- The general principle of selecting silane coupling agent
The hydrolysis rate of the silane coupling agent is taken from the silicon functional group Si-X, while the reactivity with the organic polymer is taken from the carbon functional group CY. Therefore, for different substrates or processing objects, it is very important to choose a suitable silane coupling agent. The selected method is mainly pre-selected through experiments and should be carried out on the basis of existing experience or rules. For example, in general, unsaturated polyesters mostly use silane coupling agents containing CH2=CMeCOO, Vi and CH2-CHOCH2O-; epoxy resins mostly use CH2-CHCH2O and H2N-silane coupling agents; phenolic resins mostly use Use H2N- and H2NCONH-silane coupling agents; polyolefins use vinyl silanes; use sulfur-vulcanized rubber to use hydrocarbon-based silanes. The bonding between dissimilar materials can be affected by a series of factors, such as wetting, surface energy, interface layer and polar adsorption, the effect of acid and alkali, interpenetrating network and covalent bond reaction, etc. Therefore, pre-selection by test alone is sometimes not accurate enough, and the composition of the material and its sensitivity to the reaction of the silane coupling agent need to be considered comprehensively. In order to improve the hydrolytic stability and reduce the cost of modification, trihydrocarbyl silane can be mixed into the silane coupling agent; for difficult-to-adhesive materials, the cross-linked polymer of the silane coupling agent can also be shared. When the silane coupling agent is used as a tackifier, it is mainly achieved by forming chemical bonds and hydrogen bonds with the polymer; wetting and surface energy effects; improving polymer crystallinity, acid-base reaction, and formation of interpenetrating polymer networks. of. Viscosity mainly revolves around three systems: namely (1) inorganic material to organic material; (2) inorganic material to inorganic material; (3) organic material to organic material. For the first type of bonding, it is usually required to bond inorganic materials to polymers, so the reactivity of Y in the silane coupling agent and the functional groups contained in the polymer should be given priority; the latter two belong to the bonding between materials of the same type , so the anti-hydrophilic polymer of the silane coupling agent itself and the silane coupling agent selected when the inorganic material requires viscosity increase.
- How to use
- Calculation of the amount of silane coupling
agent The number of reactive sites per unit specific surface area of the treated object (matrix) and the thickness of the surface covered by the silane coupling agent are the key factors that determine the amount of coupling agent required for the siliconization of the substrate surface. In order to obtain monolayer coverage, the Si-OH content of the substrate needs to be determined first. It is known that the Si-OH content of most siliceous substrates is 4-12/μ㎡, so when uniformly distributed, 1mol of silane coupling agent can cover about 7500m2 of the substrate. The silane coupling agent with multiple hydrolyzable groups will somewhat affect the accuracy of calculation due to self-condensation reaction. If Y 3SiX is used to treat the substrate, the monolayer coverage consistent with the calculated value can be obtained. However, Y 3SiX has no practical value because of its high price and poor coverage of hydrolysis resistance. In addition, the number of Si-OH on the surface of the substrate also changes with the heating conditions. For example, under normal conditions, the Si-OH number is 5.3/μ㎡ silicon substrate, after heat treatment at 400°C or 800°C, the Si-OH value can be reduced to 2.6/μ㎡ or <1/μm ㎡. On the contrary, if the substrate is treated with hot and humid hydrochloric acid, high Si-OH content can be obtained; if the surface of the substrate is treated with alkaline detergent, silanol anions can be formed. The wettable area (WS) of silane coupling agent refers to the area (㎡/g) that 1g of silane coupling agent solution can cover the substrate. If it is related to the surface area value (㎡/g) of the silicon-containing substrate, the amount of silane coupling agent required for monomolecular layer coverage can be calculated. Taking filler as an example, the silane coupling agent W (g) required to form a monomolecular layer on the surface of the filler is proportional to the surface area S (㎡/g) of the filler and its mass, and is proportional to the wettable area WS of the silane ( ㎡/g, which can be checked from Table 1) is inversely proportional. Accordingly, the formula for calculating the amount of silane coupling agent is as follows: amount of silane (g) = surface (S) value of some common fillers is shown in Table 1.
