Poly (lactic acid) foaming Nofar, Mohammadreza; Park, Chul B.
Progress in polymer science,
10/2014, Letnik:
39, Številka:
10
Journal Article
Recenzirano
Poly (lactic acid) or polylactide (PLA) is an aliphatic thermoplastic polyester produced from renewable resources and is compostable in the environment. Because of the massive use of foamed products ...of petroleum-based polymers, PLA foams have been considered as substitutes for some of these products. Specifically, because of PLA's competitive material and processing costs, and its comparable mechanical properties, PLA foams could potentially replace polystyrene (PS) foam products in a wide array of applications such as packaging, cushioning, construction, thermal and sound insulation, and plastic utensils. Due to their biocompatibility, PLA foams can also be used in such biomedical applications as scaffolding and tissue engineering. But PLA has several inherent drawbacks, which inhibit the production of low-density foams with uniform cell morphology. These drawbacks are mainly the PLA's low melt strength and its slow crystallization kinetics. During the last two decades, researchers have investigated the fundamentals of PLA/gas mixtures, PLA foaming mechanisms, and the effects of material modification on PLA's foaming behavior through various manufacturing technologies. This article reviews these investigations and compares the developments made thus far in PLA foaming.
Elastomer foams have been widely used in many applications and have shown potential in some advanced fields because of their excellent flexibility. Elastomers foamed with a physical blowing agent ...solve the problems of traditional chemical foaming, endow elastomer foams with advantages of environmental-friendly features, uniform cell structure, adjustable material properties, and high processing efficiency. However, unlike foaming of thermoplastic materials, low matrix modulus and high gas diffusivity leads to serious foam post-foaming shrinkage and hinders the preparation of low density elastomer foams. In the past two decades, researchers have selected different elastomer systems and applied various foaming methods and strategies to prepare elastomer foams with improved performance through understanding the foaming mechanisms. This article reviews these investigations and discusses the developments made so far in physical foaming of elastomers.
Lightweight and flexible ternary composites with graphene (Gn), silicon carbide nanowires (SiCnw), and poly (vinylidene fluoride) (PVDF) matrix were successfully fabricated via electrostatic assembly ...and solution casting followed by hot-pressing. The synergism of two-dimensional Gn and one-dimensional SiCnw with stacking fault structure improved the formation of conductive paths and multiple interfaces. This enhanced the dielectric properties, electromagnetic interference (EMI) shielding and thermal conduction performance of the fabricated composites. For instance, by the incorporation of 9.5 wt % Gn-SiCnw, the dielectric constant and the dielectric loss of the composites were increased by 4 orders of magnitude compared with neat PVDF. A maximum EMI shielding effectiveness (SE) of 32.5 dB was achieved for the composites at 1.2 mm thickness in the frequency range 8.2–12.4 GHz. The high EMI SE of the Gn-SiCnw/PVDF can be attributed to the high electrical conductivity, dielectric constant and dielectric loss. The composites also showed a high thermal conductivity of 2.13 W. m−1. K−1, due to the formation of a thermally conductive network between Gn and SiCnw. This dual functionality of the Gn-SiCnw/PVDF composites demonstrates that they are outstanding materials with potential applications in EMI shielding and thermal management for microelectronics.
The self-assembly of Graphene and SiC nanowires provided a unique microstructure, imparting the graphene/SiC nanowires/PVDF composites with high EMI shielding and thermal conductivity at low filler content. Display omitted
Conventional silica-based aerogels are among the most promising materials considering their special properties, such as extremely low thermal conductivity (~15 mW/mK) and low-density (∼0.003–0.5 ...g.cm−3) as well as high surface area (500–1200 m2. g−1). However, they have relatively low mechanical properties and entail extensive and energy-consuming processing steps. Silica-based aerogels are mostly fragile and possess minimal mechanical properties as well as a long processing procedure which hinders their application range. The key point in improving the mechanical properties of such a material is to increase the connectivity in the aerogel backbone. Several methods of mechanical improvement of silica-based aerogels have been explored by researchers such as (i) use of flexible silica precursors in silica gel backbone, (ii) surface-crosslinking of silica particles with a polymer, (iii) prolonged aging step in different solutions, (iv) distribution of flexible nanofillers into the silica solution prior to gelation, and, most recently, (v) polymerizing the silica precursor prior to gelation.
The polymerized silica precursor, as in the most recent approach, can be gelled either by binodal decomposition (nucleation and growth), resulting in a particulate structure, or by spinodal decomposition, resulting in a non-particulate structure. By optimizing the material composition and processing conditions of materials, the aerogel can be tailored with different functional capabilities.
