Comparison of Long-fibre Granule Compositions in Polypropylene Injection Moulding
April 5th, 1993
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.
| Granule Code | Wetting of fibre | Fibre content by weight | Fibre diameter (mm) | Initial Fibre length (mm) |
|---|---|---|---|---|
| FIBERFIL/G60/20/E* | Good | 20 | 17×10-3 | 12 |
| FIBERFIL/G60/10 | Poor | 10 | 10×10-3 | 6.35 |
| SAFIRE/NCA | Average | 17 | 17×10-3 | 8 |
| SAFIRE/CA* | Good | 17 | 17×10-3 | 8 |
| CELSTRAN/PPG40* | Good | 40 | 17×10-3 | 9 |
| SAFIRE/55S* | Good | 25 | 17×10-3 | 10 |
* 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.