Table 1. Specific surface area (S) of common
3.5 2.6 150-250
In addition, when using a silane coupling agent to treat the filler, it is also necessary to determine whether the water content of the filler can meet the needs of the hydrolysis reaction of the silane coupling agent. Table 2 lists the minimum amount of water required for the hydrolysis reaction of certain silane coupling agents.
Table 2 Minimum amount of water required for silane hydrolysis reaction
Silane coupling agent Water requirement for hydrolysis of 1g silane/g
CIC 3 H 6 Si(OMe) 3 0.27
CH 2 -CHOCH 2 OC 3 H 6 Si(OMe) 3 0.23
ViSi(OEt) 3 0.28
ViSi(OC 2 H 4 OMe) 3 0.19
HSC 3 H 6 Si(OMe) 3 0.28
CH 2 =CMeCOOC 3 H6 Si(OMe) 3 0.22
H 2 NC 3 H 6 Si(OEt) 3 0.25
If you do not know the specific surface area of the filler, you can first treat the filler with a 1% (mass fraction) concentration of silane coupling agent solution, and change the concentration for comparison to determine the applicable concentration.
Surface treatment method
This method uses a silane coupling agent to link the two interfaces of inorganic substances and polymers together to obtain the best wetting value and dispersibility. The surface treatment method needs to make the silane coupling agent acid into a dilute solution to facilitate full contact with the surface to be treated. Most of the solvents used are water, alcohol or water-alcohol mixture, and water without fluoride ions, cheap and non-toxic ethanol and isopropanol are suitable. Except for aminohydrocarbyl silane, solutions prepared from other silanes need to add acetic acid as a hydrolysis catalyst, and adjust the pH value to 3.5-5.5. Long-chain alkyl and phenylsilanes are not suitable for use as aqueous solutions due to their poor stability. The hydrolysis process of chlorosilane and acetoxysilane will be accompanied by severe condensation reaction, and it is not suitable for making aqueous solution or hydroalcoholic solution. For silane coupling agents with poor water solubility, 0.1%-0.2% (mass fraction) of non-ionic surfactants can be added first, and then add water to process into water emulsion for use. In order to improve the economic benefit of the hydrolytic stability of the product, a certain proportion of non-carbon functional silane can also be mixed into the silane coupling agent. When dealing with difficult-to-bond materials, mixed silane coupling agents or carbon-functional siloxanes can be used. After preparing the treatment solution, it can be treated by dipping, spraying or brushing. Generally speaking, bulk materials, granular materials and glass fibers are mostly treated by dipping; powder materials are mostly treated by spraying; if the surface of the substrate needs an overall coating, it is treated by brushing. Several specific processing methods are introduced below.
(1) Alcohol-aqueous solution treatment method using silane coupling agent The process
of this method is simple. First, 95% EtOH and 5% H 2 O are used to make an alcohol-aqueous solution, and AcOH is added to make the pH 4.5-5.5. Add silicon-taste coupling agent under stirring to make the concentration up to 2%. After hydrolysis for 5 minutes, a hydrolyzate containing Si-OH will be generated. When using it to treat the glass plate, it can be immersed in it for 1-2min under a little agitation, taken out and rinsed twice in EtOH, after drying, move it into an oven at 110°C for 5-10min, or at room temperature and relative humidity < Dry at 60% for 24 hours to get the product. If aminohydrocarbyl silane coupling agent is used, it is not necessary to add HOAc. However, the alcohol-water solution treatment method is not suitable for chlorosilane-type coupling agents, which will undergo polymerization in alcohol aqueous solution. When treated with a 2% concentration of trifunctional silane coupling agent solution, a coating with a thickness of 3-8 molecules is mostly obtained.
