UK Patent: GB 2369322, 9th June 2004

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

Abstract

Polymer composites are comprised of a polymer matrix incorporating heat-shrinkable fibres disposed within the matrix to render the composite self-thermally forming.  The composite may be an elognate article or a sheet or plate.  Application of heat, e.g. localised heating, causing shrinkage of the fibres with self-thermal forming of the composite.  The heat-shrinkable fibres may be polyethylene terephthalate fibres.  The polymer composites may be formed by pultrusion.

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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.

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 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 the Polymer Processing Society 13th Annual Meeting, Secaucus, New Jersey, USA, 6k , 10th June 1997.

S F Bush with M Esfandeh and J M Methven

Introduction

Sheet moulding compounds have been established for a considerable time as convenient materials for the compression moulding of large open structures. They have typically been mixtures of a cross linkable resin, a polymerisable monomer, fillers and discrete fibres, and a thickening agent. The most common composition is one in which the resin is an unsaturated polyester with residual carboxylic end groups, the monomer is styrene and the fibres are glass. The thickening agent is designed to turn a viscous fluid into a leathery sheet which can be rolled up, transported, and cut to fit a compression mould. The thickening agents are conventionally finely dispersed Group II metal oxide powders such as MgO. When a sheet of this material is placed in a mould and heated above about 110-120 ^oC, it softens sufficiently to allow the resin and glass to flow to the boundaries of the cavity, so that a faithful moulding is obtained. Thompson¹ describes the use of crystalline unsaturated polyesters such as poly(neopentyl glycol fumarate) as thickening agents in place of the metal oxides. Gibson and Payne² have described the use of these materials for injection moulding. In 1988 the present authors³ described the use of blends of saturated crystalline additives and crosslinkable base resins such as unsaturated polyesters and uracrylates. These additives are typically polyadipate, polyamide, or polyglycol oligomers with 8-20 repeat units and melting points in the range 40-120 ^oC. They are selected by their degree of compatibility with the base resin in the molten state. The process and blends are now available commercially.

Process and Blends

The thickened sheets are made by a process in which the molten blend of resin and additive is cooled to room temperature from just above the additive melting point. During the cooling process the blend remains a single phase, changing from a transparent liquid to an opaque solid which is malleable as a low tack sheet. As seen on the hot-stage microscope the cooling process is accompanied by the formation of a network of microcrystalline domains which provides the thickening effect^{(4, 5)}. When the sheet material is placed in the compression mould and heated above the additive melting point, the network disappears, the viscosity drops dramatically and resin plus additive chains flow easily to the boundaries of the mould. The moulding viscosity is much lower than that of conventional SMCs and this permits either smaller presses for a given moulding area, or increased areas at given press sizes, or a combination of both: National Composites in the USA have moulded complete garage doors on standard presses. Moreover the blends appear to be intrinsically shrink resistant in that they do not require low profile additives⁵. The resultant resins are conveniently referred to as Viscosity and Shrinkage Controlled Reactive (VISCOR) blends.

References

[1] Thompson S J, GB Patent 2111513 (20 July 1983)

[2] Gibson A G and Payne D J, Fib Rein Comp Conf, London (1988) p 11.1

[3] Bush S F, Methven J M, Blackburn D R, Networks as the basis of pre-thickening sheet moulding compounds, Biol and Snth Networks, Elsevier (1988) p 321-334

[4] Bush S F, High Perf Polym 8 (1966) 67-82

[5] Bush S F, US Patent 5,496,873 (5 March 1996)

[6] Coleman M M et al, Macromolecules 21 59-69

See also the section on Development of New Products & Processes.

US Patent: 5,516,819, 14th May 1996

D R Blackburn, S F Bush, J M Methven

Abstract

A method of producing a thickened organic polymeric composition useful for molding and capable of resisting post-molding shrinkage after being crosslinked comprising a cross-linkable base resin dissolved in an unsaturated monomer, and an additive resin selected from saturated polyesters and saturated amide waxes, the additive resin being crystalline at ambient temperatures and having a melting point (T_m) below a temperature (T_c) at which the base resin cross-linking reaction proceeds at a significant rate. The base resin and additive resin have only a partial degree of compatibility. When cooled from a temperature between T_m and T_c to temperature between T_m and ambient the composition thickens, whereas, when it is heated to a temperature below T_c, it reverts to a flowable composition.

To see the patent in full, go to US Patent Office. On the first page click on USPTO Patent Full-Text and Image Database (PatFT), then under the heading “Searching Full Text Patents (since 1976)”, click on Patent Number Search and enter the patent number (with or without commas) into the “Query” box, then click on “Search”. To search for another US patent, click on Pat Num in the red display at the top of the page.

