What is the difference between polyurethane prepolymer MDI and TDI series?
In the synthesis of polyurethane prepolymers, the general traditional method is to use TDI as the raw material of diisocyanate, and relatively few use MDI as raw material. In fact, MDI is not only pure MDI, crude MDI, liquefied MDI, MDI isomer Mixtures (such as MDI-50, Huntsman 3051) and more than 20 varieties, have different targeted MDI products in different fields. Compared with TDI, MDI has its own advantages, such as the toxicity of MDI is less than TDI, and the price is relatively cheap. Shanghai Hecheng produces polyester TDI polyether TDI, and also produces polyol MDI system products. MDI replaces TDI The synthetic prepolymer can effectively reduce the free TDI content. This not only protects the health of production operators and construction workers, but also protects the environment. At the same time, using MDI instead of TDI to synthesize the polyurethane prepolymer has less harm to the human body and is more conducive to environmental protection.
As an emerging organic polymer material, polyurethane is known as the "fifth largest plastic" and is widely used in many areas of the national economy because of its excellent properties. In the past 30 years, the world's polyurethane industry has developed very rapidly and has become the fastest growing industry in the chemical industry. In the 1970s, the annual global polyurethane output totaled only 1.1 million tons, and in 2001 it exceeded 9 million tons, an increase of about 9 times.
The molecular structure of MDI is symmetrical, and the coating film made of MDI has better impact resistance and flexibility. In addition, MDI has cost advantages. Currently, TDI is generally more expensive than MDI. TDI has insufficient domestic production capacity and relies on imports. In China, there are relatively large-scale MDI manufacturers such as Yantai Wanhua. Using MDI to synthesize polyurethane prepolymers has lower costs, raw materials are readily available, and has greater economic advantages.
Polyurethane Adhesive refers to an adhesive containing a urethane group (-NHCOO-) or an isocyanate group (-NCO) in the molecular chain.
Polyurethane adhesives have excellent properties and have a wide range of applications. It is divided into two major categories, polyisocyanates and polyurethanes. Because it contains highly polar and highly reactive isocyanate (-NCO) and urethane (-NHCOO-), it is compatible with materials containing active hydrogen, such as foam, wood, leather, fabric, paper, ceramics Porous materials such as metal, glass, rubber, plastic, and other smooth surface materials have excellent chemical adhesion. The hydrogen bonding effect between polyurethane and the material being bonded will increase the cohesion of the polymer. Thereby making the bonding stronger.
In addition, polyurethane adhesives also have the characteristics of adjustable toughness, simple bonding process, excellent low temperature resistance and excellent stability. In recent years, they have become the fastest growing adhesives at home and abroad.
Technological developments of polyurethane adhesives in China:
Two-component polyurethane adhesive. This is the most important class of polyurethane adhesives, with wide applications and large amounts. Polyurethane adhesive is an environmentally friendly two-component rubber powder adhesive. It has a solid content of 100% and high initial tack strength. It has excellent adhesive strength after drying. Material bonding.
