Maya Ellison
Refrigerators are a common household appliance that is used to store food and beverages at a low temperature. They are designed to keep the cold air inside, preventing it from escaping and causing the temperature to rise. One of the key features of a refrigerator is the use of plastic flaps, also known as door seals, that are made from a variety of plastic types including polyurethane, polystyrene, polypropylene, and polyethylene. These plastic flaps serve an important function in preserving the temperature inside the refrigerator by acting as insulation and preventing the warm air from rushing into the cold interior. This not only helps maintain the desired temperature but also reduces energy consumption, making the refrigerator more energy efficient.
| Characteristics | Values |
|---|---|
| Purpose | Stops warm air rushing in/cold air rushing out, reducing energy usage |
| Function | Acts as insulation |
| Alternative | Automated doors |
| Plastic Types | Polyurethane, Polystyrene, Polypropylene, Styrene-butadiene-acrylonitrile copolymer, Polyethylene |
| Plastic Benefits | Lightweight, inexpensive, recyclable, easy to clean, resists swelling and warping |
| Plastic Drawbacks | Can become brittle over time, especially with large swings in temperature |
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What You'll Learn
Plastic flaps insulate refrigerators
Plastic flaps are commonly found in the doorway of walk-in refrigerators and freezers. They serve as insulation, preventing warm air from rushing into the fridge and cold air from escaping. This helps to maintain the internal temperature of the fridge, reducing the energy required to keep the fridge cool. Plastic flaps are an older technology, and modern refrigerators often feature automated doors that provide better insulation and energy efficiency.
The use of plastic in refrigerator construction offers several benefits. Plastic is lightweight and inexpensive, making it a practical choice for manufacturers. Different types of plastic are used to fulfil various requirements and design considerations. For example, polycarbonate, known for its strength and rigidity, is commonly used for exterior doors, handles, and body panels. ABS, polypropylene, and polystyrene are used for the interior, including door and wall panels, shelves, and drawers.
Polyurethane, a type of plastic with low thermal conductivity and good processing performance, is particularly well-suited for refrigerator insulation. It forms thin strips that trap air between layers of harder plastics, enhancing the insulating properties of the refrigerator. This helps to keep the internal temperature cool and reduces energy consumption.
In addition to their insulating properties, plastics used in refrigerators offer other advantages. They are easy to clean and resist swelling and warping when exposed to moisture and temperature fluctuations. Plastics also have a relatively high degree of recyclability, making discarded refrigerators valuable to recyclers and helping to reduce landfill waste.
However, it is important to note that some refrigerator owners have reported issues with brittle and cracking plastic components, including bins, drawer guides, shelf supports, and door shelves. This may be due to temperature extremes, humidity, or the use of lower-quality plastic. Regular temperature fluctuations can accelerate the process of plastic becoming brittle over time.
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Plastic is lightweight and inexpensive
The use of plastic in refrigerators is primarily due to its lightweight and inexpensive nature. Plastic is a practical material for appliances that consume large quantities of it in their production, such as refrigerators. The average proportion of plastics in each refrigerator is around 30-50% or more, with polystyrene (PS) being the most commonly used variety, accounting for over 60% of total refrigerator plastic consumption.
Polyurethane (PU) is another essential plastic in refrigerator production, constituting 40-50% of the plastic costs. It is used for insulation, forming thin strips that trap air between layers of harder plastics. Its low thermal conductivity and good processing performance make it ideal for this purpose.
Other plastics used in refrigerators include polypropylene (PP), which has excellent mechanical properties, a simple production process, and high toughness. Acrylonitrile-Butadiene-Styrene (ABS) is also used, offering high strength, good gloss, easy processing, and low shrinkage. Polyethylene (PE) is another common plastic in refrigerators, known for its odourless, tasteless, non-toxic, and impact-resistant properties.
