Drying or dehumidifying plastics is an important phase of injection molding manufacturing. The process is necessary as it helps to get rid of complications that may be caused by excess moisture in plastic material. The best option is to get a dryer from a reliable hopper dryer manufacturer. You should note that moisture can affect the shape and quality of the manufactured part depending on the resin used.
Categories of Plastic Resin
There are two main types of plastic resins. Each type has certain manufacturing characteristics, which have a given affinity to moisture. The main types of polymers are non-hygroscopic and hygroscopic polymers.
Non-hygroscopic Polymers
Examples of these plastics are polystyrene, polypropylene, and PVC. Such plastic resins cannot absorb moisture into the pellet. Instead, the moisture gathers on the pellet’s surface. Thus, you can apply heat to get rid of the surface moisture. You should note that the moisture that gets deposited on the surface is because of condensation. In fact, you can eliminate the moisture by passing a stream of hot air over the plastic material.
Hygroscopic Plastics
Examples of these polymers are polycarbonate, PET, ABS, nylon, and polyurethane. Such resins can absorb moisture internally before releasing it into the air. As a result, any resin obtained from a store to the injection molding must be dried because of its hygroscopic properties. When the wet hygroscopic pellet gets surrounded by the hot and dry environment, the moisture inside the pellet migrates until the granules become dry.
You should note that hygroscopic polymers have an excellent affinity for moisture. It is not possible to get rid of internal moisture by using only hot air. It can absorb moisture into the molecular structure when it gets exposed to the ambient air.
Benefits of Drying Plastics
Although the moisture within plastic granules or pellets does not seem to be a big aspect, if it is not controlled, it will become difficult to make high-quality plastic parts. Therefore, drying before processing is necessary to maintain the performance of the resin. These are the benefits of drying plastics before injection molding.
Prevent Hydrolysis
If water is left in a polymer, there is a possibility for hydrolysis to occur. This is a chemical reaction that breaks covalent bonds in a polymer reduces the mechanical properties of the polymer.
Prevent Part Failure
If moisture is not expelled from the plastic granules before processing, there is a likely occurrence of structural defects and part failure.
Prevent Aesthetic Issues
The common problem that occurs when plastic granules are not dried accordingly is known as silver streaking.
Remember that there are different resin dryers available on the market. Therefore, you have to ensure you get the right hopper dryer that suits your needs. The fact that a plastic material appears dry at the normal temperature and for a long length of time does not mean it is dry enough for processing. You may be surprised to learn that the plastic material can contain a lot of moisture and can be dried for an extended period. Always ensure you measure the moisture content for injection molding. You can do this on a routine basis to eliminate the part quality problems you may have.
