Storage in a warehouse at a constant temperature of 25°C would be best for most polyurethane raw materials, although this isn’t always practical. In any case, some controls must be in place to prevent materials from experiencing the coldest temperatures of winter or the extreme heat that can occur in a warehouse in the summer. The storage requirements for raw materials differ based on their chemistry and delivery form.
Exposure of polyurethane dispersions to excessively low or high temperatures can significantly influence the performance of these products. The typical recommended storage temperature range for polyurethane dispersions is 5-25°C.
Process control is important in any weather, but for polyurethane foam users, fall and winter are particularly important times to pay attention to chemical temperatures. The changes that occur upon exposure to low temperatures range from an increase in viscosity of the polymer. The polymer with high viscosity cannot be dispersed upon stirring and cannot be transferred upon pumps. Generally speaking, chemicals shouldn’t be stored at temperatures below 10°C.
If polyurethane raw materials are subjected to elevated temperatures for an extended period of time, performance can be reduced. However, this change it is not as apparent as with cold temperature exposures. The molecular weight of the polymer backbone can see a reduction, which often leads to a drop in initial strength or a decrease in elevated temperature performance.
Isocyanates are products with limited shelf life. Shelf-life refers to the time period that you can store that polymer (PU) without loss of its qualities. Depending upon the isomer and oligomer composition, specific storage temperature and shelf life must be applied.
In isocyanates, if the storage temperature falls below recommended temperature, some crystallization will occur. Polymeric and modified pure MDI products that has been frozen, will exhibit the same dimerization characteristics as pure MDI. Unless proper action is taken to heat or melt the product. Crystallized MDI material can be re-melted at 50°C to 70°C. In other words, crystallized isocyanate can be melted, but dimer cannot be removed by heating.
Polyols are more freeze-sensitive than isocyanates, primarily, the ideal temperature for polyol storage is about 22°C to 24°C. However, it is recommended that:
- Gently rock tanks during warming process to evenly distribute chemical temperature. This can be done with rotating polyol tank.
- If the polyol material exposed to temperatures below 10°C, laboratory tests should be performed to double check processing parameters; after confirming characteristic parameters it can enter the production line.
- To warm polyol tanks, do not expose tanks or cylinders to open flame or temperatures above 49°C.
- Another way to heat polyol barrels is to use heating elements which can be carried out by setting the temperatures between 60°C up to 80°C .
- During colder months, it is extremely important to remember the temperature sensitivity of polyols; so store your sets in a warm room.
- Rock each tank before loading to prevent any possibility of phase separation.
It has to be noted that if the temperature of the chemicals rise above 25oC, the reaction times of the formulation will become faster. Accordingly, the temperature of the materials should be checked immediately after loading and prior to the mixing. Furthermore, storage of the components at high temperature causes evaporation of Low boiling point components such as blowing agents which can cause increase in product density.
Polyurethane raw material drums have to be stored indoors to protect the material from water ingress, frost and direct heat from the sun. Some components are sensitive to moisture or air so, once the lids of barrels opened it should be closed tightly to prevent air entrance to them.
When the lids of isocyanate barrels are opened, they will begin to react with moisture found in the atmosphere. This can result in the isocyanate crystallizing, and reducing its reactivity. The crystals formed can also cause blockages in injection machine filters. They cannot be removed with heating.
In polyol mixture, some catalysts will slowly react with atmospheric oxygen at ambient temperatures. This reaction may cause the material not to function properly.
In conclusion, it has to be mentioned that to achieve a good quality foam, it’s important to keep your polyurethane chemicals within a consistent temperature range, especially with temperatures dropping below freezing. The materials must be stored at room temperature (20°C to 25°C), in a dry area, for at least one day prior to use. Warming chemicals inside the tanks to proper temperatures may require up to 36 hours; however, storage at low temperatures may result in the product viscosity being too high for transfer from the storage container with the pumps available.
Generally speaking, the storage life of the polyol is 6 months and isocyanate 12 months.
