Experiment #8: recycled plastic earrings

It was time to finally make something useful with these experiments. I have a good friend who loves crazy earrings. And so, I gave myself the challenge to try to make her a gift – specifically recycled plastic earrings.

To make this gift, I originally tried to use a pineapple silicon mould, but I wasn’t happy with the texture and the inability to see the “Canberra Milk” logo properly.

So, I decided to try to make something more natural using just an egg circle mould.


Unfortunately, I forgot to take pictures during the process. After the plastic was melted, I cut the circular piece into four and remelted two of the best pieces to smooth out the cut lines.

Afterwards I bought some jewelry fixtures, drilled a hole in each, and voila! My friend love her recycled plastic earrings gift!

handmade recycled plastic earrings
Different types of recycled plastic

Experiment #7 – LDPE and PP

I’ve finally moved from melting milk bottle lids to trying out other types of plastic, specifically LDPE plastic bags and corrugated plastic signs from PP. And it’s definitely harder using my primitive equipment.

Polypropylene or #5 PP

There’s a local election this year, and I know that thousands of corrugated plastic signs will go to landfill unless there’s a recycling solution. So, if I can find a way to do this, I could do a good thing for the environment and really demonstrate the value in this discarded resource.

Election signs
Credit: Canberra Times

For the corrugated plastic signs experiments, I was specifically trying to maintain the original designs of the sign. That’s been tricky because I found it easy to burn the added ink in a convection oven. Furthermore, PP or polypropylene melts at a much higher melting point then the others and I’m finding it harder to get it to melt fully in my moulds.

Below shows my first experiments. The right “coaster” was obviously burned in the process. The one on the left wasn’t as much as I put aluminium foil over the top of it, but there are still solid pieces that weren’t full melted.

Failed PP experiments

Low-density polyethylene or LDPE #4

For LDPE, I’m trying to solve another problem that was brought up by my mates at Pushy’s Bike Store. Every bike and part that they receive comes in a plastic bag, and they have no way to recycle it.

It’s a good, clean source of mostly LDPE plastic. Furthermore, I reckon that just about every retailer in Canberra has the same issue. For Pushy’s specifically, I also asked them to give me some discarded bike gears and chains too.

My thoughts were that I might be able to embed the parts into the plastic to tell a better story of where the plastic originally came from.

Telling the story of these plastics

One of the major reasons why I have gone the extra lengths to keep the artwork on the plastic (from milk bottle lids to the signs) is to be able to share the story of where these plastics came from.

If everything is a single colour, few people will even know that it’s recycled plastic in an end product. If it comes in the typical multiple-colour tones that are the results of shredding the material without further processing, people may know it’s from recycled plastic, but they have no idea from what.

I want people to see value in this resource, and it’s much each easier to share their origin’s story if I can somehow keep the artwork when I turn it into a final product. Plus, how cool would it be if I can pull it off!

Experiment #6: Recycled Art Piece

It’s taken me forever, but I finally completed Experiment #6 – a recycled plastic art piece for my mates over at the Local Press Cafe.

Recycled Plastic Art Piece made from Milk Bottle Caps
Recycled Plastic Art Piece made from Milk Bottle Caps

For about a month now, I’ve been experimenting with milk bottle caps from their cafe. I’ve always liked how the Canberra Milk logo was on the top of the black and purple caps, and so I worked hard to preserve them in this little art piece.

I’m not too confident with how long it will stay together, but at least it was not as embarrassing as some of my previous attempts. Hopefully, they’ll like my gift.

As for what I will do next with these Plastic Experiments, I’m not sure. I want to make one more for another friend with a business. I feel like there’s something special about preserving the logos as part of the education process. Yet, it’s really time consuming to make anything this way.

So, for the moment, it’s more of a late night hobby that allows me to continue to test ideas and continue to learn more about plastic properties. Whether or not I can eventually commercialise something with milk bottle caps or really anything by melting plastic this way, I’m really not sure at this point.

Experiment #5 – Mixed plastics

I collected a bunch of bottle caps from the Clean-up Burley Griffin Day and decided to try another Plastic Experiment with what proved to be mixed plastics i.e. multiple plastic types.

They came from a range of bottles and some were really old. So, I really didn’t know what kinds of plastic they were made of. However, since all of my previous experiments seem to melt fairly consistently, I thought I should try doing something with this plastic too, betting that an old Coke bottle lid would be made of something similar to milk bottles.

