Alexei Volkov
Polymer clay is a plastic clay made of plasticizers, fillers, pigments, oils, binders, and other components. In its raw state, polymer clay can react with and damage some plastics. Certain plastics, such as polypropylene, are recommended for storing polymer clay, while others, such as polystyrene, are not. Polymer clay itself can be baked at low temperatures and is used for various crafts, from jewelry to car coverings. This article will explore the compatibility of polymer clay with different plastics, specifically polypropylene and PLA, and provide an overview of polymer clay's properties, safety considerations, and creative applications.
| Characteristics | Values |
|---|---|
| Composition | PVC powder, plasticizers, fillers, binders, pigments, lubricants, oils, and gelling agents |
| State | Raw or cured |
| Raw state | Plasticizers are 'wet' and can leach out, reacting with materials in contact |
| Curing temperature | 265 °F (129 °C) to 275 °F (135 °C) for 15 minutes per 1⁄4 inch (6.4 mm) of thickness |
| Plastic compatibility | Incompatible with some plastics, can soften or "melt" them |
| Compatible plastics | Polypropylene, polystyrene, polycarbonate |
| Incompatible plastics | Polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, low-density polyethylene |
| Safety | Classified as non-toxic but should not be ingested; long-term exposure to certain phthalate plasticizers is a concern |
| Storage | Keep away from direct sunlight and heat; store in polypropylene containers or bags |
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What You'll Learn
Polymer clay composition
Polymer clay is a type of hardenable modelling clay that contains no natural clay minerals. It is made from the polymer polyvinyl chloride (PVC) powder and a liquid plasticizer, making it a plastisol or plastigel. The plasticizer is a chemical that makes the PVC more flexible, and it can be locked in by oven curing, making the clay workable until cured. Other substances are added to the plastisol to hold it together and give the clay its other characteristics, such as colour. These substances include pigments, fillers, lubricants, oils, and binders.
Polymer clay is available in many colours, which can be mixed to create a wide range of colours or gradient blends. Special-effect colours and composites include translucent, fluorescent, phosphorescent, and faux "pearls", "metallics", and "stone". Polymer clay can be shaped easily by hand or flattened in a pasta maker, and it can be baked in an oven and hardened.
Polymer clay is generally used for making arts and craft items, and is also used in commercial applications to make decorative parts. It is known for its versatility and pliability. However, it is important to note that polymer clay can melt or soften certain plastics in its raw state due to the presence of plasticizers. Therefore, it should be stored in containers or bags made of compatible plastics, such as polypropylene.
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Plastic container compatibility
Polymer clay is made of polyvinyl chloride (PVC) powder, plasticizers, fillers, pigments, oils, and binders. In its raw state, the plasticizers are 'wet' and can leach out and react with whatever material they are in contact with. This can cause the clay to react with some plastics, eating into the surface and changing the properties of the clay.
Flexible, bendable plastic containers are generally safe for storing polymer clay. Opaque plastic containers are a good indicator that the clay will be protected. Clear plastic containers that shatter instead of bending should be avoided.
Some types of plastics and their respective temperature limits are as follows:
- PET or PETE (Polyethylene terephthalate) melts at 482°F (250°C)
- HDPE (High-Density Polyethylene) withstands 248°F (120°C) for short periods
- LDPE (Low-Density Polyethylene) withstands temperatures up to 200°F (95°C) for short periods
- PP (Polypropylene) begins to melt at 266°F (130°C)
- PS and EPS (Polystyrene and Expanded Polystyrene) begin to soften at 176°F (80°C)
- PVC (Poly Vinyl Chloride) begins to degrade at 284°F (140°C)
Polypropylene plastic containers are recommended for storing polymer clay, such as the Clay Impress 28-grid storage box. It is important to look for plastics with resin identification codes #1 (PETE), #2, #4, or #5 (PP). Plastic grocery bags with resin codes #2 or #4 can also be used, but it is important to use the inside of the bag, as the ink on the outside may come off on the clay.
To test if a plastic container is compatible with polymer clay, a mineral oil test can be performed. A drop of mineral oil or Sculpey Liquid Clay Softener is left on the container's surface for three days. If the surface starts to get rough, or if there is melting, deforming, or a gooey mess, then the container is not suitable for polymer clay storage.
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Health and safety concerns
Polymer clay is made of plasticizers, fillers, pigments, oils, binders, and lubricants. When polymer clay is in its raw state, the plasticizers are 'wet' and can react with the materials they come in contact with. This can cause the clay to eat into the surface of certain plastics and change its properties.
