Polyene Formation Research Articles

Thermal-oxidative stability of PVC compositions modified with a bromine-containing plasticizer-flame retardant

The possibility of creating polymer compositions based on polyvinyl chloride plasticized with a bromine-containing flameretarding plasticizer has been investigated. Their thermostability at introduction of plasticizer with different bromine content was evaluated. The optimal concentrations of bromine in the flame-retarding plasticizer to increase the thermal stability of the polymer composition have been established. It is noted that increasing the concentration of bromine in the flame-retarding plasticizer increases the rate of elimination of hydrogen bromide and slows down the thermal destruction of the polymer matrix. It is shown that during thermo-oxidative degradation of plasticized PVC composite, hydrogen bromide is first eliminated from flame-retarding plasticizer, which accelerates the process of polyene formation and additional cross-linking of polymer macromolecules. An increase in the tensile strength of plasticized compositions at the introduction of optimal dosages of flame-retarding plasticizer was observed.

Extended polyene formation by a cryptic iterative polyketide synthase from Rhodococcus

Investigations of the workings of a newly identified iterative polyketide synthase from Rhodococcus erythropolis PR4 reveal its ability to synthesise extended polyenes.

Enhancement of interfacial adhesion to carbon fibers via electrostatic interaction using polyvinyl chloride as a model matrix

The purpose of this study is to provide a framework for spectroscopic investigation of an enhancement mechanism of the interfacial adhesion using a polyvinyl chloride (PVC) matrix as a model. PVC dissolved in a tetrahydrofuran solution was dropped onto carbon fiber (CF) or glass fiber (GF), and the interfacial shear strength was measured after annealing at various temperatures. The interfacial shear strength of PVC/CF increased significantly with the annealing temperature compared with that of PVC/GF. As characterized by Raman spectroscopy, the polyene content (an indicator of PVC degradation) in bulk PVC was positively correlated with the interfacial shear strength. PVC radicals were not detected at the annealing temperature in the electro spin resonance spectroscopy. It was demonstrated that the interaction between the ions (C+Cl−) formed during the decomposition of PVC (formation of polyene) and the π electrons in the benzene of CF; the cation–π interaction is attributable to the enhancement of the interfacial shear strength.

Optimization of thermal degradation performance of plasticized poly(vinyl chloride)‐boron composite films using response surface methodology

AbstractThis work aims to statistically assess the dehydrochlorination of plasticized poly(vinyl chloride) (p‐PVC) films produced using boron waste sludge, heat stabilizer mixture (Ca‐ZnSt2), and plasticizer (dioctyl terephthalate). This study also focuses on providing information about the effect of boron waste sludge (BSW), heat stabilizer, and plasticizer amounts on the degradation of the films to enhance the thermal stability of flexible p‐PVC formulations. Experiments were designed using the Box‐Wilson method. The polyene formation and discoloration caused by the degradation were measured by UV spectroscopy and colorimetry, respectively. These parameters were optimized using the response surface methodology. An analysis of variance was performed to assess statistically significant differences between the parameters on p‐PVC degradation by using the Design Expert 13 statistical program. The yellowness index and amount of polyene formed differed among the films, and the film prepared at the midpoint of all parameters was determined to have greater stabilizing efficiency than the others. In this study, an effort has been made to shed light on the improvements in thermal stability in PVC. Results will serve to protect the environment via the data provided to the producers. The use of boron waste will contribute to the environment and the economy.

Iodine-Mediated Coupling of 2,2,2-Trifluorodiazoethane and Alkynes To Access Bistrifluoromethylated 1,3,5-Trienes.

Multi-component reaction of higher degree ultilization of diazo molecules for polyene formation is highly intriuging but still underexplored. We present herein an unprecedented coupling of 2,2,2-trifluorodiazoethane and aryl alkynes mediated by iodine under visible light. The multi-component reaction involving two diazo units and two alkyne units provides a straightforward and step-economic access to bistrifluoromethylated 1,3,5-trienes in high stereoselectivity by creation of three C═C bonds in a single step under mild conditions.

