No abstract

The initial aim of the paper is to dramatically improve the pretreatment stage of biodiesel production, which converts problematic free fatty acids to fatty acid methyl esters, by introduction of a microbubble mediated reactive distillation stage instead of acid pretreatment. This will shift the conventional esterification process towards completion with a yield higher than 80%, even without high excess methanol. Application of ozone microbubbles has the advantage over acid gas catalysis in that it gives higher conversion and leaves no catalyst residue and requires no further catalyst recovery separation steps (a "phantom" catalyst). Unreacted ozone breaks down into oxygen, so the off-gases are just a humid air stream that can be vented. Importantly, ozonolysis breaks carbon-carbon double bonds into aldehydes and carboxylic acids. Many ester species were found after contacting the feedstock with ozone-rich microbubbles, depending on the molecular structure of the alcohols for the ozonolysis of oleic acid with alcohols, i.e., methanol, ethanol, n-propanol, iso-propanol, and n-butanol. In the case of ozonolysis of used cooking oil mixed with methanol, the results from the GC-MS show that all saturated free fatty acids (including palmitic acid, stearic acid, and myristic acid) are converted to methyl esters within 20 hours of 60°C ozonolysis, whereas trace amounts of these chemicals remain at lower temperatures. The results also show that the conversion of oleic acid to form oleic acid methyl ester is 91.16% after 32 hours of ozonolysis at 60°C. Therefore, the free fatty acid content in used cooking oil is less than 1.33%, which makes it suitable as a reactant for biodiesel production via transesterification. However, this result is different from the result provided by ASTM D974 in that the acid numbers decrease dramatically by 25% at the beginning of ozonolysis followed by a plateau. Moreover, if the fluidic oscillator is used to generate bubbles in ozonolysis of oleic acid mixed with methanol, the results show that the yields of ozonolysis product 1-nonanal increase by 30%. This observation means that ozonolysis of oleic acid is relative to the specific interfacial area, and favoured at low liquid temperatures.

Osteoarthritis (OA) is a disease that leads to the damage of subchondral bone. To treat OA, patients can have surgery to implant biomaterials into the damaged area. In this research, biomaterials of 3D porous scaffolds were fabricated by the use of air microbubbles for subchondral bone formation proposed for OA surgery. Microbubbles were generated in a polyvinyl alcohol solution at various air flow rates of 20 (F20), 100 (F100), 200 (F200), and 300 (F300) cc min−1. Molecular organization, structure, and morphology of the scaffolds were characterized and observed by Fourier transform infrared spectroscopy, a differential scanning calorimeter, and a scanning electron microscope, respectively. Physical and mechanical properties based on swelling behavior and compressive strength of the scaffolds were also evaluated. Biological performance by means of osteoblast proliferation, protein synthesis, and alkaline phosphatase activity of the scaffolds were studied. The scaffolds showed molecular organization via interaction of –OH and C = O. They had residual water in their structures. The scaffolds exhibited a morphology of a spherical-like cell shape with small pores and a rough surface produced on each cell. Each cell was well connected with the others. The cell size and porous structure of the scaffolds depended significantly on the flow rate used. The molecular organization, structure, and morphology of the scaffolds had an effect on their physical and mechanical properties and biological performance. F100 was found to be an optimum scaffold offering a molecular organization, structure, morphology, physical and mechanical properties, and biological performance which was suitable for subchondral bone formation. This research deduced that the F100 scaffold is promising for OA surgery.

Natural rubber foams are currently produced by the two well-known processes of Dunlop and Talalay. Dunlop process, however, requires a high-speed Hobart Mixer to generate a high bubble-volume, while Talalay is complexity and expensive technique. Here, a simple and inexpensive technique for rubber foam production was introduced. The process involved air flowing with a constant flow rate through a porous diffuser, firmly connected to the bubble column containing compound latex, to generate a high bubble-volume. Microstructure of the as-produced rubber foams was examined using a scanning electron microscope (SEM), in comparison with that of the purchased Dunlop foam. Spherical cell shape with a uniform interconnected-cell structure was gained from the bubbled foams, while fractured-cell structure was obtained from the Dunlop foam.

A simple and green method for scaffold production was introduced here. The method is based on bubbling process of PVA solution. This process is superior to other conventional techniques in the matter of controllable pore size and without using of any other organic solvents. Microstructure of the scaffold was examined by a stereo microscope. Pore size and size-distribution were determined using a scanning electron microscope. Interconnected cells with uniform pores were observed without any other impurities within the pores. Average pore size was about 220 microns which is in the range required for bone tissue engineering application.