A comprehensive analysis of various types of nucleating agents: Classification, Characteristics, and Factors Affecting Their Performance

Today, we will provide a detailed explanation of the classification of the "nucleating agents" family.Factors Affecting the Performance of Nucleating Agents and Clarifying Agents。

Granular nucleating agents are typically high-melting compounds that are mixed and dispersed in a polymer melt. These particles act as unique "nucleation sites" on which polymer crystals can begin to grow.

High concentrations of nucleating agents can lead to faster crystallization (shorter cycle times) and higher crystallinity, thereby improving the strength, rigidity, and HDT of polymers. If the crystal aggregates (spherulites) are smaller in size, light scattering can be reduced and clarity can be improved. Commonly used particulate nucleating agents include salts and minerals such as talc, sodium benzoate, phosphate esters, and other organic salts.

Talcum powder and sodium benzoateIt is considered a low-performance, low-cost nucleating agent, and it provides moderate improvements in strength, stiffness, HDT, and cycle time.

High-performance, high-cost nucleating agents, such asPhosphate ester and bicycloheptane saltIt can provide better physical properties and improve transparency to a certain extent.

Soluble nucleating agents, also known as "melt-sensitive type," typically have a lower melting point and dissolve in molten PP. When the polymer melt cools in the mold, these nucleating agents crystallize first, forming a finely distributed network with an extremely high surface area. As the temperature continues to drop, the fibers constituting this network act as cores, initiating polymer crystallization.

The extremely high concentration of crystal nuclei results in very small PP crystal aggregates, thereby producing the lowest level of light scattering and optimal clarity.

All clarifying agents are nucleating agents, but not all nucleating agents are good clarifying agents. Some common nucleating agents, such as sodium benzoate and talc, cannot sufficiently reduce spherulite size, thus failing to achieve low haze and high transparency in molded parts. Typically, using soluble nucleating agents can achieve optimal transparency. Soluble organic compounds that can be used as clarifying agents include sorbitol, nonanol, and trisamide.

Although these nucleating agents are primarily used to achieve high clarity and low haze, they can also improve physical properties and reduce cycle time.

Nucleating agents and clarifying agents can also be classified according to their chemical families and crystal types.

1. Inorganic and organic nucleating agents

Inorganic additives such as talc or barium sulfate, and nanoclays (such as montmorillonite) have a nucleating effect on polypropylene, thermoplastic polyesters, and polyamides, which can accelerate the nucleation rate and increase the overall crystallinity. Additionally, the use of metal oxides (such as titanium dioxide or magnesium oxide), phosphates, carbonates, or sulfates (preferably alkaline earth metals) is also recommended.

Organic additives come in a wide variety, ranging from sorbitol derivatives to mono- or polycarboxylic acids and their salts, such as 4-tert-butylbenzoic acid, sodium benzoate, organic phosphates or phosphoric esters, adipic acid, diphenylacetic acid, sodium succinate, or sodium benzoate; norbornane carboxylate, polymers such as ionomers (ionomer resins), nitrogen and more or less complex molecules such as triphenodithiazine, dicyclohexyl-2,6-naphthalenedicarboxamide, heptanoic acid with calcium stearate or quinacridone pigment Permanent Red.

2. Classification according to the most favored crystal types: α, β, γ...

The most effective α-nucleating agents are sorbitol derivatives and organic phosphates, while β-nucleating agents include trisamide dithiazine, pimelic acid with calcium stearate, or quinacridone pigment Permanent Red.

Smaller particle sizes result in better nucleation effects, but smaller particles are also more difficult to disperse. Some nucleating particles, such as sodium benzoate, tend to re-agglomerate easily.

Some acid scavengers, such as fatty acid salts (e.g., calcium stearate), may exhibit antagonistic effects with certain nucleating agents (e.g., phosphate esters and sodium benzoate). Dihydro talc (DHT 4A®) should be used with these nucleating agents.

Do not use calcium stearate together with sodium benzoate, as calcium stearate will completely offset the nucleating effect of sodium benzoate.

Sodium benzoate often forms agglomerates and is difficult to disperse properly.

Sorbitol requires a higher melting temperature to achieve optimal transparency because they must be completely dissolved in the polymer melt. Other soluble clarifiers, such as Irgaclear® XT 386, can dissolve in polypropylene at lower temperatures and are less sensitive to melting temperature.

A resin company often adds nucleating agents to PP. It is best to use PP pellets or powder, or use nucleating agent masterbatch if mixing pure nucleating agent powder.

Antacids can have synergistic effects or antagonistic effects.

Fatty acid salts can adversely affect the modulus of phosphate nucleated polypropylene. DHT 4A® (hydrotalcite) can enhance the modulus of ADK STAB NA-11 nucleated polypropylene and allows for effective utilization with a lower amount of nucleating agent.

In talc-reinforced PP, ADK STAB NA-27 has the highest modulus.

In colored PP, Hyperform® HPN® 68L can balance the impact of pigment changes on modulus and reduce differential shrinkage and warpage.