Published Online: 10 Sep 2016 Page range: 102 - 112
Abstract
SUMMARY
A numerical model based on the finite element method has been constructed to simulate the ignition propensity (IP) tests. The objective of this mathematical model was to quantify the influence of different characteristics of the cellulosic substrate on the results of the IP-tests. The creation and validation of the model included the following steps: (I) formulation of the model based on experimental thermodynamic characteristics of the cellulosic substrate; (ii) calibration of the model according to cone calorimeter tests; (iii) validation of the model through mass loss and temperature profiling during IP-testing. Once the model was validated, the influence of each isolated parameter of the cellulosic substrate was quantified via a parametric study. The results revealed that the substrate heat capacity, the cigarette temperature and the pyrolysis activation energy are the most influencing parameters on the thermodynamic response of the substrates, while other parameters like heat of the pyrolysis reaction, density and roughness of the substrate showed little influence. Also the results indicated that the thermodynamic mechanisms involved in the pyrolysis and combustion of the cellulosic substrate are complex and show low repeatability which might impair the reliability of the IP-tests.
Published Online: 10 Sep 2016 Page range: 113 - 125
Abstract
SUMMARY
Black shank is a major annual disease threat to all types of tobacco worldwide. It is caused by the fungus Phytophthora parasitica var. nicotianae (PPN). The major tobacco growing areas in US - Kentucky, Tennessee and North Carolina can experience devastating losses, reaching in some fields up to 100%. Thus far, the main approaches to control this disease have been creation of resistant varieties, fungicide treatments, and crop rotation. Some fungicides are reported to have negative effects on the environment. The goal of this work was to test the antifungal activity of several natural products that are synthesized by certain Nicotiana species, and secreted to the leaf surface. We hypothesized that phylloplanin, cis-abienol, labdenediol and sclareol can suppress PPN-race 0- and PPN-race 1-caused disease in Burley tobaccos KY 14 and MS KY 14 × L8LC in the greenhouse. We developed methods for leaf surface extraction, spore preparation and soil drench application of the natural compounds tested. Experiments were performed on 5–8 week-old greenhouse grown seedlings. cis-Abienol showed high inhibitory properties toward the disease. Race 0 infection was completely subdued in KY 14 while race 1 infection was reduced by 70–80%, and delayed by 6–10 days in KY 14 and MS KY14 × L8LC. Sclareol was very effective in inhibiting race 0-caused disease in both tobacco cultivars. In MS KY 14 × L8LC race 1 infection was inhibited while in KY 14 it was reduced by 85% and delayed by 6 days. Labdenediol reduced the disease by half in eight week-old KY 14 plants. Tobacco phylloplanin reduced plant infection by both races by 50–60% and delayed the disease by 6–10 days. Phylloplanin was least suppressive in both tobacco cultivars. We consider sclareol to be the best candidate for future studies due to its antifungal properties and availability. cis-Abienol, despite its good antifungal activity, is not feasible for large-scale use due to the production and stability limitations.
Published Online: 10 Sep 2016 Page range: 126 - 135
Abstract
SUMMARY
A new method utilizing 13C cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectra was developed for the simultaneous quantitative determination and structure analysis of tobacco cellulose from hot water or acid detergent extraction. A reference spectrum of tobacco noncellulose components was subtracted from the spectrum of each sample to obtain a subspectrum of the cellulose components. The NMR spectra in combination with spectral fitting were analyzed in detail and some parameters, such as the content of cellulose, crystallinity, allomorph composition and lateral dimensions for cellulose elementary fibrils and microfibrils were determined. The quantitative results showed that the average recovery was 94.0% with a relative standard deviation (RSD) of 4.6–4.8%. The structure results obtained by the spectral fitting for the cellulose C1-region showed that the main allomorph composition in tobacco cellulose was Iβ. The cellulose crystallinity calculated by the spectral fitting in C4 -region was about 50%. The lateral dimensions for cellulose elementary fibrils and microfibrils were in the range of 3.0–6.0 nm and 6.0–13.0 nm, respectively. Therefore, this NMR method could provide important information on both amount and structure of cellulose in tobacco.
