Reduction of polymer surface tension by crystallized polymer nanoparticles

Recent Progress in Processing Functionally Graded Polymer Foams

Polymer foams are an important class of engineering material that are finding diverse applications, including as structural parts in automotive industry, insulation in construction, core materials for sandwich composites, and cushioning in mattresses. The vast majority of these manufactured foams are homogeneous with respect to porosity and structural properties. In contrast, while cellular materials are also ubiquitous in nature, nature mostly fabricates heterogeneous foams, e.g., cellulosic plant stems like bamboo, or a human femur bone. Foams with such engineered porosity distribution (graded density structure) have useful property gradients and are referred to as functionally graded foams. Functionally graded polymer foams are one of the key emerging innovations in polymer foam technology. They allow enhancement in properties such as energy absorption, more efficient use of material, and better design for specific applications, such as helmets and tissue restorative scaffolds. Here, following an overview of key processing parameters for polymer foams, we explore recent developments in processing functionally graded polymer foams and their emerging structures and properties. Processes can be as simple as utilizing different surface materials from which the foam forms, to as complex as using microfluidics. We also highlight principal challenges that need addressing in future research, the key one being development of viable generic processes that allow (complete) control and tailoring of porosity distribution on an application-by-application basis.

Preparation of nickel/PA12 composite particles by defect-induced electroless plating for use in SLS processing

In this work, Ni particles/PA12 powders (Ni/PA12) and graphite oxide (GO)-encapsulated Ni particles/PA12 powders (GO-Ni/PA12) composite powders were prepared by defect-included electroless plating technique, and its laser sintered behaviour was investigated. Results showed that a lot of defects could formed on the surface of CH3COOH etched PA12 powders. The defects would induce Ni and GO-Ni particles independently plated on the PA12 surface. Adding GO in the plating solution would facilitate the deposition of Ni particles, GO, and NiO on the PA 12 surface, but inhibit the growth and the crystallinity of the Ni particles. The SLS process involved the contact of PA12 powders, the formation of sintering neck, the growth of sintering neck and the formation of fused solid. Sintering process could facilitate the re-arrangement of Ni particles due to surface tension and the growth of sintering neck. The Ni particles had well wettability, and the interfaces between Ni particles and PA 12 were contacted soundly. The tensile strength and bending strength of the 10 W-sintered Ni/PA12 specimen were 50 MPa and 60 MPa. But SLS process caused the serious aggregation of GO-Ni particles due to higher concentration, activity and surface area of GO-Ni particles.

Adsorption of Surface-Modified Silica Nanoparticles to the Interface of Melt Poly(lactic acid) and Supercritical Carbon Dioxide

With the purpose of fabricating polymer nanocomposite foams and preventing coalescence in foaming processes, the interfacial tension of poly(lactic acid) (PLA)-silica composites is investigated in this work. Synthesized silica nanoparticles (SNs) with a CO2-philic surface modification are used as the dispersed nanoparticles. Interfacial tension is a key parameter in processing of polymer foams since it directly affects the final foam properties, such as cell size and cell density. Interfacial tension of silica-containing PLA and supercritical carbon dioxide (CO2) is measured using axisymmetric drop shape analysis profile (ADSA-P) pendant drop method at high pressures and high temperatures. The interfacial tension between PLA and supercritical CO2 is observed to decrease as a result of the nanoparticles' adsorption to the interface. These results indicate that the reduction in interfacial tension with increasing silica content significantly deviates from a linear trend; there is a minimum at 2 wt % loading of the SNs and then the interfacial tension curve reaches a plateau. Contact angle measurements show an affinity of the SNs for the polymer-supercritical CO2 interface, and these obtained results are used to calculate the binding energy of the nanoparticles to the PLA/CO2 interface. In addition to interfacial properties, the adsorption of silica nanoparticles at the interface is also studied in detail with scanning electron microscopy.