Key Engineering Materials Vol. 824

Abstract: This study investigates the effects of mixing condition on hardness, porosity, specific gravity, wear, and friction characteristics of automotive brake materials. In the experiment, mixing raw materials with three different conditions of impeller speed (3000, 4500, and 6000 rpm), mixing duration (up to 8 min) and mixture loading based on a mixer volume (35, 50 and 65 vol% ) were determined using the formulated mixture composition. Homogeneity in terms of density values including hardness, porosity, and specific gravity of the finished brake pads were determined. The surfaces and the distribution of friction material were studied using scanning electron microscopy (SEM). The correlation between various mixing conditions and physical and tribological properties of brake pads were discussed and reported.

Abstract: This study aims to reduce brake pad thickness and density variations by pressure equalization in the preforming process. Brake pads consist of fillers, lubricants, abrasives, reinforcing fibers, and binders. These are compacted together as raw materials. Each component is responsible for a different specific property to help the brake pad reduce the speed of the vehicle. The forming of a brake pad begins with compression of friction powder in a rigid mold with a complicated contour. It is then compacted by vertically pressing punches to form a body of complicated shape and homogeneous density. The strength of the brake pad, which is a main property in the compacted material, primarily depends on the type of fiber reinforcing material. Since the ability of fiber to flow is poor due to its high internal friction and its random arrangement. These two characteristics cause non uniformity in density and elastic modulus. Pressure equalization is an adjustment of the filling depth of the powder which otherwise would have an uneven fill inf the cavity of the mold. The pressure equalization of the filled powder is shown to correlate with the brake pad dimensional accuracy and uniformity of density.

Abstract: Biopolymer-based coatings or films can be used as an alternative to the replacement of conventional packaging, to preserve fresh fruit quality and extend their shelf life. This study aimed to prepare and characterize biopolymeric coating films based on chitosan and carboxymethyl cellulose (CMC). Film coating of biopolymers was further applied on mango fruits, and the efficacy of coating materials in post-harvest shelf life and maintaining quality parameters of mango were then determined. The coating method of the films over mango was prepared using a dipping technique. Fruit weight loss, colors and content of total soluble solids were evaluated to assess fruit quality during 14 days at 25 °C of storage. Results indicated that films formulated with CMC showed significantly higher water solubility and water vapor transmission rate. Notably, coating improved the quality of mango during storage. Between the coating types, CMC was found to be significantly more effective in maintaining fruit fresh weight during the storage period. The fruit treated with CMC lowered the change in color and had higher soluble solids content than that of chitosan coating on the fourteenth day of storage. These results demonstrate that CMC-based coating could be utilized for the extension of the fruit commercialization period.

Abstract: The aim of this research was to prepare and characterize biocomposite films from poly(lactic acid) (PLA) with spent coffee grounds (SCG). PLA can be derived from renewable resources. The SCG component consists of cellulose, hemicellulose and coffee oil 10.98%. SCG can simultaneously act as plasticizer and filler in the composites that can enhance the mixing process. The PLA/SCG biocomposite films were processed by a twin-screw extruder and blow film extruder. They were prepared by using various SCG concentrations (0%, 5%, 7.5% and 10% of SCG). The Scanning Electron Microscopy (SEM) results showed that the PLA matrix with SCG was miscible and had the SCG was well good distributed. Elongation at break was increased, when the amount of SCG was increased, with the results of PLA and PLA/SCG 10% being 5.07% and 6.63% respectively, while hardness, brittleness and tensile strength decreased. UV-vis spectrophotometric measurement of PLA/SCG biocomposite films showed a considerable reduction in transmission of all UV wavelengths (UV-A, -B and -C) and visible light with increasing SCG content. Hence, in this research, SCG can be used as filler in PLA films in order to produce biodegradable films and developed as agricultural film products. The PLA/SCG biocomposite films have shown good properties and are environmentally friendly.

Abstract: Silica extracted from rice husk ash (RHA-Si) by pretreatment with hydrochloric acid followed by calcination at 700°C, was prepared. It was investigated with regard to its chemical composition and structure using X-Ray Fluorescence spectroscopy (XRF) and X-Ray Diffractometry (XRD). RHA-Si (0, 0.25, 0.5 and 1% w/w) was incorporated into poly(methyl methacrylate) (PMMA) or acrylic resin powder. Microhardness, flexural strength and dynamic mechanical properties of RHA-Si filled PMMA were then determined. The chemical composition analysis showed that RHA-Si contains a large amount of silica with an amorphous structure. The microhardness of acrylic resin filled with RHA-Si does not change significantly with increasing RHA-Si loading. Flexural strength of filled acrylic resin increases with increasing RHA-Si loadings up to 0.25% w/w. It then decreases with increasing RHA-Si loadings. Dynamic mechanical behavior illustrates that polymer-filler interactions play an important role in reinforcement.

Abstract: Pineapple leaf fiber (PALF) having an average diameter and length of about 4 μm and 6 mm, respectively, was used as reinforcing element for natural rubber (NR) composites. PALF was coated with different amount of stearic acid at 10, 30 and 50 wt% of PALF. PALF-NR composites containing two levels of PALF at 5 and 10 part per hundred rubber (phr) were prepared in a two roll mill. Mastication times of 2, 4 and 8 min were used. Tensile stress-strain curves and fracture surfaces of both untreated PALF and stearic acid coated PALF (SA-PALF) reinforced NR prepared with different mastication times were compared. At low level of PALF where aggregation was not a problem, stearic coating had adverse effect on mechanical properties due to the slippery PALF-rubber interface. At high level of PALF, the coating gave composites with higher tensile strength and strain at break. Moreover, tensile strength and strain at break increased with increasing mastication time. This indicates that stearic acid coating reduces the formation of PALF aggregations and allows PALF to work effectively.

