Silanes for Adhesives

  Nanjing Aocheng Chemical Co.,LTD is a supplier  of silane , let's introduce the silane adhesion promoters are as follows:

Silane adhesion promoters are bifunctional organosilicone compounds which act as molecular bridges between the polymer matrix of an adhesive or sealant and the substrate, either inorganic or organic.

The silane end contains hydrolysable alkoxy groups that are activated by reaction with ambient moisture. The hydrolysable alkoxy groups attached to the silicon end of the silane are typically either methoxy or ethoxy. Once activated (hydrolyzed), the resultant silanol groups will condense with o ther silanols or with reactive groups on the surface of a substrate such as SiOH, AIOH, or other metal oxides or hydroxides.The silane’s ability to bond to a surface will generally be determined by the concentration of such sites on the surface. Selecting the optimal silane for an application requires matching the reactivity of the silane‘s organofunctional group to that of the polymer.

The silanes can be blended into an adhesive formulation or used as primers on substrates. The structure and re activity of the silane will affect the ability of the silane to migrate. The most effective way to promote adhesion is to apply the silane as a primer to the surface, followed by application of the adhesive/sealant.

In this way, the silane will be on the s urface and therefore at the interface where it can enhance adhesion between the polymer and the substrate. Silane primers are usually dilute solutions of 0.5 to 5 percent silane in alcohol or water/alcohol solvent. They are wiped or sprayed on the substrate, after which the solvent is allowed to evaporate. While the concentration needed for a specific application may vary, one percent (1%) based on resin content is recommended as a good starting point.

The organofunctional group of the silane can react, and bond to, the polymer backbone. Residual moisture activates the silane’s alkoxy groups to the active silanol form which react with each other, liberating
moisture, and forming siloxane bonds between the polymers. The resulting Si-O-Si crosslink is extremely durable, offering excellent weather, UV, temperature, chemical and moisture resistance.

The filler may either be treated with silane before it is added to the sealant formulation (pretreatment method), or it can bind with the filler during compounding (additive method).

Alkoxysilanes react very rapidly with water;they are usually used to capture excess moisture in sealants and adhesives.

Vinyltrimethoxysilane is the most common moisture scavenger , due to the electron interactions of the vinyl group it reacts with moisture faster than other alkoxy silanes, enabling it to function as a moisture scavenger in the presence of other silanes incorporated as adhesion promoters, crosslinkers or coupling agents. The amount of silane added will depend on the water content of the formulation constituents.

Methanol is formed as a byproduct, and the vinyl silane crosslinks into an inactive species in the formulation. Other alkoxy silanes, such as methyltrimethoxysilane, are also used as waters.

 
(source:http://www.ac-chem.net/news/silanes-for-adhesives-8e0b.html)

Silanes as Primers and Adhesion Promoters

Organosilanes are "molecular bridges" that are used as primers and adhesion promoters for coatings or adhesives. The addition of a silane at the interface results in high bond strength and corrosion resistance. The chemical link created by the use of a silane contributes various benefits, such as:

• A strong bond between the inorganic surface and the organic polymer to provide enhanced adhesion in both wet and dry environments;
• a barrier to prevent moisture penetration through the interface;
• improved bulk physical properties of the coating or adhesive through enhanced adhesion between the polymer and the filler particles within the formulation and the efficient transfer of stress from the resin to the filler;
• effective dispersion of fillers and reduction in the apparent viscosity of the system.

Silanes are a group of specialty organo functional compounds that possess dual reactivity. The silanes act chemically with both the metal substrate and the organic base polymer in the coating or adhesive.The silane adhesion promotes and protects the metal substrate by forming covalent bonds across the interface that are both strong and durable.

Silanes can be applied directly to the substrate, similar to conventional primers, or they can be mixed into the coating or adhesive formulation as an additive. Optimum results are generally achieved by using the silane as a substrate primer. When applied directly to the substrate, they are very thin coatings only about one monolayer in thickness. When mixed with the coating, the coupling agent is capable of migrating to the interface and reacting with the substrate surface as the coating or adhesive dries.

