Prosyma Research Ltd report to Weltonhurst Ltd.

S F Bush with J D Tonkin

Introduction

Weltonhurst supply high density polyethylene blow moulded containers to Richard Millington and Co Ltd. The containers are used to hold cleaning fluid under pressure for the purpose of cleaning out beer lines. The HDPE has come from a variety of suppliers including Dow, Atochem and Borealis, with a density around 0.95 gm/cc. The fluid has the specification:

Sodium Hydroxide: 9.2 ± 1 gm/litre

Sodium Hypochlorite: 7.6 ± 2 gm/litre

“Phosphorus butane carboxyl”: 4.8 ± 0.25 gm/litre

The precise chemical formula of the third component is unknown, but it looks like a mild detergent.

An earlier report (Ref 1) investigated the short-term mechanical properties of the polymers used, following the disintegration of a 50 litre container after six years in use. Fragments of the disintegrated container were found to be significantly less ductile than recently made containers, pointing to some long-term degradation of the polymer, exposure to sunlight being a prime possible agent.

The present investigation has been concerned with a second possible agent of long-term degradation, namely environmental stress cracking (ESC). ESC is not a well defined concept, but the essential point is that some environments reduce the mechanical properties over time. Generally these weakening effects are increased with an increase of temperature. Tests have therefore been done at both a working temperature (23 ^oC) and an elevated temperature (60 ^oC) which might be seen as the limit that the container could normally attain (by being left out in the sun for example).

References

1: S F Bush & J D Tonkin, Report on failed Bass bottle, PRL, 11.8.95.

2: S Turner, Mechanical testing of plastics, George Godwin, 1983.

Extracts from three Prosyma Research Ltd reports to the Everite Group, 6th April 1990 to 19th November 1990.

S F Bush

(The focus of the SAFIRE work moved to Santar situated in South Africa.)

SAFIRE A – Pipe extrusion (6th April 1990)

The work in the period under review (the S-runs) was taken up with extending the work of the R-runs (reported in Report 7) to a wide range of SAFIRE materials.

Altogether we have demonstrated pipe making capability in the SAFIRE polypropylene granules typical of the Santar materials as well as the Santar specified HDPE Hostalen GM5010. Note that this HDPE grade is black and this adds a dimension of potential difficulty because of the tendency for carbon black to cling to upstream discontinuities.

SAFIRE A – Pipe extrusion (1st May 1990)

The last report highlighted the likely effects of temperature on the presence or absence of weld lines. Consequently the work in the period under review (T-runs) has concentrated on repeating, where possible, the S-runs but at higher temperatures.

The results so far show that a significant decrease in polymer MFI requires a substantial increase in temperature in the mixing zone. This is particularly evident with Hostalen 5010, the HDPE grade proposed by Everite. Its MFI is about 0.3 at 230 ^oC compared with 0.4 for the PP Profax used up to now. Runs at 240 ^oC insread of 220 ^oC used in the S-runs show an appreciable increase in burst strength which may tentatively be ascribed to more complete disappearance of the weld line.

Injection Moulding (19th November 1990)

Recent results at UMIST have shown that SAFIRE granules may be injection moulded with separation and average fibre length retentions comparable with the values found in extrusion. This is achieved with a minor adaptation of a standard injection moulding machine and a simple version of the Fibre Separating Unit.

Report 6 from a series of 5 Prosyma Research Ltd reports to Ametex AG, 15th February 1989 to 14th January 1990.

Report 6 dated 31st May 1989, Report 7 dated 11th July 1989, Report 8 dated 24th July 1989.
S F Bush

Summary: Part 1

1. During the period under review, SAFIRE project A has followed up the breakthrough in finishing technology achieved in the previous six-month period.
2. On the process itself follow-up has concentrated on establishing the design and operating parameters which determine acceptable and indeed exceptional finish with the new technology, at the same time making many metres of pipe for burst and creep testing.
3. Both polypropylene (PP) and HDPE SAFIRE pipe can be made with fine finishes on a routine basis. While not of direct benefit to the project, the finishing technology gives quite remarkable mirror finishes to virgin pipe.
4. In the period under review, SAFIRE project C has concentrated on producing SAFIRE granules in a wide range of combinations of fibre and polymer, and evaluating these for use in pipes.
5. The signs are that the evaluations made for this purpose will also give a good indication of the commercial potential for SAFIRE granules in combination with Fibre Separating Devices (FSD) sold in their own right. The significance of this potential has become clear from recent information on present commercial products.

Paper to the 6th Plastics and Rubber Institute Conference on Pipes, York, UK, 25th-27th March, 1985.

S F Bush with W G Harland and S Bilgin

Abstract

In an earlier paper[1] the principle of extruding short (around ½ mm) glass fibre reinforced poly-propylene in pipe form, using a rotating mandrel and stationary outer die, was described, together with the results shown in the first section of the Table below. Generally, desirable increases in both hoop strength and hoop modulus were obtained at relatively low (around 10 rpm) rates of mandrel rotation. This improvement was ascribed to two factors (a) elimination of the weld line (this particularly affects hoop strength) and (b) partial alignment of the figures in the hoop (circumferential) direction (this particularly increases hoop modulus, and reduces longitudinal crack propagation).

The present paper reports work which extends the earlier results in three directions. These are (i) use of a wider range of fibre lengths, (ii) use of other polyolefine matrices including rubber modified types, (iii) development of the die system design. The object of (i) and (ii) has been primarily to improve further the strength-modulus-toughness combination while (iii) is aimed at enabling (i) and (ii) to be carried out and also at improving the surface quality. A third objective under (iii) has been the design of a rotating die system which is easy to install on standard machines. Basically the results indicate that a commercially applicable process for making tubes with an attractive combination of properties has been developed.

The polymer systems investigated include PP, HDPE, mixtures of the two, and PP containing a proportion of EPDM, together with varying amounts and lengths of glass fibre. The process systems investigated include inner and outer die rotation together with an optimised cooling profile. The effects of different process configurations on pipe surface finish as well as on the primary mechanical properties have been assessed. Fibre orientations have been determined as a function of process parameters and compared with model predictions. Other measurements made comprise fibre length distribution in the pipe, burst strengths and dart impact resistance, as functions of the combined polymer-process system. The results obtained for two of the many matrix-fibre combinations investigated are shown in the Table with earlier values for comparison. While not as yet quantified, the results obtained under dart impact with the latest fibre-matrix-process system are especially noteworthy: the tendency for cracks to propagate and collapse the pipe specimen is greatly if not entirely inhibited.

Key: SGF – short glass fibre; NF – new fibre; CA – coupling agent.

Ref 1: S F Bush, W G Harland, S Bilgin, “Extrusion of Fibre-reinforced Thermoplastic Pipe”, 233, SERC Polymer Engineering 2nd Biennial Review Meeting, Loughborough, 13th-15th April 1983.