# Green Extraction of Valuable Compounds from Rubber Seed Trees: A Path to Sustainability
## 7 Green Extraction of Rubber Seed Oil
### Ultrasound Assisted Extraction (UAE)
#### 7.3.1 Mechanism of UAE  
Ultrasonic-assisted extraction (UAE) is a methodology that utilizes high-frequency sound waves to optimize the retrieval of bioactive chemicals from solid substrates, including plant matter or biomass. The process of UAE encompasses a sequence of physical and chemical phenomena that are propelled by acoustic cavitation. Acoustic cavitation refers to the creation, enlargement, and forceful collapse of minuscule bubbles (referred to as cavities) inside the solvent. The following is an elucidation of the mechanism shown in Figure 6 and explicated thereafter.  
1. Formation of Microbubbles: The application of ultrasonic waves to the extraction solvent leads to the production of successive cycles of elevated pressure and reduced pressure [105]. During the phase characterized by low pressure, the solvent experiences expansion and development, leading to the enlargement of minute gas bubbles or nuclei inside it [106].
2. Growth of Cavities: During the phase characterized by low pressure, the ultrasonic waves facilitate an expansion in the dimensions of the gas bubbles [107]. The occurrence of bubbles may be attributed to the existence of dissolved gases in the solvent or the liberation of gas by the sample matrix [108].
3. Sudden Implosive Collapse: When the bubbles reach a certain size, they experience a vigorous collapse or implosion during the high-pressure phase of the ultrasound cy  
Figure 6: An illustration of the Ultrasound-assisted extraction technique employed for the extraction of rubber seed trees.  
cle [109]. The phenomenon of this collapse gives rise to the generation of shockwaves, localized intense heating, and the creation of liquid microjets.
* Physical Effects: The closeness of these bubbles to the solid sample leads to their collapse, which in turn generates microturbulence and micro-convection [110]. These phenomena cause disruptions inside the solid matrix, enhancing the rate of mass transfer between the solid substance and the solvent, hence increasing the release of certain chemicals.
* Chemical Effects: The occurrence of chemical reactions may be initiated by the elevated temperatures and pressures experienced during the collapse of bubbles [111]. The reported phenomena include the possible disruption of chemical bonds or the degradation of certain molecules, dependent upon the specific ultrasonic circumstances.
* Enhanced Extraction: In a broad sense, the aforementioned physical and chemical processes contribute to an increased efficiency in the extraction process [112]. The penetration of solvent into the solid matrix is increased, hence enhancing the release of bioactive compounds. This phenomenon leads to higher extraction efficiency and shorter extraction periods compared to conventional approaches.  
In brief, UAE functions based on the phenomenon of acoustic cavitation, whereby the generation and collapse of small bubbles lead to both physical and chemical alterations within the extraction process. The use of UAE has been shown to significantly improve the efficiency of extracting bioactive chemicals from solid materials. As a result, UAE has gained recognition as a beneficial approach in a range of sectors, such as food, pharmaceuticals, and environmental research.