Raman spectroscopic detection of polyene-length distribution for high-sensitivity monitoring of photo- and thermal degradation of polyvinylchloride

The degradation of the ubiquitous polyvinylchloride (PVC) material under the influence of various factors is known to result commonly in polyene formation. Such polyene defects occur in the form of conjugated aliphatic chains with different lengths and contents, and their sensitive and length-specific monitoring is important for the assessment of PVC degradation. Here, we report on the resonance-enhanced Raman signatures of polyene sequences of varying lengths in photo- and thermally degraded PVC films. The lengths of polyene segments have been estimated based on their selectively enhanced and spectrally resolved contributions to the Raman bands assigned to the stretching vibrations of conjugated double carbon bonds. Using deconvolution analysis of a characteristic Raman band of polyenes, we especially demonstrate that the spectral signatures of polyene segments corresponding to other various electronic resonances contribute to the Raman spectral envelope observed at a given resonant excitation. In most cases, we observe an asymmetric band profile, indicating an asymmetric length distribution of polyene defects formed in PVC films upon a mild degradation extent less than 1% mass loss. We also demonstrate that the wavenumber (ν1) of the stretching vibrations of single carbon bonds in the polyene sequences of degraded PVC is inversely related to the number (n) of double carbon bonds by an empirical equation n=476·cm-1/ν1-1082·cm-1. To the best of our knowledge, while considering different laser excitations spanning the range of possible electronic resonances from blue to near-infrared for Raman investigations, the present work includes (i) the first Raman spectral deconvolution study for the 532.0 nm excitation wavelength used in most portable Raman probes nowadays and (ii) the screening of polyene defects also beyond the red edge of the visible spectrum and the evidence of a resonance-enhanced polyene signal at 647.1 nm. Important new information has been obtained about polyene lengths and spectral distribution for PVC, whose critical physical properties ranging from flexibility to electrical resistance are severely affected by polyene formation.

Silver nanoparticles/polyvinyl alcohol film: studies of thermal characterization, AFM and corrosion protection by electrodeposition on 304L stainless steel

A composite polymeric system consisting of silver nanoparticles and polyvinyl alcohol (nAg/PVA) was characterized by thermal analysis and compared to the two basic components, namely the silver nanoparticles (nAg) and polyvinyl alcohol (PVA). The main stage of decomposition of PVA and nAg/PVA takes place in temperature range between 210 and 325 °C, when the thermal processes consist of dehydroxylation reaction and polyene formation, macromolecular chain cleavage and oxidation reactions. The finalization of the PVA decomposition reaction takes place around 420 °C. At temperature values higher than 325 °C, the composite degradation follows another trend compared to PVA, indicating the presence of silver nanoparticles inserted into polymer matrix. Due to its adsorption and inhibitory properties and relatively good thermal stability at temperature lower than 200 °C, the nAg/PVA composite was applied as protective coating against corrosion of 304L stainless steel. Over a prolonged time, the coating can deteriorate affecting the surface characteristics. To evaluate the stainless steel surface morphology and nAg/PVA electrochemical stability over time, the atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS) were used. AFM and EIS confirmed that on the stainless steel surface, a relatively uniform and smooth composite film with a good electrochemical stability were formed, ensuring a corrosion protection performance (P%) of 81.7%.

Enhanced alteration of poly(vinyl chloride) microplastics by hydrated electrons derived from indole-3-acetic acid assisted by a common cationic surfactant

In this study, a new photo-irradiated reductive dechlorination pathway and the underlying transformation mechanism are described for poly(vinyl chloride) microplastics (PVC-MPs). PVC-MPs underwent photo-reductive dechlorination process with the release of chloride ions. This reaction could be facilitated in the presence of indole-3-acetic acid (IAA) and hexadecyltrimethylammonium bromide (CTAB) under neutral pH and simulated sunlight irradiation conditions. Electrostatic interaction between IAA and CTAB produced neutral IAA/CTAB complex, which might account for the enhanced adsorption of IAA on PVC powders. Upon photo-irradiation, the adsorbed IAA was excited to generate hydrated electrons (eaq−), which could pass through a shorter distance to PVC-MP surface than that derived from homogeneous IAA molecules in aqueous solution. Transient spectra of laser flash photolysis provided direct evidence for the generation of eaq−, which supported the proposed dechlorination mechanism. Based on the results of attenuated total reflectance/Fourier transform infrared (ATR/FTIR) and Raman spectra, C-Cl bond cleavage and polyene formation were involved in the structural transformation of PVC-MPs. Due to the hydrophobic effects and π-π interactions between aromatic rings and polyene structures in PVC-MP surface, the PVC-MP powders irradiated in the presence of IAA/CTAB showed an enhanced sorption for both hydrophobic and hydrophilic aromatic chemicals.

