How to remove bubbles from PU Casting Resin ?

Polyurethane bubbles can be divided into physical bubbles and chemical bubbles.

Physical bubbles are formed during production through mechanical processes like stirring or impact.

Chemical bubbles are formed from chemical reactions, such as water reacting with isocyanate to produce carbon dioxide, or other chemical reactions.

Essentially, bubbles are created when a gas dissolved in a liquid becomes supersaturated and separates out. This often happens during high-speed stirring, where a local area of high-speed flow creates a negative pressure zone, causing the dissolved gas to rapidly come out and form bubbles.

One common method to remove bubbles is vacuum degassing. By lowering the pressure, the dissolved gas is quickly drawn out, leaving the liquid in an unsaturated state. This can prevent bubbles for a period of time. However, if the vacuum-degassed material is left for several hours and then stirred again, bubbles will reappear. This is because at normal atmospheric pressure, the gas redissolves and reaches a saturated state again. Therefore, vacuum degassing only provides a temporary solution, and the process needs to be repeated after a long period.

Other methods to reduce bubbles include lowering the viscosity of the material or adding defoaming agents.

Eliminating bubbles from resin projects is a common challenge for crafters. Here's a summary of techniques to avoid and remove bubbles from your resin work, from simple preventative measures to more advanced methods.

The best way to deal with bubbles is to prevent them from forming in the first place. You can do this by using the right tools and techniques.

• Pour slowly down the side. Instead of pouring resin directly into the center of your cup, which can pull air into the mixture, pour it slowly down the inner edge of the cup. This allows the resin to flow in smoothly.
• Use a non-porous mixing stick. Wooden popsicle sticks can be porous, potentially releasing tiny air bubbles into your resin. Use a non-porous alternative like a plastic or silicone stir stick or a small baking spatula. A spatula is also great for scraping the sides of the cup, ensuring everything is thoroughly mixed.
• Mix slowly and steadily. Mixing too fast will whip air into the resin. Take your time and mix with a slow, deliberate motion.
• Choose the right size cup. Using a mixing cup that's too large for the amount of resin you're using can make it harder to avoid stirring in bubbles. Use a cup that fits the amount of resin you're mixing to make the process easier.

Sometimes, bubbles are unavoidable. Here are several methods to get rid of them once they're in your resin.

Lowering the viscosity (thickness) of the resin allows bubbles to rise to the surface more easily. Warming the resin before mixing is an effective way to do this.

• Submerge the bottle. The easiest method is to place your resin bottle in a container of warm water for a while before you start. Be careful not to get any water inside the bottle, as this can ruin the resin.
• Work faster. A side effect of warming the resin is that it will speed up the reaction time, so you'll have less time to work with it before it starts to harden.
• Use a slower-setting resin. Choosing a resin with a longer curing time will also give bubbles more time to rise and escape on their own.
• Use an Ultrasonic Cleaner. An ultrasonic cleaner uses sound waves to force bubbles out of the resin.
• Use a Vacuum Chamber. A vacuum chamber removes air from the resin by placing it under a vacuum.
• Use a Pressure Pot. Pressure pots can be expensive and require careful use, but they are highly effective.