3 ，是目前所有塑料中最轻的品种之一。它对水特别稳定，在水中的吸水率仅为0. 01%，分子量约8万一15万。成型性好，但因收缩率大(为1%~2.5%）.厚壁制品易凹陷，对一些尺寸精度较高零件，很难于达到要求，制品表面光泽好。 Polypropylene is a non-toxic, odorless, tasteless milky white highly crystalline polymer with a density of only 0.90-"0.91 g / cm 3. It is one of the lightest varieties of all plastics at present. It is particularly stable to water , The water absorption in water is only 0.01%, the molecular weight is about 81.5 million. Good moldability, but because of the large shrinkage (1% ~ 2.5%). Thick-walled products are easy to sag, for some dimensional accuracy High parts, it is difficult to meet the requirements, and the surface of the product is good.
力学性能 Mechanical properties of polypropylene
Polypropylene has high crystallinity and regular structure, so it has excellent mechanical properties. The absolute value of the mechanical properties of polypropylene is higher than that of polyethylene, but it is still a relatively low variety in plastic materials, and its tensile strength can only reach 30 MPa or slightly higher. 再变化。 Polypropylene with a larger isotactic index has higher tensile strength, but as the isotactic index increases, the impact strength of the material decreases, but it does not change after falling to a certain value .
Temperature and loading rate have a great influence on the toughness of polypropylene. When the temperature is higher than the glass transition temperature, the impact failure is ductile fracture, and below the glass transition temperature is brittle fracture, and the impact strength value is greatly reduced. Increasing the loading rate can increase the temperature for the transition from ductile fracture to brittle fracture. Polypropylene has excellent resistance to bending fatigue, and its products can be bent 106 times at normal temperature without damage.
However, at room temperature and low temperature, due to its high molecular structure regularity, the impact strength is poor. The most outstanding property of polypropylene is its resistance to bending fatigue, commonly known as pleated rubber.
热性能 Thermal properties of polypropylene
Polypropylene has good heat resistance, and products can be sterilized at temperatures above 100 ° C, and will not be deformed at 150 ° C without being subjected to external forces. 聚乙烯 。 The embrittlement temperature is -35 ° C, embrittlement occurs below -35 ° C, and the cold resistance is not as good as polyethylene . The reported values for the glass transition temperature of polypropylene are 18qC, 0qC, 5 ℃, etc. This is also due to the use of different samples, which contain different proportions of crystalline phase and amorphous phase, which makes the chain length of the amorphous part of the molecular chain different. Caused by. The melting temperature of polypropylene is about 40-50% higher than that of polyethylene, about 164-170 ° C, and the melting point of 100% isotactic polypropylene is 176 ° C.
化学稳定性 Chemical stability of polypropylene
Polypropylene has good chemical stability. Except that it can be attacked by concentrated sulfuric acid and concentrated nitric acid, it is relatively stable to various other chemical reagents, but low molecular weight aliphatic hydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons can make polypropylene soften and Swelling, meanwhile its chemical stability will increase with the increase of crystallinity, so polypropylene is suitable for making various chemical pipes and fittings with good anti-corrosion effect.
电性能 Electrical properties of polypropylene
It has a high dielectric constant and can be used to make heated electrical insulation products with increasing temperature. It also has a high breakdown voltage, making it suitable for use as electrical accessories. Good voltage resistance and arc resistance, but high static electricity, easy to age in contact with copper.
耐候性 Weatherability of polypropylene
Polypropylene is very sensitive to ultraviolet rays. Adding zinc oxide, dilauryl thiodipropionate, carbon black or similar milky white fillers can improve its aging resistance.
Hydrophobic parameter calculation reference value (XlogP): 3.32, Number of hydrogen bond donors: 03, Number of hydrogen bond acceptors: 34, Number of rotatable chemical bonds: 15, Number of tautomers: 6, Topological molecular polar surface area (TPSA ): 29.5 Avoid strong oxidants, chlorine, potassium permanganate, keep in a cool, dry place and ensure good ventilation.