Maya Ellison
Polymer clay is a plasticine-like material made from PVC resin and a liquid plasticizer, making it a plastisol. This combination gives polymer clay its unique rheological properties, allowing it to be moulded and shaped before being cured in a standard home oven. Polymer clay is popular among artists and hobbyists for its versatility and ease of use, but its plastic composition has raised environmental and health concerns. While it offers a long shelf life and reusability, the non-biodegradability and potential leaching of chemicals have sparked debates about its sustainability and safe disposal.
| Characteristics | Values |
|---|---|
| Composition | PVC resin and a liquid plasticizer |
| Type of plastic | Polyvinyl chloride (PVC) |
| Raw materials | Salt, oil |
| Plastisol category | Plastigel |
| Rheological properties | Thixotropic |
| Curing temperature | 265 °F (129 °C) to 275 °F (135 °C) |
| Curing time | 15 minutes per 1⁄4 inch (6.4 mm) of thickness |
| Gelling agents | Aminated bentonite, metallic soaps, fumed silica |
| Additives | Fillers, colouring agents |
| Safety concerns | Phthalate plasticizers, hydrogen chloride gas release |
| Environmental impact | Lack of biodegradability, chemical leaching, dioxin release |
| Sustainability practices | Batch baking, avoiding glitter, repurposing waste |
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What You'll Learn
Polymer clay is a plastisol
PVC is a synthetic plastic polymer, derived from salt and ethylene. It is a man-made plastic. The basic raw materials for PVC are chlorine, produced from salt, and ethylene, derived from oil. PVC is used in a wide range of products, from shoes and floors to windows and water pipes.
Plastisol is a liquid at room temperature and can be poured into a mold. When heated to around 180°C (356°F), the plastic particles absorb the plasticizer, causing them to swell and fuse together, forming a viscous gel. This process is called 'curing'. Once cooled to below 60°C (140°F), plastisol becomes a flexible, permanently plasticized solid product.
Polymer clay undergoes a similar curing process. It remains workable until cured at temperatures between 265°F (129°C) and 275°F (135°C) for 15 minutes per 1/4 inch (6.4 mm) of thickness. This temperature is relatively low compared to mineral clays, and curing can be achieved using a home oven.
Plastisol has a wide range of applications due to its unique properties. It is used for coatings, particularly in outdoor settings, and for grips on tools, bicycle handlebars, and furniture handles. It is also flame retardant, electrically resistant, and chemically resistant.
The use of polymer clay has raised safety concerns due to the presence of certain phthalate plasticizers, which have been classified as endocrine disruptors. However, these types of phthalates are no longer used in polymer clay and are banned in the European Union and the United States.
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It is made from PVC resin and a liquid plasticizer
Polymer clay is a type of clay that contains a basis of PVC resin and a liquid plasticizer, making it a plastisol. PVC (polyvinyl chloride) is derived from salt, which produces chlorine, and oil, from which ethylene is derived. The liquid plasticizer is added to the PVC powder to make the clay soft and pliable.
Polymer clay plastisol is also categorized as a plastigel due to its rheological properties. It is a high-yield thixotropic material: when sufficient force is applied, the material yields, flowing like a viscous liquid until the force is removed, at which point it returns to a solid state. This plasticity is what makes it useful as modelling clay, as it retains its shape even when heat is applied.
Various gelling agents can be added to give it this property, such as aminated bentonite, metallic soaps, or fumed silica. The base resin can be modified in various ways as well. For example, mineral oil, lecithin, and odourless mineral spirits can be added to reduce its viscosity or alter its working properties.
While polymer clay has unique properties that make it useful for modelling, there are concerns about the health and environmental implications of its use. Plasticizers can remain in the cured product and leach out, potentially causing health issues for both the modeller and end user. There are also concerns about the lack of biodegradability and the release of toxins during burning, making the disposal of PVC difficult.
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It is also a plastigel
Polymer clay is a type of plasticine that contains PVC resin and a liquid plasticizer, making it a plastisol. Due to its rheological properties, polymer clay plastisol is also categorized as a plastigel. This means that it is a highly thixotropic material that can be easily shaped and moulded. When sufficient force is applied, the clay yields and flows like a viscous liquid. However, when the force is removed, it returns to its solid state. This unique plasticity is what distinguishes it from putty or paste and makes it an excellent material for modelling and sculpting.
The PVC resin base of polymer clay is modified with various additives, including plasticizers, fillers, and colouring agents. These plasticizers, such as phthalates, have been a cause for concern due to their potential health and environmental impacts. Phthalates have been classified as endocrine disruptors and are restricted or banned in both the European Union and the United States. It is important to follow safety guidelines, such as using separate utensils for clay and food and washing hands after handling clay, to minimize any potential risks associated with these additives.
