162
6
etc.) are resistant to high temperatures. In thermoplastic
matrices, T g is different from the melting and processing
temperatures, as explained in 7 Chap. 1. T g is much lower
than the melting temperature (T m ), and the melting
temperature is lower than the processing temperature (T p ),
i.e. T g < T m < T p .
5 Hygrothermal Stability—The hygrothermal stability of
thermoplastic resins is good. Ester-based thermoplastics
and amides (such as nylon) are susceptible to moisture
absorption. Polyolefins and high-temperature polymers
(PEEK, PEI, PPS, etc.) offer good resistance to moisture.
5 Post-Processing Operation—Post-processing operations are
minimal in thermoplastic composites. Embossing and
engraving are easily done on the surface of thermoplastic
matrices due to their melting characteristic. The reactivity of
the surface of thermoplastic composites makes it compatible
to printing too.
5 UV Resistance—Exposure of thermoplastic composite
products has been a major criteria for the selection of a
thermoplastic matrix. UV radiation from 290 to 400 nm
is detrimental to thermoplastic matrices—specifically
polyolefins. Ester-based thermoplastics (polymethyl
methacrylate (PMMA), polycarbonates, etc.) are inherently resistant to UV radiations. The mechanism for UV
resistance for ester-based thermoplastics is the
absorbance of UV radiation and the dissipation of UV
energy as heat energy through the oscillation of a
double bond between –C = O and –O, as explained in
7 Chap. 5.
5 Fire Resistance—Fire resistance has been a criterion for the
selection of a thermoplastic matrix. Polyvinyl chloride
(PVC) is inherently fire-resistant due to the presence of a
chloride group. Apart from PVC, all thermoplastics containing an ether group (–O–) are fire-resistant. In cases where
fire resistance is a must, bismuth oxides or antimony oxides
are added to improve fire resistance.
2. Processing Technology Driven by a Selection Criteria
5 Compatibility with the Form of Resin—Thermoplastic resins
are available in three forms: granules, films, and sheets. They
are always in solid form; therefore, their processing requires
external pressure—apart from heat—for compaction of the
composite. Granules are used to make injection-moulded
composite parts. Granules are available with different
percentages of reinforcements of glass fibres, carbon fibres,
etc. Films and sheets are primarily used for the fabrication of
composites using a compression moulding process.
5 Flow of a Matrix—The flow of a matrix is important for the
percolation of the matrix and good flow is required for the
injection moulding process. Flow requirements are dependent on the type of processing technology used and are also
related to the mould design.
Point to Ponder…
Polycarbonates are used in
headlamp covers for automobiles
due to their transparency,
high-impact strength, and UV
resistance. Polyester films are used
for making signages and displays
for outdoor advertisements due to
their UV resistance.
Chapter 6 · Processability of Thermoplastic Composites
6
etc.) are resistant to high temperatures. In thermoplastic
matrices, T g is different from the melting and processing
temperatures, as explained in 7 Chap. 1. T g is much lower
than the melting temperature (T m ), and the melting
temperature is lower than the processing temperature (T p ),
i.e. T g < T m < T p .
5 Hygrothermal Stability—The hygrothermal stability of
thermoplastic resins is good. Ester-based thermoplastics
and amides (such as nylon) are susceptible to moisture
absorption. Polyolefins and high-temperature polymers
(PEEK, PEI, PPS, etc.) offer good resistance to moisture.
5 Post-Processing Operation—Post-processing operations are
minimal in thermoplastic composites. Embossing and
engraving are easily done on the surface of thermoplastic
matrices due to their melting characteristic. The reactivity of
the surface of thermoplastic composites makes it compatible
to printing too.
5 UV Resistance—Exposure of thermoplastic composite
products has been a major criteria for the selection of a
thermoplastic matrix. UV radiation from 290 to 400 nm
is detrimental to thermoplastic matrices—specifically
polyolefins. Ester-based thermoplastics (polymethyl
methacrylate (PMMA), polycarbonates, etc.) are inherently resistant to UV radiations. The mechanism for UV
resistance for ester-based thermoplastics is the
absorbance of UV radiation and the dissipation of UV
energy as heat energy through the oscillation of a
double bond between –C = O and –O, as explained in
7 Chap. 5.
5 Fire Resistance—Fire resistance has been a criterion for the
selection of a thermoplastic matrix. Polyvinyl chloride
(PVC) is inherently fire-resistant due to the presence of a
chloride group. Apart from PVC, all thermoplastics containing an ether group (–O–) are fire-resistant. In cases where
fire resistance is a must, bismuth oxides or antimony oxides
are added to improve fire resistance.
2. Processing Technology Driven by a Selection Criteria
5 Compatibility with the Form of Resin—Thermoplastic resins
are available in three forms: granules, films, and sheets. They
are always in solid form; therefore, their processing requires
external pressure—apart from heat—for compaction of the
composite. Granules are used to make injection-moulded
composite parts. Granules are available with different
percentages of reinforcements of glass fibres, carbon fibres,
etc. Films and sheets are primarily used for the fabrication of
composites using a compression moulding process.
5 Flow of a Matrix—The flow of a matrix is important for the
percolation of the matrix and good flow is required for the
injection moulding process. Flow requirements are dependent on the type of processing technology used and are also
related to the mould design.
Point to Ponder…
Polycarbonates are used in
headlamp covers for automobiles
due to their transparency,
high-impact strength, and UV
resistance. Polyester films are used
for making signages and displays
for outdoor advertisements due to
their UV resistance.
Chapter 6 · Processability of Thermoplastic Composites