Over the last 20 years, the silane adhesion promoter marketplace has evolved to include a plethora of materials of which organosilanes have secured a prominent position. The choice of a particular silane will depend on the specific formulation of the coating or adhesive, on the substrate and on the method of application.

Optimizing the potential properties of silane systems offers a challenge.There are many parameters that can effect the performance of silane. Therefore, it is recommended that the silane supplier be contacted to assist in making a selection.

Silanes are multifunctional in that they can be used to promote crosslinking, and they can be incorporated directly into a polymer chain by various reaction mechanisms. In addition to coatings and adhesives, silanes have multiple commercial uses, such as coupling agents for reinforced plastics, crosslinking agents for polyethylene cables, and dispersants for paints and printing inks.

(source:http://www.ac-chem.net/news/silanes-as-primers-and-adhesion-promoters-b75e.html)

Amino silane

Improvement of the efficiency of carbon dioxide (CO2) separation from flue gases has been identified as a high-priority research  area to reduce the total energy cost of carbon capture and sequestration technologies in coal-fired power plants. Efficient CO2 removal from flue gases by adsorption systems requires the design of novel sorbents  capable of capturing, concentrating and recovering CO2 on a cost-effective basis. The  preparation of a novel amino silane-functionalized cellulosic polymer sorbent by grafting of amino silanes showed promising performance for CO2 separation and capture. A strategy for the introduction of N-(2-aminoethyl)-3-aminoisobutyldimethylmethoxysilane functionalities into cellulose acetate backbone by anhydrous grafting is described in this study. The dry sorption capacity of the amino silane-functionalized cellulosic polymer reached 27 cc (STP) CO2/ cc sorbent at 1 atm and 39 cc (STP) CO2/ cc sorbent at 5 atm and 308 K. Exposure to water vapor slightly  increased the sorption capacity of the sorbent, suggesting its potential for rapid cyclic adsorption processes under humid feed conditions. In addition, a strategy for the preparation of a cellulose acetate-titanium(IV) oxide sorbent by the reaction of cellulose acetate with titanium tetrachloride is presented. The organic-metal hybrid sorbent presented a sorption capacity of 14 cc (STP) CO2/ cc sorbent  at 1 atm and 49 cc (STP) CO2/ cc sorbent at 5 atm and 308 K. The novel CO2 sorbents were characterized in terms of chemical composition, density changes, molecular structure, thermal stability, and surface morphology.

silane in fiberglass

1. Glass fiber surface treatment Objective and Significance
　　Surface treatment is a processing which use the treating agent to cover the surface of reinforcement.These treating agents include treating compound, some of silane coupling agent and auxiliaries. It helps forming a well bond surface between reinforcement and substrate and also can improve various properties of compound materials.
　　Significance of treatment: We know that function of compound materials are not only related with content and property of resin and fiber, but also greatly depend on the bond of resin and fiber. Surface treatment includes interface processing which is coating a called “surface treatment agent” on the surface of glass fiber. This agent could solidly combined fiber and resin so as to increase the function of glass.
　　
2. Silane coupling agent and their reaction theories.
　　Silane coupling agent is this kind of materials which are usually have two different groups on
themselves ends. One end’s groups have the chemical action or physics action with the surface of
reinforcement, while the other end’s groups can react with base materials, so that well bond the
reinforcement with substrate to get the good bonding between interfaces and improve many respects of functions and effectively resist water.
　　Organic-functional silane is a kind of surface treating agent with many different and effective kinds and it’s normal chemical structure is RnSiX4-n.
There are four steps to treat fiber glass with Organic functional Silane coupling agent:
1. First, there are three unreliable X groups in atom Si to hydrolyze
2. Second, the silane coupling agent condensate Oligomers
3. Third, those oligomers formed hydrogen bond with the “–OH” group of the glass fiber surface
4. Last, In the process of drying and curing, silane creates covalent bonds with glass fiber surface.

