Prosyma Research Ltd presentation to Cambridge University Chemical Engineering Dept.

S F Bush

Introduction: Techno-Economic Background

• To actually enter into the market, a polymer composite product, like any other, must pass the key economic test: Can it be sold for more than it costs to make?
• The relationship between the technology of the process used to manufacture a product and the cost of that technology to build and operate is an absolutely key component in success or failure.

Key Rate-limiting Factors in Polymer Composites Processing

• Energy Transfer
• Mixing
• Fibre Wetting
• Molecular Orientation
• Fibre Organisation

Examples of changes which reduce COSTS in the processing of thermoplastic polymer composites

• Avoidance or reduction of manipulation of fibres
• Carry out wetting contact between fibre and matrix in the simplest of geometries and the highest acceptable temperatures
• Reduce the number of separate moulding operations
• Where possible substitute fluid mechanics for machine mechanics to achieve fibre and molecular order

Self Organisation

• This means in the present context a process in which a distinct materials structure is continuusly obtained without mechanical moving parts.
• In the fluid state, a powerful means of achieving this is by “Flow-shaping”.
• Examples include the use of fluid jets to achieve dispersion mixing of one substance into another instead of using mechanical stirrers.
• In polymer fluids and solids an additional approach is to activate ionic or hydrogen bonding to cause polymer chains to move into specific super molecular structures as in super absorbant polymers.

Paper to the Smart Materials Workshop, Institute of Materials and Qinetiq, London

S F Bush

Abstract

To be useful, a polymer composite, like any other material, must be formable into a product able to maintain its shape within specified tolerances under the likely imposed loads over a given temperature range, all at an acceptable economic price. When discrete fibres are used with thermoplastic polymers, the distribution, orientation, wetting, and length of the fibres in different parts of the product are all features which must be controlled if the product is to maintain its shape and functions in service. The paper discusses these factors and shows how the self-forming principle can be used to extend the range of shapes which can be made economically.

References

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

[2] S F Bush, F Yilmaz and P F Zhang, Impact Strengths of Injection Moulded Polypropylene Long Glass Fibre Composites, Plastic Rubber Composites 24 (1995) 139-147.

[3] S F Bush, Long Glass Fibre Reinforcement of Thermoplastics, Int Polymer Proc 14 (1999) 280-290.

[4] 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.

[5] S F Bush, J D Tonkin and F G Torres, Discrete Glass Fibre Reinforced Polymer Composites: Results from Blow Moulding and Thermoforming, (2003) 19th Ann Mtg Poly Proc Soc, Melbourne, Australia.

[6] D R Blackburn and O K Ademosu, Proc 9th Intl Conf Reinf Fibre Composites (2002) pp 402-07.

[7] D R Blackburn, S F Bush, J M Methven, A Neuendorf, UK Pat No. GB 2,369,322 (June 6 2004) “Self-forming Polymer Composites”.

[8] K J Jamieson, M.Phil, UMIST, August 2004.

Paper to Polymer Processing Society Americas Regional Meeting, Florianopolis, Brasil, 7th-10th November 2004

S F Bush

Introduction

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 stiffness and strength to the processed material. In the case of injection moulded thermoplastics, the glass fibres have until the 1980s been very short, usually in the range 0.3-1.0 mm.

In the case of thermoset compositions the fibres have generally either been 25-50 mm discrete fibres as in sheet moulding compounds (SMCs) or continuous woven structures. If 25-50 mm discrete fibres are used, they are usually in tows (bundles) of 30 or more individual filaments, either constructed into a loosely woven mat and then impregnated with thermoset resins or scattered in a random overlapping fashion on to a layer of resin with further resin poured on top. In either case, a form of semicoherent fibre structure is obtained within the polymer liquid, this structure being maintained after the composite sets to solid. This structure is one of the two main reasons why fibre-reinforced thermoset composites commonly show greater strength and stiffness than do the thermoplastic varieties based on short fibres, which do not usually form such structures, the other being the chemical cross-linked character of the thermoset.

Whatever the specific objectives laid down for the composite, two factors in particular will determine how it meets these objectives. These are (i) fibre-polymer contact, and (ii) fibre management. The over-arching requirement is of course that of minimum cost of the product as defined by its required shape and load-bearing characterisation.

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

S F Bush and D R Blackburn

To see the text of the abstract, please click on the link IOMDeformation.

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.

Paper to International Conference on Textile Reinforced Composite Engineering, Bolton Institute of Higher Education, 11th-13th January, 1994.

S F Bush

Synopsis

Broadly, reinforcement may be introduced into polymeric materials either by mixing discrete fibres more or less at random with polymer before injecting into a shaping mould or by constructing a predetermined textile form from staple or continuous fibres and then bringing the polymer, or more usually thermoset resin, into contact with it. The first method readily lends itself to all the high speed automatic processes which have been devised for unreinforced thermoplastics, but carries the twin penalties of:

1. short fibres (typically 0.3 to 0.6 mm) which are arranged by the adventitious action of the flow field, rather than by the need to match the imposed strains in the finished artefact, and
2. a sharp drop in the notched impact strength by comparison with virgin matrices.

 
The second method on the other hand can give large increases in tensile strength and stiffness in directions which can be closely matched to the imposed strains, but at the expense of extended manufacturing times and therefore cost.

The paper describes a set of concepts which are designed to marry the high-speed advantage of the first method to the advantages of the textile-like reinforcements obtained with the second method. The concepts provide the means by which specially compounded granules each containing bundles up to 2000 10-20 micron diameter 6-20 mm long glass filaments embedded in the host polymer prior to injection into a mould or extrusion through a die. By means of flow shaping elements placed within the injection nozzle or immediately before the extrusion die, the separated filaments are caused to assemble themselves into semi-coherent mat-like reinforcement structures which are not seriously disrupted when carried by the melt into the mould or through a die. Such structures are readily observable in the solid artefact by burning off the polymer to leave a three dimensional fibre structure which faithfully reflects the artefact shape.

The paper will summarise the mechanical properties obtainable from these Self Assembing FIbre REinforcement (SAFIRE) processes. Generally it is found that by comparison with virgin polypropylene for example the goal of achieving improved tensile strength, stiffness and notched impact strength together can be achieved.

SAFIRE technology has now entered the commercial domain and some of the resultant practical mouldings and pipe extrusions will be briefly described.

Paper to 5th Annual Meeting, Polymer Processing Society, Kyoto, Japan, 11th-14th April 1989.

S F Bush

To see the Abstract of this paper please click on the link AbstractL41.
 

References

[1] Hercules Inc, British Patent 1325468, 1 August 1973.

[2] S F Bush, S Bilgin and W G Harland, Pipe Extrusion with Rotating Die Systems, VI International Plastics Pipes Conf, Plastics & Rubber Institute, York, England, March 25-27 1985.

[3] S F Bush, Control of Fibre Structures in Polymer Melt Extrusion, 36th Annual Conference of Canadian Chemical Engineers, Sarnia, 6-9 October, 1986.