Page 38 - Plastics News May 2018

FeAtures

Figure 3 Figure 4

(A) Storage modulus and (B) tan δ of the injection moulded flame
retarded non‐reinforced and self‐reinforced PP samples
The mechanical performance of the injection moulded
samples was characterized by standard tensile tests.

Heat release rate curves of injection moulded non‐reinforced and Typical stress-strain curves are presented in Figure 5.
self‐reinforced PP sheets The non-reinforced samples, after reaching the
ultimate tensile strength, elongated non-uniformly
3.3 Mechanical properties
with necking over the entire testing region (20-mm
The storage modulus and tanδ curves collected during cross-head displacement). Apparently, the FR loading
DMA analyses performed on the non-reinforced and did not affect the character of thestress-strain curves
self-reinforced ePP sheets are plotted in Figure 4. of the non-reinforced ePP samples. By contrast, failure
In Figure 4A, drastic fall of the storage modulus of the composites occurred due to significantly higher
curves of the examined samples can be observed deforming stresses, and without preceding necking.
around −20°C which is due to the glass transition At identical tensile stress, due to the presence of FR
of the ePP matrix material. It can be seen that particles, the 10% FR containing composite (SR_FR10)
below the glass transition temperature of the ePP elongated more than the additive-free self-reinforced
matrix, the stiffness of the additive-free and the composite (SR_PP). Rupture occurred around 30 MPa
10% FR containing composites exceeds significantly for both samples. At 15% FR loading, however, the SR-
that of the non-reinforced samples indicating high PPC (SR_FR15) barely exceeded 16 MPa tensile stress
reinforcement level of the embedded hPP fibres. In and fractured after relatively high deformation. It was
the case of the SR-PP_FR15 sample, however, the found that during tensile tests, the flame retarded
stiffening effect of the fibres does not prevail. Above composites elongated more than the additive-free
the glass transition temperature of the amorphous SR-PPCbecause the presence of FR particles at the
ePP, the storage modulus of the non-reinforced fibre-matrix interphase allowed the matrix to elongate
samples holds close to zero. In this region, the storage more freely. Nevertheless, at 20% FR loading in the
moduli of all the composites preserve much higher matrix (SR_FR10), the load-bearing capacity of the
values, which is due to the stiffening effect of the SR-PPC did not change noticeably, but the presence of
unmelted semicrystalline hPP fibre. By this means, 30% FR particles in the matrix (SR_FR15) already caused
the temperature range of applicability of the flame significant deterioration of the tensile strength.
retarded SR-PPCs is broadened compared with the The results of the tensile tests are shown in Figure 6A,B.
non-reinforced ePP samples. The analysis of the tanδ It can be seen that compared with the non-reinforced
curves (Figure 4B) reveals identical glass transition ePP, a 4-fold increase of the tensile strength and a 7-
temperature of −15°C for all the measured samples, fold increase of the tensile modulus were achieved by
but significant differences occur in the damping factor preparing short-fibre reinforced SR-PPCs. The achieved
values depending on fibre content.
noticeable improvement of the tensile properties is
significantly better than achieved earlier by injection

Plastics News May 2018 38