Mineral surface treatments often have their specific application background and application areas. Minerals used as fillers and pigments, such as calcium carbonate, kaolin , mica , quartz , talc , wollastonite, etc., are often mixed into polymers such as plastics, rubber, resins, paints, and coatings. However, because the former is a polar or highly polar hydrophilic mineral, the latter has a non-polar hydrophobic surface, and has poor compatibility with each other. When mixed, it is difficult to uniformly disperse, resulting in a decrease in material properties or a large amount of filling. Therefore, the mineral surface needs to be modified to improve the hydrophobicity of the mineral surface, improve its dispersibility, stability and coverage in the organic matrix, thereby improving the performance of the material or product or reducing the production cost.
Non-metallic mineral surface modified minerals deep processing provides a broad prospect of development and utilization of its research and application of technology has greatly promoted the advancement disciplines of chemistry, materials, mining, etc., to create a huge economic and social benefits. Different types of modified chemicals and modification equipment have been developed, and a new understanding of the mechanism of the modification process has also been made. In the future, new, high-efficiency and low-cost surface modifiers will be further developed; modern analytical testing methods will be used to study the mechanism of interaction between modifiers and mineral surfaces and organic substrates to guide the improvement of modification effects and the development of new composites. material.
I. Classification and mechanism
The surface modification of minerals is mainly achieved by the adsorption and coating of chemical modifiers on the surface of the ore particles. Therefore, chemical modifiers play a decisive role in the surface modification of ore particles. There are many substances that can be used as mineral surface modifiers. This section mainly introduces surface modifiers based on surfactants. Because of the amphiphilic structure, the hydrophilic group can physically and chemically adsorb with the surface of the inorganic filler, and adsorbs on the interface to form a monolayer film with a hydrophobic base facing outward, so that the mineral surface can be modified by hydrophilicity. Becomes hydrophobic. This kind of substance is mainly divided into two categories: one is a common surfactant, mainly including various types of yin, yang and nonionic surfactants. Another reaction type surface active agents such as surfactants and silicon-containing titanium esters, zirconium aluminate coupling agent and the like metal alkoxides. A part of the group in the molecule can react with various functional groups on the surface of the powder to form a strong chemical bond, and the other part can undergo some chemical reaction or physical entanglement with the organic polymer, thereby greatly differentizing the two properties. The materials are firmly combined to create a "molecular bridge" with special functions. Therefore, such surface modifiers are often referred to as coupling agents. Different minerals have different requirements for coupling agents, and their properties mainly depend on the hydrophilic group of the coupling agent.
(a) anionic surfactant
Fatty acid salt surfactants are the earliest and most widely used anionic surface modifiers. The calcium carbonate series products, which are called "Bai Yanhua" in Japan, are examples of successful surface modification with fatty acids.
Inorganic fillers or pigments fatty acid salts commonly used surface modifiers are: oleic acid and its sodium salt, stearic acid and its sodium, ammonium, calcium, zinc and the like salts. In addition to light and heavy calcium carbonate, the modified minerals include wollastonite, attapulgite, and inorganic oxides. The dosage is 0.5% to 3% of the mass of the filler or pigment. When used, it can be directly mixed with inorganic fillers and pigments. It can also be diluted with stearic acid and sprayed on the surface of inorganic filler or pigment. Stir well and then dry to remove water.
There is also a new class of modifiers with good prospects in the carboxylate series - short carbon chain unsaturated carboxylic acids. They contain unsaturated double bonds, have good modification effect on minerals containing alkali metal and alkaline earth metal ions, and are cheaper, have wide sources and good treatment effect, and are a new surface modifier. Commonly used are acrylic acid, crotonic acid, methacrylic acid, cinnamic acid, vinyl acetate, propylene acetate, sorbic acid, maleic acid and other modifiers, minerals containing the above metals such as bentonite , mica, clay, blue asbestos , feldspar, etc. The active metal ions and modifiers on the mineral surface are stably present in the form of ionic bonds, and the stronger the acidity, the easier it is to form ionic bonds, forming a monolayer and encapsulating the mineral surface. On the other hand, since these modifiers all contain unsaturated double bonds, when mixed with the matrix, under the action of residual initiator, heat and mechanical force, the double bond is opened, and a chemical reaction such as grafting and crosslinking occurs with the matrix resin. The bridging effect of the modifier is further improved to achieve the purpose of modification.
