Paper to the Polymer Processing Society 13th Annual Meeting, Secaucus, New Jersey, USA, 6k , 10th June 1997.
S F Bush with M Esfandeh and J M Methven
Introduction
Sheet moulding compounds have been established for a considerable time as convenient materials for the compression moulding of large open structures. They have typically been mixtures of a cross linkable resin, a polymerisable monomer, fillers and discrete fibres, and a thickening agent. The most common composition is one in which the resin is an unsaturated polyester with residual carboxylic end groups, the monomer is styrene and the fibres are glass. The thickening agent is designed to turn a viscous fluid into a leathery sheet which can be rolled up, transported, and cut to fit a compression mould. The thickening agents are conventionally finely dispersed Group II metal oxide powders such as MgO. When a sheet of this material is placed in a mould and heated above about 110-120 oC, it softens sufficiently to allow the resin and glass to flow to the boundaries of the cavity, so that a faithful moulding is obtained. Thompson1 describes the use of crystalline unsaturated polyesters such as poly(neopentyl glycol fumarate) as thickening agents in place of the metal oxides. Gibson and Payne2 have described the use of these materials for injection moulding. In 1988 the present authors3 described the use of blends of saturated crystalline additives and crosslinkable base resins such as unsaturated polyesters and uracrylates. These additives are typically polyadipate, polyamide, or polyglycol oligomers with 8-20 repeat units and melting points in the range 40-120 oC. They are selected by their degree of compatibility with the base resin in the molten state. The process and blends are now available commercially.
Process and Blends
The thickened sheets are made by a process in which the molten blend of resin and additive is cooled to room temperature from just above the additive melting point. During the cooling process the blend remains a single phase, changing from a transparent liquid to an opaque solid which is malleable as a low tack sheet. As seen on the hot-stage microscope the cooling process is accompanied by the formation of a network of microcrystalline domains which provides the thickening effect(4, 5). When the sheet material is placed in the compression mould and heated above the additive melting point, the network disappears, the viscosity drops dramatically and resin plus additive chains flow easily to the boundaries of the mould. The moulding viscosity is much lower than that of conventional SMCs and this permits either smaller presses for a given moulding area, or increased areas at given press sizes, or a combination of both: National Composites in the USA have moulded complete garage doors on standard presses. Moreover the blends appear to be intrinsically shrink resistant in that they do not require low profile additives5. The resultant resins are conveniently referred to as Viscosity and Shrinkage Controlled Reactive (VISCOR) blends.
References
[1] Thompson S J, GB Patent 2111513 (20 July 1983)
[2] Gibson A G and Payne D J, Fib Rein Comp Conf, London (1988) p 11.1
[3] Bush S F, Methven J M, Blackburn D R, Networks as the basis of pre-thickening sheet moulding compounds, Biol and Snth Networks, Elsevier (1988) p 321-334
[4] Bush S F, High Perf Polym 8 (1966) 67-82
[5] Bush S F, US Patent 5,496,873 (5 March 1996)
[6] Coleman M M et al, Macromolecules 21 59-69
See also the section on Development of New Products & Processes.
Paper to the Polymer Processing Society European Regional Meeting, Palermo, Sicily, 15th-18th September 1991.
S F Bush with C A Benson
Introduction
The design of reaction injection moulding processes requires knowledge of the system chemistry, an evaluation of the possible mixing processes which can be used, and characterisation of the subsequent in-mould behaviour of the reacting mixture. Mixing times are required to be a few milliseconds, moulding filling times typically a few seconds, and cycle times from one to three minutes.
The major problems in handling the phenolics chemistry for process design are how to characterise the variety of resins used and how to reduce the complexity of the chemical mechanisms to manageable proportions.
Phenolic reinforced reaction injection depends on rapid mixing of two or more unequal reactant streams with flow rate ratios typically somewhere in the range from 1 to 20 to 1 to 3. The major stream may contain reinforcing fibres of lengths up to 1.5 mm. The work reported here has concentrated on phenolic foams of densities up to about 500 kgm-3. Fibre reinforcement at about 5% of final part weight can increase strength and modulus by about 50% for foams in the range 300 to 400 kgm-3. On the basis of the chemical and mixing models an RRIM machine and mixhead have been designed and built for maximum shot volumes of 3 litres and an injection rate of 1 litre s-1. This gives for instance a 1 m x 0.5 m x 19 mm foam moulding of 400 kgm-3 density.
See also the section on Development of New Products and Processes.
Group II Research Note, ICI Corporate Lab.
S F Bush with P Dyer and M J Shires.
Summary
Experimental results from a new device for vaporizing heat sensitive liquids are reported. Experiments have been carried out with adipic acid on a 20 lbs/hr rig at CL-B. The direct contact of liquid adipic acid and heating surfaces is minimised by injecting acid droplets into an internally circulating vapour flow, which itself receives heat from the walls of the vaporizer. The internal circulation is maintained by entrainment into an incoming ammonia jet. Some experimental optimisation of the internal geometry has been achieved.
This principle of jet-spray vaporization is designed to be directly applicable in the existing spinner shells in Petrochemicals Division with only a minimum of modifications. It should also apply to other vaporizations where a carrier gas is available or can be introduced.
See also the patents arising from this work Vaporisation Process.
Group II Research Note, ICI Central Instrument Research Lab.
S F Bush with P A Sinclair
Summary
An important method of manufacture of 1.1.1.-trichloroethane proposed by Mond Division is the vapour-phase chlorination of 1.1.-dichloroethane made from liquid-phase hydrochlorination of VC,
CH2 = CHCl + HCl → fast → CH3.CHCl2.
For this process the organic feed is conveniently brought to a preferred reaction temperature of 400-410 oC by mixing with reacted product, the whole to run autothermally. Factors limiting design on the 25,000 tons per year scale are (a) the stability of the reaction to external disturbances, particularly flow disturbances and (b) the difficulty of ensuring that the preferred steady reaction temperature can be sustained even with no flow disturbances.
The theory and models worked out for the chloromethanes process have been applied to this proposed new process with a view to (a) predicting if a process based on a chloremethanes-type reactor would be satisfactory on the scale proposed, and (b) if so, what size should the semi-technical reactor be to give adequate experimental proof of the design and the control scheme. The intricate programming and many attendant calculations have been carried out by P A Sinclair.
This note gives an interim account of the conclusions reached in this study, which is continuing, and which has involved several recomputations from changed kinetic data.
See also the section on Development of new Products and Processes.
