Polyene Sequences Research Articles

Raman Analysis of Polyvinyl Chloride Degraded under Different Temperature Conditions

In this work, the Raman spectroscopy method was used to study changes in the composition of polyvinyl chloride (PVC) during its degradation. Traditionally, such changes are analyzed optically due to the fact that during degradation, polyene sequences of different lengths are formed in the PVC structure, which change many properties of the material, including optical ones. The Raman spectroscopy method chosen in this work is characterized by high accuracy and speed of analysis, as well as the ability to diagnose the presence of polyenes in extremely low concentrations. Undegraded PVC films and films degraded in various temperature regimes are used as study samples. It is shown that the Raman spectra of the samples can be used to analyze both the length of the formed polyenes and their length distribution. It is found that the length distribution of polyenes depends on the conditions of thermal degradation of the samples.

Surface Chalking upon Weathering of Dark-Colored PVC Articles and Relevant Stabilizers.

PVC items (38% carbon atoms w/w) are environmentally friendly as, unlike polyolefins (86% carbon atoms w/w), they are mainly based on chlorine, one of the most abundant elements on Earth and, so, less based on fossil resources. However, in the eco-design context, articles' durability plays a crucial role, contributing to the enhancement of their sustainability. In this framework, the research on additives capable of increasing the weatherability of outdoor articles is essential. The theory section of the paper reviews the mechanisms of weathering that lead to PVC degradation and undermine the durability of items such as window frames or roller shutters. The weathering of PVC items is a complex phenomenon, involving photo-chemical and secondary chemical reactions, that yields the formation of conjugated polyene sequences underskin in the absence of oxygen and carbonyls in the surface. Here, the chain scission of the polymer backbone occurs, bringing about the disintegration of the surface of the item and causing the typical discoloration called chalking, especially evident in dark-colored articles. In the experimental section of the paper, the effect of different acid scavengers on item weathering has been studied using a natural outdoor and two accelerated exposures with xenon-arc and Q-UV testing devices. Results confirm that some acid scavengers are efficient in preventing chalking, but some are ineffective or even detrimental. Thus, the PVC formulations of durable articles upon weathering still depend on a complex choice of the appropriate ingredients, and several outdoor and indoor accelerated-weathering tests are needed to predict the articles' lifetime.

A New Perspective on Hydrogen Chloride Scavenging at High Temperatures for Reducing the Smoke Acidity of PVC Cables in Fires, IV: The Impact of Acid Scavengers at High Temperatures on Flame Retardance and Smoke Emission

In PVC compounds, hydrogen chloride plays a fundamental role in ·H and ·OH radical trapping, lowering the flame energy during combustion. Furthermore, it yields actual Lewis acids promoting the cross-linking of the polyene sequences from PVC degradation and bringing a char layer, protecting PVC items from flames. Therefore, PVC is inherently flame-retarded. However, plasticized PVC requires flame retardants and smoke suppressants to enhance fire performance. Low-smoke acidity PVC compounds have been developed to reduce the HCl emission during combustion and, therefore, the acidity of the smoke. They contain potent acid scavengers capable of acting at high temperatures. They react with hydrogen chloride in the condensed phase, making it unavailable in the gas and even in the condensed phase, compromising the reaction to fire and enhancing the smoke produced during the combustion. The effect of the sequestration of hydrogen chloride in PVC compounds for cables by potent acid scavengers is studied in this paper through measurements of oxygen index, heat release, and smoke production. It is noteworthy that the potent acid scavengers strongly affect parameters such as the oxygen index, the fire growth rate in cone calorimetry, the specific (total) heat capacity, and the specific heat of combustion of fuel gases in micro combustion calorimetry. In some formulations, acid scavengers reduce the oxygen index below the values of the formulations without flame retardants and double their fire growth rate. In fact, they neutralize the action of antimony trioxide and Lewis acid precursors commonly used as flame retardants and smoke suppressants in PVC items, making them prone to ignite, release smoke, and spread flame. A new generation of flame retardants and smoke suppressants is needed to keep together the low-smoke acidity and the fire performance in PVC items.

Damage function for poly(vinyl chloride) in heritage collections

Yellowing of plastic objects as a consequence of chemical degradation is a common heritage conservation challenge. In the case of poly(vinyl chloride) elimination of hydrogen chloride leads to the formation of polyene sequences that act as chromophores. The objective of this work was to quantitatively evaluate the rate of degradation observed as yellowing, as relevant to room conditions during long-term storage of heritage collections. Degradation was quantified as increase in the b* colour coordinate during accelerated degradation at 50 and 70 °C as a function of temperature, relative humidity, plasticizer content, and polymer molecular weight. The significance of each variable was investigated with multiple linear regression. Lower temperature, lower relative humidity, higher polymer molecular weight and higher plasticizer content were associated with lower degradation rates. The activation energy of 86 kJ/mol was calculated. The concept of ‘1- °C-equivalent’ is introduced to enable variable prioritisation from a heritage management aspect. The resulting model can be used to shape environmental management guidelines and identify the most vulnerable objects in heritage collections.

