Processing of all-polypropylene composites for ultimate recyclability

Abstract

This paper describes the development of so-called all-polypropylene composites, namely polypropylenes (PPs) reinforced with oriented polypropylene bres rather than glass or natural bres. These all-polypropylene composites have speci c economic and ecological advantages since, upon recycling, a polypropylene blend is obtained that can be reused to make all-PP composites again or, alternatively, be used for other PP-based applications. One of the main challenges in the development of all-PP composites is to create a processing window that is large enough to keep the oriented PP reinforcement intact while this is combined or impregnated with PP resin. The technological breakthrough in the processing of all-PP composite that has been established is based on the hot compaction (welding) of coextruded tapes. These coextruded tapes consist of an oriented polymer core, providing strength and stiffness, and a polymer skin with a lower melting temperature than the core material forming the matrix and bonding the tapes together. Consolidation is achieved by simply 'welding' the tapes together, thus avoiding typical impregnation problems encountered in traditional thermoplastic composite manufacturing. Pilot studies have already shown the potential of a wide range of manufacturing technologies including thermoforming and lament winding.

The influence of process parameters on the properties of hot compacted self-reinforced polypropylene composites

“…This process has a narrow, yet viable temperature window. An alternative process is co-extrusion, developed by Peijs and co-workers [3][4][5][6]. This process uses bicomponent tapes, in which the outer layer is a lower-melting point copolymer and the inner layer is a homopolymer.…”

Failure behaviour of self-reinforced polypropylene at and below room temperature

“…Several techniques exist for creating the matrix. The most important techniques are film stacking [9,10], co-extrusion [7,11,12] and hot compaction [1,6,[13][14][15][16][17]. The focus here is on the hot compaction process.…”

All-cellulose composites by surface selective dissolution of aligned ligno-cellulosic fibres

“…The most desirable solution to all these problems is possibly the idea of selfreinforced composites such as the all-polypropylene composites [21][22][23][24], which have recently been developed. These composites are basically monomaterials and therefore fully recyclable and environmentally friendly.…”

“…In this approach part of the highly oriented polymer fibre is melted and upon cooling under pressure, the molten fibre material recrystallises into a matrix, which bonds the fibres together and forms a perfect interface [21][22]. In order to overcome the extremely small processing temperature window which is needed to transform the optimum amount of fibre material into matrix material an alternative route was proposed by Peijs and co-workers [23][24], which is based on the consolidation of coextruded fibres. In this method a high modulus polypropylene homopolymer tape (read:…”