Common plastics classification

Plastic is a common item in our life. It is an organic synthetic polymer material with a wide range of applications. In the past few decades, along with the great convenience that plastics have brought to our production and life, the "white pollution" caused by waste plastics has become increasingly serious. If we can understand the composition and classification of plastics in detail, it will not only help us use plastic products scientifically, but also facilitate the sorting and recycling of plastics, and effectively control and reduce "white pollution".

Plastic Types:

So far, there are nearly one hundred kinds of plastic materials known. According to functional plastics, they are divided into three types: general plastics, engineering plastics and special plastics. There are seven types of commonly used plastics. If we look closely at the bottom of transparent plastic bottles (for example: plastic bottles for food and washing powder), we will notice a triangular recycling symbol composed of three arrows and 1-7. number.

This set of codes is a code for the types of plastic products used by the Society of Plastics Industry (SPI). The numbers 1-7 represent the types of resins used in plastics. With this number, the identification of plastic varieties in waste recycling plants becomes simple and easy, and the cost of recycling has been greatly reduced. Many countries in the world today have adopted this SPI identification scheme.

If the number is "1", it means that the plastic is made of a material called polyethylene terephthalate (PET); some opaque plastic bottles (for example: plastic bottles for milk), in the triangle symbol The number is "2", which means it is made of high-density polyethylene (HDPE), as shown in the figure below.

Representative products of seven common plastics and instructions for use

This part mainly introduces the representative products of these seven common plastics, and the points that we need to pay attention to in our daily life due to the characteristics of the materials.

(1)Polyethylene terephthalate — 01 PET such as: mineral water bottles, carbonated beverage bottles

Use: heat-resistant to 70°C, only suitable for warm or frozen drinks; for high-temperature liquids or heating, it is easy to deform, and substances harmful to the human body will melt out. Therefore, throw away beverage bottles when they are used up, and do not use them as water glasses or as storage containers for other items, so as not to cause health problems.

(2)High Density Polyethylene — 02 HDPE Such as: cleaning products, bath products.

Ordinary plastic bags are made of polyethylene (PE), which has better toughness. PE is also divided into HDPE (high-density polyethylene) and LDPE (low-density polyethylene). The difference in density leads to some of its properties. There is a big difference.

Use: It can be reused after careful cleaning, but these containers are usually not easy to clean, and the original cleaning products will remain, which will become a breeding ground for bacteria. It is best not to recycle them.

Polyvinyl Chloride — 03 PVC Such as: some decorative materials.

Use: This material is prone to harmful substances when it is high temperature. If it is in use, do not let it be heated. At present, containers of this material are rarely used for packaging food.

Low-density polyethylene — 04 LDPE Such as: plastic wrap, plastic film, etc.

Use: It is breathable and impervious to water, and its heat resistance is not strong. Usually, qualified PE cling film will melt when the temperature exceeds 110°C, leaving some plastic preparations that cannot be decomposed by the human body. Before putting it into the microwave oven, be sure to see whether there is a microwave heating word printed on the package of the plastic wrap. If there is no such mark, it is not suitable for microwave heating.

Polypropylene — 05 PP (can withstand temperatures above 100 degrees) such as: microwave oven lunch box.

Use: This is the only plastic box among the seven that can be put into the microwave oven and can be reused after cleaning. It is worth noting that for some microwave lunch boxes, the box body is made of No. 5 PP, but the box cover is made of No. 1 PE. Since No. 1 PE cannot withstand high temperatures, it cannot be put into the microwave oven together with the box body. Therefore, before putting the plastic box into the microwave oven, the lid can be removed first.

Polypropylene also played a big role during this year's epidemic: disposable medical protective clothing and disposable masks are mostly non-woven fabrics that are sprayed at high temperatures with filaments of tens to hundreds of nanometers, and then spun into non-woven fabrics. made of cloth.

(6)Polystyrene—06 PS (heat resistance 60-70 degrees, hot drinks will produce toxins, and styrene will be released when burned) such as: instant noodle boxes in bowls, fast food boxes.

Use: It is heat-resistant and cold-resistant, but it cannot be placed in a microwave oven, so as not to release chemicals due to excessive temperature. And it cannot be used to carry strong acids (such as orange juice) and strong alkaline substances, because it will decompose polystyrene, which is not good for the human body, and it is easy to cause cancer. Therefore, we'd better not pack hot food in fast food boxes.

Because it is cheap, it is now widely used, for example, many disposable plastic tableware is made of it. However, it is difficult to degrade itself and is harmful to the environment. It is recommended that you try not to use such plastic products in your life.

(7)Other plastic codes — 07 Others Such as: jugs, cups, bottles.

If there is no number on the plastic packaging, it will generally be regarded as number seven, other categories.

Current plastic recycling status:

Generally speaking, No. 1 and No. 2 plastic products are recyclable, and we can put them directly into the blue recyclable bin (note: all recycled items must be clean). The current recycling rate for No. 1 plastic is about 20%.

In the waste treatment plant, the recycled plastic waste will be sorted by color and type (common sorting techniques include manual sorting and machine sorting), and some will be sorted by weight through a blower. Sorted plastic waste is shredded, melted into balls and sold to manufacturers for reprocessing, and the recovered plastic can be used to make carpets, clothes, plastic packaging and other products.

Plastic #3 is currently rarely recycled. Occasionally, after direct recycling by plastic producers, it is remade into building materials.

No. 4 plastics, such as various plastic bags used in daily life, are recyclable materials, but they have been rarely recycled because the economic benefits of recycling are relatively low. At present, more and more communities and institutions are beginning to pay attention to this part of recycling. But remember that No. 4 plastic can't be thrown in the blue recyclable bin just yet.

Plastic No. 5 (polypropylene) is currently the second most used type of plastic in the world, but the recycling rate is less than 1%. Some products of No. 5 and No. 6 plastics can be recycled, such as clean lunch boxes/yogurt boxes. It is recommended to confirm the specific situation with the garbage disposal agency in the community where you live.

No. 6 plastics, such as yogurt boxes, are recycled, but due to technical limitations, they are generally downgraded and reused, and cannot be reused as raw materials for food packaging.

No. 7 plastic has not been recycled much before, but as new plastic types, such as polycarbonate, are also classified as this, it is recommended to check the local recycling policy to confirm.

How do we do in daily life?

Combined with the 3R principles (the rules of 3R): reducing, reusing and recycling, compared to plastic recycling, there are many places in our life where we can reduce the use and reuse of plastic products. Here I share a few tips for reference only.

(1). When conditions permit, use your own water cup instead of disposable water cups or disposable bottled water when you go out or in the company;

(2). Go shopping, especially to the supermarket, and use your own shopping bags;

(3). Plan ahead when shopping online, so that you can buy items at the same time and reduce the waste of packaging materials;

(4). Reuse the plastic bags left unused at home. Plastic shopping bags make great bin liners, wrapping material or lunch bags etc. Plastic bags can also be dropped off at designated plastic bag recycling locations;

(5). Some takeaway lunch boxes can also be recycled after washing (blue trash can).