TEMPERATURE AND STRAIN RATE DEPENDANT MECHANICAL BEHAVIOUR OF ALL-PP COMPOSITES-COMPARISON WITH GMT AND NMT

Polypropylenes reinforced with oriented polypropylene fibres, so-called “all-PP” composites, have specific economic and ecological advantages over composites based on glass fibres since, upon recycling a PP-blend is obtained that can be reused to make all-PP composites or can be used for other PP-based applications. Although static properties of all-PP composites at room temperature can compete with those of traditional composites (i.e. glass-fibre-reinforced PP and natural-fibre-reinforced PP), due to the highly viscoelastic character of PP, their mechanical behaviour will strongly depend on temperature and strain rate. This influence on tensile modulus and strength of all-PP tapes and composites is investigated. For the later, the same influence is investigated on the energy absorption capacity using full penetrating dart-impact tests. Similar trends on the influence of strain rate and temperature are observed of both tapes and composites revealing similarities in the failure mode. For comparison reasons, the mechanical response of these newly developed all-PP composites is compared with that of glass-mat-reinforced thermoplastics and natural-fibre-mat-reinforced thermoplastics, over a wide temperature range. The tensile strength and the impact energy of all-PP composites is superior for the whole range of temperatures tested (-40°C to 140°C), while the stiffness is higher for temperatures as high as 40°C. At higher temperatures glass-fibre-reinforced PP shows higher stiffness while natural-fibre-reinforced PP are inferior for the whole range of tested temperatures.

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