Further, polyoxyethylene ether phosphate ester can also be used for surface treatment of inorganic powder, such as talc powder coated surface of alkylphenol ether monophosphate, and the like can be improved with a polypropylene polymer interface Affinity improves the dispersion state of the organic polymer binder and increases the adsorption capacity of the polymer binder to the filler.
(B) Cationic Surfactants Cationic surfactants are mainly used to cover bentonite, sepiolite or smectite-type clay to prepare organic soil. The principle of cation exchange can be used to achieve the purpose of organicization of clay minerals. Dioctadecyl dimethyl ammonium chloride, cetyl trimethyl ammonium bromide, dialkyl methylphenyl dihydrogenated tallow ammonium chloride, coconut oleic methylphenyl ammonium chloride, bromo Cetylpyridine and the like are all commonly used modifiers for the preparation of organic soils at home and abroad. These modifiers may be used singly or in combination, and recent studies have shown that the use of a modifier in combination is better than the use alone.
The preparation of organic soil is relatively simple. After the dry crushed ore powder (Na-based) is fully suspended in deionized water, the modifier is added in an appropriate ratio, mixed well, and then allowed to stand overnight at room temperature or heated to about 40 ° C. After lh, filter and dry.
(III) Nonionic Surfactant The action mechanism of the nonionic surfactant on the filler is similar to that of various coupling agents. They can interact with the filler and polymer base separately to improve the compatibility and uniformity of the system, impart toughness and fluidity to the system, reduce the viscosity of the system, and improve processability. If the surface modification of wollastonite powder with high-grade fatty alcohol polyoxyether is shown, the results show that the filling performance of wollastonite in PVC cable material is greatly improved. [next]
(4) Silicon-containing surfactants
This is the earliest developed and most widely used coupling agent. In Japan, the silane-based surface modifier accounts for 80% of the coupling agent. Such surface modifiers have both active hydrophobic functional groups having affinity or reactivity with polymer molecules, such as amino groups, mercapto groups, vinyl groups, epoxy groups, amide groups, aminopropyl groups, etc., and can be combined with inorganic substances. A hydrophilic group such as an alkoxy group, a halogen group, an acyloxy group or the like which is easily hydrolyzed. They bind to the surface of the particle by some reaction with the surface of the inorganic mineral.
Due to the high selectivity of the silane to the filler and its high price, the application is limited. They have good coupling effect on silica , glass, clay, silica, etc. with active hydroxyl groups, and generally have effects on talc, alumina, mica and aluminum hydroxide, and calcium carbonate and titanium dioxide without free acid. , graphite, boron nitride, etc. are poor or no effect.
1. Mechanism of action The mechanism of action of silane modifiers on inorganic substances mainly includes chemical reaction, physical adsorption, hydrogen bond formation and reversible equilibrium. Each has its own characteristics and has not yet been determined. Relatively practical, a good explanation of the interaction between the silane modifier and the inorganic material is the Arkles theory.
According to this theory, the silane first contacts the moisture in the air, and a hydrolysis reaction occurs. Then, the hydroxyl groups on the surface of the particles are condensed and dehydrated with the hydrolyzate of the silane, and the silanes are polycondensed into a low polymer, and the hydroxyl groups on the low polymer and inorganic surfaces form hydrogen. The bond is dried by heating to cause a dehydration reaction to convert a hydroxyl group having a high polarity on the surface of the particle into a lower polarity ether bond (covalent bond), so that the surface of the particle is covered with an alkyl group (—R) to form an interface region.
The interfacial region typically forms only one ether bond on the surface of the substrate via each Si of the organosilane, and the remaining two silanols are either bonded to the silicon atoms of other coupling agents or present in free form, as shown in FIG.
