If you're going to 3D print utensils for use with food and drink, you need to make sure it's non-toxic. Here's how.
Low-cost 3D printers such as the Creality Ender-3 have made additive manufacturing accessible to the common folk. But food is the one thing people enjoy more than making bespoke plastic objects from the comfort of their homes.
It is only natural for these two pursuits to intersect in the form of 3D-printed utensils. Unfortunately, the two go together as well as vinegar and bleach. In other words, 3D-printed food containers are toxic enough to kill you slowly.
Read on to find out why that is the case and what you can do to get around the problem.
Plastics, in general, already have a bad reputation for causing long-term adverse effects on health and wellbeing. There are reams of warnings written on BPAs, phthalates, and other endocrinal disruptors linked to plastic.
But let's gloss over the genital shrinking horrors of plastics in general and restrict the scope of this endeavor to the more pressing toxicological aspects of 3D printed plastics.
Here are the ways in which the very process of 3D printing makes plastics unhealthier than they are otherwise accused of being, starting with the peculiar way FDM 3D printers tend to manufacture plastic objects.
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Traditional injection molded plastics are absolutely airtight because the object is created by forcing the material into a mold under extremely high pressure. The surface finish of such plastic objects is smooth and devoid of any pores or crevices.
On the other hand, 3D printed objects are manufactured by stacking hundreds and sometimes even thousands of plastic layers, with the internal geometry of parts themselves being hollowed out into numerous air pockets.
The highly porous nature of 3D printed parts makes them potent breeding grounds for deadly bacteria such as salmonella and E.coli. These pathogens are known to cause chronic sickness and are incredibly resilient to most germicidal agents.
Therefore, food-safe utensils are required to bear smooth, non-porous, and easy-to-clean surfaces, which is inherently lacking in 3D printed utensils.
The concept of particle migration is an important factor in food safety. Several hundred nanometers of particles can be exchanged between solids interacting with one another and with liquids on a microscopic level.
This is the primary mechanism by which toxic substances are transferred and leached onto 3D printed plastics and subsequently into the food consumed through such utensils.
Factors such as duration of exposure (long term storage), friction (scraping spoons), temperature (cooking utensils), and reactivity of the materials (acidic/alkaline food) involved dictate the magnitude of particle migration. That's why certain reactive foods must be stored in glass jars but are still fine when consumed off metal utensils.
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Things get pretty hot at the business end of a 3D printer. Your 3D models are rendered into physical parts by molten filament forced out of the hot end components. Of these, the filament is in close contact with the heatbreak and nozzle.
The former is usually made from stainless steel, so the risk of it leaching toxic substances into the filament is minimal. However, the stock nozzle is usually made from brass, which is known to leach trace quantities of lead into the filament.
That's definitely a no-go from the health and safety perspective.
The brass extruder gears found in most common 3D printers work by exerting massive amounts of pressure and friction on the filament. In addition to the brass nozzle, these can also leach lead into 3D printed plastics.
Most 3D printers also involve PTFE-lined tubes between the extruder and the hot end components. While that material is food safe, the ones used in 3D printers contain additives for lubrication, which can be toxic.
Other components such as the build surface, filament rolls, and lubricants used in the 3D printer are additional avenues for harmful substances to be transferred into the printed parts. Making your 3D printer truly food grade is undoubtedly a herculean endeavor.
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Although PLA is touted as a biodegradable filament synthesized from sugars found in corn or sugarcane, different brands introduce various additives to enhance printability, durability, and other physical characteristics of the printed parts. These additives themselves can be toxic, thereby rendering the printed parts unsafe for food handling.
The United States Food and Drug Administration (US FDA) issues food safety approvals for reputed filaments. And this is a great starting point to figure out which filaments can be used for printing utensils.
However, it is advised to check the approval on a per filament basis. Despite the concerns surrounding ABS printed parts leaching styrene into food, plenty of commercial ABS filaments receive the FDA nod, whereas some PLA filaments don't by virtue of the specific color pigment used.
Just because a particular brand of ABS is certified as food safe, you cannot assume that the courtesy extends to ABS filament from another brand. Different color iterations and additive blends also play major roles in FDA certification, so be sure to check the fine print.
Now that we are intimately aware of the dangers of using 3D printed utensils for food, we would be remiss to leave without giving a few tips on how to 3D print food-grade parts.
For starters, provisioning a separate 3D printer for food-grade prints is the most foolproof way of ensuring FDA compliance. That's an inconvenient requirement because toxic substances can linger over several print cycles.
Here are some tips and tricks to improve the food safety of your 3D prints.
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Knowing how brass nozzles and extruder gears can potentially introduce lead into your 3D prints, replacing these with stainless steel alternatives is the easiest way to render them food safe. Just be sure to use food-safe, stainless-steel parts because tool steel variants aren't the same. Furthermore, stay away from stainless-steel nozzles with additional non-stick coatings.
Layer lines are a significant contributing factor to the porosity of FDM 3D prints and create conditions conducive to bacterial growth. Fortunately, some filaments such as ABS, ASA, PETG, and HIPS can be chemically smoothened.
This involves partially melting away the layer lines through the process of vapor smoothing, where solvents such as acetone and ethyl acetate are allowed to react with the surface of the 3D-printed parts. The result yields parts with smooth, sealed surfaces that are easy to clean and lack the surface area required to host bacterial colonies.
For filaments that can't be chemically smoothed, you may want to reduce the layer height to make the 3D print as smooth as possible. Sanding the surfaces down further should make them smoother. Just make sure the sanding equipment doesn't introduce toxic substances.
While PLA is generally food-safe (as long as the manufacturer hasn't used toxic additives or color pigments), the 3D printed parts aren't practical for long-term food handling. The material has one of the lowest heat deflection temperatures (HDT). That means it won't survive hot beverages or heated dishwasher cycles.
The chemically inert nature of PETG filament makes it ideal for food handling, but like PLA, it also lacks the HDT required to survive hot foods and the dishwasher. However, PETG can be chemically smoothened. ABS filaments, however, yield heat-resistant 3D printed parts that can also be vapor smoothened.
Exotic filaments such as PEI (Ultem brand) have been approved by the US FDA, but these can't be printed on non-commercial 3D printers. Meanwhile, Nylon and polypropylene filaments are also FDA food safety compliant.
It's still a good idea to check the filament packaging for FDA approval.
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It's not easy to adapt your printer to a whole new material. In most cases, entry-level FDM printers aren't even capable of printing materials such as ABS out of the box. That makes dip coatings and sealants a viable alternative.
These come in different food-grade options, such as polyurethane resins, epoxies, and PTFE coatings. The options are virtually endless, so make sure you do the due diligence concerning FDA approvals and compatibility with various filaments.
It also pays to check the temperature and abrasion resistance of these solutions beforehand. You don't want to use a low-temperature coating for a coffee mug.
The concept of food-safe 3D printing is uncharted territory at the moment. Although FDA has been conducting due diligence and issuing approvals for reputed filaments, it still can't control for unknown variables of printing temperature and unpredictable use cases.
What's certified to be food-safe might not be the same after prolonged use. Furthermore, it is smarter to reduce food temperature, contact time, and generally avoid pairing 3D printed utensils with reactive foods.
It's smarter to err on the side of caution.
Nachiket has covered diverse technology beats ranging from video games and PC hardware to smartphones and DIY over a career spanning 15 years. Some say that his DIY articles serve as an excuse to pass off his 3D printer, custom keyboard, and RC addiction as “business expenses” to the wife.
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