The synthesis of polymers with active silane groups is also one of the development directions of silane coupling agents. This Guangzhou titanium ester coupling agent has better compatibility with the resin in adhesives and can form a uniform surface on the surface of the adhesive, thus having better bonding effect. One important application of newly developed silane coupling agents is for the production of water crosslinked polyethylene, a process developed by Dow Corning in the United States and currently commercialized. In recent years, it has been found that the combination of silane coupling agent and silicone lotion can improve the wearability of wool fabrics in the domestic trials of treating wool fabrics with silicone lotion.
The currently commonly used silane coupling agent is the trialkoxy type, but trialkoxy coupling agents may reduce the stability of the matrix resin. Therefore, in recent years, the research and application of dialkoxy coupling agents have received attention.
Peroxysilane is also a coupling agent that has been studied in recent years. Its characteristic is that under the action of heat, the coupling agent decomposes to generate free radicals, which can crosslink with olefin polymers and promote their adhesion.
Application fields and uses of coupling agents:
Fiberglass and fiberglass:Improve the wet physical and mechanical strength, wet electrical performance of composite materials, and enhance the bundling, protection, and processing technology of glass fibers.
Adhesives and Coatings:Improve adhesion and weather resistance under wet conditions, enhance pigment dispersion, improve wear resistance, and improve resin cross-linking.
Casting:Improve the strength of resin sand. To achieve high altitude and low gas generation.
Rubber:Improve the mechanical strength, wear resistance, wet electrical performance, and rheological properties of the product.
sealant:Improve the adhesion in wet state, enhance the dispersibility of fillers, and improve the wear resistance of products.
spin:Make textiles soft and plump, improve their waterproofness, and enhance their adhesion to dyes.
Printing ink:Improve the wettability of adhesion.
Surface treatment of fillers:Improve the compatibility, wettability, and dispersibility of fillers and resins in the resin.
Cross linked polyethylene:Used to enhance the strength of cross-linked polyethylene cables and hot water pipes. Durability and service life.
Main purpose:
Chemical substances in reinforced plastics that can enhance the interfacial bonding between resin and reinforcing materials.
At the interface between the resin matrix and the reinforcing material, Guangzhou titanate coupling agent promotes or establishes a strong binding substance.
Note:Coupling agents can be applied to reinforcing materials or added to resins, or a combination of both.
Instructions for using silane coupling agent:
1、 General principles for selecting silane coupling agents
It is known that the hydrolysis rate of silane coupling agents is determined by the silicon group Si-X, while the reactivity with organic polymers is determined by the carbon functional group C-Y. Therefore, it is crucial to choose the appropriate silane coupling agent for different substrates or processing objects. The selection method is mainly through experimental pre selection and should be based on existing experience or patterns. For example, in general, unsaturated polyesters often use silane coupling agents containing CH2=CMeCOO, Vi, and CH2-CHOCH2O -; Epoxy resins often use coupling agents containing CH2-CCH2O and H2N-silane; Phenolic resins often use coupling agents containing H2N - and H2NCONH - silane; Polyolefins often use vinylsilane; Rubber vulcanized with sulfur often uses alkyl silane and other materials. Due to a series of factors affecting the adhesion between heterogeneous materials, such as wetting, surface energy, interfacial layer and polar adsorption, acid-base interactions, interpenetrating networks, and covalent bond reactions. Therefore, relying solely on experimental pre selection is sometimes not precise enough, and it is necessary to comprehensively consider the composition of the material and its sensitivity to silane coupling agent reactions. To improve hydrolysis stability and reduce modification costs, trialkylsilane can be added to silane coupling agents for use; For difficult to stick materials, polymers crosslinked with silane coupling agents can also be shared.
When silane coupling agents are used as thickening agents, they mainly form chemical and hydrogen bonds with polymers; Wetting and surface energy effects; Improved polymer crystallinity, acid-base reactions, and generation of interpenetrating polymer networks. The thickening mainly revolves around three systems: (1) inorganic materials on organic materials; (2) Inorganic materials to inorganic materials; (3) Organic materials to organic materials. For the first type of bonding, it is usually required to bond the inorganic material to the polymer, so priority should be given to the reactivity between Y in the silane coupling agent and the functional groups contained in the polymer; The latter two belong to the adhesion between materials of the same type, so silane coupling agents are chosen for their anti hydrophilic polymers and inorganic materials that require increased adhesion.
