Maya Ellison
Plastic is a versatile material that can be moulded into various shapes and colours. The colour of plastic is determined by the addition of colourants, which are chemical compounds in the form of dyes and pigments. These colourants not only add aesthetic value but also improve the functionality of products. For example, carbon black is added to automobile bumpers to enhance weather resistance. The specific type of colourant chosen depends on the polymeric resin being used, with dyes commonly paired with polycarbonates, polystyrene, and acrylic polymers, and pigments with polyolefins. The manufacturing process and additives also influence the final colour of the plastic product.
| Characteristics | Values |
|---|---|
| Original colour of plastic | Colourless (milky white) or translucent whitish |
| Colouring methods | External (e.g. printing, painting, plating) and internal (kneading colouring materials into plastic) |
| Types of colourants | Masterbatches, coloured pellets and colouring compounds, dry colours, paste colours and liquid masterbatches |
| Colourants' functions | Functional (e.g. improving weather resistance), conductive, antistatic |
| Factors affecting colour | Thickness of material, moulding process, exposure to sunlight or other environmental factors |
| Examples of colours | Dark red, dark blue, light blue, light green, turquoise, broom yellow, traffic red, black grey, dolphin grey |
| Recyclability | Black plastic cannot be recycled as it absorbs infrared light used in the recycling process |
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What You'll Learn
- Raw plastic is colourless (milky white)
- Coloured plastic is achieved through external or internal colouring
- Colourants can improve functionality, e.g. carbon black in bumpers for weather resistance
- Black plastic is bad for the environment and potentially toxic
- The thickness of plastic and exposure to sunlight can affect its colour
Raw plastic is colourless (milky white)
Raw plastic is colourless and has a milky white appearance. It is often supplied as colourless granular bulk goods. The raw materials are weighed, mixed, melted, and kneaded before being cooled, hardened, and cut into pellets. These pellets are then packed and shipped. The base colour of plastic is determined by the raw materials used, the manufacturing process, and any additives. For example, the degree of yellowness in plastic is influenced by the contamination or impurities of the raw materials and process variations such as temperature.
To create coloured plastic products, colouring agents or colourants are added. These colourants can be added through external colouring methods such as printing, painting, or plating, which only colour the surface of the plastic. Alternatively, internal colouring methods involve kneading colouring materials into the plastic, resulting in even colouring throughout the material. The use of colourants not only adds colour to plastic products but also improves functionality. For instance, carbon black is added to automobile bumpers and containers to improve weather resistance. Similarly, colourants can be given conductive and antistatic functions to protect precision equipment from malfunction due to static electricity.
It is important to note that the colour of plastic can impact its properties. While colour additives can affect durability over time by influencing UV resistance, they generally do not affect the strength of the material. However, some sources suggest that brighter colours may indicate weaker plastic. Additionally, the colour of plastic can impact its recyclability. Black plastic, for example, accounts for 15% of all plastic recyclables but is often not recycled due to the technology used in recycling facilities, which cannot detect the colour black.
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Coloured plastic is achieved through external or internal colouring
Plastic is essentially a colourless, milky-white resin. However, plastics are often coloured, and this is achieved through external or internal colouring.
External Colouring
External colouring refers to colouring the surface of plastic and includes printing, painting, and plating.
Internal Colouring
Internal colouring involves kneading colouring materials, or colourants, into the plastic. The plastic and colouring material are mixed together, resulting in a uniformly coloured product. Colourants can be in the form of pellets, dry colours, masterbatches, paste colours, or liquid masterbatches. The ratio of colourant to plastic should be approximately 1:100 up to 5:100. As the volume of the pigment injection increases, its effect on the plastic's colour increases.
Types of Colourants
The main types of colourants include masterbatches, coloured pellets and colouring compounds, dry colours, and paste colours and liquid masterbatches. Dry colours are created by mixing pigments with natural pellets to form colours. They are cheap to produce but can be scattered easily, leading to an uneven colour. Masterbatches, on the other hand, are highly concentrated pigments kneaded into pellets, allowing for easy shade adjustments and uniform colouring.
Functional Colourants
Colourants can also improve the functionality of products. For example, carbon black is used as a colourant in automobile bumpers and containers to improve weather resistance. Colourants can also be given "conductive" and "antistatic" functions to protect precision equipment from malfunction due to static electricity.
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Colourants can improve functionality, e.g. carbon black in bumpers for weather resistance
Plastic is typically a colorless, milky white when in its raw form. To add color to plastic products, colorants are added either through external or internal coloring. External coloring involves techniques such as printing, painting, and plating, while internal coloring involves kneading coloring materials into the plastic, resulting in a uniformly colored product.
One example of a functional colorant is carbon black, which is used in automobile bumpers to improve weather resistance. Carbon black is a paracrystalline carbon material produced by the incomplete combustion of coal tar, vegetable matter, or petroleum products. It has a high surface-area-to-volume ratio, contributing to its unique properties.
