Article in Plastics & Rubber Weekly

S F Bush

Two years ago Foresight’s Materials Panel emphasised (PRW May 5 1995) the importance of fostering ‘continuous incremental advances rather than one or two giant leaps’. While not ruling out the latter, the North of England Polymer Processing Consortium (NEPPCO) has put particular emphasis on what may be termed the science of process development (SPD) as the best way of securing for existing processes systematic improvements in product quality, raw materials usage, energy usage, and capital efficiency.

While it has been mainly applied in the large chemical companies, SPD is particularly relevant to the on-going debate about technology transfer to small and medium-sized enterprises (SMEs), of which the polymer processing industry, including the trade moulding sector, is largely made up.

Actually the idea, implicit in the phrase ‘technology transfer’, that there are large quantities of something called ‘technology’ stored in universities and large companies waiting to be transferred to SMEs is largely wrong. Useful technology can only exist in industry. What universities may have is a store of scientific knowledge, some of which can assist in the development of industrial technology. What a number of large companies may have is a store of experience in applying systematic methodologies to operating plant. The science of process development as espoused and practised by UMIST Polymer Engineering marries these two important stores of knowledge with that which exists in the NEPPCO member companies.

To take a particular example, a trade blow moulder may have been blowing bottles successfully with a given grade of polyethylene and then one day finds he can no longer get a satisfactory parison. On the face of it nothing has changed in his process, so he naturally blames the failure on a change in the polymer. The polymer manufacturer checks the sample of the relevant batch, which he has retained (we hope), and declares that it is fully within the specification supplied previously. Meantime the moulder’s machine is idle, not producing anything. How can SPD help?

First it recognises that, with the moulder having eliminated the most obvious single cause and effect candidates, the problem is most likely caused by a combination of factors. Systems technology is a methodology especially evolved to deal with multi-factor problems such as those encountered in synthetic fibre factories with several machines operating in parallel, or those found in a series of processes such as in the manufacture of polyurethane elastomers. The methodology uses both the knowledge of polymer behaviour, which may reside in the university, and the processor’s own knowledge of the past behaviour of his machines in order to formulate a series of relationships between product outcomes and those machine variables which are under the processor’s direct control, such as screw speeds, and machine temperatures. Often these relationships will be quite primitive at first, but because they will be based on well-founded scientific mechanisms, they can be improved as more clues from the process are provided.

A recent application of the approach in NEPPCO was to multicavity insert mouldings where on occasion the injection moulding was incomplete for some inserts and process conditions. The systems model allowed experiments to be carried out within normal operating conditions in order to quantify the effects of the contributory factors: polymer, insert type, cavity position, injection temperature, and thus to formulate a remedy at acceptable cost.

Such an approach provides a ready means of increasing understanding of any currently operating polymer process and is thus a primary means of improving it and its product. But of course many trade moulders have built up a large store of in-house knowledge which enables them for particular polymer grades and types to quickly establish high quality and productions rates for each new mould they see. Increasingly however, customers demand a level of recyclate to be included, or a relatively expensive polymer, such as nylon, to be replaced by a cheaper one such as fibre reinforced polypropylene, which could perform the required duty in the given temperature range. In both these cases, there is a significant change in polymer rheology, and past processor experience may not be enough on its own to find a satisfactory operating window. The approach outlined above could be very helpful in rapidly getting to a satisfactory operating condition.

The systems model approach provides the framework for this to be done within the timescale which SMEs have to operate under.