(2) Treatment with aqueous solution of silane coupling agent This method is mostly used in
industrial treatment of glass fibers. The specific process is to dissolve the alkoxysilane coupling agent in water first, and make it into a 0.5%-2.0% solution. For silanes with poor solubility, 0.1% non-ionic surfactant can be added to water to prepare water emulsion, and then AcOH can be added to adjust the pH to 5.5. The glass fibers are then treated by spraying or dipping. After taking it out, solidify at 110-120°C for 20-30 minutes to obtain the product. Because the stability of the aqueous solution of silane coupling agent varies greatly, for example, the aqueous solution of simple alkylalkoxysilane can only be stable for several hours, while the aqueous solution of ammonia hydrocarbon silane can be stable for several weeks. Since long-chain alkyl and aryl silane aqueous solutions are only stable for several hours, ammonia-silicone aqueous solutions are stable for several weeks. This method cannot be used due to the low solubility parameters of long-chain alkyl and alkyl silanes. When preparing silane aqueous solution, it is not necessary to use deionized water, but water containing fluoride ions cannot be used.
(3) Treatment with a silane coupling agent-organic solvent solution When using a silane coupling agent solution
to treat the substrate, the spray method is generally used. Before processing, it is necessary to master the amount of silane and the water content of the filler. Prepare the coupling agent into a 25% alcohol solution first, then put the filler into a high-speed mixer, and pump in a fine mist of the silane coupling agent solution under stirring. The amount of the silane coupling agent is about the mass of the filler 0.2%-1.5%, it can be finished after 20 minutes of treatment, and then dried by dynamic drying method. In addition to alcohols, ketones, esters and hydrocarbons can also be used as solvents, and formulated to a concentration of 1%-5% (mass fraction). In order to hydrolyze or partially hydrolyze the silane coupling agent, a small amount of water needs to be added to the solvent, and even a little HOAc can be added as a hydrolysis catalyst. Dry and solidify at 80-120°C for several minutes to obtain the product. The powder filler is treated by spraying method, and the stock solution of silane coupling agent or its hydrolyzate solution can also be used. When dealing with metal, glass and ceramics, it is advisable to use 0.5%-2.0% (mass fraction) concentration of silane coupling agent alcohol solution, and use methods such as dipping, spraying and brushing, etc., according to the shape and performance of the substrate, It can be dried and solidified immediately, or kept at 80-180°C for 1-5 minutes to achieve dryness and solidification.
(4) Treatment with silane coupling agent hydrolyzate
That is, silane is firstly hydrolyzed by controlled hydrolysis and used as a surface treatment agent. This method can obtain better treatment effect than pure silane solution. It dries and cures without further hydrolysis.
- Integral blending method
Integral blending method is to mix the stock solution of silane coupling agent into resin or polymer before filler is added. Therefore, it is required that the resin or polymer should not react with the silane coupling agent prematurely, so as not to reduce its viscosity-increasing effect. In addition, before the material is cured, the silane coupling agent must migrate from the polymer to the surface of the filler, and then complete the hydrolytic condensation reaction. For this reason, metal carboxylate can be added as a catalyst to accelerate the hydrolysis condensation reaction. This method is particularly convenient and effective for fillers that are suitable for surface treatment with silane coupling agents, or for systems where resin and fillers need to be mixed and stirred before molding, and can also overcome some shortcomings of filler surface treatment methods. Someone used various resins to compare the advantages and disadvantages of the blending method and the surface treatment method. It is believed that in most cases, the effect of the blending method is inferior to that of the surface treatment method. The action process of the blending method is that the silane coupling agent migrates from the resin to the surface of the fiber or filler, and then interacts with the surface of the filler. Therefore, after silane coupling is incorporated into the resin, it must be placed for a period of time to complete the migration process, and then be cured to obtain better results. It is also theoretically speculated that the migration of silane coupling agent molecules to the filler surface is only equivalent to the amount of monomolecular layer formed on the filler surface, so the amount of silane coupling agent only needs to be 0.5%-1.0% of the resin mass. It should also be pointed out that in the composite material formula, when using additives with good compatibility with the filler surface and low molar mass, special attention should be paid to the order of feeding, that is, adding the silane coupling agent first, and then adding the additives, in order to obtain better Good result.
The following mainly introduces the silicon coupling agent and its application in composite materials.
