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Soft-plastic recycling – research and feasibility

This topic contains 40 replies, has 4 voices, and was last updated by  Stan 1 month ago.

4
Marc Vruggink marcvdv

Soft-plastic recycling – research and feasibility

16/05/2019 at 11:08

Dear Precious Plastic community,

I am intern in Swiss research institute working on waste management. A waste audit in one of our nepalese case studies highlighted the need for treatment solutions for soft plastics (mainly food wrappers, approximately 10kg/day). For the next two month we will  be conducting a research in Nepal on Small scale soft plastic recycling.

Among my tasks, I’ll be working with a local NGO to achieve and document the construction of a compression machine.

I’ll keep you updated on our progress through this post and I’m happy to hear about your suggestion, experience, comments, etcetera.

Suscribe to the post to stay updated!
All the best,
Marc

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warrior
25/06/2019 at 08:33
1

Hi Marc @marcvdv
Good to hear you got the oven working!

These topics have some more technical info about PET:
PET General / Common bottles melting help!
Crystal clear PET plastic ?

warrior
25/06/2019 at 13:19
1

@marcvdv – that’s odd. the link still works for me. It goes to:
https://www.surya.com.au/blogs/surya-blog/12721425-the-yak-wool-deception

starter
25/06/2019 at 16:09
2

@frogfall Apparently this website is blocked from Nepal (For telling the truth?). I could access it through my VPN.

Weekly update # 4 (2/2)
Following @donald ‘s links (thank’s, I should improve my research skills) I found out how difficult it was to recycle PET compared to PP. Moisture makes PET recycling challenging and now it’s monsoon time in Kathmandu. An additional step of drying would therefore be needed to limit PET’s breakability (more info on this nice link). @microtransactions built a vaccum drying system for extruding PET, I don’t know what’s the conclusion of this (see these links: link1 link2

Given the limited time we have, considering drying add a degree of complexity to a process that I have to present as simple and easy to replicate. So I think we won’t focus on recycling these PET wrappers on this project.

Noodle packages
Noodle packages in Nepal consist in fact of two layers. An inner transparent PP layer and an outer PET metallized layer. The two layers can relatively easily be separated by hand (it’s like unsticking a sticker from plastic matterial; depending on the wrapper’s condition).

The inner layer melts nicely at 210°C and produces a solid and resistant chip. The outter one can be melted around 270°C but leads to a brittle result (as with the PET biscuits).

I’m now considering to iron these outer layer together (not sure it would hold, though) to product some kind of canvas sheet. Otherwise, if none of you guys have an easy suggestion to cope with PET brittleness, we’ll focus on other wrappers. Future research could also focus on how to separate these two layers on a bigger scale (out of the scope of our project, but if you have suggestions, I’ll document it in my report).

Other wrappers
Today, we started melting different wrappers to see how they behave at 210°C. Many of them (metallized or not) melted nicely and allow us to press small chips (see third picture below). We are listing the PP wrappers (melting at 210°C) as well as the other/mixed wrappers to ease future replication.

For the time we have left (approximately 2 weeks) we will focus on gathering enough of these PP wrappers and to mold an usefull object (most probably small sheets to make paper boards), as a proof of concepts for the locals. We hope to end our fieldwork with a workshop/demo/discussion day.

As usual, any question, feedback, comment is welcome!
Best,
Marc

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warrior
25/06/2019 at 17:39
2

The PET sounds challenging. I guess it depends on what the overall problem that is trying to be solved. If the issue is to avoid having these pouches littering the countryside, then the brittle chunks are an improvement. Perhaps the brittleness can be used to crush it and use it as an aggregate in bricks, pavers, retaining blocks, etc. made from other plastics. Kind of like the sand is being used in making plastic roof tiles and bricks.

Interesting that you are slowed in your work by insufficient plastic material.

warrior
25/06/2019 at 21:44
1

@marcvdv

2 weeks is a very short time, so focusing on a working PoC would be key for your research, but I also agree with Stan @s2019 that ‘teasing’ the PET as a potential building material (bricks/tiles, mixed with sand) “if only you had more time…” would also keep the momentum going.

 

PM me for a more ‘tactical’ approach or if you want me to mail you the @frogfall webpage (I can confirm it works) 😉

starter
26/06/2019 at 06:54
1

@s2019 Maybe a few more words on this “plastic supply” issue could be intersting for you. Don’t take me wrong: these wrappers are laying all over the place. We partnered with a local organization to collect this material for us but it took more time than expected (someone threw away the wrappers that were saved for us).

Indeed, it could be interesting to assess the construction material opportunities. Pilot portions of “plastic roads” have been built recently (600kg waste for a 200m street). But if PET is brittle, could we still make durable construction material, without other plastic/crude oil?

warrior
24/08/2019 at 19:47
0

@marcvdv , just curious, how did you project conclude? You took on a pretty tough task with limited resources.

starter
24/09/2019 at 17:24
3

Hey guys, sorry for the delay : life is crazy (in a good way). I felt like I owned this community a feedback from my experience. Make yourself comfortable, this is going to be a long post summarizing our experience.

Background

As part of my studies in environmental engineering, I did an internship in a Swiss research institute (EAWAG; department Sandec). The municipal solid waste management group of this institution previously did a waste audit in a Nepalese boarding school and found out 10kg of plastic were openly burnt daily. This is not only an issue for this boarding school but for the whole Nepal.

