Effect of polybutylene adipate terephthalate on the properties of starch/polybutylene adipate terephthalate shape memory composites.

In this work, the starch/polybutylene adipate terephthalate (PBAT) composite films with high starch content were prepared by hot-pressing and ultraviolet cross-linking methods using cassava starch, benzophenone (BP), degradable PBAT and citric acid as film-forming substrate, photosensitizer, toughening material and solvent, respectively. The results showed that starch and PBAT had excellent performance, resulting in the composites films exhibit robust tensile strength (9.90 MPa), decent elongation at break (500.05 %) and excellent shape memory property. Under 30 % pre-tensile strain, the shape memory fixity and recovery ratios reached 96.58 % and 93.94 %, respectively. In addition, the starch-based films were successfully rendered hydrophobic by PBAT hydrophobic characteristics. PBAT not only secures the biodegradability of the starch/PBAT composites films, but also improves the mechanical properties of them, and meets the requirements of the thermal shrinkage films when subjected to large strain.

Degradable photo-crosslinked starch-based films with excellent shape memory property.

With the increasingly serious plastic pollution, people's demand for the multi-functional biodegradable plastics is becoming more and more urgent. Inspired by the crosslinked shape memory polymers, the crosslinked starch films were synthesized by inducing the decomposition of benzophenone into free radical and depriving hydrogen on starch macromolecules under UV irradiation, in order to gain a high shape memory performance. The results showed that a three-dimensional crosslinking network between starch macromolecule chains was formed. Compared with the uncrosslinked starch films, the photo-crosslinked films not only had higher mechanical property (tensile strength increased by 154%), but also had better water resistance (water contact angle from 60° to 87°) due to the reduction of free hydroxyl groups. In addition, the stable covalent bonds serving as netpoints endow photo-crosslinked films with great improvement in shape memory property, with nearly 180° bending recovery. More importantly, the maximum shape memory fixity ratio (Rf) and shape memory recovery ratio (Rr) under stretch deformation were 96.5% and 99.8%, respectively. And the Rf and Rr could reach 94.6% and 79.8% even at higher strain. In all, the excellent shape memory performance and good degradability crosslinked starch films, which have great potential application in disposable heat-shrinkable packaging materials.

Design of Ethylene-Vinyl Acetate Copolymer Fiber with Two-Way Shape Memory Effect.

One-dimensional shape memory polymer fibers (SMPFs) have obvious advantages in mechanical properties, dispersion properties, and weavability. In this work, a method for fabricating semi-crystallization ethylene-vinyl acetate copolymer (EVA) fiber with two-way shape memory effect by melt spinning and ultraviolet (UV) curing was developed. Here, the effect of crosslink density on its performance was systematically analyzed by gel fraction measurement, tensile tests, DSC, and TMA analysis. The results showed that the crosslink density and shape memory properties of EVA fiber could be facilely adjusted by controlling UV curing time. The resulting EVA fiber with cylindrical structure had a diameter of 261.86 ± 13.07 µm, and its mechanical strength and elongation at break were 64.46 MPa and 114.33%, respectively. The critical impact of the crosslink density and applied constant stress on the two-way shape memory effect were analyzed. Moreover, the single EVA fiber could lift more than 143 times its own weight and achieve 9% reversible actuation strain. The reversible actuation capability was significantly enhanced by a simple winding design of the single EVA fiber, which provided great potential applications in smart textiles, flexible actuators, and artificial muscles.