Fig.1 Chemical reaction of organosilane modifier on surface treatment of inorganic minerals
It can be seen that the combination of silane and inorganic minerals starts from the action of the oligomer of silane and the hydroxyl group on the surface of the mineral. Therefore, the effect of silane on the surface of the hydroxyl group-containing particles is remarkable, otherwise it is difficult to function, which has been proved by experiments. . Modern surface analysis techniques (such as infrared spectroscopy) have demonstrated that silane modifiers on particle surfaces (such as glass fibers) have multilayer structural features that include chemical adsorption of chemically bonded silane polymers and oligomers of silanes. Physical adsorption.
According to the surface energy theory, the mineral filler is a high-energy surface. In order to improve its compatibility with the polymer matrix, the surface energy of the matrix must be reduced by the hydrophobic group (R) of the coupling agent. The theory and practice prove that: when the R group contains a polar group (such as -NH2, -OH and an epoxy group), the modified matrix has a higher surface energy; if the -R group contains an unsaturated double bond, The substrate can have a medium surface energy; if -R is a saturated hydrocarbon bond, the surface energy can be minimized. Due to the additive nature of the dispersive forces, the long chain hydrocarbyl shorter chain hydrocarbyl groups have a higher surface energy. When the coupling agent and the resin matrix match, the resin liquid can wet the matrix, which is the most basic thermodynamic condition for the preparation of a good composite. Therefore, it is an important problem in the composite process to select different coupling agents to treat the ore particles and change the surface energy and the wetting, adsorption and bonding properties of the resin.
2. Structure and Properties When the hydrophobic group R of the silicon-containing surfactant is a vinyl group and a methacryloyl group, they are particularly effective for unsaturated polyesters and acrylic resins; when R is an epoxy group, the epoxy resin The effect is particularly good, and is also suitable for unsaturated resin; when R contains amino group, it can react with epoxy resin and polyurethane, and also has a catalytic effect on curing of phenolic resin and melamine resin, so it is suitable for epoxy, phenolic, melamine, Resin such as polyurethane; when R contains sulfhydryl groups, it has the best coupling effect on sulfur vulcanized rubber, so it is the most widely used variety in the rubber industry. [next]
The hydrophilic group of the silane modifier is also called a hydrolyzable group. When treated, the hydrophilic group X decomposes with water to form a reactive group silanol (Si-OH), and then passes through the silanol and then the inorganic mineral. The hydroxyl groups on the surface of the filler react to form a hydrogen bond and condense into a -Si-O-M covalent bond (M represents the surface of the inorganic filler). At the same time, the silanol of each molecule of the silane on the surface of the filler is associated with each other to form a network-like cover film, and the inorganic filler or pigment is organicized.
When X is -OCH 3 and -OC 2 H 5 , the hydrolysis rate is slow, and the hydrolyzed product alcohol is neutral, so the surface can be modified with water as the medium. The volume of ethoxy group is larger than that of methoxy group. The solubility of the silane in water is small, and an ethoxy group-containing silane coupling agent is currently used. In addition, -OC 2 H 4 OCH 3 is also used as the X group, which not only retains its hydrolyzability, but also improves water solubility and hydrophilicity, and is more convenient in application.
In order to meet the needs of the continuous development of new materials, a number of new silane coupling agents with better performance have been developed at home and abroad in recent decades. Its main features are as follows:
(1) Epoxy type Compared with the same type of products, the new product has a longer spacer chain, so it has application relaxation, and has excellent heat resistance and water resistance due to the absence of ether-oxygen bond. The main brands are X-12-692 and X-12-699.
(2) Isocyanate type Since the molecule contains a highly reactive isocyanate, it can be used for a resin to improve its bonding property. The main brands are KBM-9007, KBE-9007, KBM9207 and KBME-9207.
(3) Chelating type This silane coupling agent molecule has a β-ketoester structure and has the ability to coordinate with a metal, and is desirably used for metal ion localization or as a positioning metal catalyst such as X-12-715.
(4) Fluorine-containing type Since a different amount of fluorine is introduced into the hydrophobic group, it can impart lubricity, water repellency and antifouling property to the surface of the material, and has a strong affinity for the fluorine-containing resin, and it is desired to use a fluorine-containing resin to bond the primer layer. Use, such as KBM-7103, KBM-7803.
