Progress in transparent modification of polypropylene

First, the main indicators to measure the transparency of polymers are:
1. Transmittance: the ratio of transmitted light intensity to human light intensity.
2. Transparency: the ratio of directional transmittance to total transmittance.
3. Haze: Deviation from the ratio of transmitted light intensity to total transmitted light intensity.
In addition, there are some indicators such as turbidity, cleanliness (the degree of image decomposition of standard printed sizes seen through plastic sheets), etc., which are also evaluated for transparency.
2. PP is a crystalline polymer having a two-phase structure of a crystalline region and an amorphous region. The difference in density between the crystalline region and the amorphous region makes the crystalline phase have a higher refractive index than the amorphous phase. The difference in refractive index between the two phases causes scattering and refraction of light at the phase interface, so the transparency of PP is closely related to its crystallization. .
Third, to improve the transparency of PP, it is necessary to control its crystallization and destroy the formation of large spherulitic structures. The methods are as follows:
1. Reduce the crystal area (spherulitic size) so that it is close to the wavelength of light.
2. Destroy molecular chain regularity and reduce crystal inclusion.
3. The refractive indices of the crystalline phase and the amorphous phase are similar.
4. Change the shape of the PP crystal, for example, by using a stretching method to change the spherulites into platelets.
Fourth, the method to improve the transparency of PP is roughly classified as:
1. Add nucleating agent 2, blend with other polymers, 3. Graft other monomers in PP chain, process, such as quenching, stretching, etc. 5. Difference in PP transparency and its microscopic morphology ( The spherulite size is closely related, which is related to two parameters:
1. Spherical growth rate 2. The number of crystal nucleus per unit volume is slowly solidified, forming the characteristics of nucleation and crystal growth phase separation. The addition of nucleating agent can increase the nucleation rate and cause nucleation to occur at higher temperatures. Compared to homogeneous nucleation, a higher crystal growth rate is obtained, resulting in higher crystallinity and smaller spherulite size. Therefore, the addition of a nucleating agent not only improves the transparency of the polymerization (smaller spherulite size), improves the mechanical properties of the polymer (higher crystallinity), but also shortens the processing cycle of the polymer (faster crystallization rate) In addition, the addition of a nucleating agent is also beneficial to increase the dimensional stability of the PP.
6. To obtain a good nucleation effect, choose a suitable nucleating agent. A good nucleating agent should have the following characteristics:
1. Reduce the free energy of the included interface and have better compatibility with the polymer.
2. Melt above the melting point of the polymer without decomposition.
3. Non-toxic, stable, and does not react with environmental substances.
4. It should have a crystal structure similar to that of a crystalline polymer.
7. PP transparent modified nucleating agents are:
Organic category:
1, oleitol 2, organic phosphorus 3, organic amide inorganic:
1, metal oxides and their salts 2, containing silicon 3, talcum powder, carbon black

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