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.
Invited Paper to the Institute of Materials Conference “Advances in Blow Moulding”, Loughborough University, UK, 30th June-1st July 1998.
Published by the Institute of Materials, “Plastics, Rubber and Composites 1999” Vol. 28 No. 8 379, ISSN 1465-8011
S F Bush with M Dreiza and J D Tonkin
Abstract
Precompounded discrete fibres have long been used as reinforcement in injection moulding particularly with polypropylene and nylon matrixes. Usually the lengths of the fibres in the finished article have been in the range 0.2-1.00 mm and for convenience are labelled short glass fibres. The last 15 years has seen the development of precompounded long glass fibres, having lengths in the finished article of typically an order of magnitude longer than for short glass fibres.
The present paper describes experiments on the blow moulding of long glass fibre reinforced virgin and recycled polymers. The long glass fibre compounds have been made using in house technology, for which the matrix interface conditions are known and can be varied. Bottles of 2 L capacity with integral handles were blown as the primary testpieces for evaluating blowability of these new materials and for investigating the reinforcing structures obtained in the bottle walls. Mechanical properties were evaluated at room temperature before and after recycling and at elevated temperatures up to 100 oC, which are particularly relevant to the blow moulding applications envisaged. PRC/1523
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 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.
Paper (5) to the Institute of Materials 6th International Conference on Fibre Reinforced Composites, Newcastle, England, 29-31 March 1994.
Published in Plastics, Rubber and Composites Processing and Applications, Vol 24, No 3 (1995).
S F Bush with F B Yilmaz and P F Zhang
Abstract
A wide series of experiments has been undertaken to measure impact strength as a function of fibre length and concentration, the fibre/matrix interface, and induced fibre-mat structure and matrix properties. Both commercially-available long-fibre polypropylene granules and in-house polypropylene and polyethylene glass-fibre compounds have been used where the interface conditions are known and can be varied. For the fibre-mat structures achieved, notched impact strengths rise with fibre lengths and with fibre concentration, giving in all cases an improvement on the virgin polypropylenes – for some conditions a five-fold improvement at 25% w/w concentration.