A numerical model based on the finite element method has been constructed to simulate the ignition propensity (IP) tests. The objective of this mathematical model was to quantify the influence of different characteristics of the cellulosic substrate on the results of the IP-tests. The creation and validation of the model included the following steps: (I) formulation of the model based on experimental thermodynamic characteristics of the cellulosic substrate; (ii) calibration of the model according to cone calorimeter tests; (iii) validation of the model through mass loss and temperature profiling during IP-testing. Once the model was validated, the influence of each isolated parameter of the cellulosic substrate was quantified via a parametric study. The results revealed that the substrate heat capacity, the cigarette temperature and the pyrolysis activation energy are the most influencing parameters on the thermodynamic response of the substrates, while other parameters like heat of the pyrolysis reaction, density and roughness of the substrate showed little influence. Also the results indicated that the thermodynamic mechanisms involved in the pyrolysis and combustion of the cellulosic substrate are complex and show low repeatability which might impair the reliability of the IP-tests.
Black shank is a major annual disease threat to all types of tobacco worldwide. It is caused by the fungus Phytophthora parasitica var. nicotianae (PPN). The major tobacco growing areas in US - Kentucky, Tennessee and North Carolina can experience devastating losses, reaching in some fields up to 100%. Thus far, the main approaches to control this disease have been creation of resistant varieties, fungicide treatments, and crop rotation. Some fungicides are reported to have negative effects on the environment. The goal of this work was to test the antifungal activity of several natural products that are synthesized by certain Nicotiana species, and secreted to the leaf surface. We hypothesized that phylloplanin, cis-abienol, labdenediol and sclareol can suppress PPN-race 0- and PPN-race 1-caused disease in Burley tobaccos KY 14 and MS KY 14 × L8LC in the greenhouse. We developed methods for leaf surface extraction, spore preparation and soil drench application of the natural compounds tested. Experiments were performed on 5–8 week-old greenhouse grown seedlings. cis-Abienol showed high inhibitory properties toward the disease. Race 0 infection was completely subdued in KY 14 while race 1 infection was reduced by 70–80%, and delayed by 6–10 days in KY 14 and MS KY14 × L8LC. Sclareol was very effective in inhibiting race 0-caused disease in both tobacco cultivars. In MS KY 14 × L8LC race 1 infection was inhibited while in KY 14 it was reduced by 85% and delayed by 6 days. Labdenediol reduced the disease by half in eight week-old KY 14 plants. Tobacco phylloplanin reduced plant infection by both races by 50–60% and delayed the disease by 6–10 days. Phylloplanin was least suppressive in both tobacco cultivars. We consider sclareol to be the best candidate for future studies due to its antifungal properties and availability. cis-Abienol, despite its good antifungal activity, is not feasible for large-scale use due to the production and stability limitations.
A new method utilizing 13C cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectra was developed for the simultaneous quantitative determination and structure analysis of tobacco cellulose from hot water or acid detergent extraction. A reference spectrum of tobacco noncellulose components was subtracted from the spectrum of each sample to obtain a subspectrum of the cellulose components. The NMR spectra in combination with spectral fitting were analyzed in detail and some parameters, such as the content of cellulose, crystallinity, allomorph composition and lateral dimensions for cellulose elementary fibrils and microfibrils were determined. The quantitative results showed that the average recovery was 94.0% with a relative standard deviation (RSD) of 4.6–4.8%. The structure results obtained by the spectral fitting for the cellulose C1-region showed that the main allomorph composition in tobacco cellulose was Iβ. The cellulose crystallinity calculated by the spectral fitting in C4 -region was about 50%. The lateral dimensions for cellulose elementary fibrils and microfibrils were in the range of 3.0–6.0 nm and 6.0–13.0 nm, respectively. Therefore, this NMR method could provide important information on both amount and structure of cellulose in tobacco.