Paper to 19th Annual Meeting of Polymer Processing Society, Melbourne, Australia, 7th-10th July 2003

S F Bush with J D Tonkin and F G Torres

Abstract

Ref 1 (in the Society’s Carl Klason [1999] memorial issue of International Polymer Processing) summarised the main experimental and theoretical results from a major long-term programme of research to produce and apply long glass fibre compounds to the extrusion of pipes, and the injection moulding of relatively complex shapes.

This work has been commercialised over the last 10 years under the trade name SAFIRE – the acronym for Self Assembling Fibre Reinforcement – which records the fact that a major part of the technology is concerned with the use of fibre management devices which cause fibres, above a certain length dependent on concentration, to form themselves into coherent mat structures within the melt as it flows towards the shaping die or moulds. These fibre management devices have been protected by international patents during the on-going commercial exploitation phase. The formation of these all-important mat structures is dependent on the number N of virtual touches experienced by one fibre in the presence of the others. N is give as A.c(l/d) where A depends on the flow field. This paper records new results obtained with this technology for blowmoulding and for thermoforming of extruded sheet.

References

[1] S F Bush, Long Glass-Fibre Reinforcement of Thermoplastics, International Polymer Processing 14 (1999) 282-90.

[2] S F Bush, Fibre reinforced polymer compositions and process and apparatus for production thereof, US Patent 5 264 261 (1993)

[3] S F Bush, Filament Separation in Liquids, US patent 5 035 848 (1991)

[4] S F Bush, F Yilmaz, P F Zhang, Impact strengths of injection moulded polypropylene long-glass fibre composites, Plast Rubber Composites (1995) 24 (3), 139-147.

[5] S F Bush, M Dreiza, J D Tonkin, Blow moulding of long-glass fibre composites, Plast Rubber Composites (1999) 28, 379-384.

[6] F G Torres and S F Bush, Sheet extrusion and thermoforming of discrete long-glass fibre reinforced polypropylene, Composites Part A. 31 (2000), 1289-94.

[7] D R Blackburn and O K Ademosu, Investigation of the production of rotationally moulded composites, Proc 9th Intl Conf Fibre Reinforced Composites, Ed A G Gibson, Conf Design Consultants publ (2002), 402-07.

Paper to FRC 8th International Conference 13th-15th September, “Composites for the Millennium”

Published as ISBN 85573 5504

S F Bush with D R Blackburn, A J Neuendorf and J M Methven

Abstract

While much of fibre reinforcement of polymers has rightly concentrated on solid forms, there is a significant demand also for lightweight open structures of the wire-cage type. The paper will report results obtained from a variety of polymer-fibre compositions in wire form.

These wire-cage results draw on the laboratory’s extensively reported work on long-glass fibre reinforcement of thermoplastics and the pultrusion of both thermoplastics and thermosets. However, for the new wire-cage technology, the behaviour of the synthetic fibre and natural fibres in place of glass fibres has also been investigated. The results obtained show that for a number of significant applications these soft fibres are better than glass fibres in terms not only of their formability into wire structures, but also in terms of their elastic recovery from imposed stress or strain.

The development opens up a significant new field for polymer-fibre composites both as an alternative to existing metal wire structures in the food distribution and textile industries and as an alternative to certain solid structures more generally.

Paper to the International Conference on Manufacturing, Processing Composite Materials, Plymouth University, Professor of Polymer Engineering, UMIST, 12th-14th July 1999.

Published in the journal: Composites Part A: Applied Science and Manufacturing (incorporating Composites and Composites Manufacturing) ISSN 1359-835X, volume 31, issue 12, December 2000, 1421-1431.
S F Bush with F G Torres and J M Methven

Abstract

Three experimental techniques have been employed to assess the rheological behaviour of discrete long glass fibre reinforced polypropylene and propylene/ethylene copolymers. A Carri Med cone and plate rheogoniometer has been used to determine shear viscosity as a function of strain rate and time at temperatures relevant to the extrusion and injection moulding processes. A bubble inflation test (BIT) has been designed and used to characterise the behaviour of these composites under the extensional flow fields typical of blow moulding and thermoforming. Finally a squeeze load test (SLT), similar to those developed for sheet moulding compounds (SMC) and glass mat thermoplastics (GMT), has been used to explore the rheological behaviour of the long glass fibre (LGF) materials under compression moulding conditions, in particular to assess the relative importance of shear and extensional flow.

Paper to 15th Annual Polymer Processing Conference, ‘s-Hertogenbosch, Netherlands, 31st May-4th June 1999

S F Bush and F G Torres

Abstract

The work reported here results from a long term research programme on LGF composites under the generic name of Self Assembling FIbre REinforcement (SAFIRE) in which fibre reinforcing mats are created in the melt during its passage through the process equipment. Previous reports from this laboratory have described results [1, 2, 3] obtained from LGF loaded granules manufacture, from pipe and sheet extrusion, and from injection and blow moulding, all of which have been developed at the industrial scale.

