Polypropylene (PP) is a thermoplastic resin
Chinese name: Polypropylene Chinese aliases: polypropylene oil agent, polypropylene, polypropylene FDY, polypropylene filament FDY, polypropylene short fiber, polypropylene short fiber, polypropylene short fiber PP English name: Polypropylene English alias: PropyleneResin（LowM.Wt） chemical formula: (C3H6)n Molecular weight: 42.0804 (the molecular weight of polypropylene should be within a range, where 42 is the molecular weight of polypropylene monomer) CAS login number: 9003-07-0 MDL Number: UD1842000 RTECS number: UD1842000 PubChem Number: 24866797 |
Polypropylene has many excellent properties, such as a low relative density of only 0.89-0.91, making it one of the lightest varieties of plastics; Has good heat resistance, and the product can be disinfected and sterilized at temperatures above 100 ℃; Good chemical stability, except for being corroded by concentrated sulfuric acid and concentrated nitric acid, it is relatively stable to various other chemical reagents, and has good electrical insulation. Polypropylene is widely used in various fields, such as plastic products, fibers, films, etc. In daily life, common items include plastic tableware, plastic containers, car parts, packaging materials, etc.
PP characteristics
Density: 0.89~0.91g/cm³
Appearance: Colorless, odorless, non-toxic, semi transparent solid substance.
Modification: grafting, copolymerization, crosslinking, reinforcement, filling, etc
Reuse: alloying, compounding, etc
Characteristics: Thermoplastic, light weight, chemical corrosion resistance, etc
Melting point: 164-170 ℃, softens at around 155 ℃, and can be used at temperatures ranging from -30 ℃ to 140 ℃. It can resist corrosion from acid, alkali, salt solution and various organic solvents below 80 ℃, and can decompose under high temperature and oxidation.
Physical and chemical properties of PP
1. Odorless, odorless, and non-toxic.
2. Excellent mechanical properties:
Stretching strength, compressive strength, and hardness, outstanding rigidity and bending fatigue resistance, the movable hinge made of PP can withstand more than 7 × 107 folding and bending cycles without damage, and has poor impact strength at low temperatures. The tensile strength of PP is generally 21-39 megapascals; The bending strength is 42-56 megapascals, the compression strength is 39-56 megapascals, the elongation at break is 200%~400%, the notch impact strength is 2.2-5kJ/㎡, the low-temperature notch impact strength is 1-2kJ/㎡, and the Rockwell hardness is R95~105.
3. Heat resistance:
Good heat resistance, continuous use temperature can reach 110-120 ℃.
4. Chemical properties:
Good stability, except for strong oxidants, it does not interact with most chemical drugs; At room temperature, solvents cannot dissolve PP, only some halogenated compounds, aromatic hydrocarbons, and high boiling point fatty hydrocarbons can make it swell, and its water resistance is particularly good.
5. Conductivity:
Excellent electrical performance, good resistance to high-frequency electrical insulation, and good electrical insulation even in humid environments.
6. Weathering and aging resistance:
Due to the presence of many tertiary carbon atoms with methyl groups on the main chain of PP, the hydrogen on the tertiary carbon atoms is susceptible to oxygen attack, resulting in poor weather resistance and requiring the addition of antioxidants or UV absorbers.
7. Toxicity:
Mice were orally administered at a dose of 8g/kg for 1-5 times, and no significant toxic symptoms were observed. Rats inhaled the decomposition products of polypropylene heated to 210-220 ℃ 30 times, each time for 2 hours, and exhibited symptoms of irritation to the eye mucosa and upper respiratory tract. Similar to polyethylene, it is prohibited to use its recycled products to store food.
Recycling technology for waste PP
Polypropylene (PP) is currently the second largest general-purpose plastic, and with the development of industries such as construction, automotive, home appliances, and packaging, waste PP has become one of the largest waste polymer materials in recent years. At present, the main ways to deal with waste PP are incineration for energy supply, catalytic cracking for fuel preparation, direct utilization, and recycling. Considering factors such as technical feasibility, cost, energy consumption, and environmental protection in the process of disposing of waste PP, recycling is currently the most commonly used, effective, and advocated way to dispose of waste PP. Due to factors such as light, heat, oxygen, and external forces during use, the molecular structure of PP will change, causing the product to turn yellow, brittle, and even crack, resulting in a significant decrease in PP toughness, dimensional stability, thermal oxygen stability, and processability. Directly using waste PP to manufacture products is difficult to meet the requirements of processing and use. Therefore, the recycling technology of waste PP continues to develop, and the use of alloying with other polymers or compounding with fillers can significantly improve the processing performance, thermal performance, physical and mechanical properties of waste PP, achieving high performance of waste PP.