3. Glass fiber surface processing method and factors.
　1. The treatment method of silane coupling agents for the surface of fiberglass:
　（1）Post-treatment （2）Pre-treatment （3）Grafting
Most of silanes are used in treating compound of fiberglass. We will mainly introduced pre-treatment.
　　Changing the formula of treating compound appropriately, it is not only meet the requirements of fiber forming, spinning and other process, but also not hinder the infiltrating and adhesion between the resin matrix and fiberglass. And also not hinder resin base material wetting and sticking on glass fiber. In the process of fiber forming, we add the silane coupling agent into the treating compound which make the surface treating agent coated on the surface of fiberglass, and we call this process is pre-treatment, which is weaving fiber cloth with fiber which is covered by reinforced treating compound.
  2. The dosage of silane coupling agent and factors of treatment.
　a. The dosage of silane coupling agent
　　Playing the role in silane coupling agent is the micro-quantity of monolayer of silane coupling agent. And the appropriately dosage of each kind of silane is result from the experiment.
Attention: the dosage of silane coupling agent can calculate:
Computing method: V2/ V1 = M
V1: The minimum coating area of 1g silane coupling agent
V2: The surface area of 100g reinforced materials
M: The required quantity of silane coupling agent to coat a monolayer in 100g treated materials.
b. Factors of treatment:
1) The dosage of silane coupling agent
2) The temperature and time of drying
3) The pH value of treatment compound

5. Requirements on silane coupling in fiberglass industry
a. Silane coupling must be dispersed in water, because the wetting agent of fiberglass adopts water as the carrier;
b. Purity of silane coupling should be higher, such as AC-220 requires the purity is higher than 98%; if the content is low and foreign substance is too much, the strength of the compound materials will change greatly;
C. The hydrolysis rate is required to be within 30 min, affecting the production efficiency of wetting agent.
d. It can improve the strength and electric properties, etc. of fiberglass reinforced resin.

(source:http://www.ac-chem.net/news/Silane-in-Fiberglass-8a3a.html)

Typical Silane Applications

Silane Coupling Agent: Organofunctional alkoxysilanes are used to couple organic polymers to inorganic materials. Typical of this application are reinforcements, such as fiberglass and mineral  fillers, incorporated into plastics and rubbers. They are used with both thermoset and thermoplastic systems. Fiberglass applications include auto bodies, boats, shower stalls, printed circuit boards, satellite dishes, plastic pipes and vessels, and many others. Mineral-filled systems include reinforced polypropylene, silica-filled molding compounds, silicon-carbide grinding wheels, aggregate-filled polymer concrete, sand-filled foundry resins, clay-filled EPDM wire and cable, clay- and silica-filled rubber for automobile tires, shoe soles, mechanical goods and many other applications.

Silane Adhesion Promoter: Silane coupling agents are effective adhesion promoters when used as integral additives or primers for paints, inks, coatings, adhesives and sealants. As integral additives, they must migrate to the interface between the adhered product and the substrate to be effective. By using the right silane coupling agent, a poorly adhering paint, ink, coating, adhesive or sealant can be converted to a material that often will maintain adhesion even if subjected to severe environmental conditions.

 Hydrophobing and Dispersing Agent: Alkoxysilanes with hydrophobic organic groups attached to silicon will impart that same hydrophobic character to a hydrophilic inorganic surface. They are used as durable hydrophobing agents in construction, bridge and deck applications. They are also used to hydrophobe inorganic powders to make them free-flowing and dispersible in organic polymers and liquids.

Silane Crosslinking Agent: Organofunctional alkoxysilanes can react with organic polymers to attach the trialkoxysilyl group onto the polymer backbone. The silane is then available to react with moisture to crosslink the silane into a stable, three-dimensional siloxane structure. Such a mechanism can be used to crosslink plastics, especially polyethylene, and other organic resins, such as acrylics and urethanes, to impart durability, water resistance and heat resistance to paints, coatings and adhesives.

Silane Moisture Scavenger: The three alkoxy groups on silanes will hydrolyze in the presence of moisture to convert water molecules to alcohol molecules. Organotrialkoxysilanes are often used in sealants and other moisture-sensitive formulations as water scavengers.

Polypropylene Catalyst “Donor”: Organoalkoxysilanes are added to Ziegler-Natta catalyzed polymerization of propylene to control the stereochemistry of the resultant polypropylene. The donors are usually mono- or di-organo silanes with corresponding tri- or di-alkoxy substitution on silicon. By using specific organosilanes, the tacticity and properties of the polypropylene are controlled.

