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

To improve reliability, durability, and reworkability of bulk polymers utilized in ubiquitous acidic water, the authors develop a novel hyperbranched polymer capable of self-healing and recycling in a low-pH aqueous environment. The hyperbranched polymer has many hydrophilic and hydrophobic terminal groups. When it is damaged in acidic water, the hydrophilic groups are protonated, forming hydrogen bonds, and closing the crack. Meanwhile, hydrophobic interactions of hydrophobic groups are gradually established across the interface because of the intimate contact of the cracked surface, further reinforcing the rebonded portion. The amphiphilic structure proves to meet both the thermodynamic and kinetic requirements for autonomous rehabilitation. As a result, the unfavored water, which used to impede adhesion between hydrophobic polymeric materials, turns into a positive aid to crack healing. The mechanism involved is carefully analyzed and verified in terms of micro- and macroscopic techniques. The proposed...

Self-Healing of Polymer in Acidic Water toward Strength Restoration through the Synergistic Effect of Hydrophilic and Hydrophobic Interactions.

Uniform hollow magnetic mesoporous silica spheres (HMMS), with Fe3O4 nanoparticles embedded in the mesoporous shell, were successfully prepared by using carboxylic polystyrene latex and Fe3O4 heteroaggregates as the hard template together with a coating of tetraethoxysilane (TEOS) and n-octadecyltrimethoxysilane (C18TMS) mixture. The HMMS outer diameter is about 370 nm and the thickness of the mesoporous shells is around 20 nm. Both the morphology and the thickness of the shell can be easily tuned by tailoring the amount of PS latex and the concentration of ammonia. Meanwhile, the magnetic properties can be slightly changed by adjusting the weight ratios of PS/Fe3O4. In addition, the HMMS demonstrates high drug storage capacity and sustained release properties, demonstrating that this kind of HMMS could be used as a promising material in drug delivery systems.

A facile heteroaggregate-template route to hollow magnetic mesoporous spheres with tunable shell structures

To prepare self-healing thermoplastic composites, techniques of living polymerization and microencapsulation were employed. The matrix was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, in which encapsulated monomer was dispersed. Upon mechanical damage of the composites, the monomer released from broken microcapsules resumed polymerization with the living matrix, establishing chemical bonding between the cracked planes. As a result, full recovery of mechanical strength was achieved at room temperature without manual intervention. Compared to the self-healing material made by atom transfer radical polymerization (ATRP) in the authors' previous work, the present one possesses more meaningful applicability owing to the versatility and robustness of RAFT polymerization.

Self-healing of thermoplastics via reversible addition–fragmentation chain transfer polymerization

Flame-retardant epoxy resin (EP) composites were prepared by the incorporation of a phenethyl-bridged DOPO derivative (DiDOPO) and modified layered double hydroxide (OLDH) In addition, the flame-retardant behaviour, thermal stability, synergism between DiDOPO and OLDH, and mechanical properties of the flame-retardant EP composites were examined The introduction of a specific amount of OLDH in the intumescent flame-retardant EP led to considerable enhancement in flame retardancy, thermal stability, and mechanical properties Furthermore, the effects of DiDOPO and OLDH on the flame-retardant properties of the EP composites were characterised by the limiting oxygen index (LOI) as well as the UL-94 vertical burning and cone calorimeter tests (CCT) The LOI of the EP/DiDOPO5/OLDH5 composites increased from 218% to 315%, and the composites exhibited the V-0 rating in the UL-94 vertical burning test Moreover, the EP/DiDOPO5/OLDH5 composite exhibited the highest tensile strength and a low peak heat release rate and the total heat release values In addition, scanning electron microscopy observation revealed a considerably more continuous, compact char residue for the EP/DiDOPO/OLDH composite Thermogravimetric analysis and CCT revealed that DiDOPO and OLDHs exert gas- and condensed-phase flame-retardant effects Overall, different flame retardant performance is related to the characteristics of each composite; dispersion state in the EP matrix; and structural changes during burning

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Ming Qiu Zhang

Papers

Self-Healing of Polymer in Acidic Water toward Strength Restoration through the Synergistic Effect of Hydrophilic and Hydrophobic Interactions.

A facile heteroaggregate-template route to hollow magnetic mesoporous spheres with tunable shell structures

Self-healing of thermoplastics via reversible addition–fragmentation chain transfer polymerization

Flame-retardant effect of a phenethyl-bridged DOPO derivative and layered double hydroxides for epoxy resin

Friction induced mechanochemical and mechanophysical changes in high performance semicrystalline polymer