Poly(vinylidene fluoride), PVDF, and its copolymers are the family of polymers with the highest dielectric constant and electroactive response, including piezoelectric, pyroelectric and ferroelectric effects. The electroactive properties are increasingly important in a wide range of applications such as in biomedicine, energy generation and storage, monitoring and control, and include the development of sensors and actuators, separator and filtration membranes and smart scaffolds, among others. For many of these applications the polymer should be in one of its electroactive phases. This review presents the developments and summarizes the main characteristics of the electroactive phases of PVDF and copolymers, indicates the different processing strategies as well as the way in which the phase content is identified and quantified. Additionally, recent advances in the development of electroactive composites allowing novel effects, such as magnetoelectric responses, and opening new applications areas are presented. Finally, some of the more interesting potential applications and processing challenges are discussed. (C) 2013 Elsevier Ltd. All rights reserved.
Due to environment and sustainability issues, this century has witnessed remarkable achievements in green technology in the field of materials science through the development of biocomposites. The development of high-performance materials made from natural resources is increasing worldwide. The greatest challenge in working with natural fiber reinforced plastic composites is their large variation in properties and characteristics. A biocomposite's properties are influenced by a number of variables, including the fiber type, environmental conditions (where the plant fibers are sourced), processing methods, and any modification of the fiber. It is also known that recently there has been a surge of interest in the industrial applications of composites containing biofibers reinforced with biopolymers. Biopolymers have seen a tremendous increase in use as a matrix for biofiber reinforced composites. A comprehensive review of literature (from 2000 to 2010) on the mostly readily utilized natural fibers and biopolymers is presented in this paper. The overall characteristics of reinforcing fibers used in biocomposites, including source, type, structure, composition, as well as mechanical properties, will be reviewed. Moreover, the modification methods: physical (corona and plasma treatment) and chemical (silane, alkaline, acetylation, maleated coupling, and enzyme treatment) will be discussed. The most popular matrices in biofiber reinforced composites based on petrochemical and renewable resources will also be addressed. The wide variety of biocomposite processing techniques as well as the factors (moisture content, fiber type and content, coupling agents and their influence on composites properties) affecting these processes will be discussed. Prior to the processing of biocomposites, semi-finished product manufacturing is also vital, which will be illustrated. Processing technologies for biofiber reinforced composites will be discussed based on thermoplastic matrices (compression molding, extrusion, injection molding, LFT-D-method, and thermoforming), and thermosets (resin transfer molding, sheet molding compound). Other implemented processes, i.e., thermoset compression molding and pultrusion and their influence on mechanical performance (tensile, flexural and impact properties) will also be evaluated. Finally, the review will conclude with recent developments and future trends of biocomposites as well as key issues that need to be addressed and resolved. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.
Shape memory polymers (SMPs), as a class of programmable stimuli-responsive shape changing polymers, are attracting increasing attention from the standpoint of both fundamental research and technological innovations. Following a brief introduction of the conventional shape memory effect (SME), progress in new shape memory enabling mechanisms and triggering methods, variations of in shape memory forms (shape memory surfaces, hydrogels, and microparticles), new shape memory behavior (multi-SME and two-way-SME), and novel fabrication methods are reviewell. Progress in thermomechanical modeling of SMPs is also presented. (C) 2015 Elsevier Ltd. All rights reserved.
Nanoparticles and nanocomposites are used in a wide range of applications in various fields, such as medicine, textiles, cosmetics, agriculture, optics, food packaging, optoelectronic devices, semiconductor devices, aerospace, construction and catalysis. Nanoparticles can be incorporated into polymeric nanocomposites. Polymeric nanocomposites consisting of inorganic nanoparticles and organic polymers represent a new class of materials that exhibit improved performance compared to their microparticle counterparts. It is therefore expected that they will advance the field of engineering applications. Incorporation of inorganic nanoparticles into a polymer matrix can significantly affect the properties of the matrix. The resulting composite might exhibit improved thermal, mechanical, theological, electrical, catalytic, fire retardancy and optical properties. The properties of polymer composites depend on the type of nanoparticles that are incorporated, their size and shape, their concentration and their interactions with the polymer matrix. The main problem with polymer nanocomposites is the prevention of particle aggregation. It is difficult to produce monodispersed nanoparticles in a polymer matrix because nanoparticles agglomerate due to their specific surface area and volume effects. This problem can be overcome by modification of the surface of the inorganic particles. The modification improves the interfacial interactions between the inorganic particles and the polymer matrix. There are two ways to modify the surface of inorganic particles. The first is accomplished through surface absorption or reaction with small molecules, such as silane coupling agents, and the second method is based on grafting polymeric molecules through covalent bonding to the hydroxyl groups existing on the particles. The advantage of the second procedure over the first lies in the fact that the polymer-grafted particles can be designed with the desired properties through a proper selection of the species of the grafting monomers and the choice of grafting conditions. (C) 2013 Elsevier Ltd. All rights reserved.
