Synthesis, characterization and Stydy thermal stabilization effect of calcium complex of anthocyanin on the poly (vinyl chloride)

In this study, calcium complex of anthocyanin was synthesized from anthocyanin, a flavonoid type natural phenolic product, which was extracted from eggplant peel. The structure of Ca-anthocyanin was characterized by FTIR spectroscopy. Its efficiency as bio-based thermal stabilizer to stabilize poly (vinyl chloride) was investigated and compared to that of Reapak B-NT/7060, a Ca/Zn-based commercial stabilizer. The influence of Ca-anthocyanin complex on the thermal degradation reaction of PVC was monitored by differential scanning calorimetry (DSC). The results indicated that the Ca-anthocyanin complex is an efficient thermal stabilizer and it reduces the rate of dehydrochlorination reaction of PVC already at a concentration as small as 2 phr, part per hundred of PVC resin. The thermal degradation reaction of PVC through the first degradation stage is clearly limited by the addition of Ca-anthocyanin complex as single (primary) stabilizer. Its efficiency is similar to that of Reapak B-NT/7060 used as reference stabilizer and it can enhance the performance of commercial stabilizer when used as co-stabilizer at mixing ratio (1:1). This study has allowed verifying and validating the usefulness of environmental friendly thermal stabilizer for PVC with very evident stabilization effect.

Thermal Stability of Nanosilica-Modified Poly(Vinyl Chloride)

The thermal stability of PVC with 1 wt % of spherical porous nanosilica, prepared by roll milling at processing time varied from 1 to 20 min, was investigated by means of visual color changes, Congo red, and thermogravimetric tests (TGA and DTG), as a function of rolling time and composition of PVC matrix. The melt flow rate (MFR) measurements were realized to identify the degradation-induced changes of processing properties. A high level of gelation of the PVC matrix for all samples was verified by DSC (differential scanning calorimetry). It was found that the addition of porous nanosilica to absorb a certain volume of HCl, produced by dehydrochlorination reaction, leads to an improvement of thermal stability, an effect observed in a form of minor color changes of the samples, lower evolution of gas hydrogen chloride, and slight changes of the MFR value. It was demonstrated that the TGA measurements are not sufficiently sensible to detect the degradation of PVC at the processing conditions, i.e., at the temperature equal to 220 °C and below this temperature.

Theoretical insight on the treatment of β-hexachlorocyclohexane waste through alkaline dehydrochlorination

The occurrence of 4.8–7.2 million tons of hexachlorocyclohexane (HCH) isomers stocked in dumpsites around the world constitutes a huge environmental and economical challenge because of their toxicity and persistence. Alkaline treatment of an HCH mixture in a dehydrochlorination reaction is hampered by the low reactivity of the β-HCH isomer (HCl elimination unavoidably occurring through syn H–C–C–Cl arrangements). More intriguingly, the preferential formation of 1,2,4-trichlorobenzene in the β-HCH dehydrochlorination reaction (despite the larger thermodynamical stability of the 1,3,5-isomer) has remained unexplained up to now, though several kinetic studies had been reported. In this paper, we firstly show a detailed Density Functional study on all paths for the hydroxide anion-induced elimination of β-HCH through a three-stage reaction mechanism (involving two types of reaction intermediates). We have now demonstrated that the first reaction intermediate can follow several alternative paths, the preferred route involving abstraction of the most acidic allylic hydrogen which leads to a second reaction intermediate yielding only 1,2,4-trichlorobenzene as the final reaction product. Our theoretical results allow explaining the available experimental data on the β-HCH dehydrochlorination reaction (rate-determining step, regioselectivity, instability of some reaction intermediates).

Kinetics of poly(vinyl chloride) thermal degradation by ionizing radiation

In this study, the relationship between ionizing radiation treatment and thermal degradation kinetics of Poly (vinyl chloride) (PVC) polymer film was investigated. The unirradiated and 25 kGy irradiated samples treated with gamma rays or electron beam radiation were submitted to thermogravimetric analysis (TGA) at different heating rates (10 – 30 K.min-1). The TGA data was used to obtain the apparent activation energy values (Ea) according to Flynn-Wall-Ozawa method. TGA analysis suggested that electron beam radiation promotes a slight increase on maximum temperature for dehydrochlorination reaction on PVC. Gamma-rays irradiation caused a small reduction of maximum temperature of HCl evolution of PVC. Thermal degradation kinetics results showed that 25 kGy irradiated samples presents an apparent activation energy values from 104 - 109 KJ.mol-1. The apparent Ea values suggested that 25 kGy gamma radiation or 25 kGy electron beam radiation convert PVC polymer films more prone to HCl evolution due to radiolysis of polymer. Evaluation of the Ea values by Flynn-Wall-Ozawa method allows a good analytical instrument to comprehend dehydrochlorination reaction on irradiated PVC polymer films.

SYNTHESIS OF GLYCIDYL AND THIOGLYCIDYL ETHERS OF DIACETYLENE SERIES AND THEIR USE AS A MODIFIER OF PHENOL-FORMALDEHYDE OLIGOMERS

It has been shown that the chlorine-containing unconjugated enyne alcohols react with epichlorohydrin in the presence of boron trifluoride etherate with formation of chlorohydrines, which further without their isolation, under the action of potassium hydrochloride are dehydrochlorinated with formation of the corresponding glycidyl ethers. Under the action of an alcoholic solution of potassium hydroxide at temperature of 75-80 °С on synthesized chlorine-containing ethers the dehydrochlorination reaction on double С=С bond proceeds and glycidyl ethers of 1,4-diine series are formed. It has been revealed that the synthesized glycidyl ethers are the very reactive compounds. In patricular, it has been shown that the ethers of 1,4-diine series with the participation of oxirane ring undergo the reaction with thiurea medium of methanol at 30-35 °С, forming the corresponding tyrants. The data of IR- and NMR-spectra of the prepared compounds have been presented and their modifying properties in relation to phenol-formaldehyde oligomers in acidic and alkaline media have been revealed. The prepared modified oligomers are the products of liquid-viscous consistency, soluble in acetone, tetrahydrofuran, dimethyl formamide and dioxane. It has been proved by the carried out analyses that the prepared PhFOs, modified by glycidyl and thiglycidyl ethers of diacetylene series are not mechanical mixtures of phenol, formaldehyde and modifier. On the basis of obtained results the formation mechanism of modified resol and novolac PhFO has been also revealed. It has been established that the physical-chemical and physical-mechanical parameters of the prepared phenol-formaldehyde oligomers modified by modifiers proposed by us, in comparison with unmodified ones, are improved. From the proposed diglycidyl and thiodiglycidyl ethers for the modification of PhFO the best results on all parameters are achieved at modification with thioglycidyl ether of diacetylene series.

Construction of chain segment structure models, and effects on the initial stage of the thermal degradation of poly(vinyl chloride)

Comparing two models, the dehydrochlorination reaction of PVC was predominantly initiated at the internal allylic chlorine sites, further promoting degradation.

Insights into the electron-donating and withdrawing effect of the functional groups on mechanochemical dehydrochlorination reactions

The effect on electron depletion in a partially fluorinated ligand has been evaluated in a dehydrochlorination reaction by converting outer sphere adducts into a coordination complex using experimental and DFT data.

Dehydrochlorination mechanism of γ-hexachlorocyclohexane degraded by dehydrochlorinase LinA from Sphingomonas paucimobilis UT26

The biotransformation pathway from γ-HCH to 1,3,4,6-TCDN catabolized by dehydrochlorinase LinA contains two discontinuous dehydrochlorination reactions and a conformational transition for the product of the first dehydrochlorination reaction.