Maya Ellison
Plastic can often be found sticking to human skin, and this phenomenon can be attributed to a combination of static electricity and adhesives. Plastic materials, such as polyethylene, have low surface energy, which causes them to adhere to surfaces with higher energy, like human skin. The friction between the plastic and the skin creates a temporary bond, resulting in the plastic sticking to our hands. Additionally, plastic wrap is an insulator, which means it does not allow electrons to flow freely. As human skin is easily positively charged, the negatively charged plastic wrap is attracted to it due to the opposite charges. This attraction can be observed when plastic clings to our hands or other surfaces.
| Characteristics | Values |
|---|---|
| Reason | Static electricity, low surface energy, friction, adhesive |
| Plastic | An insulator, negatively charged |
| Human Skin | Positively charged |
| Cleaning Methods | Baking soda and water paste, alcohol, liquid dish detergent and water solution, soap and water solution |
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What You'll Learn
Static electricity and human skin's positive charge
The human body has a weak electrical charge, which can be positive or negative. The Earth has a slight negative charge, so humans also have a slight negative charge if they are standing on the bare ground without shoes.
However, the human skin is very high on the Triboelectric Series, so if one scuffs their feet on a carpet, they are almost guaranteed to get a positive charge, no matter what the carpet is made of. This is because human skin, hair, and hands are considered to be positively charged.
Static electricity can be generated by the triboelectric charge separation on clothing. This phenomenon was first observed by Plato around 400 B.C., who described how amber worn by people attracted dry hair. The human body's triboelectricity has been studied in relation to cosmetics, electrostatic discharge, and triboelectric nanogenerators.
When plastic wrap sticks to one's hands, it is due to both static electricity and an adhesive. The static charge is built up during the processing of the plastic, causing it to be attracted to the human hand.
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Adhesives added to plastic during processing
Plastic wrappers often stick to our hands due to static electricity and adhesives added during processing. The former is a result of a static charge built up during the processing of the plastic, which causes the plastic to be attracted to our hands.
Some common types of adhesives used for plastic bonding include acrylics, epoxies, urethanes, silicones, and cyanoacrylates. The adhesive bonding process involves applying the adhesive to the substrates and joining them together, sometimes using heat, light, or pressure to cure the adhesive and create a strong bond.
Solvent bonding is another method of joining plastics, which involves dipping the ends of two plastic components into a solvent to soften the surfaces before bonding them together with pressure. Additionally, plastic can be bonded to other materials such as metal, glass, and ceramics using adhesives, heat, ultrasound, radiation, or other methods.
The use of adhesives and other additives in plastics has raised concerns about their potential to contaminate the environment and expose humans to harmful substances during their use, disposal, and recycling. Therefore, proper waste management and sound recycling practices are crucial to mitigate these risks and protect environmental and human health.
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Plastic's low surface energy
The surface energy of materials can be classified into three groups: high, medium, and low surface energy. Materials with a surface energy below 36 dynes/cm are considered low surface energy (LSE) materials. These materials are difficult to bond with other materials and have limited adhesive options. Molecules on the surface of LSE materials are not very attracted to other molecules, especially adhesive molecules.
LSE plastics are generally soft, low-density, and have a low melting point. They are easy to process and mold, even in high volumes, and are lightweight. Some common LSE plastics include polypropylene (PP), polyethylene (PE or HDPE), polystyrene, acetal, EVA (ethylene vinyl acetate), and powder-coated paints.
The low surface energy of plastics can make it challenging to bond them with other materials. This can be an issue in manufacturing, as it limits the ability to create complex shapes and designs. However, some companies have developed specific adhesives and tapes designed to bond LSE plastics, allowing for more design flexibility and improved aesthetics.
Additionally, external factors such as surface cleanliness, texture, and permeability can also affect the bondability of LSE plastics. Providing a converter with a sample of the substrate for adhesive testing can help determine the best adhesive for a particular application.
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Friction creating a temporary bond
When two objects come into contact, the force that resists their motion against each other is called friction. This force can create a temporary bond between the objects, which is why sometimes plastic items seem to stick to your hand. The surface of the plastic and the texture of your skin play a significant role in this phenomenon. Plastic items often have smooth surfaces, but upon very close inspection, they may have microscopic ridges, indentations, or bumps. Similarly, the skin on your hand is not perfectly smooth, and it too has a unique texture, with tiny crevices and ridges. When you press a plastic item against your hand, these microscopic imperfections on both surfaces interlock, creating a temporary bond.
