Paper to Polymer Processing Society Americas Regional Meeting, Florianopolis, Brasil, 7th-10th November 2004
S F Bush
Introduction
It has long been appreciated that the addition of glass or other stiff fibres to a thermoplastic or thermoset in a suitable fashion usually brings increased stiffness and strength to the processed material. In the case of injection moulded thermoplastics, the glass fibres have until the 1980s been very short, usually in the range 0.3-1.0 mm.
In the case of thermoset compositions the fibres have generally either been 25-50 mm discrete fibres as in sheet moulding compounds (SMCs) or continuous woven structures. If 25-50 mm discrete fibres are used, they are usually in tows (bundles) of 30 or more individual filaments, either constructed into a loosely woven mat and then impregnated with thermoset resins or scattered in a random overlapping fashion on to a layer of resin with further resin poured on top. In either case, a form of semicoherent fibre structure is obtained within the polymer liquid, this structure being maintained after the composite sets to solid. This structure is one of the two main reasons why fibre-reinforced thermoset composites commonly show greater strength and stiffness than do the thermoplastic varieties based on short fibres, which do not usually form such structures, the other being the chemical cross-linked character of the thermoset.
Whatever the specific objectives laid down for the composite, two factors in particular will determine how it meets these objectives. These are (i) fibre-polymer contact, and (ii) fibre management. The over-arching requirement is of course that of minimum cost of the product as defined by its required shape and load-bearing characterisation.
Paper published by Elsevier, “Biological and Synthetic Polymer Networks”, 321-334 (Editor: O Kramer) 1987.
S F Bush with J M Methven and D R Blackburn
Abstract
The formation of a temporary network by a saturated polyester added to an unsaturated resin appears to provide both an attractive route to the pre-thickening of such resins when used in Sheet Moulding Compounds, and a means of controlling their shrinkage during moulding. It is believed that this is the first report of a successful method of achieving both goals with a single material. The network is based upon the formation of precrystalline clusters of polymer chain segments. The density and character of the network are determined by the compatibility of the saturated polyester and the unsaturated resin.
Proceedings of the 8th IUPAC Biological and Synthetic Polymer Networks Conference, Elsinore, Denmark, 31st August-5th September 1986.
Elsevier Applied Science, Editor O Kramer, p321, ISBN 1 85166 166 2.
S F Bush with J M Methven and D R Blackburn
Abstract
The formation of a temporary network by a saturated polyester added to an unsaturated resin appears to provide both an attractive route to the pre-thickening of such resins when used in Sheet Moulding Compounds, and a means of controlling their shrinkage during moulding. It is believed that this is the first report of a successful method of achieving both goals with a single material. The network is based upon the formation of precrystalline clusters of polymer chain segments. The density and character of the network are determined by the compatibility of the saturated polyester and the unsaturated resin.
References
[1] Brydson J A, Plastics Materials, Butterworth, London, 4th edn, 1982.
[2] Burns R, Polyester Molding Compounds, Marcel Dekker Inc, New York, 1982.
[3] Flory P J, Principles of Polymer Chemistry, Cornell University Press, Ithaca, New York, 1953.
[4] Hildebrand J H and Scott R L, Solubility of Non-electrolytes, 3rd edn, Rheinhold, New York, 1950.
[5] Van Krevelin D W, Properties of Polymers, 2nd edn, Elsevier, Amsterdam, 1977, Chapter 8.
[6] Williams R J J, Barrajo J, Adabbo H E and Rojas A J, ACS Sym, Ser, 1984, 208 195-213.
