Polymer Processing – Resin Moisture After Drying (Support Table)

 Hello and welcome to this blog post on resin drying before processing them. In this post I provide you with a drying table of the most used polymers which can support you in your processing operations.

A word on resin drying

If material is not properly prepared for processing operations such as injection moulding, the moisture will break down the polymer in the barrel at the processing temperatures. In general, this is referred to as hydrolysis.

This can occur for many different polymers, including:

-Polyamides (all types)

-Polyesters (PET, PBT)

-Polycarbonate

-Polysulfones

-Polyurethanes

 

There are five keys to remember which ensure good drying of resins [1]:

1. Pellet / regrind incoming moisture level

2. Air temperature

3. Dewpoint/ Desiccant

4. Residence time

5. Air flow

In this video below here, I discuss the topic of material drying and troubleshooting of moisture streaks in detail:

 

The table below shows the different maximum moisture levels after resin drying to ensure proper processing.

 

Table: maximum moisture content after resin drying of most used polymers

Analyzing the moisture level after drying can be done over a Carl Fischer titration (lab equipment needed) or over the Tomasetti’s Volatile Indicator (TVI). The TVI represent a more practical approach since you need only a hot plate and a glass plate to place the pellets after drying. The temperature of the hot plate is increased till the pellets melt and then it is important to check if there are bubbles. The bubbles are an indicator for moisture and there can be few bubbles (0.02-0.03% moisture), numerous bubbles (0.05-0.1% moisture), or many large bubbles (moisture above 0.1%) or no bubbles at all (dry material). If you do not have a hot plat you can also use the heater band of the injection moudling machine. 

Thank you for reading and #findoutaboutplastics

Greetings,

Herwig

 #polymerprocessing #herwigjuster

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Literature:

[1] GE Plastics – Moulding Guide

[2] Saechtling Kunststoff Taschenbuch, Hanser-Fachbuch