Synthesis of tunable thickness-to-diameter ratio microcapsules via a diffusion-controlled process for temperature-responsive release.

Designing microcapsules with a complicated functionalized shell to respond to an external stimulus has attracted much attention for triggered release; however, simplifying the synthesis process remains a significant challenge. Herein, we initially propose a novel, simple synthesis strategy that utilizes a mixed solvent as the organic phase to control the diffusion of common monomers during interfacial polymerization, resulting in the successful preparation of microcapsules with tunable thickness-to-diameter ratios (T/D). The morphology of microcapsules is confirmed by scanning electron microscopy. We also observe that the T/D of the designed microcapsules progressively increases as the diffusion of monomers occurs, and the glass transition temperature of microcapsules is controlled. Furthermore, microcapsule-based crosslinking agents are applied to investigate the crosslinking reaction of poly(vinyl chloride). Rotational rheometer results indicate that the microcapsules exhibit an excellent external stimulus response, precisely triggering release at the predetermined temperature. This simple approach for the preparation of microcapsules with tunable physical properties has great potential for triggered release in diverse applications.

A Novel One-Step Reactive Extrusion Process for High-Performance Rigid Crosslinked PVC Composite Fabrication Using Triazine Crosslinking Agent@Melamine-Formaldehyde Microcapsules.

In this work, we propose, for the first time, a simple, fast, and efficient strategy to fabricate high-performance rigid crosslinked PVC composites by continuous extrusion. This strategy improves the poor processing fluidity of composites and solves the impossibility of conducting extrusion in one step via using microcapsule-type crosslinking agents prepared by in situ polymerization to co-extrude with PVC blends. The results demonstrate that the PVC/microcapsule composites were successfully prepared. Within the studied parameters, the properties of crosslinked PVC gradually increased with the addition of microcapsules, and its Vicat softening temperature increased from 79.3 °C to 86.2 °C compared with pure PVC. This study shows the possibility for the industrial scale-up of the extrusion process for rigid crosslinked PVC.

A facile strategy for preparation of strong tough poly(lactic acid) foam with a unique microfibrillated bimodal micro/nano cellular structure.

This work reports the design and fabrication of strong tough poly(lactic acid) (PLA) foam by combining pressure-induced-flow (PIF) processing with supercritical CO2 foaming. PIF processing widened the foaming window of PLA to 40-120 °C, while supercritical CO2 foaming released the undesired internal stress of PLA samples with PIF processing (P-PLA). The prepared PLA foams displayed a unique microfibrillated bimodal micro/nano cellular structure which is strongly affected by saturation temperature (Ts). Both micron and nano cells showed decreasing cells size and increasing cell density as Ts elevated. The orientation factor as well as internal stress of PLA foams decreased with increased Ts. Compared with P-PLA samples, PLA foam prepared at Ts of 40 °C showed negligible reduction of orientation from 0.45 to 0.41 and release of internal stress characterized by the rightward shift of Raman peak (stretching vibration of CO bond from 1763 to 1766 cm-1). Furthermore, PLA foam prepared at Ts of 40 °C presented excellent impact strength (32.3 kJ/m2), tensile strength (42.0 MPa), and ductility (14.2%). The combination of PIF processing and supercritical CO2 foaming provides a facile and effective method to prepare strong tough PLA foam that has immense potential in biomedical, aerospace, automotive, and other structural applications.

Synthesis of Transition Metal Complexes and Their Effects on Combustion Properties of Semi-Rigid Polyvinyl Chloride.

Using introduction of MoO42- and Fe3+, Cu2+, or Zn2+ into amphiphilic polymers (DN) via an ion-exchange reaction, different transition metal complexes, as retardants and smoke suppressants, including (DN)Mo, Fe(DN)Mo, Cu(DN)Mo, and Zn(DN)Mo were synthesized. Combined with the results of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), it could be determined that ionic bonding of these ions with DN occurred. Subsequently, the influence of flame-retardant, smoke-suppression, and mechanical properties of (DN)Mo, Fe(DN)Mo, Cu(DN)Mo, and Zn(DN)Mo on polyvinyl Chloride (PVC) were tested. It was demonstrated that transition metal complexes of three metal elements, Fe(DN)Mo, Cu(DN)Mo, and Zn(DN)Mo, showed better flame retardancy, smoke suppression, and thermal stability as confirmed by microcalorimetry, limiting oxygen index (LOI), smoke density, and thermogravimetric analysis (TGA) tests, in which Cu(DN)Mo worked best due to the Lewis acid mechanism and reductive coupling mechanism. Scanning electron microscopy (SEM) showed that the addition of (DN)Mo, Fe(DN)Mo, Cu(DN)Mo, and Zn(DN)Mo promoted the formation of a dense carbon layer on the PVC surface during combustion, which could protect the interior PVC. The addition of these transition metal complexes hardly impaired the mechanical properties of PVC.