Dependence of C[dbnd]C stretching wavenumber on polyene length in degraded polyvinyl chloride: a comparative empirical, classical mechanics, and DFT study

Mathematically describing the length-dependence of vibrational fingerprints of polyenes is challenging, yet crucial in understanding and predicting polyene-associated molecular properties of industrially-important and vital substances. To this end, we develop an analytical relationship between the wavenumbers ν∼C=C of the Raman-active CC stretching mode in polyene sequences (CHCH)n and the polyene length (n) using classical mechanics laws. Noteworthy, this relationship is derived from Newton’s equations instead of regression approximations and validated against experimental data for degraded polyvinyl chloride (PVC), t-butyl end-capped all-trans polyenes, β-carotenes, and carotenoids. Furthermore, given this fundamental tool, we carefully re-examined or validated the up-to-now applied empirical tools; we find that: (i) A phenomenological exponential regression function ν~C=C=1461+151.2×exp-0.07808n proves fairly suitable for describing polyenes with lengths below 24 in degraded PVC. (ii) The derived analytical relationship agrees more closely with a long-established reciprocal-length regression function ν~C=C=1459+720/n+1 for describing carotenoids. Moreover, extensive DFT calculation results on all-trans polyenes H(CHCH)nH (n = 3–30) and polyenes end-capped with terminal vinyl chloride oligomers agree with experiment for shorter polyenes and are similar, showing that complicated calculations of ν∼C=C for infinite degraded PVC chains reduce to the calculations on finite polyene sequences. Noteworthy, unlike other polyene length-determination tools, the proposed analytical polyene length-determination based on intrinsic physical properties could well prove to be an even more versatile tool, as it comes with the added potential for determining or correcting the elasticity constants of carbon bonds in polyene chains.

Investigation on the thermal decomposition of the elastomer containing fluoroolefin segment by DSC‐TG‐MS‐FTIR

AbstractBased on the cross‐linking reaction of bisphenol A epoxy resin and liquid carboxy‐terminated poly(tetrafluoroethylene‐hexafluoropropylene‐vinylidene fluoride) copolymer (CTTHV), the elastomer containing fluoroolefin segment was prepared. The bis(2,2‐dinitropropyl)‐acetal/formal (BDNPA/F) was used as an energetic plasticizer for this fluoroolefin segment‐containing elastomer (FO elastomer). The compatibility of CTTHV and BDNPA/F was evaluated by the combination of differential scanning calorimetry (DSC) and derivative thermogravimetry (DTG) methods. Thermal decomposition of the FO elastomers was investigated by TG‐DSC. The kinetic parameters of the FO elastomers were calculated by Kissinger‐Akahira‐Sunose method. DSC‐TG‐MS‐Fourier transform infrared spectroscopy analysis was used to detect the thermal decomposition products. The thermal decomposition mechanisms of the FO and FO/BDNPA/F elastomers were discussed. The results show that CTTHV has a good compatibility with BDNPA/F, and the prepared FO/BDNPA/F elastomers have good thermal stability. BDNPA/F can promote the thermal decomposition of the FO elastomer and bring more heat for the binder system according to the thermal decomposition behaviors and kinetic calculation results of FO/BDNPA/F elastomers. The FO elastomer preferentially undergoes depolymerization, HF elimination with the formation of polyene sequences, and subsequent main‐chain cleavage, polyaromatization. The H ion fragments of the decomposition of BDNPA/F can be an important factor in the improvement of HF concentration at the initial thermal decomposition of FO elastomer. An abundant HF released during all decomposition of FO/BDNPA/F elastomers may be beneficial to the ignition and combustion of aluminum particles in future applications.

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.

Controlled Dehydrochlorination of Poly(vinyl chloride) for Fabrication of Membranes with Polyacetylene-Like Structure: XPS Analysis and Ion Exchange Membrane Discussion

Poly(vinyl chloride) (PVC) can be dehydrochlorinated by strong bases, e.g. tert-butoxide and hydroxide, to attain polyacetylene-like highly conjugated polymer chains. Dehydrochlorinated PVC (DHPVC) can be further functionalized by additional reactions to obtain ion exchange membranes, battery membranes, semiconductors, etc. However DHPVC resin is not available for membrane casting because of its low solubility. Therefore dehydrochlorination was performed directly on PVC membranes in this research. The extent of dehydrochlorination and the length of conjugation were controlled by adjusting conditions such as base/PVC ratio and solvent type. X-ray photoelectron spectrometry and elemental analysis were used to detect Cl, C, O, and H contents of the products. A calculation method that uses parameters of atomic approximations, was proposed to mathematically express trends of “degrees of dechlorination, dehydrochlorination, unsaturation, and substitution” with respect to the amount of base used. Up to 64.5% unsaturation and 96.6% dechlorination of PVC membranes were achieved. In addition, theoretical ion exchange capacity (IECtheo) was defined with a suggestion that charged functional groups can be attached to the polymer backbone by double bonds, allowing ion exchange membranes to be manufactured. By tailoring the degree of unsaturation in dehydrochlorinated species, theoretically up to 18 meq/g of IEC would be reached if all double bonds would be functionalized. Scanning electron microscopy analysis showed that tert-butoxide products had a porous structure. FTIR and UV-Visible spectroscopy results verified the formation of long polyene sequences. Dehydrochlorination may be a legitimate method for recycling PVC waste into functional membrane materials.

