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I'm A Little PP. Let Me Introduce My Features
Aug 31, 2017

Polypropylene resin, referred to as PP, is one of the five major plastics. In 2016, China's apparent consumption of PP amounted to about 22000000 tons, widely used in automobiles, household appliances, daily necessities, films, fibers and other fields. Here's a detailed introduction of my shortcomings":

1, density: PP is the lowest density of all synthetic resins, only 0.90~0.91g/cm3, that is, the same size of products, PP materials products are the lightest.

2, mechanical properties: PP tensile strength and rigidity are better, but the impact strength is poor, especially in low temperature, poor impact resistance. In addition, if the orientation or stress of the product is formed, the impact strength will also be reduced significantly. Although the impact strength is poor, the mechanical properties of concrete can be compared with the cost of engineering plastics in many fields after modification such as filling or strengthening.

3, surface hardness: PP surface hardness in the five types of general plastic is lower, only better than PE. When the crystallinity is higher, the hardness increases correspondingly, but still less than PVC, PS, ABS and so on.

4, thermal properties: in the five general plastic, PP heat resistance is the best. PP plastic products can work at 100 degrees for a long time. Without external force, the PP products will be heated to 150 degrees Celsius and will not deform. When the nucleating agent is used to improve the crystalline state of PP, the heat resistance can be further improved, and can even be used for making containers for heating food in a microwave oven.

5, stress resistance cracking: molded products residual stress, or products for a long time under continuous stress, will cause stress cracking. Organic solvents and surfactants significantly promote stress cracking. Therefore, stress cracking tests were carried out in the presence of surfactant. The commonly used additive is alkyl aryl polyethylene glycol. Experiments show that the PP in surfactant immersion stress cracking resistance and in the air, have a good ability to resist, and the melt flow rate of PP is small (the higher the molecular weight), stress crack resistance is strong.

6, air tightness (gas barrier): PP of oxygen, carbon dioxide and water vapor permeability are certain, compared to Niron (PA) and polyester (PET) have obvious difference, for high barrier plastics, such as PVDC, EVOH becomes more. But compared with other non plastic materials, the air tightness is quite good. By adding barrier material or applying barrier plastics on the surface, the tightness of the plastic can be greatly improved.

7, chemical stability: PP chemical stability, excellent for most acids, alkalis, salts, oxidants are inert. For example, the concentrated phosphoric acid, hydrochloric acid, 40% sulfuric acid and their salts solution at 100 DEG C are stable. Only a few strong oxidants, such as fuming sulfuric acid, can make them change. PP is a nonpolar compound that is very stable with polar solvents, such as alcohols, phenols, aldehydes, ketones, and most carboxylic acids, but does not readily dissolve or swell in some nonpolar organic solvents.

8. Electrical properties: PP is a non-polar polymer, has good electrical insulation, and PP water absorption is very low, the electrical insulation will not be affected by humidity. The dielectric constant and dielectric loss factor of PP are very small, and are not affected by frequency and temperature. The dielectric strength of PP is very high and increases with the increase of temperature. These are beneficial to electrical insulating materials in wet and hot environments. On the other hand, the surface resistance of PP is very high. In some cases, antistatic treatment must be carried out first.

9. Aging properties: the presence of tertiary carbon atoms in PP molecules is extremely easy to break down under the action of light and heat. The PP without stabilizer is heated for more than half an hour at 150, or exposed to a sunny spot for 12 days, and becomes noticeably brittle. The PP powder without stabilizer can be degraded in the room for 4 months, and it will degrade seriously and give a clear sour flavor.

Adding more than 0.2% antioxidants to the PP powder before granulation can effectively prevent the degradation and aging of PP during processing and use. Antioxidants are divided into free radical chain reaction termination agent (also known as the main antioxidant) and peroxide decomposers (also known as secondary antioxidant) two categories, two kinds of main auxiliary mix, antioxidant, will play a good synergistic effect.

At present, the recommended B215 antioxidant is the main antioxidant 1010 (phenol) and auxiliary antioxidant 168 (Phosphite), according to the ratio of 1:2 compound. To prevent photoaging, UV absorbers are added to PP to convert ultraviolet absorption of wavelength 290~400nm to a longer wavelength without destruction. For PP plastic products buried in the soil or indoors for light avoidance, only the main and auxiliary antioxidants can be added, without adding UV absorbers.

10, processing performance is good: PP belongs to crystalline polymer, less than a certain temperature, its particles will not melt, unlike PE or PVC in the process of heating, as the temperature increased softening. Once a temperature is reached, the PP particles melt rapidly and melt into a molten state within a few degrees.

The melt viscosity of PP is relatively low, so the molding process has good flowability, especially when the melt flow rate is higher, the melt viscosity is smaller and suitable for injection molding of large thin-wall products, such as the inner barrel of the washing machine.

After PP leaves the die, if it is cooled slowly in the air, a larger grain will be produced and the product will be low in transparency. The result is a rapid cooling in water (following blowing a water cooled film), the molecular motion of PP is rapidly frozen, and no crystals can be formed. The film is completely transparent at this time. PP molding shrinkage is relatively large, reaching more than 2%, far greater than ABS plastic (0.5%).


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