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 5th International Conference on Manufacturing, Processing Composite Materials, Plymouth University, 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.

S F Bush with F G Torres

Abstract

The present paper summarises the main aspects and the developments in sheet extrusion and thermoforming of discrete long glass fibre (LGF) composites using the SAFIRE (Self Assembling Fibre Reinforcement) technology. During extrusion the long glass fibres are organised into coherent fibre mats which persist into the solid state, and are able to withstand the deformation process that takes place during thermoforming. A process analysis has been performed for extrusion and thermoforming indicating the main individual operations. Both processes have been studied with regard to their performance with the materials used in the studies, namely polypropylene homo and copolymer, with and without LGF reinforcement. Significant improvements in mechanical properties relative to the unreinforced materials have been found for the extruded sheets and the thermoformed products. Major improvements in processability relative to unreinforced PP have been found for the LGF materials. These are discussed in terms of the coherent fibre mat concept.

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

Paper to the Polymer Processing Society 15th Annual Meeting, ‘s-Hertogenbosch, Holland.

Published in International Polymer Processing XV (2000) 2.
S F Bush with F G Torres

Abstract

This paper lays out the main procedures for performing morphological characterisations of Long Glass Fibre (LGF) composites with particular reference to the sheet extrusion and thermoforming processes as they may be configured for production. The techniques used, including optical microscopy, scanning electron microscopy and image analysis, are described both with regard to their laboratory application to these materials and to their potential for monitoring the performance of the industrial manufacturing process. Results obtained from the different techniques at the three various stages of the manufacturing route are presented and discussed in terms of the structure property relationships obtained and the reinforcing fibre mat system typical of these types of material.

Paper

S F Bush with F G Torres

Abstract

Thermoforming is a major process with a wide range of applications in several fields. One of the most interesting possibilities is the thermoforming of PP. It is well known that Long Glass Fibre (LGF) composites present better mechanical properties than unreinforced PP. In addition to that, long fibres increase the thermal stability and the melt strength of the unreinforced polymer. In this paper, the thermoformability of LGF reinforced PP is studied using dynamic mechanical analysis (DMA), hot tensile tests, sheet sag tests, and microscopical techniques for the characterisation of the fibre mat deformation process. DMA is used to characterise the anisotropy and the softening behaviour of the LGF extruded sheets. Hot tensile testing is used for assessing stretchability. Sheet sag studies under Infra-red (IR) conditions showed that LGF reinforced materials present a much lower degree of sag and a higher resistance to localised heating than the unreinforced polymers. Finally, scanning electron microscope (SEM) pictures are presented to verify the mat deformation processes occurring during thermoforming.

Paper to the Polymer Processing Society 14th Annual Meeting, Yokohama, Japan, 8th-12th June 1998, paper 9-03.

S F Bush with F G Torres

Introduction

Discrete long glass fibre (LGF) reinforcement of thermoplastics has been applied successfully to conventional polymer processing techniques, such as extrusion, injection moulding and blow moulding. The results of the studies covering those processing techniques and their advantages with respect to other types of fibre reinforcement have been summarised elsewhere¹. One of the most important potential applications of discrete long glass fibre (LGF) reinforcement of thermoplastics is sheet extrusion. The fibres can be induced to form mats of more or less defined mean orientations in the melt state, so that extruded sheets of controlled anistropy can be obtained. The sheets can then be processed by thermoforming.

Thermoplastics, especially, PP have many desirable solid state properties for a thermoformed product. However it presents a very narrow processing window for thermoforming, because the stretching process of the sheet has a tendency to be unstable. High melt strength PP (HMPP)² and reinforced or filled PP have been used in order to improve the stretchability and broaden the processing window. In this context, discrete long glass fibre (LGF) reinforcement has proved to be one of the best methods of achieving these goals, increasing the melt viscosity (shear and elongational)³, and in addition increasing strength and stiffness in the solid state, in particular at high temperatures.

In the present paper, Dynamic Mechanical Analysis (DMA) is used as a method for measuring the properties of the extruded sheets in a wide range of temperatures.

