microwave and dishwasher safe packaging

[sebastianc21]

This question may seem silly but please do help me out in anyway possible.

My company is looking to manufacture clear household containers like ziploc brand containers that is microwave and dishwasher safe.

What exactly makes the container microwave safe? Do we have to use a special resin? A special additive? (Like use more anti oxidents) Use a lower mfi resin? Does the container need a minimum wall thickness? etc

Same question for dishwasher safe?

We want to ensure when we place the logo on the bottom of our container we know exatly why we placed it there.

Thank you.

 

[rickfischer51]

First, identify the max temperatures the parts will see in both the microwave and the dishwasher, and the duration. I think the microwave temp will be a function of what is being heated in the dish. Compare that to the heat deflection temperature at 264 psi. That temp represents the temperature at which Young's modulus has fallen to about 110 ksi.

Are these single use or reusable?

I think the material most commonly used in the microwave is crystallized PET, or CPET. The formation of crystals in a post molding operation raised the HDT significantly and allows use at elevated temps. Unfortunately, it is opaque, as are most all crystalline resins. You are probably headed to something like PEI, which is expensive to buy and process. An issue to consider is staining of the polymer by the contents. Repeated use with a variety of contents will make staining likely. Also, consider leaching of low molecular weight polymer species or additives that could contaminate the contents.

In the dishwasher, you have to consider exposure to surfactants at elevated temperatures. This may attack and degrade the polymer, and they may accelerate the leaching mentioned above. I think this was the primary concern behind contamination of polycarbonate sports water bottles and infant formula bottles with bisphenol-A.


Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[sebastianc21]

This will be for reusable containers. We are looking at PP. Lock & Lock containers would be another example.

From what I understand, you are saying I'll need to test these containers with the food inside and test the migration of chemicals and additives to the food?

If the migration of these chemicals is whithin the limites, we can put a microwave stamp on the products?

Dishwasher I would have to test with hot water and a surfactant and see the degradation?

Is there a specific PP I should get? (Apart from it being food grade)

Thank you for the help.

 

[rickfischer51]

1. PP is cheap and non-polar, so it resists staining. But it is semicrystaline. It has a glass transition temp of about -12C, which means it needs crystalinity to have any rigidity. Crystals diffuse light, so it is not transparent.
2. Yes.
3. I have no idea what officially constitutes microwave usability, or if there is a standard, etc.
4. Yes. Not so much degradation, but leaching of any chemical substance onto a surface that contacts food.
5. I have trouble with using PP in a microwave. We have some Tupperware containers that float in the sink, so they are some type of olefin, and they are stained and melted from zapping lasagna in the microwave. PP is a low temp material.

This isn't really my area, and the advise I've given is based on basic polymer science fundamentals. If this were mine, the first thing I would do is check and see what industry standards apply. There may be standards that define safe in the dishwasher or microwave. Next I would do a survey of the existing product out there. Categorize them by material and microwave/dishwasher suitability. Test any microwave rated product to determine what material it's made from. This can be done in any good lab with FT-IR capability.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[CoryPad]

Most plastic food containers are made from polypropylene, although higher-end ones use Tritan, a copolyester from Eastman. There are standards that cover this area, check FDA, NSF and ISO among others. For microwave usage, examples you should consider are resistance to hot animal fat and hot tomato sauce. For the dishwasher, add in resistance to temperature (the drying cycle can warp and/or melt some plastics), and resistance to hot sodium hypochlorite and other bases like sodium hydroxide, and lastly resistance to hydrolysis.

 

[rickfischer51]

If you stay away from PA, PC and PET, hydrolysis is usually not a problem. There are additives to reduce hydrolysis, but I think they are consumed over time and eventually used up.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[rickfischer51]

I checked some of the newer plastic containers in my wife's collection. There are some Rubbermaid brand containers that are marked PP with symbols for freezer, dishwasher and microwave safe. Looks like I was wrong (again!). Have not tried them in the microwave as we have Corning bowls with plastic lids for anything that gets reheated. Go out and purchase some latest offerings from the big names (Tupperware, Rubbermaid, etc.), test them in dishwashers and microwaves and see if they perform they way you would want your product to perform, and get them FT-IR analyzed for material. Also, run TGA to check for non-organic fillers and DSC to check for degree of crystalinity (Demon3, you out there? What else?). No point in reinventing the wheel. There are no style points here. It's OK to cheat. Remember, a dwarf can see farther than a giant if he sits on the giant's shoulders.

Rick Fischer
Principal Engineer
Argonne National Laboratory