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.

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.

Keynote paper to the Polymer Processing Society Euro Meeting, Gothenburg, Sweden, 19th-21st August 1997.

S F Bush

Introduction

For many years two forms of fibre reinforced polymers have been predominant: thermoplastic granules with predispersed short glass fibres in the length range around 0.5-1.5 mm and thermosets used with preformed mat like structures made up of glass fibres of length 25 mm upwards.

To varying degrees glass fibre mats or preforms may be prepositioned in a mould to provide reinforcement in the directions of the stresses applied to the made artefact. In the case of the short fibre thermoplastics however the flow fields set up by the die or moulds exercise a major adventitious influence on the distribution and orientation of the fibres. In particular for flows with a predominant velocity component in one direction as in extrusion and many mouldings, the fibres tend to be disposed very largely in that direction, which will only rarely be the direction of major applied stress in the solid artefact.

In recent years, thermoplastics compounds with much longer glass fibres, in the range 6-13 mm, have become widely available. While earlier predictions¹ of explosive growth in sales of these long fibre reinforced compounds have not so far been realised, in particular applications they do show considerable advantage over their short-fibre counterparts⁽², 3). The principal reason for their advantage is their ability to form mat-like structures in the melt which then persist into the solid state. These can readily be seen by burning off the polymer. We thus get something like the reinforcing structures of the preformed thermoset compounds, without the time-consuming necessity of a separate processing step.

The significance of this mat-forming property is two-fold: it greatly increases the melt strength and it provides a means of overcoming the tendency of the die or mould to align the fibres in directions which are undesirable from an end-use point of view. Thus in blow moulding we need fibres oriented at right angles to the parison extrusion direction so that during the stretching phase the moulding doesn’t pull apart. Likewise in the extrusion of reasonably isotropic sheet, we need as many fibres oriented in the transverse direction as in the flow direction, and for pipe extrusion arguably twice as many. In injection moulding isotropy is generally desirable, particularly if the part is subject to temperature variations. While some transverse orientation is often obtained adventitiously, to obtain the lace-like isotropic fibre separation, specific fibre management devices of the types previously described⁽², 5) are necessary in most applications.

References

[1] Plastics Brief 15 23, (1991)

[2] Bush S F, Harland W G and Bilgin S, Pipe Extrusion with Rotating Die Systems, 6th Plastics and Rubber Institute Pipes Conference, York, England, 25th-27th March 1985

[3] Gibson A G et a, ECCM-I Conf. (24-29 Sept. 1985)

[4] Bush S F, US Patent, 5,264,261 (1993)

[5] Bush S F, Yilmaz F B, Zhang PF, Impact Strengths of Injection Moulded Polypropylene Long Glass Fibre Composites, Inst Mats 6th Int Conf on Fibre Reinf Comp, Newcstle, England, 29-31 March 1994, 24 139-147

[6] Torres F, Private Communication, UMIST (1997)

[7] Bush S F, Ademosu O K, Blackburn D R, Yilmaz F B, Zhang P F, Relationship of impact strength, tensile strength and the fiber-matrix interface in varieties of polypropylene long-glass fiber injection moldings, Poly Proc Soc, 9th Ann Mtg, Akron, USA, paper 6-28 (1994)

[8] Bush S F and Tonkin J D, Polymer packaging as an environmental benefactor, Antec Technical Papers 43 3081-86 (1997)

Paper to Institute of Materials Conference on Deformation and Fracture of Composites, 24th-26th March 1997.

S F Bush with J D Tonkin

Abstract

Despite the high levels of improved mechanical properties in glass fibre reinforced thermoset composites, difficulties and restrictions in processing methods have limited their application in manufacturing to high value added products. In addition, the prominence of green issues in the commercial environment is forcing the selection of readily recyclable composite materials that still offer enhanced specific properties. These factors have all contributed to the increased use of thermoplastic composites despite their lower glass concentrations and specific mechanical properties compared to thermoset composites. The term long glass fibre is generally used to describe filaments with a sufficiently high aspect ratio as to allow several fibre touches or near touches (interactions), even at relatively low fibre concentrations (e.g. fibre lengths approximately > 1 mm and preferably > 5 mm.

Under the generic title of SAFIRE (Self Assembling FIbre REinforcement) research has been successfully carried out into the production of long glass fibre granules, the development of static fibre management systems to optimise distribution and production of long fibre composites using conventional processing techniques (injection moulding, blow moulding, extrusion, and compression moulding).

Using results obtained from injection moulded tensile test specimens of different thermoplastic (PP, HDPE & LDPE) base polymers the following mechanical properties were observed:

• Tensile strengths improved by approximately 100% for a 7% glass v/v composite, with strengths of 68 MPa reached in a PP homopolymer composite.
• Contrary to expectation, the addition of long glass fibres to PP has given a significant increase (over 200%) in impact strength. Other materials such as recycled HDPE showed no significant change. Although glass fibres reduced the impact strength of LDPE it still remained high at almost three times that of recycled HDPE. The significance of the coupling agent on the fibres is shown by a doubling of impact strength in PP copolymer before glass fibres were added. When 7% glass was added to HDPE without coupling agent there was a 50% reduction in impact strength compared to the composite containing the coupling agent.
• Creep properties have also shown perhaps the larges improvement due to the presence of long glass fibres. At loadings of 7% glass v/v LDPE has shown a 400% increase in load bearing resistance and recycled HDPE a 200% increase in load bearing resistance.

