Plastic is an indispensable material in our life. It has many good properties, such as strong corrosion resistance, acid and alkali resistance, low manufacturing cost, durable, waterproof, light, and easy to be shaped into different shapes.

Plastic can meet the needs of Chinese side in daily life, so it is widely used, such as plastic water pipe, plastic cup, plastic basin, etc. But we have all experienced that some plastic products will become hard in winter. Why?

Plastic is a kind of macromolecular compound, which is made from monomer by addition polymerization or condensation polymerization. The combination between molecules is very close, and it is not easy to move. For example, PVC is a kind of plastic, which is formed by many vinyl chloride molecular monomers connected together through reaction. There are two carbon atoms in each vinyl chloride molecule, and the carbon atoms are connected with each other. After a small amount of catalyst is added, part of the connection between the carbon atoms will be loosened and connected with the carbon atom in another vinyl chloride. As a result, many vinyl chloride are tightly connected to form long molecular chains, which together form PVC, and because of their tight connection, they are very hard.

The reason why plastic products used in life are relatively soft is that plasticizers are added during manufacturing. Like lubricating oil, these plasticizers weaken the attraction between polymer molecules, enabling molecules to move between them, thus making plastics soft.

Some plasticizers have poor cold resistance, and their lubrication effect becomes weaker at low temperatures in winter. The molecules in the plastic are tightly combined again and cannot rotate flexibly, causing the plastic to harden. When the temperature gets warmer and the plasticizer recovers lubrication, the plastic will still be as soft as before.

In addition, the plasticizer has a certain volatility. When the plastic products are used for too long, the plasticizer will slowly volatilize, the lubrication effect will decline, and the plastic will also become hard.

With the deepening and development of scientific research, the application demand is also expanding. Plasticizers with cold resistance, low temperature resistance and weak volatility are gradually emerging. Plastic products with plasticizers with these characteristics can also remain soft in winter.