Plastic is an indispensable material in today's social life and industry. It has good properties such as strong corrosion resistance, acid and alkali resistance, low manufacturing cost, durability, waterproof, light weight, and easy molding. wait. Plastic products can meet all aspects of daily life, so they are widely used in agriculture, industry, construction, packaging, defense industry and people's daily life.
Common household items such as plastic water pipes, plastic cups, plastic basins, etc. But we've all been through this. Some plastic products harden in the winter. Why? Plastic is a polymer compound made from monomers as raw materials and polymerized through addition polymerization or condensation polymerization reaction. Molecules bind very tightly to each other and are difficult to move. For example, polyethylene (PE) is a type of plastic. It is a high molecular organic compound. It is made of ethylene and is divided into low molecular weight and high molecular weight.
Those with low molecular weight are generally liquid, colorless, odorless, insoluble in water, with a density of 0.92 g/cm3, and can be used as lubricants and coatings; those with high molecular weight are generally solid, milky white, highly thermoplastic, and feel waxy. The density is between 0.92 and 0.96 grams/cubic centimeter. It is corrosion-resistant and has good insulation properties. High-density polyethylene has the characteristics of rigidity, hardness and high mechanical strength. It can be used as high-frequency electrical insulation material for containers, pipes, radars and televisions.
It is insoluble in water and has very low water absorption. Even some chemical solvents, such as toluene and acetic acid, will only dissolve slightly at temperatures above 70°C. However, granular polyethylene will melt or solidify as the temperature changes between 15°C and 40°C. When the temperature rises, it melts and absorbs heat; when the temperature falls, it solidifies and releases heat. The reason why plastic products used in daily life are relatively soft is because plasticizers are added during the manufacturing process.
These plasticizers act like lubricants, weakening the attraction between polymer molecules and allowing them to move between molecules, making the plastic softer. Some plasticizers have poor cold resistance, and their lubrication effect becomes weaker at low temperatures in winter. The molecules in the plastic become tightly bound again and cannot rotate flexibly, causing the plastic to harden. As the temperature rises and the plasticizer regains lubrication, the plastic will remain as soft as ever.
In addition, plasticizers have a certain volatility. When plastic products are used for a long time, the plasticizer slowly evaporates, the lubrication effect decreases, and the plastic becomes hard. With the deepening and development of scientific research, application requirements are also expanding, and plasticizers that are cold-resistant, low-temperature resistant, and weakly volatile are gradually emerging. Plasticizer plastic products with these properties can stay soft during winter.