 
In conclusion, it has been shown that at only 7% glass fibre concentrations the tensile strength, creep resistance and even the impact properties of certain polyolefins can be increased significantly. Even more important is the fact that these composites can be processed on conventional plastic processing equipment with only minimal modification to optimise properties. Finally, as the base polymer used in the matrix is thermoplastic the composite may be granulated and recycled.

Prosyma Research Ltd report to Weltonhurst Ltd.

S F Bush with J D Tonkin

Introduction

Weltonhurst supply high density polyethylene blow moulded containers to Richard Millington and Co Ltd. The containers are used to hold cleaning fluid under pressure for the purpose of cleaning out beer lines. The HDPE has come from a variety of suppliers including Dow, Atochem and Borealis, with a density around 0.95 gm/cc. The fluid has the specification:

Sodium Hydroxide: 9.2 ± 1 gm/litre

Sodium Hypochlorite: 7.6 ± 2 gm/litre

“Phosphorus butane carboxyl”: 4.8 ± 0.25 gm/litre

The precise chemical formula of the third component is unknown, but it looks like a mild detergent.

An earlier report (Ref 1) investigated the short-term mechanical properties of the polymers used, following the disintegration of a 50 litre container after six years in use. Fragments of the disintegrated container were found to be significantly less ductile than recently made containers, pointing to some long-term degradation of the polymer, exposure to sunlight being a prime possible agent.

The present investigation has been concerned with a second possible agent of long-term degradation, namely environmental stress cracking (ESC). ESC is not a well defined concept, but the essential point is that some environments reduce the mechanical properties over time. Generally these weakening effects are increased with an increase of temperature. Tests have therefore been done at both a working temperature (23 ^oC) and an elevated temperature (60 ^oC) which might be seen as the limit that the container could normally attain (by being left out in the sun for example).

References

1: S F Bush & J D Tonkin, Report on failed Bass bottle, PRL, 11.8.95.

2: S Turner, Mechanical testing of plastics, George Godwin, 1983.

Paper to the Polymer Processing Society 12th Annual Meeting, Sorrento, Italy, 27th-31st May 1996, paper 10-9.

S F Bush with J D Tonkin

Introduction

Too often, when attacked as wasteful of natural resources and a cause of litter, the polymer industry adopts a defensive stance, seeking to show that plastics usage, in particular plastics packaging, is not as bad as it is painted. Those who work for the polymer industry may know themselves that the charges are generally unfounded. However it is clear from the recent example of the Brent Spar that even the largest of the world’s oil and chemical companies can feel forced by environmental groups using inaccurate data, to abandon a course of action which had actually been calculated to be in the best interests of the environment.

In fact the science and engineering underpinning the polymer industry is a major environmental benefactor, but to show this it is important to consider the relevant total system. To bound the problem in a short paper, we will concentrate on packaging in the food system, noting that while packaging at about 40% is the largest single category of polymer use, it accounts for 1.6% only of oil usage in Western countries.

Paper to the Polymer Processing Society 12th Annual Meeting, Sorrento, Italy, 27th-31st May 1996.

S F Bush with J D Tonkin

Introduction

Continuing the work of processing long glass fibre reinforced thermoplastics, under the generic title of Self Assembling Fibre Reinforcement (SAFIRE), the blow moulding of 2-litre bottles has been achieved, complementing advances made using other major processing techniques (injection moulding and pipe and sheet extrusion).

The sample bottles were processed on a Latymer HYD6 accumulator head blow moulding machine. The initial problems encountered when processing the long fibres were the reduced levels of parison die swell compared with the unreinforced material. The thinner walled parison produced a thinner blown bottle and the narrower width parison resulted in the incomplete blowing of complex non-symmetrical geometries. To compensate for this reduced parison die swell, larger diameter dies with larger width annuli were used.

Besides a fully blown shape, a good quality SAFIRE glass fibre granule is required that allows the separation of fibre bundles into individual filaments that can form a network structure. Some characteristics that determine a quality granule include wetting the glass fibre-polymer interface and the presence of a coupling agent⁽¹, 2). In addition the use of a Fibre Separating Device (FSD)³, a mechanical unit that forces the fibre-bearing melt through narrow channels, using differences in flow velocities to cause separation of the filaments from the bundles, improves the final fibre network structure.

References

[1] S F Bush, F Yilmaz and P F Zhang, “Impact strengths of injection moulded polypropylene long glass-fibre composites, Plast Rubb Comp Proc, App 24, (1994) 139-147

[2] D R Blackburn and O K Ademosu, Poly Proc Soc 9th Ann Mtg (5-8 April 1993) paper 06-14

[3] S F Bush, “Filament Separation in Liquids”, Euro Pat 0355 116B1 (31 March 1993)