Abstract
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.
Highlights
Polymer foams find a wide range of applications, including in pillows and mattresses, physical insulation, furniture, engineering materials, housing decoration, and electronic devices, etc
The interfacial energy of polymer/gas, and Interestingly, among conventional polymer foams, the different cell sizes (graded density the plasticization of the polymer/gas attract farprofile more attention compared withsystem a uniform cellthe structure, because functionally graded exhibits better mechanical properties compared with conventional temperature, the glass (Tg), ofstructure polymer matrix)
The results show that the internal pressure of foam increases when the amount of azodicarbonamide is increased; this affects final density by inducing significant gas absorption in silicone at the surface
Summary
Polymer foams find a wide range of applications, including in pillows and mattresses, physical insulation, furniture, engineering materials, housing decoration, and electronic devices, etc. Polymer foams with supercritical CO2 do not usually require the use of harmful organic solvents Such an advantage provides the method suitable for processing porous structures from biocompatible polymers as scaffolds for biomedical applications [11,12,13]. The porous structure is produced by either a chemical or a physical blowing agent for gas bubble production in a polymer matrix. Production with a solid polymer is performed by gas diffusion processes (induced by a chemical blowing agent) between the foam and molten polymer matrix. This type of process can be controlled by the formulation and process of polymer to be foamed [26]
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