Paper to the 17th Annual Meeting of the Polymer Processing Society, Montreal, Canada

M Esfandeh with S F Bush and J M Methven

Abstract

This paper describes a Differential Scanning Calorimetry (DSC) study of a new class of thermosetting polymer blends. The blends are made by physical thickening in which a particular crystalline additive is capable of forming a thickened system when it is melt blended with a thermoset resin. The blends are now used commercially in the manufacture of sheet moulding compounds (SMC) where they exhibit important advantages over conventional systems. In previous reports from this laboratory the morphology of these blends was studied[6] and on the basis of secure physical foundations, a model for blend morphology was presented. In this paper the effect of the presence of resin on melting and crystallisation temperature of thickening additive is studied using DSC technique. The corresponding enthalpies of transition are also measured and are compared with values expected from dilution effect. Finally the interaction parameter between resin and additive is calculated from a depression in the melting point of the blend.

[6] Bush S F, Esfandeh M and Methven J M, “New Blend Morphologies for Low Pressure Moulding Compounds”, Polymer Processing Society, 15th International Meeting, Hertogenbosch, The Netherlands, May 31st-June 4th (1999)

Prosyma Research Report to Permali Ltd

S F Bush

Summary

This report details the experimental work carried out since the meeting between BTR Permali and UMIST in the November of 1987. At that meeting the following list of subjects was suggested for further research in the time available:

• Characterising the cooling of the new SMC paste systems by means of DSC (Differential Scanning Calorimetry).
• Investigating the thickening of the SMC paste using a penetrometer, rather than a ball and tube viscometer. This was principally to characterise the later stages of thickening.
• Some form of investigation into the tack behaviour of the sheets thickened by this new process.
• If possible some moulding trials could be carried out at BTR.

 
It was also agreed to confine the work to two resin-filler systems, namely MODAR-ATH and UP-Hydrocarb. PHMA was used as the thickening additive for all this work.

The work done using DSC improved upon that carried out for the previous report in that it was possible this time to control the cooling of the paste, rather than just its heating. A cooling rate was chosen which corresponded to the fastest possible which could occur on a production SMC machine, (in other words, the worst possible conditions from the point of view of the wet-out of the glass fibres). This has given an indication of the differing thickening behaviour of the paste for different systems.

The penetrometer was constructed here at UMIST. The results obtained show that the behaviour of the paste in the later stages of thickening is consistent with its behaviour in the early stages of thickening. A calibration using conventional MgO thickening has been carried out on the penetrometer.

It has not proved possible in the time available to devise and construct a reliable device to measure the degree of tack of the sheets. Monitoring of the change of tackiness was therefore carried out by observation of sheets on the laboratory bench. It was found that a more effective thickening of the polyester resins was obtained than with the MODAR resins. It was also found that reduction of tack is not directly connected with reduction in viscosity, and that in general, the first noticeable effects of a reduction in tack occurs some 15 minutes after the thickening process is complete.

Some mouldings were carried out at BTR, from which an indication of the upper limit of adipate that may be present in a MODAR based SMC was obtained.