THERMOPLASTIC COMPOSITES | MATERIALS Moulding tests
Injection moulding tests were then carried out at Engel’s technology centre in Schwertberg, Austria, on the regranulate to assess the processability and the component quality to be achieved. Processing trials focused on the process behaviour of the regranulate compared to series production. Sample parts were made from a long glass fibre reinforced virgin material, type GB477HP PP GF40 from Borealis as a reference material and the virgin material was processed on the same machine that produced the sample parts from the regranulate, an Engel E-victory hybrid 1640/300 injection press. Both materials were plasticised at three different screw speeds to assess the process consistency. The regranulate was premixed in a masterbatch
load-bearing capacity, which is a key factor in lightweighting engineering applications, in addition to stiffness. The tests used Progano brand thermoplastic
sheets from Profol, based in Halfing, Germany, which are comprised of unidirectional (UD) tapes with 72% weight glass fibres in a PP matrix. An ISEC Evo 302 production unit from Pure Loop was used to regranulate the offcut waste. The infeed thermo- plastic composite sheet was supplied in strips with a length of approximately 1.5 m. The strips were fed by conveyor belt to a hopper and then to the cutting elements of the Pure Loop unit. The equipment from Pure Loop is designed so that the shredder and extruder screw are mounted on a shared shaft. The shredded material passes through a compactor section to an iris valve that controls the material throughput. As part of the process, unreinforced PP in pellet form is also fed into the Pure Loop unit, creating a material mixture between the two components. A filter is deliberately not used in the extrusion section as it would remove the long glass fibres. The plasticised material is hot pelletised and dried in a centrifuge. The resulting pellets are analysed for their qualities by incineration. An optical glass fibre length evaluation is conducted on the incinerated material. Glass fibres with a length of more than 4 mm were found in the incineration residue. It was reasoned that fibre content can be adjusted and optimised when cutting the trim parts for feeding into the shredder. The smaller the parts, the more uniformly the fibres will be ground and mixed with the matrix material. Calculated back from the density, the recycled material has a fibre weight content of around 35% by weight.
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mixer on a trial basis to simulate the influence of an optional homogenisation step – for example in a silo by means of an agitator. The plasticising time fluctuations of the two materials were comparable. With a target shot weight of 400 g, tests showed the standard deviation when processing the regranulate was in the region of 0.7 g, which compares to a standard deviation of the virgin material of about 0.15 g. Engel said that, in absolute terms, the standard deviation was very small for both materials. Engel confirmed through further testing that since
the materials are well homogenised during injection moulding, no significant differences were expected between the regranulate and the virgin material when evaluating the fibre lengths and proportions. The additional homogenisation in the masterbatch mixer did not bring any further improvement as the plasticising already yielded good values for the regranulate. Engel said that in summary it can be stated that the regranulate incorporating recycled tape thermoplastic composite sheets can be processed in injection moulding just as well as the virgin thermoplastic composite material.
Left: Sheet offcuts were used in a project
involving Engel and Pure Loop
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Below: Glass fibre PP sample parts were made using regranulated material and compared with virgin material parts
January/February 2023 | INJECTION WORLD 17
IMAGE: ENGEL
IMAGE: ENGEL
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