Uniformity in the properties of raw materials is essential for the
desired processability of polymeric composites. It is quite common
in reinforcements that their mechanical properties diminish once
their useful life is expired. In glass fabrics, it is also seen that wet resin
does not stick to its surface, indicating the loss of the coupling agent
on glass fibres, thus making them hydrophilic [1, 2]. The presence of
additives influences the properties of thermosetting composites,
including curing of the matrix, interphase with the reinforcement,
etc. The right selection of the processing method and its parameters
aids in processability. Mould design and tooling too have an influence on the efficiency and quality of thermosetting composites being
manufactured. The surrounding environmental conditions (such as
humidity, dust, and temperature) have an influence on raw materials
and processing conditions. Handling a manufactured part requires
care so that further processing and finishing operations (such as
printing, embossing, metalizing, etc.) can be carried out.
These factors influence the processability of thermosetting composites, and the following sections delve into more details for a better insight on the processability of thermosetting composites.
5.1 Interface and Interphase in Thermosetting
Composites
Interface is the surface of the adherent (i.e. reinforcement or matrix)
that comes in contact with each other. The interphase is the continuous region of dissimilar composition between the reinforcement
and the matrix, thus bonding them. Interfacing is bonding the surface between the reinforcement and the matrix and across where a
discontinuity in some parameter occurs. Due to dissimilarity in the
surface properties of the reinforcement and the matrix, the region
between them forms the third phase in the composites, which is
called the interphase. An interphase is the region through which
material parameters (such as crystal structure, atomic structure,
tensile modulus, density, coefficient of thermal expansion, etc.)
change from one side to the other. The chemical composition of the
interphase is such that one end of interphase binds with the reinforcement and the other end binds with the matrix. One end of the
coupling agent makes a covalent bond with matrix, while the other
end forms a hydrogen bond with the inorganic reinforcement. The
hydrogen bond remains labile and does not break on experiencing
minor strains during a fibre-to-fibre load transfer through shear in
composites. In composites, a fibre-to-fibre load is transferred
through the matrix. Therefore, the matrix experiences shear force
during the load transfer. The classical theory of interphase advocates that the bond between the reinforcement and the matrix is
strong and rigid [3–5]. In such a situation, the interphase bond fails
on the slightest strain and, thus, causes failure of composites during
Chapter 5 · Processability of Thermosetting Composites