Ethan Clarke
The process of recycling plastic is complex and challenging, with less than 10% of plastic waste globally ever being recycled. One of the key barriers is the presence of coloured pigments in plastic, which makes it harder to obtain recycled plastic with vibrant and distinct colours. The recycling process itself does not change the chemical composition of plastic, but it does affect the molecular weight. Coloured plastic often ends up as grey or black plastic due to the challenges of sorting and processing. Sorting mechanisms include magnets, eddy currents, mesh sieves, and optical sensors, but the presence of colour and pigment complicates the process. Clear and white plastic are the most recyclable, with coloured plastic often being sent to landfill. However, companies are working on innovative ways to improve the recyclability of coloured plastic, such as creating sorting mechanisms to identify and separate pigments and polymers.
Characteristics of Coloring Recycled Plastic
| Characteristics | Values |
|---|---|
| Plastic Types | PET, HDPE, LDPE, PVC, PP, PS |
| Plastic Sorting Mechanisms | Magnets, Eddy Currents, Sieves, NIR Sensors, Optical Sensors |
| Coloring Process Challenges | Inconsistencies, Color Variations, Sorting Difficulties, Market Value |
| Coloring Techniques | Re-extrusion, Chemical, Energy Recovery |
| Pigment Removal | Solvent-based Extraction, Waste Stream Separation |
| Environmental Impact | Greenwashing, Landfill, Marine Life, Energy Recovery |
| Consumer Actions | Reuse, Recycle, Clean, Dry |
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What You'll Learn
Sorting coloured plastics
There are several methods for sorting coloured plastics. One method is to use a plastic colour sorter, a machine that uses photoelectric detection technology to automatically sort out heterochromatic particles in granular materials according to the differences in their optical characteristics. The material is conveyed along a channel and passes between a sensor and a background plate. The system then generates an output signal to drive the solenoid valve to blow out particles of different colours to the waste hopper, while the selected materials continue to fall to the finished hopper.
Another method is to use visible (VIS) reflectance spectroscopy to separate plastics based on their colour. This method has been proposed for distinguishing polypropylene (PP) plastics and has been demonstrated to be fast and accurate, even with the presence of different labels and surface contamination.
Standard plastic recycling systems typically include a range of sorting mechanisms, including magnets and eddy currents to remove metals, mesh sieves to remove dust and dirt, and plastic sorting systems to sort plastic waste by polymer type and colour. Near-infrared (NIR) sensors identify the polymer type, and optical sensors separate the plastic by colour. Clear and white plastic can be recycled back into clear and white plastic, while coloured plastic is typically recycled into less versatile grey or black plastic or sent to landfill.
To improve the accuracy and efficiency of the sorting process, it is essential to have more data about the packaging and its history. Stringent standards mean that plastics intended for food contact must be separated from the rest, and factors such as colour, smell, food contamination, and exposure to sunlight all impact whether a polymer can be recycled and what it can be used for.
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$12.99
Removing coloured inks
Identify the Stain:
Locate the ink stain on the plastic surface and assess its size and severity. This will help you determine the best removal method and the amount of effort required.
Choose Your Solvent:
Select an appropriate solvent to break down the ink. Common household solvents like acetone, hydrogen peroxide, chlorine bleach, denatured alcohol, or ordinary rubbing alcohol are effective for removing ink stains. These solvents are likely to be available in your home supply closet. Remember to exercise caution and wear protective gloves when handling these chemicals.
Apply the Solvent:
Apply a small amount of your chosen solvent to a clean cloth. Gently rub the cloth over the stained area in smooth, circular motions. You should notice the ink starting to fade and dissolve within seconds. If you're dealing with a large surface or an item that can be soaked, you can fill a container with the solvent and let the item sit in it for 5-10 minutes.
Remove Residue:
Once the ink has faded, use a damp cloth to wipe away any remaining solvent and ink residue. Rinse the area thoroughly with water to ensure all traces of the solvent are removed.
Alternative Methods:
If you prefer a gentler approach or don't have access to the solvents mentioned above, you can try using hand sanitizer or distilled white vinegar. Keep in mind that these methods may require more effort or multiple applications. Additionally, baking soda is another effective and gentle option. Its abrasive properties help break down the ink while being mild enough to not damage plastic surfaces.
Safety Precautions:
Always prioritize safety when working with chemicals. Wear gloves to protect your skin from the solvents, and consider wearing a mask to prevent the inhalation of fumes, especially when using rubbing alcohol or other strong cleaning agents. Avoid using cloth or textile gloves, as absorbent fabrics can soak up the solvents and potentially harm your skin.
By following these steps and choosing the appropriate solvent, you can effectively remove coloured inks from plastic items, giving them a like-new appearance.
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Coloured plastic contamination
The presence of coloured pigments in plastic recycling streams makes it harder to obtain recycled plastic with vibrant and distinct colours. The resulting product is usually restricted to being used for grey or black products. This contributes to the demand for virgin, often oil-derived plastic, which can be coloured exactly as desired. Coloured plastic is a significant contributor to recycling contamination.
