Key Engineering Materials Vol. 908

Abstract: Photovoltaic (PV) modules are supposed to be a reliable source of power for at least 25 years. Its component needs to work very efficiently to ensure electrical panels continue to perform. Backsheet film has been used to help insulating electrical components of PV modules to ensure PV can operate safely and protect them over their servicing life. PV modules are usually produced using encapsulated polymer such as polyvinylidene fluoride (PVDF), ethylene-vinyl acetate (EVA), polyamide (PA) or polyethylene terephthalate (PET). However, under continuous environmental stresses the components of solar panel including backsheet film are prone to malfunctions and failure after long term services. Thus, the service lifetime of PV systems may be shorter than the predicted lifetime. To overcome these issues, efforts have been made to enhance the performance of backsheet films by using radiation crosslinking method. The effects of electron-beam irradiation on mechanical and thermal properties for PVDF commercial backsheet film were studied. It was found that degree of crosslinking increased as irradiation dose increased. Irradiated PVDF has adequate mechanical properties to be used as backsheets for solar cells according to industrial reference. The result of SEM resulted in increased strength and stiffness of irradiated PVDF, which support the result of tensile test. In addition, the TGA analysis showed a good thermal stability with no degradation below 400°C. These studies help in quantifying long-term behavior and estimate a module lifetime especially in specific environment such as tropical country like Malaysia.

Abstract: Glycerol is a by-product produced from biodiesel production through the transesterification process. The excessive amount of glycerol generated during this process may become an environmental problem since it cannot be disposed on the environment. One of the possible applications is its use in biofilm production as a plasticizer. This research aims to characterize the physicochemical properties of biofilm produced from Dioscorea hispida (Ubi Gadong) starch with a different formulation of glycerol extracted from recycling cooking oil. Dioscorea hispida starch has shown great potential as a major component in bioplastic production due to its faster degradation rate, while glycerol acted as a plasticizer. The contact angle, water absorption, water content, and degradation rate of biofilm were also studied. Biofilm with the highest ratio of glycerol content showed the highest water absorption, which achieved 75.75%, and the biodegradable rate of biofilm was 97.99% on day 3. The lowest glycerol content in biofilm showed the lowest contact angle and completely biodegradation after five days buried in the soil.

Abstract: There are various different types of nanocellulose such as nanofibrillated cellulose (NFC), nanocrystal cellulose (NCC), and nanocrystal sphere (NCS). Each nanocellulose contains ordered nanocrystallites and low-ordered nano domains (amorphous). Nanocellulose can be used in several different applications such as coating for a wearable sensor device, film for supercapacitors, flexible fire-resistant foams for architecture, manufactory, and aerospace. All of these were made, following some chemical and mechanical processes. Some nanocellulose has a highly crystalline structure that has the potential to improve mechanical properties for industrial applications. Therefore, the present review compiles the most recent information on nanocellulose crystallinity influence on the polymer composites. In this review, the crystallinity of nanocellulose from different sources is discussed. The preparation of several nanocrystals cellulose via chemical treatment, particularly cellulose hydrolysis are described. It can be concluded that , the cellulose crystalline structure as filler or reinforce was responsible for the improvement of polymer matrix properties.

Abstract: Microcrystalline cellulose (MCC) from bamboo is a natural biodegradable polymer that can be applied as barrier materials in the form of films. Bamboo contributes to 90% of the total mass of the dry weight comprised of cellulose, hemicellulose, and lignin. In this study, Gigantochloa albociliata (Buluh Madu) was chosen due to the fast-growing species, cheaper and abundance in Malaysia. This bamboo was undergone Kraft pulping process to get the pure cellulose and then continued with the acid hydrolysis process to produce microcrystalline cellulose (MCC). In this study, thin-film PLA/PBAT reinforced with microcrystalline cellulose derived from Gigantochloa albociliata were produced. PLA is high in strength and ductility, but it is brittle while PBAT is elastic and strong. Therefore, PBAT is a great candidate for PLA hardness. The thin film was characterized with XRD, DSC and TGA to compare the thin film from microcrystalline cellulose derived from bamboo (B-MCC) with the commercial microcrystalline cellulose (C-MCC). The C-MCC was used as reference material. From the results, B-MCC has the same crystallinity index as C-MCC with a value of 51.3%. It can be concluded that B-MCC is can be one of the alternatives for the microcrystalline cellulose due to the abundance of bamboo as fast-growing species. Furthermore, it exists naturally, has low cost, is biodegradable, is a low-density compound, and fits best in the field of renewability.

Abstract: Metal matrix composites based on aluminium reinforced natural waste are a well-known material industry application because they can reduce environmental pollution. This paper presents the hardness and microstructure analysis of recycling milled aluminium (AA7075) at various composition of rice husk silica. Recycling milled AA7075 reinforced with rice husk burned at 1000°C at various composition i.e., 2.5, 5, 7.5, 10 and 12.5 wt.%, were investigated. Metal matrix composites samples were prepared by cold compaction method due to the lower energies consumption and operating cost compared to conventional recycling by casting. The results reveals that the hardness of metal matrix composites samples increased at increasing of rice husk silica up to 5 wt.%. The addition of rice husk silica increased the irregularities of pore shape and it resulted in higher porosity and random pore shapes compared to unreinforced metal matrix composites samples. Based on investigation of metal matrix composites samples, rice husk silica has good potential to improve the material behavior with appropriate composition of rice husk silica to metal matrix composite.

