Biocomposites reinforced with natural fibers: 2000–2010

There have been a number of review papers on layered silicate and carbon nanotube reinforced polymer nanocomposites, in which the fillers have high aspect ratios. Particulate–polymer nanocomposites containing fillers with small aspect ratios are also an important class of polymer composites. However, they have been apparently overlooked. Thus, in this paper, detailed discussions on the effects of particle size, particle/matrix interface adhesion and particle loading on the stiffness, strength and toughness of such particulate–polymer composites are reviewed. To develop high performance particulate composites, it is necessary to have some basic understanding of the stiffening, strengthening and toughening mechanisms of these composites. A critical evaluation of published experimental results in comparison with theoretical models is given.

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Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate–polymer composites

Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).

A review of electrolyte materials and compositions for electrochemical supercapacitors

Studies on the use of natural fibers as replacement to man-made fiber in fiber-reinforced composites have increased and opened up further industrial possibilities. Natural fibers have the advantages of low density, low cost, and biodegradability. However, the main disadvantages of natural fibers in composites are the poor compatibility between fiber and matrix and the relative high moisture sorption. Therefore, chemical treatments are considered in modifying the fiber surface properties. In this paper, the different chemical modifications on natural fibers for use in natural fiber-reinforced composites are reviewed. Chemical treatments including alkali, silane, acetylation, benzoylation, acrylation, maleated coupling agents, isocyanates, permanganate and others are discussed. The chemical treatment of fiber aimed at improving the adhesion between the fiber surface and the polymer matrix may not only modify the fiber surface but also increase fiber strength. Water absorption of composites is reduced and their mechanical properties are improved.

Chemical Treatments of Natural Fiber for Use in Natural Fiber-Reinforced Composites: A Review

This paper provides an overview of recent progress made in the area of cellulose nanofibre-based nanocomposites. An introduction into the methods used to isolate cellulose nanofibres (nanowhiskers, nanofibrils) is given, with details of their structure. Following this, the article is split into sections dealing with processing and characterisation of cellulose nanocomposites and new developments in the area, with particular emphasis on applications. The types of cellulose nanofibres covered are those extracted from plants by acid hydrolysis (nanowhiskers), mechanical treatment and those that occur naturally (tunicate nanowhiskers) or under culturing conditions (bacterial cellulose nanofibrils). Research highlighted in the article are the use of cellulose nanowhiskers for shape memory nanocomposites, analysis of the interfacial properties of cellulose nanowhisker and nanofibril-based composites using Raman spectroscopy, switchable interfaces that mimic sea cucumbers, polymerisation from the surface of cellulose nanowhiskers by atom transfer radical polymerisation and ring opening polymerisation, and methods to analyse the dispersion of nanowhiskers. The applications and new advances covered in this review are the use of cellulose nanofibres to reinforce adhesives, to make optically transparent paper for electronic displays, to create DNA-hybrid materials, to generate hierarchical composites and for use in foams, aerogels and starch nanocomposites and the use of all-cellulose nanocomposites for enhanced coupling between matrix and fibre. A comprehensive coverage of the literature is given and some suggestions on where the field is likely to advance in the future are discussed.

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Review: current international research into cellulose nanofibres and nanocomposites

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Enthalpy Relaxation in Poly(aryl ether ketone bearing phthalidylidene group)

The phenomenon of solvent-induced crystallization observed in some polymer–solvent pair was well documented. It is generally believed that solvent-induced crystallization occurs during sorption of the solvent. However, this is actually a hypothesis and needs to be proven. To clarify the true situation, the present article investigates crystalline structural variation of polyetheretherketone before and after treatment of methylene chloride. The results indicate that crystallization of the polymer was induced by the solvent mainly when the solvent was desorbed. The possible mechanism is discussed in the light of molecular motion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3376–3379, 1999

Solvent‐induced crystallization in polyetheretherketone exposed to methylene chloride—during solvent sorption or during solvent desorption?

The compatibility and relaxation behavior of poly(phenylene sulfide) (PPS)/poly(ethersulfone) (PES) blends and their composites reinforced by carbon fiber (CF-PPS/PES) have been studied by internal friction analysis method. The experimental results show: (1) There is interaction on a molecular-scale between PPS and PES in blends and blending ratio is the key factor to determine the degree of such interaction; (2) There is a rather wide continuous distribution of relaxation times for the secondary relaxation of PES in both blends and composites, and the half-width of the relaxation time distribution function for the relaxation process bears a relation to the relative content of the PPS component; (3) Peak height and peak temperature originating from the glass transition of PPS decrease with increasing the starting temperature of the internal friction measurement; (4) PPS/PES blends and CF-PPS/PES composites are thermodynamically metastable, and thermal history exerts considerable influence on phase separation behavior.

Study on Internal Friction Characteristics of Poly(phenylene sulfide)/Poly(ethersulfone) Blends and Composites Reinforced by Carbon Fiber

The present work developed carbon-black-filled waterborne polyurethane composites, in which cyclodextrins acted as the hard segments The composites proved to be accompanied by selective gas sensitivity Upon exposure to certain organic solvent vapors, electrical resistance of the composites drastically increased The maximum magnitude of resistance variation was found to be a function of the molecular size of the analyte Besides, the composites containing different cyclodextrins exhibit different maximum responsivity against identical gaseous analytes According to these characteristics, molecular discrimination and screening, which used to be conducted by expensive analytical instruments, might be done simply by examining the resistance change in an analyte's vapor It was found that selective adsorption on cyclodextrins should be responsible for the specific response habit of the composites

Gas sensing conductive composites capable of size-dependent molecular discrimination and screening

Herein, to prepare an extrinsic self-healing system with high heat resistance to tolerate the processing of thermoplastics, a group of new healants based on atom transfer radical polymerization is developed. It consists of microencapsulated acrylate monomers (2-methyl-2-adamantylmethacrylate or trimethylolpropane trimethacrylate), macroinitiator poly(methyl methacrylate)–Br, and supported catalyst (coordination compound of cyclic 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane and cuprous bromide). Composites containing the healing agent with polystyrene, poly(methyl methacrylate) and acrylonitrile-butadiene-styrene copolymer as matrices were successfully manufactured by compression molding. Impact tests indicate that the composites can regain their mechanical strength as a result of polymerization of the released acrylate monomers at room temperature. The strong interaction between the cyclic ligand and CuBr obviously enhances the thermostability of the ligand and depresses the negative influence of cupric ions on the aging properties of the matrix polymers. The present work offers a new route for the design and application of self-healing thermoplastics.

Ming Qiu Zhang

Papers

Enthalpy Relaxation in Poly(aryl ether ketone bearing phthalidylidene group)

Solvent‐induced crystallization in polyetheretherketone exposed to methylene chloride—during solvent sorption or during solvent desorption?

Study on Internal Friction Characteristics of Poly(phenylene sulfide)/Poly(ethersulfone) Blends and Composites Reinforced by Carbon Fiber

Gas sensing conductive composites capable of size-dependent molecular discrimination and screening

Self-healing of thermally molded commodity plastics based on heat-resistant and anti-aging healing systems