What is MS sealant? What is MS polymer sealant used for?
The full name of MS sealant is modified silane polyether sealant. It is a new generation of building sealant developed after polysulfide sealant, silicone sealant and polyurethane sealant. Because it does not contain formaldehyde, isocyanate, solvent, and has outstanding environmental protection characteristics such as affinity to environment and human body, it can adapt to the vast majority of building materials.
Meanwhile, it also has good constructability, adhesion, durability and weatherability, especially non-pollution and paintability. It has a wide range of applications in building decoration, mainly used in the fields of construction engineering and decoration, such as bonding, caulking, seam, sealing and waterproofing, reinforcement and so on.
In recent years, because people know the advantages of MS sealant better, its application in industrial fields such as refrigerated trucks, containers and elevators has also continued to expand.
Main raw material of MS sealant
The main raw materials of MS sealant include: alkyl-terminated polyether (MS prepolymer), plasticizer (dioctyl phthalate, referred to as DOP; dibenzyl phthalate, referred to as DCP; dibutyl phthalate grease, referred to as DBP, etc.), gas phase white carbon black, silane coupling agent, catalyst, anti-aging additives, dewatering agent, etc.
The strength of MS prepolymer is not high, if it is used to make sealant, it is necessary to add fillers which can play a certain role in reinforcing. The type and amount of fillers significantly affect the mechanical properties and rheological properties of the sealant. For example, in the preparation of transparent MS sealant, silica pigment is usually used as reinforcing filler.
The main function of plasticizer is to weaken the van der Waals force between polymer molecules, thereby increasing the mobility of molecular chain and reduce the crystallinity of molecular chain, that is, increasing the shape of polymer. The performance is the decreasing of hardness, modulus, softening temperature, brittle temperature, and the increasing of elongation, yield property, flexibility. Adding DOP to the sealant can increase the fluidity, reduce the hardness, and adjust the modulus. However, if it is added in excess, it will not only cause the migration and exudation of DOP, but also affect the sag and mechanical properties of the sealant.
The catalyst has two main functions:
(1) speeding up the crosslinking curing at room temperature and shortening the curing time;
(2) making the sealant have good storage stability. The main catalysts of MS sealant are stannous caprylate, tin butyrate, dibutyltin diacetate, dibutyltin dioctoate , chelated tin, dibutyltin dilaurate, trialkylamine and so on. One of the most common catalysts is dibutyltin dilaurate.
Silane coupling agent molecules have two functional groups with different chemical properties at the same time. the alkoxy group at one end can react with moisture in the air to form an active silanol group. The silanol group can undergo condensation reaction with the hydroxyl group on the surface of substrate, forming a stable chemical bond. The reactive functional group at the other end can react with the polymer to form a bridge-like effect between the sealant and the substrate. At the same time, silane coupling agent can also be used as a crosslinking agent in polymer curing reaction to improve the crosslinking density of the final MS sealant product.
The molecular chain of MS polymer is mainly composed of C—C bond and C—O bond. Compared with Si—O bond, its bond energy is lower, and it is easier to break under ultraviolet light irradiation, which will affect the aging resistance of MS sealant. Therefore, it is necessary to add aging resistance additives into the formula system to improve its aging resistance.
The moisture curing mechanism of one-component MS sealant determines that the less water in the system, the better, to ensure that its performance does not change basically during the storage period (360d). Vinyl trimethoxy silane (WD-21) or vinyl triethoxy silane is often used as sealant dehydrating agent. Because its alkoxysilane has high reaction activity with water, it can quickly consume the water in the system and improve the storage stability of sealant.
Performance of MS sealant
Most domestic construction sealant is silicone sealant, compared with it, MS sealant has more prominent advantages:
1. Excellent performance
In the production of MS sealant, there is no solvent addition, no formaldehyde, toluene, xylene and other harmful substances released to human body. It is non-toxic, odorless and has the lowest VOC content. The VOC release is far lower than the national standard.
2. larger bonding range and strength
Due to the low surface energy and high penetration of MS base sealant (silyl-terminated polyether), it has good wetting ability for most inorganic, metal and plastic substrates. Simple processing of the material can make it have good adhesion. It is completely suitable for the vast majority of building materials, and has a good adhesion to engineering plastics such as acrylic, ABS, plexiglass and porous materials such as concrete. It has more extensive applications than silicone sealant and can adapt to most buildings without primer.
3. Strong stability
The silane-modified polyether sealant will form a network structure connected by flexible polyether long chains with Si—O—Si bond as the crosslinking point after humidity curing at room temperature. This system not only has excellent resistance to weather, water, aging and good durability, but also can effectively inhibit and avoid the surface cracks of the sealant after long-term use. Directly exposed to use, meet the double standard of Japan JS and national standard (9030), and have the heat and cold resistance of -30℃～90℃. In addition, MS sealant will not escape oily molecules to contaminate the surface and joints of building materials, and maintain the beauty of the building for a long time. Silicone sealant will precipitate small molecules, which together with rain and dust will form difficult-to-remove stains on the appearance of the building.
4. Good compatibility
The surface of ordinary silicone sealant cannot be painted and colored, and can only be adjusted to specific colors according to users’ needs. While MS sealant is compatible with most paints and coatings, and can be directly painted on the surface of it, which can perfectly realize the uniform color of the exterior wall and maintain the beauty of buildings. However, the traditional silicone sealant will not maintain the appearance of coatings due to the shrinkage of the surface tension.
5. Non pollution
Because it does not add any volatile solvents or easy-to-migrate plasticizers, it does not contain silicone oil or silicone resin, and will not absorb dust in the air to cause pollution.
6. Excellent genes
The main chain of MS Polymer is a flexible segment of polyoxypropylene ether. It adopts special molecular design and polymerization process. The molecular weight is between 12000-15000. It can be regarded as very uniform in organic chemistry, and has stable performance. It has the advantages silicone sealant and polyurethane sealant.
7. Mechanical properties
The molecular structure and crosslinking characteristics of MS Polymer determine the performance and quality of modified silicone sealants (MS sealant). It has low modulus and suitable stress relaxation ability and high elastic recovery rate. It can follow joint expansion and shear deformation of the structure caused by environmental influences such as thermal expansion and contraction, wind load, earthquake action, and uneven settlement.
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