As the top stream in the rivers and lakes of supper, who can resist the "temptation" of a "red and full" "spicy crayfish"? Sitting in front of the fragrant and delicious crayfish, put on gloves, pull off the shrimp head, pinch the body of the crayfish back and forth with both hands, pull it outward, and a delicious shrimp meat will be exposed in front of you like this. However, have you ever encountered such a trouble: every time you finish eating crayfish, you find that the plastic gloves given by the store seem to be useless, and you will still eat your hands full of oil? Is it because the quality of the gloves is not up to par? Today we will study: what is the reason for the oil leakage of gloves? Since there is still oil leakage, why do you still wear disposable gloves?
What are disposable gloves made of?
At present, there are three main types of disposable gloves on the market: latex gloves, PVC gloves and PE gloves. Latex gloves are easy to understand, the material is known at a glance, but its cost is relatively high, often used in medical, beauty and other industries; the main material of PVC gloves is polyvinyl chloride, its heat resistance is low, and in the manufacturing process, in order to increase the plasticity of plastics, manufacturers will add plasticizers that are harmful to the human body, so it is not suitable for the food field.
PE gloves are disposable plastic gloves that we use when eating crayfish. It is a polyethylene (PE) glove with low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) as the main raw materials, which is safe for humans and also very cheap.
Why can't gloves resist oil?
From the above introduction, we already know the main raw materials for making PE gloves, and they all have one thing in common, that is, there are many branch chains on the long chain of polyethylene. To use an analogy, it's like a branch with many tiny forks.
Low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), both of which have many branched chains on long chains
Compared to LDPE, linear LDPE has shorter branching chains and more uniform lengths. The presence of these branched chains makes the polyethylene material softer and more malleable, making it suitable for gloves.
At the same time, these branches also provide opportunities for oil penetration. Due to the presence of branched chains, the accumulation between the long chains of polyethylene is not too tight, leaving a large gap between the chains. Of course, the larger size here is in terms of the size of the oil molecules. The oil molecules pass through the gaps larger than our own, slowly break through the barrier of the glove, and after a long time, they get on our hands.
Why do gloves leak oil and water?
Friends with life experience may find a strange phenomenon: gloves can be water-tight, but not oil-free. Obviously, water molecules are much smaller than oil molecules, and since oil molecules can pass through the gaps between the long chains of polyethylene, water molecules should be able to do it?
Before answering this question, let's start with a concept: polarity. To put it simply, everything in the world is made up of molecules and has "polarity". A molecule is polar if its internal charge is not evenly distributed, and a non-polar molecule if it is evenly distributed. Depending on whether the polarity is the same, the substances will exhibit the characteristics of "soluble in the same sex and insoluble in the opposite sex".
Taking the most common types of water and oil as an example, water molecules show strong polarity on the outside, while oils and fats are mostly composed of non-polar molecules, which do not show polarity on the outside, that is, non-polar. When water and oil are mixed together, they show a clear repulsive force towards each other. That's why water and oil don't mix together when poured into a bottle and become layered over time.
With this knowledge in hand, we can go back to the question we just asked, and we will be able to answer it well. Although the water molecule is smaller than the oil molecule, it is a polar molecule, so it is difficult to get too close to the non-polar polyethylene molecule and it is difficult to pass through the glove. On the contrary, oil molecules, which are both non-polar molecules, are "like-minded" with polyethylene molecules, so they can easily pass through the gaps between polyethylene molecules. Therefore, in addition to the size of the molecule, the type of properties of the molecule also determines whether it can break through the protection of gloves.
Are PE gloves safe?
PE gloves are oily, always dirty, and the price is so cheap that the boss gives it away for nothing, you may have begun to worry about the safety of disposable gloves, so what is the safety of PE gloves?
In general, it is quite safe to wear this kind of glove to catch something to eat. First of all, low-density polyethylene as a raw material is inherently non-toxic. Secondly, there is little need for additives in the process of processing into such finished products, and at most a powder such as silica is used as a release agent to facilitate the removal of the finished gloves from the mold. The toxicity of silica is negligible.
In addition, when it comes to plastic products, we inevitably consider its heat resistance. The heat resistance of low-density polyethylene is really not good, and when the temperature reaches about 70 °C or 80 °C, it will begin to deform. However, it is limited to deformation and does not release any harmful substances. Taking a step back, we don't dare to grasp something so hot with our hands.
Many people will have a question when they see this: why do you wear it if you can't protect against oil? Have you ever thought that PE gloves may not protect against grease, but bacteria on your hands. Therefore, the next time we eat crayfish, we should wear it obediently, in order to reduce the amount of oil seeping into our hands, we can choose to change gloves frequently or bring a few more layers of gloves. Of course, if you can find a person who is willing to peel crayfish for you, then the problem of oil seeping into your hands will be completely avoided!
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