Abstract: Green composites, especially that are reinforced with natural fibers, have received a great deal of attention due to the problems of global warming and resources depletion. Pineapple leaf fiber (PALF) is an interesting choice because of its high mechanical properties and it is obtained from agricultural waste. In this work PALF is combined with natural rubber (NR) to produce green rubber composite with enhanced mechanical properties. Since the two materials are so different in their stiffness and polarity, poor interfacial adhesion and thus low stress transfer, between NR and PALF may be expected. Attempts were made to use urea formaldehyde (UF) resin to improve the adhesion between PALF and NR. PALF was coated with different amounts of UF resin in solution. The fiber was characterized with FTIR, XPS and SEM. Uniaxially aligned PALF reinforced rubber composites with a fixed amount of 10 parts per hundred of rubber (phr) PALF were prepared. The adhesion between PALF and NR was evaluated from the tensile stress-strain curve and fracture surface of the composite. It was found that UF resin had negligible effect in improving the stress transfer but rather reduced it as shown in the stress-strain curve. Thicker coating of UF resin led to lower reinforcement effect and, hence, lower modulus. Stress at break, on the other hand, increased with increasing the coating thickness.

Abstract: Activated carbon can be prepared from any kind of hydrocarbon-based material, and that from agricultural wastes is attractive for many reasons. The use of natural fiber in various industries gives rise to some associated waste streams. In this work, activated carbon, produced from the non-fibrous material waste from pineapple leaf fiber production, was studied for its heavy metal adsorption behavior. The material was carbonized at different temperatures and chemical activation was carried out using phosphoric acid. Pore size and pore volume of the adsorbent were determined using the Brunauer–Emmett–Teller (BET) method, and surface morphology by scanning electron microscopy (SEM). Fourier Transform Infrared Spectrophotometry (FT-IR) was used to identify the functional groups in the material. It was found that the surface area, pore volume and morphology of the surface depended on the carbonization temperature. The best adsorbent was obtained using a carbonization temperature of 500 °C and an activation temperature of 600 °C. Adsorptions of several heavy metals were studied over the concentration range of 4 - 800 mg L⁻¹ and pH 2-10. The optimum amount of the adsorbent was found to be 1.20 g per 100 ml of solution, removing up to 92.67% of lead ions. The adsorption behaviour was closer to the Freundlich isotherm than to the Langmuir isotherm. So this waste could be a useful bio-source for activated carbon production.

Abstract: The upcycling process of agricultural waste for cellulose production has been attempted. In this study, cellulose was extracted from sawdust of the rain tree using 4% (w/v) NaOH solution. 1.5 g of extracted cellulose was soaked in water and N,N-dimethylacetamide (DMA) respectively. The soaked cellulose was dissolved in dimethylacetamide/LiCl and reacted with hexamethyldisilazane (HMDS) yielding tetramethylsilylcellulose (TMSC). The IR spectrum shows the presence of-Si (CH₃)₃ groups: ν_Si-O at 1047 cm^-1, ν_C-Si at 1252, 843 and 750 cm^-1. The ¹H-NMR result confirms the presence of-Si (CH₃)₃ groups at  0 ppm and pyranose ring protons in the range of 2.8-4.5 ppm. SEM image of TMSC shows the fibrous characteristics of cellulose while the EDX shows the presence of Si. The degree of substitution (DS) values calculated from FT-IR and EDX data are 2.33 and 2.08 respectively. 1.0% w/v TMSC solution in THF was prepared. A Small piece (2.0 cm x 4.0 cm) of filter paper was dipped into the TMSC solution for 30 min. The coated paper has an average contact angle of 116o. However the characteristic bands of the TMSC were not observed from FT-IR analysis. While the EDX shows the presence of Si on the paper surface..

Abstract: The acid purification of calcium citrate from citric acid production using sulfuric acid as a reagent resulted in citrogypsum waste. The identification of citrogypsum by XRD technique indicates that the main component consists of CaSO₄∙2H₂O (DH). Furthermore, the comparison of the colours between citrogypsum and natural gypsum are also different. Hence, this research mainly focused on the phase transformation of DH to α-CaSO₄ ∙0.5H₂O (α-HH) due to high strength and heat resistant. The preparation of α-HH carry out in different volume ratios of ethylene glycol (EG): water solutions at 95oC for 7 hrs under atmospheric pressure. The FT-IR spectra of DH and α-HH results reveal that the absorption frequencies at 1700 and 1800 cm^-1 of –OH group are 0.5 and 1.5 water molecule in CaSO₄ respectively. TGA thermograms show the theoretical crystal water content of DH approximately 20.1 wt% and the converted α-HH about 4-5 wt%. DSC thermograms of the citrogypsums show two endothermic peaks regarding to two steps of water molecule loss at 151.2oC and 168.5oC respectively. In addition, the α-HH shows exothermic peak at 238.7oC. The morphology of citrogypsum and α-HH are observed by SEM, showing the plate-like shape of citrogypsum and hexagonal shape of α-HH. Moreover, the products could be applied to several other industries for increasing the value and reducing the environmental concerns.