This interlocking action is similar to how the tiny hooks on a Velcro strap catch onto each other, providing a strong temporary hold. In the case of plastic sticking to your hand, the force required to separate the two surfaces is relatively small, but it is enough to create that momentary sticking sensation. The amount of friction and the strength of the temporary bond depend on several factors. One key factor is pressure: the harder you press the plastic item against your hand, the greater the force bringing the two surfaces together, and thus the stronger the friction and temporary bond. Another factor is temperature: when the plastic is warmer, its molecules move more vigorously, and this can make the surface slightly softer and more pliable, increasing the interlocking with your skin and thus the friction.
Additionally, moisture can play a role. If your hands are slightly sweaty or damp, the moisture can act as a very thin layer of glue, enhancing the friction and temporary bond. This is because the water creates hydrogen bonds with both the plastic and your skin, effectively helping to "grab" the two surfaces together. The duration of contact also matters: the longer the plastic item is pressed against your hand, the longer the friction force has time to act, and the stronger the temporary bond may become. Finally, the material of the plastic item itself is a factor. Different plastics have varying levels of flexibility and softness, and these properties influence how easily the plastic surface can conform to the microscopic contours of your skin, thus affecting the strength of the friction bond.
In summary, the friction between your hand and a plastic item creates a temporary bond due to the interlocking of microscopic surface imperfections. This effect is influenced by factors such as pressure, temperature, moisture, duration of contact, and the specific material of the plastic. Understanding these factors can help explain why that peculiar sticking sensation occurs when handling certain plastic items. This phenomenon is a reminder that even on the smallest scales, the world is full of intricate interactions that lead to surprising behaviors in our everyday experiences.
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Cleaning sticky plastic with household products
Plastic can get sticky due to a disintegrating rubber coating or a build-up of static electricity and adhesive chemicals during the processing of the plastic. To clean sticky plastic, there are several household products you can use:
Baking Soda and Water
Make a paste with a pinch of baking soda and water. Scrub the paste onto the sticky plastic item with your hands. After about 10 minutes, use a damp cloth to remove the residue.
Rubbing Alcohol
Rubbing alcohol (isopropanol/isopropyl alcohol) can be used to clean sticky plastic. However, it requires a fair amount of rubbing and primarily prevents the readhesion of rubber rather than dissolving it.
Orange Essential Oil
Orange essential oil is effective at removing price stickers from plastic and can also help with stickiness.
Mother's Plastic Polish
This product can be used to buff and shine plastic parts on cars. It can instantly fix sticky spots and make the surface look shiny and new.
Dish Detergent
Dampen a washcloth with hot water and dish detergent, then wring out the excess water. Clean the sticky plastic surface and rinse the washcloth before wiping the surface again.
Murphy's Oil Soap
Dampen a washcloth with hot water and wring out the excess. Apply Murphy's oil soap to the washcloth and clean the sticky plastic. Rinse the washcloth and wipe the surface again.
Citrus Degreaser
Citrus degreaser can be effective in removing sticky residue from plastic.
It is important to note that some products, like acetone, may damage plastic, so it is recommended to test any cleaning solution on a small area first. Additionally, if you are cleaning the plastic of electronic devices, be sure to wipe out the battery compartment and let it dry to avoid corrosion.
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Frequently asked questions
Plastic has low surface energy, which causes it to adhere to surfaces with higher energy, like human skin. The friction between the plastic and the skin creates a temporary bond, making the plastic stick to your hand.
Plastic wrap is an insulator, meaning it does not allow electrons to flow from one to the other. Human skin is easily positively charged, and the plastic wrap is negatively charged. Opposite charges attract each other, which is why plastic sticks to your hand.
You can try cleaning the plastic with common household ingredients like baking soda, isopropyl alcohol, water, or mild dish detergent.
You can use a soft cloth or a microfiber cloth to wipe down the plastic item with a soap and water solution or isopropyl alcohol. Make sure to scrub any particularly sticky areas until you get all the residue off.
Many common plastic items have a soft plastic coating that can deteriorate and become sticky over the years. This can also happen due to the accumulation of residue from your hands, spills, or leftover adhesive from stickers or glue.