Silicate Stabilizer: A siliconate derivative of a phosphonate-functional trialkoxysilane functions as a silicate stabilizer to prevent agglomeration and precipitation of silicates during use. The predominant application is in engine coolant formulations to stabilize the silicate corrosion inhibitors.

(source:http://www.ac-chem.net/news/typical-silane-applications-80ac.html)

Silane coupling agents

Silane coupling agents are silicon-based chemicals that contain two types of reactivity–inorganic and organic–in the same molecule. A typical general structure is (RO)3SiCH2CH2CH2-X,where RO is a hydrolyzable group, such as methoxy, ethoxy, or acetoxy, and X is an organofunctional group, such as amino, methacryloxy, epoxy, etc.
A silane coupling agent will act at an interface between an inorganic substrate (such as glass, metal or mineral) and an organic material (such as an organic polymer, coating or adhesive) to bond, or couple, the two dissimilar materials.
A simplified picture of the coupling mechanism is shown in Figure 1.

(source:http://www.ac-chem.net/news/Silane-Coupling-Agents-9338.html)

Adhesion Accelerator

To provide an adhesion accelerator composition of a rubber and a metal not only good in initial adhesiveness, but also in heat resistant adhesiveness, wet heat adhesiveness, and destruction resistance characteristic.SOLUTION: This rubber composition containing an adhesion accelerator contains 0.5-5 pts.wt. bisphenol A derivative resin which is prepared by reacting a polyhydroxybenzene, a bisphenol A epoxy compound, and an aromatic compound containing a vinyl group, a cobalt salt of an organic acid whose cobalt content is 0.15-0.25 pts.wt., 2-12 pts.wt. sulfur, and 0.5-5 pts.wt. hexamethylene tetramine or a melamine derivative to 100 pts.wt. rubber component.

Vinyltrimethoxysilane

Vinyltrimethoxysilane is suitable for PE and copolymers of different density and plastic products of complicated profiles. It is suitable for use at high temperature. It provides the polymer with high resistance to decomposition at pressure, abrasion and impact as well as shape memory effect. To modify PE and other polymers, it can be grafted to the backbone chain of polymer so the side chain of polymer is provided with ester group as the active point for cross-linking in hot water. It can be used for the jacketing and insulation of wire and cables, tubing and other extruded or molded products.

Silane adhesion promoter

A second system that has been studied extensively because of its technical importance is the adhesion between epoxy resins and glass, particularly glass fibres. To improve the hydrolytic stability of the composite, the glass surfaces are normally modified by covering them with a thin layer of a silane adhesion promoter. These silanes are well known to self-assemble into mono-molecular and multi-molecular layers on surfaces such as glass or silicon dioxide. One end of the silane molecule typically has di or tri methoxy or ethoxy functionality whilst the other end normally has amine or epoxy functionality. The ethoxy functionality is believed to condense with the hydroxyl functionality on the surface of the glass whilst the amine functionality can react with the epoxy, as shown in Figure 2. Hence it is attractive to suggest a simple picture of a single molecular layer of silane adhesion promoter between the epoxy and the glass. However the real situation is much more complex. The amount of silane typically used is much too great to form a monolayer. Also as the silane has multi methoxy or ethoxy functionality it can self condense. The relatively thick layer of silane is believed to form a network and then the epoxy both mixes into and reacts with the network. Although it is clear that the silane causes covalent bonding between the glass and the epoxy, there is no way to estimate the actual density of coupling produced. It is interesting to note that fairly good adhesion can be obtained in dry conditions without the silane, however it has a profound effect on adhesion in the presence of water.

