(1) Introduction
Polypropylene is obtained by polymerizing propylene under the action of a catalyst of methyl aluminum and titanium trichloride at 20 atmospheres and 50 ° C in a solvent of gasoline. Its trade name is abbreviated as "acrylic", the English abbreviation is: PP.
(2) Identification features
It is milky white translucent when uncolored, soft; relative density is less than water, can float on horizontal surface; softening in boiling water is not significant, invariable type, softening temperature is 110 °C; hand touch lubrication, but no greasy feeling, texture is quite hard toughness. Brittle fracture occurs when the strip is stretched.
(3) Combustion characteristics
It is flammable and can continue to burn after leaving the fire. It has a special smell to escape; the tip of the flame is yellow, with less smoke, burning while melting and dripping.
(4) Structure and performance
CH3
The structural formula of polypropylene is: [—CH 2 —CH—] n , which belongs to linear macromolecules, but the methyl side chains of polypropylene have three different arrangements, which make them have higher crystallinity. Due to the influence of the methyl side chain, the properties of polypropylene and polyethylene plastic are different, mainly in the following aspects:
1. Chemical stability is better than polyethylene
In addition to fuming nitric acid and fuming sulfuric acid, it is resistant to other chemical corrosives. In the laboratory, 80% sulfuric acid and concentrated hydrochloric acid can reach 100 ° C without destroying polypropylene.
2. Outstanding heat resistance
It can be used for a long time at 100-120 ° C; however, the impact strength is drastically reduced at low temperatures, and the impact strength at 0 ° C is half that at 20 ° C.
3. Breathability and water permeability are lower than polyethylene.
4. Rigidity and tensile strength are better than polyethylene.
5. Directional stretching
The tensile strength is improved, the bending resistance is good, the flexibility is increased, and the bending is not changed white when the bending is bent 1 million times.
6. The aging resistance is worse than polyethylene
The long chain of polypropylene has a methyl tertiary carbon atom, which is unstable, and it is used in the long-term contact with copper to produce "copper damage".
(5) Modification
The use properties of polypropylene plastics have certain disadvantages, such as poor cold resistance, low impact strength, and poor aging resistance. In order to overcome these shortcomings, modification measures are often employed.
Copolymerization modification
Copolymerization with monomers such as vinyl chloride and acrylic acid can improve the cold resistance, flammability and molding fluidity of polypropylene.
2. Blending modification
Blending with other thermoplastics and elastomers to prepare blends can improve the cold resistance of polypropylene.
3. Filling - enhanced modification
Adding filler materials and reinforcing materials to increase the rigidity of polypropylene at high temperatures and reduce the molding shrinkage.
4. Tensile modification
The orientation of the molecules by stretching increases the mechanical strength. For example, when the polypropylene is biaxially stretched, the strength can be increased by 3 times.
5. Cross-linking modification
The linear structure of polypropylene is crosslinked into a network structure to improve heat resistance and mechanical strength.
(6) Use
Polypropylene plastic is mainly used for film, pipe, bottle products and so on. Due to the higher heat softening point, it can be used to make tableware, such as bowls, pots, cups, etc.; sterilization containers for medical equipment; daily necessities such as buckets, thermos bottles, etc.; can also make pencil cases, instrument boxes, etc.; Materials and low foaming sheets that replace wood. It is also suitable for making a variety of ropes and packaging ropes.
China's demand for polypropylene will soon surpass that of the United States and become the world's largest consumer. Five years ago, the demand for polypropylene in China was only 60% of the demand for polypropylene in the United States. At present, this indicator has increased to 95%. The report pointed out that China's polypropylene demand growth rate will be twice that of the US in the next five years. By 2007, China's polypropylene demand will be 20% higher than the US demand.
According to industry analysts, Sinopec and PetroChina have now entered the ranks of the world's largest polypropylene producers. Currently, Sinopec's polypropylene production capacity ranks second in the world, and CNPC ranks 13th. PetroChina has signed a licensing agreement with Basell to double its production capacity by 2007.
Although China's polypropylene production capacity is strong, the annual demand gap for polypropylene is still 2.5 million tons, and South Korea, the Middle East and India will supplement this as potential polypropylene exporters.
In 2002, the global demand for polypropylene reached 34 million tons, an increase of 7% over 2001 and a net increase of 2.2 million tons. It is predicted that the total demand for polypropylene in the world will increase at a rate of 6.6%/year. By 2007, the world demand for polypropylene will reach more than 47 million tons.
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