Coloured plastic contaminates recycling streams, causing problems with the sorting process, and is often not recycled at all. The standard plastic recycling system includes sorting mechanisms such as magnets and eddy currents to remove metals, mesh sieves to remove dust and dirt, and plastic sorting systems to sort the plastic waste by polymer type and colour. The initial sort uses near-infrared (NIR) sensors to identify polymer type, and then optical sensors to separate by colour. Clear and white plastic can be recycled back into clear and white plastic, while coloured plastic is typically recycled into much less versatile grey-ish or black plastics.
Pigmented and dyed plastics are a challenge for most material recovery facilities (MRF) due to their lower market value and the trouble of finding a home for the material. There is a lack of infrastructure to sort PCR, which would ideally be separated by resin composition, weight, colour, transparency, and size. This is why there are large volumes of PCR in black (all colours mingled), some in white, and fewer volumes in natural colours (which are considered a "premium" product).
The presence of contaminants in a load of recycling can result in the items being sent to landfill, even if some of them are viable for recycling. This is because recycling is a business, and if the extra costs of separating out the contamination are too high, it is likely that the money will be spent elsewhere. Contaminants can also endanger recycling workers, who may be exposed to hazardous waste, vector-borne diseases, and other physically damaging items.
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Coloured plastic recycling methods
The presence of coloured pigments in plastic recycling streams makes it harder to obtain recycled plastic with vibrant and distinct colours. The resulting product is usually used for grey or black products. This contributes to the demand for virgin, often oil-derived plastic, which can be coloured as desired.
One method to colour recycled plastic is to use masterbatches. These are substances that are mixed with the plastic raw material to colour it. They are the most economical method to colour plastics and can be provided in small volumes. Masterbatches consist of concentrated pigments dispersed into a polymer carrier resin. During moulding, the masterbatch is fed into natural resin at a predefined ratio to achieve the desired colour.
Another method is to use cube blends, which are colour systems that feature a masterbatch dry-blended with a natural polymer that is ready to use.
A third method is to use pre-colours.
Coloured PCR (post-consumer recycled material) will never conform to the cleanliness of uncoloured PCR or the purity of virgin polymer. However, it is important to embrace the imperfections of coloured PCR because it adds value to global recycling efforts.
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Coloured plastic market value
Coloured plastic is a challenge for most recycling facilities due to the lower market value and difficulties in finding a use for the material. The presence of coloured pigments in plastic recycling streams makes it harder to obtain recycled plastic with vibrant and distinct colours. The resulting product is usually restricted to grey or black products. This contributes to the demand for virgin, often oil-derived plastic, which can be coloured as desired.
The market value of coloured plastic is lower than that of clear or white plastic because it is more difficult to recycle and has limited end uses. Clear and white plastic can be recycled back into clear and white plastic products, while coloured plastic is typically recycled into less versatile grey or black plastics. The sorting process for coloured plastic is more complex and requires additional steps to separate the plastic by colour.
The challenges associated with recycling coloured plastic have led to companies switching to clear or white plastic, which is more recyclable. For example, the UK retailer Co-op removed coloured milk bottle tops from its shelves. Additionally, innovations in ink recycling have been developed to remove coloured inks from plastic surfaces, improving their recyclability. However, these processes do not change the colour of the plastic itself.
Despite the lower market value of coloured plastic, it still has value and can be used in various applications. Coloured plastic can be used in products such as detergent bottles, motor oil bottles, household cleaners, lawn products, and packaging films. Embracing the imperfections of coloured recycled plastic adds value to global recycling efforts. Coloured recycled plastic can be used to create products with unique colours and visual imperfections that can be desirable to consumers.
The global plastics market was valued at 712 billion U.S. dollars in 2023 and is projected to grow to over 1,050 billion U.S. dollars by 2033. The demand for plastic goods is expected to increase due to rising populations and buying power. At the same time, there is also a growing demand for more eco-friendly materials, such as biodegradable plastics. The global biodegradable plastics market is projected to reach a value of more than 20 billion U.S. dollars by 2026.
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Frequently asked questions
Coloured plastic is harder to sort and often ends up as grey or black plastic, or even sent to landfill. Sorting coloured plastic is made more difficult by the presence of coloured pigments in the plastic, which can contaminate the recycling stream.
The first step is to identify the type of plastic. This can be done by looking for the Resin Identification Code, which is represented by a 'chasing arrows' symbol with a number in the middle. Once the type of plastic is known, the next step is to clean and dry the plastic before taking it to a recycling centre.
Coloring recycled plastic is a challenging process that often creates inconsistencies in the final product. The colour of the resin will vary, and the quality may be lower. Colortech is one company that offers coloured concentrates with PCR carriers to create coloured recycled plastic products.
Recycling coloured plastic can add value to global recycling efforts and promote sustainable recycling practices. It can also be used to create visually appealing and distinctive products that can enhance brand recognition.
