Types and choices of powder

1. Selection of Dispersant An effective dispersant must meet several key criteria to ensure optimal performance in polymer systems. It should provide excellent dispersion properties, preventing the agglomeration of filler particles. The dispersant must also exhibit good compatibility with both the resin and the filler, as well as strong thermal stability. During the molding process, it should enhance fluidity without compromising the final product's properties. Additionally, it should not cause color shifts or negatively impact the mechanical or functional characteristics of the material. Safety is another important factor—ideally, the dispersant should be non-toxic, cost-effective, and easy to handle. Typically, the recommended dosage of dispersant in a masterbatch is around 5% by weight. 2. Types of Dispersant (1) Fatty acid derivatives such as aliphatic amides and esters, including stearic acid amide, can be combined with higher alcohols to improve lubricity and thermal stability. These are usually used at concentrations between 0.3% and 0.8%. They can also serve as lubricants for polyolefins. Another common option is hexenyl bis stearamide (EBS), a high-melting-point lubricant used at 0.5% to 2%. Stearic acid monoglyceride (GMS) and glyceryl tristearate (HTG) are also widely used. Oleic acid-based compounds are typically added at 0.2% to 0.5%. Paraffinic hydrocarbons, like solid paraffin wax with a melting point of 57–70°C, are generally less compatible with resins and have poor dispersibility, so they are used at low levels, typically below 0.5%. (2) Paraffin Wax Paraffin wax is commonly used as an external lubricant. However, it is a non-polar linear hydrocarbon that does not wet metal surfaces effectively, meaning it cannot prevent PVC from sticking to metal walls on its own. It works best when combined with stearic acid or calcium stearate to achieve better synergy. Liquid paraffin has a freezing point ranging from -15°C to -35°C and is often used in extrusion and injection molding processes. Its compatibility with resins is limited, and it is typically added at 0.3% to 0.5%. Excessive amounts may reduce processing efficiency. Microcrystalline paraffin, derived from petroleum refining, has a higher molecular weight and more isomers, with a melting point between 65°C and 90°C. It offers good lubricity and thermal stability but has limited dispersibility. It is usually used at 0.1% to 0.2%, and is best combined with butyl stearate and higher fatty acids. (3) Metal Soaps Metal soaps, which are salts of higher fatty acids, are commonly used in plastic formulations. For example, barium stearate (BaSt) is suitable for various plastics and is typically used at about 0.5%. Zinc stearate (ZnSt) is ideal for polyolefins and ABS, with a recommended dosage of 0.3%. Calcium stearate (CaSt) is often used for general-purpose plastics as an external lubricant, with a dosage range of 0.2% to 1.5%. Other options include cadmium stearate (CdSt), magnesium stearate (MgSt), and copper stearate (CuSt). (4) Low Molecular Waxes Low molecular waxes are oligomers formed through cracking and oxidation of polymers such as polyethylene, polypropylene, or polystyrene. Common types include homopolymer, oxidized homopolymer, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, and low molecular ionomer. Among these, polyethylene wax is the most frequently used. Standard polyethylene wax has an average molecular weight of 1500–4000 and a softening point of around 102°C. Higher molecular weight versions (10,000–20,000) have a slightly higher softening point (106°C). Oxidized polyethylene wax contains ester or soap groups, offering a balanced internal and external lubrication effect for materials like PVC, PE, PP, and ABS. It also improves transparency and overall performance.

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