The role and classification of nucleating agents

The nucleating agent is suitable for incompletely crystallized plastics such as polyethylene and polypropylene. By changing the crystallization behavior of the resin, accelerating the crystallization rate, increasing the crystal density and promoting the grain size, the molding cycle is shortened, the transparency of the product is improved, and the surface is improved. New functional additives for physical and mechanical properties such as gloss, tensile strength, rigidity, heat distortion temperature, impact resistance, and creep resistance.

The polymer modified by the nucleating agent not only retains the original characteristics of the polymer, but also has better cost performance than many materials, and has good processing performance and wide application range, which makes the nucleating agent have been widely concerned at home and abroad.

The mechanism of action of the nucleating agent:

Impurities in the polymer have a great influence on the crystallization process, some hinder crystallization, and some promote crystallization. These impurities which promote crystallization act as nucleation during the crystallization of the polymer. An impurity capable of promoting crystallization. The addition of a nucleating agent to polypropylene accelerates the crystallization rate and forms fine and dense spherulitic particles, which makes the molecular chain have a rapid crystallization rate at a higher temperature. The spherulites can grow relatively regularly, and the number is very large. small.

Classification of nucleating agents:

1, alpha crystal nucleating agent

It mainly improves the transparency, surface gloss, rigidity, heat distortion temperature, etc. of the product, and also has the name of transparent agent, anti-reflecting agent and strengthening agent. It mainly includes diboric sorbitol (dbs) and its derivatives, aryl phosphate esters, substituted benzoates, etc., especially the application of dbs nucleating transparent agent is the most common. The α crystal nucleating agent can be further classified into inorganic, organic and polymeric according to the structure.

2. β crystal nucleating agent

The polypropylene product intended to obtain a high β crystal form content has the advantages of improving the impact resistance of the product, but does not reduce or even increase the heat distortion temperature of the product, so that the contradiction between impact resistance and heat deformation resistance is taken into consideration. One class is a small number of fused ring compounds with quasi-planar structures. The other type consists of certain dicarboxylic acids and oxides, hydroxides and salts of metals of Group IIA of the Periodic Table. It can modify PP by changing the proportion of different crystal forms in the polymer.

3. Inorganic

Inorganic nucleating agents mainly include talc, calcium oxide, carbon black, calcium carbonate, mica, inorganic pigments, kaolin and catalyst residues. These are the earliest developed cheap and practical nucleating agents. The most research and application are talcum powder and mica.

4, organic

Carboxylic acid metal salts: such as sodium succinate, sodium glutarate, sodium hexanoate, sodium 4-methylvalerate, adipic acid, aluminum adipate, aluminum monobutyl benzoate (Al-PTB-BA) , aluminum benzoate, potassium benzoate, lithium benzoate, sodium cinnamate, sodium β-naphthoate, and the like. Among them, alkali metal or aluminum benzoate and aluminum salt of tert-butylbenzoate have better effects, and the history of use is relatively long, but the transparency is poor.

Metal phosphates: Organic phosphates mainly include phosphate metal salts and phosphate basic metals and their compounds. For example, 2,2'-methylenebis(4,6-tert-butylphenol)phosphine aluminum salt (NA-21). Such nucleating agents are characterized by good transparency, rigidity, crystallization speed, etc., but poor dispersibility.

Sorbitol Benzene Derivative: It has significant improvement effect on transparency, surface gloss, rigidity and other thermodynamic properties of the product, and has good compatibility with PP. It is a kind of transparent which is currently being studied in depth. Nucleating agent. Its performance is good and its price is low. It has become the most active type, the most variety, and the largest production and sales of nucleating agents at home and abroad. There are mainly dibenzylidene sorbitol (DBS), di(p-methylbenzylidene) sorbitol (PM-DBS), di(p-chloro substituted benzalkonium) sorbitol (P-Cl-DBS) and the like.

High melting point polymer type nucleating agent: At present, there are mainly polyvinyl cyclohexane, polyvinyl pentane, ethylene/acrylate copolymer and the like. It has poor blendability with polyolefin resin and good dispersibility.