Recent progress in micro‐/nano‐fibrillar reinforced polymeric composite foams

Abstract

Manufacture of thermoplastic foams with a fine cellular structure (a higher expansion ratio, a higher cell density, and smaller cell sizes) is challenging work due to the weak viscoelastic behavior and the unsuitable crystallization behavior of common thermoplastic materials. In this work, a novel method of making microcellular foams with micro‐/nano‐fibrillar reinforced polymeric composites (M/NFC) is introduced, which shows various advantages compared to conventional foams. The M/NFC foams have improved cellular structures, excellent mechanical properties, and enhanced thermal insulation properties, which make them popular candidates for structural applications and insulative products. Various methods to manufacture of M/NFC foam are summarized. To understand the fundamental mechanisms of the foaming enhancement by incorporating micro‐/nano‐size fibrils, the rheological and crystallization behavior of the M/NFC are analyzed. It is shown that the micro‐/nano‐fibrils can strengthen the melt strength, induce faster crystallization, and increase the number of crystals. Due to the improvement of the cell morphology and the stiffness of the cell walls, the reinforced foams have superior mechanical properties. A hierarchically porous structure in high expansion ratio reinforced foams has also been developed. It is believed that the nano‐size holes in the cell walls can further reduce the thermal conductivity of the foams.

Construction, Physical Properties and Foaming Behavior of High-Content Lignin Reinforced Low-Density Polyethylene Biocomposites

“…To investigate the cellular structure of lignin/LDPE biocomposite foams, their cryofractured surfaces were observed by SEM (Figure 4), and their foam characteristics are summarized in Table 2. The SEM micrograph of the neat LDPE foam showed typical polygonal geometries, consistent with previous reports [3,4]. For the pristine-lignin/LDPE biocomposite foams, only the one containing 10 wt-% pristine lignin exhibited cell and size morphologies similar to those of the neat LDPE foam; at a higher lignin content, the foam quality decreased drastically, resulting in a smaller cell size [Figure 4A-E].…”

“…Their commercial application has expanded rapidly to various industrial areas, such as construction, transportation, sport and leisure, packaging, and agriculture [1][2][3]. Their success in so many fields is because of their unique properties, including a low density and water absorption, a high strength-to-weight ratio, and good thermal insulation, chemical resistance, and cushioning performance [3][4][5].…”

Rheological Considerations in Processing Self-Reinforced Thermoplastic Polymer Nanocomposites: A Review

“…Applications using the nanofibrillar composite technology will most probably be extended to include novel ones with a high added value, such as fused filament fabrication 3D printing [ 86 ], gas-assisted injection molding of polymer foams [ 87 ], and forced assembly coextrusion for the development of packaging films with high permeation properties [ 88 ]. A further evolution of the NFC concept is the selective loading of nanofibrils by carbon nanotubes [ 89 ], which would give rise to a double reinforcing effect, or, in other words, to the reinforcement of a reinforced polymeric material.…”

Microwave foaming of carbon dioxide saturated poly lactic acid

“…Polymer foams with micro‐ and nano‐sized pores have gained significant attention in the recent past as they find numerous applications such as in filtration, energy absorption, thermal insulation, catalysis, and tissue engineering scaffolds. [ 1–7 ] The current techniques to fabricate polymer foams include particulate leaching, [ 8,9 ] thermal induced phase transition, [ 10,11 ] gas foaming, [ 12 ] block co‐polymers, [ 13 ] immiscible polymer blending, [ 14 ] and solid‐state foaming. [ 15,16 ] However, majority of these techniques result in thin films with low porosity and do not offer control over the resulting pore morphology.…”