Let’s look a little bit closer at the waste generated. Half of has a recycling market (PET bottles, Hard plastics, milk and oil pouches). There were little plastic bags within this boarding school. The majority of the remaining plastics were “soft-plastics”, mainly food (biscuit, instant noodle) packages. How could we deal with these plastics at the community level?

This waste fraction is currently not recycled in Nepal for three main reasons:

– Quality: The amount of printing decreases the commercial value the plastic. Often, the plastics are dirty
Quantity: These wrappers are disposed by diffuse source, all over Nepal. Their weight is little and one has to gather a big volume before a recycler is interested.
Diversity: Of polymers, mixtures (multi-layer) of polymers, mixture of materials (aluminium foil, …) making recycling difficult or impossible.

Machine building

We did a fieldwork of 2 month. This was my first working experience in a developing country. We collaborated with a local NGO (Clean Up Nepal) and, in particular, I worked as a tandem with a local mechanical engineer. We were both new to the field of plastic recycling.

Several solutions are possible for handling such waste (incineration, pyrolysis, use as construction material (ecobricks, roads, …), handicraft) but Precious Plastics was the one we decided to go for, as their option was:
-Cheap
-Scalable to the community
-Generating revenue (multiple objects)
-Maintaining the plastic lifecycle (further recycling) possible

Among the 4 Precious plastic machines, we choose compression as the injection and extrusion required solid fragments, and as the shredder is not designed to shred films. The compression machine allowed us to melt films directly, without preliminary shedding. We built the compression machine for 170 CHF (~170 USD, ~155 Euros; excl. masks, small equipment and workspace rental).

We followed the precious plastics blueprints. Electronic components were bought in Switzerland before leaving. We had to solve SSR-relay over-heating issues that were not anticipated by reading the Precious Plastics documentation. We found a pretty big oven and we decided to not set it on top of the compression frame. We built a higher compression frame (1m20) to not break our backs during operations.

Material characterization

In a first phase, we had to experiment with the plastics. Understanding what worked, what didn’t and why. We found out that most of the wrappers were multilayer films, composed of different plastics and materials. Moreover, most of these items were heavily printed. We developed a procedure allowing to asses the dominating polymer by melting successively at different temperatures.

Few biscuits were PET-based (can’t guarantee this was pure PET). These were not recyclable using compression, as the product was brittle (breaking like a cookie). Other wrappers (biscuits, rice, …) were made of distinct PP and PET layers (clear incomplete melting at 215°C), usually not separable by hand. A notable exception were the instant noddle packages, present all over Asia. These were made of an outer, metallized and heavily printed outer PET-based layer and of an inner, transparent, PP layer. These layers could be separated by hand (time intensive, but possible).  The inner layer melted completely at 215°C and produced a nice and solid product. As no solution was found for the outer layer and as it was time intensive to gather enough inner layers, no further work was done on the noodle packages. Rising awareness about the impossibility to recycle such packages could wake-up policy makers and manufacturers… but I don’t expect a rapid radical change.

Other food packages were mainly PP. They melted completely at 215°C and samples produced nice and solid plastic chips when compressed. Melting was achieved with transparent packages (often wrapping veggies in local markets), toast bread packages, (imported) pasta packages, (imported) korean ramen packages and biscuit packages (I don’t want to blame Nepal, but often imported from India). Melting was achieved with both metallized and non-metallized wrappers.

Recycling process 1.0

Based on the knowledge acquired, the second phase was dedicated to make value out of non-recycled waste. Our attempts were mainly done using toast-breads packages (that could be recycled but have little value due to printing), that were collected in significant amount (7 kg in 2 hours, by 2 persons) thanks to a local waste management company (Doko recyclers).

The process is described in the Figure below. We melted toast bead packages in an antiadhesive baking plate on which we added a tin frame (Second picture, sorry for the quality). Plastics were added by batches of 50-100g (10 to 20 previously cleaned and dried wrappers). Melting temperature was set at 218°C. I recommend carefully checking if the plastic is totally melted (use a wooden spatula) before adding more plastic : sometimes, a kind of air-bubble shielded wrappers from melting, in the middle of this “dough”. After melting sufficient amount, this sticky dough was transferred in a a pre-heated mold before compression.

Our best achievement was a clip board (see third picture below). As it was our first experience, we learned by doing:
– The mold was a bit convex. Once I pressed too hard and the product broke when releasing the pressure.
– Soldering was not continuous, and plastic infiltrated in the jointure.
-Air bubbles were in the product. Maybe due to a “too rapid” pressing.
-Plastic did not spread in the mold corners (Maybe due to too rapid pressing too).

The project was reconducted for a second phase. Three new interns started last week (@Gem.Wrong is one of them)! Their mission is to remediate to the previous issues, to think about other end-products, to produce nicely finished end-products and to optimize the process. I think they are doing well (see 4th picture).

As for me, I’m out. Starting my master thesis on another passionating topic (Organic waste conversion through Black Soldier Fly conversion). In a few months, I’ll almost be able to set-up a complete waste recycling facility :D.

I’ll do my best to answer further questions and comments, but can’t guarantee this.

Thank’s again to all of you for your support!

Marc

Attachments:
starter
24/09/2019 at 17:28
0

(Last picture, Product trial made by the new team)

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warrior
24/09/2019 at 22:09
0

@marcvdv , thank you for the great summary. Great work, especially given the limited resources you had. Hopefully the new team will connect with the forum and share their experience.

Thanks again and good luck in your studies.

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