Besides changes in mechanical properties relative to unreinforced grades, LGF polypropylene exhibits very different thermal behaviour compared with unreinforced polypropylene. Broadly speaking, heat distortion temperatures increase by 7 ^oC for every 1% v/v glass fibre and thermal conductivity normal to the predominant flow plane increases by a factor of 2 for about 6% v/v.

The original theory [1] of the fibre reinforcing mats is based on the idea of the number of fibre-fibre touches (N) creating a coherent structure approximately according to the formula N = A.c.ld. In order to understand how the mat structure affects the thermal conductivity of the composite, thermal conductivity experiments have been carried out in the steady state at temperatures in the range 50-200 ^oC using an improved Lee’s Disc apparatus. The reinforcing fibre mats have also been characterised using a scanning electron microscope (SEM) and the average number of touches between the fibres has been calculated and compared with the theoretical equation. The paper proposes a model for thermal conductivity of LGF reinforced composites based on the touch and fibre orientation concepts.

References

[1] Bush S F, Yilmaz F, Zhang P F, Plastic & Rubber Composite Process Applications, Impact strengths of injection moulded polypropylene long-glass-fibre composites, 24 (1995) 139-147

[2] Bush S F, Tonkin J D, Short and Long Term Behaviour of Long Glass Fibre Reinforced Polyolefins, Antec Technical Papers, 43 (1997) 3081-3086

[3] Bush S F, Torres F T, Erdogan E S, Mechanical Properties of Discrete Long Glass Fibre Reinforced Polymer Sheets and their Application to the Thermoforming Process, Proceedings of 7th International Fibre Reinforced Composites Conference (1998) 237-244

Invited Paper to the Institute of Materials Conference “Advances in Blow Moulding”, Loughborough University, UK, 30th June-1st July 1998.

Published by the Institute of Materials, “Plastics, Rubber and Composites 1999” Vol. 28 No. 8 379, ISSN 1465-8011

S F Bush with M Dreiza and J D Tonkin

Abstract

Precompounded discrete fibres have long been used as reinforcement in injection moulding particularly with polypropylene and nylon matrixes. Usually the lengths of the fibres in the finished article have been in the range 0.2-1.00 mm and for convenience are labelled short glass fibres. The last 15 years has seen the development of precompounded long glass fibres, having lengths in the finished article of typically an order of magnitude longer than for short glass fibres.

The present paper describes experiments on the blow moulding of long glass fibre reinforced virgin and recycled polymers. The long glass fibre compounds have been made using in house technology, for which the matrix interface conditions are known and can be varied. Bottles of 2 L capacity with integral handles were blown as the primary testpieces for evaluating blowability of these new materials and for investigating the reinforcing structures obtained in the bottle walls. Mechanical properties were evaluated at room temperature before and after recycling and at elevated temperatures up to 100 ^oC, which are particularly relevant to the blow moulding applications envisaged. PRC/1523

Paper to the Society of Plastics Engineering Conference, Toronto, Canada

Published in the Society of Plastics Engineering Antec Tech Papers, 43 3251-6 (1997)

S F Bush with J D Tonkin

Abstract

For given end-uses there are basically three strategies for minimising polymer consumption: redesign of the original articles, recycle for re-use, and recycle for reprocessing. Results are presented relevant to all three strategies in blow moulded and injection moulded articles. In thermoplastic packaging, discrete long-glass fibre compounds allow redesign to thinner sections and higher operating temperatures, while retaining acceptable impact strength. Re-use in the food packaging chain is increased by higher heat distortion temperatures to meet sterilisation requirements. The SAFIRE long-fibre compounding technology extends the range of high value outlets for reprocessed mixed recyclates by increasing their strength, stiffness, heat distortion temperatures and creep resistance.

Proposal made to Ametex AG

S F Bush

Summary

The project is split into three programmes, A, B, C. Programmes A and B are designed to carry the present technology to the point of commercial production using bought-in fibre granules. Programme C is designed to provide the technology for in-house fibre granule production.

Reinforcement of polymers: the general position

It has long been appreciated that the addition of glass or other stiff fibres to a thermoplastic or thermoset in a suitable fashion usually brings increased strength and stiffness to the processed materials. Fibre reinforcement is readily incorporated in both thermosetting and thermoplastic materials. However, in the case of thermoplastics the glass fibres have until recently been comparatively short – in the range 0.3 to 1.00 mm, while in the case of thermosets, the fibres have usually either been long discrete fibres woven into a loose mat (e.g. chopped strand mat) or actually continuous through a considerable portion of the structure.

If, for thermoset materials, long discrete fibres are used, they are either constructed into a loose woven mat and then impregnated with resin (as in conventional polyester GRP) or scattered in a random overlapping fashion on to a layer of resin with further resin poured on top as in Sheet Moulding Compounds. In either case a form of semi-coherent structure is obtained within the polymer liquid, this structure being maintained after the composite sets solid. This coherent structure is one of the two main reasons (the other being the cross-linked nature of a thermoset polymer) why fibre reinforced thermoset composites show much greater strength and stiffness than do the thermoplastic varieties based on short fibres which do not usually form such structures.

All three programmes were carried out at the Polymer Engineering labs at UMIST from 1987 to 1990, when the project moved to South Africa.