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 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 Processing Society European Meeting, Stuttgart, Germany, 26th-28th September 1995.
S F Bush with E S Erdogan
Introduction
The work reported here results from a long-term programme of research under the generic title of Self Assembling Fibre Reinforcement (SAFIRE) processes. This work is aimed at providing means by which deformable lace-like structures are obtained within resins and melts in ways which do not interfere with established processing methods such as extrusion, injection moulding and blow moulding. Earlier results, principally on the resultant solid properties, have been reported at PPS conferences (1, 2) and elsewhere3. The processes involved are now patented world-wide (4, 5) and products dependent on the processes have entered commercial production.
The SAFIRE processes provide: (a) masterbatch granules consisting of the chosen polymer matrix in which fibres of any defined length are disposed to minimize breakage during processing, and (b) fibre management devices which when placed in the melt flow, manoeuvre the filaments into deformable but coherent lace-like structures which persist into the solid state(4, 5). The devices are introduced upstream of dies or moulds in ways which do not interfere with the functioning of the process or add materially to its mechanical complexity. Criteria for obtaining fibre mat or lace structures, and factors affecting the polymer-fibre interface are described elsewhere(2, 3). Hitherto work has concentrated on extruded pipe(1, 3) and injection mouldings(2, 3) using polypropylenes and high, medium and low density polyethylenes, and polybutylene. The present paper describes the application of the SAFIRE concepts to sheet extrusion. As it stands this application is not optimized so the results should be seen as preliminary ones only.
References
[1] Bush S F, Extrusion of Melts Containing Semi-Coherent Fibre Structures, 5th Poly Proc Soc Ann Mtg, Kyoto, Japan (1989) paper 11-02.
[2] Bush S F, Ademosu O K, Blackburn D R and Yilmaz F B, Factors Affecting the Strength of Long-Fibre Reinforced Injection Moldings, Poly Proc Soc, European Mtg, Prague (21-24 Sept 1992) paper 6-06.
[3] Bush S F, Yilmaz F and Zhang P F, Impact Strengths of Injection Moulding Polypropylene Long Glass Fibre Composites, VI Inst. Mats. Conf. Fibre Resin Comp., Newcastle (29-31 March 1994) paper 1-05.
[4] Bush S F, Fibre Reinforced Polymer Compositions and Process and Apparatus for Production Thereof. US Patent 5,264,261 (23 Nov 1993)
[5] Bush S F, Filament Separation in Liquids, US Patent 5,035,848 (30th July 1991)
Paper to the Institute of Materials 4th International Conference on Automated Composites, University of Nottingham, 6th-7th September 1995, pp 134-241.
S F Bush with E S Erdogan
Abstract
Broadly, reinforcement may be introduced into polymeric materials either by mixing discrete fibres into a polymer before injecting the fibre containing melt into a shaping mould, or by constructing a predetermined textile form from staple or continuous fibres and then bringing it into contact with the polymer or resin. The first approach readily lends itself to all the high speed automatic processes which have been devised for unreinforced thermoplastics, but carries the penalty of inefficient reinforcement. The fibres are short (typically 0.3 to 0.6 mm), distributed and oriented more by the adventitious action of flow in the mould than in the directions needed to resist imposed stresses and strains.
The second approach 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 this reinforcement efficiency is obtained at the expense of extended manufacturing times and therefore cost.
This paper describes results obtained from processes designed to marry the high-speed advantage of the first approach to the reinforcement efficiency advantage of the second approach. By means of specially designed fibre management devices, well-wetted glass filaments, typically 6-15 mm long, are caused to assemble themselves into semi-coherent mat-like reinforcement structures which are not seriously disrupted when carried by the polymer melt into a mould or 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’s shape.
Earlier papers (1, 2, 3, 4) describe the features of the fibre-mat reinforcing structures and the mechanical properties obtainable from these Self Assembling Fibre Reinforcement (SAFIRE ©) processes. The present paper describes the heat distortion (HDT) temperatures (BS2872 method 121A) obtained from glass fibre reinforced polypropylene injection moulded plaques, with and without SAFIRE fibre management devices, at three different glass fibre concentrations.
The results show that there is a skin-core effect, though smaller than with short-fibre compositions. As a result of this effect the measured HDTs are a few percent greater in the transverse direction than in the flow direction. This low degree of anisotropy is similar to that found previously for tensile3 and impact4 strengths and is a product of the fibre-mat structures obtained(1, 2).
The general result is that for polypropylene the HDT rises by about 6 oC for every 1% fibre volume. This is of considerable commercial significance for polypropylene since mass-produced, largely isotropic, high speed long fibre reinforced mouldings, thermoformings, and extrusions can now be obtained with heat distortion temperatures of around 120 oC (with 25% glass w/w reinforcement) instead of 55 oC for the unreinforced polymer, greatly extending the range of potential applications.
References
[1] BUSH S F, Control of Fibre Structures in Melt Extrusion, 36th Conf. Can. Soc. Chem. Eng., Sarnia, Canada, 6-10 Oct. 1986, paper 32d.
[2] BLACKBURN D R and ADEMOSU O K, Factors affecting Fibre-matrix Contacting in Fibre-filled Granules, Poly. Proc. Soc. IX Ann. Mtg., Manchester, England, 5-8 Apr. 1993, paper 06-14.
[3] BUSH S F, Factors Affecting the Tensile Strength of Long-fibre Reinforced Injection Mouldings, Poly. Proc. Soc. Eur. Mtg., Prague, 21-24 Sep. 1992, paper 6-06.
[4] BUSH S F, YILMAZ F B and ZHANG P F, Impact Strengths of Injection Moulded Polypropylene Long Glass Fibre Composites, VI Fibre Reinforced Composites Conference, Newcastle, England, 29-31 Mar. 1994, paper 5.
