rPET Quality Report

with screened flake. It was less yellow and there was a measured 26% improvement in the
b-value of the 90% rPET sheet.
Figure 27: Sheet extrusion trial using screened flakes (Courtesy of Anson Packaging).
9.2 TDX sheet extrusion trial using screened flake
Sheet extrusion trials using screened flake from a UK recycler were run at TDX. The purpose
of these trials was to evaluate whether screened recycled flake was less contaminated and
reduced the level of clogging on filter packs that was previously experienced when
unscreened hot washed rPET flake was trialled. A further objective of the trial was to also
visually evaluate whether the screened flake resulted in sheet with fewer visual solid particle
defects and reduced levels of gels and black specs.
The screened flake was sieved in a batch process using an automated machine using a 3mm
screen for a period of 20 minutes. Quality testing of the screened flake showed that
reduction of fines and particles under 2mm in size was only 50% effective, that is there were
still 50% of fines still remained in the flake even after screening trials. The limited removal of
fines was due to limitations in current design of screening equipment and due to dust and
fines being more easily trapped in PET flake. Improvements to screening systems are
needed to achieve 90% removal of small particles and effective removal of trapped fines and
dust particles from PET flakes.
The recycled content of the screened flake in the sheet was set to 30% and the remaining
70% was made up of 10% virgin, 30% PCR rPET flake from another UK recycler and 30%
reuse of thermoformed PET trim. The extrusion sheet was produced at 950kg/hr and was
filtered with a 40-micron 4-layer screen. The automated filtration set-point on the sheet
extrusion line was set to 50 bar pressure, at which point the filters were back-flushed and
contaminants removed. The graph in Figure 28 shows processing times between filter
flushing. Longer intervals mean that less PET material is lost to flushing also improving the
processing life of filter screen packs, leading to lower costs associated with screen
replacements.
Improving food grade rPET quality for use in UK packaging 43