Polylactic acid, or PLA, is a polymer material produced through a polymerization reaction of lactic acid extracted from renewable resources such as corn and sugarcane. PLA is generally considered safe and non-toxic for human use. It does not contain harmful chemicals like Bisphenol A (BPA) and has been certified by regulatory authorities, including the U.S. Food and Drug Administration (FDA), as suitable for food contact. However, caution should be exercised when using PLA for hot food or beverages due to its lower melting point, which could lead to deformation or the release of unknown substances.
PLA has also been recognised for its safety in 3D printing, especially when compared to other plastics. However, some people argue that the chemicals in unregulated products pose exposure risks, and that 3D prints are generally porous, making them unsuitable for long-term food storage.
Polypropylene, which is derived from petroleum, is considered a safer choice than some other types of plastics by the Environmental Protection Agency (EPA). It is widely used in food storage containers and is generally recognised as safe by the FDA. However, it is important to note that polypropylene should not be heated, as this increases the chances of chemicals seeping into food. Additionally, some newer research suggests that certain polypropylene containers can affect androgen hormones and cause a toxic or stress response in cells.
Overall, while PLA and polypropylene are generally considered safe, it is important to follow safety guidelines and stay informed about the latest research to minimise potential health risks.
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Clay storage recommendations
Clay storage is a challenge for anyone who works with polymer clay, especially when dealing with limited space. When storing unbaked polymer clay, avoid placing it in just any plastic container, as the clay may react with the plastic and become unusable. Polymer clay in its raw state contains "wet" plasticizers that can leach out and react with the material they come into contact with, potentially softening or "melting" the plastic.
To avoid issues, store clay in soft plastic containers, such as those made of polypropylene plastic, which is compatible with polymer clay. Avoid using rigid plastic containers, as the clay can eat through them. Keep the clay away from painted and wooden furniture, as it may damage some finishes.
For those with large blocks of clay, consider making holes in the block and filling them with water to keep the interior moist. Then, squeeze out any air, reseal the bag, and return it to storage. Alternatively, wrap the clay in plastic sheeting or store it in large plastic tubs or Zip-Loc bags. Ensure that the bags are clear, airtight, and sealed to prevent excess moisture and mould or mildew growth.
Some artists use floss boxes to store their clay, keeping the clay in its original "block" form from the manufacturer. This helps them identify the original colours and create custom blends.
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Baking and curing methods
Polymer clay is a modelling material that can be cured or baked at home in a regular oven. It is important to cure polymer clay by baking it in the oven, as it will not air-dry. Baking polymer clay enhances its durability and prevents it from getting misshapen or damaged.
To bake polymer clay, preheat your oven to the manufacturer's advised temperature, usually between 230°F and 275°F. The recommended temperature varies from one brand to another. If you are using more than one brand of clay in a project, find the midpoint temperature between the two recommended temperatures to avoid burning or under-baking. You can test your oven temperature with an oven thermometer, as most ovens run either too hot or too cold.
The time you need to leave the clay in the oven depends on the thickness of the unbaked clay. The thicker the clay, the longer it needs to be baked. As a general rule, bake your clay for a minimum of 20 minutes per 1/4 inch of thickness, although some sources recommend a minimum of 35 minutes. If you are baking thicker pieces, you should initially bake for 15 minutes, then add additional 5-minute increments. It is recommended that you bake a test sample first to avoid burning or undercooking your piece. Polymer clay stays soft in the oven and will harden as it cools.
You can bake polymer clay on a variety of surfaces, including foil, paper, and parchment-lined baking pans. However, the shiny surface of aluminium foil can leave shiny spots on the underside of your project, so you may want to use a piece of plain paper to prevent this. Covering your work can help to protect it from the heating element and keep the heat contained, leading to a more complete cure.
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Frequently asked questions
Polymer clay is a plastic clay made from a combination of plasticizers, fillers, pigments, oils, binders, and PVC powder. It is an oven-bake modelling material that is known for its versatility and pliability.
Yes, polymer clay can melt or soften certain plastics in its raw state. The plasticizers in the clay can soften incompatible plastics and cause them to "melt" or become unstiff.
Polypropylene plastic containers or bags are recommended for storing polymer clay. Polymer clay can be baked on surfaces made of wood, cardboard, glass, metal, and some plastics that can withstand the low baking temperatures.