The lightweight and inexpensive nature of plastic makes it a cost-effective choice for refrigerator manufacturers, allowing them to produce appliances that are more affordable for consumers. Additionally, plastic's ability to resist thermal transmission helps keep the refrigerator's interior cooler for longer, reducing energy consumption.
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Plastic resists thermal transmission
The plastic flaps on refrigerator doors are designed to stop warm air from rushing into the refrigerator and cold air from escaping. This helps the refrigerator maintain its temperature and reduces energy consumption.
Heat-resistant plastics, such as Vespel®, Torlon®, and Noryl®, can withstand repeated heating up to 300°C without changing their thermal or mechanical properties. These plastics are often used in high-heat applications such as jet engines and car parts. They are also used to make aircraft hardware and fasteners, as well as mechanical and structural components.
The thermal conductivity of plastics can be measured using ASTM C177 and ISO 8302 standards, and it is an important factor in material selection for applications requiring temperature isolation, such as appliance handles or coffee cups. The thermal insulating capacity of plastics is rated by measuring thermal conductivity, which is denoted by the letter k.
The thermal conductivity of plastics decreases with an increase in temperature above their glass transition temperature (Tg). For amorphous plastics at 0-200°C, the thermal conductivity lies between 0.125-0.2 Wm-1K-1.
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Plastic is easy to clean
The use of plastic in refrigerators is ubiquitous, with modern refrigerators using several different types of plastic to serve essential functions better than other materials. The average proportion of plastics in each refrigerator is between 30-50% or more.
The ease of cleaning plastic is especially important given that most plastics will get brittle over time, especially in the presence of large swings in temperature and humidity. This is a common issue with refrigerator plastics, with some users reporting that the plastic parts in their refrigerators started getting brittle and cracking within three years of purchase.
The ease of cleaning plastic also contributes to the relatively high degree of recyclability of refrigerators. According to Panasonic, up to 40% of a refrigerator's total weight may be made up of plastics, making discarded refrigerators valuable to recyclers and scrap dealers, and helping to keep them out of landfills.
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Plastic is recyclable
Plastic is a versatile material used in many household appliances, including refrigerators, which demand the largest amount of plastic raw materials among household appliances. The average proportion of plastics in each refrigerator is between 30-50% or more. The main types of plastics used in refrigerators include polyurethane (PU), polystyrene (PS), polypropylene (PP), styrene-butadiene-acrylonitrile copolymer (ABS), and polyethylene (PE).
However, not all plastic is widely recyclable, and certain types, like plastic bags, can be challenging to recycle due to tangling in machinery. Some plastics are also not economically viable to recycle, like low-density polyethylene (LDPE) bags, which are cheap and low-quality. Despite these challenges, recycling plastic is still possible and beneficial. The majority of recycled plastic comes from post-consumer sources, such as milk jugs, bottles, and packaging films that can be transformed into new products.
The most widely recycled plastic globally is PET, which is commonly found in plastic bottles. Recycled PET is used to create fashion items like polar fleece clothing, backpacks, and carpets. It can also be used for construction in third-world countries by filling plastic bottles with sand and stacking them to form walls. Another easily recyclable plastic is HDPE, which is accepted at most recycling centres and used for non-food application bottles like detergent and motor oil.
Mechanical recycling is the most common method, involving melting and reforming plastic into new items. Chemical recycling, on the other hand, breaks down plastic into monomers to form new polymers. While recycling is essential, reduction and reuse are more favourable long-term solutions for sustainability.
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Frequently asked questions
The plastic flaps in the doorway of walk-in refrigerators and freezers help to stop warm air from rushing in and cold air from rushing out, allowing the fridge to use less energy.
The plastic flaps are made from polystyrene, which is the most used plastic variety in refrigerator production.
Other types of plastic used in refrigerators include polyurethane, polypropylene, polyvinyl chloride (PVC), polycarbonate (PC), polyoxymethylene (POM), and polymethyl methacrylate (PMMA).