1 Silane coupling agent
Chemical structural formula: RnSiX4-n
R: is a non-hydrolyzable organic functional group that can be combined with a high molecular weight polymer. Can be: methyl, vinyl, amino, epoxy, mercapto, acryloxypropyl, etc.;
X: It is a hydrolyzable group, which can be hydrolyzed when encountering aqueous solution, moisture in the air or moisture adsorbed on the surface of inorganic substances, and has good reactivity with the surface of inorganic substances. It can be: alkoxy, aryloxy, acyl, chloro, etc. Among them, the most commonly used are methoxy and ethoxy.
Note: The inorganic end reacts with the inorganic interface after hydrolysis, and the organic end interacts with the organic interface, thus improving the interaction between the components of the composite material
(1) The X group is hydrolyzed into a hydroxyl group;
(2) The hydroxyl group and the hydroxyl group existing on the surface of the inorganic substance form a hydrogen bond or dehydrate into an ether bond;
(3) The R group is combined with organic matter.
2 Mechanism of action in composite materials
Wetting Effect and Surface Energy Theory
In 1963, when ZISMAN reviewed the known aspects of surface chemistry and surface energy related to adhesion, he concluded that in the manufacture of composite materials, good wetting of the adherend by liquid resin is of paramount importance, If complete wetting can be achieved, then physical adsorption of the resin to the energetic surface will provide a bond strength higher than the cohesive strength of the organic resin.
deformable layer theory
In order to alleviate the interfacial stress caused by the difference in thermal shrinkage between the resin and the filler when the composite material is cooled, it is hoped that the resin interface adjacent to the treated inorganic substance is a flexible deformable phase, so that the toughness of the composite material maximum. The inorganic surface treated with the coupling agent may preferentially absorb a complexing agent in the resin, and the uneven curing of the interphase region may result in a much thicker multimolecular layer than the coupling agent between the polymer and the filler. Flexible resin layer. This layer is called a deformable layer, which can relax the interfacial stress and prevent the expansion of interfacial cracks, thus improving the bonding strength of the interface and improving the mechanical properties of the composite material.
constraint layer theory
Contrary to the deformable layer theory, the constrained layer theory believes that the resin in the inorganic filler region should have a modulus between the inorganic filler and the matrix resin, and the function of the coupling agent is to “tighten” the polymer structure. ” in the interphase area. From the point of view of the performance of the reinforced composite material, in order to obtain the maximum adhesion and hydrolysis resistance, a constrained layer is required at the interface.
As for the titanate coupling agent, its combination with organic polymers in thermoplastic systems and filler-containing thermosetting compounds is mainly based on the compatibility and mutual entanglement of long-chain alkyl groups, and forms a copolymer with inorganic fillers. price key. The above hypotheses all reflect the coupling mechanism of the coupling agent from different theoretical aspects. In the actual process, it is often the result of several mechanisms working together.
3 Application in composite materials
resins Inorganic fillers and inorganic reinforcing materials combined with thermosetting resins are the most widely used composite materials, and the application of silane coupling agents in this area is also the earliest and most mature.
Table 1 Commonly used silane coupling
agents Chemical name
PR-1003 Vinyltrimethoxysilane KBE
KBE-9007 γ-Isocyanate Propyl Triethoxysilane
PR-5103 (A-1310) Acryl Propyl Trimethoxy Silane
PR-903 (PR-550, A-1110) γ-Aminopropyl Triethoxy Silane
PR- 603 (A-1120) N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane
PR-403 (PR-560 , A-187) γ-glycidyloxypropyltrimethoxysilane
PR-503 (PR-570, A-175,) γ-methacryloxypropyltrimethoxysilane PR
-803 (PR- 580, A-189) γ-Mercaptopropyltrimethoxysilane
PR-703 (A-143) γ-Chloropropyltriethoxysilane
4 How to use silane coupling agents There are two basic ways
to use silane coupling agents. Silanes can be used for surface treatment of inorganic materials before they are mixed with resins, or silanes can be added directly to organic resins.
Surface Treatment of Inorganic
Materials There are two general methods that can be used to prepare the surface of inorganic filler materials before inorganic materials are added to organic materials.