Thermal management is critical to the performance, lifetime, and reliability of electronic devices. With the miniaturization, integration and functionalization of electronics and the emergence of new applications such as light emitting diodes, thermal dissipation becomes a challenging problem. Addressing this challenge requires the development of novel polymer-based composite materials with enhanced thermal conductivity. In this review, the fundamental design principles of highly thermally conductive composites were discussed. The key factors influencing the thermal conductivity of polymers, such as chain structure, crystallinity, crystal form, orientation of polymer chains, and orientation of ordered domains in both thermoplastics and thermosets were addressed. The properties of thermally conductive fillers (carbon nanotubes, metal particles, and ceramic particles such as boron nitride or aluminum oxide) are summarized at length. The dependence of thermal conductivity of composites on the filler loading, filler aggregate morphology and overall composite structure is also discussed. Special attention is paid to recent advances in controlling the microstructure of polymer composites to achieve high thermal conductivity (novel approaches to control filler orientation, special design of filler agglomerates, formation of continuous filler network by self-assembly process, double percolation approach, etc.). The review also summarizes some emerging applications of thermally conductive polymer composites. Finally, we outline the challenges and outlook for thermally conductive polymer composites. (C) 2016 Elsevier Ltd. All rights reserved.
Lignins are now considered as the main aromatic renewable resource. They represent an excellent alternative feedstock for the elaboration of chemicals and polymers. Lignin is a highly abundant biopolymeric material that constitutes with cellulose one of the major components in structural cell walls of higher vascular plants. Large quantities of lignin are yearly available from numerous pulping processes such as paper and biorefinery industries. Lignin extraction from lignocellulosic biomass (wood, annual plant) represents the key point to its large use for industrial applications. One of the major problems still remains is its unclearly defined structure and its versatility according to the origin, separation and fragmentation processes, which mainly limits its utilization. While currently often used as a filler or additive, lignin is rarely exploited as a raw material for chemical production. However, it may be an excellent candidate for chemical modifications and reactions due to its highly functional character (i.e., rich in phenolic and aliphatic hydroxyl groups) for the development of new biobased materials. Chemical modification of lignin has driven numerous efforts and researches with significant studies during the last decades. After an overview with some generalities concerning the main extraction techniques along with the structure and the properties of lignins, this review describes in details the different chemical modifications of lignins. They are classified into three groups: (1) lignin fragmentation into phenolic or other aromatic compounds for fine chemistry, (2) synthesis of new chemical active sites to impart new reactivity to lignin, and (3) functionalization of hydroxyl groups to enhance their reactivity. In that frame, the potential applications of lignin as precursor for the elaboration of original macromolecular architecture and the development of new building blocks are discussed. Finally, the major achievements and remaining challenges for lignin modifications and its uses as a macromer for polymer synthesis are also mentioned with emphasis on the most promising and relevant applications. (C) 2013 Elsevier Ltd. All rights reserved.
Alginate is a biomaterial that has found numerous applications in biomedical science and engineering due to its favorable properties, including biocompatibility and ease of gelation. Alginate hydrogels have been particularly attractive in wound healing, drug delivery, and tissue engineering applications to date, as these gels retain structural similarity to the extracellular matrices in tissues and can be manipulated to play several critical roles. This review will provide a comprehensive overview of general properties of alginate and its hydrogels. their biomedical applications, and suggest new perspectives for future studies with these polymers. (C) 2011 Elsevier Ltd. All rights reserved.
The introduction of graphene-based nanomaterials has prompted the development of flexible nanocomposites for emerging applications in need of superior mechanical, thermal, electrical, optical, and chemical performance. These nanocomposites exhibit outstanding structural performance and multifunctional properties by synergistically combining the characteristics of both components if proper structural and interfacial organization is achieved. Here, we briefly introduce the material designs and basic interfacial interactions in the graphene-polymer nanocomposites and the corresponding theoretical models for predicting the mechanical performances of such nanocomposites. Then, we discuss various assembly techniques available for effectively incorporating the strong and flexible graphene-based components into polymer matrices by utilization of weak and strong interfacial interactions available in functionalized graphene sheets. We discuss mechanical performance and briefly summarize other physical (thermal, electrical, barrier, and optical) properties, which are controlled by processing conditions and interfacial interactions. Finally, we present a brief outlook of the developments in graphene-based polymer nanocomposites by discussing the major progress, opportunities, and challenges. (C) 2014 Elsevier Ltd. All rights reserved.