US Patent: 5,496,873, 5th March 1996

D R Blackburn, S F Bush, J M Methven

Abstract

A thickened organic polymeric composition useful for molding and capable of resisting post-molding shrinkage after being cross-linked comprises a cross-linkable base resin dissolved in an unsaturated monomer, and an additive resin selected from saturated polyesters and saturated amide waxes, the additive resin being crystalline at ambient temperatures and having a melting point (T_m) below a temperature (T_c) at which the base resin cross-linking reaction proceeds at a significant rate. The base resin and additive resin have only a partial degree of compatibility. When cooled from a temperature between T_m and T_c to a temperature between T.sub.m and ambient the composition thickens, whereas, when it is heated to a temperature below T_c, it reverts to a flowable composition.

To see the patent in full, go to US Patent Office. On the first page click on USPTO Patent Full-Text and Image Database (PatFT), then under the heading “Searching Full Text Patents (since 1976)”, click on Patent Number Search and enter the patent number (with or without commas) into the “Query” box, then click on “Search”. To search for another US patent, click on Pat Num in the red display at the top of the page.

Also

European Patent: EP 0396 625 B1, 14th November 1990

Abstract

Polymer compositions useful for moulding comprise a cross-linkable base resin, an unsaturated monomer in which the base resin is dissolved and a saturated additive resin which by itself is crystalline at ambient temperatures with a melting point (T_m) below that temperature (T_c) at which the base resin cross-linking reaction is designed to proceed at a significant rate. The composition is such that on cooling from a temperature between T_m and T_c, to a temperature between Tm and ambient the additive resin forms distributed microcrystalline domains connected severally by chains of the additive resin threading through the base resin chains. This produces a thickening network which may be reversibly broken down to the original additive resin molecules by heating to a temperature below T_c. The additive resin molecules swell the permanent base resin network created by the said cross-linking reaction which occurs during moulding, and thereby providing resistance to post-moulding shrinkage.

Paper published in the Journal of High Performance Polymers (1996) 8 67-82.

S F Bush with J M Methven and D R Blackburn

Abstract

This paper describes a new class of thermosetting polymer blends. The blends are now used commercially in the manufacture of sheet moulding compounds (SMC) where they exhibit important advantages compared with conventional systems. The new compositions comprise a cross-linkable base resin and unsaturated monomer in which the base resin is dissolved and a saturated additive resin which has a crystalline melting temperature T_m below the temperature T_r at which cross-linking occurs. Between T_r and T_m the additive and base resin form a single liquid phase, which on cooling thickens reversibly to a leathery sheet with no bulk phase separation. The paper describes the mechanisms underlying this viscosity switch phenomenon and the partial compatibility criterion used to select the resin-additive combinations which exhibit this behaviour.

Eleventh Annual Meeting of the Polymer Processing Society, Seoul, Korea, 27th-30th March 1995, paper 08-10

S F Bush, with J M Methven

Synopsis

In Ref 1 the authors describe a novel process for sheet moulding compounds in which the standard Group II metal oxide thickening agents are replaced by organic compounds chosen to have what may be termed partial compatibility with an unsaturated base resin. The purpose of the thickening agent in both cases is to produce from a liquid resin with viscosity typically 1 poise, a leathery moulding compound of viscosity in the range 10⁵ to 10⁶. This blend is usually in the form of a sheet which may be cut at a later time to fit into a compression mould. The new process is the subject of world-wide patenting (Ref 2) and the resultant products entered commercial production earlier this year.

The present paper describes recent experimental results and discusses the mechanisms underpinning the huge reversible changes in viscosity which are obtained over a 15 ^oC temperature interval. Such a viscosity switch principle enables reinforcing fibres to be thoroughly wetted at basically the resin viscosity before a modest lowering of temperature produces a material which can be cut and manipulated. At the heart of the mechanism is the formation of a network made up of the additive polymer chains connected at intervals by a series of micro crystalline domains formed by the same additive. When the thickened sheet is placed in the mould and heated to the reaction temperature of the unsaturated base resin, the micro crystalline domains melt and the resin then flows freely to the internal surfaces of the mould.

Experiments show that the requisite partial compatibility of resin-additive polymer pairs can be determined in many cases by requiring their solubility parameter differences Δδ to lie within a given range. If Δδ is too small, the additive polymer remains in solution with the base resin; if Δδ is too large it separates completely. The paper discusses the advantages and limitations of the Δδ approach to estimating partial compatibility.

References

[1] S F Bush, J M Methven, D R Blackburn, Networks as the basis of pre-thickening sheet moulding compounds, Biol Synth Poly Networks, ed O Kramer, Elsevier 1987, pp 321-334.

[2] S F Bush, J M Methven, D R Blackburn, Polymer Compositions, Intl Patent WO 8906258, 13 July 1989 and European Patent EP 0396625, 14th November 1990.