Wet method: mixing inorganic material slurry with silane coupling agent diluent. By mixing inorganic material slurry, a highly uniform and fine inorganic material surface treatment can be obtained.
Dry method: such as high shear, high speed mixer is used to disperse the silane coupling agent into the inorganic material. Silanes are generally used pure or in concentrated liquid form.
The wet method is compared to the dry method, which is more often suitable for large-scale production, processes a large amount of fill material in a relatively short period of time and generates relatively little mixed waste. It’s just that this method is more difficult to get a uniform treatment.
Addition to Organic
Materials Compared to inorganic surface treatment methods, the addition of silanes to organic materials is more widely used in industry because of its excellent processing efficiency, although it may be more difficult. There are two general methods.
Integral Mixing Method
This method involves simple agitation of the silane coupling agent with a composite formulation consisting of inorganic and organic materials mixed together.
In this method the silane coupling agent is first added to a small amount of organic resin material to form a so-called masterbatch. Usually in the form of pellets or large pellets, when producing synthetic materials, in pellets or form-sized pellets, when producing synthetic materials, the masterbatch can be easily added together with organic material pellets.
Preparation of silane coupling agent solution
We know that when silane coupling agent is used, the silane coupling agent solution needs to be diluted. The preparation method of these solutions is as follows:
Silane is usually diluted with water to a concentration of about 0.1~2%. If silane is insoluble in water, it is recommended to use 0.1 ~2.0% acetic acid aqueous solution or ethanol aqueous solution (acetic acid, ethanol, water together) is used in combination, acetic acid is used to control the hydrolysis rate, and the adjustment of pH value greatly affects the stability of silanol.
(1) Add acetic acid to water to prepare an aqueous solution with a final concentration of 0.1-2%. If the silane is more soluble, a lower concentration of acetic acid solution is recommended. For aminosilanes, no acetic acid needs to be added.
(2) Add the silane coupling agent dropwise to the aqueous acetic acid solution and mix until the final concentration is 0.1~2.0%. Slowly add the silane dropwise and stir the aqueous solution rapidly to prevent gel formation.
(3) After adding silane, continue to vibrate for 30-60 minutes until the solution becomes completely transparent, indicating that silane has been completely hydrolyzed.
(4) Subsequent filtration if required. Filtration is recommended if solid impurities are present. If the silane solution is used continuously, it is recommended to use a sieve below 0.5μ for circulation filtration.
(5) The stability of each silane coupling agent is shown in Table 3. The alkylmethoxysilane functional group reacts with water to form an unstable silanol functional group, which quickly condenses to form a siloxane structure. Silanols are generally unstable in the presence of water, but are more stable in weak acid solutions. Aminosilanes are an exception because the amino functionality helps the silane become more stable in aqueous solution. Table 3 gives information on the aqueous solutions of several products and their most stable pH values.
The stability of table 3 silane coupling agent solution
Product solubility (PH value of aqueous solution) Stability (storage days)
PR-303 (4.0) 30days
PR-303 (5.3) 30days
PR-403 (4.0) 10days
KBE-403 (4.0) 10days
PR-502 (4.0) 1day
PR-503 (4.2) 1day
PR-602 (10.0) 30days
PR-602 (10.0) 30days
PR-602 (10.0) 30days
PR-602 (10.0) 30days
PR-602 (10.0) 30days
PR-573 (4.0) 1day
PR-703 (3.9) 10days
PR-803 (4.0) 1day
PR-5103 (4.2) 3days
Completely dissolved in 0.1~1.0% concentration of acetic acid aqueous solution (pH=3-5)
When using silane coupling agents in composite materials, it is necessary to fully consider the characteristics of organic polymers and inorganic materials, select suitable silanes, and choose the correct method of use according to their production process characteristics, so as to achieve economical and applicable satisfactory results.
The group in silane is hydrolyzed — the hydroxyl group reacts with the inorganic filler after hydrolysis — when the inorganic filler treated with the coupling agent is filled to prepare the composite material, the R group in the coupling agent will interact with the organic polymer, Finally build a bridge between inorganic fillers and organic matter.
