Advantages of Calcium-Zinc Stabilizers Compared to Other Types of Stabilizers
Calcium-zinc stabilizers are the primary focus of research in stabilizer development. These stabilizers are cost-effective but have relatively poor heat stability, which means their price performance still cannot compete with lead salt stabilizers. The development trend of inorganic tin stabilizers is to use smaller alkyl groups in the inorganic tin compounds (such as monomethyl, monobutyl, or mono-octyl tin), supplemented by low molecular weight, more effective thiols or inorganic sulfur compounds. This can be enhanced by incorporating thiol mixtures to better meet the above requirements.
Rare earth stabilizers and new inorganic stabilizers have become key research directions in recent years. Among them, diketone compounds are rapidly developing as a category of non-metallic stabilizers globally, and have gained significant attention in the industry. Most of these products are inorganic compounds combined with auxiliary stabilizers, such as metal complexes, to create a synergistic effect. Calcium-zinc stabilizers typically appear as white powders, flakes, or pastes. The powdered form is commonly used as a PVC stabilizer in various applications, including food packaging, medical devices, and wire and cable materials. Currently, the industry has developed calcium-zinc stabilizers for use in rigid PVC pipes.
Traditional environmentally friendly products like calcium/zinc stabilizers, due to their higher electronegativity compared to lead, interact with PVC resin's functional groups, forming strong complexes. This weakens or neutralizes the repulsive forces between PVC particles, making it easier for the resin's molecular segments to diffuse. This process improves the plasticization of PVC. However, this also causes an increase in melt pressure, a decrease in melt viscosity, and a rise in temperature during the plasticizing phase. The lower processing temperature leads to excessive plasticization of the dry blend, and because traditional PVC processing equipment is designed for lead salt stabilizers, there is a lack of sufficient lubricant (often cheap lubricants like paraffin or stearic acid are used) to prevent further plasticization of the resin. Additionally, the imbalance in lubrication can prevent the PVC melt from reaching the desired viscosity and elasticity, thus failing to meet the needs of rigid PVC production. This issue must be addressed when using calcium-zinc stabilizers in replacement of lead salts.
Calcium-zinc stabilizers can be categorized into solid and liquid types. These stabilizers are composed of calcium salts, zinc salts, lubricants, antioxidants, and other components synthesized using special composite techniques. They can replace toxic stabilizers such as lead-cadmium salts and organic tin compounds, offering good heat stability, light stability, transparency, and coloring power. In practical applications, calcium-zinc stabilizers exhibit good processing performance and thermal stability, making them a suitable alternative to lead salt stabilizers. The price of powdered calcium-zinc stabilizers varies, and there is no standardized national regulation to standardize the price.
Liquid calcium-zinc stabilizers typically appear as pale yellow oily liquids. These stabilizers share similar rigidity with the powder form but generally offer better dispersibility in PVC resin powder and have a less significant effect on color stability. Calcium-zinc stabilizers can be divided into two main systems: hydrotalcite and zeolite systems. Rare earth heat stabilizers, a class of PVC stabilizers in China, demonstrate excellent heat resistance, weatherability, processing properties, and storage stability. Especially notable is their environmentally friendly nature, making rare earth stabilizers one of the few heat stabilizers that meet environmental requirements. With abundant rare earth resources in China, low material costs, and relatively underdeveloped processing technology, further research and development of rare earth heat stabilizers is a key focus for replacing toxic heavy metal stabilizers and some lower-cost organic tin stabilizers in the future development of China's stabilizer industry.