Key Engineering Materials Vol. 751

Abstract: Degradable materials from 20wt% chitosan loading and natural rubber (CS/NR) were prepared by solution casting without surface treatment to study their thermal and mechanical properties after degradation test in aging condition. The test was done in an acrylic degradation box with 600 W light and high humidity for accelerate degradation condition. Samples included high ammonia concentrated latex (HA) with no filler, fresh latex (FL) with no filler, HA with chitosan filler, FL with chitosan filler, and natural rubber with shrimp shell filler to compare the result with chitosan filler. After degradation test, thermal properties from TGA both before and after degradation showed that the fillers effected on these composite materials. TGA result of CS/NR composite with aging at temperature 100 °C for 10 h and 20 h showed that chitosan slightly effected on thermal stability of composites when compare to natural rubber. SEM images were compared before and after degradation of HA and FL with no filler, chitosan filler, and shrimp shell. It was clearly seen that the samples degraded as the shape and size were changed. Tensile testing values showed that longer aging time could lead to the degradation in CS/HA and lower the tensile strength.

Abstract: For fresh-cut and ready-to-eat packaging films, antifog additives (AFs) are commonly used to suppress the formation of water droplets on film surface. To date, the type and dosage of antifogging for PLA based film are less studied. Therefore, in this research, films incorporated with antifog additive were fabricated by cast extrusion technique. The migration behavior of commercial polyglycerol ester as selected AF was investigated. The cold fog test results showed that 3.5 and 5 wt% of AF in 20PBAT/80PLA single layer film can provide clear films without droplet of water within 7 days and 3 hours, respectively. For 2-layer films, the presented of AF in seal layer as 95(20PBAT/80PLA)/5 (polyglycerol ester) and core layer of PLA were prepared having different thicknesses of seal layer/core layer of 20/15 and 10/15 μm. The migration rate of AF in thin 2-layer film (10/15 μm) appeared to be higher than that in 20/15 μm film. Films’ surface could become clear without water droplet (rating scale > 8) within 4 days for 10/15 μm and 7 days for 20/15 μm films. Haze of films was analyzed by haze meter. Haze of 10/15 μm film was decreased from 7 to 4.4, while that of 20/15 μm film was also decreased from 10 to 7.9 when AF appeared on its surface. Both films can be a peelable PLA based lidding film product with low haze (< 10 %) and antifog performance (within 1 month). In addition, 10/15 μm film can be an easy peel lidding film since its peel strength was in an easy peel range (6-10 N/15 mm).

Abstract: This research aimed to investigate the possibility of pyrolytic carbon black (PCB) used as filler in natural rubber (NR) and its effect on Mooney viscosity, cure characteristics and mechanical properties compared with commercial carbon black (N774). The results revealed that Mooney viscosity, stiffness and heat build-up tended to increase with increasing both PCB and N774 loading, whereas elongation at break decreased. However, the maximum tensile and tear strengths appeared at the optimum filler loading for both PCB and N774. At similar filler content, PCB-filled NR compounds have higher cure time, heat build-up and thermal resistance. Nevertheless, they exhibited lower Mooney viscosity and mechanical properties compared to N774-filled NR. Finally, it can be concluded that PCB could be utilized as filler in NR compound to act as semi-reinforcing filler and was classified as a filler to reduce costs.

Abstract: The thermal and mechanical properties of poly (lactic acid) blended with high molecular weight PEG, i.e. PEG1000 and PEG6000 were compared. The contents of PEG added were 10, 12.5 and 15 % by weight, with respect to PLA. The PLA/PEG blends were modified by addition of organic peroxide in order to induced crosslinking. Addition of organic modified montmorrillonite (Cloisite 30B, C30B) was also performed in order to modify mechanical performance of PLA/PEG blends. C30B was prepared via master batch in PLA. Morphology, crystallization, thermal stability and mechanical properties of the blends were investigated using SEM, DSC, TGA and universal testing macine, respectively. Morphology of cryogenic fracture surface showed smooth brittle surface. PEG1000 well plasticized PLA where as PEG6000 shows better thermal stability and mechanical properties. The presence of PEG induced PLA to perform cold crystallization. T_m in PLA was slightly changed whereas degree of crystallinity of PLA was improved by PEG but slightly decreased by peroxide. The thermal stability of PLA was enhanced with the addtion of PEG6000. The toughening of PLA was confirmed by the increment of elongation at break. The exfoliation of C30B was interfered by the crosslink PLA. Then tensile strength of PLA/PEG/C30B/Luperox101 was then suppressed. The optimum properties, in term of toughening and thermal stability, were found at PEG content of 10 % rather than 15% by weight, for both PEG1000 and PEG6000.

Abstract: Polymer blends of poly (lactic acid) (PLA) and polybutylene succinate (PBS) containing activated carbon (AC) were foamed by using Azodicarbonamide (ADC) through an extrusion process. The composite foams containing 5 phr of AC had lower density than those without AC loading for PLA:PBS ratios of 90:10, 80:20, 70:30, and 60:40. The incident of higher void fraction was the consequences of more foaming nucleation centers which were induced by adding AC in the composite foam. Maximum reduction of density by 50% with the void fraction of 50% was achieved when both ADC and AC were applied at 5 phr with the PLA:PBS ratio of 80:20. The addition of AC in composite foams enhanced the crystallization in PBS phase but had no effects on PLA crystallinity. The thermal stability of composite foams with and without AC dosages for each PLA:PBS proportion was slightly changed. For PLA-PBS blend foams, the more PLA loading there was the more tensile strength and modulus there would be. For PLA-PBS-AC composite foams, AC could improve the modulus and tensile strength of composite foams in PBS-rich samples whereas no effect on PLA-rich samples.

