Moisture is both necessary in and potentially detrimental to nylon applications. The effects of under-drying nylon can lead to degradation of the material, and ultimately, poor part performance. Similarly, over-drying nylon increases polymer viscosity and slows nylon flow. Both interfere with optimum processing and performance of nylon.
Appropriate management of moisture levels in nylon resins is a delicate balance. It requires precision equipment, applied knowledge, and expert guidance from a custom compounder.
As the name suggests, moisture analyzers are instruments that determine the amount of moisture present in a given material. Moisture analyzers are a logical solution for managing moisture in nylon but it’s important to note that they are not a universal solution.
There are two types of moisture analyzers. To invest in the one that best serves your needs, it’s important to understand the differences:
Gravimetric moisture analyzers measure the total change in weight of the material when a sample is heated at a specific temperature. The loss by weight method focuses on moisture burn-off to calculate moisture presence, but it can lead to inaccurate results since volatiles burn off along with moisture. Moisture values may be overestimated in a nylon resin which could lead to over-drying.
Moisture specific analyzers use a chemical process to specifically detect moisture levels. Volatiles do not factor into the calculations or results, testing temperatures are more closely controlled, and ASTM D7191 compliance is met. Karl Fischer and CompuTrac® are reliable names in this type of highly accurate moisture measurement equipment.
Dryers are instrumental in proper nylon moisture management and molding within correct moisture ranges. Calculating the dryer size based on part weight, cycle time, and bulk density conversion of dryer to material is the first step to reaching the goal of 4-5 hour residence time; however, working within the parameters of an uncontrolled or controlled dryer system influences moldability:
Uncontrolled dryer systems typically date to years prior to 2006. Air flow, temperature, and time are all fixed. There is no deviation in runs and there is no allowance for input-output communication. Moisture study DOEs are required to create contour plots to follow prior to and during production, which introduces the potential for inconsistencies and nylon over-drying.
Controlled dryer systems are circa 2006 and newer. The additive control systems automatically adjust airflow and temperature to achieve ideal drying temperatures. Dryer inputs and outputs operate on a continuous feedback loop, providing data prior to and during production that aids in monitoring and steadying moisture ranges for optimum nylon drying and moldability.
This brief look into a few of the many variables that influence moisture levels of nylon resins underscores the importance of partnering with a knowledgeable custom materials compounder like Teknor Apex.