Nucleating agent
The nucleating agent is suitable for incomplete crystalline plastics such as polyethylene and polypropylene. By changing the crystallization behavior of the resin, it can accelerate the crystallization rate, increase the crystal density and promote the miniaturization of the crystal grain size, so as to shorten the molding cycle and improve the transparency and surface New functional additives for physical and mechanical properties such as gloss, tensile strength, rigidity, heat distortion temperature, impact resistance, and creep resistance.
Adding a nucleating agent can increase the crystallization speed and degree of crystallization of the crystalline polymer product, not only can increase the processing and molding speed, but also greatly reduce the phenomenon of secondary crystallization of the material, thereby improving the dimensional stability of the product.
The influence of nucleating agent on product performance
The addition of the nucleating agent improves the crystalline properties of the polymer material, which affects the physical and processing properties of the polymer material.
01 Influence on tensile strength and bending strength
For crystalline or semi-crystalline polymers, the addition of a nucleating agent is beneficial to increase the crystallinity of the polymer, and often has a reinforcing effect, which increases the rigidity of the polymer, the tensile strength and the bending strength, and the modulus, but The elongation at break generally decreases.
02 Resistance to impact strength
Generally speaking, the higher the tensile or bending strength of the material, the impact strength tends to be lost. However, the addition of nucleating agent will reduce the spherulite size of the polymer, so that the polymer exhibits good impact resistance. For example, adding a suitable nucleating agent to PP or PA raw materials can increase the impact strength of the material by 10-30%.
03 Influence on optical performance
Traditional transparent polymers such as PC or PMMA are generally amorphous polymers, while crystalline or semi-crystalline polymers are generally opaque. The addition of nucleating agents can reduce the size of the polymer grains and have the characteristics of microcrystalline structure. It can make the product show the characteristics of translucent or completely transparent, and at the same time can improve the surface finish of the product.
04 Influence on polymer molding processing performance
In the polymer molding process, because the polymer melt has a faster cooling rate, and the polymer molecular chain has not completely crystallized, it causes shrinkage and deformation during the cooling process, and the incompletely crystallized polymer has poor dimensional stability. It is also easy to shrink in size during the process. Adding a nucleating agent can speed up the crystallization rate, shorten the molding time, improve production efficiency and reduce the degree of post-contraction of the product.
Types of nucleating agent
01 α crystal nucleating agent
It mainly improves the transparency, surface gloss, rigidity, heat distortion temperature, etc. of the product. It is also called a transparent agent, a transmittance enhancer, and a rigidizer. Mainly include dibenzyl sorbitol (dbs) and its derivatives, aromatic phosphate ester salts, substituted benzoates, etc., especially dbs nucleating transparent agent is the most common application. Alpha crystal nucleating agents can be divided into inorganic, organic and macromolecules according to their structure.
02 Inorganic
Inorganic nucleating agents mainly include talc, calcium oxide, carbon black, calcium carbonate, mica, inorganic pigments, kaolin and catalyst residues. These are the earliest cheap and practical nucleating agents developed, and the most researched and applied nucleating agents are talc, mica, etc.
03 Organic
Carboxylic acid metal salts: such as sodium succinate, sodium glutarate, sodium caproate, sodium 4-methylvalerate, adipic acid, aluminum adipate, aluminum tert-butyl benzoate (Al-PTB-BA) , Aluminum benzoate, potassium benzoate, lithium benzoate, sodium cinnamate, sodium β-naphthoate, etc. Among them, the alkali metal or aluminum salt of benzoic acid, and the aluminum salt of tert-butyl benzoate have better effects and have a long history of use, but the transparency is poor.
Phosphoric acid metal salts: Organic phosphates mainly include phosphate metal salts and basic metal phosphates and their complexes. Such as 2,2'-methylene bis(4,6-tert-butylphenol) phosphine aluminum salt (NA-21). This type of nucleating agent is characterized by good transparency, rigidity, crystallization speed, etc., but poor dispersibility.
Sorbitol benzylidene derivative: It has a significant improvement effect on the transparency, surface gloss, rigidity and other thermodynamic properties of the product, and has good compatibility with PP. It is a type of transparency that is currently undergoing in-depth research. Nucleating agent. With good performance and low price, it has become the most actively developed nucleating agent with the largest variety and the largest production and sales at home and abroad. There are mainly dibenzylidene sorbitol (DBS), two (p-methylbenzylidene) sorbitol (P-M-DBS), two (p-chloro-substituted benzal) sorbitol (P-Cl-DBS) and so on.
High melting point polymer nucleating agent: At present, there are mainly polyvinyl cyclohexane, polyethylene pentane, ethylene/acrylate copolymer, etc. It has poor blending properties with polyolefin resins and good dispersibility.
β crystal nucleating agent:
The aim is to obtain polypropylene products with high β crystal form content. The advantage is to improve the impact resistance of the product, but does not reduce or even increase the thermal deformation temperature of the product, so that the two contradictory aspects of impact resistance and heat deformation resistance are taken into account.
One type is a few fused ring compounds with quasi-planar structure.
The other is composed of oxides, hydroxides and salts of certain dicarboxylic acids and metals of group IIA of the periodic table. It can modify the ratio of different crystal forms in the polymer to modify PP.
