What are the commonly used surface modification agents for calcium carbonate? how to use?
Calcium carbonate is currently the most used inorganic filler in polymer-based composite materials. However, since the calcium carbonate filler is an inorganic powder and has poor compatibility with organic polymers, it is difficult to evenly disperse when it is directly added to the polymer material, and it will also affect the processing performance and mechanical properties of the material. Therefore, generally, before filling the polymer material It is surface modified.
At present, surface modification has become one of the most important and necessary deep processing technologies for calcium carbonate (including light calcium carbonate, nano-calcium carbonate, and,avy calcium carbonate). The method is mainly chemical coating, supplemented by mechanochemistry; The surface modifier used includes stearic acid (salt), titanate coupling agent, aluminate coupling agent, and then,e like.
1. Stearic acid (salt)
Stearic acid (salt) is the most commonly used surface modifier for calcium carbonate. The modification process can be either dry or wet. Typically wet processes use stearates, such as sodium stearate.
(1) Dry process
The technological process of dry treatment of calcium carbonate with stearic acid: first, dry calcium carbonate to remove moisture (if the moisture content of calcium carbonate is less than 1%, it can not be dried), and then add metered stearic acid on the surface The duration of calcium carbonate powder is completed in the modification machine. When continuous powder surface equipment is used, the material and surface modifier is fedisntinuously and synchronously. Stearic acid can be directly added in solid powder form. The dosage depends on the particle size or specific surface area of the powder, generally calcium carbonate. 0.8%-1.2% of the mass; when surface coating modification is carried out in high-speed mixers, horizontal paddle mixers, and ot, her temperature-controlled mixers, it is generally an intermittent operation. Add fatty acid into the modifier together, stir and mix for 15-60min, and then discharge and pack. The amount of stearic acid is about 0.8%-1.5% of the mass of calcium carbonate, and the reaction temperature is controlled at about 100 °C.
In ordeTohe stearic acid better disperse and act on the calcium carbonate particles uniformly, the stearic acid can also be diluted with a solvent (such as absolute ethanol) in advance. Other additives can also be added in an appropriate amount during modification.
(2) Wet process
Wet modification is the surface modification of calcium carbonate in an aqueous solution. The general process is to saponify stearic acid first, then add it to the calcium carbonate slurry, filter and dry it after a certain time of reaction.
The dispersion of calcium carbonate in the liquid phase is easier than that in the gas phase. In addition, by adding a dispersing agent, the dispersing effect is better, so the effect of calcium carbonate particles and surface modifier molecules in the liquid phase is more uniform. When calcium carbonate particles adsorb stearate, the surface energy decreases. Even if secondary particles are formed after pressure filtration and drying, their agglomeration binding force is weakened, and hard agglomeration will not be formed. its redistributed. Although wet surface modification can also be carried out at room temperature, the reaction time is long. Therefore, surface modification is generally carried out by heating, and the modification temperature is generally about 50-100 °C.
Wet surface modification is generally used for the surface modification of light calcium carbonate and wet ground ultrafine heavy calcium carbonate.
In addition to stearic acid (salt), other fatty acids (esters), such as phosphates and sulfonates, can also be used for surface modification of calcium carbonate. After surface modification of calcium carbonate with a special structure of polyphosphate (ADDP), the surface of calcium carbonate particles is hydrophobic and lipophilic, and the average agglomeration particle size in oil is reduced. The modified calcium carbonate is filled in PVC. Plastic systems can significantly improve the processability and mechanical properties of plastics.
Activated calcium carbonate modified with fatty acid (salt) is mainly used to fill PVC plastics, cable materials, adhesives, inks, coatings, etc.
2. Coupling agent
The coupling agents used for surface modification of calcium carbonate are mainly titanate and aluminate coupling agents, or composite coupling agents. Calcium carbonate (including light calcium carbonate and heavy calcium carbonate) treated with couplina g agent is widely used as filler and pigment for adhesives, inks, coatings, etc., in addition to being used as a functional filler for rigid PVC .
(1)Titanate coupling agent
In ordeToe, the uniformity of the interaction between the titanate coupling agent and calcium carbonate, inert solvents such as liquid paraffin (white oil), petroleum ether, transformer oil, absolute ethanol, etc. are generally used to dissolve and dilute. The dosage of titanatthe e coupling agent depends on the particle size and specific surface area of calcium carbonate, generally 0.5%-3.0%. The modification temperature of calcium carbonate should be as low as possible below the flash point of the coupling agent, generally 100-120°C. The titanate coupling agent and the inert solvent are mixed and added to the high-speed mixer in the form of spray oa r dropwise addition, which can better disperse and mix with the calcium carbonate particles for chemical coating on the surface. If continuous surface modification equipment is used, the titanate coupling agent can also be diluted in advance without a solvent.
Calcium carbonate treated with titanate coupling agent has good compatibility with polymer molecules. At the same time, since the titanate coupling agent can form molecular bridges between calcium carbonate molecules and polymer molecules, it enhances the interaction between organic polymers or resins and calcium carbonate, which can improve the performance of thermopthermoplastic-filledites. Mechanical properties such as impact strength, tensile strength, flexural strength, and elongation. Compared with the untreated calcium carbonate filler or the calcium carbonate treated with stearic acid (salt), the properties of the modified calcium carbonate coated with titanate e coupling agent are obvious.
(2) Aluminate coupling agent
Aluminate coupling agent has been widely used in the surface treatment of calcium carbonate and processing filled plastic products, such as PVC, PP, PE, and fi, ling masterbatches.
Studies have shown that the viscosity of calcium carbonate/liquid paraffin mixed system can be significantly reduced by light calcium carbonate treated with aluminate, which indicates that the modified calcium carbonate has good dispersibility in organic media.
In addition, the surface-modified and activated calcium carbonate can significantly improve the mechanical properties of the CaCO3/PP (polypropylene) blend system, such as impact strength, toughness, etc.
For the same calcium carbonate filler, different coupling agents are used for surface modification treatment, and the effect after filling will be different.
Surface modification of calcium carbonate with polymers can improve the stability of calcium carbonate in organic or inorganic phases (systems). These polymers include oligomers, polymers, and water-soluble polymers such as polymethyl methacrylate (PMMA), polyethylene glycol, polyvinyl alcohol, polymaleic acid, polyacrylic acid, alkoxy styrene A copolymer of styrene sulfonic acid, polypropylene, polyethylene, etc.
The process of coating the modified calcium carbonate on the surface of the polymer can be divided into two types. One is to first adsorb the polymer monomer on the surface of calcium carbonate, and then initiate its polymerization to form a polymer coating layer on the surface; The polymer is dissolved in an appropriate solvent, and then the calcium carbonate is surface-modified, and the solvent is excluded to form a coating as the polymer gradually adsorbs on the surface of the calcium carbonate particles. These polymers are directionally adsorbed on the surface of calcium carbonate particles to form a physical and chemical adsorption layer, which can prevent the agglomeration of calcium carbonate particles, improve dispersibility, and make calcium carbonate have better dispersion stability in applications.