Super-toughened poly(l-lactic acid) fabricated via reactive blending and interfacial compatibilization

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

Melt blending of homopolymers is an effective way to achieve an attractive combination of polymer properties. Dynamic vulcanization of fatty-acid-based polyester polyol with glycerol and poly(l-lactic acid) (PLLA) in the presence of hexamethylene diisocyanate (HDI) was performed with the aim of toughening PLLA. The dynamic vulcanization in an internal mixer led to the formation of a PLLA/PU biobased blend. Melt torque, Fourier transform infrared (FTIR), and gel fraction analysis demonstrated the successful formation of cross-linked polyurethane (PU) inside the PLLA matrix. Scanning electron microscopy (SEM) analysis showed that the PLLA/PU blends exhibit a sea-island morphology. Gel fraction analysis revealed that a rubbery phase was formed inside the PLLA matrix, which was insoluble in chloroform. FTIR analysis of the insoluble part shows the appearance of an absorption band centered at 1758 cm-1, related to the crystalline carbonyl vibration of the PLLA component, thus suggesting the partial involvement of PLLA chains in the cross-linking reaction. The overall content of the PU phase in the blends significantly affected the mechanical properties, thermal stability, and crystallization behavior of the materials. The overall crystallization rate of PLLA was noticeably decreased by the incorporation of PU. At the same time, polarized light optical microscopy (PLOM) analysis revealed that the presence of the PU rubbery phase inside the PLLA matrix promoted PLLA nucleation. With the formation of the PU network, the impact strength showed a remarkable increase while Young's modulus correspondingly decreased. The blends showed slightly reduced thermal stability compared to the neat PLLA.

Facile Preparation and Characterization of Short-Fiber and Talc Reinforced Poly(Lactic Acid) Hybrid Composite with In Situ Reactive Compatibilizers

Hybrid composites of fillers and/or fibers reinforced polymer was generally produced by masterbatch dilution technique. In this work, the simplified preparation was introduced for the large volume production of 30 wt % short-fiber and talcum reinforced polymer hybrid composite by direct feeding into twin-screw extruder. Multifunctional epoxide-based terpolymer and/or maleic anhydride were selected as in situ reactive compatibilizers. The influence of fiber and talcum ratios and in situ reactive compatibilizers on mechanical, dynamic mechanical, morphological and thermal properties of hybrid composites were investigated. The morphological results showed the strong interfacial adhesion between fiber or talcum and Poly(lactic acid) (PLA) matrix due to a better compatibility by reaction of in situ compatibilizer. The reactive PLA hybrid composite showed the higher tensile strength and the elongation at break than non-compatibilized hybrid composite without sacrificing the tensile modulus. Upon increasing the talcum contents, the modulus and storage modulus of hybrid composites were also increased while the tensile strength and elongation at break were slightly decreased compared to PLA/fiber composite. Talcum was able to induce the crystallization of PLA hybrid composites.

Overcome the Conflict between Strength and Toughness in Poly(lactide) Nanocomposites through Tailoring Matrix-Filler Interface

Strength and toughness are the two most important prerequisites for structural applications. Unfortunately, these two properties are often in conflict in materials. Here, an effective and yet practical strategy is proposed to simultaneously strengthen and toughen poly(l-lactide) (PLLA) using a simple rigid-rubber "reinforcing element." This element consists of a rigid graphene oxide (GO) sheet covalently coupled with poly(caprolactone-co-lactide) (PCLLA) rubbery layers, which can be easily synthesized and incorporated into PLLA matrix to develop composites with well-tailored GO/PLLA interfaces. It is demonstrated that by adding the "reinforcing element," i.e., GO-graft-rubber-graft-polyd-lactide), PLLA exhibits higher strength and higher toughness, which could be attributed to the synergy of rigid GO and rubbery PCLLA working in tandem during deformation. It is further demonstrated that this strategy can also be applied to other filler systems, such as clay and particulate polyhedral oligomeric silsesquioxane, and other polymer systems, such as poly(methyl methacrylate). The strategy could be considered as a general design principle for reinforcing materials where both strength and toughness are the key concerns.