Silane modified starch for compatible reactive blend with poly(lactic acid)

• The reactive blend between PLA and starch by silane coupling agent is proposed.
• The detailed structures of starch coupled with PLA by silane are clarified.
• Chloropropyl trimethoxysilane gives the reactive PLA/starch blend.
• Compatibility and PLA crystallization are induced by modified starch (CP-starch).
• The film obtained from the reactive blend maintains the high strength of PLA.

A reactive blend of poly(lactic acid) (PLA) and a surface modified starch by silane coupling agent to achieve compatibility is proposed. A detailed structural analysis by using 1H–1H TOCSY NMR spectrum clarifies, for the first time, that chloropropyl trimethoxysilane (CPMS) forms covalent bonds with starch during starch modification and consequently forms covalent bonds with PLA in the step of blending to produce a reactive blend of PLA and CP-starch. The CP-starch covalently bound with PLA provides the compatibility between PLA and starch and also plays the role as nucleating agent as identified from a significant increase of degree of crystallinity (as high as 10–15 times), as well as induces chain mobility, as identified from a slight decrease in glass transition temperature (∼5–10 °C). The PLA/CP-starch film performed as well as neat PLA with slight increases in tensile strength and elongation at break, as compared to other PLA/silane modified starch films.