1) One Explanation may be the kind of preparation: today it is standard to use the ATR-FT-IR method, which is an surface sensitive method (penetration of the light into the sample is very low, micrometer); due to surface tension during preparation of your blend, it can be possible that your "surface" consists mainly of PLA (Often it is possible to detect a process additive - like Bisstearamides  -which are enriched on the surface of a PLA blend)

2) Phosphate bands around 1000 cm-1 are broad and not very intense,

so combining 1) and 2)  you  see no change in the general pattern of PLA in this region

KR Rodion;

Dear Adven Hutajulu

After Blending PLA and BSA, what method you use for making them as 3D printing filament?

Dear Hutajulu,

Is it possible to see the ftir spectrum? One of the reason can be overlapping the PLA and hydroxyapatite ftir spectrum. One solution can be analyze powders individually via FTIR first, than the blend should be analyzed. I think you can find some distinct characteristic FTIR peaks.

Fatih.

Hi, I suggest you to use ATR-FTIR (surface sensitive method) for scanning your composite sample. And try to observe individual FTIR spectra first before you gonna see the difference of your composite sample.