Plastics in Heritage Collections: Poly(vinyl chloride) Degradation and Characterization

Museums and galleries house increasingly large collections of objects and contemporary art made of plastic materials, many of which undergo rapid material change. The main degradation processes of poly(vinyl chloride) (PVC) are elimination of HCl and plasticizer migration or leaching. This results in visible discolouration, stickiness and cracking. Degradation is known to be a multi-stage process that includes HCl elimination, formation of conjugated polyenes and cross-linking. Elimination of HCl begins due to structural irregularities (allylic and tertiary chlorides) and results in the formation of polyenes. When at least 7 conjugated double bonds are present, discolouration of PVC becomes visible. Non-invasive techniques, such as IR and Raman spectroscopy are used for polymer identification and plasticizer quantification. Plasticizer degradation and particularly the late stages of PVC degradation can be investigated using SEC, GC-MS, TGA and DSC. Studies in heritage collections have revealed that, apart from HCl, PVC objects emit 2-ethylhexanol and other volatile degradation products, however, there is currently no indication that HCl is emitted at usual indoor conditions. There seems to be a general lack of systematic research into PVC degradation at the conditions of storage and display, which could result in the development of dose-response functions and in the development of preventive conservation guidelines for the management of PVC collections.

Photo-aging of polyvinyl chloride microplastic in the presence of natural organic acids

In this study, a new photo-aging pathway in the aquatic environments and the underlying transformation mechanism were described for polyvinyl chloride microplastic (PVC-MP). Our results indicated that the photo-aging of PVC-MP was strongly dependent on particle size and the aging reaction could be facilitated in the presence of low-molecular-weight organic acid (LMWOA) and LMWOA-Fe(III) complex under simulated and natural sunlight irradiation and ambient conditions. The hydroxyl radical (OH•) generated from the photolysis of LMWOA or its ferric complexes played a dominant role in enhancing PVC-MP degradation. In situ Fourier transform infrared and Raman spectroscopic techniques and theoretical calculations further confirmed that C–Cl bond cleavage and formation of polyene and carbonyl underwent on the PVC-MP surface, especially in the presence of LMWOA and LMWOA-Fe(III). Moreover, PVC-MP surface oxidation also led to the increase of the specific surface area and affinity towards water as indicated by the results of scanning electron microscopy, Brunauer-Emmett-Teller tests and contact angles for water, which would further enhance the adsorption of polar contaminants on PVC-MP and thus increase the health risk of PVC-MP on aquatic organisms.

Evaluation of the thermal stabilization behavior of hydrotalcite against organic stabilizers for plasticized PVC films

This study focuses on the systematic comparison of the thermal stabilization behavior of the hydrotalcite which is present in the nature and is non-toxic, with organic stabilizers (mixed metal salts, maleimide and tri-nonyl phenyl phosphite) having high stabilizing efficiency. For the purpose of this study, first plastisols were prepared by mixing plasticizer and thermal stabilizers into the PVC resin. Then films were obtained from plastisols, which were applied on a glass plate as 150μ thick films with the help of a film applicator. The films were cured for 15 min in oven at 160 °C to produce plastigel films. The stabilization behavior of these films was measured by applying various stabilization testing methods: thermal aging test, oxidation index, polyene formation measurement and discoloration. Thermal aging studies for these plastigel films were carried out at 100 and 150 °C up to 420 min. Oxidation index values are associated with oxidized surface layer that is formed after the aging and degradation of the films, which are determined by FTIR spectroscopy. Thermal stability behavior in terms of concentration of polyenes formed due to the released HCl has been investigated by UV–visible spectroscopy. Color changes of the degraded films were followed by observed colorimetry. According to the results, number of the polyenes for all degraded films increased with increasing time and temperature. The results have proved the greater stabilizing efficiency of hydrotalcite relative to that of the thermal stabilizers in terms of the number of the conjugated double bond, polyene concentration, polyene formation rate and change in color. It is believed that the results will contribute to the thermal stability of PVC by different stabilizers and blends, and an effort has been made in this article to throw light on this issue.

