Amine Blush as Related to Composites - Page 3

1.) Proper handling of the resin and curing agent
are necessary so that they are not contaminated with water and carbon dioxide. It is best to minimize the time that the lids or bungs are left off of the containers or drums so that the curing agent/hardener (Part B) has less exposure to the atmosphere. This is especially necessary when there is only a small quantity of hardener remaining in the container since the surface area will be maximized per volume. The remaining small quantity of hardener will therefore be affected to a greater extent than if the surface is exposed in a full drum. While it is usually not necessary to purge the drum head space with dry inert gas, this will insure the highest purity and consistency of the product. Another way to limit atmospheric exposure to the curing agent/hardener is to pour the drum out into smaller use bottles if it is going to be opened many times and small quantities are going to be used. It is also best practice to limit the exposure of the epoxy resin side (Part A) container or drum to the atmosphere since it will also absorb moisture, which will eventually put water into the mixed resin. All lids should be kept tight when not in use.

The mixing of the Part A and Part B should also be done in a way to reduce exposure to the atmosphere if at all possible. It is recommended that air entrainment in the mixed resin should be minimized as much as possible since this can add a lot of moisture and carbon dioxide into the resin before application, not to mention problematic air bubbles. Therefore, avoid large vortexes and high shear mixing. Oftentimes this is found with mixing with a drill type mixer or variable speed mixer. If working in a high humidity environment and one with excess carbon dioxide, try to cover the mix as much as possible or mix under purged inert gas or under vacuum. While it is cautioned against aggressive mixing, incomplete mixing can also lead to more amine blush. The curing agent/hardener (Part B) needs to be mixed thoroughly with the resin side (Part A) or there can be areas of high amine concentration that blush more readily.

2.) Off mix ratios (Part B to Part A) are often found to affect the extent of amine blush. If more curing agent is used, not only can the resin matrix mechanical properties and thermal performance be compromised, but the amine blush may be significantly greater. This is due to the excess active hydrogens on the amines not being consumed by the epoxy groups, which are capable of reacting with carbon dioxide and moisture. It is important to always use the specified mix ratio.

3.) The laminating/curing environment is a major factor in amine blush and oftentimes the consistency of the atmosphere is the reason more or less amine blush is observed on the surface of an exposed part. It is common to have times or seasons of the year when more amine blush is observed in uncontrolled manufacturing environments. This can be due to humidity and temperature changes which can also deviate significantly from day to day. Humidity and temperature also vary widely based on geographic area. This can be noticed especially when comparing Houston, Texas with an average relative humidity of 75% versus Phoenix, Arizona with an average humidity of 37%. Often the humidity range throughout the day can be quite significant. In indoor environments, higher humidity areas may be found within a single building. Concrete buildings and areas near walls and corners are especially prone to higher humidity. It is best to measure the humidity when it doubt and see what the range is in the laminating area or worksite daily. If outside it can be helpful to check the daily weather report to know the temperature, humidity, and dew point.

When taking the ambient temperature into account, and the temperature of the substrate; laminating table, fabric, concrete structure, it is best to laminate or apply the resin when the temperature is at least 10 ⁰F above the dew point, and not less than 5 ⁰F above the dew point. This is especially important for outside applications where temperature changes can occur more rapidly than in a building.

< Prev