Komang Widhi Widantha, S.T., M.T. is a lecturer and researcher in the field of mechanical and materials engineering at Politeknik Negeri Bali. His research interests focus on material characterization, environmentally friendly materials, green technology, hydroxyapatite-based biomaterials, corrosion and surface engineering, as well as filtration and wastewater treatment materials. He is also actively involved in vocational education development, laboratory management, scientific publication, and international conference organization. In addition to research activities, he has experience in non-destructive testing (NDT), engineering design, and applied mechanical engineering for vocational and industrial applications.
Materials Engineering Material Characterization Green and Sustainable Materials Biomaterials Hydroxyapatite Corrosion and Surface Engineering Wastewater Treatment Materials Filtration Technology Mechanical Engineering Applications Non-Destructive Testing (NDT) Manufacturing Processes and Vocational Engineering Education.
Hydroxyapatite (HA) coatings have been widely used to improve biocompatibility of metal alloys. This paper discusses the effect of hydroxyapatite (HA) and HA/alumina coated NiTi on their corrosion and dissolution behavior in Phosphate Buffer Saline (PBS) and Ringer's lactate solutions. The HA was synthesized from biogenic method and used as initial powder in High-Velocity Oxygen Fuel (HVOF) spray technique for the deposition of two coating types, fully HA and HA + 15 wt.% alumina composite coating. The as-synthesized HA had irregular porous structure with relatively low Ca/P ratio of 1.52. Tafel polarization curves obtained from electrochemical test had showed that both coatings increased the corrosion resistance of the NiTi substrates significantly. The ICP-MS analysis results that indicated a low nickel dissolved in both solutions after immersion in 21 days had supported these findings. The nickel levels in the solutions from all samples, either bared substrate or coated samples, in fact below the maximum limit for allergies of the human body. Immersion testing showed the stability of HA and HA/alumina layers as a barrier which maintains its morphology in PBS solution but slightly changed in Ringers.
Food packages and kitchen utensils made of thermoplastic are very popular due to their low production costs. However, thermoplastic is easily degraded at high temperatures and has low mechanical properties. When degraded, thermoplastic produces carcinogenic monomers that can contaminate food. Thus, natural fiber-based composites are introduced. Most commercial products nowadays are made of thermosets that are difficult to degrade. In order to produce fully biodegradable composite materials, we mixed PLA (polylactic acid) pellets with bamboo. PLA is a thermoplastic polyester that is synthesized from the fermentation of plant starch. The mechanical properties of PLA/bamboo composites depend on the surface interaction between PLA and bamboo. Thus, we studied the effect of the chemical treatment of bamboo prior to composite making on the mechanical properties of PLA and bamboo. Furthermore, the morphology of bamboo was varied into powder, fiber, and strip. A four-year-old bamboo trunk was harvested and dried to minimize the moisture content. Then, it is soaked separately in cold water and 5% NaOH for 72 hours. After it is rinsed and re-dried, the fiber and powder of bamboo are extracted through mechanical treatment. The composite is made with 10% bamboo reinforcement by hot press molding technology at 220°C for 40 minutes. The tensile testing shows that only bamboo strips can improve the mechanical properties of composites. Besides, the alkali treatment was found to increase the brittleness of bamboo, causing an increase in modulus elasticity and a decrease in ductility.
In Indonesia, the reliance on foreign countries for military components persists, including tank track links which are crucial for combat vehicles. These components require mechanical properties such as wear resistance and toughness to ensure high safety standards. High Strength Low Alloy (HSLA) steel is used, necessitating precise composition and appropriate heat treatment processes. This study varied compositions and heat treatments to achieve desired properties, producing prototypes with five predetermined compositions. The heat treatment process involves initially heating the samples to 860°C for 30 minutes for uniformity, followed by various treatments including quenching in oil, normalizing, and multiple cycles of quenching with tempering at different temperatures and durations to refine microstructure and adjust hardness of the alloy. Results showed optimal mechanical properties in composition no. 4 after normalizing with a blower, achieving a hardness of 31 HRC. This research aimed to optimize mechanical performance during operational conditions through variations in temperatures and holding times.
