Page 37 - Plastics News May 2018

FEATURES
FeAtures

expected increasing rate (the FR additive has higher to the beneficial effect of the presence of highly
density than the ePP). This tendency is the same for the oriented hPP fibres, in accordance with our earlier
non-reinforced and reinforced samples; therefore, it was findings.14, 15, 18 However, it has to be declared that
concluded that the difference between the measured the contribution of the short hPP fibres to the synergism
and theoretical densities is not the consequence of with the IFR system is almost negligible compared with
the void fraction between the fibres19 but more likely the winded hPP yarns or woven fabrics composed of
of the detachment of the polar FR particles from the highly stretched filaments.
apolar polymer matrix. The relative density of the SR- Table 3. Comparison of the UL94 classifications and LOI
PPCs is practically identical with their non-reinforced values of injection moulded ePP sheets and SR-PPCs
counterparts indicating that in all the composites the
fibres are properly impregnated by the matrix material. Sample UL94 [rating] LOI [v/v%]
Table 2. Relative density of the injection moulded ePP HBa (4.4) 18
specimens ePP_FR10 HBa (2.8) 24
ePP_FR15 V-2b(0/5) 29.5
Sample Relative density [%]
SR-PP HBa (3.5) 18
ePP 99.8
ePP_FR10 96.5 SR-PP_FR10 HBa (2.9) 24.5
ePP_FR15 95.1 SR-PP_FR15 V-2b (3/5) 29.5
SR-PP 99.7
a. In parenthesis, the flame spreading rates [mm/min]
SR-PP_FR10 96.6 are indicated.
SR-PP_FR15 95.4 b. In parenthesis, the proportion of self-extinguishing
3.2 Flammability characteristics specimens (with respect to the 5 tested specimens)
is indicated.
It was proposed earlier18 that the type (organic,
inorganic, char-forming, or non-char forming polymer) The burning behaviour of the injection moulded SR-
and structure (degree of molecular orientation, fibre PPCs was compared with non-reinforced ePP sheets
alignment, weave type) of reinforcement have particular also using cone calorimeter tests. The obtained heat
effect on the effectiveness of an intumescent FR system release rate (HRR) curves are presented in Figure 3.
in SR-PPCs. In this work, this phenomenon is further It can be seen that the HRR curves of the 2 types of
investigated using a new structure, ie, in disordered, samples are very similar. The increment of FR loading
short fibre reinforced SR-PPCs. from 10% to 15% resulted more in time shift than in
moderation of HRR values; approximately 35% to 40%
The UL94 and LOI flammability test results of the 2 reduction of peak of heat release rate (pkHRR) was
types of flame retarded injection moulded sheets are reached compared with the additive-free references in
summarized in Table 3. The additive-free samples are both cases. Nevertheless, each composite outperformed
inherently highly flammable; HB rating according to the its non-reinforced counterpart of same FR contents;
UL94 standard and a LOI of 18 v/v% were determined however, the degrees of pkHRR reductions are not
for both types of samples. With FR addition, the remarkable. Based on these results, it was concluded
flammability properties could be significantly improved. that the incorporation of conventional FR additives in
At 15% FR loading, V-2 rating and noticeably increased the matrix of injection moulded SR-PPCs has roughly
LOI of 29.5 v/v% were reached. No significant difference the same effect on the flammability properties as in
could be evinced between the flammability behaviour non-reinforced PP compounds. In contrast to continuous
of the non-reinforced and the self-reinforced samples hPP fibres or woven fabrics,18 randomly aligned, short
of identical FR contents. Slightly better FR performance hPP fibres do not influence noticeably the foam forming
was observed for the composites during vertical burning process and the combustion behaviour of an intumescent
tests; some of the 15 wt% FR containing specimens flame retarded PP system.
showed self-extinguishing behaviour even after the
second 10-second long ignition, which could be ascribed

37 May 2018 Plastics News