In the context of bumpers, carbon black enhances weather resistance by providing protection against temperature changes, wind, and rain. Additionally, carbon black is an excellent absorber of ultraviolet radiation, which helps prevent the degradation of the bumper material over time. This property is especially advantageous for maintaining the structural integrity and longevity of the bumper.
Carbon black also finds application in other rubber and plastic products, such as hoses, belts, and conveyor wheels. In these products, carbon black serves as a reinforcing filler, enhancing tensile strength and abrasion resistance. Furthermore, carbon black is electrically conductive, making it useful as an antistatic additive in fuel caps and pipes.
The versatility of carbon black extends beyond the automotive industry. It is utilized as a pigment in inks, coatings, and plastics, contributing to the rich black color of these products. Carbon black from vegetable sources is even used as a food coloring additive, known as E153 in Europe.
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Black plastic is bad for the environment and potentially toxic
Plastic is essentially a colorless, milky-white resin that is altered by the addition of colorants or pigments. Black plastic, however, is particularly harmful to the environment and human health. It comprises 15% of all plastic recyclables, yet most of it ends up in landfills, incinerators, or the environment due to challenges in recycling it.
Black plastic is created by adding carbon black, a substance that absorbs infrared light. Recycling facilities use infrared light to sort plastics by color, but since carbon black absorbs this light, the machinery fails to register black plastics for sorting. Consequently, black plastic items often end up as waste after just a single use.
The creation of black plastic is also concerning. It is largely sourced from electronic waste, such as old computers, TVs, and appliances, which contain toxic chemicals like phthalates, flame retardants, and heavy metals (cadmium, lead, nickel, chromium, and mercury). When this electronic waste is melted down and mixed with food-grade plastics, it poses a significant risk to human health.
Even at very low levels, these toxic chemicals can cause serious health issues, including reproductive and developmental problems, brain and kidney poisoning, thyroid function disruption, and long-term neurological damage. Items of particular concern are black plastic cooking utensils, stirrers, food containers, and hot cup lids, as heat increases the likelihood of toxic chemicals leaching into food and drinks.
Furthermore, black plastics are more likely to contain unregulated amounts of toxic chemicals, including heavy metals and flame retardants. The presence of these chemicals in black plastic household goods has been confirmed by studies and researchers, highlighting the urgency of addressing this issue.
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The thickness of plastic and exposure to sunlight can affect its colour
Plastic is essentially colorless (milky white) in its original state. The addition of colorants, such as pigments, creates plastic products in a variety of colors. There are two main methods of coloring plastic: external coloring, which involves techniques like printing and painting, and internal coloring, where coloring materials are kneaded into the plastic for a uniform color.
The thickness of plastic and its exposure to sunlight can significantly impact its color and overall properties. When it comes to the thickness of plastic, the relationship between color and plastic properties is complex. Different colors have varying molecular bonds with polymers, and adding colors or substances to polymers weakens their bonds. Certain colors have a stronger molecular bond with polymers, and understanding this relationship requires a deep understanding of science and technology.
The thickness of plastic plays a role in determining the extent of UV exposure and subsequent degradation. Plastics exposed to sunlight undergo visual and physico-chemical modifications, including photo-oxidative and thermal degradation. Thicker plastics may offer some protection against UV radiation, slowing down the degradation process. However, the specific polymer type, formulation, and exposure conditions also influence the fragmentation and degradation of plastic.
Additionally, the color of plastic can influence its response to UV exposure. Different colorants used in plastics have unique responses to UV radiation. For example, white colorants containing titanium dioxide can cause rapid degradation of polycarbonate when exposed to high temperatures. On the other hand, carbon black, used in automobile bumpers and containers, improves weather resistance by enhancing resistance to temperature changes, wind, and rain.
The thickness of plastic can also affect the colorant's ability to provide functional benefits. For instance, a conductive colorant added to protect precision equipment from static electricity may be more effective in thinner plastics, allowing for a more efficient escape of electricity to the outside environment.
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Frequently asked questions
Plastic is made from synthetic or semi-synthetic organic compounds. These are typically derived from petrochemicals and can be moulded into a range of products.
Plastic colourants are chemical compounds used to colour plastic. They come in the form of dyes and pigments. The type of colourant chosen depends on the type of polymeric resin being coloured.
Plastic can come in a wide variety of colours, including dark red, dark blue, light blue, light green, turquoise, yellow, black grey, dolphin grey, red, blue, and green, among others.
There are several methods for colouring plastic, including masterbatches (concentrates), cube blends, surface coating, and pre-coloured resins. The chosen method depends on factors such as cost, desired colour concentration, and compatibility with the base resin.
The colour of plastic can be affected by factors such as the thickness of the material, the moulding process used, and exposure to sunlight or other environmental factors. For example, plastics exposed to UV radiation may yellow or discolour over time.