There are many kinds of silane coupling agents, and the different R groups in the general formula are suitable for different types of polymers. This is because the group R is selective for the reaction of the polymer, such as containing vinyl and methyl It is a silane coupling agent based on acryloxy group, especially effective for unsaturated polyester resin and acrylic resin. The reason is that the unsaturated double bonds in the coupling agent and the unsaturated double bonds in the resin undergo a chemical reaction under the action of initiators and accelerators. However, the effect of the coupling agent containing these two groups is not obvious when it is used in epoxy resin and phenolic resin, because the double bond in the coupling agent does not participate in the curing reaction of epoxy resin and phenolic resin. However, silane coupling agents with epoxy groups are particularly effective for epoxy resins, and because epoxy groups can react with hydroxyl groups in unsaturated polyesters, silanes containing epoxy groups are also suitable for unsaturated polyesters; and silanes containing epoxy groups are also suitable for unsaturated polyesters; Amino-based silane coupling agents are effective for resins such as epoxy, phenolic, melamine, and polyurethane. Silane coupling agents containing -SH are widely used in the rubber industry.
Common Silane Coupling Agents
- PR-550 (γ-aminopropyltriethoxysilane)
Solubility : Soluble in organic solvents, but acetone and carbon tetrachloride are not suitable as release agents; soluble in water. Hydrolyzed in water, alkaline.
It is mainly used in mineral-filled phenolic, polyester, epoxy, polyamide, carbonate and other thermoplastic and thermosolid resins, which can greatly improve the physical and mechanical properties of reinforced plastics such as bending strength in dry and wet states, compressive strength, and shear strength. Performance and wet electrical performance, and improve the wettability and dispersion of fillers in polymers.
- PR-151 (vinyltriethoxysilane)
Solubility : Soluble in organic solvents, but acetone and carbon tetrachloride are not suitable as release agents; soluble in water. Hydrolyzed in water, alkaline.
Mainly used for polyethylene crosslinking; glass fiber surface treatment of unsaturated polyester, polyethylene, polypropylene resin and other glass fiber reinforced plastics; synthesis of special coatings; adhesives; surface moisture-proof treatment of electronic components; inorganic silicon-containing fillers Surface treatment, etc.; also used for surface treatment of composite glass interlayer. Reply to ” Auxiliary ” to inquire about more related articles
- PR-560 (γ-glycidyl etheroxypropyl trimethoxysilane)
Solubility : Soluble in water, hydrolysis reaction occurs at the same time, and methanol is released from hydrolysis reaction. Soluble in alcohols, acetone and most aliphatic esters at normal use levels below 5%.
PR-560 is a coupling agent containing epoxy groups, used for caulking and sealants of polysulfides and polyurethanes, adhesives for epoxy resins, filled or reinforced thermosetting resins, glass fiber adhesives and It is used for inorganic-filled or glass-reinforced thermoplastic resins, etc.
- Titanate coupling agent
- General chemical structure
R group: It can react with the hydroxyl group on the surface of the inorganic filler to form a monomolecular layer of coupling agent, thereby performing chemical coupling.
-O-group: Various types of ester conversion reactions can occur, so that the titanate coupling agent can be cross-linked with polymers and fillers, and can also undergo esterification reactions with the hydroxyl groups in EP.
X: The atomic group connected to the titanium-oxygen bond, or the bonding group, determines the characteristics of the titanate coupling agent. It can be: alkoxy, carboxyl, sulfuryloxy, phosphoryloxy, phosphorousyloxy, pyrophosphoryloxy, etc.
R’: It is the long chain part of the titanate coupling agent molecule, mainly to ensure the entanglement and miscibility with the polymer molecule, improve the impact strength of the material, reduce the surface energy of the filler, and significantly reduce the viscosity of the system , and has good lubricity and rheological properties.
Y: It is the functional group for crosslinking by titanate coupling agent, including unsaturated double bond groups, amino groups, hydroxyl groups, etc.
