Renewable and Tough Poly(l-lactic acid)/Polyurethane Blends Prepared by Dynamic Vulcanization

Area of Science:

• Polymer Science and Engineering
• Materials Science
• Biomaterials Engineering

Background:

• Melt blending offers a route to combine desirable polymer properties.
• Poly(l-lactic acid) (PLLA) requires toughening for broader applications.
• Fatty-acid-based polyester polyols provide a sustainable component for polymer modification.

Purpose of the Study:

• To toughen PLLA by creating a cross-linked polyurethane (PU) network within a PLLA matrix using dynamic vulcanization.
• To investigate the morphology, structure, and properties of the resulting PLLA/PU biobased blend.
• To understand the effect of PU content on the mechanical, thermal, and crystallization characteristics of PLLA.

Main Methods:

• Dynamic vulcanization of a fatty-acid-based polyester polyol with glycerol and PLLA using hexamethylene diisocyanate (HDI) in an internal mixer.
• Characterization using melt torque, Fourier transform infrared (FTIR) spectroscopy, gel fraction analysis, scanning electron microscopy (SEM), and polarized light optical microscopy (PLOM).

Main Results:

• Successful formation of a cross-linked PU phase within the PLLA matrix, confirmed by FTIR and gel fraction analysis.
• Sea-island morphology observed via SEM, indicating dispersed PU domains within the PLLA matrix.
• Increased impact strength and decreased Young's modulus of the PLLA/PU blends due to the rubbery PU phase.
• Reduced PLLA crystallization rate but promoted PLLA nucleation by the PU rubbery phase.
• Slightly reduced thermal stability of the blends compared to neat PLLA.

Conclusions:

• Dynamic vulcanization effectively creates a toughened PLLA/PU biobased blend with a distinct morphology.
• The incorporated PU network significantly enhances impact strength while modifying mechanical and crystallization behaviors.
• The study demonstrates a viable method for improving PLLA's toughness through in-situ PU formation, with potential for sustainable material development.