PP is a crystalline polymer that is lightweight among commonly used plastics, with a density of only 0.91 g/cm³ (less than water). Among general-purpose plastics, PP has good heat resistance, with a heat distortion temperature of 80-100°C, allowing it to be boiled in water. PP has good resistance to stress cracking and a high bending fatigue life, commonly known as "bendable adhesive." The overall performance of PP is superior to that of PE. PP products are lightweight, flexible, and have good chemical resistance. The disadvantages of PP include low dimensional accuracy, insufficient rigidity, poor weather resistance, and susceptibility to "copper corrosion." It exhibits a phenomenon of shrinkage after molding, aging easily, becoming brittle, and deforming. 1. Density: PP has one of the lowest densities among synthetic resins, ranging from 0.90 to 0.91 g/cm³, which is about 60% of the density of PVC. This means that the same weight of raw materials can produce a greater quantity of products with the same volume. 2. Mechanical properties: PP has relatively good tensile strength and rigidity but poor impact strength, particularly at low temperatures. Additionally, if there is orientation or stress during the molding of the product, the impact strength will significantly decrease. Although the impact strength is poor, its mechanical properties can compete with higher-cost engineering plastics after modification through filling or reinforcement. 3. Surface hardness: The surface hardness of PP is low among five general-purpose plastics, only slightly better than PE. When the crystallinity is higher, the hardness also increases accordingly, but it still does not reach the levels of PVC, PS, or ABS. 4. Thermal properties: Among the five major general-purpose plastics, PP has good heat resistance. PP plastic products can work at 100°C for extended periods, and when heated to 150°C without external force, PP products will not deform. After using nucleating agents to improve the crystallinity of PP, its heat resistance can be further enhanced, making it suitable for making containers for heating food in microwaves. 5. Stress cracking resistance: Residual stress in molded products or prolonged work under continuous stress can lead to stress cracking. Organic solvents and surfactants can significantly promote stress cracking. 6. Chemical stability: PP has excellent chemical stability and is inert to most acids, bases, salts, and oxidizers. For example, it remains stable in concentrated phosphoric acid at 100°C, 40% solutions, and other salt solutions, with only a few strong oxidizers like fuming agents potentially causing changes. PP is a non-polar compound and is very stable against polar solvents; substances like alcohols, phenols, aldehydes, ketones, and most carboxylic acids do not cause swelling, but it can dissolve or swell in some non-polar organic solvents. 7. Gas permeability (gas barrier properties): PP has a certain permeability to oxygen, carbon dioxide, and water vapor, showing a significant difference compared to nylon (PA) and polyester (PET), and it fares much worse against high-barrier plastics like PVDC and EVOH. However, compared to other non-plastic materials, its gas permeability is still quite good. Adding barrier materials or coating the surface with barrier plastics can greatly enhance its gas permeability. 8. Aging performance: The presence of tertiary carbon atoms in PP makes it prone to breakage and degradation under light and heat. Unstabilized PP heated at 150°C for more than half an hour or exposed to sunlight for 12 days will become noticeably brittle. Unstabilized PP powder stored indoors away from light for four months will also degrade severely, emitting a noticeable acidic smell. Adding more than 0.2% antioxidants before granulating PP powder can effectively prevent degradation and aging during processing and use. 9. Electrical properties: PP is a non-polar polymer with good electrical insulation properties, and it has extremely low water absorption, so its electrical insulation is unaffected by humidity. The dielectric constant and dielectric loss factor of PP are very low and are not influenced by frequency or temperature. PP has a high dielectric strength, which increases with temperature. These traits are favorable for electrical insulation materials in humid and hot environments. On the other hand, PP has a very high surface resistivity, and in some applications, it must first undergo antistatic treatment. 10. Good processing performance: PP is a crystalline polymer that does not melt until it reaches a certain temperature, unlike PE or PVC, which soften as the temperature increases during heating. Once a certain temperature is reached, PP particles melt rapidly, transitioning entirely to a molten state within a few degrees.