Paper published in International Polymer Processing XIV (1999) 3, 282-290, ISSN-0930-777X, 1999.
S F Bush
Abstract: Experimental and Theoretical Results for Injection and Blow moulding, Sheet and Pipe extrusion.
The paper summarises the main experimental and theoretical results from a long-term programme of research (SAFIRE) to produce and apply long glass fibre compounds to the extrusion of pipes, sheets and profiles and to injection, blow and roto moulding. The overall objective is to obtain the processing speeds associated with short fibre reinforced thermoplastics with the reinforcement efficiencies associated with prepositioned or prepreg thermoset composites. Extrusion and injection moulding are now in the commercial domain, with industrial scale trials underway in the other technologies.
Long glass fibres are defined by their ability to form lace-like mat structures within the polymer melt which persist into the solid state. Such structures, which greatly increase both melt strength and solid state thermo mechanical properties, can be formed with fibre volume concentrations (c) as low as .0l. The formation of mat structures depends on the number N of virtual touches per filament. A minimum of around five touches is generally needed. From earlier work N is given as A.c l/d. A varies with mean fibre orientation in the mat: for the random in-plane case it is approximately 8/π2, so that in contrast with typical fibre suspensions (c <d/l) extremely strong particle-particle interactions are involved in the melt state.
In the solid state, tensile strength is measured and modelled in terms of number average fibre length (l) and diameter (d), polymer yield strength, fibre distribution efficiency, interfacial shear strength and a specially defined matrix stress magnification factor M. The role of patented fibre management devices in optimising these variables as they appear in the solid state is defined and described.
Paper to the Polymer Processing Society European Meeting, Strasbourg, 29th-31st August, paper 5-3.
S F Bush
Introduction
To view the introduction, please click on the link: ModellingLace
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.