Abstract: We report a novel soft chemical synthesis method, water assisted solid state reaction (WASSR) method. This method is very simple and can synthesize many ceramic materials just by storing or mixing raw materials added a small amount of water in a reactor at low temperature below 373 K. For example, well-crystalline SrMoO₄ was obtained using the WASSR method.

Abstract: The effect of slip degassing on the microstructure and mechanical properties of slip cast and reaction bonded Si₃N₄ was studied. The slip was prepared by aqueous ball milling of silicon (Si) powder. Hydrogen bubbles, a result of Si oxidation during milling, were degassed from the slip using a combination of vacuum and heat. The slip was then cast into a plaster mould to obtain rectangular green bodies. The Si green samples were sintered in a nitrogen atmosphere at 1500°C to convert the Si to Si₃N₄. After that the nitrided samples were polished to dimensions of 3 x 4 x 30 mm. The density, porosity, flexural strength, phase content and microstructure of the sintered samples were studied. The results showed that the degassing process increased the slip density. After casting and subsequent nitridation, it was found that the average apparent density of the samples increased from 2.89 to 2.95 g/cm³, the porosity decreased from 52.9 to 49.5 %, and the flexural strength increased from 8.1 to 9.3 MPa, when the degassed slip was used. A microstructural examination showed that the pores in the samples were filled with whiskers, which most likely resulted from a vapor phase growth mechanism. The samples produced from the degassed slip tended to have fewer whiskers, due to the reduced pore size and volume. A comparison of the XRD patterns showed no phase differences between the samples. The appearance of Si₂N₂O, and SiC likely resulted from the reactions between O₂ and C impurities with Si₃N₄.

Abstract: Anodic Aluminum Oxide (AAO) membrane has been successfully fabricated from two-step anodization with aluminum low grade (Al6061). The pore density, the pore diameter, and the interpore distance can be controlled by varying anodization process conditions. However, there are limits to control the mechanical strength and growth of AAO arrays, such as pore density, pore diameter and interpore distance. In this research the self-organized two-step anodization is carried out varying time at 24, 48 and 72 hours, respectively with 40V at the low temperature 2-5°C. The optimum conditions of AAO with two-step anodization is 40V for 48 hr. Finally, AAO substrate is separated from aluminum low-grade and enlarged pore diameter with pore widening process by 5% H₃PO₄. The physical properties were investigated by mean of field emission scanning electron microscope (FE-SEM) show that the average pore diameter and average interpore distance increase with the anodization time. Al6061 Aluminum substrate can be used to fabricate a nanoporous AAO film with an average pore diameter and average interpore distance larger than 70 and 90 nanometers, respectively but less mechanical stability.

Abstract: This study reported the preparation of nanocrystalline CoFe₂O₄ in single step by the sonochemical method in highly basic aqueous solution without requiring of high temperature calcination process. To prepare nanocrystalline CoFe₂O₄, the mixed solution of the required molar ratio of cobalt nitrate hexahydrate (Co (NO₃).6H₂O) and ferric nitrate nonahydrate (Fe (NO₃).9H₂O) was precipitated in high concentration of sodium hydroxide medium solution (NaOH) under high intensity ultrasonic irradiation (20 kHz, 150 W/cm²). The effect of NaOH concentration (5, 10, 15 and 20 M) on phase formation, microstructure and magnetic property of CoFe₂O₄ was investigated. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) results showed that the as-prepared powders were single phase CoFe₂O₄ with cubic spinel structure. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) study showed that nanocrystalline CoFe₂O₄ had monosized distorted spherical morphology and an agglomeration of the nanocrystalline CoFe₂O₄ into nanoparticles was observed when increasing the NaOH concentration. The nanocrystalline CoFe₂O₄ exhibited superparamagnetic property and the saturation magnetization (M_s) obtained from vibrating sample magnetometry (VSM) was found to correlate with the crystallite size and varied from 39-45 emu/g_.

Abstract: In this study, the properties and crystallization of re-melted soda-lime silicate glass cullet added with Al₂O₃, CaCO₃ and ZrO₂ were investigated in order to study the potential usage as a parent glass for glass-ceramics. Al₂O₃, CaCO₃ and ZrO₂ were added into the 71SiO₂-10Na₂O-6K₂O-5CaO-4MgO-2SrO-ZrO₂-Al₂O₃ glass cullet to increase the crystallization of the glass. The glass batches (%wt) of (65-x) Cullet:13Al₂O₃:22CaCO₃:xZrO₂ (x = 0, 1, 2, 4, 6 and 8) were melted at 1500°C for 3 hours. The crystallization was investigated by Differential Scanning Colorimetry technique (DSC) and it was found that the glasses with 6 and 8 %wt of ZrO₂ crystallized rapidly. It means that ZrO₂ acted as the nucleating agent in this glass system. The major crystallines determined by X-ray diffraction technique (XRD) were silica (SiO₂), wollastonite (CaSiO₃) potassium silicate (K₆Si₃O₉) and zirconium oxide (ZrO₂). The thermal expansion of glasses determined by dilatometric method indicated the characteristic of glass-ceramics and the effect of ZrO₂ on the thermal properties of glass. In conclusion, modifying the composition of soda-lime silicate cullet with Al₂O₃ CaCO₃ and ZrO₂ had potential to produce glass-ceramics.