But I was wrong. I found that the usual 180C melting temperature for HDPE was only slightly melting most of the other pieces. So, I turned up the temperature and hoped for the best.

Unfortunately, the results were mostly of burned HDPE #2 and half melted other plastic(s) – maybe PP #5. Furthermore, the higher temperatures actually melted the silicon mould too, resulting to it sticking to the melted plastic and destroying my mould.

Burned plastic and moulds
My burned moulds

This Plastic Experiment is a really good example of why recycling plastics is so hard when there are so many variations of plastic with different properties including melting point – creating mixed plastics to be sorted. I still have a few bottle caps left and may try again, but first I have to order a new mould. Sigh…

Experiment #4 – Microplastics

Despite being flat out the last two weeks with the Clean-up Lake Burley Griffin Day, I did managed to get one new experiment done around microplastics or Plastic Experiment #4.

In reality, the project didn’t start out this way. Instead, I went to a friend’s house to try to use a mitresaw to see if I could I smooth out the edges of the lumpy larger pieces. However, it turned out that he didn’t have the right tool, and so I proceeded to just use his hand saw.

What resulted from this process was purple plastic dust everywhere – essentially microplastics, which can end up in the water streams if I wasn’t careful. So, as I was sweeping up everything, it suddenly occurred to me that I could melt this dust down again and so I did.

This time, I used silicon moulds that just arrived from the US. The dust fit in there easily, but I quickly realised that there were other things in that mix too like saw dust from wood shavings and various leaves and twigs. I expected that my melting process would burn them, and I wasn’t wrong. The fumes were horrible!

After that lesson, I finally created some space on my balcony to attempt it again outside, and despite the extra particles in the plastic it worked really well. The small shapes held their form even while shrinking per usual, and I could easily get them out of the mould.

There were still quite a few bubbles in the final letters as I didn’t want to risk melting the silicon mould by accident again, but I think it actually gives the shapes some character.

So, overall I was happy with the results of this experiment with microplastics, and I feel really close to creating something that I wouldn’t mind sharing soon with friends.

Experiment #3: plastic air bubbles

Following on the back of Experiment #1 and #2, this next Plastic Experiment #3 is designed to see if I can remove the plastic air bubbles by blasting the melted plastic with a heat gun afterwards. This idea was given to me by a friend who used this technique with something else.

The results were encouraging for the small silicon mould that I used. Unfortunately, I also accidentally melted the mould in this process too. The difference is very obvious in the green sections below.

Pineapples in recycled plastic

Unfortunately, it didn’t work as well for a larger piece that I tried to make in a baking tin.

Bubbles in plastic

This muffin size piece of plastic weighs about 2k and is made from nearly 100 bottlecaps. As I can see once again, the larger the piece, the harder to control the plastic air bubbles – especially on the top without pressure. Unfortunately the form was also slightly disformed just like my previous square silicon mould test – a product of HDPE’s features when it cools down.

Conclusion for Plastic Experiment #3. Plastic air bubbles will continue to be an issue especially with larger pieces with HDPE if I do not use a pressurised mould. I wonder though whether or not I can use a millsaw to cut the plastic to smooth out the rougher edges? Next test!

Plastic Milk Bottle Lids melted into cactus

Experiment #2: melt plastic with oven

One convection oven and a meat grinder, please!

After testing a heat gun to melt plastic – specifically milk bottle lids last week, I decided to take it to the next level for Plastics Experiment #2 by trying to shred and melt plastic with a cheap convection oven and a metal meat grinder.

New convection oven

The oven’s purpose is to melt the plastic better. I supposed I could have used my kitchen oven, but I was worried about contaminating it with plastic if I accidentally burned something. I bought the meat grinder to try to find a better way to cut up the plastic as my hands were tired from doing it with a pair of garden secateurs.

The Results?

After melting two buckets of HDPE bottle caps into many different types of metal and silicon moulds, I’ve learned a lot, but still don’t have a viable process or product.

The meat grinder was a waste of time as it just crushed the plastic rather than shredding it. I was ready to try various kitchen appliances next when I decided to first see if anyone else posted their results online. They all said NOT to waste your time and money.


No Description

The meat grinder only crushed the plastic rather than cutting it.

