Understanding Plastics - ABS vs. PLA vs. PVA

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Understanding Plastics - ABS vs. PLA vs. PVA Hammerhead 11/14/12 6:18 PM
Can someone help me understand the basic characteristics and differences among the three common 'reprap' plastics?  I'm looking for a more clear picture of what the attributes of each type of plastic are, so that I can make a more informed decision, depending on the project.

Here's what I understand so far:

ABS: Toughest, strongest, most resistent to chemicals of the three, but also most difficult to use - less forgiving in the printing process.  Fewer color choices, not available in clear / translucent colors.  Best choice for harder-use projects, daily-use items, or where stresses on the model will require a more robust material.

PLA: Environmentally friendly, biodegradable, easier to use than ABS - more forgiving - adheres better, curls less.  Wider variety of color choices, also available in translucent shades.

PVA: ???

Thanks in advance!
Re: [MakerBot] Understanding Plastics - ABS vs. PLA vs. PVA Shawn 11/14/12 6:41 PM
- oil based
- melts at a little higher temperature than PLA
- better choice for warmer applications (such as extruders)
- a little stronger than PLA (this is unsupported evidence for me, I
haven't really seen the numbers on this, but this is a common point)
- more expensive than PLA
- available in many colors, including transparent.  But you may need to
shop around to find em.

- starch based (corn/plants/goats milk etc.)
- more environmentally friendly
   - from a renewable resource
   - if disposed of properly it will biodegrade
- cheaper
- melts at a lower temperature than ABS
- not as suitable for applications where heat is a concern
- considered a little weaker than ABS
- cheaper than ABS

- water soluable plastic
- possible uses as supports for more complex prints (when using FDM
- troublesome to work with - the ambient humidity may be enough to begin
the dissolving of the filament, so care is needed to keep the filament
dry when not in use.
- expensive (twice the cost of ABS)

- I have zero experience with PVA (yet), so cannot comment on strength
or other properties.
- I have not had a need to print with PLA either (yet), but have some
exposure to it.  Still the info above is general knowledge, I think.

- PLA may make for a cheaper solution for most objects.
- Use ABS when you need more strength or the object will be exposed to
heat (above 150-ish degrees celcius)
- avoid PLA unless you have a specific need, or have cash to throw around.

Other than that, the "difficult to use" comments seem to be a matter of
opinion.  I find the ABS easy enough to use, if I understand/configure
my machine properly.  Getting a properly levelled platform, and using
the correct temperatures for my environment, I see little or no peeling
or adhesion issues.  Taller prints may de-laminate in the middle if not
allowed to cool off at an even rate (hence the hoods and side panels
you'll often see in use...).  But that is just a knowledge thing.  I've
yet to see anything done in PLA that couldn't be made to look as good in
ABS, unless the semi-transparent colors are needed.  That said, I have
picked up a roll of PLA to experiment with.


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Re: [MakerBot] Understanding Plastics - ABS vs. PLA vs. PVA dnewman 11/14/12 9:40 PM
Putting on my (old and dusty) rheologist's hat, note that ABS has been around
for a long time and there's been decades of research aimed at making ideal
formulations for the myriad ways of processing it, including what all fillers
to use to get different behaviors during processing (e.g., increase viscosity,
reduce viscosity, increase non-newtonian behavior, decrease non-newtonian
behavior, release from molds easily, etc.) and post processing (e.g., strength).

PLA is a relative newcomer and there's a lot of ongoing research aimed at making
it easier to use in manufacturing as well as making it a more viable alternative
to other thermoplastics such as ABS.  So, I figure that PLA is going to
improve over the next decade or so.  Unfortunately, it may also get smellier if
they start adding volatiles to it like they do ABS.  (ABS has some volatiles of
its own, but others are added to improve its behavior for injection molding and
extrusion.)  And while we like the fact that PLA doesn't shrink when it cools,
that can actually be a problem in some manufacturing processes (e.g., releasing
from molds).  I worry that the more common PLAs in a decade or so will have some
shrinkage as a property as well.

Re: [MakerBot] Understanding Plastics - ABS vs. PLA vs. PVA Hammerhead 11/20/12 10:48 AM
Been thinking about this for a while.  Wondering if there's a general recommendation on what material to use for what purpose.  For example, for prototpying proof-of-concept products, would PLA be better than ABS?  For items that we print for daily use (like Thing 31819) would ABS be better than PLA?

Just trying to see if there are any recommendations on what's better to use given certain conditions, or which plastic to AVOID for certain purposes.  Obviously, anything that'll be exposed to acetone or other strong solvents is a gimme, but I'm just wondering if in the case of a daily use item, if PLA would hold up as well as ABS.
Re: [MakerBot] Understanding Plastics - ABS vs. PLA vs. PVA Cymon 11/20/12 11:20 AM
I was surprised to see the comment on http://www.thingiverse.com/thing:33975 that it begs to be PLA because of "the size of the chimney and where the hole is situated." Being and ABS person myself would someone explain this to me?