What Materials Should Never Go Into Sterimelt, Styromelt or Massmelt?

Not every waste stream belongs in the same machine.

Sterimelt is built for suitable polypropylene materials, including sterile wrap, curtains, suitable gowns, masks, bedding and similar nonwoven synthetic products.

Styromelt is built for expanded polystyrene and suitable styrene-based materials, including fish boxes, meat boxes, trays and some venue or catering cups.

Massmelt is built for compressible mixed or heterogeneous waste streams where volume, movement and site pressure are the problem.

The material has to fit the machine. Sterimelt should take suitable polypropylene. Styromelt should take suitable polystyrene. Massmelt should take compressible mixed waste, but never compressed gas, aerosol cans or lithium batteries.

If the wrong material goes in, the site gets a weaker output.

Key Takeaways

• Sterimelt is for suitable polypropylene and nonwoven synthetic materials, not nitrile gloves, paper, cotton or general waste.

• Styromelt is for expanded polystyrene and suitable styrene-based material, not mixed plastic waste.

• Massmelt can process compressible mixed waste, but never put compressed gas, aerosol cans, or lithium batteries in.

• Glass, metal and stone should be separated before Massmelt where practical, because they already have their own value.

• The real question is not only “can it go through?” It is “what does it become afterwards?”

  
  

Why Does The Input Matter Before The Machine Starts?

Most recovery problems start before the machine is switched on.

A clean polypropylene stream is not the same as expanded polystyrene. Neither is the same as mixed station waste, fast-food waste or a back-of-house retail stream.

Sterimelt turns suitable polypropylene into dense, sanitised PP blocks for secondary material routes. Styromelt turns bulky EPS or suitable styrene-based material into a denser, more manageable output. Massmelt reduces volume, re-expansion, movement and site pressure from compressible mixed waste.

The route matters because material value is often lost before processing begins.

GOV.UK’s 2024 packaging waste data shows the wider issue: UK plastic packaging had 2,156 million tonnes of waste arising, with 1,154 million tonnes recycled, giving a 53.5% recycling rate. The issue is not whether the material sounds recyclable on paper. It is whether it reaches the right route in the right condition.

What Should Never Go Into Sterimelt?

Sterimelt is not a general waste machine.

It is designed for suitable polypropylene and nonwoven synthetic materials. That includes sterile wrap, suitable gowns, curtains, bedding, masks and similar clinical products.

Nitrile gloves should not go into Sterimelt. They may sit close to the same waste route in a hospital, but they are not the same material. Nitrile gloves are not the thermoplastic stream Sterimelt is designed to process, so they do not melt into the intended polypropylene output.

Paper should also stay out. Not because the machine is fragile, but because paper creates an avoidable fire risk. The machine is sealed and has built-in fire suppression, but paper is still the wrong input. If paper causes a fire event, the machine has to be cleaned, reset and brought back into service.

Solids should also be avoided. A solid object may not damage the machine, but it can interrupt the process and reduce the quality of the finished block. Recyclers want pure material. If solids end up inside the block, the output becomes less useful.

Lightly soiled compatible material is different. If suitable polypropylene is damp with blood or urine, that is not automatically a problem. The issue is unsuitable material, solid contamination or anything that weakens the finished block.

Sterimelt should take the material it is built for, not whatever happens to be in the same waste area.

For more context, see Sterimelt’s article on why it is not a waste compactor, but a resource recovery machine.

What Should Never Go Into Styromelt?

Styromelt is designed for expanded polystyrene. That includes fish boxes, meat boxes, polystyrene trays and suitable styrene-based cups from venues, stadiums, shopping centres or catering sites.

Styromelt should not be treated as a general plastic machine. Different plastics melt at different temperatures. Expanded polystyrene behaves differently from polypropylene, so a plastic item should not go into Styromelt simply because it is light, bulky or looks similar.

Mixed plastics, food waste, cotton, paper-heavy loads and non-plastic contamination turn a material-specific recovery route into a sorting problem.

Styromelt works best when the site keeps the polystyrene stream recognisable. If the site is paying to move bulky EPS, the answer is not to mix it with everything else. The answer is to keep the material separate enough to recover.

What Should Never Go Into Massmelt?

Massmelt can handle the broadest range of the three machines.

