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The success of polyvinyl chloride (PVC) in the processing is critical to its thermal stability. This work presents a novel natural-based and solvent-free thermal stabilizer for PVC, namely calcium-humate (Ca-humate), obtained for the first time from naturally occurring humic acid, an organic-type natural product. Ca-humate and also zinc-humate (Zn-humate) were synthesized through single-step reaction in an aqueous solution. The structures and thermal properties of these derivatives were investigated by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The potential use of humic acid-based derivatives as PVC thermal stabilizers was explored in this work. The degradation behavior of PVC in the presence of Ca- and Zn-humates has been quantified by means of thermogravimetric analysis (TGA). The results demonstrated that the thermal stability of PVC is positively enhanced in the presence of Ca-humate. Zn-humate can effectively stimulate the "zinc burning" of PVC. Humic acid containing both metal ions (Ca/Zn-humates) at various substitution ratios was also synthesized and did not show demonstrated self-synergistic effect. Hydrogen chloride scavenging ability has been proposed to explain the stabilization mechanism by Ca-humates indicating a straightforward way to develop a bio-based additive that can significantly improve the thermal stability of PVC with low cost and high efficiency. [ABSTRACT FROM AUTHOR]

In this study, thermal properties and curing kinetics of composites based on epoxy resin and talc as safer bio-based filler were investigated by differential scanning calorimetry (DSC). The study revealed that the curing profiles of all epoxy composites with talc were slightly identical with that of neat epoxy. Initial curing temperatures and curing rates of all composites were lower than that of neat epoxy. The glass transition temperature (Tg) of the neat epoxy and its composites was also studied using DSC and found at (95, 94.4, 86.5, and 86.6 °C, for pure epoxy, epoxy/talc: 10%, 20%, and 30 wt%, respectively). Kinetic parameters such as activation energy (Eα), pre-exponential factor (A), and curing temperatures at four different heating rates (10, 15, 20, and 25 °C/min) were also evaluated by means of two isoconversional models, namely Kissinger and Ozawa methods. The results obtained by both models showed that the composites have smooth and single exothermic peak which occurs in the same temperature range correspond to that of neat epoxy as well as comparable kinetics parameters. The obtained activation energy values for curing of epoxy with different talc contents calculated by two methods were ranging from 50 to 65 kJ/mol., while the typical value of the neat epoxy resins is 45 kJ/mol. Furthermore, all curing enthalpy values of composites were (127–140 J/g) and lower per the normal range for curing enthalpy of neat epoxy systems (148 J/g). Finally, it was proved that the incorporation of talc in epoxy resin allows manufacturing low-cost composite with acceptable thermal and curing properties. [ABSTRACT FROM AUTHOR]

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 amine-based 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. [ABSTRACT FROM AUTHOR]

The effects of natural polyphenol-based thermal stabilizer synthesized from tannin, a flavonoid-type natural polyphenol, on the processing, rheological and viscoelastic behaviors of polyvinyl chloride (PVC) were investigated in this work. Rheological properties of PVC were studied via three different types of rheometry techniques: torque by an instrumented batch mixer, dynamic oscillating shear rheometry, and dynamic mechanical thermal analysis (DMTA). In the course of the investigation, rotational melt rheological properties in terms of shear complex viscosity, storage modulus, and loss modulus were studied in order to evaluate the performance of tannin–cadmium complex as bio-based PVC additive and as a thermal stabilizer. Experimental results of this study for all PVC formulations with this derivative at loading percentages of 1, 2, and 3 parts per hundred of PVC resin (phr) reveal that the processing and dynamic thermal stability of PVC monitored by torque curves and rheological tests can be enhanced with the addition of this derivative. Rheological behavior of PVC stabilized with tannin derivative is superior or very close to that of PVC stabilized with trade-grade thermal stabilizer. Additionally, DMTA was carried out to see the effect of tannin–cadmium at 2 phr on the thermo-mechanical properties of PVC. All DMTA-related terms such as storage modulus and damping factor and glass transition region point out that the PVC has good viscoelastic properties compared to that of PVC stabilized with commercial thermal stabilizer. [ABSTRACT FROM AUTHOR]

With the aim to understand the effect of bio-polyphenols and calcium-based thermal stabilizer on the rheological and thermal degradation properties of polyvinyl chloride (PVC), this paper practically investigates the rheological and thermal degradation behaviors of PVC using melt rheology method. Thermal degradation study was carried out by monitoring the complex viscosity of PVC using a parallel-plate rheometer run by time sweep mode at 215 °C. The presence of calcium into tannin structure after modification allows the later to have HCl scavenger ability which is considered as an essential property of most PVC thermal stabilizers. The thermal stability monitoring by time sweep rheology measurements was further corroborated by dynamic rheological data, indicating that the increase in loading value of tannin-calcium into PVC from 1 to 3 part per hundred of PVC resin resulted in a notable enhancement of the PVC storage modulus and complex viscosity due to the increased thermal stability, stable chemical structure and a higher level of polymeric chain entanglements. The rheological parameters obtained by frequency sweep at 165 °C in terms of storage and loss moduli and damping factor proved simultaneously that the PVC formulations with tannin-calcium exhibit an obvious improvement in the rheological properties which were comparable to that of PVC stabilized with Reapak B-NT/7060, an industrial-type thermal stabilizer. The results obtained indicated a promising correlation between the thermal stabilization performance of tannin-calcium as a new and fully bio-based thermal stabilizer and the rheological properties of PVC. [ABSTRACT FROM AUTHOR]

