Refer the following article 

Polylactic acid/polypropylene polyblend fibers for better resistance to degradation,  Polymer Degradation and Stability 93 (2008) 233-241

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The question is not really clear,

if by bonding you mean the bonding strength between PLA and PP, you can estimate that from the work of adhesion and the surface energy data of these polymers :

for PP:

http://www.surface-tension.de/solid-surface-energy.htm

For PLA;

http://pubs.acs.org/doi/abs/10.1021/bm400784j

If you mean any chemical interactions (hydrogen bonding ....), I dont expect any specific interaction between these two polymers

Your question implies that you want to measure and compare bonding of poly(lactic acid) (PLA) and polypropylene (PP) in composites, that is bonding to the filler (rather than bonding between PLA and PP (since you do not mention that you are forming polymer blends). If the filler is a fibre you can use a fibre pull-out test with a small bead of polymer melted onto the fibre. The stress (based on contact area with polymer) required to pull the fibre from the polymer is measured. Particulate fillers are more difficult to assess adhesion with polymer; a semi-quantitative estimate is to observe fracture surfaces using scanning electron microscopy (SEM). Poor adhesion will leave clean filler surfaces, good adhesion will results in fragments or strands of polymer remaining on the filler surfaces. Polymer(PLA)–polymer(PP) blends can be assessed in the same way using SEM to assess the extent of separation at surfaces.

In addition to all suggestions mentioned above , if you really want to look at the bonding between the PLA and PP you can do the FTIR and also the backscattered SEM which will enables you to find the distribution of the fillers into the matrix. Secondly do the tensile test of the composites and do the SEM analysis of the fractured surface to the fracture mechanism of the composites . Any pulls-out of fibres will lead to poor adhesion b/w the matrix and reinforcements.

Dear Ramachandran,

Dear Ramachandran,

" The interfacial tension of PLA/PP blend studied in this work has been determined using the solubility parameter of the pure polymers. The solubility parameter of a polymer (δ) consists of dispersive (δd), polar (δp) and hydrogen-bond (δh) components  as follows :

δ² = ( δd² + δp² + δh )  "

Rheological and mechanical characterization of poly (lactic acid)/polypropylene polymer blends.

J Polym Res (2011) 18:1799–1806

Good luck