- Monoalkoxy type
- Monoalkoxy pyrophosphate type
- Chelating type
- Ligand type
- Mechanism of action
The mechanism of action of titanate coupling agent is relatively complicated, but its multi-functionality and the characteristics of one agent with multiple uses are very attractive.
Monoalkoxy groups can react with hydroxyl hydrogen atoms on the filler surface to form chemical bonds. The other three long organic chains can be entangled with the polymer molecules, thus tightly binding the polymer and the filler together.
The monoalkoxy titanate forms a monomolecular layer on the surface of the filler instead of forming a multimolecular layer like a silane coupling agent.
If the filler or polymer contains a large amount of water, the monoalkoxy titanate is prone to hydrolysis and loses the coupling effect. Therefore, this type of coupling agent is especially suitable for dry filler systems that do not contain free water, but only contain chemically bonded water or physically bonded water, such as calcium carbonate, hydrated alumina, etc.
② Monoalkoxy pyrophosphate coupling agent
This type of coupling agent is suitable for filler systems with high moisture content, such as clay, talc, kaolin, etc.
In these systems, in addition to the reaction of the monoalkoxy group with the hydroxyl group on the surface of the filler to form a coupling, the pyrophosphate group can also be decomposed to form a phosphate group and combine with a part of water.
A typical species of this type of coupling agent is tris(dioctylpyrophosphoryloxy)isopropyl titanate (TTOPP-38).
③ Chelating titanate coupling agent
This type of coupling agent is suitable for high-humidity fillers and water-containing polymer systems, such as wet-process silica, clay, talcum powder, aluminum silicate, water-treated glass fiber, carbon black, etc.
In the high temperature system, the general monoalkoxy titanate has poor coupling effect due to its poor hydrolytic stability, while the chelated titanate has excellent hydrolytic stability and is suitable for use at high temperature.
According to the different chelating rings, this type of coupling agent is divided into two basic types: chelating 100 type, the chelating group is oxoacetoxy; chelating 200 type, the chelating group is dioxyethylene.
④ Ligand type titanate coupling agent
Developed to avoid side reactions of tetravalent titanate in certain systems, including: transesterification in polyester; reaction with hydroxyl in epoxy resin; reaction with polyether and isocyanate in polyurethane reaction etc. This type of coupling agent is suitable for many filling systems, and its coupling mechanism is similar to monoalkoxy titanate.
- The organophilic part of the titanate coupling agent is usually a long-chain hydrocarbon group (C12-18), which is combined with the polymer chain through the intermolecular Van der Waals force. This type of coupling is especially useful for thermoplastics such as polyolefins. The winding of long chains can transfer stress and strain, improve impact strength, elongation and shear strength, and increase the filling amount while maintaining tensile strength.
- In addition, long-chain hydrocarbon groups can also change the surface energy at the interface of inorganic substances, reducing the viscosity, and highly filled polymers show good melt fluidity.
- The use of titanate coupling agents should be avoided as much as possible in combination with surface-active additives, which will interfere with the coupling reaction of titanate at the interface. If these additives are not used, they should be used in fillers, coupling agents and polymerization Add after mixing thoroughly.
- Most titanates undergo transesterification reactions with ester plasticizers to varying degrees. Therefore, the addition of ester plasticizers should also be done after the filler, coupling agent and polymer are fully mixed to form coupling.
- The monoalkoxy titanate has the best effect in the dry or calcined filler system, and the effect is poor in the wet filler containing free water. At this time, pyrophosphate titanate should be used. For wet fillers with a large specific surface area, it is best to use a chelating titanate coupling agent.
Titanate coupling agent and silane coupling agent can be used together to produce a synergistic effect. For example, the coupling effect is greatly improved by treating the glass fiber treated with silane coupling agent with chelating titanate.
The amount of titanate coupling agent is usually 0.5% of the amount of filler, or 0.25% of the amount of solid resin, and the optimal amount is finally determined by performance. Its dosage is generally 0.2%~0.25% of the inorganic filler.
- How to use
- Wet mixing method
Monoalkoxy type, ligand type and other coupling agents can be diluted with solvents such as gasoline, benzene, ethanol, etc., and then mixed with fillers or pigments evenly, and then the solvent is removed by heating or decompression.