Reconstitution of a Type II Polyketide Synthase that Catalyzes Polyene Formation

AbstractWhile type II polyketide synthases (PKSs) are known for producing aromatic compounds, a phylogenetically new subfamily of type II PKSs have been recently proposed to synthesize polyene structures. Here we report in vitro analysis of such a type II PKS, IgaPKS for ishigamide biosynthesis. The ketoreductase (Iga13) and dehydratase (Iga16) were shown to catalyze the reduction of a β‐keto group and dehydration of a β‐hydroxy group, respectively, to form a trans double bond. Incubation of the acyl carrier protein (Iga10), the ketosynthase/chain length factor complex (Iga11–Iga12), Iga13 and Iga16 with malonyl and hexanoyl‐CoAs and NADPH followed by KOH hydrolysis resulted in the formation of four unsaturated carboxylic acids (C8, C10, C12, and C14), indicating that IgaPKS catalyzes tetraene formation by repeating the cycle of condensation, keto‐reduction and dehydration with strict stereo‐specificity. We propose “highly reducing type II PKS subfamily” for the polyene‐producing type II PKSs.

Reconstitution of a Type II Polyketide Synthase that Catalyzes Polyene Formation.

While type II polyketide synthases (PKSs) are known for producing aromatic compounds, a phylogenetically new subfamily of type II PKSs have been recently proposed to synthesize polyene structures. Here we report in vitro analysis of such a type II PKS, IgaPKS for ishigamide biosynthesis. The ketoreductase (Iga13) and dehydratase (Iga16) were shown to catalyze the reduction of a β-keto group and dehydration of a β-hydroxy group, respectively, to form a trans double bond. Incubation of the acyl carrier protein (Iga10), the ketosynthase/chain length factor complex (Iga11-Iga12), Iga13 and Iga16 with malonyl and hexanoyl-CoAs and NADPH followed by KOH hydrolysis resulted in the formation of four unsaturated carboxylic acids (C8 , C10 , C12 , and C14 ), indicating that IgaPKS catalyzes tetraene formation by repeating the cycle of condensation, keto-reduction and dehydration with strict stereo-specificity. We propose "highly reducing type II PKS subfamily" for the polyene-producing type II PKSs.

Assessment of degradation of plasticized poly(vinyl chloride) films through polyene formation under isothermal conditions

ABSTRACTThe aim of this work is to assess the degradation of flexible poly(vinyl chloride) (PVC) films produced using orthophthalate based and recently introduced nonorthophthlate plasticizers which have compliance with recent environmental regulations. The plasticized PVC films were subjected to several heat treatments at 85–160 °C up to 420 min. Ultraviolet–visible spectroscopy was utilized to follow polyene formation upon dehydrochlorination of PVC. The amount of polyenes formed exhibited difference amongst the films those plasticized with diethyl hexylphthalate, diisodecyl phthalate, dioctyl terephthalate (DOTP), and diisononyl 1,2‐cyclohexanedicarboxylic acid (DINCH). The order of polyene concentration formed at the utmost level severe heat treatment is in line with the molecular weight ranking from highest to lowest, as the films with diisodecyl phthalate > DINCH > DOTP > diethyl hexylphthalate. Discoloration assessed in terms of yellowness index revealed that the films having recently introduced plasticizers as DOTP and DINCH were competing well with the films having orthophthalate based plasticizers. Scanning electron microscopy images revealed that the longer times for gelation during their production would improve the maturation of the films although they are already coherent and strong. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46092.

Colorimetric analysis of thermal degradation of plasticized poly(vinyl chloride): Potentials and limitations

The kinetics of formation and consumption of polyenes is studied by measuring the change in color coordinates and color difference during the thermal aging of plasticized poly(vinyl chloride) at a temperature of 60–130°С under vented conditions and in a closed volume. It is shown that the initial rate of accumulation and the quasi-stationary concentration of polyenes at 100–130°С grow with temperature. The energy of activation of dehydrochlorination is 70 ± 3 kJ/mol. At a lower temperature (60–80°С), the intensity of color of the samples that are preliminarily aged at increased temperatures decreases. The reduction in the rate of this process with temperature in the range of 60–80°С and the presence of the quasi-stationary level at 100–130°С are related to competition of the processes of formation and oxidation of polyenes.

