Sandwich composites from waste polyolefins and plant fibres

Wanda Meissner, Ryszard Steller, Grażyna Kędziora Politechnika Wrocławska, Wydział Chemiczny, Zakład Inżynierii i Technologii Polimerów, ul. Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland

Quarterly No. 3, 2007 pages 135-139

DOI:

keywords: polyethylene, polypropylene, foaming, properties

article version pdf (0.18MB)

abstract Some problems connected with preparation and properties of sandwich composites based on waste low density poly¬ethylene and polypropylene with addition of bromine flame retardants in amount od 810% are presented. The composites consist of internal layer (core) created from PE-LD or PP and foamed with 24% of azodikarbonamide and of two external layers (claddings) created from the same polymers but filled with 1030% of short (4 mm) flax fibre. Layer compositions were prepared by means of two-roll-mill at temperatures below 175°C to prevent the flowing agent decomposition or fibre degradation. Compositions were pressure moulded at similar temperatures to obtain samples in form of plates of ca. 2 mm thickness, which were used for investigations and for preparation of sandwich composites. Core layer foaming (separately and in composites) was done by compression moulding at temperatures above 200°C. Physicochemical (density, water uptake), mechanical (tensile, flexural and creep tests), rheological (melt flow rate) and thermal (oxygen index, Vicat temperature) properties were measured. I was found that cladding density increases with increasing content of fibre in composition and the polypropylene core has a better foamability in comparison with polyethylene core. These factors affect in the similar way the densities of sandwich composites. Flowability (MFR) measurements performed only for the layer compositions have shown that MFR decreases if the fibre content in composition becomes higher. It was also found that foaming agent lowers MFR, which is probably due to polymer cross-linking caused by radicals from foaming agent decomposition (PE-LD) or very fine dispergation of gas phase (PP). Flexural tests for PE-LD show that at low fibre content in cladding the rigidity of composites decreases, and then it increases with higher fibre content. In tensile tests performed for PP composites surprisingly low tensile strengths for sandwich composites were measured. They are comparable with core strengths, which are ca. 10 times lower than the strengths of claddings. It can be a sign of very specific stress distribution in sandwich composites. Creep tests demonstrate that the composite compliance depends on loading direction with respect to layers that reflects the compo¬site anisotropy. Composites with higher fibre content have a lower compliance for both loading directions.