Injection moulding of long glass fibre reinforced polyamide 6-6: guidelines to improve flexural properties

Abstract

Abstract. Based on a previous optimisation of set-up parameters for injection moulding of polyamide 6-6 (PA 6-6) reinforced with 40 wt% of 10 mm long glass fibre, the aim of this paper is to define suitable guidelines to further improve the mechanical performances of PA 6-6/glass long fibre thermoplastic (LFT) injection mouldings. Different solutions have been considered: screw and non-return valve design modification so as to adapt them to LFT processing, increase of the initial fibre content (up to 50 wt%) and length (up to 25 mm) in the LFT pellets. Using a LFT dedicated plasticating unit has allowed decreasing the fibre breakage amount by about 80% at the nozzle exit, however without improving the flexural properties. Increasing the initial fibre content has logically permitted to improve the flexural properties. Increasing the initial fibre length has not brought any improvement of the properties and has even amplified the structural heterogeneities and anisotropy of the parts. These trends have been explained on the basis of cavity pressure records highlighting significantly different rheological behaviours, and of resulting residual fibre lengths and through-the-thickness fibre orientation profiles modifications.

Characterisation of low-odour emissive polylactide/cellulose fibre biocomposites for car interior

“…Many types of fibres, natural (wood, flax, hemp, kenaf…) or synthetic (glass, carbon, aramide), were associated to petroleum-based polymers and more recently to bio-based plastics [10][11][12][13][14][15][16]. The vegetal fibres are an interesting eco-friendly reinforcement system, as they are annually renewable, lighter, cheaper and less reliant on foreign oil sources than synthetic fibres [17].…”

Mechanical properties of polyamide/carbon-fiber-fabric composites

“…This study focuses on an engineering polymer, with a high potential, i.e., polyamide 6. Most literature studies present polyamide 6 composites reinforced with short fibers (carbon, glass or aramid) processed by melt extrusion [9][10][11][12] , a few studies present fabric-reinforced polyamide 6 composites [13][14] , because of the technological processing difficulties arising from fabric-impregnation issues generated by the molten polymer and fiber wet out. 15 Moreover, the data concerning the optimum solution viscosity range and the optimum polymer/solvent ratio when using the solvent-impregnation method is very briefly discussed, although its importance is underlined [16][17][18] , as the rheological properties of the matrix are important for establishing the composite's processing parameters.…”

Injection moulding of long glass fibre reinforced poly(ethylene terephtalate): Influence of carbon black and nucleating agents on impact properties

“…Indeed, according to the literature, sodium 2,2!-methtylene-bis(4,6-di-tert-butylphenyl)phosphate (R3) is likely to induce smaller spherulites than sodium benzoate (R2) in non-reinforced plastics [28,29]. However, in the case of fibre-reinforced plastics, a more perfect crystalline structure (small spherulite sizes, homogeneous spherulite structure, possibly transcrystalline interphase -as expected in the case of R3) increases the internal stresses in the fibre/matrix interface region and therefore the material brittleness [10]. These stresses concentrated around the fibres are easily revealed by means of a soda-ethanol chemical attack which induces material cracking due to stress relaxation (Figure 11).…”

“…The shear and fountain flows occurring during cavity filling actually induce a well-known multilayer structure with skin layers showing a fibre orientation in the flow direction and a core layer where the fibres are oriented transversally to the flow [10,11,24].…”

“…The impact strength quickly drops above these limits. Moreover, as for the tensile or flexural strengths [5,8,10,14,15] different authors evidenced that the residual fibre length and the fibre orientations influence the impact strength [8,21]. In the case of PP reinforced with 50 wt% glass fibres having initial fibre length of 10 mm (reduced to 1.8-2.0 mm after injection moulding), Skourlis et al [22] furthermore highlighted the influence of the thickness of the skin and core layers of the part, induced by the shear and fountain flows during processing.…”