Formation of linear polyenes in poly(vinyl alcohol) films catalyzed by phosphotungstic acid, aluminum chloride, and hydrochloric acid

Formation of linear polyenes–(CH=CH)n–via acid-catalyzed thermal dehydration of polyvinyl alcohol in 9- to 40-µm-thick films of this polymer containing hydrochloric acid, aluminum chloride, and phosphotungstic acid as dehydration catalysts was studied by electronic absorption spectroscopy. The concentration of long-chain (n ≥ 8) polyenes in films containing phosphotungstic acid is found to monotonically increase with the duration of thermal treatment of films, although the kinetics of this process is independent of film thickness. In films containing hydrochloric acid and aluminum chloride, the formation rate of polyenes with n ≥ 8 rapidly drops as film thickness decreases and the annealing time increases. As a result, at a film thickness of less than 10–12 µm, long-chain polyenes are not formed at all in these films no matter how long thermal duration is. The reason for this behavior is that hydrochloric acid catalyzing polymer dehydration in these films evaporates from the films during thermal treatment, the evaporation rate inversely depending on film thickness.

Polyene Formation Catalyzed by Phosphotungstic Acid and Aluminum Chloride in Thin Films of Poly(Vinyl Alcohol)

Formation of linear polyenes –(CH=CH) n – during thermal dehydration of thin layers (9–20 μm) of poly(vinyl alcohol) containing phosphotungstic-acid and aluminum-chloride catalysts was investigated. It was found that the concentration of long-chain (n ≥ 8) polyenes in films containing phosphotungstic acid increased smoothly with increasing annealing time although the kinetics of the dehydration were independent of the film thickness. The polyene (n ≥ 8) formation rate in films containing aluminum chloride dropped quickly with decreasing film thickness and increasing annealing time. As a result, long-chain polyenes practically did not form regardless of the annealing time for a film thickness of 11 μm.

FTIR ANALYSIS OF IRRADIATED FOOD-GRADE PVC FILMS

This work aimed to investigate the influence of ionizing radiation (gamma radiation and accelerated electrons) at commercial doses of 1, 2 and 4 kGy on optical properties of PVC films used as food packaging. FTIR was carried out for range of 4000 to 400 cm -1 by direct measurement. Polyene formation was measured with spectrophotometry at wavelength of 400 nm. FTIR of irradiated samples reveals reduction of absorbance of carbon-hydrogen (methylene) and carbon-chloride bands suggesting PVC scission due to dehydrochlorination reactions. Furthermore, polyene formation demonstrated increase on irradiated samples because of scission reactions on food-grade PVC films. This observation confirms polymeric radiolysis mechanisms promoted by gamma-rays or accelerated electrons.

Formation of Linear Polyenes in Thermal Dehydration of Polyvinyl Alcohol, Catalyzed by Phosphotungstic Acid

In order to obtain linear polyenes in polyvinyl alcohol films via acid-catalyzed thermal dehydration of the polyvinyl alcohol, we used phosphotungstic acid as the catalyst: a safe and heat-stable solid chemical compound. We established that phosphotungstic acid, introduced as solid nanoparticles into polyvinyl alcohol films, is a more effective dehydration catalyst than hydrochloric acid, since in contrast to HCl it does not evaporate from the film during heat treatment.

Photothermally controlled structural switching in fluorinated polyene-graphene hybrids.

Fluorination of graphene enables tuning of its electronic properties, provided that control of the fluorination degree and of modification of graphene structure can be achieved. In this work we demonstrate that SF6 modulated plasma fluorination of monolayer graphene yields polyene-graphene hybrids. The extent of fluorination is determined by the plasma exposure time and controlled in real time by monitoring the change in the optical response by spectroscopic ellipsometry. Raman spectroscopy reveals the formation of polyenes in partially fluorinated graphene (F/C < 0.25), which are responsible for changes in conductivity and for opening a transport gap of ∼25 meV. We demonstrate that the cis- and trans-isomers of the polyenes in graphene are tunable using the photothermal switching. Specifically, the room temperature fluorination results in the cis-isomer that can be converted to the trans-isomer by annealing at T > 150 °C, whereas photoirradiation activates the trans-to-cis isomerization. The two isomers give to the polyene-graphene hybrids different optical and conductivity properties providing a way to engineer electrical response of graphene.