I would suggest the following method for FTIR (Fourier Transform Infrared Spectroscopy) transmission analysis of wax samples ― (i) place a small piece of wax by the centre of a KBr disk, intended to be used as window; (ii) heat until the wax melts over the KBr window while heating together a second KBr window; (iii) superimpose the second KBr window to the first, gently squeezing both against each other, so that a thin film of wax, of uniform thickness, spreads in the between space, due to the combined action of pressure and capillary attraction; (iv) keep the sample in desiccator at room temperature until analysis, never touching it with bare fingers; (v) It might be found convenient to previously obtain a background spectrum with the same pair of windows simply juxtaposed, before being used for the sample.

Alternative methods ― For expedite qualitative analysis, you may try the following alternative simpler procedure: gently rub the wax over a KBr window, to spread a pasty-like residue. ― Windows of alternative infrared transparent materials could be used as well, as long as they don't react with the sample. ― If the sample can be powdered, you can alternatively use the usual KBr pellet method.

FTIR spectroscopy is most often applied for qualitative identification and structural analysis at the molecular (vibrational) level. Semi-quantitative analysis may, nevertheless, be attempted, by comparing the sample spectra with the spectra of best known reference (standard) samples in a normalized absorbance scale. Quantitative FTIR analysis may be also tried; in principle by the internal standard method. 

About the melting point of waxes you may want to check my answer at: https://www.researchgate.net/post/Where_are_the_melting_points_and_viscosities_of_waxes_tabulated2

I would suggest the following method for FTIR (Fourier Transform Infrared Spectroscopy) transmission analysis of wax samples ― (i) place a small piece of wax by the centre of a KBr disk, intended to be used as window; (ii) heat until the wax melts over the KBr window while heating together a second KBr window; (iii) superimpose the second KBr window to the first, gently squeezing both against each other, so that a thin film of wax, of uniform thickness, spreads in the between space, due to the combined action of pressure and capillary attraction; (iv) keep the sample in desiccator at room temperature until analysis, never touching it with bare fingers; (v) It might be found convenient to previously obtain a background spectrum with the same pair of windows simply juxtaposed, before being used for the sample.

Alternative methods ― For expedite qualitative analysis, you may try the following alternative simpler procedure: gently rub the wax over a KBr window, to spread a pasty-like residue. ― Windows of alternative infrared transparent materials could be used as well, as long as they don't react with the sample. ― If the sample can be powdered, you can alternatively use the usual KBr pellet method.

FTIR spectroscopy is most often applied for qualitative identification and structural analysis at the molecular (vibrational) level. Semi-quantitative analysis may, nevertheless, be attempted, by comparing the sample spectra with the spectra of best known reference (standard) samples in a normalized absorbance scale. Quantitative FTIR analysis may be also tried; in principle by the internal standard method. 

About the melting point of waxes you may want to check my answer at: https://www.researchgate.net/post/Where_are_the_melting_points_and_viscosities_of_waxes_tabulated2

Thanks a lot CARLOS 

But I dont have exactly waxes but its properties close to waxes.

yes, you can get FTIR analysis for liquid material, and you can determine composition the co-polymer material like the (Quantitative and Qualitative IR Studies of Some Synthesized Aromatic Polysulfides.

by: I.K.AHMED,M.A.M.RASHID. and J.K.JAWAD

Journal of Applied Polymer Science,31,2315-2323(1986)

Why not explore the Nijol method instead of the KBr method so as to compare the results since the latter requires sample in form of pellet.

Thank you Olasupo Malomo, I will try the Nijol method 

 Thanks a lot Kuestan Ibrahim, so useful

The problem, as I see it, consists of two important moments. The first is the problem of sample preparation, which can be easily solved with the help of set-top boxes for FTIR spectrometers, such as Single-Reflection ATR or Multy-Reflection ATR. In this case, to obtain the spectrum is not difficult.

Because, again as I see it, from the decomposition of PET may turn out oligomeric chains of different sizes, an accurate quantitative groups analysis is only possible when using the method of calibration samples of known composition beforehand. Such techniques there is a sufficient amount.

Thanks a lot Alex