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

Preface. 1 Basics of Self-Healing: State of the Art. 1.1 Background. 1.1.1 Adhesive Bonding for Healing Thermosetting Materials. 1.1.2 Fusion Bonding for Healing Thermoplastic Materials. 1.1.3 Bioinspired Self-Healing. 1.2 Intrinsic Self-Healing. 1.2.1 Self-Healing Based on Physical Interactions. 1.2.2 Self-Healing Based on Chemical Interactions. 1.2.3 Self-Healing Based on Supramolecular Interactions. 1.3 Extrinsic Self-Healing. 1.3.1 Self-Healing in Terms of Healant Loaded Pipelines. 1.3.2 Self-Healing in Terms of Healant Loaded Microcapsules. 1.4 Insights for Future Work. References. 2 Theoretical Consideration and Modeling. 2.1 Molecular Mechanisms. 2.1.1 Self-Healing Below Glass Transition Temperature. 2.1.2 Self-Healing Above Glass Transition Temperature. 2.2 Healing Modeling. 2.2.1 Percolation Modeling. 2.2.2 Continuum and Molecular-Level Modeling of Fatigue Crack Retardation. 2.2.3 Continuum Damage and Healing Mechanics. 2.2.4 Discrete Element Modeling and Numerical Study. 2.3 Design of Self-Healing Composites. 2.3.1 Entropy Driven Self-Assembly of Nanoparticles. 2.3.2 Optimization of Microvascular Networks. 2.4 Concluding Remarks. References. 3 Extrinsic Self-Healing via Addition Polymerization. 3.1 Design and Selection of Healing System. 3.2 Microencapsulation of Mercaptan and Epoxy by in situ Polymerization. 3.2.1 Microencapsulation of Mercaptan. 3.2.2 Microencapsulation of Epoxy. 3.3 Characterization of Self-Healing Functionality. 3.3.1 Self-Healing Epoxy Materials with Embedded Dual Encapsulated Healant: Healing of Crack Due to Monotonic Fracture. 3.3.2 Factors Related to Performance Improvement. 3.3.3 Self-Healing Epoxy Materials with Embedded Dual Encapsulated Healant: Healing of Fatigue Crack. 3.3.4 Self-Healing Epoxy/Glass Fabric Composites with Embedded Dual Encapsulated Healant: Healing of Impact Damage. 3.4 Concluding Remarks. References. 4 Extrinsic Self-Healing via Cationic Polymerization. 4.1 Microencapsulation of Epoxy by UV Irradiation-Induced Interfacial Copolymerization. 4.2 Encapsulation of Boron-Containing Curing Agent. 4.2.1 Loading Boron-Containing Curing Agent onto Porous Media. 4.2.2 Microencapsulation of Boron-Containing Curing Agent via Hollow Capsules Approach. 4.3 Characterization of Self-Healing Functionality. 4.3.1 Self-Healing Epoxy Materials with Embedded Epoxy-Loaded Microcapsules and (C2H5)2O*BF3-Loaded Sisal. 4.3.2 Self-Healing Epoxy Materials with Embedded Dual Encapsulated Healant. 4.4 Concluding Remarks. References. 5 Extrinsic Self-Healing via Anionic Polymerization. 5.1 Preparation of Epoxy-Loaded Microcapsules and Latent Hardener. 5.1.1 Microencapsulation of Epoxy by in situ Condensation. 5.1.2 Preparation of Imidazole Latent Hardener. 5.2 Self-Healing Epoxy Materials with Embedded Epoxy-Loaded Microcapsules and Latent Hardener. 5.3 Self-Healing Epoxy/Woven Glass Fabric Composites with Embedded Epoxy-Loaded Microcapsules and Latent Hardener: Healing of Interlaminar Failure. 5.4 Durability of Healing Ability. 5.5 Self-Healing Epoxy/Woven Glass Fabric Composites with Embedded Epoxy-Loaded Microcapsules and Latent Hardener: Healing of Impact Damage. 5.6 Concluding Remarks. References. 6 Extrinsic Self-Healing via Miscellaneous Reactions. 6.1 Extrinsic Self-Healing via Nucleophilic Addition and Ring-Opening Reactions. 6.1.1 Microencapsulation of GMA by in situ Polymerization. 6.1.2 Self-Healing Epoxy Materials with Embedded Single-Component Healant. 6.2 Extrinsic Self-Healing via Living Polymerization. 6.2.1 Preparation of Living PMMA and Its Composites with GMA-Loaded Microcapsules. 6.2.2 Characterization of Self-Healing Functionality. 6.3 Extrinsic Self-Healing via Free Radical Polymerization. 6.3.1 Microencapsulation of Styrene and BPO. 6.3.2 Self-Healing Performance of Epoxy Filled with Dual Capsules. 6.4 Concluding Remarks. References. 7 Intrinsic Self-Healing via Diels-Alder Reaction. 7.1 Molecular Design and Synthesis. 7.1.1 Synthesis and Characterization of DGFA. 7.1.2 Reversibility of DA Bonds and Crack Remendability of DGFA Based Polymer. 7.1.3 Synthesis and Characterization of FGE. 7.1.4 Reversibility of DA Bonds and Crack Remendability of FGE-Based Polymer. 7.2 Blends of DGFA and FGE. 7.2.1 Reversibility of DA Bonds. 7.2.2 Crack Remendability of Cured DGFA/FGE Blends. 7.3 Concluding Remarks. References. 8 Applications. 8.1 Coatings and Films. 8.2 Elastomers. 8.3 Smart Composites. 8.4 Tires. 8.5 Concluding Remarks. References. Appendix: Nomenclature. Index.