- Dry mixing method
In the plastic industry, titanate coupling agents are mainly used for dry mixing. In order to uniformly coat a small amount of titanate on the surface of the filler, a small amount of diluent is generally added, so that a small amount of titanate is evenly distributed on the surface of the filler.
- Other coupling agents
Aluminate coupling agent
Its structure is similar to that of titanate coupling agent. There are two types of active groups in the molecule, one can interact with the surface of inorganic fillers; the other can entangle with resin molecules, thus creating a gap between the inorganic filler and the matrix resin. Coupling. It has the characteristics of light color, non-toxic, and convenient use. Its thermal stability is better than that of titanate coupling agent, and its price is only half of that of titanate coupling agent.
The amount of aluminate coupling agent is generally 0.3% to 1.0% of the filler amount of the composite material. For plastic hard products that are injection molded or extruded, it is about 1.0% of the filler, and for other process-shaped products, soft products and foamed products, the amount of filler used is 0.3% to 0.5%. Fillers with high surface area such as aluminum hydroxide, magnesium hydroxide, and white carbon black can be used at 1.0% to 1.3%
Zirconium coupling agent
Zirconium coupling agents can not only promote the combination of inorganic and organic substances, but also improve the performance of the filler system. Its characteristic is that it can significantly reduce the viscosity of the filler system. It can inhibit the interaction between filler particles and reduce the viscosity of the filler system, thereby improving the dispersion of the system and increasing the filling amount.
Zirconium coupling agent has a good modification effect on filling systems such as calcium carbonate, silica, alumina, titanium oxide and clay. Mainly suitable for different polymer filling systems such as polyolefin, polyester, epoxy resin, nylon, polyurethane, synthetic rubber, etc.
Organic chromium coupling agent
Coordinated metal complexes are formed from unsaturated organic acids and trivalent chromium atoms. In glass fiber reinforced plastics, it has better application effect.
The cost of organic chromium coupling agents is low, but the variety is monotonous, and the scope of application and coupling effect are not as good as silane coupling agents and titanate coupling agents. The main reason is the toxicity of chromium ions and the resulting environmental pollution. leading to a gradual reduction in current usage
- Composite coupling agent
(1) Aluminum-titanium composite coupling agent
The aluminum-titanium composite coupling agent replaces part of the central atom of the coupling agent with aluminum, which reduces the content of titanium, which is expensive in the coupling agent, and reduces the cost. It has the characteristics of titanium-based and aluminum-based coupling agents, and its coupling effect is better than that of a single titanate, aluminate or a simple mixture of the two.
(2) Aluminum zirconate coupling agent
This type of coupling agent is a low polymer of organic complexes containing aluminum and zirconium elements. The alumino-zirconate lipid coupling agent has the following characteristics:
- a) The price is low, its price is about half of that of silane coupling agent;
- b) Good application effect and good hydrolytic stability;
- c) Good thermal stability, can withstand heat up to 300°C;
- Selection principle of coupling agent
- Silane coupling agents are mainly suitable for glass fiber and silicon-containing fillers, such as quartz, wollastonite, etc., and can also be used for some metal oxides and hydroxides, but not for CaCO3. The resin is mainly a thermosetting resin.
- The titanate coupling agent has a wide range of applications for fillers, such as CaCO3, titanium dioxide, etc., and can also be used in glass fibers. The resin is mainly a thermoplastic resin.
- Acidic fillers should use coupling agents containing basic functional groups, while basic fillers should use coupling agents containing acidic functional groups.
- The amount of coupling agent added. The amount of silane coupling agent can be about 1% of the filler; the amount of titanic acid is generally 0.25~2% of the filler.
- Some surfactants will affect the performance of the titanate coupling agent, such as HSt, etc., so they must be added after the filler, coupling agent, and resin are fully mixed.
- Most titanate coupling agents are prone to transesterification reactions with ester plasticizers. Therefore, such coupling agents need to be added after the coupling agent is added. The combination of titanate and silane coupling agent has a good synergistic effect.