It is designed for compressible mixed or heterogeneous waste. That can include fast-food waste, industrial packaging, general waste and other high-volume streams where plastic is already present in the material mix.

Safe, reliable operation starts with keeping the right materials in the waste stream.

Compressed gas, aerosol cans and lithium batteries should be kept out of Massmelt and all other mechanical compactors or balers because they can potentially cause explosions or fires.

Massmelt combines robust construction with patented safeguards and built-in fire suppression designed to protect the machine and its surroundings. Keeping these items in their dedicated disposal routes supports safe, reliable operation and helps prevent disruption.

There is also no point in putting fluids into Massmelt because they will simply run out. Large amounts of wet organic material are also a poor use of the machine because most of that load is water.

Massmelt works best when there is a useful plastic element in the waste stream. That plastic content helps form the skin of the log. That is why fast-food waste, industrial packaging and mixed commercial waste can make sense, while mostly wet organic material does not.

Metals, glass and stone should also be removed where practical. A small amount may not stop the machine, but those materials already have their own routes. They can also reduce the value or energy profile of the Massmelt output.

Massmelt is for compressible mixed waste where volume, movement and site pressure are the problem. It should not become the place where clearly recoverable materials are lost into a lower-value mixed stream.

Which Input Mistakes Change The Output?

The best question before loading any machine is simple: What output are we trying to create?

This is not about making waste handling complicated. It is about protecting the output before the site loses control of the material. Output weight matters too.

Sterimelt and Styromelt produce blocks around 23kg because the finished material has to be manageable for real operators on real sites.

HSE reports that handling, lifting or carrying accounted for 17% of employer-reported non-fatal injuries under RIDDOR in Great Britain in 2024/25.

What Checks Should Sites Make Before Loading A Machine?

Before material goes into any on-site waste machine, the site should be able to answer five practical questions that are:

• Is this the material the machine is designed for?

• Is the stream still identifiable?

• Is there anything in the load that creates a safety risk?

• Has valuable material such as metal or glass been separated where practical?

• Will this input create an output that a recycler, recovery partner or energy route can actually use?

These questions should not slow the site down. They should sit inside the normal waste route.

In hospitals, that may mean clear theatre signage and simple staff guidance. In food logistics, it may mean keeping EPS boxes separate before Styromelt processing. In venues, stations and airports, it may mean making sure aerosol cans, gas cylinders and lithium batteries do not enter Massmelt.

This is not complicated segregation for the sake of it. It’s doing the right checks before anything gets loaded.

Is The Right Material Going Into The Right Machine?

Sterimelt, Styromelt and Massmelt all reduce waste pressure.

But they do it in different ways.

Sterimelt protects suitable polypropylene by processing it at the point of use. Styromelt tackles the empty-space problem created by bulky expanded polystyrene. Massmelt reduces the site pressure created by mixed or heterogeneous high-volume waste.

Those streams are not interchangeable. If the input is wrong, the output becomes weaker and the recovery route becomes harder to defend.

So the question is simple: Is your site putting the right material into the right machine before the material loses value in the wrong route?

Book a meeting with Sterimelt to check which machine fits your waste stream before the material loses value.

FAQs

1. Can nitrile gloves go into Sterimelt?

No. Nitrile gloves should not go into Sterimelt because they are not the type of thermoplastic material the machine is designed to process.

2. Can paper go into Sterimelt?

Paper should not go into Sterimelt. It can create an avoidable fire risk and lead to cleaning and reset work.

3. Can lightly soiled clinical material go into Sterimelt?

Yes, if the material itself is suitable polypropylene. Lightly soiled material, including items damp with blood or urine, is not automatically a problem. The issue is solid contamination or unsuitable material.

4. What should never go into Massmelt?

Compressed gas, aerosol cans and lithium batteries should never go into Massmelt because they create explosion or fire risks.

5. Can glass or metal go into Massmelt?

Glass and metal should be separated where practical. They have their own recovery value and can reduce the value or energy profile of Massmelt output.

6. What is Styromelt designed for?

Styromelt is designed for expanded polystyrene and suitable styrene-based materials, such as fish boxes, meat boxes, trays and some venue or catering cups.

7. Why does the right input matter so much?

The right input protects the output. A clean polypropylene block, an EPS ingot and a Massmelt log all depend on the material stream being suitable before processing.