Porous plastic refers to a class of polymeric materials characterized by a network of micro- or macroscopic pores or channels, giving it unique physical and chemical properties. These pores typically result in a porosity greater than 15%, distinguishing porous plastics from conventional solid polymers. Common forms include membranes, foams, aerogels, and microspheres.
Porous plastics are primarily composed of synthetic resins, foaming agents, and additives, which collectively form a lightweight structure through a controlled foaming process. Common resins include:
A. Polyethylene (PE): Known for its flexibility and chemical resistance. (View HDPE and LDPE products.)
B. Polystyrene (PS): Favored for thermal insulation and lightweight properties.
C. Polyvinyl Chloride (PVC): Valued for its mechanical strength and durability.
D. Polypropylene (PP): Widely used for its low density and versatility.
E. Polyurethane (PU): Offers excellent cushioning and shock-absorbing characteristics.
The pore architecture in these materials can vary significantly, ranging from interconnected open-cell structures to isolated closed cells, depending on the intended application.
Porous plastics are lighter than solid plastics, so overall material consumption and transport costs are reduced. Their porous nature carries impact, so these materials are ideal for protection packaging.
Porous plastics can resist acids, alkalis, and salts - ideal for harsh industrial environments. Low hygroscopicity means they will not deform in moisture and can therefore be used as insulation and waterproofing materials. Porous plastics are porous and have pores to help with thermal and acoustic insulation.
Porous plastics are produced using diverse fabrication methods tailored to the desired properties and applications:
| Method | Description | Applications |
| Physical Foaming | Involves gas or volatile liquids to create pores during resin solidification. | Packaging, insulation. |
| Chemical Foaming | Utilizes chemical reactions or thermal decomposition of agents to generate gas bubbles. | Lightweight materials, energy-absorbing foam. |
| Mechanical Foaming | Uses mechanical agitation to introduce air bubbles into resin mixtures. | Structural foams for lightweight panels. |
| 3D Printing | Techniques like FDM, PBF, and BJ allow the precise creation of complex porous structures. | Biomedical implants, advanced filtration. |
| PTFE Membrane | Creates microporous structures in PTFE to impart breathability and chemical resistance. | Gas filtration, medical applications. |
| Biological Methods | Employs natural agents like fungi for creating bio-based porous polymers. | Eco-friendly filtration, fuel cells. |
Interbody fusion implants and custom orthotics with customized bone density can be designed and produced by computer-aided design and 3D printing. These porous forms are better biocompatible and mechanically strong and help to regenerate bone tissue. Porous tantalum hip filler blocks, widely used in femoral head necrosis repair, joint replacement, and bone defect repair because of their biocompatibility and mechanical durability, are already developed by tech companies.
Figure 1: Porous plastics with high performance and functionality. a) A production route for large-scale preparation of low-cost, environmentally friendly, high-performance PLA foams was developed by combining in situ nanofiber reinforcement with high-pressure microporous injection molding (HPMIM). b) Schematic detailing the fabrication process of flame-retardant PVA/KSi composite foams. (c) Hierarchical porous components were fabricated by in situ melt deposition of CO2-saturated PEI filaments as well as honeycombs and cylinders. (d) Polyvinylidene fluoride energy harvesters with enhanced piezoelectric efficiency by in situ chemical foaming-assisted FDM[1].
Porous plastic like Styrofoam are also widely applied in thermal insulation as they are lightweight, thermally insulating, sound absorption, shock-resistant, and corrosion-resistant. Foam usually consists of low-density polyethylene resin physically foamed to form hundreds of small air bubbles - the sort of structure that makes it very thermally insulate. Expanded polystyrene (EPS), for instance, which is a tough porous plastic material formed by forming beads or pellets of foamable polystyrene or its copolymers, is used in the production of insulation.
Porous plastics, in general, are insulating with regard to their gas-pressure ratio. Experiments indicated that the efficient thermal conductivity of the fibre porous media with the evolution of residual gas pressure inside the gaps was an "S" curve; there are two threshold pressures above and below. It also influences the heat transfer of the open-cell foam substance by the air pressure; the smaller the bubble diameter, the bigger the critical pressure, more easily attain the thermal insulation effect. Furthermore, the thermal conductivity of the porous media with nanoparticles is decreased with increasing air pressure, but when the air pressure is dropped to the lower critical pressure, the thermal conductivity mainly resides in the thermal conductivity of the solid matrix.
Figure 2: Monolithic porous polymers based on ionic liquids (ILs) as efficient flame retardants[2].
But, in practice, thermal insulation with porous plastics also depends on a number of other variables, including water absorption and mechanical behaviour. For instance, apart from thermal conductivity, water vapor transmission properties, water absorption, and mechanical qualities are all vital aspects of choosing insulation materials for buildings. Therefore, when designing and using porous plastics as insulation, these performance parameters should be considered to keep the material stable and reliable in various environmental situations.
Porous plastics make good insulation materials, which is why they can be used in various sectors such as construction, aerospace, and so on.
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References
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