Page 40 - Plastics News May 2018

FeAtures

the prepared flame retarded SR-PPCs still outperforms that When considering all the examined mechanical
of a common polypropylene. As expected, high ductility characteristics of the prepared SR-PPCs, it can be
indices are accompanied with the plastic deformation of concluded that good balance between the strength,
the non-reinforced ePP samples, while decreased ductility stiffness, and impact resistance was reached as a result of
factors are characteristic for the SRPCs with more rigid combining high tenacity fibres with elastomer matrix. Up
rupture. to 10% FR content, the composites keep this advantageous
mechanical performance, but at 15% FR loading loss of
Figure 8
mechanical properties occurs. To further investigate the
change in the structure of the composites as a function of
increasing FR content, SEM micrographs were taken from
the fracture surfaces. During SEM observation (Figure 10),
prominent fibre-matrix adhesion was observed for all
SR-PPCs; the hPP fibres are properly impregnated by the
matrix material. It is also visible that the polar FR particles
are well dispersed in the ePP matrix. Nevertheless, when
exposed to tensile stress, the FR particles became easily
detached from the apolar matrix, and therefore as fault
locations decreased the tensile strength of the flame
retarded samples (see in Figure 6). Based on the SEM
Comparison of (A) perforation energy and (B) ductility factor of injection images, it became also obvious that in the SR-PP_FR15
moulded flame retarded non‐reinforced and self‐reinforced PP samples composite, the structure of the reinforcing hPP fibres got
Common Charpy impact tests could not be performed damaged during processing likely due to the increased
on the ePP-based samples because the elastomer-based thermo-mechanical and abrasive stress caused by the FR
specimens did not break during testing; therefore, tensile particles being present at 30 wt% in the matrix. At lower
impact test was performed to further characterize the FR loading (20 wt%) of the matrix (Figure 10B), however,
impact resistance. It can be seen in Figure 9 that the the hPP fibres seem to be intact. It is proposed that in the
tensile impact strength shows decreasing tendency with case of the SR-PP_FR15 composite, the high amount of FR
increasing FR content for both types of injection moulded particles causes significant changes in the shear forces and
samples. It is proposed that the FR particles function as thermal conditions during injection moulding, which result
defect location in the matrix and thereby decrease the in undesirable molecular relaxation, structural damage,
mechanical resistance. Considering the tensile impact and partial melting of the reinforcing hPP fibres during
strength results, the non-reinforced samples outperform processing and consequently in remarkable property loss
their self-reinforced counterparts because during failure of this composite.
plastic deformation absorbs more energy than fibre pull- Figure 10
out or breakage (see also in Figure 7).

Figure 9

SEM micrographs taken from the fracture surface of (A) SR‐PP, (B)
SR‐PP_FR10, and (C) SR‐PP_FR15 samples

Comparison of the tensile impact strength (notched) of injection
moulded flame retarded non‐reinforced and self‐reinforced PP samples

Plastics News May 2018 40