How to identify the low-quality sealant?

Silicone sealant and dimethyl silicone oil

Silicone sealant, whose main component is polydimethylsiloxane, has a molecular structure dominated by Si-O chemical bonds, has high molecular chain breaking energy, and has good UV resistance.

The basic compound of silicone sealant is hydroxyl-terminated polydimethylsiloxane, which has the same molecular structure as dimethyl silicone oil and has good compatibility. Therefore, dimethyl silicone oil is often used as a silicone sealant. Plasticizer. During the use of silicone sealant, dimethyl silicone oil will not evaporate or leak out over time, allowing the silicone sealant to maintain a high elasticity.

However, due to the relatively high price of dimethyl silicone, some manufacturers, in order to reduce costs, start with plasticizers and use white oil instead of dimethyl silicone as the plasticizer for silicone sealants, which reduces the performance of the silicone sealant and provides a better environment for buildings. Safety has also posed hidden dangers.

"White oil", an inferior substitute for dimethicone

White oil, also known as liquid paraffin, is a colorless, odorless, transparent oily liquid. Its main component is a mixture of C16~C31 alkanes. The molecular chain is dominated by C-C bonds and is flammable and volatile.

As a plasticizer, white oil can increase the gloss of silicone sealant and increase the extrusion speed. Compared with dimethyl silicone oil, it can reduce the cost by about 10%. This is also the fundamental reason why some unscrupulous businesses choose white oil in order to reduce production costs and increase profits.

What are the hazards?

What are the dangers of using silicone sealant containing white oil? Specific manifestations: embrittlement and cracking of silicone sealant, dissolution of butyl sealant, contamination of exterior facades, etc.

Hazard 1: Embrittlement and cracking of silicone sealant

White oil has a low molecular weight and is easily volatile. As time goes by, the tensile strength of the sealant containing white oil gradually decreases and the hardness gradually increases. The sealant will become hard and brittle. There are phenomena such as early failure of insulating glass and leakage of doors, windows and curtain walls. Causes the insulating glass to "cry". In strong sunlight or high temperature environments, white oil will evaporate from the silicone sealant, affecting the aesthetics of the building and making the glass sealing worse.

Hazard 2: Dissolved butyl sealant

If white oil penetrates into butyl sealant, it can also dissolve the butyl sealant and cause oil flow. Butyl sealant for insulating glass in a certain project flowed.

This is because the main component of butyl sealant is polyisobutylene, which is also dominated by C-C bonds. It has a similar polarity to white oil. According to the principle of similar miscibility, white oil is a good solvent for butyl sealant.

The water vapor sealing performance of insulating glass mainly relies on butyl sealant. The dissolution and failure of butyl sealant greatly shortens the life of insulating glass.

Hazard 3: Contamination of the facade

The use of white oil-filled silicone sealant for stone curtain walls will cause surface contamination of the stone and make it difficult to clean, requiring the stone to be replaced.

How to distinguish "white oil sealant"?

1. "Thin Film Method"

Take a slightly thick piece of polyethylene plastic film, apply silicone sealant on the film, and scrape it flat. Wait for a while and then open it. If the film becomes uneven, the sealant contains white oil.

2. Look at the appearance

If the color of the silicone sealant is too bright, it may be mixed with white oil, so you need to pay more attention.

3. Look at the price

Be especially vigilant about silicone sealants that are priced lower than the market price, because the cost of dimethicone is higher than that of white oil. If the price difference from the price of commercially available products is more than 10%, you must carefully identify it before purchasing.

4. "Butyl sealant" contact method

Silicone sealant containing white oil will dissolve butyl sealant. You can take butyl sealant and put it into silicone sealant. If the butyl sealant dissolves, it means that the sealant contains white oil.

5. Instrumental analysis method

GB/T 31851-2015 "Detection Method for Alkane Plasticizers in Silicone Structural Sealants" provides thermogravimetric analysis and infrared spectroscopy analysis methods, which can be compared and analyzed if conditions permit.