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 the Polymer Processing Society Regional Meeting, Florianopolis, Brazil, 7th-10th November 2004

O K Ademosu and S F Bush

Abstract

Recent papers ^2, 3 have described the Rotofoam© process which combines in one stage the rotomoulding of hollow shapes with the in situ generation of foam to fill the cavities. The foam is usually polystyrene driven by a combination of blowing agents, but other systems may be used. This paper defines the material quantities and the processing variables needed to reconcile three competing objectives in making panels for applications in the storage and transportation of chilled and frozen foods. These objectives are maximum bending stiffness to weight ratio, maximum thermal insulation, and minimum manufactured cost. Results of experiments at both the laboratory and industrial scales are reported. Panel stiffness, short and long-term resistance to indenting, density and thermal conductivity measurements have been done to generate an algorithm for the overall optimisation of the process and product.

References

[1] O K Ademosu and D R Blackburn, Fibre-impregnation in Rotational Moulding and its effect on Mechanical and Thermal Properties, Advances in Materials and Processing Technologies, Dublin 2003.

[2] S F Bush and O K Ademosu, Combined Foaming and Rotomoulding: the Rotofoam Process, Eurofoam Conference 7-10 July 2002, Manchester, UK.

[3] S F Bush and O K Ademosu, Combined Foaming and Rotomoulding in the Rotofoam Process, Polymer Processing Society 19th Annual Meeting, Melbourne, Australia, 7-10 July 2003.

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

S F Bush with O K Ademosu

Abstract

Rotomoulding is an established process for forming relatively large hollow structures by rotating a mould containing polymer powder (typically polyethylene) either about two perpendicular axes or about one axis combined with a rocking back and forth motion along the second, perpendicular axis. Up to now, if such a rotomoulded hollow form needed to be foam-filled, the hollow form has had to be made first in one operation, demoulded, and then, as a comparatively costly second operation, taken to another station where it is filled with polyurethane foam. The UMIST Rotofam process allows the foaming step to proceed at the same time as the moulding step, giving a solid outer skin of one material and a foamed interior made of another. The paper describes experiments on the Rotofoam process at both laboratory scale and full-scale as rotation speeds, feed materials and temperature-time profiles are varied. Large bore steam pipe insulators, damage resisting post covers, cold store doors, harbour fenders and pallets, all made on our industrial collaborators’ plants will illustrate the results obtained in practice from this new industrial proces. A further variant – Rotofil – in which long glass fibre filaments are distributed into the polyethylene skin will also be briefly described.

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

S F Bush with D R Blackburn and K J Jamieson

Abstract

This paper describes a new process for the production of certain types of smart composite materials, which under prescribed temperature fields spontaneously adopt prescribed shapes. These shapes are quite stable at room temperature plus about 50 ^oC. At or near the forming temperatures the shapes may revert to their original forms. Articles of this type can thus be seen as the polymer composite equivalent of bimetallic strips or shape memory metal alloys.

The purpose of this process which is under commercial development under the acronym SMARTFORM^© is to be able to make shapes from straight rods and flat sheet feedstock which are either impossible to mould or very expensive to do so by conventional processes. The key to the new process is the placing of mixtures of heat shrinkable synthetic and natural fibres in precise positions in the cross-section of pultruded profiles – notably rods and sheet. When subsequently cut to size, the rods or sheet elements are passed on belts through a series of heating zones for prescribed times which cause them to curl or twist into the shapes required. The process is economical since both the pultrusion stage and the thermal forming stage are continuous, not requiring manual intervention.

Paper to the 17th Annual Meeting of the Polymer Processing Society, Montreal, Canada

M Esfandeh with S F Bush and J M Methven

Abstract

This paper describes a Differential Scanning Calorimetry (DSC) study of a new class of thermosetting polymer blends. The blends are made by physical thickening in which a particular crystalline additive is capable of forming a thickened system when it is melt blended with a thermoset resin. The blends are now used commercially in the manufacture of sheet moulding compounds (SMC) where they exhibit important advantages over conventional systems. In previous reports from this laboratory the morphology of these blends was studied[6] and on the basis of secure physical foundations, a model for blend morphology was presented. In this paper the effect of the presence of resin on melting and crystallisation temperature of thickening additive is studied using DSC technique. The corresponding enthalpies of transition are also measured and are compared with values expected from dilution effect. Finally the interaction parameter between resin and additive is calculated from a depression in the melting point of the blend.

[6] Bush S F, Esfandeh M and Methven J M, “New Blend Morphologies for Low Pressure Moulding Compounds”, Polymer Processing Society, 15th International Meeting, Hertogenbosch, The Netherlands, May 31st-June 4th (1999)

Keynote paper to 17th Annual Meeting of the Polymer Processing Society, Montreal, Canada, 21st-24th May 2001

J M Methven with S F Bush and A J Hulme

Summary

The conventional pultrusion process allows continuous manufacture of a fibre-reinforced composite profile of constant cross section. Important refinements to the basic process have been made within the UMIST Polymer Research Laboratory over the past few years and this work describes a further development.

For manufacture of hollow profiles, the outer surface of a mandrel forms the inner surface of the profile while the inner surface of the die forms the outer surface of the profile. Many profiles are made hollow to increase the bending stiffness-to-weight ratio. This can also be achieved by making a solid profile with a centre section composed of a light organic polymeric foam such as a polyurethane or a cross-linked phenolic resin. However, synchronising the blowing and chemical cross-linking of the foam with the gelation of the outer glass-reinforced resin as it passes through the die is difficult to achieve reproducibly in a factory environment. The paper describes an alternative approach in which the organic foam is replaced by resin impregnated inorganic particles such as clay or glass which are expanded by vacuum rather than by reaction. This creates, in effect, a controllable, low density, low cost mandrel which is incorporated into the profile.

