Page 34 - Plastics News May 2018

FeAtures

researchers also drew attention to the advantages of using focus of our interest. Furthermore, we expected that
organic10and inorganic11-13 fibres and fillers in SRPCs, but based on the example of FR loading, important conclusions
the feasibility of such hybrid composite preparation with could also be drawn regarding the feasibility of loading
the injection moulding technology was not yet studied. injection moulded SR-PPCs with other commonly used
fillers, reinforcements, and other solid particles.
SRPCs have found mainly applications in transportation
and electronics fields, where fire hazard is an issue. 2 MATERIALS AND METHODS
Although the application of SRPCs, made entirely of
highly flammable components, is accompanied with a 2.1 Materials
high fire-risk, until recently no research were conducted As matrix material, polypropylene-based thermoplastic
towards their flame retardation. Our pioneering activity elastomer (ePP) (Versify 4200, Dow Chemical Company)
in the field of intumescent flame-retarded self-reinforced was selected. This matrix was characterised in our
polypropylene composites (SR-PPCs) resulted in some previous work.9 As reinforcement, highly oriented
relevant progress; furthermore, a completely new flame polypropylene homopolymer (hPP) multifilament (Stradom
retardant (FR) mechanism was proposed.14, 15 It was S.A., Czestochowa, Poland) was used. This reinforcing hPP
found that in intumescent flame retarded SR-PPCs, when multifilament has a linear density of 7.2 g/den, melting
exposed to intense heat, the synergistic coincidence of temperature of 173.0°C (determined by DSC), single fibre
expansion (foaming), induced by the intumescent FR diameter of 40.1 ± 1.8 μm, tensile strength of 581 ± 30 MPa,
(IFR), and shrinking (relaxation) of the high tenacity and tensile modulus of 6432 ± 490 MPa (measured in single
reinforcing fibres results in a unique heat protecting layer fibre tensile tests). Exolit AP766 (received from Clariant
of extraordinary fire extinguishing efficiency. This novel, International AG, Muttenz, Switzerland), a combined
physical interaction-based FR synergism was successfully ammonium polyphosphate and charring agent containing
utilized in recycled SRPCs, made entirely of secondary IFR additive, was used as FR agent.
polyolefins,16 and also in biodegradable self-reinforced 2.2 Composite preparation
poly (lactic acid) composites.17 It was evinced that the
formation and efficiency of the special surface protecting The fibre reinforced composite sheets were manufactured
layer are influenced by the structure of reinforcement (ie, according to a multi-step procedure. The fibre containing
weave type), fibre alignment, and degree of molecular granules, suitable for injection moulding, were obtained
orientation of the reinforcing fibres. Best FR performance by cutting the unidirectionally reinforced SR-PPCs
was found in SR-PPCs reinforced with unidirectional prepared by film stacking of flame retarded matrix foils
fibres. These composites, when prepared at optimum and reinforcing polypropylene fibres. The details of
consolidation temperature, pass UL94 V-0 rating with preparation are as follows: First, 0, 20, and 30 wt% FR
additive content as little as 7.2 wt%, one third of the additive (Exolit AP 766) was melt-compounded with the
amount needed in non-reinforced polypropylene matrix.18 neat ePP matrix material from which 50-μm-thick films
were manufactured by Labtech LCR300 cast-film extrusion
In this work, we had a dual purpose. On the one hand, our line (Labtech Engineering Co. Ltd. Samutprakarn,
aim was to manufacture injection mouldable SR-PPCs in Thailand) (screw rotation speed: 22 1/min; extruder
flame retarded form and to investigate the presence of temperature profile from feed zone to die: 205, 205, 215,
synergism, evinced earlier both in primary and recycled 215, and 215°C, temperature of coat-hanger die: 235, 230,
film-stacked SR-PPCs. In contrast to the unidirectional and 235°C; winding speed: 10 1/min). Additive-free and
or bidirectional plain-woven fabric reinforcement (used flame retarded consolidated SR-PPC sheets with 50 wt%
in multi-layered composite structures), the injection nominal reinforcement content and unidirectional (UD)
moulded composites comprise the reinforcing polymer fibre direction were manufactured by filament winding
fibres in short and randomly aligned form. This difference followed by film-stacking method and compression
was expected to have significant influence on the moulding process. Actually, the processing window was
cooperation of the expanding (intumescent FR) and the 90°C. The filament-wound, film-stacked packages were
shrinking (oriented fibres) domains. On the other hand, the inserted in between the preheated moulds to 140°C and
investigation of the effect of ammonium-polyphosphate held for 240 seconds without pressure, then compressed
based FR particles on the morphology and mechanical for 480 seconds under a pressure of 5.26 MPa and finally
performance of the injection moulded SR-PPC was in the
cooled to 45°C (under pressure). The thickness of the

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