2、 Usage method
As mentioned earlier, one of the main application areas of silane coupling agents is the treatment of inorganic fillers used in organic polymers. The latter can be treated with silane coupling agents to transform its hydrophilic surface into an organic friendly surface, which can avoid particle aggregation and rapid thickening of the polymer in the system, and improve the wettability of the organic polymer to the reinforcing filler. Carbon functional silane can also achieve strong bonding between the reinforcing filler and the polymer. However, the effectiveness of using silane coupling agents is also related to the type and dosage of silane coupling agents, the characteristics of the substrate, the properties of the resin or polymer, as well as the application scenarios, methods, and conditions. This section focuses on two methods of using silane coupling agents, namely surface treatment method and bulk blending method. The previous method involves treating the substrate surface with a dilute solution of silane coupling agent; The latter method involves directly adding the original solution or solution of silane coupling agent into a mixture of polymer and filler, making it particularly suitable for material systems that require stirring and mixing.
1. Calculation of dosage of silane coupling agent
The number of reactive sites per unit specific surface area of the processed material (substrate) and the thickness of the silane coupling agent covering the surface are key factors determining the amount of coupling agent required for siliconization of the substrate surface. To obtain monolayer coverage, it is necessary to first determine the Si OH content of the substrate. It is known that most of the Si OH content in the silica matrix of Guangzhou titanium ester coupling agents is 4-12/μ When uniformly distributed, 1mol of silane coupling agent can cover approximately 7500m2 of the substrate. Silane coupling agents with multiple hydrolyzable functional groups may affect the accuracy of calculations to some extent due to their own condensation reactions. If Y3SiX is used to treat the substrate, a monolayer coverage consistent with the calculated value can be obtained. However, due to its high price and poor hydrolysis resistance, Y3SiX has no practical value. In addition, the Si OH number on the surface of the substrate also varies with heating conditions. For example, under normal conditions, the number of Si OH is 5.3/μ After heating treatment at 400 ℃ or 800 ℃, the Si OH value of the ㎡ silicon matrix can be correspondingly reduced to 2.6/μ ㎡ or less than 1/μ ㎡. On the contrary, treating the matrix with moist heat hydrochloric acid can result in high Si OH content; Treating the surface of the substrate with alkaline detergent can form silanol anions.
The wettable surface area (WS) of silane coupling agent refers to the area (㎡/g) that a solution of 1g silane coupling agent 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 monolayer coverage can be calculated. Taking the treatment of fillers as an example, the amount of silane coupling agent W (g) required to form a monolayer on the surface of the filler is directly proportional to the surface area S (㎡/g) and its mass of the filler, and inversely proportional to the wettable area WS (㎡/g, as shown in Table 4-29) of silane. Based on this, the calculation formula for the amount of silane coupling agent is as follows:
2. Surface treatment method
This method uses silane coupling agents to connect inorganic and polymer interfaces together to achieve optimal wetting values and dispersibility. The surface treatment method requires the silane coupling agent to be acidified into a dilute solution to facilitate sufficient contact with the treated surface. The solvents used are mostly water, alcohol, or a mixture of water and alcohol, and it is advisable to use water without fluoride ions and inexpensive and non-toxic ethanol and isopropanol. Except for aminoalkylsilane, solutions prepared from other silanes require the addition of acetic acid as a hydrolysis catalyst and the adjustment of pH to 3.5-5.5. Long chain alkyl and phenylsilane are not suitable for use as aqueous solutions due to their poor stability. During the hydrolysis process of chlorosilanes and acetoxysilanes, severe condensation reactions will occur, and Guangzhou titanium acid ester coupling agents are not suitable for use in aqueous or aqueous alcohol solutions. For silane coupling agent with poor water solubility, 0.1% -0.2% (mass fraction) of non-ionic surfactant can be added first, and then water can be added to process it into water lotion for use. In order to improve the economic benefits of hydrolysis stability of the product, a certain proportion of non carbon functional silane can also be added to the silane coupling agent. When dealing with difficult to stick materials, mixed silane coupling agents or carbon functional siloxanes can be used in combination.
After the treatment solution is prepared, it can be treated by dipping, spray or brushing. Generally speaking, block materials, granular materials, and glass fibers are often treated by impregnation method; Powder materials are mostly treated by spray method; If the surface of the substrate needs to be coated as a whole, the brush coating method is used for treatment.