The paper describes the techniques used to establish the conditions for manufacturing 30 mm simulated hardwood poles in a factory. By using a conventional mix of glass fibres, unsaturated polyester with a relatively high maleic element, and a peroxide catalyst to create the outer annulus of the profile, together with a decorative PET film on the outside film, a pole of acceptable quality and cost has been made at a line speed of 1.2 m/minute. Broader conclusions are drawn for applications of the technology to other shapes and moulding processes.

Keynote paper to Polymer Processing Society Euro 2000 Meeting, Brno, Czech Republic, 16th-18th August 2000

S F Bush

Abstract

This paper will review some of the major developments in polymer engineering over the last 25 years with a view to identifying themes likely to be of importance in the first decade of the new millennium.

The paper will seek to highlight the interactions between the three branches of the field which are used to achieve particular goals: polymer science, polymer processing, and product design. The twin system concepts of order and organisation, as illustrated by molecular sequencing, crystalline architectures, material combinations, processing pathways, geometrical design, will be used to analyse where we are now and where we might go.

The paper will take as its starting point those consumer and societal demands which polymer based products can provide or contribute to. These demands may be classified under the following headings:

• the elimination of routine personal services (e.g. easy-care textile fabrics, dirt-resistant decorative laminates)
• more efficient living space (e.g. foamed insulation)
• fuel efficient and comfortable transportation (e.g. weight reduction through polymeric components)
• increased variety and quality of food (e.g. multilayer film packaging)
• extended leisure facilities (e.g. lightweight equipment)
• upgrading the environment (e.g. reduction of industry-generated wastes)
• improved health-care (e.g. polymer prostheses, implants, drug delivery systems)
• ever more powerful information technology (e.g. compact disks, polymeric display systems)

A requirement which applies to all these demands is for further reduction in the time between recognition of a market need and manufacture of the final product for sale. The future growth of the polymer industry will depend in part on how well it is able to respond to this imperative. On-going developments in rapid prototyping and low cost mould making will continue to make a big contribution to this objective.

Paper to 16th Annual Meeting of the Polymer Processing Society, Shanghai, China, 18th-23rd June 2000

S F Bush with O K Ademosu, S A Harrison, J M Methven and S Smith

Introduction

The generally poor fire resistance of hydrocarbon polymers has greatly inhibited their application in places where human beings are expected to congregate in confined spaces. Underground transportation systems, leisure centres, and apartment blocks are all examples where the flammability of polymers has been implicated in substantial loss of life in different parts of the world.

Public concern is also focussed on the recycling and reuse of polymers issue. Arguably, used tyres constitute the single largest, most predictable and most intractable recycling problem in the mass car-owning parts of the world. This is because of the numbers involved (around one tyre per adult per year in the industrialised world) and the fact that as a thermoset, rubber cannot be reprocessed by melting into a new tyre or some other object.

The present paper introduces a new technology which aims to provide potential large scale applications of rubber from used tyres and to provide sufficient fire resistance to allow use in public areas. Besides the various mixing sequences involved, the technology encompasses in some of its forms the chemical grafting of the rubber on to other hydrocarbon matrices and the use of different fire retardants. This laboratory’s long-fibre reinforcement technology is also used to provide another degree of freedom in meeting both technical and economic goals^[1].

Fire resistance is typically characterised by the Limiting Oxygen Index (LOI) test^[2] and mechanical properties are characterised by tensile strength and stiffness.

References

[1] S F Bush, Long glass fibre Reinforcement of Thermoplastics”, International Polymer Processing 14 (3) 1999, 282-290

[2] Determination of flammability by Oxygen Index BS 2782 Part 1: Method 141: 1986m ISO 45891 – 1984

Paper to 16th Annual Meeting, Polymer Processing Society, Shanghai, China, 18th-23rd June 2000

S F Bush

Introduction: Market Needs and the Role of Polymer Processing

While there will always be room for serendipity in research, nonetheless ‘chance favours prepared minds’. Research opportunity will increasingly flow from a preparedness to respond to market needs. Particular goals will be achieved by the interaction of polymer science, polymer processing and product design.

The needs which the polymer industry responds to may be summarised under the following eight headings:

• The elimination or reduction of routine personal services, (e.g. easy-care textile fabrics, dirt-resistant decorative coatings and laminates)
• More efficient living space, (e.g. foamed insulation, corrosion resistant pipework)
• Fuel efficient, and more secure transportation, (e.g. weight reduction through polymeric components, elastic end sections for moving vehicles)
• Increased variety and quality of food and drink, (e.g. multilayer film packaging, lightweight bottles)
• Leisure, (e.g. lightweight, moisture repellent clothing and textiles)
• Economising on natural resource usage, (e.g. reduced energy in materials procesing, hardwood substitutions)
• Improved health-care, (e.g. contact lens, polymer prostheses, implants, drug delivery systems)
• Ever more powerful information technology, (e.g. compact disks, polymeric display systems)

Pressure is also unremitting to reduce the time between recognition of a market need and manufacture of the final product for sale. The future growth of the polymer industry will depend in part on how well it is able to respond to this imperative. It is the role of polymer processing to translate the desired features of the polymer architecture into a shaped artefact which meets a market need. Superimposed on all of these needs is the need to recycle by re-use or reprocessing.