The most important mechanical properties of ABS are impact resistance and toughness. A variety of modifications can be made to improve impact resistance, toughness, and heat resistance. The impact resistance can be amplified by increasing the proportions of polybutadiene in relation to styrene and also acrylonitrile, although this causes changes in other properties. Impact resistance does not fall off rapidly at lower temperatures. Stability under load is excellent with limited loads. Thus, changing the proportions of its components ABS can be prepared in different grades. Two major categories could be ABS for extrusion and ABS for injection moulding, then high and medium impact resistance. Generally ABS would have useful characteristics within a temperature range from -20 to 80 °C (-4 to 176 °F).
Lego bricks are made of ABS.
The final properties will be influenced to some extent by the conditions under which the material is processed to the final product. For example, molding at a high temperature improves the gloss and heat resistance of the product whereas the highest impact resistance and strength are obtained by molding at low temperature. Fibers (usually glass fibers) and additives can be mixed in the resin pellets to make the final product strong and raise the operating range to as high as 80 °C (176 °F). Pigments can also be added, as the raw material original color is translucent ivory to white. The aging characteristics of the polymers are largely influenced by the polybutadiene content, and it is normal to include antioxidants in the composition. Other factors include exposure to ultraviolet radiation, for which additives are also available to protect against.
What is PLA?
PLA, or Polylactic Acid, is a biodegradable plastic with a lot of features that make it great for 3D printing -- it doesn't give off fumes like ABS does, or warp nearly as much. It's also really shiny.
PLA is harder than ABS, but more brittle, but that doesn't mean that it's easily breakable -- it's actually super strong -- just that when it does give, it's more likely to snap than bend. And it also stays flexible for a short while as it cools, which can be handy. And it doesn't warp and crack on larger objects the way ABS can. Basically, each is better for different kinds of things, and getting comfortable with PLA will give you choice and flexibility.
Before you start printing, there are a couple of things you should do: first, if your extruder is compatible, make sure you're using a MK8 nozzle. If you're printing with The Replicator you've already got one, and if you have a MK7 Stepstruder it's an easy upgrade. Then forget what you might have read about printing with PLA in the past -- there's a lot of information about PLA out there, but much of it won’t apply when you're printing with an MK8 nozzle.
When you first load your PLA filament, you'll want to make sure all the ABS filament has been purged before you start printing. Running the extruder for 300 seconds should flush out all remnants of ABS. Purging old filament will also get rid of any degraded PLA, so if your bot is already loaded with PLA filament and you're worried that the plastic inside the extruder has been heated for too long, run the extruder for a little while to get fresh plastic into the extruder -- fifteen seconds should do it.
Before you start printing, you should also make sure you're using an appropriate build surface. Blue painter’s tape makes a great surface for printing PLA -- the PLA will adhere well whether or not you're printing on a heated plate, and your printed objects will be pretty easy to remove. You should be able to find blue tape at any hardware store. The Acrylic plate on the Replicator 2 is another great printing surface, although sometimes items stick so well to the acrylic that it's difficult to remove them. For those occasions, we recommend a thin metal metal spatula. Users have also reported that a heated glass plate is great with PLA.
You can print with PLA on Kapton tape, but it's not a good idea. In order to get it to stick to the Kapton, you have to heat your platform, sometimes just as much as you would with ABS. And PLA retains heat, so the hot platform can degrade the plastic and have negative effects on your print, like causing the lower layers to sag or discolor.
The default profile on The Replicator is calibrated to work well with both ABS and PLA, but it's a good idea to learn how to change your Heated Build Platform temperature. PLA will stick well to blue painter's tape even on a cool build platform, so for most prints you can just delete the line of code that heats the platform altogether.
PLA can warp a little in cold spaces, or on large objects. There are a couple of ways of dealing with those conditions: if you have a heated build plate, you can set the platform temperature to 40° or 50° C, which will relax the lower layers of your print without overheating them. The easiest way to deal with this, though, is to have an active cooling fan cooling down the PLA immediately after it exits the nozzle.