The modulus of elasticity of PU is between rubber and plastics. It is characterized by both hardness and elasticity, which is not found in other rubber and plastics.
TPU is divided into two types: polyester type and polyether type. Comparing the physical properties, polyester type is better for low hardness rubber, and polyether type is better for high hardness rubber. Polyester rubber has better oil resistance, heat resistance and adhesion with metal, while polyether rubber has better hydrolysis resistance, cold resistance and antibacterial properties.
1 environmental characteristics
TPU genera。lly has a good temperature resistance, continuous long-term use of the temperature of 80 ~ 90 degrees Celsius, short time to 120 degrees Celsius. Polyurethane also has good low temperature resistance. The brittleness temperature of polyester polyurethane is - 40 C, while polyether polyurethane is - 70 ~ - 80 C, but it will harden at low temperature.
TPU has good oil resistance, but its water resistance varies from structure to structure. The TPU degradation caused by the reversibility of ester formation reaction is serious. When the ester is in contact with water, the formation of acid is the cause of the autocatalytic reaction leading to molecular disintegration. Polyester polyurethane dissolves in air and in contact with moisture, much more than that completely immersed in water. This is because the acid formed in water will be washed away.
The hydrolysis resistance of polyether-based polyurethane is 3-5 times that of polyester-based polyurethane, because the ether group does not react with water.
There are two reasons for the deterioration of polyurethane properties caused by water intrusion. First, the hydrogen bond between the water intrusion and the polar groups in polyurethane weakens the hydrogen bond between the polymer molecules. This process is reversible, and the physical properties are restored after drying.
Two, the invaded water causes hydrolysis of polyurethane, which is irreversible.
Polyurethane will change color and dark when exposed to sunlight for a long time, and its physical properties will gradually decrease. Enzyme bacteria can also lead to the degradation of polyurethane, so the industrial production of polyurethane rubber used in the addition of antioxidants, ultraviolet absorbers, antienzymes and so on.
2. Mechanical properties
Tensile strength: Polyurethane rubber tensile strength is higher, generally up to 28-42 MPa, TPU in the middle, about 35 MPa.
Elongation: generally up to 400~600, * 1000%.
Elasticity: the elasticity of polyurethane is relatively high, but its hysteresis loss is relatively large, so the heat generation is high. It is easy to damage under the condition of multiple bending and high speed rolling.
Hardness: The hardness range of polyurethane is wider than that of other rubbers, * 10 for Shaw hardness, most of which have a hardness of 45-95. When the hardness is higher than 70 degrees, the tensile strength and elongation strength are higher than natural rubber. At 80-90 degrees, the tensile strength, elongation and tear resistance are quite high.
Tear strength: The tear strength of polyurethane is higher, when the test temperature rises to 100 ~ 110, the tear strength is equivalent to SBR.
Wear resistance: polyurethane has excellent wear resistance, 9 times higher than natural rubber and 1~3 times higher than styrene butadiene rubber.
TPU has the dual characteristics of plastics and rubber. It is precisely this unique physical and chemical characteristics that require special treatment in mold design and injection molding.
Deqing Sanhe Rubber Plastic Co.,Ltd