Had an interesting talk with our material guy at the office today.
I started to talk about how I just finished printing my 3 year old PLA roll. Never dried, never protected from the elements. Still printed without any problems. I found that interesting to tell, as it’s currently unknown how quick filament degrades and under which conditions.
(I most likely did store it dry enough, as we do know moister can effect prints)
Anyhow, what I really wanted to say. Is that he told me that PLA is transparent for UV. Meaning it does not degrade with sunlight. While ABS does. So ABS gets fragile from sunlight over time, while PLA stays in shape (unless it gets too hot). Which is kinda the opposite of what most RepRap people are saying. As they want ABS for structural parts.
Now I do know PLA and warm weather do not really mix. But for colder locations, might PLA be better then ABS for structural parts?
I would think it would depend on the application. PLA is more brittle than ABS, and this might be worse in the cold (anybody know?).
Natural ABS will quickly degrade in sunlight, becoming brittle and yellow. Which is why black ABS is much better suited for outdoor applications, as the carbon black colorant will have absorbed almost all UV light after a very short depth into the object.
I’ve had a black ABS part sitting in direct sunlight for the last two or three years and it’s still good as new.
I wonder if this is an argument to move to PET for structure.
Brittle is a term that describes a material which has a low strain-to-failure. It is also sometimes used in lay terms to describe a material that is notch sensitive.
Yes PLA is more brittle than ABS. When cooled both will become more brittle but that does not necessarily imply that their ultimate breaking strengths would decrease. At room temperature ABS has 4 times the strain to failure of PLA. It is unlikely that any reasonable cold conditions would cause ABS to become more brittle than PLA. Depending on the specific grades of plastic, PLA generally has a higher ultimate strength and modulus. than ABS.
If you consider that the molecules which make up thermoplastics as a group can only support a certain range of stresses then it is easier to see the relationship between increased modulus causing a material to behave in a more brittle manner. (not that that relationship is by any means linear) Where as a material with a lower modulus will obviously be more ductile.
http://plastics.ides.com/generics/1/c/t/acrylonitrile-butadiene-styrene-abs-properties-processing
http://plastics.ides.com/generics/34/c/t/polylactic-acid-pla-properties-processing
Ultimately, the material you use depends on what your design goals are… There is no single material that should be used for structure applications. (it also depends on you describe structure) Some structures are designed to be flexible to a certain extent. Other structures are meant to be extremely rigid.
This may or may not be relevant to the discussion: PLA smells like food to some animals. I’ve had raccoon eat and nibble on PLA prints that were placed outside, and eventually destroy them.
PLA is a bio plastic that is made from food sources. It can be corn strach, sugarcane or another natural renewables. To the raccoons it smells like what they might eat in the wild. I hadn’t heard of it being eaten by animals before but it makes sense.
I’ve never recommended ABS over PLA for resistance to UV. I’ve frequently recommended ABS over PLA for resistance to heat, e.g. from a stepper motor mounted to the printed part. Who’s telling people that ABS is more UV resistant?
Nobody is. People are recommending ABS over PLA for structural things.