Abstract:
Short fibre
reinforced thermoplastic pipe was
produced by an extrusion process which oriented the fibre
reinforcement
predominantly into the pipe hoop direction.
The fibre reinforcement was
thereby used to maximise the
internal
pressure resistance and resistance to crack
propagation of the pipe in the axial direction.
Careful selection of materials and
development of
a suitable
compounding method enabled polyethylene, glass
fibres and a
coupling agent to be combined such that fibre
length retention and effective coupling gave worthwhile
improvements in the physical properties over the
polyethylene matrix polymer.
Extrusion
configurations developed were based
upon the use of motionless dies having a diverging mandrel,
and other
methods, to bring about melt hoop expansion. Die
geometry was varied to assess the influence of such factors
as melt
expansion ratio, divergence angle and die land
length.
_ Study of the complex fibre orientation
distribution
produced during extrusion and the die geometry
variables has
led, with the application of the classical
particle rotation theory proposed by Jeffrey, to the
development of predictive computer software for different
die
configurations. Predictions have been found
to
agree qualitatively with measured fibre orientation '
distributions in
pipes.
Physical testing has enabled characterisation of
a
range of pipes produced under different conditions having
different levels of fibre reinforcement and with different
fibre orientation distributions.
