Keywords: properties of polypropylene nucleating agent
Polypropylene has the advantages of low specific gravity, high tensile yield strength, high flexural modulus and hardness, and good environmental stress cracking resistance. In addition, it is rich in raw materials and low in price, which is very suitable for injection molding plastic products. Polypropylene is a kind of crystalline polymer, in which there are large spherulites, which leads to low impact strength of polypropylene and serious shrinkage of products, which seriously affects the use of polypropylene resin in injection molding field. Adding nucleating agent to produce polypropylene with microcrystalline structure, and modifying the resin to realize the high performance of polypropylene. Effect of crystallization state of 1. polypropylene molecule on properties. When polymer materials crystallize in the melt, polygonal grains, dendritic grains and spherulites are easy to form, and their sizes play an important role in the mechanical, physical and optical properties of polymers. Large spherulites usually reduce the elongation at break and toughness of polymers.
2, the principle of nucleating agent
Impurities in polymers have a great influence on the crystallization process. Some impurities hinder crystallization, while others can promote crystallization. These impurities can promote crystallization and play the role of crystal nucleus in the crystallization process of polymers. Nucleating agent is the impurity that can promote crystallization. Adding nucleating agent into polypropylene can accelerate the crystallization speed and form fine and compact spherulites, so that the molecular chain can crystallize quickly at higher temperature, and spherulites can grow regularly, with a large number and small size. Adding nucleating agent into polypropylene can promote the crystallization process, accelerate the crystallization speed of molecules, and make molecules have microcrystalline structure, which is not only beneficial to improve the impact strength and yield strength of products, but also has a certain impact on the appearance and processing of products.
Effect of 1 on tensile strength
Effect of nucleating agent on tensile properties of polypropylene (see table-1)
Table-1 Effect of Nucleating Agent on Tensile Strength of Polypropylene
Tensile strength of additive * 10N/㎡ elongation at break%
No. 160 20 cadmium benzoate 178 80
Bismuth salicylate 20 1 790
Titanium oxalate 235 850
2. Impact strength.
The sensitivity of polypropylene resin to impact increases with the formation of large spherulites. Larger spherulites can crack radially, while smaller spherulites or microcrystals are beneficial to improve the impact strength of materials. According to statistics, the increase rate is about 10 %-30%. Impact strength should be reduced.
3. Increase the transparency of products. Due to the microcrystal structure formed after adding nucleating agent, the turbidity of the polymer is reduced and the transparency is improved (see Table -2).
Table 2 Relationship between the addition of nucleating agent and turbidity of polypropylene products
Add 40.30% turbidity% of sample material and relative turbidity% of standard sample.
2mm thick PP injection sample 0 40 97
0.05 30 90
0. 10 29 88
0.20 29 87
4. Nucleating agent can improve the surface hardness of products.
The increase of microcrystalline structure can improve the surface hardness of products. By testing polypropylene injection samples with a thickness of 3 mm, the results are shown in Table -3.
Table -3 Relationship between Addition of Nucleating Agent and Hardness of Polypropylene Products
4030 dose% rockwell hardness (ASTMD785)
0 36.0
0. 1 48.6
5. Adding nucleating agent can improve the surface smoothness of products.
Adding nucleating agent 4030 can improve the surface smoothness of some pigment formulation materials (see Table -4).
Table 4 Relationship between the amount of nucleating agent added and the surface gloss of polypropylene products
Pigment formula 4030 adds% surface finish.
& lt20 & lt60
1 %3RJ brown (brown 4 1) 0 40 66
0. 15 58 74
1 %B (black 7) 0 44 66
0. 15 50 68
6. Adding nucleating agent can shorten the injection cycle and improve the productivity.
Adding nucleating agent can obviously shorten the cooling time of injection mold, thus shortening the whole injection cycle and improving production efficiency. Effect of nucleating agent on isothermal crystallization time of polypropylene (see table -5)
Table -5 Isothermal Crystallization Time of Polypropylene with Different Nucleating Agent Concentrations 4030 Addition% 1 15℃ 120℃ Homopolymer * * * homopolymer * * polymer 0 203 247172 220 0 0.05146 60 206 0.0128186 68602118137187 7. Reduce the post-shrinkage of injected products.
The reason for the shrinkage of injection molded products after production is that during the injection molding process, the molten resin cools quickly and the molecular chain crystallizes after cooling and solidification. Adding nucleating agent into polypropylene melt can accelerate crystallization and form fine and compact spherulite morphology. Even if the cooling rate is fast during injection molding, PP can still crystallize well, thus reducing the post-shrinkage degree of the product.
8。 Influence on light stability of products
Adding nucleating agent such as 4030 to polypropylene has no effect on the photostability of the product. (See Table 6)
Table 6 Effect of nucleating agent on photostability of polypropylene products
Exposure time of material 4030 plus% in artificial climate box
0.30㎜ thick PP film 0 420
0. 15 420
9. Effect on long-term heat resistance of products
The addition of nucleating agent 4030 will not affect the heat resistance of polypropylene resin. The following table shows the experimental results of 0.50mm thick polypropylene samples placed in 150c oven. (See Table 7)
Table -7 Effect of Nucleating Agent on Heat Resistance of Polypropylene Products
4030 dosage% 150℃ constant temperature furnace
Brittle cracking days (days): yellowness index 0 days and yellowness index 10 days.
0 15 5.3 1 1.0
0. 15 14 4.9 9.9
Conclusion: To sum up, adding nucleating agent into polypropylene can promote the crystallization process and speed of molecules and make the molecules have microcrystalline structure, which is not only beneficial to the impact strength and yield strength of products, but also can improve the appearance of products, shorten the injection period and improve productivity. With the development of new polypropylene products and brands, nucleating agents will be more widely used in various fields of new polypropylene product development.