Alloy
Alloying is the process of mixing waste PP with other polymer materials to prepare macroscopically uniform materials. By selecting different polymer materials for alloying, the processing performance, physical and mechanical properties of waste PP can be improved. For example, using elastomers can significantly enhance the impact toughness of waste PP.
There is research on the mechanical properties and thermal deformation behavior of waste PP/RU composite rubber (natural rubber and styrene butadiene rubber each account for 50%) blends. It was found that refining RU composite rubber into small rubber particles and uniformly dispersing them in the continuous phase of waste PP can significantly improve the impact strength and elongation at break of waste PP, but it can lead to a decrease in PP rigidity and heat deformation resistance.
Due to the incompatibility between the vast majority of elastomers and waste PP, the interface bonding is poor, and there is phase separation during processing and use, which affects their performance. In order to improve the interfacial compatibility of waste PP alloys and enhance interfacial bonding, many scholars have conducted extensive research and discovered two types of compatibilizers that can enhance the interfacial bonding of blended materials, improve the storage modulus, loss modulus, and system viscosity of blended materials. Vulcanizing agents can improve the impact and tensile strength, melt viscosity, elongation at break, and ductility of blended materials; The addition of peroxide crosslinking agent can further improve the compatibility of the blend material, enhance the impact and tensile strength of the blend material, but it leads to a slight decrease in the elongation at break.
Composite
Recombination is the process of mixing waste PP with non polymer materials to prepare composite materials, which is the main way to achieve high-performance and functionalization of waste PP. The compounding of waste PP can improve its physical and mechanical properties such as rigidity, strength, thermal and electrical properties, and reduce costs.
According to the composition of fillers, they can be divided into inorganic fillers and organic fillers.
Inorganic filler composite
Inorganic fillers commonly used in PP composites can be combined with waste PP materials, such as calcium carbonate, talc powder, montmorillonite, metal oxides, fly ash, and glass fibers. Research has found that although these inorganic fillers can significantly improve the rigidity of waste PP and reduce costs, they have a significant difference in polarity with waste PP, high surface energy, poor compatibility, and lead to a decrease in the fracture elongation and impact toughness of composite materials.
Organic filler composite
Common organic fillers include wood flour and wood fiber, starch, wheat straw, hemp fiber, and discarded newspapers. There is research on the technology of filling waste PP micropores with wood fibers, and the results show that when the melting temperature is 180 ℃ and the holding pressure is 12.5MPa, the micropore structure is uniformly distributed. Due to the microporous structure, it can extend the propagation path of cracks, absorb external impact energy, and thus improve impact strength. Natural fiber is an emerging waste PP filling material, and surface treatment is the main method to achieve high performance of natural fiber filled waste PP composite materials due to its high water absorption and incompatibility with waste PP. In addition, waste polyester can also be used to modify waste PP. Scholars have studied the crystallization behavior of β - nucleated waste PP/waste polyester fabric composites, and the results show that waste polyester and β - nucleating agents have heterogeneous nucleation effects on the crystallization of waste PP, increasing the crystallization temperature of waste PP and inducing the formation of β - crystals.
Hybrid composite
Hybrid compounding is the process of preparing composite materials by filling polymers with two or more fillers. Due to the limitations of a single filler, hybrid composites can improve the overall performance of polymers by complementing and synergizing the advantages of different fillers. Therefore, research on the preparation and related properties of waste PP composite materials filled with mixed fillers has attracted attention, mainly involving the mixing of different inorganic fillers and inorganic/organic fillers.
Alloy composite
In order to fully utilize the advantages of alloying and compounding, researchers have begun to combine alloying and compounding to further improve and enhance the physical and mechanical properties of waste PP, achieving high-performance and industrialization of waste PP, such as organic fillers and elastomers, inorganic fillers and elastomers combined to modify waste PP.
The research results in this regard indicate that the fracture behavior of waste PP and talc powder filled waste PP composite materials at low temperatures is brittle, and the addition of EOC (ethylene octene copolymer) can significantly improve the impact resistance of the composite materials; The dynamic mechanical behavior of EOC toughened talc powder filled waste PP composite materials does not change with increasing recycling times.
