Facile fabrication of high nanofiller-content natural rubber nanocomposites for reversible plasticity shape memory polymers

Abstract

Reversible plasticity shape memory (RPSM) polymers that undergo a large deformation at room temperature and subsequently recover to their original shape upon heating is a new type of shape memory material just discovered in recent years. Herein, the RPSM polymers based on crosslinked natural rubber (NR) composites were fabricated by a simple ultrasonic mixing of zwitterionic chitin slurry, the precursor of chitin nanofibers (ChNFs), and sulfur-prevulcanized natural rubber latex (NRL) in aqueous media. The results showed that with the increase of the nanofiller content, the elastomer deformation of ChNFs/NR composites turned to plasticity deformation under uniaxially stretching. Meanwhile, the room-temperature plasticity deformation of ChNFs/NR composites with high nanofiller loading (>20 wt%) could be rapidly recovered in hot water (90 °C). Interestingly, it was also found that the stretch-induced crystallization of NR occurred at low strain (λ = 1) for the plasticity deformed ChNFs/NR composites, which is far lower than that of neat NR (λ > 4). Moreover, the stretch-induced crystals even persisted in the stretched high-content ChNFs/NR composites when the stress was unloaded. The significantly advanced stretch-induced crystallization of NR indicated the presence of strong interfacial interaction between ChNFs and NRL. To explain the RPSM behavior of as-prepared ChNFs/NR composites, the formation of ChNFs network and its water-induced softening mechanism were proposed to resist or give way to the recovery force of chemical crosslinking network in NR. This work provides a new insight into the fabrication of RPSM composites for promising applications.