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Meccaniche Moderne S.p.A. has recently developed a new patented process for the low-cost production of composite sheets reinforced by long fibres.
(Published on May 2005 – JEC Magazine #17)
BY ALBERTO LORIOLI, SALES MANAGER, MECCANICHE MODERNE S.P.A.
The new process features a special singlescrew vacuum extruder equipped with an innovative mixing chamber where mineral fibres (such as glass and carbon), natural fibres (such as jute, hemp, long flax, kenaf, coconut fibres, sisal, wood fibres and saw dust), or synthetic fibres (such as PET) are easily blended in a molten matrix of extruded thermoplastic polymer (such as PP, PE, PET, PA and PC). The whole system is designed so that fibres are preserved intact and undamaged by heat. The extruded composite sheets are processed through suitable multi-roll calenders. Coating capabilities (films, woven fabrics or nonwovens) and/or coextrusion can be added. These are extremely flexible machines. A key advantage of the process is the high fibre-dispersion capability, which makes it possible to achieve high fibre contents.
The sheets produced can be up to 2,000mm wide, 0.5 to 5mm thick, and of virtually unlimited length. Fibre contents can reach 40% for mineral fibres and up to 70% for vegetable fibres, with fibre lengths up to 20mm. In terms of mechanical strength, the elastic modulus of the sheets can be up to three times that of thermoplastic-matrix polymers, ensuring high impact resistance. Extrusion capacity is up to 1,000kg/h.
The process can be used to produce impact resistant, fully recyclable parts for the automotive, nautical and aeronautical industries; technical components for the building sector (especially wall panels and corrugated roofing products matching structural strength, fire performance and atmospheric/UV resistance standards); and components for the furnishing industry (such as composite panels containing up to 70% vegetable fibres).
Meccaniche Moderne’s lines can produce four different solutions for the automotive-door segment, including one four-layer solution that offers remarkable impact resistance. The first layer is a sheet made with PP and properly ground recycled production scrap (mainly from edge trimming). The second and third layers are woven fabrics (e.g. flax), PET needle-punched spunbonded nonwovens (240g/m2 each layer), or needle-punched nonwoven fabrics made with natural fibres such as kenaf or jute, and coated on both faces of the first sheet. Finally, the fourth layer is a 150-mm-thick, coextruded adhesive film made with PP-PE copolymer, reinforcing the second layer. Total thickness is typically around 2.2mm.