(5) Ethylene type Compared with the common vinyl type, the new product has different spacer chain lengths or different functional groups. The purpose is to impart room temperature curability, adhesion, weather resistance and solvent resistance to the organic resin. The main brands are KBM-1063, 1103, 1203, 1303, 1403, 5102, 5103 and 5403.
(6) a-functional silane The silane coupling agent currently used at home and abroad is a γ-functional group, that is, three methyl groups are separated between a silicon atom and an organic functional group. It is generally believed that the thermal stability of such a coupling agent is better than that of the a-functional group, but the latter has a simple synthesis method, easy availability of raw materials, and good thermal stability. If strong alkali medium is avoided during synthesis and use, stability can also meet the requirements, such as NS and Nanda-42, 73, 24.
(7) Polymeric silanes such as MMCA in Japan:
Wherein X is an alkoxysilyl group; Y is a reactive organic functional group such as an epoxy group or a hydroxyl group; and Z is a group which is compatible with an organic substance such as a polyether or an alkyl group. Such modifiers can change the structure as needed to give it some unique properties. Therefore, in addition to the function of the conventional silane coupling agent, it also has the function of an inorganic-organic interface bonding aid, which imparts unique heat resistance, wear resistance, corrosion resistance, water repellency and the like to the composite silicone.
(5) Metal alkoxide modifiers
Such surface modifiers include titanates, aluminates, stannates , zirconates, zirconium aluminates, and phosphates and borates. Among them, titanate and aluminate are widely used.
1. Mechanism of action (1) Role of modifiers and inorganic minerals The mechanism of action of metal alkoxides and inorganic minerals is far less than that of silane-based modifiers. In general, titanium, aluminum-based modifiers and minerals act like silanes, ie, the hydrophilic end of the modifier interacts with the hydroxyl groups on the mineral surface. For minerals that do not contain hydroxyl groups (such as calcium carbonate), Solomon et al. believe that Ca 2+ Ca 3 2- on the surface of calcium carbonate can react with water attached to its surface and hydrolyze to produce a layer that is alkaline. Hydrophilic hydroxyl-containing surface. [next]
The hydroxyl groups on the surface are bonded to the pro-organic end of the titanium-based (or aluminum-based) modifier molecule to form modified calcium carbonate particles.
The surface of the wollastonite treated with the titanate modifier KRTTS was determined by thermogravimetric analysis. The KRTTS slowly started heating reduction around 150 °C, while the heating reduction of the wollastonite treated with KRTTS was from It started near 230 °C, which indicates that the KRTTS on the wollastonite surface is different from the original KRTTS, which proves that the KRTTS and wollastonite surface bond is very strong. Differential thermal analysis of the calcium-based modifier DL-411-A treated calcium carbonate also showed that the adhesion of the aluminum-based modifier to the surface of the calcium carbonate is not only a physical effect but also a chemical action. Calver et al. found through the X-ray photoelectron spectroscopy that titanium is indeed present on the surface of the titanate-modified filler.
(2) The action of the modifier and the organic matrix Unlike the silane modifier, the metal alkoxide and most of the resin matrix are subjected to van der Waals forces. When the particles of the surface-attached organic group are blended with the resin, these organic groups (the pro-organic end) and the resin are entangled or crosslinked, thereby achieving the purpose of reinforcing and modifying the resin. In practical applications, a highly hydrophobic modifier should be used for the highly hydrophobic resin. Conversely, a less hydrophobic modifier should be used. The carboxylic acid type in the titanium-based modifier has good hydrophobicity, so most of the polyolefins having high hydrophobicity in the resin are KRTTS, and moderately wettable acrylic resins, PVC and epoxy resins are mostly made of phosphite and coke. Phosphate type. Polyamides having a high hydrophilicity are mostly composed of an amino group-containing titanate KR44, and since the amino-type organic functional group has an amino group at the terminal, it has high hydrophilicity. This rule also applies to other types of modifiers.
2. Titanate type Titanate type modifier is a new type of product developed by Kenrich Petrochemical Company in the 1970s. It has a unique structure and has dozens of varieties so far. It is a widely used inorganic filler. And surface modifiers such as pigments.
