Physical properties: Polypropylene is a non-toxic, tasteless, odorless, highly crystalline milky white polymer with a density of only 0. 90-0.9 1g/m3 is one of the lightest varieties of all plastics. It is particularly stable to water, and its water absorption in water is only 0. 0 1%, and the molecular weight is about 80,000-1.5 million. Good formability, but due to the large shrinkage rate (1%~2.5%), thick-walled products are easy to sag, and it is difficult to meet the requirements for some parts with high dimensional accuracy, and the products have good surface gloss and are easy to be colored.
Mechanical properties: polypropylene has high crystallinity and regular structure, so it has excellent mechanical properties. The absolute value of mechanical properties of polypropylene is higher than that of polyethylene, but it is still a low variety in plastic materials, and its tensile strength can only reach 30 MPa or slightly higher. The tensile strength of polypropylene with large isotactic index is high, but with the increase of isotactic index, the impact strength of the material decreases, but it does not change after falling to a certain value.
Temperature and loading rate have great influence on the toughness of polypropylene. When the temperature is higher than the glass transition temperature, the impact failure is ductile fracture, and when it is lower than the glass transition temperature, it is brittle fracture, and the impact strength value decreases greatly. Increasing loading rate can increase the transition temperature from ductile fracture to brittle fracture. Polypropylene has excellent bending fatigue resistance, and its products can be bent 106 times at room temperature without damage.
However, at room temperature and low temperature, due to its high molecular structure regularity, its impact strength is poor. The most outstanding performance of polypropylene is bending fatigue resistance, commonly known as hundred-fold adhesive.
Heat resistance: Polypropylene has good heat resistance. The product can be sterilized at the temperature above 100℃, and it will not deform at 150℃ without external force. Brittle temperature is -35℃, and it will be brittle below -35℃, and its cold resistance is not as good as that of polyethylene. The reported glass transition temperatures of polypropylene are 18qC, 0qC, 5℃ and so on. This is also because people use different samples, which contain different proportions of crystalline phase and amorphous phase, resulting in different chain lengths of amorphous parts in molecular chains. The melting temperature of polypropylene is about 40-50% higher than that of polyethylene, about 164- 170℃, and the melting point of 100% isotactic polypropylene is 176℃.
Chemical stability: Polypropylene has good chemical stability, and is relatively stable to other chemical reagents except for being corroded by concentrated sulfuric acid and concentrated nitric acid. However, low molecular weight aliphatic hydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons can soften and swell polypropylene, and at the same time, its chemical stability increases with the increase of crystallinity, so polypropylene is suitable for making various chemical pipelines and fittings with good anticorrosion effect.
Electrical properties: It has a high dielectric coefficient and can be used to make electrical insulation products that heat up with the increase of temperature. Its breakdown voltage is also very high, and it is suitable for electrical accessories. Good voltage and arc resistance, but high static electricity, easy to age in contact with copper.
Weather resistance: Polypropylene is very sensitive to ultraviolet rays. Adding zinc oxide, tdpa lauryl ester, carbon black or similar milky white filler 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, polar surface area (TPSA) of topological molecules: 29.5. Store in a cool and dry place to ensure good ventilation.
Features: non-toxic, tasteless, low density, better strength, rigidity, hardness and heat resistance than low-pressure polyethylene, and can be used at around 100℃. Good electrical performance, high-frequency insulation, not affected by humidity, but brittle at low temperature, not wear-resistant, easy to age. Suitable for manufacturing general mechanical parts, corrosion-resistant parts and insulating parts. Common organic solvents such as acid and alkali have little effect on it and can be used for tableware.
Polypropylene has many excellent characteristics:
The relative density of reinforced polypropylene pipe 1 is only 0.89-0.9 1, which is one of the lightest varieties of plastics.
2, good mechanical properties, except impact resistance, other mechanical properties are better than polyethylene, and the molding processability is good.
3. High heat resistance, and the continuous use temperature can reach 1 10- 120℃.
4, good chemical properties, almost no water absorption, no reaction with most chemicals.
5, pure texture, non-toxic.
6. Good electrical insulation.
7. The transparency of polypropylene products is better than that of high density polyethylene products.
It has many advantages, but it also has disadvantages:
1, the product has poor cold resistance and low impact strength at low temperature.
2. The product is easy to age due to light, heat and oxygen in use.
3, poor coloring.
......& gt& gt
Question 2: What's the difference between polyethylene and polypropylene? Polyethylene PE
When uncolored, it is milky white and translucent wax-like; Touching the product by hand feels greasy, soft and tough; Slightly scalable. Generally, low density polyethylene is soft and transparent; High density polyethylene is very hard.
Common products: handbags, water pipes, oil drums, beverage bottles (calcium milk bottles), daily necessities, etc.
Polypropylene PP
When uncolored, it is white, translucent and waxy; Lighter than polyethylene. Transparency is also better than polyethylene, which is harder than polyethylene.
Common products: pots, barrels, furniture, films, woven bags, bottle caps, car bumpers, etc.
