Most of biobased polyols for polyurethanes are synthesized from vegetable oils. In the first part, the present review goes into details of these different synthetic routes to obtain polyols. First, olefinic functionalities of triglycerides could easily be epoxidized, leading to reactive epoxide groups. Second, triglycerides double bonds could undergo a wide ranges of reactions to yield polyols. Finally, the carbonyl group could also be used as a reactive group to yield various polyols. In the second part, the present review is dedicated to the commercial biobased polyols, and, based on the patent literature focuses on the industrial synthetic routes.
Advances in the use of poly (methyl methacrylate) (PMMA) have opened up a wide range of applications in the field of nanotechnology. The knowledge of the properties of PMMA has contributed a lot to the recent boosts in the synthesis, modification, and applications of the polymer. However, there is a need to condense these developments in the form of an article for better understanding and easy access. This review highlights the fundamental physical properties of PMMA, coupled with experimental evidence of its essential chemistry, such as solubility, hydrolysis, grafting, combustion reactions, reactions with amines, and thermal decomposition. The recent developments in the applications of PMMA in biomedical, optical, solar, sensors, battery electrolytes, nanotechnology, viscosity, pneumatic actuation, molecular separations, and polymer conductivity were also revealed.
Organic thin film transistor (OTFT) based device modeling and circuit application is a rapidly emerging research area. Taking cognizance of this fact, our paper reviews various basic to advanced OTFT structures, their performance parameters, materials of individual OTFT layers, their molecular structures, OTFT charge transport phenomena, and fabrication techniques. The performance of p- and n-type conducting polymer and small molecule organic semiconductors are reviewed primarily in terms of field effect mobility, current on/off ratio, and operating voltage for various OTFT structures. Moreover, different organic/inorganic materials for realizing the dielectric layer, electrodes, and the substrate in an OTFT are analyzed. Some of the compact models that are essential for predicting and optimizing the device performance are described that takes into account the mobility enhancement factor and channel length modulation. A detailed study of the single gate, dual gate, vertical channel, and cylindrical gate OTFT structures is carried out. Furthermore, the paper discusses some of the interesting and upcoming applications of organic transistors such as inverters, light emitting diodes (LEDs), RFID tags, and DNA sensors. Although organic transistors boast of a bright future with a wide spectrum of applications, but they still face several challenges in terms of mobility, voltage swings, noise margins, sub-threshold slope, stability, etc., that needs to be resolved to make them a commercially sustainable and viable technology.
During the last decade the field of polymer photovoltaics has seen a tremendous improvement in both device efficiency and understanding of the underlying physical processes. One has come to a point in which the prototypical large bandgap material system P3HT:PCBM is nearing optimal device performance. In order to enhance efficiencies even further, research activities for new materials are needed with better aligned energy levels. One interesting approach is by narrowing the donor bandgap to enhance light absorption. Recent developments on small band gap (<2.0 eV) materials for photovoltaic applications are reviewed. First, an introduction is given regarding the processes governing the exciton dissociation, charge transport requirements, energy level engineering of both donor and acceptor materials, and other parameters determining the photovoltaic performance. The focus is on polymeric donor materials, which are subdivided by the type of monomeric units that constitute the backbone. Finally, the synthetic methods and conditions, processing of the devices, and the device performances are summarized.
The field of polymers derived from non-petrochemical feedstocks is gaining a great deal of momentum from both a commercial and academic sense. Using annually renewable feedstocks, such as biomass, for the production of new plastics can have both economic and environmental benefits. Fundamental research in the production, modification, property enhancement, and new applications of these materials is an important undertaking. The new materials, concepts, and utilizations that result from these efforts will shape the future of polymers from renewable resources. This issue of Polymer Reviews focuses on the production and properties of renewable resource polymers and highlights current trends and research directions.
Natural fibers today are a popular choice for applications in composite manufacturing. Based on the sustainability benefits, biofibers such as plant fibers are replacing synthetic fibers in composites. These fibers are used to manufacture several biocomposites. The chemical composition and properties of each of the fibers changes, which demands the detailed comparison of these fibers. The reinforcement potential of natural fibers and their properties have been described in numerous papers. Today, high performance biocomposites are produced from several years of research. Plant fibers, particularly bast and leaf, find applications in automotive industries. While most of the other fibers are explored in lab scales they have not yet found large-scale commercial applications. It is necessary to also consider other fibers such as ones made from seed (coir) and animals (chicken feather) as they are secondary or made from waste products. Few plant fibers such as bast fibers are often reviewed briefly but other plant and animal fibers are not discussed in detail. This review paper discusses all the six types of plant fibers such as bast, leaf, seed, straw, grass, and wood, together with animal fibers and regenerated cellulose fibers. Additionally, the review considers developments dealing with natural fibers and their composites. The fiber source, extraction, availability, type, composition, and mechanical properties are discussed. The advantages and disadvantages of using each biofiber are discussed. Three fabric architectures such as nonwoven, woven and knitted have been briefly discussed. Finally, the paper presents the overview of the results from the composites made from each fiber with suitable references for in-depth studies.
