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Dramatic Improvements in Strain Hardening and Crystallization Kinetics of PLA by Simple Reactive Modification in the Melt State



Poly(lactic acid) (PLA) is chemically modified by radical mediated solvent-free, peroxide-initiated grafting of triallyl trimesate (TAM) coagent in the melt state. When compared with the parent material and with PLA samples treated with peroxide alone, coagent-modified materials demonstrate higher molar mass and improved melt rheological properties, including substantial improvements in melt elasticity and strain hardening under uniaxial extension. Although similar rheological modifications are obtained by PLA chain extension using a multi-functional epoxide oligomeric chain extender, the coagent-modified material demonstrates significantly enhanced crystallinity and crystallization rates. The appearance of a distinct crystallization exothermic peak and the disappearance of the cold crystallization temperature point to a nucleation effect in the coagent modified PLA, which together with the rheological enhancements can promote the processability of this material in conventional thermoplastics operations.mame201400078-gra-0001