There is growing interest in developing bio-based polymers and innovative process technologies that can reduce the dependence on fossil fuel and move to a sustainable materials basis. Bio-nanocomposites open an opportunity for the use of new, high performance, light weight green nanocomposite materials making them to replace conventional non-biodegradable petroleum-based plastic packaging materials. So far, the most studied bio-nanocomposites suitable for packaging applications are starch and cellulose derivatives, polylactic acid (PLA), polycaprolactone (PCL), poly(butylene succinate) (PBS) and polyhydroxybutyrate (PHB). The most promising nanoscale fillers are layered silicate nanoclays such as montmorillonite and kaolinite. In food packaging, a major emphasis is on the development of high barrier properties against the diffusion of oxygen, carbon dioxide, flavor compounds, and water vapor. Moreover, several nanostructures can be useful to provide active and/or smart properties to food packaging systems, as exemplified by antimicrobial properties, oxygen scavenging ability, enzyme immobilization, or indication of the degree of exposure to some detrimental factors such as inadequate temperatures or oxygen levels. Challenges remain in increasing the compatibility between clays and polymers and reaching complete dispersion of nanoparticles. This review focuses on the enhancement of packaging performance of the green materials as well as their biodegradability, antimicrobial properties, and mechanical and thermal properties for food packaging application. The preparation, characterization and application of biopolymer-based nanocomposites with organic layered silicate and other fillers, and their application in the food packaging sector are also discussed. (C) 2013 Elsevier Ltd. All rights reserved.
During the last years the performance of bulk heterojunction solar cells has been improved significantly. For a large-scale application of this technology further improvements are required. This article reviews the basic working principles and the state of the art device design of bulk heterojunction solar cells. The importance of high power conversion efficiencies for the commercial exploitation is outlined and different efficiency models for bulk heterojunction solar cells are discussed. Assuming state of the art materials and device architectures several models predict power conversion efficiencies in the range of 10-15%. A more general approach assuming device operation close to the Shockley-Queisser-limit leads to even higher efficiencies. Bulk heterojunction devices exhibiting only radiative recombination of charge carriers could be as efficient as ideal inorganic photovoltaic devices. (C) 2013 Elsevier Ltd. All rights reserved.
This review presents a literature survey of recent work on poly(ionic liquid)s or polymerized ionic liquids (PILs), a class of polyelectrolytes that has attracted rapidly increasing interest over the past few years. The review begins with a short explanation of the interconnection as well as the intrinsic differences between PILs and ionic liquids. Recently reported PIL homopolymers with new chemical structures and synthetic trends are introduced as a complement to the overall PIL synthesis schemes reported previously. In addition, block copolymers and colloidal particles of PILs are described, followed by a discussion of the limitations of PILs due to structural instability under certain conditions and the efforts to understand PIL physics. Examples of recent applications of PILs across a multitude of fields, such as thermoresponsive materials, carbon materials, catalysis, porous polymers, separation and absorption materials, and energy harvesting/generation as well as several biological applications are described in detail. (c) 2013 Elsevier Ltd. All rights reserved.
Nitroxide-mediated polymerization (NMP) is a controlled/living radical polymerization (CLRP) technique that enables the design of well-defined, functional and complex macromolecular architectures. This comprehensive review covers all aspects, features and achievements of NMP, from its discovery to 2012. All topics related to NMP are thoroughly discussed and detailed in-depth: synthetic approaches to nitroxides and alkoxyamines, kinetic aspects and polymerization features, range of controllable monomers, polymer characterization, polymerization processes (ionic liquids, dispersed media, etc.), macromolecular coupling approaches, functionalization strategies, macromolecular architectures, bio-related and hybrid materials, industrial applications as well as environmental constraints. (C) 2012 Elsevier Ltd. All rights reserved.
Shape memory polymers (SMPs) represent a highly interesting class of materials. As one representative of the intelligent polymeric systems, these materials gained significant interest in recent years. Consequently, the variety of materials investigated virtually exploded and several promising shape memory effects have been developed. The present review will provide a short overview on the history of SMPs as well as the current developments and concepts for shape memory polymers. Additionally, future developments in this field will be discussed. (C) 2015 Elsevier Ltd. All rights reserved.
In the framework of environmentally friendly processes and products, polylactide (PLA) represents the best polymeric substitutes for various petropolymers because of its renewability, biodegradability, biocompatibility and good thermomechanical properties. Initially, most of its applications concerned biomedical sector and short-time uses such as packaging, particularly for the biodegradable properties of PLA. Interestingly, due to the depletion of petroleum resources, PLA is now viewing more and more as a valuable biosourced polymer alternative in long-term applications such as automotive and electronics. However, for such applications, PLA suffers from some shortcomings such as low thermal resistance, heat distortion temperature and rate of crystallization, whereas some other specific properties are required by different end-use sectors (flame retardancy, antistatic to conductive electrical characteristics, anti-UV, antibacterial or barrier properties, etc.). Therefore, adding nanofillers represents an interesting way to extend and to improve the properties of PLA. There are many nanofillers (three-dimensional spherical and polyhedral, two-dimensional nanofibers or one-dimensional sheet-like nanoparticles) that have been studied, with satisfactory achievements, in the design of PLA nanocomposites. This review hence highlights the main researches and developments in PLA-based nanocomposites during this last decade. (C) 2013 Elsevier Ltd. All rights reserved.
