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Check for Food Use Mark: First, look for the “food use” mark on the plastic bag. This logo is usually on the front of the packaging bag in a more prominent position. If it is intended for food contact, it should have the appropriate food-grade certification or indication, which means it has met certain safety standards for direct contact with food.
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Examine the Color: Generally, colored plastic bags are more likely to be made from recycled waste plastics and are not suitable for food packaging. For example, some black plastic bags used to hold fish, shrimp, or meat in vegetable markets may originally be used to hold garbage. In contrast, regular plastic bags for general use are usually milky white or transparent, with a more uniform color and a finer texture.
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Look for Impurities: Place the plastic bag under sunlight or bright light to check for black spots, openings, or other impurities. The presence of such impurities indicates that the plastic bag may be made from inferior raw materials or recycled plastics of poor quality.
Good quality plastic bags produced by reputable manufacturers usually do not have any peculiar smell because no additional harmful substances are added during the production process. However, if a plastic bag emits a pungent, unpleasant, or nauseating smell, it is likely that additives or recycled materials of poor quality have been used, and such bags should not be used to hold food or other items that may come into contact with the human body.
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Tensile Strength: Gently pull the plastic bag to test its tensile strength. A high-quality plastic bag has a certain strength and will not break easily when pulled or stretched moderately. In contrast, inferior plastic bags are often weak in strength due to the addition of impurities or the use of low-quality materials and are prone to tearing or breaking.
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Thickness and Uniformity: The thickness of the plastic bag also affects its quality. Regular supermarket shopping bags are relatively thick and uniform in thickness, which makes them more durable and less likely to be damaged during use. On the other hand, inferior plastic bags may be thinner in some areas or have inconsistent thickness, which reduces their load-bearing capacity and service life.
When you shake a good quality plastic bag, it will produce a relatively crisp sound, while a poor-quality plastic bag often makes a dull, muffled noise. This is because the material and structure of high-quality plastic bags are more regular, resulting in a clearer sound when vibrated.
Put the plastic bag in water and press it to the bottom by hand. Wait for a while, and you will find that non-toxic plastic bags usually rise to the surface, while toxic plastic bags sink to the bottom. This is because the density of non-toxic plastics is generally lower than that of water, while some toxic plastics or those with a large amount of impurities may have a higher density and sink.
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Smoothness: Run your hand over the surface of the plastic bag. A good quality plastic bag has a smooth surface, which not only feels comfortable but also indicates that the manufacturing process is more refined. In contrast, a poor-quality plastic bag may feel rough, sticky, or astringent to the touch, which may be due to the use of inferior materials or problems in the production process.
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Flexibility and Resilience: Gently squeeze or fold the plastic bag to feel its flexibility and resilience. High-quality plastic bags are usually more flexible and can quickly return to their original shape after being deformed, while inferior plastic bags may be stiff, lack elasticity, and are prone to leaving creases or even breaking.
Cut a small corner of the plastic bag and place it on fire. A non-toxic plastic bag will continue to burn after leaving the fire, with a yellow flame, and the molten plastic will drip like a candle, emitting a paraffin-like odor. In contrast, a toxic plastic bag is not easy to burn, and after burning, it may turn into a green flame and produce a pungent, choking smell.
By using these methods comprehensively, you can better distinguish the quality of plastic bags and choose the ones that are more suitable for your needs while ensuring safety and environmental protection.