Resin Modifier

In order to study the influence of resin modifiers materials on the performance of  hot mix asphalts (HMA), two types of  resin modifiers were selected. One  was an Unsaturated Polyester Resin (UPR) and the other was an Epoxy Resin (ER). Also, unsaturated polyester resin mixed with 3% epoxy resin (UPRER) was used according to test results, which  gave preference to 3%  additions. Marshal test was conducted to study the stability, flow, bulk density, air voids (AV), voids in mineral aggregate (VMA) and voids filled with bitumen (VFA) for  controlled hot asphalt mixtures and  resin: modified  mixtures at various resin modifiers contents. A computer program named BISAR was also used to determine the total stress, strain and displacement in x-y, and z-direction for flexible pavements constructed with these  hot mix  asphalts modified with resin additives.Experimental results showed that all resin-modified asphalt mixtures have higher flow, bulk density and VFA compared with control mixture. The stability of asphalt mixtures with UPPER was always higher than the control mixture. Unlike, for type ER and UPR the stability was lower than the control mixture up to 1% and 2% respectively then they increase. The UPRER gave higher stability, flow, AV and VMA than the other types. Moreover, the UPR gave the highest value of bulk density and VFA. The maximum stability occurs at 3% resin modifiers content for all types. The total stress and strain relatively increase with the increase of mix depth till 10 cm, then they decrease for all types of resin modifiers. The maximum total stresses and strain in case of UPRER are higher values than those achieved by ER and UPR respectively. The total displacement in case of UPRER is higher than that achieved by ER and UPR respectively. As resin modifiers can improve the field performance of asphalt mixes comprehensively, they
will be of great benefit to the engineering field.

Vinyltrimethoxysilane

Vinyltrimethoxysilane is suitable for PE and copolymers of different density and plastic products of complicated profiles. It is suitable for use at high temperature. It provides the polymer with high resistance to decomposition at pressure, abrasion and impact as wellas shape memory effect. To modify PE and other polymers, it can be grafted to the backbone chain of polymer so the side chain of polymer is provided with ester group as the active point for cross-linking in hot water. It can be used for the jacketing and insulation of wire and cables, tubing and other extruded or molded products.  

silane crosslinkers

The corrosion behaviour of amine-cured epoxy silane sol-gel coatings has been studied by different authors The diethylenetriamine (DETA) is one of the most common epoxy crosslinkers used and an optimum amine concentration in terms of the best anticorrosive properties achieved by the coatings was reported by Vreugdenhil et al.  and by Davis et al.  of, respectively, 1.3 and 1 relative to the molar ratio ''epoxy group/amine reactive hydrogen''. Khramov et al.  also studied epoxy silane sol-gel coatings crosslinked with epoxy silanes and found significant improvement in these coatings corrosion performance in comparison to those of DETA crosslinked ones. In another study involving the addition of amino-silane crosslinkers , the above optimum molar ratio found ranged between 1 and 1.5. The aminosilanes present the advantage of contributing also to the inorganic network formation. Besides amino-silanes, other amines have been studied as alternative to DETA like di-amines of longer carbon chain  or branched amines , the resultant coatings showed better corrosion protection properties compared to those derived from formulations containing DETA as crosslinking agent. The epoxy-silane based coatings curing process (by heating or by the addition of crosslinking agents) is determinant for the establishment of both inorganic and organic networks of these hybrid coatings and should be appropriate to the precursors used in their synthesis. All the studies referred are focused on solely silane derived sol-gel coatings. In this work, a zirconium alkoxide precursor is used in addition to the epoxy silane one to produce the hybrid sol-gel coating for corrosion protection of the aluminium alloy EN AW 6063. This type of sol-gel coatings usually is thermally cured. The aim of this work is to study the corrosion properties of epoxy-silica-zirconia hybrid sol-gel coatings cured at room temperature by the addition of amine crosslinkers. Therefore, in the present work, epoxy-silica-zirconia hybrid sol-gel coatings were synthesized from glycidoxypropyltrimethoxysilane (GPTMS) and zirconium n-propoxide (TPOZ) precursors, applied to the aluminium alloy by dip-coating and cured at room temperature using two types of amine crosslinkers: diethylenetriamine (DETA), in different concentrations (GPTMS/amine-Hreactive molar ratios: 1.5 and 1), and a tri-functional amino-silane in that molar ratio of 1. A sol-gel coating prepared from the same precursors but without amine addition was also synthesized for comparison. The evolution of the curing process and the corrosion behaviour of the hybrid coated aluminium alloy specimens were evaluated by Electrochemical Impedance Spectroscopy (EIS). The morphology and surface chemistry of the hybrid coatings were also characterized by Energy Dispersive Spectroscopy (EDS) coupled to Scanning Electron Microscopy (SEM) and by Fourier Transform Infrared Spectroscopy (FTIR).