Abstract: Cultivated timber species that focus on fast-growing are slowly being utilized as an alternative source of materials by the timber industry worldwide. Most of them are cultivated as mono-species and, upon harvesting, possess lower properties than those harvested from the forest. To utilize them for a longer service span requires preservatives or some other treatment. The environmentally friendly heat treatment process can improve the wood properties by improving their durability against insects and fungi attacks. Each species requires optimum temperature and treatment duration without affecting its properties. Applying the heat treatment at extreme temperatures and duration can reduce the strength properties. This paper investigated the ultrastructure of heat-treated cultivated 10- and 15-years-old Tectona grandis after a three-month grave ground contact test. A Scanning Electron Microscope (SEM) was used in the investigation. The correlations were drawn between the treated and untreated teak before and after three-month periods. The inspections concentrate essentially on the cell structure changes due to the heat treatment process. No significant difference was observed between the two age groups. However, heat-treated samples at extreme temperatures experience elongated and collapsed vessels, deformed fibers, and decreased microfibrils in the cell walls of fibers. The study intimates that heat treatment alters the cell structure of cell walls in teak wood and increases the durability of the wood in the long term.

Abstract: The implementation of glass in various industries may cause some problems due to its brittleness characteristic. Its usage in the transportation sector has led to death and serious injuries to drivers and passengers in vehicles. It shows that the manufacturing process of the materials used requires an improvement in terms of brittleness to provide better protection to the consumer. Therefore, rubber toughened PMMA (RT-PMMA) was introduced as the rubber has the ability to increase the ductility of PMMA. PMMA and two different grades of RT-PMMA namely RT-PMMA65 and RT-PMMA100 were taken into consideration to investigate the effect of different rubber contents on the ductility of PMMA. Other than strain rate and temperature, humidity is also one of the factors that affect the ductile properties of PMMA. In this study, tensile tests at different humidity levels (11% and 98%) will be carried out by immersing the specimens in two different solutions which are lithium chloride (LiCl) and potassium sulfate (K₂SO₄) beforehand. The output from the experimental works proved that the tensile properties of RT-PMMA are affected by the presence of humidity for all three grades of PMMA under consideration. It is also proved that RT-PMMA100 is more ductile compared to RT-PMMA65 on the tensile test.

Abstract: Gamma irradiation is a particularly effective method for inducing crosslinking, which leads to improved composite characteristics. The effects of gamma irradiation on swelling percentage, flammability and morphological analysis were investigated. Ethylene Propylene Diene Monomer (EPDM) rubber composites were prepared with various amounts from 10-60 phr (part per hundred part of rubber) of the sepiolite particles using a two-roll mill machine. The composites were subjected to 50 kGy of gamma irradiation and compared with unirradiated composites. The results demonstrate a reduced in swelling percentage at all sepiolite loadings. The crosslinks of rubber chains into sepiolite/EPDM composites generated by gamma rays resulted in improvements in the swelling resistance. The irradiation composites, however showed lower flammability resistance to the non-irradiated composites.

Abstract: Porous NiTi shape memory alloy is of special interest for biomedical purposes especially for human bones application due to its attractive features such as lower stiffness to minimize the effect of stress shielding and good strength to prevent deformation and fracture apart from its shape memory effect and superelastic behavior. With all these great benefits, however, the challenge is to produce porous NiTi which resembles cancellous bone. Therefore, in this research, pore forming agent such as calcium hydride, CaH₂, is added to the equiatomic of Ni and TiH₂ powder mixture to produce porous NiTi with higher porosity level using powder metallurgy technique. Here, the effect of composition of pore forming agent on porosity level, phase formation and transformation behaviour of porous NiTi were investigated. From the observation, the pores formation exhibits small closed pores instead of interconnected pores. The result also shows that by adding 3wt% composition of pore forming agent, the porosity level of sample sintered can reach up to 32%. For phase transformation behavior, there are martensitic transformation peaks observed both upon cooling and heating for all samples, however the overall enthalpy changes are significantly lower (<2 J/g). This due to undesirable phase such NiTi₂, Ni-rich phase and also Ni₃Ti that co-exist with NiTi formation, thus jeopardize the transformation enthalpy for porous NiTi.

Abstract: In this study, a composite of bioactive glass and cordierite (BG/cordierite) was proposed to increase the strength of bioactive glass (BG). Both BG and cordierite were separately synthesized with the method of glass melting and used to fabricate BG/cordierite with sintering temperature in the range from 600 to 1000 °C. The BG/cordierite were characterized using X-ray diffraction (XRD), density, bulk density, porosity and hardness test. The XRD pattern shows amorphous phase and crystalline phase such as combeite, wollastonite and larnite appeared after sintering. The highest hardness value show by BG/cordierite with sintering temperature 950 °C (BG/C950) with 251 Hv.