Vitrimeric Polylactide by Two-step Alcoholysis and Transesterification during Reactive Processing for Enhanced Melt Strength

Abstract

Because of its rather low melt strength, polylactide (PLA) has yet to fulfill its promise as advanced biobased and biodegradable foams to replace fossil-based polymer foams. In this work, PLA vitrimers were prepared by two-step reactive processing from commercial PLA thermoplastics, glycerol, and diphenylmethane diisocyanate (MDI) using Zn­(II)-catalyzed addition and transesterification chemistry. The transesterification reaction of PLA and glycerol occurs with zinc acetate as the catalyst, and chain scission will take place due to the alcoholysis of the PLA chains by the free hydroxyl groups from the glycerol. Long-chain PLA with hydroxyl groups can be obtained and then cross-linked with MDI. Rheological analysis shows that the formed cross-linked network can significantly improve melt strength and promote strain hardening under extensional flow. PLA vitrimers still maintain the ability of thermoplastic processing via extrusion and compression. The enhanced melt strength and the rearrangement of network topology facilitate the foaming processing. An expansion ratio as large as 49.2-fold and microcellular foam with a uniform cell morphology can be obtained for PLA vitrimers with a gel fraction of 51.8% through a supercritical carbon dioxide foaming technique. This work provides a new way with the scale-up possibility to enhance the melt strength of PLA, and the broadened range of PLA applicability brought by PLA vitrimers is truly valuable in terms of the realization of a sustainable society.

Blowing tough polylactide film enabled by the in situ construction of covalent adaptive networks with epoxidized soybean oil as dynamic crosslinks

“…7d), suggesting that the introduction of ESO into PLA to broaden its application range is of real value for realizing a sustainable society. In addition, compared with glycerol-based PLA CANs, 69 the green and nontoxic ESO replaces methylene diphenyl diisocyanate (MDI) as the crosslinker in the covalent adaptive network, avoiding the toxicity and harm caused by the migration of small molecules during the use of modified PLA.…”

Sustainable polyester vitrimer capable of fast self-healing and multiple shape-programming via efficient synthesis and configuration processing

“…As a typical example, 0.8BT3PMDA is shown in Fig. 2(b), where the torque curve could be divided into four stages, as follows: (1) a peak was formed in the rst stage, ascribing to the melting of the mixture (PET and BIS-TRIS); (2) the torque decreased gradually, which is ascribed to the shorter molecular chain resulting from the degradation reaction, and the transesterication between the PET chains and BIS-TRIS; 47,48 (3) the torque increased gradually and plateaued aer the addition of PMDA, which is ascribed to the crosslinking reaction between the PET chains and PMDA; and (4) the torque curve reached a plateau with minor uctuation, resulting from the exchange reaction between the ester groups. The torque curves of the other samples are shown in Fig.…”

Preparation of Silica Composite Vitrimers via One‐Shot Transformation from Simple Polyesters

“…Due to these reasons, some recent reports tackled the oneshot transformation of ordinary commodity polymers into vit-rimers, which must be ideal for practical application. [45][46][47] As an example, Ma et al have reported a transformation of PET into vitrimers via reactive processing using multi-functional hydroxyl molecules, [48] where trans-esterification was the key to obtain cross-linked structures. Similarly, Heuts et al has reported oneshot transformation of poly(butylene terephthalate) (PBT) into vitrimers by reacting with multi-functional hydroxyl molecules via trans-esterification.…”

“…Due to these reasons, some recent reports tackled the one‐shot transformation of ordinary commodity polymers into vitrimers, which must be ideal for practical application. [ 45–47 ] As an example, Ma et al. have reported a transformation of PET into vitrimers via reactive processing using multi‐functional hydroxyl molecules, [ 48 ] where trans‐esterification was the key to obtain cross‐linked structures.…”