The potential use of tannin-Ca complex derived from tannins as bio-based thermal stabilizer and antioxidant additive for polyvinyl chloride (PVC) was investigated in this work. For this project, Reapak B-NT/7060 was applied as reference thermal stabilizer. Variable compositions: (1, 2, and 3) part per hundred ratio (phr) of tannin-Ca complex in the presence of 10 phr Dioctyl phthalate (DOP) as plasticizer in all PVC formulations were prepared by melt mixing by internal mixer at 165˚C. Tannin-Ca complex was characterized by FT-IR spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) analysis as well as by means of differential scanning calorimetry (DSC). The tannin derivative stabilization efficiency under inert atmosphere was determined by using thermogravimetric analysis (TGA). In addition, its thermal stabilization effect has been assessed in air as oxidizing atmosphere by DSC in dynamic conditions. According to TGA thermograms, the initial degradation temperature (Ti) and optimum degradation temperature (T op) for the main degradation stage of PVC stabilized with this derivative were about 280˚C and 310˚C, respectively. While these were about 255˚C and 293˚C, respectively for PVC stabilized with commercial thermal stabilizer. Global results of TGA, DSC, SEM and EDX show that the tannin-Ca complex provides the best properties and results in stabilizing both against thermal degradation and thermal oxidation degradation of PVC.
In order to find partial substitution for bisphenol A-based commercial epoxy resin (CE), a bio-based epoxy resin was prepared from eucalyptus tannins through a typical glycidylation reaction with epichlorohydrin. The structure of tannin-based epoxy resin (TE) was confirmed by Fourier transform infrared spectroscopy (FTIR) analysis. Herein, mixtures of TE and CE (TE-CE) were prepared using varying loading amounts (20, 40 and 60) wt/wt%of TE. Tannins used here are produced by solid-liquid extraction from the outer bark of eucalyptus tree, mainly consisting of condensed tannins. Through the use of differential scanning calorimetry (DSC) and FTIR techniques, the reactivity of tannin epoxy with and without commercial epoxy resin to form cross-linking network was investigated. TE was successfully cured with aminebased curing agent. Furthermore, compared to commercial epoxy resin (CE), TE exhibited broad low exothermic peak, insignificant cross-linking properties and low curing enthalpy at different levels of curing agent. Moreover, to study the influence of TE substitution on the curing properties of CE, curing behavior of TE-CE mixtures was investigated by DSC. It was found that TE at high loading levels such as 40 and 60 wt/wt% increases slightly the reactivity of CE by decreasing curing characteristics temperatures such as the initial of curing, peak exotherm and completion of curing temperatures. TE can serve as curing accelerator and has a non-desirable impact on the curing performance of CE resin such as curing enthalpy. And up to 20 wt/wt% of CE could be replaced by TE without any significant reduction in the curing behavior of CE.
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