Solidoodle Wiki

Understanding ABS; by Kendall

Plastic resins are made by heating Hydrocarbons in what is known as the "Cracking Process". Once the Cracking Process has been completed, the Compounds are formed into Chains that are known as Polymers. In our scenario; Then the Polymer is Extruded into Long Strings, with a Specific Diameter, and Melt Flow Index; during this process Colorants and other Additives are added.

Acrylonitrile Butadiene Styrene (Co-Polymer)

Understanding the chemical structure of ABS, and its relationship to heat.

Polymer

• Polymer: made up from two words; Poly meaning 'Many', & Mer meaning 'Units'.
  • ABS is a large Molecule composed of repeating Many structural Units (elements/chemicals) in one long chain.
  • A Molecule of ABS is about 1000 times longer than its diameter, making it easily Degraded.

Degrading

• Degrading: the breaking of this molecules structure.

Crystalline

• Crystalline: a mass (material) with crystalline structure. Crystalline structured masses, have a 'Change of State' at a given temperature.
  • Crystalline Change of State: example; (Water) H2O at 0°C is Ice, H2O at 100°C is steam, any between temperatures it is water; H2O is crystalline, it has a 'Change of State' at a specific temperature.
  • Some Plastic Resins are classified Crystalline, some are Amorphous. Resins that are classified Crystalline, are not true Crystalline, they do have the 'Change of State', but it happens over a specific temperature range.

Amorphous

• Amorphous: a mass (material) without a crystalline structure. Amorphous materials have a continuous degree of 'Change of State' during all temperature changes.
  • Amorphous 'Change of State' example: Wax gets softer and softer as temperature is introduced, and harder and harder, as the heat is removed.

MFI

• Melt Flow Index: is a measurement of the ease of flow of the melt. It is defined as the mass of a polymer, in grams, flowing in ten minutes, through a capillary, of a specific diameter/length, feed by a prescribed gravity weight, at a prescribed temperature.
  • The Melt Flow has a direct relationship with the viscosity of the material at a given temperature. Thus, how it is flowing out of our extruders.
  • The Melt Flow Index of the FFF filament that we purchase, is an unknown to us (I do not see it specified by the manufacture on the websites that are selling it, and it probably varies by the manufacture that is extruding it).

Hygroscopic

• Plastic materials that absorb moisture from the air are called Hygroscopic Resins. Hygroscopic Resins have a strong affinity to attract moisture and absorb it into their molecular structure.
  • Moisture does affect the melt flow index
  • Moisture does affect degrading

Drying ABS

• As we learned above; Resins get their strength from long Polymer Chains that are entangled. Short Chains provide easier flow but sacrifice Strength and the other Physical Properties. Even if your material supplier dries the Filament and immediately packs them in plastic bags, the resin will still contain moisture when you receive them, and will start absorbing more, at at a faster rate, when removed from the packaging. Hygroscopic Resins contain Carbon and Hydrogen but, also have a ‘Polar’ segment of Atoms that behave like a small magnet with north and south poles. Moisture is also a Polar Substance; you’re getting two mini-magnets that attract each other.
  • Why, do you Dry Hygroscopic Resins? To get the moisture out, but more importantly to ensure Maximum Polymer Consistency and Performance during your Extruding, with the best Structural Strength for your Final Product.
    • Professionals use Equipment; Descendant Dryers (sealed dryer systems), Due Point Meters (an instrument for measuring the amount of moisture in the air), Moisture Meters (analyzing tool for measuring the actual moisture content of the polymer). All of these listed items are; "Mucho Dinero".
  • Option Moisture content for Extruding is .01% to .02%; less that this will make the material harder to push; more, and you will start loosing physical properties.
• Suggested drying conditions for ABS resins are 80 - 90 C (176 - 195 F) for a minimum of 2 hours, but 4 hours is recommended.

Drying Filament at home

• Back in the late 60’s; only the cash rich companies had dryers that were designed to dry resins. The rest of us used conventional electric ovens with wire mesh trays, and dried the material pretty much like today's specifications for heat and time, but we had no way of knowing until trying the material, if it was dry enough. Once the material was exposed to the atmosphere, it started gaining moisture content again. We had constantly be rotating trays out of the oven and dumping them into the hopper, just before the hopper ran out, tray after tray.
  • Today most of us have convection ovens (re-circulating air oven’s); this seems to me, to be better method of accomplishing the same goal with a lot less inconsistency.

• How much does drying affect us?
  • If you are having problems, it could be related to wet material.

• Do I have to stop and dry my material?
  • Maybe not, just applying some understanding, you might be able to make some adjustments to compensate.
    • If you have a part that requires high tolerance, high quality, you might want to plan the drying step in your preparation.

• When I dry my material, how can I store it?
  • It will need to be in an air tight container, and also will require a desiccant added to the container. You can purchase some self-contained packets; like made for a Gun Safe’s, I have seen some that make claims to last for 30 days, and can be recharged in your oven in a couple of hours.

Colorants

• Dyes and Pigments are made in various ways. Their formulations vary from color to color, and the additives are different for each. The Compounder will try and match the melt flow of the material, but this is not always an easy task.
  • Red's, Gold's, Florescent's, and Glow in the dark Colors may be especially effected.

Enjoy the coolness of the day!

• Return to 'All Materials' Page
  • • Go to 'Recycling ABS' Page
    • Go to 'Safety Info about ABS' Page