Whisker matrix interactions

Although several excellent reviews analyze the effect of whisker addition on the mechanical behavior of ceramics [4, 5, 24], this review focused on the effect of phase chemistry on whisker-matrix interactions and on the relationships among the chemistry of the ceramics components, their grain morphologies, and their fracture toughnesses. 

The hydrophilic surface of the cellulose-based nanoreinforcements leads to poor interaction between matrix and the filler [29]. Furthermore, the chemical compatibility is very important in controlling the dispersion and the adhesion among them. Therefore, it is common to see weak filler-matrix interactions when hydrophilic whiskers were added to hydrophobic matrices [4]. The miscibility of cellulose nanofillers with hydro-phobic matrices can be improved by various surface modifications, for example, esterification and acylation. The increment in the filler/matrlx compatibility produces the enhancement of mechanical and thermal properties but also enhances the barrier properties [30]. 

The main objective of this study was to evaluate chemical, thermal and dynamic mechanical properties of the resulted nanocomposite from kenaf and cellulose acetate butyrate (CAB). Whiskers-matrix compatibility was evaluated by all of the characterizations to see the interaction between whiskers and matrix. Based on the findings, FTIR analysis showed no intermolecular hydrogen bonding between CAB and whiskers. Thermal analysis foxmd that whiskers reinforcement did not affect the decomposition temperature of resulted nanocomposite. However, good miscibility was detected... 

Thermal shock testing of an alumina/20 vol.% SiC whisker composite showed no decrease in flexural strength with temperature transients up to 900°C.33 Monolithic alumina, on the other hand, shows significant decreases in flexural strength with temperature changes of >400°C. The improvement is a result of interaction between the SiC whiskers and thermal-shock induced cracks in the matrix, which prevents coalescence of the cracks into critical flaws. 

Above the threshold, deformation occurs as a consequence of direct particle interaction. Several mechanisms of interaction have been suggested solution-precipitation flow of fluid between particles and cavity formation at the particle matrix interface. These theories of creep suggest several rules to improve creep behavior (1) increase the viscosity of the matrix phase in multiphase materials (2) decrease the volume fraction of the intergranular phase (3) increase the grain size (4) use fiber or whisker reinforcement when possible. As the creep rupture life is inversely proportional to creep rate, lifetime can be improved by improving creep resistance. 

The toughening of a ceramic by the addition of whiskers that are different from the matrix material is the most traditional and the best explored methodology. The advantage of this method is the broad spectrum of ceramics that can be prepared in whisker form. Consequently, there is the potential for a broad range of ceramic matrix-ceramic whisker combinations. Since the whiskers are manufactured in a separate process, it is possible to control their size, morphology, and surface chemistry without affecting the matrix material. Additionally, whiskers can be chemically or thermally treated to change their future interactions with the matrix. 

The interactions between the whiskers and the matrix are very significant The high form ratio of the nanoparticles (50-200) and the high specific surface area ( 170 m. g ) enable us to obtain major phenomena at the interphase. Indeed, in relation to traditional biocomposites based on cellulose fibers or microfibrils, the overall behavior of whisker-based materials is primarily linked to the interface/interphase between the matrix and the nanofiller, which controls the properties and overall performances of the material (mechanical properties, permeability, etc.). 

Interactions between CNRs and hydrophilic matrices are usually satisfactory [119] due to the presence of the hydrophilic cellulose surface. The simplest technique to process a nanocomposite material is using water suspensions of whiskers because of their high stabihty and the expected high level of dispersion of the whiskers within the host matrix in the resulting films. But this technique is mostly restricted to hydrophilic polymeric material. Another alternative to processing nanocomposites using whiskers is the addition of surfactants and chemical modification of the whiskers by substistuents so that they will be compatible in hydrophobic matrix [120,121]. Some chemical modifications of the surface of cellulose whiskers that increase its hydrophobicity include surface acylation [122] and... 

Any factor that affects the formation of the percolating whisker network, or interferes with it, changes the mechanical performances of the composite [38], Three main parameters were reported to affect the mechanical properties of such materials, viz. the morphology and dimensions of the nanoparticles, the processing method, and the microstructure of the matrix and matrix-filler interactions. 

The use of layer-by-layer (LBL) technique is expected to maximize the interaction between cellulose whiskers and a polar polymeric matrix, such as chitosan (de Mesquita et al. 2010). It also allows the incorporation of high amounts of cellulose whiskers, presenting a dense and homogeneous distribution in each layer. 

The glass-rubber transition temperature, Tg, of cellulose whisker filled polymer composites is an important parameter, which controls different properties of the resulting composite such as its mechanical behavior, matrix chain dynamics, and swelling behavior. Its value depends on the interactions between the polymeric matrix and cellulosic nanoparticles. These interactions are expected to play an important role because of the huge specific area inherent to nanosize particles. For semicrystalline polymers, possible alteration of the crystaUine domains by the cellulosic filler may indirectly affect the value of Tg. 

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