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· 3 min read

Choosing the right glue for the right plastic​

It's important when gluing plastic onto anything to know what kind of plastic you're dealing with. If you get it wrong, in the most extreme cases, the glue can disolve the plastic rather than bond to it, but in normal use even, not identifying the type of plastic and matching that to the glue will need to bonds that rapidly come unstuck.

The key to getting this right is to:

  1. Find the plastic type logo on the thing you want to bond.
  2. Read the info sheet on the glue you want to use.
  3. Make sure it explicitly recommends it's use with that specific type of glue.

These are usually embossed into the plastic item at the time of manufacture. They look like a triangle with a number in it.

Types of Plastic logo table

You may have to look around for it, but in most countries it's a legal requirement to have this standardised logo present on anything made predominantly of plastic.

The different types of plastic​

  1. PET (Polyethylene Terephthalate)
    • Mostly used in water bottles, soda/pop bottles and packaging. Generally a single use plastic.
    • Glues to consider: Hot glue, super glue and foaming polyurethane.
  2. HDPE (High-Density Polyethylene)
    • A stiffer plastic used in detergent bottles, oil bottles and most plastic toys.
    • Glues to consider: Plastic cement, cyanoacrylates or epoxies.
  3. PVC (Polyvinyl Chloride)
    • A flexible plastic used in the likes of cooking oil bottles.
    • Glues to consider: cyanoacrylates or UV Curable adhesives.
  4. LDPE (Low-Density Polyethylene)
    • A very low density sheet plastic used for example on dry-cleaning bags and shrink-wraps.
    • Glues to consider: Plastic cement, cyanoacrylates or epoxies
  5. PP (Polypropylene)
    • A heat-resistant plastic that's quite tough and gives a barrier to grease and chemicals. Mostly used in butter tubs and to seal in food.
    • Glue to consider: hot melt glue that's made of polypropylene
  6. PS (Polystyrene)
    • A very light-weight plastic used in disposable foam cups, clamshell food containers and the like.
    • Glues to consider: PVA (white craft glue, wood glue), Hot glue.
  7. Other (BPA, Polycarbonate and LEXAN)
    • A tough general use category. This is the sort of plastic used in baby bottles, car bumpers and water-cooler bottles. -= Glues to consider: Methyl Methacrylate (quite hard to find), Superglue, Epoxy, Polyurethane glue.

· 3 min read

What does food-safe or food-grade glue mean?​

Food regulations around glue apply to any application where the bond may, in the future, come close to or in contact with food. That can be direct or indirect contact.

What does food-safe or food-grade glue not mean?​

Food-safe or food-grade glue is not talking about whether you shouldn't eat a particular glue, or whether you need to wash it off your hands before eating - that's just common sense - don't eat it, don't lick it, and you'll be fine.

What kind of situations does it pay to check if glue is food-grade?​

So, for example:

  1. Sticking a coffee cup back together
  2. Sticking a wooden chopping board
  3. Building a craft project that's intended to carry food (wrapped or not)

and so on.

Why it matters to check if glue can be used around food​

Some of the glues that we can buy off the shelf have chemicals that can be exceptionally harmful to health.

The various laws are written to protect the end user from any danger from carcinogens, toxins or poisons after the bond has cured. Some of those ingredients may not have an immediate effect, but in the glue applications that we'd be using around food, repeated exposure over a long period of time can also be a real problem.

What's behind the food-safe glue regulations?​

The thing that the regulations are set up to minimise is "migration." Migration is the chance that toxins or poisons that are needed in the glue move from the bond site into the food itself, and are then consumed. Migration is impacted by:

  1. The type and soluability of the glue.
  2. The type and contents of the food.
  3. Whether the food is in direct contact (ie the food can leach directly out of the glue bond), or indirect (is there some sort of other barrier between the bond and the glue.)
  4. General conditions of use - is it used in high or low temperatures, held over a long time, and so on.

What are the regulations?​

I can't give legal advice of course, but here are a few links that I hope you'll find helpful:

  1. A good post on the FDA's approach to food safety and glue
  2. In the European Union the situation is more complex, with regulations also coming under plastics. This is a fair guide
  3. Although the UK is now out of the EU, it hasn't replaced any of the food standards yet. Here's a very readable and official site to get a view
  4. Canada, Japan and South America also have similar guidelines and laws.

Each jurisdiction has laws that apply to the use of glue in circumstances where the bond may come into contact with food, and laws on expressly saying whether those laws allow the manufacturer to claim that it can be used in an environment where food may come into contact.

Advice​

If a bond could come into contact with food, always, always read the safety card or packaging. Look for what their claims are as to whether it's food-safe or food-grade. If it's from a good brand, they have a lot of skin in the game and so you can trust their guide, but it's down to us to read them.