The general formula for such modifiers is as follows:
(RO) m —Ti—(OX—R ′ —Y) n
Wherein R—the short carbon chain alkyl group;
(RO) m — the group bound to the surface of the modifier and the mineral, m is the number of the group 1 ≤ m < 4;
Ti——the core of the modifier molecule, TiO- is a transesterification and exchange functional group, which is the organic skeleton of titanate, exchanges with the carboxyl group of the polymer, and functions as an ester group and a transalkylation reaction. The combination of titanium and oxygen is relaxed, and the organic acid in the system is easily released as a catalyst or a slowing agent to affect the reaction;
X———C, N, P, S and other elements;
R ′ ———Long carbon chain alkyl, often having a carbon number of 12-18. It entangles with the chains of the polymer and combines them with the force of the molecules to transfer stress and improve impact strength, shear strength and elongation. In addition, long-chain hydrocarbons can also change the surface energy of minerals, reduce the viscosity of the system, and make high-filled polymers also show better melt fluidity, so this coupling agent is especially suitable for thermoplastic resins such as polyolefins;
Y—amino group, hydroxyl group, double bond, epoxy group or terminal hydrogen atom. When these reactive groups are attached to the organic skeleton of titanium, the modifier and the organic polymer can be chemically reacted, and the mineral and the organic matrix are combined by a coupling agent;
N—— The number of functional groups, when n>2, is a polyfunctional titanate, but m+n<6.
Depending on the molecular structure and the configuration of the mineral surface coupling agent, such modifiers are of the following types.
(1) Monoalkoxy type This type has the widest variety and has various functional groups and characteristics. It has a wide range of applications and moderate price. It is widely used in plastics, rubber, coatings and adhesives. In addition to the monoalkoxy type containing ethanolamine and pyrophosphate groups, most varieties (such as hydroxy acid type TTS) have poor water resistance and are only suitable for the treatment of dry fillers and pigments such as calcium carbonate, hydrated alumina, titanium dioxide, etc. And pyrophosphate type, such as KR-38S, is suitable for systems with high moisture content, such as talc, kaolin and other minerals, which is divided by the monoalkoxy group and the hydroxyl group on the surface of the mineral, and the pyrophosphate group is also It can be decomposed to form a phosphate group and combines a part of water, so it has good water resistance and is suitable for minerals with a large moisture content.
(2) Chelating type Chelating type titanate modifier has good hydrolytic stability and is suitable for high temperature and high water content filling and pigment surface treatment. There are two types of 100 and 200 types depending on the chelate ring. Chelating Form 100 contains an oxyacetic acid chelating group and Chelating Form 200 contains an ethylene glycol chelating group. Hydrolytic stability type 100 is better than type 200, and system viscosity drop type 200 is more effective than type 100.
Since the chelating type titanate has good water resistance, it can be dissolved in an organic solvent to coat the powder material, or the powder material can be coated in the aqueous phase. However, it is mostly insoluble in water and can usually be emulsified and dispersed in water by a co-solvent, a surfactant or high-speed stirring. The titanate containing a phosphate group, a pyrophosphate group, and a sulfonic acid group can be quaternized with an amine reagent and dissolved in water. When the calcium carbonate powder is modified with a KR-138S chelating modifier, 1 part of KR-138S and 0.5 part of triethylamine are mixed to prepare a quaternary ammonium salt, and dispersed into 600 parts of water, and then 200 parts are added. Calcium carbonate, fully stirred, dehydrated, dried. [next]
(3) Coordination-coordinated titanate coupling agent is to avoid side reactions of tetravalent titanate in some systems, such as transesterification in polyester and reaction with hydroxyl groups in epoxy resin Developed in a variety of minerals and polymers, the effect on minerals is similar to monoalkoxy titanates. The titanium atom is converted from a tetravalent bond to a hexavalent bond, which reduces the reactivity of the titanate and improves the water resistance, and can be used in a solvent-based paint or a water-soluble paint. Most of these modifiers are insoluble in water. They can be directly pulverized and dispersed in water by high-speed grinding. They can also be dispersed in water by adding a common surfactant or a hydrophilic cosolvent to surface-treat the filler and pigment.
