Effects of different raw materials (structures) on the properties of polyurethane elastomers
发布时间： 2018-05-11 15:17 Author: Polyurethane foam machine Source: http: //motokone.com
Published: 2018-05-11 15:17
Polyurethane elastomers have a wide variety of raw materials, complex group composition and arrangement in the macromolecular structure, and polyurethane elastomers are synthesized and processed in a variety of ways. The difference, which incurs a change in the properties of the polyurethane elastomer.
Polyurethane elastomer is used in a solid state, and its mechanical strength under various external forces is an important indicator of its performance. Generally speaking, polyurethane elastomers, like other polymers, have properties and molecular weights, intermolecular forces, toughness of the segments, crystallization tendency, branching and crosslinking, and the position, polarity and volume of the substituents. Other factors have a close relationship. However, polyurethane elastomers are different from hydrocarbon-based (PP, PE, etc.) polymers. Their molecular structure is composed of soft segments (oligomeric polyols) and hard segments (polyisocyanates, chain extensions). Cross-linking agents, etc.) block, the electrostatic force between its macromolecules, especially between the hard segments is very strong, and often a large number of hydrogen bonds are generated, this intense electrostatic force, in addition to direct In addition to affecting the mechanical properties, it can also promote the collection of hard segments, produce micro phase separation, and improve the mechanical properties and temperature properties of elastomers.
1.Relationship between mechanical properties and structure
The mechanical properties of polyurethane elastomers depend on the crystallization tendency of polyurethane elastomers, especially the crystallization tendency of soft segments. However, polyurethane elastomers are used in a highly elastic state and do not want to exhibit crystallization. Therefore, formulation and Process design, find a balance between elasticity and strength, so that the prepared polyurethane elastomer does not crystallize at the application temperature, has good elasticity, and can crystallize rapidly when highly stretched, and the ablation temperature of this crystal is at room temperature Up and down, when the external force is released, the crystals melt rapidly. This reversible crystalline structure is very beneficial to improve the mechanical strength of the polyurethane elastomer.
Whether a polyurethane elastomer has reversible crystallization depends mainly on the polarity, molecular weight, intermolecular forces, and structural regularity of the soft segment. The molecular polarity and intermolecular force of polyester are greater than those of polyether, so the mechanical strength of polyester polyurethane elastomer is greater than that of polyether polyurethane elastomer; the side groups in the soft segment will reduce the crystallinity, which will reduce the product's Mechanical behavior. The structure of polyurethane hard segments also has a direct and indirect impact on the mechanical properties of polyurethane elastomers. Generally, aromatic diisocyanates (such as MDI, TDI) are larger than ester diisocyanates (such as HDI); diisocyanates with symmetrical structure ( Such as MDI) can give polyurethane elastomers higher hardness, tensile strength and tear strength; the effect of chain extension crosslinker structure on the mechanical properties of elastomers is similar to that of diisocyanates.
2.Relationship between heat resistance and structure
The thermal stability of a polymer can be weighed against the softening temperature and the thermal synthesis temperature. Under normal conditions, the thermal synthesis temperature of the polyurethane elastomer is lower than the softening temperature. Generally speaking, the heat resistance of polyester polyurethane elastomer is better than that of polyether polyurethane elastomer. For aromatic diisocyanate, the heat resistance is PPDI> NDI> MDI> TDI.
3. Relationship between low temperature performance and structure
The low temperature elasticity of polymers is usually weighed by the glass transition temperature and the cold resistance coefficient (or brittleness temperature). Under normal conditions, the low-temperature compliance of polyether polyurethane elastomer is better than that of polyester.
4.Relationship between water resistance and structure
The effect of water on polyurethane elastomers: the plasticizing effect (water absorption) of water and the degradation effect of water. When the relative humidity is 100%: the water absorption of polyester polyurethane elastomer is about 1.1%, and the performance drop is about 10%; the water absorption of polyether polyurethane elastomer is about 1.4%, and the performance drop is about 20%; However, the hydrolysis stability of polyether polyurethane elastomer is greater than that of polyester polyurethane elastomer.
5, the relationship between oil resistance and chemical resistance and structure
Polyurethane elastomers are very resistant to grease and non-polar solvents. Ordinary polyester polyurethane elastomers have better resistance to grease than polyether polyurethane elastomers; the higher the hardness of polyurethane elastomers, the better their grease resistance; the chemical resistance of polycaprolactone polyurethane elastomers (Such as sulfuric acid, nitric acid, etc.) performance is better than other types of polyurethane.
The overall alkali resistance of polyurethane elasticity and the resistance to strong polar solvents (such as cyclohexanone, Tianna water, etc.) are not good. 6, NDI, PPDI high-performance polyurethane elastomer
NDI polyurethane elastomer with high tear strength, good abrasion resistance, good heat resistance (heat resistance up to 100 ～ 120 ℃), low shrinkage and permanent deformation, good resilience, excellent oil and solvent resistance, extremely Good dynamic mechanical properties and excellent cutting resistance, etc .; In the temperature range of 20 ～ 80 ℃ and high dynamic load conditions, it has lower damping value, lower internal heat, and is more durable than TDI and MDI systems durable.
PPDI polyurethane elastomer has excellent physical and mechanical properties, resilience, abrasion resistance, fatigue resistance, heat resistance and damp heat resistance, solvent resistance, etc. are much better than MDI / 1.4-BD system and TDI / MOCA system. The mechanical properties are better than NDI elastomers.
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