107
4
sates would cause the improper curing of the composite,
leading to delamination. In most of the processing technologies (such as compression moulding, injection moulding,
matched die moulding, etc.), pressure ensures good compaction and dimensional accuracies in composite products. In
injection moulding, the high injection pressure may cause
overpacking of the mould, leading to warpages and dimensional inaccuracies in the moulding [8]. In resin transfer
moulding (RTM), a vacuum and pressure cause wetting of the
reinforcement, leading to proper impregnation.
4. Raw Materials—The primary raw materials for composites are
reinforcement and matrix. The secondary raw materials are
additives—if needed. Reinforcement must have a hydrophobic
surface for its compatibility with resin. In case the reinforced is
quite old and has not been kept under proper storage conditions, the coating of the coupling agent gets eroded. For
example, if glass fibre is kept under high humid conditions, the
coupling agent over it gets eroded. This could be experimentally observed by smearing a layer of resin over it using a paint
brush, and it could be observed that the resin gets collected in
patches without adhering to the surface of glass fibre evenly.
Therefore, proper storage and handling will keep the reinforcement good for use. Similarly, the storage temperature and
humidity for resin is important. The resin gets little crosslinked during a prolonged period of storage at ambient or high
temperatures so that small lumps of resin may be seen in the
storage drum. All of this occurs due to the advancement of a
reaction, and the main cause for this advancement is an
incorrect storage temperature followed by exposure to atmospheric air and moisture. The wrong temperature leads to an
increase in viscosity over a period of time, and high viscosity
and the formation of lumps do not allow the resin to flow and
percolate as discussed.
The role of an additive is also important in polymer
processing. Additives either impart required properties or
facilitate the polymer processing. Additives, such as particulate
reinforcements (i.e. reinforcing carbon black, nanoparticles,
etc.), improve the mechanical, thermal, and electrical properties of composites, whereas additives, such as diluents, lower
the viscosity of highly viscous resins with some compromise to
the overall properties of the composites [9].
4.6 Influence of Rheology on Composite
Products
The effect of rheology on the quality and properties of polymeric
composites has been generally described in the previous sections.
Rheology is responsible for the flow of the matrix in the polymeric
composite and also the movement of the additives and fillers that it
carries. Therefore, rheology influences the final properties of poly4.6 · Influence of Rheology on Composite Products
4
sates would cause the improper curing of the composite,
leading to delamination. In most of the processing technologies (such as compression moulding, injection moulding,
matched die moulding, etc.), pressure ensures good compaction and dimensional accuracies in composite products. In
injection moulding, the high injection pressure may cause
overpacking of the mould, leading to warpages and dimensional inaccuracies in the moulding [8]. In resin transfer
moulding (RTM), a vacuum and pressure cause wetting of the
reinforcement, leading to proper impregnation.
4. Raw Materials—The primary raw materials for composites are
reinforcement and matrix. The secondary raw materials are
additives—if needed. Reinforcement must have a hydrophobic
surface for its compatibility with resin. In case the reinforced is
quite old and has not been kept under proper storage conditions, the coating of the coupling agent gets eroded. For
example, if glass fibre is kept under high humid conditions, the
coupling agent over it gets eroded. This could be experimentally observed by smearing a layer of resin over it using a paint
brush, and it could be observed that the resin gets collected in
patches without adhering to the surface of glass fibre evenly.
Therefore, proper storage and handling will keep the reinforcement good for use. Similarly, the storage temperature and
humidity for resin is important. The resin gets little crosslinked during a prolonged period of storage at ambient or high
temperatures so that small lumps of resin may be seen in the
storage drum. All of this occurs due to the advancement of a
reaction, and the main cause for this advancement is an
incorrect storage temperature followed by exposure to atmospheric air and moisture. The wrong temperature leads to an
increase in viscosity over a period of time, and high viscosity
and the formation of lumps do not allow the resin to flow and
percolate as discussed.
The role of an additive is also important in polymer
processing. Additives either impart required properties or
facilitate the polymer processing. Additives, such as particulate
reinforcements (i.e. reinforcing carbon black, nanoparticles,
etc.), improve the mechanical, thermal, and electrical properties of composites, whereas additives, such as diluents, lower
the viscosity of highly viscous resins with some compromise to
the overall properties of the composites [9].
4.6 Influence of Rheology on Composite
Products
The effect of rheology on the quality and properties of polymeric
composites has been generally described in the previous sections.
Rheology is responsible for the flow of the matrix in the polymeric
composite and also the movement of the additives and fillers that it
carries. Therefore, rheology influences the final properties of poly4.6 · Influence of Rheology on Composite Products