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

Natural fiber reinforced composites is an emerging area in polymer science. These natural fibers are low cost fibers with low density and high specific properties. These are biodegradable and non-abrasive. The natural fiber composites offer specific properties comparable to those of conventional fiber composites. However, in development of these composites, the incompatibility of the fibers and poor resistance to moisture often reduce the potential of natural fibers and these draw backs become critical issue. This review presents the reported work on natural fiber reinforced composites with special reference to the type of fibers, matrix polymers, treatment of fibers and fiber-matrix interface. © 1999 John Wiley & Sons, Inc. Adv in Polymer Techn 18: 351–363, 1999

Natural fiber polymer composites: A review

Because of their wide abundance, their renewable and environmentally benign nature, and their outstanding mechanical properties, a great deal of attention has been paid recently to cellulosic nanofibrillar structures as components in nanocomposites. A first major challenge has been to find efficient ways to liberate cellulosic fibrils from different source materials, including wood, agricultural residues, or bacterial cellulose. A second major challenge has involved the lack of compatibility of cellulosic surfaces with a variety of plastic materials. The water-swellable nature of cellulose, especially in its non-crystalline regions, also can be a concern in various composite materials. This review of recent work shows that considerable progress has been achieved in addressing these issues and that there is potential to use cellulosic nano-components in a wide range of high-tech applications.

Cellulosic nanocomposites: a review

A concerted survey is presented of the existing theories for predicting the strength and modulus of particulate-filled polymeric composites. The macroscopic behaviour of particulate composites is affected by the size, shape, and the distribution of the inclusions. The interfacial adhesion between the matrix and inclusion is also important. The limitation of theoretical models in describing these parameters and expressing the experimental data on the macroscopic behaviour is demonstrated.

A review of particulate reinforcement theories for polymer composites

http://www.diva-portal.org/smash/get/diva2:711917/FULLTEXT01

Polymer modification of bitumen : Advances and challenges

The esterification reaction between wood fibers and maleated polypropylenes was investigated. The reaction was conducted in a reactor in the presence of xylene used as a solvent and sodium hypophosphite as catalyst. The reaction between wood fibers and pure maleic anhydride was also investigated. The appearance of an infrared absorption band near 1730 cm−1 indicated that maleated polypropylene chemically reacted by esterification with bleached Kraft cellulose. However, no direct evidence of an esterification reaction was obtained between thermomechanical pulp and maleated polypropylene. The Fourier transform infrared (FTIR) studies showed also that both bleached Kraft cellulose and thermomechanical pulp reacted with maleic anhydride with the formation of ester links. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1163–1173, 1997

Diffuse reflectance Fourier transform infrared spectra of wood fibers treated with maleated polypropylenes

A theoretical relationship has been developed which relates the ultimate strength of a composite containing spherical fillers to the size, volume fraction, and surface adhesion of the dispersed phase. The theoretical predictions are compared to experimental data using glass beads of known diameters in polyester resin matrix. Results were compared for the case of poor adhesion between the glass beads and the matrix and for the case of good adhesion. The derived relationships should be useful in helping to optimize the strength properties of particulate reinforced systems.

The strength of polymeric composites containing spherical fillers

In cold regions, transverse cracking of asphaltic paving materials is a serious problem which has not been completely resolved despite much effort. In this investigation, the low temperature stress–strain properties of bitumen containing dispersed polyethylene were measured over the temperature range from −40 to 0°C and compared with unmodified bitumen in an attempt to develop a tougher, more ductile crack-resistant binder for paving materials. Several grades of polyethylene were individually dispersed in liquid, heated bitumen to produce therein colloidal suspensions of polyethylene. The viscosities of these suspensions were determined at various temperatures and concentrations for each grade of polyethylene. Despite rather large differences in composition, molecular weight, and crystallinity of the polyethylenes, the differences in viscosity at the same concentration were relatively minor. However, the viscosity was very sensitive to the polyethylene concentration and the mixture became difficult to process at concentrations greater than 10 percent by weight. Thesee hot mixtures were then cast into rectangular beams for flexural testing at temperatures below zero degrees Celsius. Near the optimum polyethylene concentration of 8 percent by weight, the bitumen mixture possessed increased flexural strength, increased flexural modulus, increased elongation, and increased fracture energ at temperatures near −30°C. In one example the energy to fracture was increased ninefold compared to a standard 80/100 pen. bitumen control at −20°C. Mix design results are presented for a typical aggregate and compared with a MTC HL4 hot-mix paving formulation which is used extensively throughout Ontario. The polyethylene-modified asphalt concrete mix displayed a curious increases in both the Marshall flow and the Marshall stability values. Dynamic mechanical measurements confirmed the expected increase in resilient modulus at temperatures above zero degrees Celsius. The Marshall briquets containing polyethylene also exhibited slightly greater wet strength retention after prolonged immersion in water. These observations are consistent with the published data for commercial Novophalt paving materials developed in Austria and predict that the use of polyethylene in asphaltic hot-mix paving materials can extend service temperature range at both high and low temperatures, thereby simultaneously reducing both pavement distortion (rutting) and low-temperature cracking, so that pavement lifetimes can be more than doubled. The cost of such modification can be substantially reduced if scrap or reclaim polyethylene is employed instead of virgin polyethylene. Dispersing agents, such as Shell Chemical Kraton G block copolymers were advantageously employed to control the emulsion stability, particle size, and compatibility of the dispersed polyethylene phase.

Polyethlene‐modified bitumen for paving applications

The esterification reaction between lignocellulosic materials (ALCELL lignin and Bleached kraft cellulose) and maleated polypropylenes (graft copolymerization of maleic anhydride into polypropylene chains) was investigated The reaction was conducted in a reactor in the presence of xylene used as a solvent and sodium hypophosphite as a catalyst The reaction between lignocellulosic materials and pure maleic anhydride was also conducted to determine the effect of the long polypropylene chains on the formation of ester bonds The XPS studies of maleated bleached kraft cellulose showed the emergence of C4 carbon type on high resolution spectra, which was related to ester carbonyl functionality formed by esterification reaction No evidence of esterification was observed between ALCELL lignin and maleated polypropylenes The XPS studies demonstrated that both ALCELL lignin and bleached kraft cellulose chemically react with maleic anhydride with the formation of ester bonds

X-ray photoelectron spectroscopy of lignocellulosic materials treated with maleated polypropylenes

The esterification reaction between several wood fibers and maleated polypropylenes, and its role in determining the mechanical properties of wood fiberpolypropylene composites was investigated. The modification technique used in this study involved bulk treatment in a thermokinetic mixer. The treatment of wood fiber with maleated polypropylene had a significant effect in increasing the mechanical properties of the composites. However, no direct evidence of ester links was detected between wood fiber and maleated polypropylene by FT-IR. Thus, the effectiveness of maleated polypropylene in improving the mechanical properties was attributed to the compatibilization effect which is accomplished by improving the wettability of wood fiber by the matrix polymer, lowering the fiber to fiber interactions, improving fibers dispersion and orientation, and enhancing the adhesion between wood fiber and polypropylene matrix.

R. T. Woodhams

Papers

Diffuse reflectance Fourier transform infrared spectra of wood fibers treated with maleated polypropylenes

The strength of polymeric composites containing spherical fillers

Polyethlene‐modified bitumen for paving applications

X-ray photoelectron spectroscopy of lignocellulosic materials treated with maleated polypropylenes

Effect of Ester Linkages on the Mechanical Properties of Wood Fiber-Polypropylene Composites