While the crowdfunding cogs are turning in the background we’re getting back to the most important part of the process of recycling used fishing nets, the shredding !
Below are two close up photos, to the same scale, of two of the three nylon monofilament nets that Fishing for Litter (SW) and the Newlyn fishing fleet supplied. I’ll point some things out.
Recent news that some species of sea birds are attracted to floating marine litter partly because they can smell the release of dimethyl sulfide from algal films that coat items of litter once they have been in the water for some time is certainly a concern. It prompted me to take a closer look at my samples.
You can see from these samples that algal films are quite rare on the main parts of these nylon nets, and focussed on the knots. I can’t say what impact that might have on seabirds, but it could make it easier to upgrade the shredded and washed nylon. The knots are the part of monofilament nets that is most resistant to shreddding, so with my mineral processing hat on I can see a way of selectively removing the knots and with them the bulk of any algal films remaining within the net sample.
This focus of algal growth in the knots in monofilament nets is not true for the larger HDPE trawl net sample that I have, or indeed samples of aquaculture support ropes and netting that I have seen. The majority of those use braided lines into which algae of several types can penetrate and find a hideaway from simple washing. The knots are not as important as anchor sites for algal growth, which means that I have to approach the pre-processing differently if I want an end product that is free of biology.
The first net that Fishy Filaments took all the way from harbourside to 3D printed form was given the ID ‘Net 4’. It was the finest gauge of the three nylon monofilament samples we had, with average diameter of 0.35-0.45mm.
‘Net 1’ has the largest average diameter filament of 0.65-0.75mm and you can clearly see the difference between the two samples (shown at the same scale below).
This simple difference has impacts on overall yield (the amount of final product per bag of litter incoming), on the potential for colour variation in a blended product, the potential for multiple products of different colour and defined engineering parameters, and the amount of rejects due to biological contamination.
Simple washing removes the vast majority of biological contamination, but it is not 100% perfect. A visual estimate of 99% clearance by volume may or may not be enough in an industrial process that then goes on to heat the sample to well over 200°C, but in understanding where the remaining biology is hiding we can be fairly sure that there will be mechanisms available off-the-shelf to help raise the quality further if needed. It helps knowing about mineral processing here.
Its worth looking at the detail !