Ahmed,

What were the conditions you used for the FTIR spectrum?  Thin film, KBr pellet, attenuated total reflectane, diffuse reflectance?

If the PLA you purchased has a plasticizer it will be part of the IR spectrum of the sample if it is present at concentrations above ~1%.  The dye may also be part of the spectrum if it has IR active bands.

Please provide some more information on the sample and conditions you used to obtain the spectrum.

The spectrum does not look like it is from PLA.  It resembles ABS more (quite a few peaks that also appear in polystyrene, and some unsaturation related peaks).  ABS I believe is used in 3d printing as well, so this would be my best guess at this point.

I agree: some peaks of added plasticizer mask the PLA's peaks

I think that Dr. Kaoru Aou is right - in the spectrum one can see the evidence of CN bond at 2239 cm-1, so my guess is also that the material is very probably acrylonitrile-butadiene-styrene terpolymer.

check your baseline first,  you have bad image

Dear Yanfei Hu , Thanks for reply 

How can I check it pls , what should I do .I attached you good photo above pls check 

Dear Angela Kleinova , Thanks for reply 

My commercial PLA included white dye and may be plasticizer but whether it is ABS I do not agree bcs as an initial test it is softer than ABS , in addition ,I have FTIR for ABS under my hand .

Dear Leonid V Vladimirov  , 

This is good point and it is what Iam searching .PLA may not take more than 4 peaks of test above and other how  I have to deal with them ?

Dear Kaoru Aou , 

Yes I agree with you both PLA and ABS used in 3D printing but Iam testing right now PLA , but this PLA is processed by white dye and plasticizer and those materials afftect the test .

Dear John Hiltz  , 

Thaks for sharing us your knowledge , yes we used Kbr and PLA as powder .

Semicrystalline PLA is not easily soluble in most solvents, but plasticizers usually are, so you might consider dissolving away the plasticizer (which might have aromatic groups, like phthalates) so that you have a cleaner spectrum.

If your PLA all dissolves, at least your white pigment  (assuming it's inorganic) should stay insoluble, so that you will have a material with simpler a spectrum.

In any case, if there is PLA, it may be a very small amount, as I don't see the strong ~1750 cm-1 peak in the infrared spectrum that I expect -- something else with a C=O peak  (phthalates may be a possibility) may be drowning out your signals. 

FTIR spectrum support that the material is ABS. You may try to find its solubility in acetone. ABS is soluble in acetone but not PLA. Density is also good evidence. Density of PLA:  1.2-1.4 and ABS: 1.08.

I´ve had try to solve this riddle, so I´ve searched my library of spectra of some polymers. Attached please find the spectra of the neat PLA and also of the neat ABS; these materials don´t contain additional chemicals. Also I´ve made some maths - adding  the spectrum of PLA to the spectrum of ABS (assuming that your material is a blend of these two materials, PLA and ABS) and I´ve uploaded also this addition result. Possibly your purchased material is really a blend of PLA (and I suppose, it contains less PLA than ABS)  and ABS (which can be used as a plasticizers for PLA). In order to prove it, you can make some blends of PLA and ABS with various content of constituents, then make KBr pellets and measure the spectra. Or, you can also determine whether your material contain nitrogen, by simple CHN analysis.  Best wishes, AK

Dear Ahmet Akar , 

Thanks for sharing , I tested density and it is 1.005 g/cm3 . I also solve it in acetone and it is  solved . I solved the ABS that I bought it from same supplier  , as supplier said it is ABS , and it is not solved in acetone . I read that PLA can dissolve in acetone .

Dear Angela Kleinova ,

Thanks for efforts  ,your charts above is very helpful . 

I agree, with the previous comments, that is clearly not PLA, there is evidence of aromatic groups (which would account for styrene) and no intense ester C=O stretch, which is the dominant feature of PLA spectrum.

I would also suggest if you want to know the tacticity of the PLA samples that you should do NMR (13C is easier), as the IR signals isotactic PLA can be very weak. DSC can also be helpful as isotactic, syndiotactic and atactic PLA have very different thermal profiles. Atactic is often blended into isotactic PLA to improve the processing conditions. 

To improve your baseline on the FTIR, I would suggest dissolving the polymer in Chloroform (5-10 wt%) and dropcasting or spincoating onto a KBr or NaCl plate, a thinner layer will improve signal.

Dear T H Hill , 

Pleased to share us your answer .while there is three types of PLA ; PDLA ( amorphous in DSC ) , PLLA ( crystalline ) and PDLLA ( apart crystalline and the reset is amorphous ) where Iam talking here copolymer technique not blend , do you agree with me ? we do not have NMR .

Regarding of improving IR signal I will check your idea but our FTIR device require test sample as a powder . 

I attach you here FTIR supposed belong to PLA , pls check it . 

@A S Kareem:  the spectrum just posted is indeed that of PLA (semicrystalline, but nearly amorphous PLA, judging from the weak 923 cm-1 peak, which would be much more intense for very crystalline PLA).  In this transmission FT-IR spectrum, the film is too thick such that the absorption is too strong from the film to be very well measured. As a remedy, Dr. Hill already suggested dissolving the polymer and dropcasting onto a salt plate (KBr or NaCl), and I think that is sound advice.