Biology Assignment 代写 :Microparticles Of Menthol Palmitic Acid
Fig 1.3 CO2 Phase Diagram[29]
The specific features of a supercritical fluid allows for the control and manipulation of operating temperature and pressure [28]. Some advantages of supercritical fluids-based processes are: the possibility of avoiding (or at least minimizing) the use of organic solvents; the flexibility or ease to apply to a wide range of materials, including thermo labile substances; the ability to produce particles with a wide range of sizes, shapes and morphologies; fig 1.4 illustrates the possibility of loading the particles with an active substance [33], which can be dispersed in a matrix (composites or microspheres) or surrounded by a shell (microcapsules or encapsulates) [31].
Fig 1.4. [31]
a) Composites or microspheres b) Encapsulate or microcapsules
For the case of supercritical CO2, additional advantages are mild operating temperature and the ease of solvent separation, recovery and recycle since depressurization causes the supercritical to revert to its gaseous standard state and to provide a solvent-free product [28].
Among all the supercritical fluid particle formation techniques in Table 1, Particles from gas-saturated solution (PGSS) process is a promising technique that uses fluids at supercritical conditions to produce fine particles under mild operating conditions [32].
Table 1.1
Supercritical particle formation techniques
Antisolvent effect + solvent evaporation
The PGSS process makes good use of the advantage that a compressed gas is more soluble in a liquid than the corresponding liquid is in the same compressed gas [32]. In this particular process, the SCF is dissolved in a melted substrate (or substrates), or a solution of the substrate(s) in a solvent, or a suspension of the substrate(s) in a solvent, then followed by a rapid expansion, at moderate pressures, of the saturated solution through a nozzle [33,37].The expanding gas supports the formation of fine droplets. Owing to the Joule-Thomson effect the gas cools down extremely rapidly below the solidification temperature, removing heat from the droplets of the molten solute[14,35]. The time for the solidification process is in the range between some 10ms up to a few100ms [35]. Depending on the type of system, fine solid particles or liquid droplets are formed [36-37].
Solubility of either the carrier or core material in the SCF is not a requirement. However, the SCF used must be very soluble in the liquid phase. This technique is particularly suited for the encapsulation of drugs into polymer or lipid matrices [13] which generally absorb a large amount of carbon dioxide. CO2 is generally used as a supercritical fluid in PGSS for several polymers mainly due to its high solubility.[39] One of the key features of PGSS is the strong reduction of the melted substance viscosity once it is mixed with the supercritical fluid.[40] A second effect of mixing the melted substance with the supercritical fluid is the melting point temperature depression; this phenomenon prevents the solidification inside the nozzle as well.[40] Through the choice of the appropriate combination of solvent and operating conditions for a particular compound, PGSS can eliminate some of the disadvantages of other SCF and conventional methods. Some other well known advantages are that the process is versatile process; applicable for several substances (example mixtures and water-soluble ingredients to form composite microparticles ); uses moderate pressures; has low gas consumption; and uses no harmful organic solvents [13]; gives solvent-free powders; is suitable for highly viscous or sticky products; gives fine crystalline and amorphous powders with a narrow, controllable size-distribution, thin films, and is easy to scale-up [14]. Because to the low operation costs PGSS can be used for a wide variety of substances not only for highly valuable, but also for commodity products.[14]
Since other individual cigarette brand preferences tend to diminish fairly early with time but the menthol brand can capture smokers because it provides the same enjoyment of normal cigarettes plus giving freshness feel with a cooling effect [4,29]. The need to for further research to produce new and improved menthol flavor will continue.
Therefore, the primary aim of this research is to produce menthol/ palmitic acid composites using the novel PGSS process, investigates the effect of operation conditions such as composition, pressure and temperature on the particles formed and last but not the least undertake flavor release studies to determine the factors that could lead to menthol flavor loss.[43]
1.2 MATERIALS
1.2.1 Menthol
Menthol (2-Isopropyl-5-Methylcyclohexanol, C6H9OHCH3C3H7) is a waxy, crystalline substance, clear or white in color. Figure below shows the l- or -(-) form of menthol. It is this form that has characteristic minty smell. For this research menthol was selected as the core material, its purity ˃99%, melting point 43.5oC and was supplied by
Fig. 1.5 Chemical Structure of menthol [44]
Biology Assignment 代写 :Microparticles Of Menthol Palmitic Acid
