Study on the preparation and properties of the polylactide/clay nanocomposite with controlled nanostructure

Abstract

The development of polylactide as a biodegradable commodity plastic was studied by introduction of clay into high molecular weight polylactide. Improvement of shear thinning and toughness of polylactide was mainly focused because the two properties are inherent problems originated from rigid chain structure of polylactide and should be solved preferentially for commercial application of polylactide to the commodity plastic. In contrary to conventional polylactide/clay system, commercialized clay was modified with aliphatic polyester such as poly(L-lactide), poly(ε-caprolactone), and poly(ε-caprolactone-co-L-lactide) by grafting ring-opening reaction onto clay surface followed by melt compounding the modified clay with high molecular weight polylactide.

The poly(L-lactide) grafted clay/polylactide nanocomposite showed highly improved shear thinning compared to polylactide and conventional polylactide/clay nanocomposite, and the degree of shear thinning was comparable level to commercialized polypropylene when molecular weight of grafted poly(L-lactide) was over the critical molecular weight of chain entanglement and inorganic content was 3wt%. This result was originated from end-tethered structure of the modified clay, and the chain entanglement/slippage between grafted poly(L-lactide) and matrix polylactide with frequency variation. Although the shear thinning is highly improved, toughness of the nanocomposite depressed with increase of inorganic content, and finally, brittle fracture of the nanocomposite occurred at 3wt% inorganic content. The mechanical behavior was originated from highly hardened clay effective domain which composed of end-tethered structure of modified clay, and entangled rigid polymer chains (grafted poly(L-lactide) and matrix polylactide) each other. Thus, flexible and compatible polymer with matrix polylactide was introduced into clay surface instead of poly(L-lactide). For this purpose, in first, poly(ε-caprolactone) is introduced in...