Polymer clay becomes workable when cured at temperatures between 265 °F (129 °C) and 275 °F (135 °C) for 15 minutes per 1/4 inch (6.4 mm) of thickness. This curing process can be achieved using a home oven, and it is important not to exceed the recommended temperature and baking time to avoid burning the clay. Burning clay can release a small amount of hydrogen chloride gas, which may cause eye and nose irritation.
The plastigel nature of polymer clay allows it to retain its shape even when heat is applied during the curing process, preventing it from melting or drooping. This property is due to the addition of gelling agents such as aminated bentonite, metallic soaps, or fumed silica. The rheological properties of polymer clay, including its thixotropic behaviour and shape retention, make it a versatile and useful material for various crafting and artistic applications.
While polymer clay has unique advantages due to its plastigel properties, it is important to consider its environmental impact. The base material, PVC, has been identified as environmentally damaging, and the disposal of PVC products can be challenging due to their lack of biodegradability and the potential leaching of chemical components. However, recycling practices and alternatives, such as oil-based clays, are being explored to mitigate these environmental concerns. Overall, the plastigel nature of polymer clay makes it a valuable material for creative endeavours, and with proper handling and disposal, its environmental impact can be minimized.
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It is thixotropic
Polymer clay is a thixotropic material. Thixotropy is a time-dependent shear-thinning property. Certain gels or fluids that are thick or viscous under static conditions will flow (become thinner, less viscous) over time when shaken, agitated, shear-stressed, or otherwise stressed. They then take a fixed time to return to a more viscous state.
Polymer clay is a plastigel due to its rheological properties. It is a high-yield thixotropic material: when a sufficient force is applied, the material yields, flowing like a viscous liquid until that force is removed, whereupon it returns to being a solid. This plasticity is what makes it useful as modelling clay as opposed to putty or paste.
Some non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity. A thixotropic fluid is a fluid that takes a finite time to attain equilibrium viscosity when introduced to a steep change in shear rate. Some thixotropic fluids return to a gel state almost instantly, such as ketchup, and are called pseudoplastic fluids. Others, such as yogurt, take much longer and can become nearly solid. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated.
Thixotropic behaviour in clays has been the subject of various studies, with researchers investigating the phenomenon in clay deposits found in caves and in normal clay with water contents lower than the liquid limit. The findings suggest that thixotropy is a process in which the dispersed structure is transformed into a flocculent structure through the homogenization of pore size distribution caused by particle movement. This phenomenon may be due to changes in the interaction of attractive and repulsive forces between particles.
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It is not biodegradable
Polymer clay is a synthetic polymer derived from non-renewable resources such as petroleum or natural gas. It is made from PVC (polyvinyl chloride) resin and a liquid plasticizer, making it a plastisol. This combination of PVC and plasticizer makes the clay soft and pliable.
Polymer clay is not biodegradable. Once baked, it can last for years without breaking down, contributing to plastic pollution. This lack of biodegradability means that discarded clay products contribute to long-term waste in landfills. The clay can also leach chemical additives like phthalate plasticizers, which are linked to health issues like reproductive problems and developmental disorders.
The non-biodegradability of polymer clay poses environmental challenges, particularly given the significant carbon emissions associated with its production and disposal. While polymer clay constitutes a small fraction of the approximately 40 million tonnes of PVC produced annually, its environmental impact is still significant.
To address the environmental concerns associated with polymer clay, artists can adopt practices such as recycling and repurposing. Additionally, some artists have explored eco-friendly alternatives, including air-dry clay, paper clay, homemade clay, and natural clay. These alternatives offer similar workability and flexibility while being more environmentally conscious.
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Frequently asked questions
Polymer clay is made from PVC (polyvinyl chloride) resin and a liquid plasticizer, making it a plastisol.
Polymer clay has been the subject of safety concerns due to the presence of certain phthalate plasticizers, which are classified as endocrine disruptors. However, these types of phthalates are no longer used in polymer clay and are banned in the European Union and the United States. It is important to follow the instructions and use common sense when working with polymer clay to minimize any potential health risks.
Polymer clay is cured in a home oven at temperatures between 265 °F (129 °C) and 275 °F (135 °C) for 15 minutes per 1/4 inch (6.4 mm) of thickness. It is important to follow the instructions on the package to avoid burning the clay, as burning can release a small amount of hydrogen chloride gas, which may cause eye and nose irritation.
