Key Engineering Materials Vol. 757

Abstract: A latex cup is used to collect latex from a rubber tree which is an economic plant in Thailand. The fresh latex or crude rubber consists of organic compound and water which can wet and adhere to surface of the collecting cup. In this research, surface of the latex cup was treated with polymethylhydrogen siloxane-functionalized silica compound to improve hydrophobicity so that it could repel the dirt and latex, resulting in an anti-adhesion between the latex and the cup. Surface of the latex cup was etched with 10 % v/v hydrofluoric acid for 30 min before application of the siloxane coating which was performed by immersion in the solution, painting and spraying, respectively. The result revealed that the immersion method exhibited optimum property justified by high value of water contact angle, low surface free energy, surface roughness and the field test. At the optimum polymethylhydrogen siloxane : fumed silica ratio of 3 : 1 wt%, the treated sample had water contact angle of 139.24 ± 0.78 degrees and possessed surface energy of 1.07 mJ/m². The field test conducted in the rubber field in Trang province revealed good durability of the coating. The water contact angles were 132.15 ± 2.05 and 129.20 ± 2.34 degrees after 2 weeks and 1 month, respectively, of the field service.

Abstract: Silica extracted from rice husk ash (RHA-Si) was incorporated in deproteinized natural rubber (DPNR) latex compounds up to 20 phr. The cast films were prepared after the prevulcanization at 70°C for 2 hours. The effect of RHA-Si loading on swelling and tensile properties was investigated. Scanning electron microscope (SEM) was used to examine morphology of the prevulcanized films. Dynamic mechanical behaviors of filled prevulcanizates were studied using the dynamic mechanical analyzer (DMA). Two types of tests, namely, temperature sweep and strain sweep test were performed. Swelling test revealed the decrease in crosslink density with increasing RHA-Si loading more than 10 phr. Tensile strength and elongation at break decreased with increasing RHA-Si loading. Conversely, the presence of RHA-Si increased the modulus at 100% strain of the prevulcanized DPNR latex films. The poor filler-rubber distribution was evidenced by SEM image. The DMA results exhibited that storage modulus (G′) and damping factor (tanδ) increased with increasing RHA-Si loading. The narrow linear viscoelastic (LVE) region was noticed for prevulcnizates filled with high RHA-Si content. Glass transition temperature (Tg) of highly filled DPNR shift to low temperature.

Abstract: In this study, diglycidyl ether of bisphenol A (DGEBA) cured cycloaliphatic polyamine was modified with functionalized celluloses for improved thermal and mechanical properties. Three different types of surface-modified cellulose, polyacrylamide-g-cellulose (PGC), aminopropoxysilane-g-cellulose (SGC), and carboxymethyl cellulose (CMC), were investigated and used as reinforcing agents in epoxy resins. The storage modulus of these modified epoxy systems was found to significantly increase with addition of cellulose fillers (up to 1 wt. % cellulose content). An improved fracture toughness (K_IC) was also observed with increasing cellulose loading content with PGC and SGC. Among the surface-modified celluloses, epoxy modified with SGC was found to have the highest fracture toughness followed by PGC and CMC at 1.0 wt.% cellulose addition due to the chemical surface compatibility. The toughening mechanisms of the cellulose/epoxy composites, measured by scanning electron microscopy (SEM), revealed that fiber-debonding, fiber-bridging, and fiber-pull out were responsible for increased toughness.

Abstract: Carboxylated polymer can be used as an anti-scaling agent in circulating water cooling systems. Poly(acrylic acid) and homopolymer have some drawbacks such as slight solubility in water and low calcium tolerance leading difficulty to determine the remaining quantity of polymer in water. This research is mainly focused on synthesis and ability of poly(acrylic acid-co-2-acrylamido-2-methylpropane sulfonic acid) (PAA-PAMPS) for scale inhibition. These terpolymers varied in mole ratios of monomers were prepared via solution polymerization. The obtained polymers are then characterized by FT-IR, ¹H-NMR, TGA, turbidity, and UV-visible spectroscopy. For a scale inhibition test, GB/T 16632-2008 standard is applied. The scale inhibition efficiency for 100% was found in PAA-PAMPS copolymer (7:3). Afterwards this polymer was chosen for synthesizing an ultraviolet-tagged PAA-PAMPS-PNaSS terpolymer. UV-visible spectroscopy was used to monitor benzene sulfonate structure in sodium styrene sulfonate of the polymer chain at 224 nm.

Abstract: Fabrication and mechanical properties of the bio-composites between water hyacinth natural fiber and paper mulberry have been investigated. The fabrication was performed using the hand lay-up technique. Untreated and treated water hyacinth fiber were used as reinforcements, in the ratio of 5%, 10%, 15%, and 20% by weight, with paper mulberry as a biomatrix. It has been found that paper mulberry reinforced with 15 % treated WH fiber showed maximum tensile strength and impact energy. The optical and scanning electron microscopic morphology of the obtained composites displayed a rougher surface and the decrease in the fiber diameter when treated with sodium hydroxide (NaOH). This improved the interlocking between the matrix and its reinforcement.

