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This paper reports on comprehensive characterization of wettability and interfacial properties of kenaf fibers (KF) and its unsaturated polyester (UPR) composites fabricated by resin transfer molding (RTM). KF were chemically modified by immersing in 6% NaOH concentration for 1, 2, 3, 4, and 5 h to enhance the interaction between KF and UPR. FTIR spectral data showed the chemical changes in KF after treatment which induced the modification of physical and wettability characteristics of KF. The changes in crystalinity index (CrI) and thermal stability of KF content were analyzed using X-ray diffraction (XRD) and thermogravimetry (TGA) techniques, respectively. Scanning electron microscope (SEM) shows a cleaner KF surface upon KF treatment and atomic force microscopy (AFM) signify an increasing in available fiber–matrix specific contact area. Wettability of KF was investigated by means of surface energy measurement using Washburn contact angle principle via Owens–Wendt–Rabel–Kaelble (OWRK) method. Surface energy was found to increase with longer soaking time. The effect of soaking time of alkaline treatment in enhancing the interface bonding characteristic between the KF and UPR matrices can be reflected by the ILSS value of the composites. The highest value of ILSS was recorded by 3 h treated KF composite. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

In the present study, mechanical and water absorption properties of the nonwoven kenaf fiber (KF)/unsaturated-polyester composites manufactured by resin transfer molding were investigated. Nonwoven KF mats with an aerial density of 1350 g/m2 were treated with a 6% NaOH solution for 3 h. The influence of the fiber treatment on the properties of the composites was investigated with Fourier transform-infra red (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscope (AFM), and dynamic contact angle technique (DCAT). Mechanical properties measurements were conducted via determination of flexure and fracture toughness. A general trend was observed whereby alkalized KF composites gave superior mechanical properties compared to as-received KF composites. The XRD and DCAT results indicated an enhancement of the crystallinity index and surface energy of the alkali-treated KF. SEM and AFM of the treated KF showed the removal of impurities and a reduction of roughness on the KF surface with alkalization. Water immersion induced a drastic loss of the mechanical properties of the composites albeit better retention of properties was observed in the case of alkalized KF composites. The fracture surfaces were inspected by SEM which confirmed the quality of the interface. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

The interfacial and mechanical properties of nonwoven kenaf fibre (KF) reinforced acrylic based polyester composites fabricated by resin impregnation process were studied. Different types of treatments were applied to KF, i.e. alkali treatment with NaOH at concentration of 6% (at room and elevated temperature of 60°C) and heat treatment at 140°C for 10h. FT-IR spectral data showed the chemical changes in KF that induced the modification of physical and interfacial characteristics of KF. Alkali treated KF was found to have smaller diameter but higher density. Significant increase in the crystallinity index of treated KF contributed to the improved fibre strength. AFM analysis revealed the exposure of cellulose micro-fibril network and the increase in the area peak density value of treated KF. Surface energy of KF and surface tension of acrylic resin were obtained through Owens–Wendt–Rabel–Kaelble (OWRK) equation and Du Nouy ring approach, respectively, for the interfacial properties determination. The improved wettability of alkali treated KF was confirmed as higher surface energy of the fibre was recorded exceeding the surface tension of acrylic resin, thereby imparting better flexural properties and dynamic mechanical behavior, but conversely deteriorating the fracture toughness of the reinforced composites. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

The Riccati equation arises in various problems, particularly in practical engineering problems. It is required to solve the resulting Riccati algebraic matrix equation instead of solving the time-invariant optimal control problem in one of its standard forms. In this paper an unconstrained minimization technique referred to as the Davidon–Fletcher–Powell (DFP) method is used in solving such an equation by minimizing its norm. The positive-definite solution of the equation is also obtained, which is desirable in most engineering problems.