Composite water-resistance behavior

Between mercerized and benzoylated fibers-reinforced UPE composites, benzoyl chloride grafted fibers-reinforced UPE matrix has been found to have better water resistant behavior, which may be due to better compatibility of benzoylated fibers and hydrophobic matrix. 

The water absorption behavior of the clay-epoxy nanocomposites in terms of maximum water uptake and diffusion coefficient are given in Table 9.18 [47]. The presence of nanoparticle as reinforcement reduces the water absorption of the composite system. The maximum water uptake of epoxy decreases gradually with the increase in clay content. The maximum water absorption decreases by 14.1,17.9 and 24.8% after the incorporation of 1, 3 and 5 wt% nano-clay, respectively, compared with neat epoxy. The presence of high aspect ratio nanofillers can create a tortuous pathway for water molecules to diffuse and enhances the resistance to water absorption. The diffusivity also decreases in the same manner and a significant reduction in diffusivity is obtained for the composites containing 5 wt% clay [112]. 

Supri and Ismail [46] prepared modified and unmodified low-density polyethylene (LDPE) and mixed it with water hyacinth fiber (WHF) composites by melt blending. Tensile test, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and water absorption behavior test of the composites were conducted. The NCO-polyol-modified LDPE/AAfHF showed higher tensile strength, modulus of elasticity, and water absorption resistance as compared to the unmodified LDPE/WHF composites. However, the elongation at break was better when the LDPE was immodi-fied. Moreover, the modified LDPE/WHF offered better thermal properties in comparison to the unmodified LDPE/WHF. The NCO-polyol was reported to create better dispersion of WHF in the LDPE matrix. 

The presence of natural fillers causes a slightly increased water resistance and could improve the apphcation property of these composite films. This behavior could be due to the presence of hydrogen bonding interactions between starch polymer matrix and crystaUine part of wood and fir tree needles fillers (which comprise cellulose in their chemical composition). The hydrogen bonds network occurred within the composite films tends to stabilize the starch polymer matrix when it is subjected to high moisture content environment. 

There is a great interest in these treatments because the hydrophobic/hydrophilic behavior conditions the compatibility with other materials. This is especially important for the development of composites, in which dissimilar materials are employed with the aim of obtaining a product that combines the desired properties of the components. For instance, the incorporation of starch to synthetic polymers renders a biodegradable, water resistant material however, the components must be made compatible by modifying the hydrophobicity or hydrophilicity of one or both of them. Hydrophobic starch has been obtained with a SiCl4 plasma treatment, followed by a reaction with either ethylene diamine or dichlorodimethysilane thus, a hydrophilic material was converted into a hydrophobic one. There are also many... 

The reaction is reversible and therefore the products should be removed from the reaction zone to improve conversion. The process was catalyzed by a commercially available poly(styrene-divinyl benzene) support, which played the dual role of catalyst and selective sorbent. The affinity of this resin was the highest for water, followed by ethanol, acetic acid, and finally ethyl acetate. The mathematical analysis was based on an equilibrium dispersive model where mass transfer resistances were neglected. Although many experiments were performed at different fed compositions, we will focus here on the one exhibiting the most complex behavior see Fig. 5. 

Effective reactive pressureless sintering of SiC-TiB2 composites was recently reported by Blanc, Thevenot, and Treheux [155]. In addition they studied the tribological behavior using a pin on flat configuration (flat SiC, pin SiC-TiB2). In dry conditions the composites showed less wear resistance than monolithic SiC, however, with water as lubricant the opposite was the case. 

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