Silane coupling agents

Natural fiber reinforced polymer composites (NFPCs) provide the customers with more alternatives in the material market due to their unique advantages. Poor fiber–matrix interfacial adhesion may, however, negatively affect the physical and mechanical properties of the resulting composites due to the surface incompatibility between hydrophilic natural fibers and non-polar polymers (thermoplastics and thermosets). A variety of silanes (mostly trialkoxysilanes) have been applied as coupling agents in the NFPCs to promote interfacial adhesion and improve the properties of composites. This paper reviews the recent progress in using silane coupling agents for NFPCs, summarizes the effective silane structures from the silane family, clarifies the interaction mechanisms between natural fibers and polymer matrices, and presents the effects of silane treatments on the mechanical and outdoor performance of the resulting composites.

Amino Silane

A provision for the use of structure activity relationships (SAR) to reduce testing needs is included under EPA’s HPV Challenge Program. Specifically, categories may be formed based on structural similarity, through analogy, or through a combination of category and analogy for use with single chemicals. The benefits of using a category approach are numerous and include(1) accelerated release of hazard information to the public, as category analysis and testing is proposed to be initiated within the first two years of the HPV Program;(2) reduction in the number of animals used for testing; and (3) an economic savings as a result of a reduced testing program.
Two amino silane materials proposed to be categorized based on structural similarity are:
•  1-Propanamine, 3-(triethoxysilyl)- (CAS No. 919-30-2)
•  1,2-Ethanediamine, N-[3-(trimethoxysilyl) propyl]- (CAS No. 1760-24-3).  
Both of these amino silanes are listed as HPV Challenge Program chemicals. The development of this amino silane category follows current EPA guidance1

Effect of silane coupling agent on natural rubber filled with silica generated in situ

The effect of silane coupling agent was investigated for the novel in situ silica loading to the natural rubber (NR) matrix. The silica was generated in situ by the sol-gel reaction of tetraethoxysilane in the NR matrix before its crosslinking. γ-mercaptopropyltrimethoxysilane (γ-MPS) significantly prevented the delay of sulfur curing and increased the wettability of NR onto in situ silica, which resulted in the increase of reinforcement effect for the NR vulcanizate. γ-MPS decreased the interaction between the in situ silica particles followed by dispersing the in situ silica particles homogeneously and decreasing the hardness, compression set, hysteresis loss and storage modulus at the rubbery state of in situ silica-filled NR vulcanizate. The NR/in situ silica composite with γ-MPS is a promising material for a high performance rubber product.

Silane Coupling Agent for Attaching Fusion-Bonded Epoxy to Steel

We describe the possibility of using γ-aminopropyltriethoxysilane (γ-APS) to increase the durability of epoxy powder coating/steel joints. The curing temperature of epoxy powder coatings is frequently above 200 °C, which is seen so far as a major limitation for the use of the heat-sensitive aminosilane coupling agent. Despite this limitation, we demonstrate that aminosilane is a competitive alternative to traditional chromate conversion to enhance the durability of epoxy powder coatings/steel joints. Fourier-transform reflection–absorption infrared spectroscopy (FT-RAIRS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) were used to identify the silane deposition conditions that influence the adhesion of epoxy powder coatings on steel. We show that AFM analysis provides highly sensitive measurements of mechanical property development and, as such, the degree of condensation of the silane. The joint durability in water at 60 °C was lower when the pH of the γ-APS solution was controlled at 4.6 using formic acid, rather than that at natural pH (10.6). At the curing temperature of 220 °C, oxidation of the carbon adjacent to the amine headgroup of γ-APS gives amide species by a pseudofirst-order kinetics. However, a few amino functionalities remain to react with oxirane groups of epoxy resin and, thus, strengthen the epoxy/silane interphase. The formation of ammonium formate in the acidic silane inhibits the reaction between silane and epoxy, which consequently decreases the epoxy/silane interphase cohesion. We find that the nanoroughness of silane deposits increases with the cure temperature which is beneficial to the wet stability of the epoxy/steel joints, due to increased mechanical interlocking.