This review outlines the new developments on chitosan-based bioapplications. Over the last decade, functional biomaterials research has developed new drug delivery systems and improved scaffolds for regenerative medicine that is currently one of the most rapidly growing fields in the life sciences. The aim is to restore or replace damaged body parts or lost organs by transplanting supportive scaffolds with appropriate cells that in combination with biomolecules generate new tissue. This is a highly interdisciplinary field that encompasses polymer synthesis and modification, cell culturing, gene therapy, stem cell research, therapeutic cloning and tissue engineering. In this regard, chitosan, as a biopolymer derived macromolecular compound, has a major involvement. Chitosan is a polyelectrolyte with reactive functional groups, gel-forming capability, high adsorption capacity and biodegradability. In addition, it is innately biocompatible and non-toxic to living tissues as well as having antibacterial, antifungal and antitumor activity. These features highlight the suitability and extensive applications that chitosan has in medicine. Micro/nanoparticles and hydrogels are widely used in the design of chitosan-based therapeuticsystems. The chemical structure and relevant biological properties of chitosan for regenerative medicine have been summarized as well as the methods for the preparation of controlled drug release devices and their applications. (C) 2011 Elsevier Ltd. All rights reserved.
Polyimides rank among the most heat-resistant polymers and are widely used in high temperature plastics, adhesives, dielectrics, photoresists, nonlinear optical materials, membrane materials for separation, and Langmuir-Blodgett (LB) films, among others. Additionally, polyimides are used in a diverse range of applications, including the fields of aerospace, defense, and opto-electronics; they are also used in liquid crystal alignments, composites, electroluminescent devices, electrochromic materials, polymer electrolyte fuel cells, polymer memories, fiber optics, etc. Polyimides derived from monomers with noncoplanar (kink, spiro, and cardo structures), cyclic aliphatic, bulky, fluorinated, hetero, carbazole, perylene, chiral, non-linear optical and unsymmetrical structures have been described. The syntheses of various monomers, including diamines and dianhydrides that have been used to make novel polyimides with unique properties, are reported in this review. Polyimides, with tailored functional groups and dendritic structures have allowed researchers to tune the properties and applications of this important family of high-temperature polymers. The synthesis, physical properties and applications of advanced polyimide materials are described. (C) 2012 Elsevier Ltd. All rights reserved.
Dendrimers are novel three dimensional, hyperbranched globular nanopolymeric architectures. Attractive features like nanoscopic size, narrow polydispersity index, excellent control over molecular structure, availability of multiple functional groups at the periphery and cavities in the interior distinguish them amongst the available polymers. Applications of dendrimers in a large variety of fields have been explored. Drug delivery scientists are especially enthusiastic about possible utility of dendrimers as drug delivery tool. Terminal functionalities provide a platform for conjugation of the drug and targeting moieties. In addition, these peripheral functional groups can be employed to tailor-make the properties of dendrimers, enhancing their versatility. The present review highlights the contribution of dendrimers in the field of nanotechnology with intent to aid the researchers in dendrimers in the field of drug delivery. (C) 2013 Elsevier Ltd. All rights reserved.
This paper reviews recent advances in the modification of graphene and the fabrication of graphene-based polymer nanocomposites. Recently, graphene has attracted both academic and industrial interest because it can produce a dramatic improvement in properties at very low filler content. The modification of graphene/graphene oxide and the utilization of these materials in the fabrication of nanocomposites with different polymer matrixes have been explored. Different organic polymers have been used to fabricate graphene filled polymer nanocomposites by a range of methods. In the case of modified graphene-based polymer nanocomposites, the percolation threshold can be achieved at a very lower filler loading. Herein, the structure, preparation and properties of polymer/graphene nanocomposites are discussed in general along with detailed examples drawn from the scientific literature. (C) 2010 Elsevier Ltd. All rights reserved.
Research on shape-memory polymers (SMPs) has been actively conducted for more than three decades. Recently, interest in this area has intensified. Even though there have been a number of related review papers published in the past 3 years, a generalized view on the important aspects of SMPs that would give a holistic picture of this promising area of research is still lacking. This paper will provide a comprehensive review that integrates the achievements in studying SMPs and their derivatives, such as composites and compound structures, as well as their current applications. Concepts, principles/modelings, structures and related synthesis methods, applications and future trends will be examined. (C) 2012 Elsevier Ltd. All rights reserved.