In this study, the thermal degradation, dynamic mechanical and morphological properties of polyvinyl chloride (PVC) stabilized with tannin-based epoxy resin and with Ca/Zn-based thermal stabilizers were studied. The efficiency of tannin epoxy resin as thermal stabilizer and additive for PVC was explored in this work using thermogravimetric analysis, dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM) techniques. The obtained TG results reveal that the tannin-based epoxy resin as well as Ca/Zn-based thermal stabilizer has a significant effect on the thermal stability of PVC. The viscoelastic properties of PVC with and without tannin epoxy resin were evaluated by dynamic mechanical thermal analysis technique (DMTA). It was observed that the tannin derivative has an improvement effect on the viscoelastic properties of PVC. The glass transition temperature of PVC/tannin epoxy resin occurs at about 90-93 °C and it is close to that of PVC formulated with Ca/Zn-based commercial thermal stabilizer and without using a plasticizer. DMTA properties show that PVC incorporated with tannin epoxy resin have relatively more recognized flowing stage which occurs smoothly at 160 °C. Other analytical techniques such as SEM and energy dispersive X-ray spectroscopy are employed on PVC morphological properties. Experimental results confirm that the tannin epoxy increase thermal stability of PVC which exhibits smooth and homogenous surface properties compared to the commercial thermal stabilizer. [ABSTRACT FROM AUTHOR]

The effects of tannin-cadmium complex on the thermal and oxidation stability of PVC were investigated. Tannin-cadmium complex has been successfully synthesized and characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray analysis techniques. Thermal degradation and thermal oxidation-degradation behaviors of PVC formulations obtained by thermal mixing method were evaluated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) under inert and oxidizing atmospheres, respectively. The obtained results such as the onset, maximum and final degradation temperatures as well as the degradation rates from TG and DTG curves revealed that the tannin-cadmium has significant impact on the thermal stability of PVC. The experimental data of PVC thermal degradation obtained by DSC studies also clearly showed that the stabilizing efficiency of tannin-cadmium is superior to that of synthetic thermal stabilizer applied as reference. Due to the HCl scavenging and antioxidation activities of tannin-cadmium, the global thermal and morphological properties of PVC stabilized by this product proved the best in morphology and stabilization properties both against thermal and thermal oxidation-degradations. Graphical abstract: [ABSTRACT FROM AUTHOR]

In this study, an attempt is made to investigate the rheological behavior and thermo-rheological properties of PVC in the presence of new tannin based thermal stabilizer. Tannin based epoxy resin has been used as nonmetallic thermal stabilizer additive to study its effects on the rheological behavior of PVC. Frequency sweep tests were applied for monitoring and evaluating the rheological properties of PVC formulations with different levels from this derivative (0, 5, 10, and 20) parts per hundred ratio (phr) using a parallel plate rheometer at 165 °C. The general results indicate that the adding of tannin epoxy resin to PVC can provide enhanced dynamic thermal and process stability and improved the rheological properties. In these formulation systems, the rheological properties of PVC with tannin epoxy resin were more closed to that of PVC without plasticizer so that the plasticization effect of tannin epoxy resin was at very limited level. The rheological properties, such as storage modulus, complex viscosity and damping factor proved simultaneously that the PVC stabilized with tannin derivative exhibits excellent rheological behavior and melt thermal stability properties which were very comparable to that of PVC stabilized with 2 phr Reapak B-NT/7060; a commercial type thermal stabilizer. Graphical abstract: [ABSTRACT FROM AUTHOR]

The current study describes the efficiency of tannins, a flavonoid-type natural polyphenolic compound, and its synergistic effect with commercial-type thermal stabilizer into polyvinyl chloride (PVC). Thermal stabilization of PVC has been assessed in an oxidizing atmosphere by rheometric studies and thermogravimetric analysis (TG). In addition, the effect of this phenolic compound on the dynamic mechanical thermal properties has been quantified with the use of dynamic mechanical thermal analysis (DMTA). Also the polymer surface morphology has been estimated by scanning electron microscopy technique. The main degradation stage of PVC samples in TG curves is slightly increased with increasing the tannin compositions in the polymer system. DMTA measurements were done to investigate the tannin effects on the viscoelastic properties of PVC. Before the glass transition temperature, , of PVC, the DMTA curves show that the values of storage modulus and tan delta of PVC with and without tannins are very similar. In a sequence, after the glass temperature of PVC samples, the DMTA curves confirmed that the PVC samples with tannins have relatively longer flowing stage occurred at lower temperatures by (15-17) °C, as well as lower by about (4-7) °C per that of PVC sample free from tannins. Global results of TG (DTG) and DMTA show that the thermal stability and thermal flexibility of PVC are slightly increased with the incorporation of tannins. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]