Search

Polylactide(PLA) composites containing graphene nanosheets were prepared by theapproach of solution mixing for a crystallization study. The resultsrevealed that the graphene nanosheets are well distributed in thePLA matrix, leading to an evident viscosity increase despite theirdispersion as multilayered structures in stack form. Both the coldand melt crystallization behaviors of PLA were found to depend stronglyon the presence of the graphene nanosheets. During cold crystallization,the graphene nanosheets merely act as an inert filler, and the increasedviscosity results in a decrease of the overall crystallization rateof the composite relative to neat PLA. However, the graphene nanosheetscan act as a heterogeneous nucleating agent, which is their dominantrole during melt crystallization. As a result, the composite showsa higher crystallization rate than neat PLA under these conditions. [ABSTRACT FROM AUTHOR]

The carbon nanotubes (CNTs)–filled poly(vinylidenefluoride) (PVDF) composites (PCTs) were preparedby melt compounding for rheological study. The steady and oscillatoryflow behaviors were then explored. The results show that the presenceof CNTs enhances the pseudoplastic flow accompanied by the increasedflow activation energy. However, the linear flow region is not sensitiveto the temperature whether driven by shear rate or by strain. Duringoscillatory shear flow, the solid-like response is attributed to thepercolation of CNTs, but the formation of a percolated CNT networkis temperature-dependent, and the percolation threshold values reducewith an increase of temperature. The two-phase viscoelastic modelwas then used to further describe the linear responses of composites,aiming at relating hierarchical structures of the CNTs to flow behaviorsof the composites. [ABSTRACT FROM AUTHOR]

Randomly oriented fiber mats and well-aligned fiber bundlesofthe biodegradable polylactide (PLA)/poly(ε-caprolactone) (PCL)blends were successfully produced by electrospinning in the presentstudy. For the reticulate fibers, the effects of the blending ratioof two polymers and compositions of mixed solvents on fiber morphologywere investigated. The results reveal that the fibers with lower PCLmass fraction show better morphology with larger average fiber diameterthan those of the fibers with higher PCL mass fraction. Besides, asmall addition of dimethylformamide (DMF) as the assistant solventfavors further improvement of fiber morphology because of the synergisticeffects by improved conductivity and altered viscosity of the electrospunsolutions. Although the as-obtained blend fibers show smooth surfacestructure, the phase separation between PCL and PLA occurs insidethe fibers because the two components are thermodynamically immiscible,and the discrete phase shows an elongated morphology along with thefiber axis, instead of the droplet structure. For the aligned fiberbundles collected on a rotating disk, the degree of order increaseswith increase of the tangential velocity, accompanied by reduced averagefiber diameter. Hierarchical orientations including the macroscopicfiber alignment, the elongation of discrete PCL phase, and the molecularorientation of both the PLA and PCL can be observed within the alignedblend fibers. [ABSTRACT FROM AUTHOR]

Biodegradable poly-(butylene succinate)/polylactide (PBS/PLA) blends with various blending ratios were prepared by melt mixing for morphological and rheological studies. Dynamic rheological measurements were performed on the blend systems and the viscoelastic responses were analyzed with several emulsion models. The results show that the PBS/PLA is an immiscible blend system with very narrow cocontinuous region and high percolation threshold. The phase inversion point could be precisely predicted by the small-amplitude oscillatory shear (SAOS) response. The Palierne model gave a better description of the viscoelastic response of PBS/PLA blends than that of the Gramespacher and Meissner (G-M) model. In addition, the interfacial tension between the two polymers was measured by several techniques, such as surface property characterizations, deformed drop retraction, and rheological approaches. The differences observed by these various methodologies were then further explored. Moreover, the melting and crystallization behaviors of the blends were also studied in order to reach a deeper insight into the relations between the phase behavior and the macroscopic thermal properties of the PBS/PLA blends. [ABSTRACT FROM AUTHOR]

Bilayer hydrogel-based actuators have attracted much interest because inhomogeneous structures are easily constructed in hydrogels. We used three kinds of polysaccharides, including anionic carboxymethyl cellulose (CMC), cationic chitosan (CS), and amphoteric carboxymethyl chitosan (CMCS), as both structure-constructing units and actuation-controlling units in this work to fabricate physically crosslinked poly(vinyl alcohol) bilayer hydrogels. The spatial heterogeneity was tuned by changing the types and concentrations of polysaccharides in different layers, to regulate pH- and humidity-driven actions of bilayer hydrogels. Based on the distortion of the ionic channel during the humidity-motivated deformation of bilayer hydrogels, a two-in-one flexible device integrating a humidity-driven actuator and humidity-responsive sensor was then developed, which could detect the alterations of environmental humidity in real time. Moreover, good tensile toughness and interfacial bonding as well as the strain-resistance effect endowed the bilayer hydrogels with the capability of identifying human motion as a strain sensor, unlocking more application scenarios. This work provides an overall insight into the heterogeneity regulation of bilayer hydrogels using polysaccharides as stimulus-responsive units and also proposes an interesting strategy of manufacturing hydrogel-based flexible devices with both actuating and sensing capabilities.

Poly(epsilon-caprolactone)/polylactide blend (PCL/PLA) is an interesting biomaterial because PCL and PLA present good complementarity in their physical properties and biodegradability. However, the thermodynamic incompatibility between two component polymers restricts further applications of their blend. In this work, we used functionalized multiwalled carbon nanotube (MWCNT) to control the morphology of immiscible PCL/PLA blend. The ternary PCL/PLA/MWCNTs composites were hence prepared by melt mixing for the morphology and the properties investigation. It is interesting to find that the functionalized MWCNTs are selectively dispersed in the matrix PCL phase and on the interface between two polymer phases, leading to simultaneous occurrence of thermodynamically and kinetically driven compatibility. Those interface-localized MWCNTs prevent coalescence of the discrete domains and enhance the phase interfacial adhesion as well. As a result, the phase morphology of the ternary composites is improved remarkably in contrast to that of the blank PCL/PLA blend. Owing to that unique selective interface-localization and improved phase morphology, the ternary composites present far lower rheological and conductive percolation thresholds than those of the binary composites, and also present extraordinary mechanical properties even at very low loading levels of the MWCNTs. Therefore, the amphiphilic MWCNTs are believed to act as the reinforcements as well as the compatibilizer in the immiscible PCL/PLA blend.