Vegetable oils are excellent but very heterogeneous renewable raw materials for polyols and polyurethanes. This review discusses the specific nature of vegetable oils and the effect of their structures on the structure of polyols and polyurethanes. One section is dedicated to polyols for rigid and flexible foams and methods of their preparation such as direct oxidation of oils, epoxidation followed by ring opening, hydroformylation, ozonolysis, and transesterification. The next section deals with preparation and structure-property relationships in polyurethanes from different groups of polyols, different isocyanates, and different degrees of crosslinking. The final section covers the environmental aspects of bio-based polyurethanes, i.e., thermal stability, hydrolytic stability, and some aspects of biodegradability.
The review summarizes recent developments in the preparation and use of new initiators for the ring opening polymerization of lactide. The review compares different classes of initiator including metal complexes, classed according to their group in the periodic table, and carbon-based initiators/organocatalysts. Emphasis is placed on the polymerization kinetics and the control exhibited by the different types of initiators. Where useful properties, such as high rates or stereocontrol, have been observed a more detailed examination of the initiator is provided. A further focus of the review is initiators displaying low toxicity and biocompatibility.
The tunability of the chemical composition of ionic liquids (ILs), achieved by pairing various organic cations with numerous anions, allows for fine control of their physicochemical properties and has been widely used for the adjustment of the IL solvent characteristics. Exploitation of IL structural modularity coupled with chemical modification of the cation or anion to incorporate polymerizable groups is now an active area of research, resulting in the development of polymeric ionic liquids (poly(IL)s). The emergence of poly(IL)s as functional materials in the areas of polymer electrolytes, sorbents, dispersing agents, and nanomaterials is reviewed.
This paper reviews recent developments in carbon fibers. Intensive studies focus on relationships among processing conditions, chemical/physical structures and tensile properties of polyacrylonitrile and meso-phase pitch based carbon fibers. Carbon fibers with specific geometry, such as hollow, porous, and patterned, have been fabricated for specific applications. Additionally, carbon nanotubes (CNTs), which have excellent mechanical properties, have been processed into macroscopic continuous fibers. Incorporating CNTs in precursor fiber also improves tensile strength and modulus of the resultant carbon fiber. Although extensive studies have been conducted for improving carbon fiber tensile strength and modulus as well as for reducing their production cost, these issues remain amongst the main challenges for broadening their applications.
Electrospinning is a fabrication technique, which can be used to create nanofibrous non-wovens from a variety of starting materials. The structure, chemical and mechanical stability, functionality, and other properties of the mats can be modified to match end applications. In this review, an introduction to biopolymers and the electrospinning process, as well as an overview of applications of nanofibrous biopolymer mats created by the electrospinning process will be discussed. Biopolymers will include polysaccharides (cellulose, chitin, chitosan, dextrose), proteins (collagen, gelatin, silk, etc.), DNA, as well as some biopolymer derivatives and composites.
Since its introduction in the early 1990s, nitroxide-mediated radical polymerization (NMP) has been widely adopted for the preparation of a panoply of new polymer architectures. While NMP provides a number of advantages for the preparation of specific types of polymers, several inherent limitations with NMP have led to the more widespread use of other reversible-deactivation radical polymerization (RDRP) methods, chiefly atom transfer radical polymerization (ATRP) and reversible addition-fragmentation-chain transfer (RAFT) polymerization, in polymer synthesis. This short review discusses strategies that have been adopted for dealing with the difficulties of NMP and also surveys the use of NMP to prepare new polymers and copolymers over the past several years.
The increase in energy production costs for fossil fuels has led to a search for an economically viable alternative energy source. One alternative energy source of particular interest is solar energy. A promising alternative to inorganic materials is organic semiconductor polymer solar cells due to their advantages of being cheaper, light weight, flexible and made into large areas by roll-to-roll processing. However, the conventional architecture that is typically used for fabricating solar cells requires high vacuum to deposit the top metal electrode which is not suitable for roll-to-roll processing. Recently an inverted device architecture has been investigated as a suitable architecture for developing the ideal roll-to-roll type processing of polymer-based solar cells. This review will go over the recent advances and approaches in the development of this type of inverted device architecture. We will highlight some of the work that we have done to integrate materials, device, interface, and processing of the inverted device architecture platform to produce more idealized polymer-based solar cells.
