Annealing HTPLA (+)
There are many questions that surround the annealing process of PLA's and what the benefits are.
A few people have sent us reports about their adventures annealing the HT materials.
You can see the part on the left is much more opaque than on the right. The part on the left has been annealed in an oven and the one on the right has not.
After annealing, the part on the left has been thrown into boiling hot water for several minutes and then taken out to cool. As you can see there is no distortion to the part.
The part on the right has not been annealed and also thrown into boiling hot water for several minutes. This results in an instant failure of its structure. It is important to note that each part was stressed in a similar way when removed from the boiling water, but again, annealing is the clear winner.
So many questions are asked about how / why to anneal parts and I will try to cover some here.
1. What is annealing?
Annealing is a process that is used to slowly heat a part to a defined temperature and keep it at that temperature for a certain time to allow the crystalline structure of an object to "relax".
2. What does annealing do?
In this case, it makes the material more robust. It allows the material to relax and become stronger and more resistant to temperature changes that would normally cause distortions.
3. How will annealing affect my part?
Most times, the common factors are shrinkage and a slight opaqueness change. Shrinkage is typically less than 1% but can be more significant in larger parts.
4. What is required to anneal a part correctly?
According to Natureworks, the correct temp is 110c (230f). It can be done at a lower temperature if you feel your oven cannot maintain a good temp, but the safer option is to bake it for a longer time. You can tell it's finished annealing when the opaqueness changes to milky.
5. How long does it take to anneal a part?
This is a great question! Times vary depending on the size and weight of the part. Typically a part that weights 100 grams and is 75mm x 75mm will take about 15 minutes. Larger parts are difficult to estimate. The best way to tell is by checking for the appearance change of a white / milky color hue as the crystals develop.
6. What will happen if I don't anneal my part?
Typically nothing negative will happen unless you are trying to use when combined with something hot. Plenty of people just want to print and go, annealing isn't really something that concerns them. This is OK. It is not required to anneal PLA, it's only really needed when it will be exposed to high temperatures. While annealing is not required to print with HTPLA, the process of Annealing can be used to increase the resin's temperature resistance
7. Would printing HTPLA+ extra hot (like 270C) affect the heat resistance? Would printing it that hot be like annealing it already, or not really?
Printing HTPLA+ (or any amorphous) resin at higher temps won't anneal it. Annealing is the process of growing crystals (a transition from amorphous to crystalline) to temper the material. Extruding it at any temp makes it amorphous. Imagine it like this.... The plastic is solid when cooled, annealing allows the plastic to soften, but not melt. When the plastic is in its "softened" state the solubility in the resin changes allowing the latic part of PLA to form crystals. This is similar to allowing all the water in a salt solution to evaporate and all your left with is salt crystals. The evaporation forced the solubility to change since the salt solution got more and more salty to the point where the salt fell out of solution. This is kind of similar to how HTPLA+ "grows" crystals...only it is growing under slight heat. If the plastic is reheated to its extrusion temp, the solubility changes again and makes it go back to amorphous (basically the latic in PLA re-dissolves again).
If there are any more questions you'd like us to answer, please email us!