Synthesis and characterization of a novel blend of polypropylene with Chlorella

A novel blend of polypropylene (PP) with Chlorella, a natural microalga, was synthesized successfully by a melt-mixing method with maleic anhydride-modified polypropylene (MPP) as a compatibilizer. The adhesion of hydrophobic PP to hydrophilic Chlorella is based on the formation of chemical bonds between the maleic anhydride groups of MPP and hydroxy groups of Chlorella through solid-phase esterification. The single maleic anhydride groups have the highest reactivity with Chlorella. From the comparison with PP-Chlorella blends without MPP, the ester bonds between MPP and Chlorella cause a decrease in crystallinity of the MPP matrix which is a primary origin of the decrease in melting and solidification enthalpies of the MPP-Chlorella blend, and induce intensive expansion of the MPP matrix around the Chlorella particles which decreases the glass transition temperature. Consequently, the PP-Chlorella blend with MPP exhibits a marked increase in tensile strength and Young's modulus compared with the blend without MPP because of the stronger interactions between MPP and Chlorella than those between Chlorella cells.