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A polymer is a long-chain molecule formed by linking numerous simpler repeating chemical units, known as monomers, with identical structures. Over the past two centuries, there has been a significant increase in the global production and use of petrochemical-based plastics. This surge has led to widespread ecological imbalances, affecting air quality, terrestrial and marine ecosystems, food chains, and plant life. Consequently, the excessive use of such polymers has created challenges in solid waste management, with methods like bio- or photo-degradation, incineration, landfilling, and recycling proving to be time-consuming and laborious. Therefore, there is a growing urgency for biodegradable polymers due to increasing demand. Biodegradable polymers consist of interconnected monomers with unstable links in the backbone, facilitated by various functional groups. Throughout the degradation process of these polymers, numerous biologically acceptable molecules are produced. This study examines the significance of biopolymers over petroleum-based counterparts, offering a detailed analysis. It is noteworthy that within the spectrum of biodegradable polymers, polyhydroxyalkanoates (PHAs) emerge as exceptionally promising candidates for substituting petroleum-derived polymers, owing to their remarkable physical attributes. Therefore, this study provides a systematic overview of PHAs, including their classification, historical background, methods of production, potential challenges to commercialization, and diverse applications.
Keywords:
biopolymer; polyhydroxyalkanoate; microorganism; biodegradation
The incorporation of graphene into cellulose matrices has emerged as a promising strategy for enhancing the structural and functional properties of composite materials. This comprehensive review provides a critical analysis of recent advances in optimizing graphene content in cellulose matrices and its impact on composite performance. Various optimization techniques, including response surface methodology, particle swarm optimization, and artificial neural networks, have been employed to identify optimal graphene concentrations and processing conditions. Quantitative analyses demonstrate significant improvements in mechanical properties, with notable increases in tensile strength and Young’s modulus reported for graphene/microfibrillated cellulose composites. Substantial enhancements in thermal stability have been observed in lysozyme-modified graphene nanoplatelet–cellulose composites. Electrical conductivity has been achieved at low graphene loading levels. Additionally, barrier properties, biocompatibility, and functionality for applications such as energy storage and environmental remediation have been substantially improved. This review explores case studies encompassing the optimization of thermal conductivity, viscosity, durability behaviors, pollutant removal, and various other properties. Despite promising results, challenges remain, including uniform dispersion, scalability, cost-effectiveness, and long-term stability. Strategies such as surface functionalization, solvent selection, and protective coatings are discussed. Future research directions, including novel processing techniques like 3D printing and electrospinning, as well as the incorporation of additional functional materials, are outlined. This review synthesizes current knowledge, identifies emerging trends, and provides a roadmap for future research in the rapidly evolving field of graphene–cellulose composites.
Keywords:
graphene; cellulose; composites; optimization; response surface methodology (RSM); particle swarm optimization (PSO); artificial neural networks (ANNs); mechanical properties
Worldwide use of high global warming potential (GWP) hydrofluorocarbon (HFC) refrigerants for space conditioning and food storage results in significant equivalent greenhouse gas (GHG) emissions. This is further exacerbated in developed countries by the current transition from hydrochlorofluorocarbon (HCFC) refrigerants to HFC refrigerants. Under the Kigali amendment to the Montreal Protocol, the proposed phase-out of currently used HFC and HCFC refrigerants has initiated a re-evaluation of some pre-existing refrigerants as well as the development and evaluation of new refrigerants. Making the ideal refrigerant selections for heating, ventilation, air-conditioning, and refrigeration (HVAC&R) applications is thereby difficult in an already overabundant refrigerants market. In this paper, a study of key parameters required of a good refrigerant is conducted, followed by the analysis of refrigerants desired and refrigerants used in two major sectors of the HVAC&R industry, namely commercial refrigeration and residential air-conditioning and heat pumps. Finally, keeping in consideration the global environmental regulations and safety standards, a recommendation of the most suitable refrigerants in both sectors has been made.
Keywords:
refrigerants; thermodynamics; global warming potential; natural refrigerants; hydrocarbons; refrigerant blends
Frequently, the addition/subtraction of water molecules to matter modifies the matter nature. For example, there are many molecules capable ‘to mutate’ in presence of water or a dehydrating agent. All inorganic substances (i.e., oxides, hydroxides, anhydrides, acids, etc.) are generated by the addition/subtraction of one water molecule to another chemical compound. Similarly, in organic chemistry, a very common type of reaction is the ‘condensation reaction’, that is the reaction between two molecules to produce a product and water. Examples of this type of reaction is the Fischer esterification, the peptide bond formation, the polymerization by polycondensation, etc. The inverse reaction does also exist for each of these processes; indeed, inverse types of reactions are hydrolysis and saponification, where water addition to a molecule generates two new molecules. In general, matter (i.e., elemental substances, molecules, polymers and other types of substances) can modify in presence of water. Like an example, in the above picture, it is shown as water removal from a poly(vinyl alcohol) (PVOH) film by dipping in concentrated sulfuric acid leads to the formation of a polyacetylene film[1].
Keywords:
Polyacetylene; Dehydration; Sulfuric acid; Poly(vinyl alcohol); Water
Rosin (named also colophony and principally made of abietic acid) is a natural resinous product with great applicative potentialities and, for such a reason, this substance has been widely technologically exploited throughout the history of humanity. Rosin represents a typical example of ‘multifunctional material’ because it shows countless functional properties. The early use of this substance has been as ‘surface polarity-reversing’ coating. Owing to the carboxylic group (-COOH) present in the abietic acid molecule, the substance easily graft polar surfaces like that of wood, paper, cotton, natural fibers, etc. When the carboxylic group has reacted (condensed) with the surface hydroxyls (-OH), being not-polar the remaining part of the molecule, the substrate surface results coated by a continuous hydrophobic layer. This coating layer also increases the surface friction coefficient and has sealant capability. In addition, this nature-made resin shows strong fluorescence (blue light emission)[1] for the presence of one diene group (i.e., C=C-C=C) in the hydrophobic part of the molecular structure, antiseptic/antimicrobial characteristics, a yellow or red visible coloration, etc., these useful technological properties make this substance a real ‘multifunctional material’. However, there are still unknown, technologically useful potentialities of rosin that have never been mentioned in the literature, like the following one which deals with the optical field. A perfectly transparent, amber glass of rosin can be obtained by cooling molten rosin at room temperature. This completely amorphous solid phase is a very inhomogeneous optical-grade medium in a meta-stable state, that is capable to remain practically unchanged for years. The inhomogeneity of rosin arises principally from a fluctuating density value and residual stresses in the solid body, that in turn causes variations of the glass refractive index. This unusual optical property generates an exceptional light-scattering phenomenon, when the glass is irradiated by a red laser beam. Scattering can be ascribed also to the presence of small fracture surfaces in the solid body, irregularities of the solid surface, impurities or small air bubbles in the solid body, etc. As visible in this picture, dispersion of coherent light (laser light) in inhomogeneous optical solids like the rosin glass is capable to produce very impactful visual effects quite similar to fireworks...
Keywords:
Rosin; Colophonia; Light-scattering; Laser; inhomogeneity