This review paper presents a literature survey of precursor modification toward increased connectivity in the backbone, and the synthesis of inorganic and hybrid systems containing siloxane in the backbone of the silica-based aerogels and its composite version with carbon nanofillers. This review also explains the novel properties and applications of these material systems in a wide area. The relationship among the materials-processing-structure-properties in these kinds of aerogels is the most important factor in the development of aerogel products with given morphologies (particulate, fiber-like, or non-particulate) and their resultant properties. This approach to advancing precursor systems leads to the next-generation, multifunctional silica-based aerogel materials.
The overview of silica-based aerogels in terms of both fabrication and precursor system advancement Display omitted
•An overview on conventional chemistry and synthesis methods of silica-based aerogels is given.•An overview on trending and the most recent synthesis methods of silica-based aerogels is given.•A literature survey of precursor modification toward increased connectivity in the backbone is given.•A literature survey on methods for multifunctionality and mechanical enhancement of silica-based aerogels is given.•A literature survey on precursor enhancement with carbonaceous material is given.
In this study, we report the development of polylactide (PLA) bead foams with a double crystal melting peak structure. PLA bead foams with 3- to 30-fold expansion ratios and average cell sizes ranged ...from 350 nm to 15 μm were prepared. We found that the PLA's foam structure was significantly affected by the amount of perfected crystals (that is, crystals with a high melting temperature) generated during CO2 saturation. The structure was also affected by crystals with a low melting temperature that formed during foaming and cooling. Various CO2 pressures further influenced the crystallization kinetics of the crystals with a high melting temperature during the saturation. At various pressures, different crystallization kinetics also significantly affected the PLA foam's cell morphology and its uniformity. At a high saturation pressure, the increased content of dissolved CO2 in the PLA promoted the cell nucleation rate through the increased degree of thermodynamic instability. On the other hand, at high pressures, small-sized perfect crystals were induced as high-melting peak crystals. Thus, the heterogeneous cell nucleation around these crystals was further improved, which also caused the generation of a more uniform foam structure. Moreover, this study introduces this bead foam technology as an innovative new way to produce nanocellular foam products.
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•Expanded PLA (EPLA) bead foams are developed with a double crystal melting peak.•Generation of double crystal peak significantly improves PLA's foaming properties.•CO2 pressures influenced the kinetics of the high-melting temperature crystals.•The high-melting peak crystals enhanced the PLA's cell nucleation/foam expansion.•Nanocellular foam products can be produced by this bead foaming approach.
Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial ...applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes’ sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.
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•Advances in metals and metalloids removal from wastewater were reviewed and evaluated.•Existing and emerging methods for metals removal from water were discussed.•Mechanisms, environmental aspects, cost-effectiveness, and feasibility were analyzed.•Metals recovery as value-added products were evaluated towards circular economy.•Current limitations and challenges, and future research directions are identified.
Although many oil absorption materials have been developed, it still remains a great challenge to achieve rapid absorption and efficient recovery. Over the past decade, research has focused on the ...development of freeze casting technology using water as a solvent. The materials prepared by this method have poor water resistance and are difficult to apply to oil absorption in aqueous environments. Here, an organic solvent freeze casting strategy is proposed to fabricate ultralight hydrophobic plastic foams with aligned channel structures. Through microscopy in situ observation, we revealed the growth morphology of ice crystals during directional freezing process. Moreover, aligned porous foams with various channel sizes are fabricated by regulating the cooling rate. We found that organic solvent-assisted freeze casting can enhance the hydrophobicity of the matrix material. These aligned porous foams exhibit excellent liquid absorption performance, with high absorption speed and large absorption capacity over a wide viscosity range. This approach has general applicability and can be used to tailor a wide variety of engineering plastic-based aligned porous foams, as long as they can dissolve in organic solvents.
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•Organic solvent freeze casting ultralight hydrophobic plastic foams with aligned channels.•In situ observation of ice crystal growth patterns during freeze casting.•Channel size of aligned porous foams was controlled by the cooling rate.•Aligned porous foam exhibits fast liquid absorption speed and large absorption capacity.•Ultralight hydrophobic foam shows excellent oil-water separation performance.
In recent decades, problems with electromagnetic interference (EMI) radiation problems have arisen, that can seriously reduce the performance of precision devices nearby and threaten human health. In ...consequence, it is important to seek high efficiency materials to suppress EMI pollution. Generally, high magnetic permeability or electrical conductivity is essential for efficient EMI shielding. Conventionally, various forms of metal construction (sheet/films, coatings,
etc.
