Alexei Volkov
Plastic bags are commonly used for storing water, especially in emergency situations. However, it is unclear whether water can penetrate plastic bags over time due to their water absorption properties. While some people have observed that water can leak out of plastic bags, others have conducted experiments, such as poking holes in plastic bags filled with water, and found that the water does not leak. This has led to questions about whether water absorption and water transmission in plastics are related. Understanding the behaviour of water in plastic bags is crucial for long-term water storage and shipping goods in plastic packaging to prevent moisture damage.
| Characteristics | Values |
|---|---|
| Can water go through plastic bags? | Water can go through plastic bags if there are holes in the bag. However, plastic bags are often used to protect goods from moisture damage. |
| Plastic bags and water absorption | Plastic bags have moisture absorption properties, and water can penetrate plastics over time. However, the rate of absorption depends on factors such as the surface area of the bag, the thickness of the bag, and the duration of exposure to water. |
| Preventing water leakage | Plastic bags can be sealed to prevent water leakage, even when punctured by sharp objects like pencils. This is due to the flexibility of the plastic molecules, which shift and mould around the puncturing object to create a seal. |
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What You'll Learn
Plastic bags are used to protect shipped goods from moisture damage
Plastic bags are commonly used to protect shipped goods from moisture damage. However, it is important to note that they are not impermeable and do not provide a one-size-fits-all solution. The effectiveness of plastic bags in preventing moisture damage depends on various factors, including the type of plastic, thickness, and duration of exposure.
The Moisture Vapor Transmission Rate (MVTR) of a plastic bag indicates how much moisture can penetrate over time. Different types of plastics have varying MVTR values, with low-density polyethylene (LDPE) bags having a higher MVTR than aluminum foil laminate, for example. Thickness also plays a role, as thicker plastics may offer better protection.
In some cases, plastic bags can cause more problems than they solve. For instance, if the packaging area has high humidity, the sealed bag can trap moisture, leading to condensation and potential damage to the contents, especially if the products themselves have moisture content. This is known as the pre-existing moisture problem. Additionally, some products release moisture when the temperature rises, and sealing them in plastic can lead to condensation and damage when temperatures fluctuate.
To mitigate these issues, desiccants can be added to sealed bags to absorb excess moisture. However, this adds cost and time to the packaging process. An alternative solution is to manage container humidity, which can be more cost-effective and environmentally friendly. By addressing the underlying causes of moisture, the use of plastic bags or desiccants may be reduced or avoided altogether.
When shipping goods, it is essential to consider the unique characteristics of the products and the shipping environment. While plastic bags can provide some protection against moisture damage, they may not be sufficient for all scenarios. In conclusion, while plastic bags are commonly used for moisture protection during shipping, they should be carefully evaluated and combined with other measures to ensure effective moisture control.
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Plastic bags are used for emergency water storage
Plastic bags are sometimes used for emergency water storage, but they may not be the best option. While plastic bags can be useful for short-term water storage in an emergency, they may not be ideal for long-term use due to their thin walls and potential for leaks.
In an emergency, such as a power outage or natural disaster, having access to clean drinking water is crucial. Plastic bags can be filled with water and stored in a bathtub or other container as a temporary solution. This method ensures that individuals have a supply of water for drinking, cooking, and sanitation during the immediate aftermath of a disaster when access to clean water may be limited.
However, it is important to recognize that plastic bags are not designed for long-term water storage. Over time, the water can absorb into the plastic, leading to leaks and a reduction in water volume, as observed in an experiment where a plastic bag was used to store water for 41 days. The thin walls of plastic bags make them more susceptible to punctures and tears, which can result in water loss and contamination.
For longer-term emergency water storage, it is recommended to use FDA-approved food-grade water storage containers made from durable materials, such as polyethylene plastic. These containers are specifically designed to prevent leaks and minimize the transfer of toxic substances into the water. Additionally, individuals can disinfect their water using liquid chlorine bleach to ensure it remains safe for consumption.
By following guidelines from organizations like the CDC and state departments of environmental quality, individuals can effectively prepare for emergencies and ensure they have access to clean drinking water when needed. This includes storing at least one gallon of water per person per day for a minimum of three days and up to two weeks, if possible. Proper labelling, storage conditions, and regular replacement of stored water are also essential to maintain its quality and safety.
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Water absorption and water transmission are different
Water can go through plastic bags under certain conditions. Plastic bags are often used to protect valuable cargo from dripping water. However, it is important to note that water absorption and water transmission are two different concepts.
Water absorption refers to the ability of a material to absorb and take in water. Plastic bags, particularly those made of HDPE, have low water absorption rates. This means that they do not easily absorb water molecules. However, over time and under certain conditions, such as prolonged exposure to water or high humidity, plastic bags may absorb some moisture.
