# Thermal Triggered Release of Menthol from Different Carriers: A Comparative Study
## 1 Introduction  
Fragrance is widely used in daily care and food products, such as soap, detergent, cosmetics, drinks, candy, and so on. The key to the successful application of fragrance in commercial products is the protection of fragrance under storage conditions and the controlled release of fragrance under working conditions [1]. The use of a proper carrier for fragrance is an ideal approach that can potentially stabilize and release fragrance on-demand, simultaneously [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12]. Among all the fragrance carriers, thermal-responsive fragrance carriers are an important type of carrier material commonly used in a wide range of fields such as the tobacco industry [13].  
For the practical applications of fragrance carriers, a number of factors should be considered. For example, a suitable carrier should be non-toxic to secure its use in daily products. In addition, the carrier should also have an intermediate binding strength with the fragrance, which is particularly important for the on-demand perseverance and release of the fragrance. Furthermore, an ideal carrier material should be cost-competitive to enable large-scale application. Additionally, the carrier should be processable and can be easily integrated into the industrial process. The constraints above make an appropriate choice of carrier material challenging.  
Polymeric materials are the prevailing thermal-responsive carrier for fragrance due to the good combability with fragrance and low cost. A number of thermal-responsive polymers have been designed as potential fragrance carriers. For example, nanoparticles formed by thermal-responsive poly(stearyl acrylate) have been fabricated and used for the thermal-induced release of fragrance [14].  
The loaded fragrance can be released upon gentle heating near the temperature of human skin due to the reversible transition of the polymer chain from the ordered state to the disordered state at \(\sim\)45 \({}^{\circ}\)C.  
Poly(n-isopropyl acrylamide-costyrene)/SiO\({}_{2}\) composite hollow spheres have also been used [15]. The thermo-responsive property of the composite is inherited from the poly (n-isopropyl acrylamide-costyrene) component, which undergoes a temperature-dependent transition of the polymer structure. The controlled thermal induced release of cyclamen aldehyde was demonstrated in ethanol. While many thermal-responsive polymers have been reported so far, the composition and microstructure of the reported polymers has to be finely tailored, which leads to a high cost that may hinder their application. More importantly, these synthetic polymers might contain contaminants, such as unreacted monomer and residual solvents, thus limiting their application in food industries.  
In order to realize the controllable thermal triggered release of fragrance from carriers, two representative thermal-responsive polymers were chosen for the loading of menthol, which is a widely used fragrance for generation of the sense of refreshment. The compatability of menthol with the carrier substrate is studied with both theoretical and experimental investigations to provide an insight into the interaction between the fragrance and carrier. The stabilization effect and capability of the on-demand thermal menthol release of the carriers are evaluated to screen a possible carrier for practical applications and establish the structure-performance relation of the carriers.