References

[1] BUSH S F, “Long glass Fibre Reinforcement of Thermoplastics: Results from Injection and Blow Moulding, Sheet and Pipe Extrusion”, Poly Proc Soc (PPS Euro Mtg) Gothenburg, Sweden, 19-21 Aug (1997)

[2] MORAD J J, “High Melt Strength Polypropylene for Large Part Thermoforming”, ANTEC 95, Vol I, Boston, USA, May (1995)

[3] TORRES F G, “Modelling of Polymer and Polymer Composite Flows: Molecular Chain Orientation and Reinforcing Fibre Orientation”, MPhil Thesis, UMIST, Manchester, UK (1997)

[4] ERDOGAN E S, Private Communication, UMIST 1997, also in PhD Thesis, UMIST 2000.

Paper to the Polymer Processing Society 14th Annual Meeting, Yokohama, Japan, 8th-12th June 1998, paper 2-6.

S F Bush with F G Torres

Introduction

A model proposed by Bush1 has been extended and numerically implemented to produce molecular chain conformations in polymer flows. The effect of shear and extensional flows is studied. The chain shape is defined as a primary transport variable and viscosity is predicted thereof.

Two main approaches have been used in the modelling of polymer flows: the continuum mechanics approach and the molecular approach. The present work is based on the second one. Chain shape is a term used to express the actual conformations of a single entangled polymer chain at a specific time and place in the flow domain. The chain shape and the number of entanglements determine the resistance to flow of a polymer melt. So, viscosity is obtained as a function of the actual chain shape. To allow for the simulation of chain conformations, equivalent chain segments have been defined as primary transport variables, which are convected from one point to another in the flow field. Due to its formulation, the present model allows for polymer viscoelasticity to be represented in a natural way, with the shear and normal stresses being calculated as a function of the chain shape and of the velocity gradients. The treatment followed in this work can be extended in a straightforward manner for the modelling of polymer crystallisation and the prediction of shrinkage in plastic parts.

References

[1] BUSH S F, “Representation of Polymer Chain Shape in Injection Moulding simulation” Poly Proc Soc (PPS European Regional Mtg) Sept 1988, Brunel Univ, UK.

[2] TORRES F G, MPhil Thesis, UMIST, Manchester, UK, 1997.

[3] BUSH S F and DYER P, “The Experimental and Computational Determination of Complex Chemical Kinetics Mechanisms”, Proc Royal Soc, London, A 351, pp 33-53, 1976

See also the section on Mathematics & Computation.

Paper to the 7th International Conference on Fibre Reinforced Composites, FRC’98, University of Newcastle-upon-Tyne, UK, 15th-17th April 1998

Published by Woodhead Publ, Ed A G Gibson, pp 237-244, ISBN 1855 73 3757.

S F Bush with F G Torres and E S Erdogan

Abstract

The mechanical properties of discrete long glass fibre (LGF) reinforced polymer sheets have been studied pre and post thermoforming. Extruded sheets have been produced using different grades of PP and PE at different fibre concentrations. Novel fibre management devices have been employed in order to control fibre mat formation during sheet extrusion. Tensile and dynamic mechanical properties of the sheets are reported. In addition, thermoformability studies have been carried out by varying the processing parameters. The coherence of the reinforcing fibre mat has been observed before and after uniaxial and biaxial stretching in the thermoforming process. The operating temperature window for these materials has been defined.

Paper to the Polymer Modelling Scales of Structures Conference, Institute of Physics, London

F G Torres and S F Bush

Abstract

A model proposed by Bush^{(1, 2)} has been extended and numerically implemented to produce molecular chain conformations in polymer flows. The effect of shear and extensional flows is studied. The chain shape is defined as a primary transport variable and viscosity is predicted thereof. Shear thinning of melt viscosity is verified in the simulations. The formulation can be extended to crystallisation and shrinkage studies.

References

[1] Bush S F, Polymer Model: Flow, Orientation and Crystallization, ICI Europa Ltd, Technical Note 55, 1975

[2] Bush S F, Representation of Polymer Chain Shape in Injection Moulding Simulation, Poly Proc Soc, PPS European Regional Meeting), Brunel University, UK, 18-19 September 1988

[3] Torres F G, Modelling of Polymer and Polymer Composite Flows: Molecular Chain Orientation and Reinforcing Fibre Orientation, MPhil Thesis, UMIST, Manchester, UK, 1997

[4] Agassant J F, Avenas P, Sergent J P and Carreau P J, Polymer Processing Principles and Modeling, Hanser Publishers, Munich, 1991

[5] Bush S F and Dyer P, The Experimental and Computational Determination of Complex Chemical Kinetics Mechanisms, Proceedings of the Royal Society, London, A. 351, pp 33-53, 1976