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.