| The work in this dissertation investigate the oxidation kinetics of abietic acid and neoabietic acid in gum rosin and pine oleoresin with the aim of solving the problems of deterioration in quality, safety and other properties caused by the oxidation of rosin and modified rosin. The research on the oxidation of these materials at room temperature has played a significant role in understanding the theory of gum rosin and its derivatives in manufacturing, storage and application processes, and would lay a theoretical foundation for further studies on the weatherability of gum rosin and its derivatives similarly. The results and conclusions drawn are as follows.(1) The quantitative analysis of abietic acid and neoabietic acidBoth t test and Ftest were used to investigate and compare the variances of the UV standard addition method, the UV improved method and gas chromatography method. The result indicated that both of improved UV method and UV standard addition method were suitable for quantitative analysis of abietic acid in gum rosin and pine oleoresin. GC method and the UV standard addition method can’t be applied as a rapid measurement for kinetic analysis, although they are the accurate methods for quantitative analyzing of abietic acid in gum rosin and pine oleoresin. The UV Improved method is more suitable for kinetic analysis.The fast analysis method for detecting the mole of neoabietic acid was established via the UV improved method. The plot of absorption(A1) against the mole (n1) was linear:A1=0.7390×l06n1+0.2403, with0.9995of correlation coefficient of standard curve and in the range of0.6420×10-6to3.854×10-6mol. The method has good precision, stability and recovery. The quantitative analysis method of the solid abietic acid on the flat membrane reactor was established by using the Fourier transform infrared spectroscopy (FTIR). The flat membrane reactor was FTIR detection membrane simultaneously. A characteristic band of hydroxyl function group at3400cm-1during the oxidation process has been illustrated by the FTIR spectrum.(2) The oxidation reaction and its kinetics of abietic acidThe oxidation kinetics of abietic acid was studied under254and365nm ultraviolet irradiation by using the UV improved method. The photo-oxidation of abietic acid fitted apparent first-order kinetics under irradiation at the two wavelengths. The relationship between the rate constant (kb) and light intensity (I) was linear under irradiation at two wavelengths. Under365nm UV irradiation, the linear equations were kb=0.4329×l0-4I+0.2044×10-2, kb=0.4871×l0-4I+0.2546×10-2, and kb=0.602×l0-4I+0.4308×10-2at20,25, and35℃, respectively. Under254nm UV irradiation, the linear equations were kb=1.370×l0-4I+0.5041×10-2, kb=1.393×l0-4I+0.3366×10-2, and kb=1.453×l0-4I+0.8058×10-2at the same temperatures, respectively. Under the same reaction conditions, the kinetic constants of abietic acid under254nm UV irradiation were much higher than those under365nm UV irradiation.The initial quantum yield of abietic acid did not vary with the UV light intensity. At20℃, the quantum yield under254and365nm UV irradiation were0.471and0.1681on average. Abietic acid more easily oxidized under254nm than under365nm UV irradiation.The oxidation processes of abietic acid were investigated by FTIR. FTIR observed the characteristics of resultant peaks at3400cm-1, which was OH stretching band. The conversions of resultant (a) could be determined according to the changes of peak area. The oxidation kinetic model using the conversions of resultant as the parameter is set up. FTIR is used to measure the conversion changing with reation time during the oxidation at different temperatures. The result shows the thermal oxidation reaction order of abietic acid is first order. (3) The oxidation reaction and its kinetics of neoabietic acidThe thermal oxidation of neoabietic acid was an apparent first-order-kinetic process, and the rate constants of oxidation were0.2437×10-2,0.4037×10-2,0.8285×10-2and1.681×10-2min-1at25,30,40, and50℃, respectively. The reaction activation energy was61.39kJ·mol-1.The photo-oxidation of neoabietic acid fitted apparent first-order kinetics at25,30and40℃, under254and365nm UV irradiation. The relationship between the rate constant (k) and light intensity (I) was linear under irradiation at two wavelengths. Under365nm UV irradiation, the linear equations were k=0.4665×l0-4I+0.2624×10-2, k=0.5149×l0-4I+0.4171×10-2, and k=0.6355x10-7+0.8627×10-2at25,30, and40℃, respectively. Under254nm UV irradiation, the linear equations were k=0.8735×l0-4I+0.4046×10-2,k=0.8943×l0-4I+0.5426×10-2and A=1.063×l0-4I+0.7217×10-2at the same temperatures, respectively. Under the same reaction conditions, the oxidation rate constants of neoabietic acid under254nm UV irradiation