First, it is divided into high pressure and low pressure. The pure low-pressure bag feels hard and will rattle when rubbed by hand. The high-pressure bag is soft, and its nature is opposite to that of the low-pressure bag. If the recycled materials are mixed in it, they can be divided according to the smell. Pure material has no taste. The bigger the smell, the more recycled materials are mixed. Now, take the bag and look in the direction of the light to see if it is even. The bag made of pure material is clear. If mixed with recycled materials, there will be spots or snowflakes, which can be seen if you look closely. If it is colored, the bag made of pure material is transparent, and the transparency of regeneration will be reduced. Haha, I pay a lot of attention, but I can't say it for a while, and I need practical experience to distinguish it.
Question 3: The difference between polyester, polyethylene and polypropylene. Polyester is a general term for polymers obtained by polycondensation of polyols and polybasic acids. Mainly refers to polyethylene terephthalate (PET), but also includes linear thermoplastic resins such as polybutylene terephthalate (PBT) and polyarylate (see color card). It is an engineering plastic with excellent performance and wide application. It can also be made into polyester fiber and polyester film.
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The English name of polyethylene: polyethylene, abbreviated as PE, is a thermoplastic resin polymerized from ethylene. In industry, it also includes * * * polymers of ethylene and a small amount of α-olefins. Polyethylene is odorless and nontoxic, feels like wax, and has excellent low temperature resistance (the lowest service temperature can reach -70 ~- 100℃), good chemical stability, resistance to most acids and alkalis (oxidation-resistant acids), insolubility in general solvents at room temperature, low water absorption and excellent electrical insulation.
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Polypropylene, English name: polypropylene (PP), Japanese name: ポリプロピレン, molecular formula: (C3H6) n. CAS registration number: 9003-07-0, is a thermoplastic resin polymerized from propylene.
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To sum up:
* * * Similarity: They are all polymers and they are very useful polymers.
Difference: Different sources.
Polyester is formed by polycondensation of polyhydric alcohol and polybasic acid.
Polyethylene is polymerized from ethylene.
Polypropylene is polymerized from propylene.
The chemical and physical properties of polymers formed in this way are also very different.
Question 4: Are both polyethylene and polypropylene plastics? What's the difference between them? Polyethylene and polypropylene are both plastics, and polyethylene is milky white, translucent and waxy when it is not colored. Touching the product by hand feels greasy, soft and tough; Slightly scalable. Generally, low density polyethylene is soft and transparent; High density polyethylene is very hard. Polypropylene is white, translucent and waxy when colorless; Dan: Polyethylene is light. Transparency is also better than polyethylene, and rigidity is also greater than polyethylene.
Question 5: Which is more expensive, polypropylene or polyethylene? At present, the price of PP raw materials is slightly higher, depending on the brand. The price of PE of some brands may be higher than that of PP of some brands.
Question 6: The difference between polyethylene and polypropylene Polyethylene (PE for short) is a thermoplastic resin polymerized from ethylene. In industry, it also includes * * * polymers of ethylene and a small amount of α-olefins. Polyethylene is odorless and non-toxic, feels like wax, and has excellent low temperature resistance (the lowest service temperature can reach-100 ~-70℃), good chemical stability and resistance to most acids and bases (not oxidative acids). Insoluble in general solvents at room temperature, low water absorption and excellent electrical insulation.
Polypropylene is a thermoplastic resin polymerized from propylene. According to the arrangement position of methyl groups, they can be divided into isotactic polypropylene, atactic polypropylene and syndiotactic polypropylene.
When methyl groups are arranged on the same side of the molecular backbone, it is called isotactic polypropylene; If methyl groups are arranged on both sides of the molecular main chain in disorder, it is called random polypropylene; If methyl groups are alternately arranged on both sides of the molecular main chain, it is called syndiotactic polypropylene. In general industrial polypropylene resin, the isotactic structure content is about 95%, and the rest is random or syndiotactic polypropylene. Industrial products are mainly composed of isotactic substances. Polypropylene also includes a copolymer of propylene and a small amount of ethylene. Usually a translucent colorless solid, tasteless and nontoxic. Because of its regular structure and high crystallinity, its melting point can reach 167℃. Its outstanding advantages are heat resistance and corrosion resistance, and the product can be sterilized by steam. Low density, it is the lightest general plastic. The disadvantages are poor impact resistance at low temperature and easy aging, but they can be overcome by modification respectively.
* * * Polymer-based PP material has low thermal deformation temperature (100℃), low transparency, low gloss and low rigidity, but it has strong impact strength, and the impact strength of PP increases with the increase of ethylene content. The Vicat softening temperature of polypropylene is 65438 050℃. Because of its high crystallinity, this material has good surface hardness and scratch resistance There is no environmental stress cracking problem in PP.
The melt mass flow rate (MFR) of PP is usually 1~ 100. PP with low MFR has better impact resistance, but lower tensile strength. For materials with the same MFR, the impact strength of poly type is higher than that of homopolymer type. Due to crystallization, the shrinkage of PP is quite high, generally 1.6~2.0%.
Question 7: What's the difference between polyethylene and polypropylene packaging bags? Is it a packaging bag for packaging these two raw materials or a packaging bag made of these two raw materials?
If it is the former, there is little difference, but polypropylene packaging bags have higher requirements for shading.
If it is the latter, as long as it is a product below 90 degrees Celsius, polyethylene bags can be packed. Polypropylene is similar. The longitudinal tensile strength of polypropylene products is higher than that of polyethylene products, but the transverse tensile strength is smaller.
Polypropylene products can withstand high temperature, generally around 100 degrees.
Food packaging bags do not necessarily use polyethylene, but the cost is lower than other varieties.