This research investigates the effects of particle size and compaction pressure on the dissolution behavior of hydroxyapatite scaffolds synthesized from bovine bone in acidic neutral and basic solutions. Hydroxyapatite was extracted through a process involving cutting, cleaning, boiling, soaking in NaOH, sun drying, grinding into powder and calcination at 800°C. The powder was then sieved into two size fractions (75 and 150 microns) and compacted at pressures of 200, 250, and 300 MPa. The mass and dimensions of the scaffolds were measured to calculate porosity, followed by immersion in the respective solutions for 24 hours to determine dissolution rates. Results indicated that smaller particle sizes and higher compaction pressures resulted in reduced porosity and enhanced structural integrity. The dissolution rates varied significantly with pH levels, exhibiting the highest rates in acidic conditions up to 215.83 mg/cm2 and the lowest in basic solutions up to 11.32 mg/cm2. Additionally, scaffolds with smaller particles and higher compaction pressures demonstrated lower dissolution rates across all pH levels due to lower porosity. In conclusion, both particle size and compaction pressure are critical factors influencing the dissolution behavior of hydroxyapatite scaffolds. These findings have significant implications for the design and optimization of hydroxyapatite-based materials for biomedical applications, where controlled dissolution rates are crucial for performance and longevity.
One way to address environmental problems caused by the use of synthetic materials is by exploring the potential of new materials that are more environmentally friendly. This research aims to develop PLA/bamboo green composites by investigating the effects of fiber composition and alkali treatment on the thermal stability and immersion behavior of the composites. PLA/bamboo composites were produced using the hot press method with bamboo fibers at 10, 20, and 30 wt.% concentrations. Alkaline treatment was conducted using a 5% NaOH concentration for 24 hours. The PLA/bamboo composite exhibited weight gain due to water absorption during the soaking process. The inclusion of bamboo composition increases the water absorption of the composite, whereas alkali treatment decreases the water absorption of the composite. Furthermore, the introduction of fibers also reduces the degradation temperature of the composite. This research is expected to provide valuable insights for the broader utilization of green composite materials.
Food storage and food packaging materials belong to a group of food contact materials (FCM) that is highly regulated to ensure the health and safety of consumers.The choice of FCM is crucial because all types of FCM produce non-intentionally added substances (NIAS).The unknown substances are mixed together with the food and are consumed together.Therefore, bio-based and biodegradable materials are recommended since the excretion substances can be decomposed by human metabolism.One example is polylactide acid (PLA).PLA is made from potato or corn starch and comprises lactide acid monomers.However, the mechanical and thermal stability of PLA is relatively low.A fouryear-old bamboo is incorporated into the PLA matrix to improve the mechanical stability of PLA.A freshly harvested bamboo is sun-dried for a week before it undergoes alkali treatment with NaOH 5%.After 72 hours of alkali soaking, the bamboo is rinsed and re-dried.The strip, short fiber, and powder of bamboo were obtained mechanically.The PLA/bamboo composites are made with 10% bamboo reinforcement by using a hot press molding machine.The flexural test was done to observe the bamboo shape's influence on the mechanical stability of composites.We found that each form of bamboo has a different surface contact with the PLA matrix.So, it significantly influences the bending strength of PLA/bamboo composites.In addition, the alkali treatment also influences the flexural properties as it modifies the interface adhesion between bamboo and PLA.The composites made of bamboo immersed in NaOH solution have a higher flexural modulus of elasticity indicating better rigidity.
The use of aluminum is widely spread from beverage cans, car parts, airplanes, trains, and household furniture. This is due to its lightweight and good corrosion resistance. However, as a metal aluminum waste is difficult to be decomposed naturally. Aluminum metal takes 80 to 100 years to decompose. So the accumulation of untreated scrap aluminum can pollute the environment. One of the solutions is to recycle aluminum by melting and re-casting it into a new shape: a mold for polymer processing. The waste of beverage cans was cleaned from any dirt and adhesive. Then, they were turned into small parts by a crusher. The melting process was done at 650oC. The molten aluminum was poured into a sand mould in the shape of mould of a tensile testing specimen. The recycled product can be used to prepare tensile testing samples of polymer or polymer-based composite with injection molding technique. To evaluate the quality of recycled aluminum, a hardness test was done with a value of 69.31 + 3.02 HB. This value is lower than first-use aluminum. This is due to a combination of microstructural changes due to repeated heating, the presence of additives and impurities, and the effects of heat treatment and open cooling. Metallographic testing was carried out to evaluate the microstructure of the material resulting from the smelting of scrap aluminum using sand molds. In this test, the etching solution used consisted of 100 ml of water and 20 g of sodium hydroxide. The results of the metallographic images on the recycled aluminum material show the presence of a stand-alone silicon (Si) element and an aluminum-copper alloy (CuAl₂).