Self-Healing Polymers and Polymer Composites

Woven glass fabric reinforced epoxy composite laminates were provided with crack healing capability by pre-dispersing a novel repair system in the composites’ matrix. The healing agent consisted of epoxy-loaded microcapsules and latent hardener CuBr2(2-MeIm)4 (the complex of CuBr2 and 2-methylimidazole). Compression after impact (CAI) tests were conducted to evaluate mechanical performance of the laminates before and after crack healing. Moreover, healing efficiency was studied as a function of impact energy, repair pressure, content and size of the microencapsulated epoxy. The experimental results indicated that the healing agent worked in repairing matrix cracks generated by impact. The composites should be heated to 140 °C for 0.5 h to achieve healing and moderate pressure was needed to close larger crack damage for good healing.

Healing of impact damage in woven glass fabric reinforced epoxy composites

Grafted inorganic nanoparticles can greatly improve the mechanical performance of polymers. To examine the effects of the interfacial characteristics generated by the grafting polymer bonded to nanoparticle surfaces, we chemically grafted nano-silica with different polymers and then melt-mixed it with polypropylene (PP). We extracted the homopolymers produced during the graft polymerization from the grafted products before the composites were manufactured to get rid of the side effects of the nongrafting polymers. We tailored the interfacial interaction between the grafted nano-SiO2 and PP matrix by changing the amount of the grafting polymers on the nanoparticles, that is, the grafting percentage. Mechanical tests indicated that all the composites incorporated with grafted nano-SiO2 particles possessed much higher impact strength than untreated SiO2/PP composites and neat PP. The greatest contribution of the particles was made at a low grafting percentage. Tensile measurements showed that the treated nanoparticles could provide PP with stiffening, strengthening, and toughening effects at a rather low filler content (typically 0.8 vol %) because of the enhanced interfacial adhesion resulting from molecular entanglement and interdiffusion between the grating polymers on the nanoparticles and matrix macromolecules. The presence of grafting polymers on the nanoparticles provided the composites with a tailorable interphase. The tensile performance of the composites was sensitive to the nature of the grafting polymers. Basically, a hard interface was beneficial to stress transfer, whereas a soft one hindered the development of cavities in the matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1771–1781, 2004

Interfacial effects in polypropylene–silica nanocomposites

In this study, high-water-content boron-cross-linked graphene oxide/polyvinyl alcohol (B-GO/PVA) hydrogels were prepared by a freeze/thaw method and immersion in boric acid solution for boron cross-linking. High-water-content B-GO/PVA hydrogels with a water/polymer mass ratio ranging from 19 : 1 to 49 : 1 (water content 95–98) could be obtained. It is found that a small addition of GO can lead to significant reinforcement of the tensile strength of B-GO/PVA hydrogels with an increase in elongation. Compared to B-PVA hydrogel, a 144% increase of fracture tensile strength is achieved when the content of GO is 0.1 wt% (∼0.609 MPa, water content ∼ 95%). Meanwhile, compression and shear strength (0.1 MPa and 0.201 MPa, water content ∼ 95%) of such hydrogels are increased by 26% and 35%, respectively. A method of acquiring high-water-content PVA hydrogels and the reinforcing mechanism of B-GO/PVA hydrogels are suggested. It is believed that such new high-water-content hydrogels are promising materials in the application of biomedical engineering and polymer electrolytes.

Ming Qiu Zhang

Papers

Self-Healing Polymers and Polymer Composites

Healing of impact damage in woven glass fabric reinforced epoxy composites

Interfacial effects in polypropylene–silica nanocomposites

High-water-content graphene oxide/polyvinyl alcohol hydrogel with excellent mechanical properties

Irradiation graft polymerization on nano-inorganic particles: An effective means to design polymer-based nanocomposites