On the other hand, water transmission, or water vapour transmission rate (WVTR), refers to the ability of water vapour to pass through a material. It is measured by the amount of water vapour that can pass through a given area of a material in a specific time. Even plastics with low water absorption rates can still allow water vapour to transmit through them. This is because the molecules in the plastic may not be tightly packed together, allowing water vapour to pass through the tiny gaps.
In the context of plastic bags, while they may have low water absorption rates, they are not completely impermeable. Over time, water molecules can pass through the plastic, a process known as water transmission or permeation. This is different from water absorption, where the plastic itself takes in and retains water molecules.
Additionally, other factors can contribute to water escaping from a plastic bag. For example, a leak in the bag or changes in temperature can cause water to leak or condense, forming puddles on top of the bag. Therefore, it is important to consider not only the properties of the plastic but also the external factors that may affect the integrity of the water-plastic system.
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Plastic bag molecules are flexible and mould around objects
Plastic bags are made of polymers, which are long chains of carbon atoms. The flexibility of a plastic bag depends on its molecular structure. Some plastics are completely amorphous, meaning they lack a highly ordered molecular structure. These plastics are flexible and can mould around objects.
The plasticity of polymers is due to the rotation of their molecular bonds. When thermal kinetic energy is high enough, the bonds allow independent movement of individual molecules, making the plastic flexible and deformable. This flexibility is observed at the glass transition temperature (tg).
At a higher temperature, the melting point (tm), the crystalline regions of semi-crystalline plastics break apart, turning the material into a viscous liquid. This liquid state is ideal for moulding objects of various shapes.
The bag-moulding process involves placing a specialised bag over a plastic workpiece inside a mould cavity. The bag is usually made of a flexible, impermeable material. Rollers are used to squeeze out air pockets as pressure is applied, and heat is often introduced to aid in the process.
The flexibility and mouldability of plastic bag molecules are utilised in various applications, such as construction materials, automotive bodies, and shipping containers. However, the absorption properties of plastics can lead to moisture damage, requiring the use of desiccants or alternative moisture barriers.
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Water can be supported by a hole of any size
Water can pass through plastic bags, as they are not completely impermeable. Over time, water can permeate plastics due to their moisture absorption properties. This is a concern for those who use plastic bags for long-term water storage. For example, a user on Reddit noticed that after 41 days of storing water in a plastic bag, the bag was wet with puddles on top of it, and the water level seemed lower.
However, it is important to note that the absorption of water by plastic does not necessarily mean that water can penetrate it. The permeability of plastic and the accumulation of humid air sealed inside can also contribute to moisture damage. To prevent this, desiccants can be used inside the bag to reduce the risk of water damage. Alternatively, container humidity can be managed to remove the underlying cause of moisture.
Now, regarding your statement, "Water can be supported by a hole of any size," it is important to clarify that this statement is not entirely accurate. While surface tension and adhesion forces allow water to be supported by small holes, there is a limit to the size of the hole that water can withstand without leaking. The smaller the hole, the greater the "pressure of surface tension," which can prevent leakage. However, even if the hole is smaller than a water molecule, water can still leak out through quantum effects.
Additionally, the properties of the pipe and the water can also influence the leakage. For example, if the pipe is hydrophobic and the water has fewer dissolved salts, the strength of the water tension may resist leakage better than a rusty copper or iron pipe carrying salty water.
To summarize, while water can pass through plastic bags due to their moisture absorption properties, the statement "Water can be supported by a hole of any size" is not entirely accurate. The size of the hole, the properties of the pipe, and the characteristics of the water itself all play a role in determining whether leakage occurs.
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Frequently asked questions
Plastic bags are often used to protect goods from moisture damage. However, it is important to note that some plastics have moisture absorption properties, and over time, water can penetrate plastics. The absorption of water by the plastic bag may lead to a decrease in the water level inside the bag, as observed in some experiments.
The absorption and penetration of water through plastic bags depend on various factors, including the surface area of the bag, the thickness of the bag, and the duration of exposure to water. Larger bags with thinner material may absorb more water, and prolonged exposure can increase the likelihood of water penetration.
To prevent moisture damage, it is recommended to manage container humidity and avoid using plastic whenever possible. Desiccants can be used inside the bag to reduce moisture levels, but this may be costly and time-consuming. Alternative packaging materials with better moisture barrier properties can also be considered.
When a sharp object, such as a pencil, penetrates a plastic bag, the flexible molecules of the plastic shift and mould themselves around the object, creating a temporary seal. This flexibility prevents water or air from leaking out, even with multiple punctures.
