Page 39 - Plastics News May 2018

FeAtures
FEATURES

moulding technology using co-extruded composite As with increasing stiffness, the impact resistance usually
pellets or bicomponent PP fibres as raw materials.7, 8 deteriorates; it is important to investigate this property
of the SR-PPCs with increased modulus. The impact
Figure 5
resistance of the injection moulded ePP and SR-PPC sheets
was compared using instrumented falling weight impact
tests. Based on the fractograms of Figure 7, it can be seen
that in the case of the non-reinforced samples, plastic
deformation dominates, and failure of the specimens
occurs under quasi-constant energy absorption, typically
with disruption. By contrast, in the case of the composites,
the impact load increases linearly with time until fracture
and the triangle-shape fractogram indicates rather rigid
behaviour. After fracture initialization, a slight plastic
zone can also be observed, likely due to the disruption
of the elastomer matrix. Failure of composites occurs
typically within 8 ms compared with the 14 ms of the
non-reinforced plates. The adverse consequences of the
fibre damage of the 15% FR containing composite are also
Comparison of the stress‐strain curves of injection moulded flame visible based on this test, and failure of the SR-PP_FR15
retarded non‐reinforced and self‐reinforced PP samples composite occurs at significantly lower impact load than

In our system, the homopolymer fibres did not aggregate the other self-reinforced composites.
and could maintain their mechanical performance during Figure 7
processing and thus serve as adequate reinforcement in
the composite. Furthermore, suitable adhesion could be
formed between the hPP fibres and the ePP matrix even
when 10% FR was added. The 15% FR containing composite,
however, showed weaker mechanical performance, and
its tensile strength deteriorated by 50% and tensile
modulus by 15%, respectively, compared with the SR-PPC
of lower FR content, likely due to the structural damage
of the reinforcing fibres occurred during the composite
preparation and thermo-mechanical processing.

Figure 6

Comparison of the impact load‐time curves of injection moulded
flame retarded non‐reinforced and self‐reinforced PP samples
The calculated perforation energy and ductility index
values are shown in Figure 8A,B, respectively. It can be
seen that the perforation energy of the composites is
Comparison of the (A) tensile strength and (B) tensile modulus of approximately 50% of that of the non-reinforced samples;
injection moulded flame retarded non‐reinforced and self‐reinforced furthermore, the 15% FR containing composite reached
PP samples only 30% of the perforation energy of the ePP sample of
identical FR content. The impact damping capability of

39 May 2018 Plastics News