DETERMINATION OF THE EFFECT OF EXTRACTED OXYGEN HETEROCYCLE ON THE DEHYDROCHLORINATION OF VINYLIDENE CHLORIDE COPOLYMER:

SOURCE:

Faculty: Physical Sciences
Department: Pure And Industrial Chemistry

CONTRIBUTORS:

Ifiora, U. F.
Ekejiuba, I. O. C.
Okoye, P. A. C.

ABSTRACT:

Thermally induced degradation of vinylidene copolymers has resulted in considerable loss of polymer material during production process through dehydrochlorination (DHC). The incorporation of an oxygen heterocyclic compound into the copolymer reduces this loss, hence the search for an effective oxygen heterocycle, precocene I. CHCl3 solvent was used to extract precocene I from Ageratum conyzoides (AC) and it was separated and isolated using the gas chromatograph (GC) which gave the retention time for precocene I, and afforded the use of cryoscopy (liquid nitrogen) for the isolation of the extractant. Mass spectrometry (MS) combined with the GC yielded the fragmentation pattern for precocene I. Beynons’ Table, National Institute of Standards and Technology (NIST) chemical webbook and Atomic Absorption Spectroscopy (AAS) was used to assign the chromene molecular formula and structure. The precocene I was further characterized using FTIR, density, refractive index and melting point. The incorporation was effected by heating and dissolving the copolymer and additive in solvent methanol inside a three-necked Quickfit flask. Dry N2 gas was used to flush the system of flask and contents during the dissolution. The incorporated product was recovered on cooling and evaporation of excess solvent methanol and a weighed portion was subjected to thermogravimetric analysis to obtain weight loss data. The resulting weight loss data obtained at three different temperatures (170, 180 and 190) °C were subsequently plotted according to first-order kinetics. The rate constants (ki and kp) obtained were thereafter plotted against their respective temperatures to yield thermodynamic parameters. Analysis of the MS fragmentation pattern resulted in the assignment of the chromene molecular formula and structure using appropriate Beynon Table, AAS result and expression for the hydrogen deficiency index. Obtained IR was used along with the assigned formula and the fragmentation pattern from the MS to check the NIST Webbook to authenticate the assigned molecular formula and structure. The structure of precocene I was confirmed using both 1H nmr and 13C nmr spectra supplied by NIST Website. Other parameters used to further characterize precocene I included the density (1.036 g mL-1), refractive index (1.54), and boiling point (292 °C / atmosphere). The GC-MS instrument yielded the retention time of 19.933 min. (GC) necessary for the isolation of precocene I before trapping in liquid N2 , while the MS yielded the fragmentation ions, m/z 190 (M+), m/z 191 (M+1), m/z 175 (base peak), and m/z 132 essential for structure determination. FTIR recorded characteristic prominent lines at 2975, 2890, 1650, 1438, 1275 and 738 cm-1. The AAS recorded the elemental analysis of AC as follow in mg per 100g Ca (372.3), Fe (203.6), Zn (12.4), Al (0.9), Mg (0.2), Pb (0.03), Cr (0.015), N (0.009), Cu (0.007), Co (0.006), Cd (0.002) whereas elements such as K, S, P and Na were not detected. A second possible natural source of precocene I, namely, Moringa oleifera, which was similarly extracted with solvent CHCl3, did not show any chromene content. The thermogravimetric analyzer yielded mass loss data of the copolymer / precocene I combination. Plots of each isothermal mass loss / time data resulted in values of two rate constants of DHC at each of three experimental temperatures, the rate constant for initiation of DHC (ki), and rate constant for propagation of DHC (kp). Values are, for ki, 1.16 x 10-5 s-1 at 170 °C, 2.50 x 10-5 s-1at 180 °C, and 5.58 x 10-5 s-1 at 190 °C. kP values are 2.32 x 10-5, at 170 °C, 4.41 x 10-5, at 180 °C, and 7.60 x 10-5 s-1 at 190 °C. Plots of these ki and kp against temperatures at which they were obtained enabled the derivation of thermodynamic parameters of activation, namely, Arrhenius parameter ∆Ea = 133 kJ mol-1 from the initiation plots; Enthalpy of activation, ∆H# = 98 kJ mol-1; Entropy of Activation, ∆S# = -128 J mol-1 K-1. Secondly, derived thermodynamic parameters indicated a relative lowering of the energy requirement for DHC of the vinylidene chloride / methylacrylate with precocene I additive compared with other additives so far reported in the literature. Established absolute rate data as well as derived thermodynamic parameters which indicated a relative lower energy required for DHC of the vinylidene chloride / methyl acrylate with precocene I additive compared with other additives so far reported in the literature were used to draw conclusions regarding the relative stability of the copolymer / precocene I additive entity.