I’m so glad I researched this first. From blenders to food processors and credit card shredders – nothing is strong enough to properly shred the plastic apparently.

So if I want to continue down this path, I have to either continue to cut the plastic by hand (UGH!), melt the lids as is (which is guaranteed to result in lots of air bubbles or buy a proper shredder. Out of all of the machines I need, an used shredder is the cheapest. So that may the right thing to do if I keep going.

Plastics Experiment #2:

Let’s go bigger!

Up to this point, I had a been playing around with cookie cutter sized moulds. With Recycled Plastics Experiment #2, it was time to try something bigger now that I had the oven. In the picture below, you can see that the square silicon baking tray failed to hold it’s form when it cooled down.

Failed test of melting HDPE in a silicon mould
Can I make a flower pot?

I was curious to see if I could make some sort of a flower pot using these two metal mixing bowls as a mould below. It came out better than I expected, but looking a bit like an ashtray instead. The unfortunate part was all the air bubbles in the none-pressed edges. I want to see if I can tidy it up with a friend’s mitre saw later.

Pressure Test

I decided to use pressure in this test by clamping two baking sheets together. The funky design was only because I ran out of the purple lids. This turned out pretty good even if a bit uneven. The pressure eliminated most of the bubbles from the sheet. Yay!

What’s creating the tiny bubbles?

In the final test, I wanted to know what was causing the tiny air bubbles in the cactus below. I tried cutting the plastic in different sizes, putting water drops into the mould and using a different colour lid (to ensure it wasn’t just an issue with the green colour lid).

When all of those tests still resulted in tiny bubbles, I cut up two of the little cacti I made earlier, and and remelted them into a metal pineapple mould resulting in no bubbles.

This makes me believe that it’s actually the silicon mould that is causing the bubbles, but I need to get another small silicon mould to double check this theory. It’s probably correct though given how much the large square mould had changed in shape once cooled.

Silicon versus metal mould experiment

Lessons Learned from Recycled Plastics Experiment #2:

  1. HDPE seems to melt best at 180 degrees Celsius (at least in my oven). However, if there’s any leftover milk, coffee, food etc residue, that will burn and usually turn into an ugly brown.
  2. Water and plastic don’t mix. I’d heard that before, but I thought it was because it was harder to cut the plastic in shredders. Instead, what I found was that wet plastic resulted in more bubbles in the end product especially in the bigger pieces.
  3. I don’t have to cut the lids for the larger moulds. They’re small enough to melt just fine. The main problem is that they seem to trap air bubbles as they melt because of their shape. So, if I care about a perfect shape, I still have to cut up the pieces, and the smaller the better to reduce the air bubbles it seems – unless it’s in a silicon mould which guarantees bubbles regardless.
  4. There’s no way to create a perfect flat surface with HDPE (#2) without using force to hold the form into shape while it’s cooling down. The prohibited cost of steel moulds is why I started down this pathway. So far, all the experiments are just confirming what I’ve already been told.
  5. Silicon moulds are by far the easiest when it comes to removing the form inside. In the large shallower pans, the plastic shrinks to make the removal easy too. However, it’s a fight for most other metal moulds.

Final thoughts?

Right now, I’m using these experiments to learn more about the properties of plastic, and to see if I can make something useful without having to spend a fortune on a traditional steel mould.

While, these plastics experiments have been a lot of fun in the process, I am also consciously noting the lessons learned for each test. I have learned heaps already, but I’m still a long way off a viable product. More to do.

Experiment #1 – milk bottle lids

Given the crazy cost of creating my products using the old fashion manufacturing method of injection moulding, I decided to experiment with plastic using even older methods, but that would cost me only my time. My raw ingredient? Milk bottle lids.

Instead of coming up with a solution to a problem where recycled plastic can be the main ingredient, I thought I would work backwards and use a known waste plastic and see what I could do with that.

There’s a charity in town that started collecting lids for a company that makes prosthetic limbs for children. However, they are way over capacity now. So, I knew that there were buckets of lids just lying around, and I managed to grab a bucket from my friends over at Local Press. Most of them were milk bottle lids from the local milk company.

This is the experiment I just did to see if I could make a minimum viable product.

Cleaning and sorting milk bottle lids

More work to do, but a truly interesting process in any case to see if I could replicate some of the things I’ve seen online and heard about, but using my own methods to experiment with milk bottle lids as my plastic source.