Some important aspects in designing high molecular weight poly(L‐lactic acid)–clay nanocomposites with desired properties

BACKGROUND: The main aim of the work reported here was to investigate the effect of clay aspect ratio and functional edge group on the dispersion, degree of order of clays and interfacial strength of high molecular weight poly( L ‐lactic acid) (PLLA)–clay amorphous nanocomposites and consequently their properties. Three kinds of clays (two montmorillonites (SMMTC18 and NMMTC18) and one fluoro‐mica (MC18) with the same surfactant) were used to synthesize three amorphous nanocomposites. Thermomechanical properties, permeability, etc., were compared among composites and with pure PLLA. RESULTS: From X‐ray diffraction and transmission electron microscopy, both MMTs with lower aspect ratio showed better dispersion and greater degree of disorder, which led to stronger interfacial strength and consequently higher storage modulus than MC18‐based composites. All composites showed better properties than pure PLLA. The oxygen barrier efficiencies of SMMTC18‐ and NMMTC18‐based composites were higher than that of the MC18‐based composites. Due to the highest exposed area and probably stronger interactions, SMMTC18 had the highest nucleating efficiency. CONCLUSIONS: Along with aspect ratio, dispersion and degree of intercalation, the interfacial strength of composites and degree of order of clays are also important issues for property development. Compared to reported results in the literature, our amorphous composites showed less of an improvement of thermomechanical properties as real reinforcement was solely from clays.