Paper (6-2-8) to the 10th International Annual Meeting of the Polymer Processing Society, Akron, USA, 5th-8th April 1994.

S F Bush with D R Blackburn, O K Ademosu, F B Yilmaz and P F Zhang

Introduction

Earlier papers^{(1, 2, 3, 4)} have described the factors affecting fiber-matrix cntacting, the organization of long fibers into coherent lace-like or mat-like structures, and the dependence of tensile strength on these two classes of variable. Equations for the mean number of touches¹ in the fiber structure and tensile strength² have been proposed which allow for the main variables present in moldings and extrusions, including differing matrix properties. Fiber management technology developed under the generic acronym SAFIRE⁴ (Self Assembling Fiber Reinforcement) has recently been applied commercially to practical moldings such as hard hats and pallets, in both of which examples impact strength is a key property.

Accordingly, a wide series of experiments has been carried out using the Izod method to determine the variation of impact strength as a function of the fiber length, fiber concentration, the fiber-matrix interface, fiber reinforcement structure and matrix properties. Both commercially available long-fiber granules and laboratory-compounded types have been used with different mold configurations and molding conditions for a variety of polypropylene and polyethylene matrices.

References

[1] S F Bush, Control of Fiber Structures in Melt Extrusion, 36 Ann Mtg Can Soc Chem Eng, Sarnia, Canada (1986) paper 32d.

[2] S F Bush, O K Ademosu, D R Blackburn, F B Yilmaz, Factors Affecting the Strength of Long-Fibre Reinforced Injection Moldings, Poly Proc Soc Eur Mtg, Prague (1992) paper 6-06.

[3] D R Blackburn and O K Ademosu, Factors Affecting Fiber-Matrix Contacting in Fiber-filled Granules, Poly Proc Soc, 9th Ann Mtg, Manchester 1993, Paper 6-14.

[4] S F Bush, Self Assembling Fibre Reinforcement (SAFIRE) processes, “Textile-reinforced Composites for Engineering”, Bolton Institute, Bolton, England, 12-14 January, 1994.

Paper (5) to the Institute of Materials 6th International Conference on Fibre Reinforced Composites, Newcastle, England, 29-31 March 1994.

Published in Plastics, Rubber and Composites Processing and Applications, Vol 24, No 3 (1995).
S F Bush with F B Yilmaz and P F Zhang

Abstract

A wide series of experiments has been undertaken to measure impact strength as a function of fibre length and concentration, the fibre/matrix interface, and induced fibre-mat structure and matrix properties. Both commercially-available long-fibre polypropylene granules and in-house polypropylene and polyethylene glass-fibre compounds have been used where the interface conditions are known and can be varied. For the fibre-mat structures achieved, notched impact strengths rise with fibre lengths and with fibre concentration, giving in all cases an improvement on the virgin polypropylenes – for some conditions a five-fold improvement at 25% w/w concentration.

Paper to the Polymer Processing Society 9th Annual Meeting, UMIST, 5th-8th April 1993, 02-35.

F B Yilmaz with S F Bush

Introduction

There are a number of different techniques for the production of long glass-fibre reinforced polypropylene (LGFRPP) granules for injection moulding. Dispersion and wetting of glass-fibre in the granule will be different according to the type of polypropylene grade and the compounding methods. Most of the materials used in this study were produced by the melt coating method and contain two bundles of filaments. The granules which are used in this study are given in Table 1.

* They have coupling agent.

Injection moulding is a two-step operation which involves first the plasticization of solid materials in a screw extrusion unit, followed by the high pressure pumping of molten material into a mould cavity. Most fibre breakage occurs in the screw extrusion unit with injection moulding of fully dispersed LGFRPP granules[1]. There is in fact an advantage in using melt coated granules. When glass-fibre bundles are travelling in the screw unit, they protect each other against severe fibre breakage. On the other hand to disperse the fibre bundles a separator is necessary. In tis study a proprietary dispersion device was used between the mould and the screw unit.

References

[1] R S Bailey and H Kraft, Int. Polymer Process. 22, p94-101 (1987)

[2] S F Bush, O K Ademosu, D R Blackburn, F B Yilmaz, “Factors Affecting the Strength of Long-fibre Reinforced Injection Moldings”, Polymer Processing Society 1992 European Meeting, Prague, 21-24 September, paper 06-06.