(4) Quaternary ammonium salt water-soluble type The quaternary ammonium salt water-soluble coupling agent is obtained by reacting a phosphate group, a pyrophosphate group, and a sulfonic acid group chelating titanate with an amine. It has the advantages of wide application and ease of use.
The amount of the titanate modifier is 0.5% to 3% of the mass of the mineral material. In the course of use, special attention should be paid to the following problems:
1 Strictly control the temperature of use to prevent decomposition of titanate.
2 Titanate modifiers should be avoided as much as possible with surface-active additives because they interfere with the coupling reaction at the titanate interface. If these additives are necessary, they should be in the filler, coupling agent and polymerization. These additives are added after the mixture is thoroughly mixed.
3 Most titanates undergo transesterification with ester plasticizers to varying degrees. Therefore, the order of addition should be noted that first contact with these substances to avoid side reactions and failure.
4 Note that the dispersion is uniform. Since the titanate coupling agent is generally used in an amount of 0.5% to 3%, it is not easy to be uniformly mixed with a large amount of filler or pigment, and may be uniformly dispersed and mixed by a suitable amount of a diluent and a spray.
5 pay attention to the combination of technology to improve the coupling effect. For example, the combination of titanate and silane coupling agent can produce a synergistic effect.
3. Aluminate-based aluminate is a new surface modifier developed by Fujian Normal University in the 1980s. Its cost is not only lower than that of titanium, but also non-toxic and thermal stability. Other properties It is similar to titanium, superior to stearic acid, and has a wide application range. It can be used to improve the dispersibility of various fillers, pigments, and the vividness of pigments, and enhance gloss and adhesion. If the product is compounded with titanic acid or stearic acid, a synergistic effect is produced, which further improves product performance and reduces costs.
The aluminate modifier has the general formula RO-AI-(OR') 2 , wherein R and R' are hydrocarbyl groups, RO- is a pro-inorganic end, AI is a central atom, and -OR' is a pro-organic end.
At present, such modifier brands produced by Fujian Normal University and Jiangsu Tiansu Chemical Plant are DL-412, DL-411-A, DL-881, DL-482, NC-1, DL-812, etc. In addition, macromolecular aluminate is synthesized, which has surfactant properties and can be used as a mineral surface modifier. It is expected to be used as a blending solubilizer and a polymer phase transfer catalyst for preparing high polymer alloys.
4. Zirconium aluminate coupling agent Zirconium aluminate is a type of modifier developed by Cavedon Chemical Company in the early 1980s under the trade name Cavco Mod. Zirconium aluminate modifiers have better performance and are less expensive, and in many cases can replace silane modifiers. The zirconium aluminate is synthesized by using hydrated zirconium oxychloride, aluminum chlorohydroxide, propylene alcohol, carboxylic acid or the like as a raw material. Its molecular structure is shown in Figure 2. In the formula, X is an organic functional group.
Figure 2 Molecular structure of Cavco Mod zirconium aluminate coupling agent
Since the zirconium aluminate modifier molecule contains two inorganic moieties (zirconium and aluminum) and one organic functional ligand, a significant feature of the zirconium modifier compared to the silicone modifier is that The specific gravity of the inorganic part of the molecule is generally 57.7%~75.4%, while the silanes are less than 40% except A-100. Thus, zirconium modifier molecules have more inorganic reaction sites than silanes and enhance the interaction with inorganic fillers or pigment surfaces.
The zirconium aluminate-based modifier forms a covalent bond with the hydroxylated surface by condensation of zirconium hydroxide and aluminum hydroxide groups. More importantly, it forms a complex of oxygen bridges with the metal surface. According to the metal content in the molecule (ie, the ratio of the inorganic characteristic portion) and the nature of the organic ligand, the zirconium aluminate can be classified into seven types, which are respectively suitable for filling polyolefin, polyester, epoxy resin, nylon, acrylic. Surface treatment of inorganic fillers such as resins, polyurethanes, and synthetic rubbers.
Zirconium-aluminum modifiers are all liquid. When used, they can be directly added to the slurry of water or non-aqueous slurry of the filler, and mixed by high-speed shear mechanical stirring; or the modifier can be dissolved into the solvent or directly added The matrix resin is further compounded with an inorganic mineral filler or the like.
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