) are used for EMI shielding. However, metallic shielding has drawbacks that include high density, lack of corrosion resistance and expensive processing, which restrict its use in the modern electronic world. By contrast, conductive polymer composites (CPCs), formed from insulative polymers and conductive fillers, have attracted more and more interest from both industry and academia. CPCs have properties that offer great potential for application in efficient EMI shielding. These include low density, high flexibility, good chemical stability and easy processing and forming. From a theoretical viewpoint, it is generally accepted that the shielding of EM waves is due to the three basic mechanisms of reflection, absorption and multiple internal reflections. However, it must be recognized that the SE of CPCs has a close relation to the reflection mechanism, which can cause secondary EMI pollution. Therefore, materials with charge carriers or magnetic/electric dipoles as well as cellular structure should be the focus for the development of EMI shielding materials with strong absorption properties. On that basis, the main aim of this paper is to review the current position in research of the design of inorganic based foams (metal, carbon or MXene) and polymer composite foams as EMI shielding materials. On the one hand, these composite foams have the merit of being lightweight, and on the other hand, the special porous structure can effectively harvest microwaves by prolonging the travel path. As a result, absorption dominates EMI shielding, which satisfies current requirements of EMI shielding applications. This review also points out the future challenges and gives guidelines for finding solutions for the next generation of shielding applications using composite foams.
In recent decades, problems with electromagnetic interference (EMI) radiation problems have arisen, that can seriously reduce the performance of precision devices nearby and threaten human health.
Removing contaminants from wastewater is critical towards resolving global water pollution problems. However, the variety of oily contaminants composition, and the unsatisfactory performance and ...efficiency of current separation systems are still big challenges, thus developing efficient and scalable oil-water separation (OWS) methods is needed. Here, the performance of a novel pilot-scale oil-water separator skimmer (OWSS) prototype is fully investigated using an upflow fixed bed column system packed with polypropylene (PP) fibrous sorbent materials for dual continuous OWS and in situ oils/organic solvents recovery. The mechanism of oil sorption by the PP fibrous sorbents, as well as capillary and vacuum assisted oil flow within the inter-fiber voids is fully explored. A series of pilot-scale column experiments were performed with different bed heights (7.5–30 cm) and using different types of oil/solvent in order to determine their influence on the oil flux, OWS efficiency and recovered organic solvent purity. The OWSS provided excellent and stable performance. A trade-off relationship between oil flux and OWS efficiency can be obtained: The maximum flux was attained at the lowest sorbent bed height (7.5 cm), while the maximum OWS efficiency (>99%) was achieved at the highest sorbent bed height (30 cm). The materials’ morphology and wettability were examined showing outstanding stability and recyclability, which demonstrates their efficient integration into the overall OWSS. This study is expected to provide significant insights into the feasibility and scalability of an advanced, environmentally friendly, and relatively cost-effective OWS system, towards promising industrial implementation to overcome large-scale oil spill cleanup and oily wastewater treatment shortcomings.
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•PP fibrous materials could separate oils from water with excellent recyclability.•The developed OWSS was very efficient (>99%) for cleaning oil/chemical spills.•Excellent performance was achieved by dual continuous OWS and in situ oil recovery.•Oil flux, OWS efficiency and separation selectivity depend on the column height.•A trade-off relationship between oil flux and OWS efficiency can be achieved.
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•Lightweight and strong foams with outstanding surface appearance were fabricated using foam injection molding.•Uniform nanocellular foaming was achieved using the mold-opening foam ...injection molding.•Nanocellular PP/PTFE nanocomposite foam shows dramatically enhanced mechanical properties.
Lightweight plastic materials are important for saving resources and energy, reducing environmental pollution, and achieving sustainable development. Foam injection molding is a promising technology for manufacturing lightweight plastic components. However, these plastic components present poor mechanical properties and imperfect surface appearances. Herein, we reported a novel strategy to prepare lightweight and tough polypropylene (PP)/polytetrafluoroethylene (PTFE) nanocomposite parts with defect-free surfaces by combining in situ fibrillation and nanocellular injection molding technologies. The nano-fibrillary PP/PTFE nanocomposite was firstly prepared using an in situ method based on twin-screw compounding. Scanning electron microscopy (SEM), rheological and differential scanning calorimetry (DSC) analysis, combined with online optical microscopy observation, demonstrated the network structure of PTFE nanofibrils and its positive effects on melt strength and promoting crystallization. Using nanofibrillary nanocomposites, we achieved nanocellular foaming, for the first time, using the foam injection molding process. The nanocellular PP/PTFE nanocomposite foam thus obtained significantly enhanced mechanical properties compared to the regular PP foam, and even superior strength and ductility compared to unfoamed PP. In particular, the impact strength of the nanocellular foam was 700% higher than that of the regular foam and 200% higher than that of the unfoamed product. Moreover, unlike regular foam, the nanocellular PP/PTFE nanocomposite foam showed outstanding surface appearance without any silver or swirl marks. More importantly, the whole process was facile, flexible, efficient, and easy to scale-up, and could be easily extended to other materials. The remarkable mechanical performance and surface appearance, combined with the flexible and extendable process, confers nanocellular PP/PTFE nanocomposite foams a promising future in many advanced applications where both lightweight and mechanical integrity are required.
