Page 345 - Plastics Engineering

328 Processing of Plastics

thermoplastics to try to overcome these problems. One approach has been to
produce continuous fibre tapes or mats which can be embedded in a thermo-
plastic matrix. The best known materials of this type are the Aromatic Polymer
Composites (APC) and the glass mat reinforced thermoplastics (GMT). One
of the most interesting of these consists of unidirectional carbon fibres in a
matrix of polyetheretherketone (PEEK). The material comes in the form of a
wide tape which may be arranged in layers in one half of a mould to align the
unidirectional fibres in the desired directions. The assembly is then pressurised
between the two matched halves of the heated mould. The result is a laminated
thermoplastic composite containing continuous fibres aligned to give maximum
strength and stiffness in the desired directions.
Another recent development has been the arrival of special injection
moulding grades of thermoplastics containing long fibres. At the granule
production stage the thermoplastic lace contains continuous fibres and to
achieve this it is produced by pultrusion (see Section 4.10.3) rather than the
conventional compounding extruder. The result is that the granules contain
fibres of the same length as the granule (210 mm).
These long fibres give better product performance although injection
moulding machine modifications may be necessary to prevent fibre damage
and reduce undesirable fibre orientation effects in the mould.

4.10 Processing Reinforced Thermosets
There is a variety of ways in which fibre reinforcement may be introduced into
thermosetting materials and as a result there is a range of different methods
used to process these materials. In many cases the reinforcement is intro-
duced during the fabrication process so that its extent can be controlled by
the moulder. Before looking at the possible manufacturing methods for fibre
reinforced thermosetting articles it is worth considering the semantics of fibre
technology. Because of their fibre form, reinforcing materials have borrowed
some of their terminology from the textile industry.
Filament This is a single fibre which is continuous or at least very long
compared with its diameter.

Yarn or Roving Continuous bundle of filaments generally fewer than 10,OOO
in number.

Tow A large bundle of fibres generally 10,OOO or more, not twisted.

Fabric, Cloth or Mat Woven strands of filament. The weave pattern used
depends on the flexibility and balance of strength properties required in the
warp and fill directions. Fig. 4.65 shows a plain weave in which the strength is
uniform in both directions. The warp direction refers to the direction parallel to