Polymer flooding is one of the most promising techniques for the recovery of remaining oil from light oil reservoirs. Water soluble polymers are used to enhance the viscosity of displacing fluid and to improve the sweep efficiency. In this paper, water soluble polymers used for chemical enhanced oil recovery are reviewed. Conventional and novel modified polymers are discussed along with their limitations. The review covers thermal stability, rheology, and adsorption behavior of various polymer systems in sandstone and carbonate reservoirs. Field and laboratory core flooding data of several polymers are covered. The review describes the polymer systems that are successfully applied in low-temperature and low-salinity reservoirs. Comprehensive review of current research activities aiming at extending polymer flooding to high-temperature and high-salinity reservoirs is performed. The review has identified current and future challenges of polymer flooding.
Research into polymers incorporating polyhedral oligomeric silsesquioxane (POSS) has intensified during the past several years, revealing new fundamental polymer physics, new synthetic routes, and unexpected applications. The present review article critically examines the recent scientific literature on POSS polymers with an emphasis on structure-property relationships. We conclude that it is an exciting time to work on such materials and we expect the field to continue to grow in the foreseeable future.
Hypercrosslinked polymers (HCPs) represent a class of nanoporous materials with a wide range of practical and potential applications such as gas sorption and separation, heterogeneous catalysis, drug delivery, and chromatographic separation. First introduced by Davankov and Tsyurupa in the early 1970s, HCPs have developed rapidly over the past few decades. Mostly based on Friedel-Crafts chemistry, HCP materials can be prepared from the post-crosslinking of polystyrene-type precursors in their swollen state, or from the condensation of small building blocks. HCP materials manifest numerous important advantages, including moderate synthetic conditions, an enormous stockroom of inexpensive monomers, robust structures, and good thermal and chemical stabilities. This review article aims to provide an overview of recent publications on HCPs, and the emphasis is positioned on the synthetic approaches, theoretical studies, characterizations, structure-property relationships, and applications of these HCP materials.
Poly(lactic acid) (PLA) is regarded as one of the most promising biobased and biodegradable polymers due its various advantages including high mechanical strength, easy processability, high melting temperature, renewability, biodegradability, and biocompatibility. However, the inherent brittleness significantly restricts its wide application. Therefore, toughening PLA has attracted more and more attention and various materials have been used to blend with PLA for toughening. Considering the fact that the use of petroleum-based species to toughen PLA would partially sacrifice the sustainability, various renewable polymers have recently been employed to toughen PLA. A series of important achievements have been obtained but not reviewed. This article aims to review progress in toughening PLA with renewable polymers. The toughening theories and compatibilization strategies are also briefly introduced.
Epoxy resins have been used as structural materials since the late 1940s. Despite their desirable properties such as high strength, excellent creep resistance, and good adhesion, they suffer from low fracture energy. Rubber modification as a major toughening approach to overcome the inherent brittleness of epoxy polymers was introduced during the early 1970s. Since then, a large number of investigations have been conducted to elucidate different aspects of rubber-toughened epoxies. The present work is a critical review of the field focusing on the important parameters affecting rubber-toughening. The studies reviewed are classified in five categories including roles of matrix ductility, rubber concentration, blend morphology, particle cavitation, and particle/matrix interface. It has been tried to provide an in-depth view of the state-of-the-art knowledge in the field and to direct future studies towards exploring new approaches for toughening of epoxy polymers.
Polylactide is a commercially-produced thermoplastic that is derived from renewable resources and is environmentally degradable. Due to these attributes, polylactide holds tremendous promise as an alternative to the ubiquitous petroleum-based materials. However, in situations that require a high level of impact strength, the toughness of polylactide in its pristine state is often insufficient. As such, there has been tremendous effort in developing ways to improve this material property deficiency. In this review we summarize these approaches for increasing the toughness of polylactide with an eye toward how the toughening protocols influence the overall mechanical properties of the resultant materials.
In this review, insight into the use of bio-based fibers as composite reinforcement has been addressed. Specifics on the varieties of natural fibers, and the resultant properties from their constituents and hierarchal structures are described. The methods used to enhance the interface of these fibers with a variety of polymer matrices are reviewed. In addition, the influence of textile operations on creating various fiber architectures with resulting reinforcing capabilities, along with the methods in which natural fiber reinforced composites can be processed, are addressed. Finally, discussion of the correlation between structure, processing, and final composite properties are provided.