Chemical modification of silane coupling agent

Silane coupling agent is made from silicon chloroform (HSiCl3) and unsaturated olefin with reactive groups under the platinum chlorate catalytic addition, then through alcoholysis. Quartz powder or other surface chemical modification of silica powder mainly using silane coupling agent, amino, epoxy group, including methyl allyl trimethyl, and vinyl silane coupling agent. - RO functional groups of the silane coupling agent can be in the water (including the packing surface adsorption of free water) hydrolysis to produce silanol group, a group that can be combined with SiO2 for chemical or combined with the original silicon ether glycol is an organic whole, become a homogeneous system. Like this, is to remove the moisture on the surface of the SiO2, and its oxygen atoms to form silicon ether bond, so that the silane coupling agent on the other side of the carried by the polymer and the polymer has the very good affinity of organic functional groups -R' covered tightly in quartz or silicon dioxide particles surface, form covering film with reaction activity.

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The application of silane coupling agent

Silane coupling agent of different plastics and filler system coupling effect is different. Commonly used, for example, three different stearic acid isopropyl ester, acyl titanium for calcium carbonate filled polypropylene, polyethylene, polystyrene can significantly improve the impact resistance, and the glass fiber reinforced polyester or epoxy resin, chooses gamma - methyl acryloyl need oxygen radicals propyl silane, three oxygen radicals can significantly improve the mechanical strength. Therefore, we should fully consider and main use resin, filling system, to select the best coupling agent.In order to produce the best effect selected coupling agent, still should according to certain operating conditions for filling agent processing.Usually, according to the solubility and stability of the coupling agent, the mixture solution or the solution of methanol, ethanol, acetone, etc, under proper temperature mixed with inorganic filler, join other additives in succession again, to ensure that coupling agent on the surface of the fillers, uniform distribution, to avoid interference between additive.Ester titanate coupling agent should avoid as far as possible with plastic additives and surface activity, so as not to interfere with the coupling reaction. At the same time, most titanate can occur in different degrees and esters plasticizer of ester exchange reaction, therefore, esters plasticizer in coupling agent and the synthetic resin and filler mix and coupling effects to join.Ester titanate coupling agent and silane coupling agent and can produce synergies.

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Theory of action of silane coupling agent

The mechanism of silane coupling agent in polymer matrix composites is mainly the following theory:
(1) the chemical bonding theory that silane coupling agent containing two different chemical functional groups, to the end and inorganic materials, such as glass fiber, the silicate, the silanol groups on the surface of the metal oxides reacts covalent bond; At the other end and polymer binders or covalent bonding resin, thereby to coupling two incompatible materials.
(2) the surface infiltration theory, think silane coupling agent to improve the surface tension of the glass fiber or other inorganic materials, and even make it is greater than the surface tension of resin matrix, and thus to resin on the surface of the inorganic matter, infiltration and deployed, improve the wetting ability of the resin for inorganic reinforced material, make resin and inorganic reinforced material sticking together well.
(3) deformation layer theory, that silane coupling agent is plastic in the interface, it can be on the interface to form a flexible deformation is greater than 10 nm layer, the deformation layer has the ability to heal the damage, not only to relax the prestressed interface, and can prevent the crack extension, it can improve the interface bonding strength.
(4) constrained layer theory, composite reinforced material high modulus and low modulus resin between the interface zone, and silane coupling agent as one part of it.Silane coupling agent can not only with inorganic adhesive surface, but also can react with resin, polymer can be "binding" on the interface.When this interface OuDeMo between inorganic reinforcing materials and resin, the amount of stress can be evenly.
(5) reversible hydrolysis theory, think the presence of water silane coupling agent and glass fibers produced by stress fracture, but can be reversible to heal.Such on both the theory of constraint layer at the interface between the rigid area by resin and silane coupling agent (crosslinked), but also allows the stress relaxation, the chemical bond theory and constraint theory and deformation layer into harmony theory.This mechanism can not only explain the interface coupling mechanism, but also can explain the effect of stress relaxation and the function of the resistance on the surface of the water conservation.
Inorganic pigments and fillers in the coating liquid organic phase dispersion can be divided into the wetting, depolymerization and stabilization of resistance (flocculation) three stages.Due to these natural hydrophilic inorganic pigments and fillers, easy adsorption on the surface of a layer of water, so the nonpolar hydrophobic makings is difficult to make its wetting and dispersing.With silane coupling agent pretreatment of inorganic pigments and fillers, surface modification, silane can replace pigment or filler on the surface of the water, coated particles, the R group, become oil-wet, hydrophobic, and easy to be basic material wetting.After wetting, binders molecules insert between inorganic pigment or filler particles, to separate them, dispersion stability, prevents the  precipitation and agglomerate. Inorganic pigment and filler surface after silane coupling agent treatment, reduced and have been structured effect, make the paint viscosity reduce, eliminate the flocculation and even increase the amount of pigments and fillers to add will not affect the coating liquid, and pigments, good dispersion of filler particles makes the final film covering power, color and tinting strength were improved.

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Using method of silane coupling agent

Application method of silane coupling agent has two kinds: one is to mix the silane with aqueous solution, and use it again after treatment of inorganic powder mixed with organic polymer or resin binders, namely pretreatment method; Another method is to silane and inorganic powder (such as packing or pigment) and organic polymer binders, namely migration method. The former method of surface modification treatment effect is good, is a common method of surface modification.
Most of the silane coupling agent to match into aqueous solution before use, even if its hydrolysis in advance. Hydrolysis time according to the varieties of the silane coupling agent and pH value of solution vary, ranging from a few minutes to tens of minutes. General control configuration of the aqueous solution pH value between 3 ~ 5, pH value is higher than 5 or less than 3 will promote the formation of polymer. Therefore, has been configured, hydrolysis of silane coupling agent can't placed too long, otherwise it will polycondensation and failure on its own.
The dosage of the silane coupling agent is related with coupling agent varieties and the area of the packing, silane coupling agent the parcel cover according to the different varieties of the silane coupling agent vary. When it is not know the specific surface area of inorganic powder data or the minimum coated area of the silane coupling agent, dosage of silane coupling agent can be selected for the quality of inorganic powder 0.10% ~ 1.5%.
Most of the silane coupling agent can be used for surface modification of dry, can also be used for wet surface modification.

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