| Moisture content of cigarette has an important impact on the processing conditions andsensory quality of tobacco industry. Stable moisture content is desirable for cigaretteprocessing and sensory evaluation. However, the cigarette is a solid material with porous,while a large number of proteins and hydrophilic colloid material exist in tobacco, that makestobacco easily absorb water. Therefore, it is very important to explore the mechanisms ofcigarette moisture absorption and control water content for guiding cigarette productsprocessing and improving products quality. Currently, the study of cigarette moistureabsorption still remains in equilibrium moisture content, moisture absorption rate and otherbasic indicators; it is lack of in-depth study of the mechanism of moisture absorption. In thisstudy absorption rates, moisture equilibriums, adsorption isotherms and water activity ofdifferent tobacco samples were measured. In order to explore the mechanism of tobaccomoisture absorption the changes of water status and surface microstructure were alsoobserved and analyzed during moisture absorption. The main results are as follows:Firstly, the water absorption of cigarette was studied. Different tobacco samplesequilibrium water content, rate of absorption, water activity and adsorption isotherms weremeasured respectively to study the common absorption rules and the effect of temperaturesand chemicals were evaluated. Experiments show that the tobacco moisture was first absorbedthrough the physical and chemical way on the surface, and then absorbed through thecapillary condensations. The initial absorption rate is mainly determined by the physicaladsorption, the limited factor is the temperature and the environment. The added humectantsin cigarette products have an important influence on tobacco water adsorption. Sugar andother hydrophilic materials on one hand increase water content by enhancing chemicaladsorption, and on the other hand it may shields capillary condensation adsorption in somedegree and thus results the different moisture content from the blank samples.Secondly, relaxation time and relaxation area integral indicators of different cigarettesamples were measured by low-field NMR techniques to study the moisture adsorptionmechanism. Distributed exponential analysis of the NMR transverse relaxation date revealedthe existence of the three distinct water populations: T21, T22and T23, respectively,representing chemically bound water, capillary bound water and free water, in which T21values are the most sensitive indicators reflected the bonding strength of water, and thechange of that may be the shifting of monolayer water adsorption to multilayer adsorption.The dominated way of tobacco absorption is through the capillary sorption while after addinga polar group such as hydroxyl the absorption mechanism steering chemisorptions.Finally, surface microstructure among different tobacco samples of different watercontent were compared by environmental scanning electron microscopy and then the pore sizeand its distribution were analyze through graphics software. Experimental results show thatmain difference of the epidermal cell structure among different cigarette samples is thequantity of surface pores and the tightly extent of cells. Spongy tissue and palisade tissue areimportant organizational form of tobacco, its present state and organizational structure is subjected to the combined effect of moisture and chemicals adding. In dry cigarette samplescapillary pore radius distributed between1~0.5μm, with the adsorption processing, largecapillary pore radius gradually turn into smaller micro-capillaries, which the pore radius wasless than0.5μm.The micro-capillaries become the main capillary organizational form intobacco products. Different chemical added has different influence on the change of thiscapillary pore radius, which causes the different effects on cigarette absorption capacity. |
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