were much higher than those under365nm UV irradiation. The temperature was found to have a minimal effect on the rate constant when the light intensity was fixed. The rate constant for photo-oxidation of neoabietic acid were much larger than for thermal oxidation at the same temperature. Decreasing the intensity of illumination might ease the oxidation of neoabietic acid effectively. The reaction activation energies decreased with increased light intensities.The initial quantum yield of neoabietic acid did not vary with the UV light intensity. At25℃, the quantum yield under254and365nm UV irradiation were0.1315and0.1722on average. The values approximated to the quantum yield value of abietic acid of0.1681, under365nm UV irradiation at20℃.(4) The oxidation kinetics of gum rosinThe UV improved method for detecting the mole of gum rosin was established by using gum rosin as standards. The linear equations of gum rosin and its oxides were Arl=0.6106×106nr1+0.3397and Ar2=0.3911×106nr2+0.0238. The oxidation kinetics of gum rosin was investigated. The change of the mole of gum rosin during the oxidation process was determined by using the working curves of abietic acid and gum rosin, respectively. The thermal oxidation of gum rosin was an apparent first-order reaction with two methods. Using the working curve of gum rosin, the reaction activation energy was83.97kJ·mol-1in the range of30to50℃.In the working curves of abietic acid and gum rosin, the photo-oxidation of gum rosin fitted apparent first-order kinetics under near-ultraviolet irradiation, in the range of35-45℃, respectively. The relationship between the rate constant and light intensity was linear under365nm UV irradiation. In the working curves of abietic acid, the linear equations were kb=0.9512×l0-4I+0.1035×10-2, kb=1.176×l0-4I+0.1302×0-2, and kb=1.403×l0-4I+0.2392×10-2at35,40, and45℃, respectively. In the working curves of gum rosin, the linear equations were kr=0.9489×l0-4I+0.7273×10-3,kr=1.144×l0-4I+0.1089×10-2, and kr=1.360×l0-4I+0.2114×10-3,at the same temperatures, respectively. The influence of temperature on the rate constant was much less than that of light intensity. The photo-oxidation of gum rosin was affected by the near-ultraviolet irradiation. Therefore, gum rosin oxidation can be significantly suppressed by effectively controlling the light incident. Both methods had resemblance in the change regularities, and can be used to study the oxidation kinetics of gum rosin.The initial quantum yield of gum rosin did not vary with the UV light intensity. In the working curves of abietic acid and gum rosin, the quantum yields were0.3318and0.3258on average, under365nm UV irradiation at35℃.(5) The oxidation kinetics of pine oleoresinThe UV improved method for detecting the mole of pine oleoresin was established by using pine oleoresin as standards. The linear equations of gum rosin and its oxides were Ap1=0.3985×106np1)+0.0346and AP2=0.1869×106np2+0.1644.The oxidation kinetics of pine oleoresin was studied. The change of the mole of pine oleoresin during the oxidation process was ascertained with the utilization of working curves of abietic acid and pine oleoresin, respectively. The thermal oxidation of pine oleoresin was an apparent first-order reaction with two methods. In the working curve of pine oleoresin, the reaction activation energy was105.2kJ-mol"1in the range of30to50℃.In the working curves of abietic acid and pine oleoresin, the photo-oxidation of pine oleoresin fitted apparent first-order kinetics under near-ultraviolet irradiation, in the range of35-45℃, respectively. The relationship between the rate constant and light intensity was linear under365nm UV irradiation. In the working curves of abietic acid, the linear equations were kb=0.4608×l0-4I+0.4477×10-3, kb=0.5209×l0-4I+0.5519×10-3, and kb=0.5405×l0-4I+1.326×10-3at35,40, and45℃, respectively. In the working curves of pine oleoresin, the linear equations were ko=0.4783×l0-4I+0.6747×10-3, ko=0.5285×l0-4I+1.037×10-3, and ko=0.5529×l0-4I+1.743×10-3at the same temperatures, respectively. The influence of temperature on the rate constant was much less than that of light intensity. The photo-oxidation of pine oleoresin was affected by the near-ultraviolet irradiation. Therefore, pine oleoresin oxidation can be significantly inhibited by effectively controlling the light incident on the pine oleoresin. Both methods had resemblance in the change regularities, and can be used to study the oxidation kinetics of pine oleoresin.The initial quantum yield of pine oleoresin did not vary with the UV light intensity. In the working curves of abietic acid and pine oleoresin, the quantum yields were0.2933and0.3072on average, under365nm UV irradiation at35℃. |
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