Poly (D, L lactic-co-glycolic) acid (PLGA) is very famous with its biodegradability property. In the formed of nanocapsules (NPs), it is applied as contrast agent or for drug encapsulation. To pursuit better function of PLGA NPs, a study about degradation behaviour is necessary because it is related to NPs drug release pattern. To conduct this research, PLGA NPs was prepared by emulsification solvent-evaporation method and incubated in phosphate, acetate, and carbonate buffer to observe the effect of different pH into degradation rate of PLGA NPs. The acidic environment tends to have fast destructuration with less lactate monomer produced indicating less breaking of ester bonds. While in the basic condition, the degradation is done slowly with high production of lactate. This phenomena is related to the solubility of oligomers. So, it is clear that different pH affects the degradation mechanism of PLGA NPs and it can be applied to encapsulate drug for gastric or small intestinal cancer which have acidic and basic environment respectively.

Bamboos are often used due to their abundance, fast growth rate, cheap price, ductility, and formability in the sector of transportation, musical instrument, cooking ware, etc. For construction purposes, Dendrocalamus asper, (locally known as “Bambu betung”), is used as bamboo composites. The properties of bamboo are highly improved by using phenolic resins (phenol-formaldehyde) as an adhesive in bamboo composites. Bamboo is stronger and more susceptible to any liquid. The liquid is the most common enemy to plant-based structure due to the softening effect. Thus, the wettability of bamboo is an important matter as it indicates the ability of a liquid to spread and penetrate on the surface. The objective of this study was to analyze the effect of various heating times to wettability properties of heat-treated D. asper strands during the bamboo-composite making process. Before testing, the bamboo was cut, cleaned, and sand-grinded. The bamboo strands were heated at 140°C for 1, 2, and 3 hours. Then, the surface of bamboo was evaluated by measuring the contact angle based on the sessile drop method. The constant contact angle was obtained by calculating the regression formula between time (t) and contact angle (θ). The wettability was indicated by the value of K. The color of heat-treated bamboo strands was measured by portable color difference meter model CDX 105 and characterized by CIE Lab. The results showed that the longer the holding time, the surface became more hydrophobic, showed by a highercontact angle. Longer heating gives more time to the resin to spread more evenly into the pores of bamboo so that the hydrophobicity of bamboo composites is increased. The lightness value (L*) of heat-treated bamboo strands tended to decrease with increasing temperature and time of heat treatment. To conclude, for further making the process of bamboo composites using D. asper, we recommend curing the composites for 3 hours.

The abundance, rapid growth characteristics and good mechanical properties have made betung bamboo as good alternative materials to replace the slow growing wood. To adress the susceptibility to insects and water attack, the making of bamboo composites, using resin as matrix, has been widely practiced. Thus, the surface properties of bamboo strands are crucial to determine the optimum interaction with resin. This study evaluate the effect of heat treatment to improve the surface properties of bamboo strands, such as the wettability and the color change. Beforehand, the freshly cut bamboo was cut, cleaned and sand-grinded. The heat treatment was done at 140o and 160oC for 1, 2, and 3 hours. After cooling down to room temperature, the contact angle of bamboo’s surface was measured by sessile drop methode. The wettability was indicated by constant of contact angle change rate, K. Besides, the change of color was also determined. After the experiments, it was obtained that the bamboo surface tends to be more hydrophobic and has darker color with longer duration of heat treatment. Higher temperature and longer duration of heat treatment can cause more evaporation of liquid inside bamboo and decrease hydrophilicity of the surface.

No abstract

Plasma cutting is a method of cutting metal, especially steel, with relatively low cost and effectiveness, with satisfactory results. Where in the cut, it is enough to need a plasma cutting machine/inverter that is quite affordable, widely available in the market, and simple tools, an air compressor (no special oxygen/gas needed as in gas/oxygen and acetylene/LPG cutting), a power source, the material being cut and the cutting process can be carried out. How to use plasma cutting is relatively easy, namely by setting the machine and then directing the plasma torch to the cutting plane as needed by maintaining a stable movement and height. However, when we make repeated cuts, our concentration and physical strength will automatically decrease, so we need a tool that can help us direct/adjust the plasma torch, which is called a plasma cutting mechanism. After paying attention to these needs, a plasma cutting mechanism was designed with a working space/cutting length of 1200 mm, with a tool size of 1400 mm x 300mm x 200 mm length, width and height, estimated cost of Rp. 3,050,000,-, with a cutting speed setting of 100 mm/minute to 1000 mm/minute, a cutting height of 0 to 10 mm with an angle of 0 degree to 90 degree.