This study investigates the effect of citric acid surface treatment on wood sawdust used as reinforcement in epoxy-based composites, with a focus on improving bending strength. Wood sawdust was subjected to surface modification using citric acid and sodium hydroxide (NaOH) under equivalent molar concentrations. Bending strength tests showed that both citric acid and NaOH treatments significantly improved mechanical performance compared to untreated samples, with average strengths of 33.83 MPa and 32.82 MPa, respectively, versus 21.83 MPa for the untreated group. Statistical analysis was conducted to compare the two treatments. After confirming normal distribution but unequal variances, a Welch two-sample t-test was performed, yielding a p-value of 0.742. This result indicates no statistically significant difference in bending strength between citric acid and NaOH treatments.
The environmental concerns associated with petroleum-based plastics have driven the development of biodegradable alternatives. This study investigates the biodegradation kinetics of cassava starch–coffee grounds bioplastics under soil and aqueous conditions. Bioplastic films were prepared using the solution casting method with 10% (w/w) spent coffee grounds and glycerol as a plasticizer. Biodegradation tests were conducted over 14 days, measuring weight loss at predetermined intervals. The results showed that the bioplastics degraded significantly faster in soil, with 61.3% weight loss within seven days, compared to 34.2% in aqueous media. The degradation trends followed first-order kinetics, indicating that the rate of biodegradation depended on the remaining bioplastic mass. The addition of coffee grounds enhanced biodegradability by promoting microbial colonization and water absorption, while soil conditions accelerated enzymatic breakdown. This study demonstrates that cassava starch–coffee grounds bioplastics are promising sustainable materials, offering a pathway for organic waste valorization and supporting circular economy principles.
Penelitian ini bertujuan untuk menganalisis pengaruh variasi gaya kompaksi terhadap sifat fisik dan kekuatan tekan pelet hidroksiapatit (HAp) berbasis tulang sapi. Penelitian ini dilakukan karena limbah tulang sapi memiliki potensi untuk dimanfaatkan sebagai sumber HAp yang memiliki karakteristik berpori dan berpeluang untuk berbagai aplikasi material. Serbuk HAp dibuat melalui proses pembersihan, perendaman, kalsinasi, penggerusan, dan penyaringan, kemudian dikompaksi menjadi pelet dengan variasi gaya 15, 20, dan 25 kN. Pelet yang dihasilkan diuji densitas, porositas, penyerapan air, serta kekuatan tekan. Hasil penelitian menunjukkan bahwa peningkatan gaya kompaksi menyebabkan densitas dan kekuatan tekan pelet meningkat, sedangkan porositas dan penyerapan air mengalami penurunan. Pada gaya kompaksi 25 kN, pelet menunjukkan densitas tertinggi (2,11–2,22 g/cm³), porositas terendah (20–24%), penyerapan air terendah (5,74–7,14%), serta kekuatan tekan tertinggi sekitar 15 MPa, yang mengindikasikan terjadinya pemadatan partikel yang lebih intensif. Hasil ini menunjukkan bahwa variasi gaya kompaksi berpengaruh terhadap struktur dan sifat mekanik pelet HAp. Struktur berpori yang dihasilkan menunjukkan potensi untuk dikaji lebih lanjut pada aplikasi yang memerlukan keseimbangan antara kekuatan mekanik dan porositas.
Open for research collaboration in hydroxyapatite-based filtration systems and sustainable water treatment materials. My current research f…
Project Overview Magnesium-based alloys are emerging as next-generation biodegradable materials for orthopedic implant applications due …