Abstract: This work prepared and characterized of chitosan (Cs)-gelatin (Gel) films for the controlled release of the nitrofurantoin (NF) antibacterial drug. The side effects of NF are nausea and emesis due to its high absorption rate immediately after oral administration. The use of Cs-Gel films enables economic production of the drug carrier system. Cs-Gel films were prepared by mixing Cs with Gel at different ratios and were cross-linked with Na₂SO₄ with different concentrations. NF was loaded into the films by soaking of drug solution. Films were characterized by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and evaluated for thickness, water absorption capacity, swelling behaviour and in vitro NF drug release in phosphate buffer solution pH 5.8 and pH 7.4. The results indicated that additional amount of gelatin and sulfate ion cross-linked to the films increased the swelling, water absorption ability and also improved NF release.

Abstract: This study aimed to fabricate electrospun poly(lactic acid) (PLA) fiber mats containing 3 kinds of rice extract (rice bran, riceberry and LeumPhum rice extracts) by using electrospinning. The rice extract has been reported to exhibit antioxidant activities. The neat and rice extract-loaded PLA fiber mats were smooth and no beads formed on the fiber surface with diameters ranging from 450-656 nm. Release characteristics of the rice extract-loaded electrospun PLA fiber mats were investigated using total immersion methods. The scavenging ability of LeumPhum rice extract-loaded electrospun fibers showed superior scavenging activity as determined using the DPPH radical scavenging method. The results suggested that rice extract incorporated in PLA nanofibers had no negative effect on antioxidant activity when using an electrospinning process.

Abstract: Silver-modified bismuth vanadate (Ag-BiVO₄) photocatalysts were easily prepared via the co-precipitation method. The effects of silver contents on the chemical properties of BiVO₄ were evaluated. The prepared Ag-BiVO₄ samples were characterized by several techniques such as X-ray diffractometry (XRD), scanning electron microscopy (SEM), and diffused reflectance UV-Vis spectroscopy (DRS). The mixed phase of monoclinic scheetlite structure and characteristic peaks of silver particles were found. Silver contents strongly affect the morphology of the prepared Ag-BiVO₄ samples. DRS spectra revealed that the synthesized Ag-BiVO₄ samples exhibited strong absorption in the visible region. The absorption in the visible zone is responsible for the high photocatalytic activity of Ag-BiVO₄ under visible light irradiation. The photocatalytic degradation of methylene blue under visible light irradiation was studied using the BiVO₄ as photocatalysts. The photocatalytic results reveal that the prepared Ag-BiVO₄ samples could degrade the methylene blue dye.

Abstract: Zirconium-based Metal-organic framework ((Zr₆O₄(OH)₄(1,4-benzenedicarboxylate)₆), UiO-66) is one of the most outstanding MOFs for heterogeneous catalysis owning to its high thermal and chemical stabilities. 1,4-benzenedicarboxylate, which is an organic linker of UiO-66, can be functionalized by a sulfonic acid group (UiO-66-SO₃H) for several acid-catalyzed reactions. In this work, the structures and acidity of the synthesized UiO-66 and UiO-66-SO₃H were characterized using X-ray diffraction, IR-spectroscopy and adsorption experiments. The adsorption of ammonia on UiO-66 type frameworks was studied on the C₁₆₂H₁₂₂O₆₇SZr₁₂ cluster model by different DFT functionals including B3LYP, CAM-B3LYP, M06-L, PBE, TPSS and ωB97X-D. The adsorption energies were calculated to be -16.4, -19.2, -18.0, -19.7, -17.4 and -19.3 kcal/mol, respectively, which agreed well with the value from MP2 calculation (-17.9 kcal/mol). This study provides a guideline on the suitable calculation models and yield more insights on the adsorption in acid-functionalized UiO-66 MOF framework.

Abstract: The aldol condensation of acetone in zirconium-based metal-organic framework functionalized by a sulfonic acid group (UiO-66-SO₃H) has been theoretically investigated using the density functional theory. Acetone adsorbed on the UiO-66-SO₃H with the adsorption energy of -17.4 kcal/mol. The catalyzed reaction has been proposed to be a two-step mechanism: the tautomerization of keto form to produce enol form of acetone, and the aldol condensation to produce diacetone alcohol. The activation energies were calculated to be 27.2 and 6.4 kcal/mol, respectively. For the experimental part, UiO-66-SO₃H catalyst was synthesized and characterized by X-ray diffraction and IR spectroscopy. The catalytic reaction was carried out in a stirred batch reactor at different temperatures to optimize the reaction conditions. The obtained products were analyzed by ¹H-NMR spectroscopy and chromatography techniques. This study demonstrated that UiO-66-SO₃H can be used as a solid catalyst for the aldol condensation reaction.