Moisture curable toughened poly(lactide) utilizing vinyltrimethoxysilane based crosslinks

Abstract

Vinyltrimethoxysilane (VTMOS) was grafted on to the backbone of poly(lactide) (PLA) through a free radical grafting reaction using reactive extrusion (REX) processing. The methoxy groups of the silane provide the modified PLA sites for crosslinking through a moisture induced pathway. VTMOS grafting efficiencies of up to 90% were obtained. The newly created methoxy functionality of the modified PLA readily undergoes hydrolysis and condensation forming siloxane crosslinks in the material. Crosslinking with VTMOS exhibited improved modulus, strength, and impact toughness while showing a decrease in ductility. Incorporating silanol-terminated poly(dimethylsiloxane) (OH-PDMS) resulted in the formation of longer siloxane crosslinks. These samples showed an increase in modulus and impact toughness due to the crosslinking, while the longer siloxane linkages resulted in improved ductility and tensile toughness. This is unusual for polymers toughened through crosslinking reactions. Scanning Electron Microscopy (SEM) of the fractured surfaces showed the presence of these elongated siloxane crosslinks. This enhanced ability for the modified PLA to deform and absorb energy results in the increase in both impact and tensile toughness.

Keywords

• Biodegradable polymers
• Reactive Extrusion
• PLA
• Free Radical Grafting
• Moisture Induced Crosslinking