Understanding the pyrolysis mechanism of polyvinylchloride (PVC) by characterizing the chars produced in a wire-mesh reactor

The study aims to understand the fundamental mechanism of the pyrolysis of polyvinylchloride (PVC) by investigating the chars produced in a wire-mesh reactor, where the interactions of evolving volatiles and pyrolysing PVC particles as well as the secondary reactions of the volatiles are minimized. The initiation of PVC pyrolysis can start at a temperature as low as 200°C on the surface of PVC particles via dehydrochlorination, as confirmed by the surface color change and the X-ray photoelectron spectroscopy (XPS) results. However, significant dehydrochlorination reaction mainly starts at ∼300°C, leading to the formation of conjugated polyene sequences. The results also suggest that the cyclization/aromatization reaction may take place at the early stage of the dehydrochlorination process, as the hydrocarbon release already starts (i.e., at ∼350°C with a Cl loss of ∼80%) before the termination of the dehydrochlorination process. The initial released hydrocarbons have an H/C atomic ratio close to 1, more likely via intramolecular cyclization/aromatization reaction. However, the contribution of the hydrocarbon release to weight loss is small at low temperatures (<450°C), and the majority of the weight loss is caused by the dehydrochlorination.

Thermal Degradation and Microhardness Analysis of Polyene with Modified Oil Resin

Thermal degradation of polyene synthesized from recycle polyvinyl chloride (PVC) and hardness of polyene coated with modified oil has been studied by thermogravimetric analysis (TGA) and microhardness test. The synthesized polyene from reaction of recycle PVC were varied from 30 minutes, 1 hour, 2 hours and 4 hours and their thermal stability has been analyzed. From differential thermal gravimetric, DTG curve, polyene from two hours reaction showed the highest degradation temperature up to 445°C due to degradation of polyene sequences. Microhardness test performed by Shimadzu DUH 211/DUH-211S dynamic ultra microhardness tester according to ASTM E384 showed that polyene derived from 2 hours PVC with modifed oil resin resulted in the highest microhardness ~ 107.99 MPa.

Photodegradation profiles of PVC compound and wood/PVC composites under UV weathering

This work aimed to study the effect of different ultraviolet (UV) weathering conditions (natural and accelerated) on the photodegradation of polyvinyl chloride (PVC) and wood/polyvinyl chloride (WPVC) composites by considering the structural and physical changes of PVC and WPVC samples as well as examining the photodegradation profiles at different depths from the sample surfaces. The photodegradation of PVC and WPVC composites under natural weathering condi- tions were lower than those under accelerated weathering conditions. The addition of Tinuvin P stabilizer at 2 phr was suf- ficient to stabilize PVC and WPVC composites, whereas the presence of wood appeared to accelerate the photodegradation of PVC under both natural and accelerated weathering conditions. When considering the photodegradation profiles at dif- ferent depths of the samples, it was found that the polyene and carbonyl sequences of PVC and WPVC composites were high at the sample surfaces and tended to decrease rapidly with increasing depth from the specimen surface before stabiliz- ing at a depth of 60 µm for PVC and 80 µm for WPVC composites. The differences in specimen depths for the stabilization of polyene and carbonyl sequences in PVC and WPVC samples implied that the presence of wood particles enhanced the absorption of UV radiation by the WPVC composite samples.

Mechanical and thermal properties of nanosized titanium dioxide filled rigid poly(vinyl chloride)

Nano-sized rod-like titanium dioxide (TiO2) filled rigid poly(vinyl chloride) (PVC) nanocomposites were prepared by using injection-molding method. Vicat, Charpy impact and tensile tests as well as thermogravimetric and dynamic mechanical analyses were used to characterize the structure and properties of the nanocomposites. The results showed that nano-TiO2 could improve Vicat softening temperature and also improve thermal stability of PVC during the stages of dehydrochlorination and formation of carbonaceous conjugated polyene sequences, which can be ascribed to restriction of the nanoparticles on the segmental relaxation as being evidenced by raises in glass transition and β-relaxation temperatures of PVC upon filling TiO2. Addition of TiO2 nanoparticles less than 40 phr (parts per hundreds of resin) could significantly improve impact strength of the composites while the TiO2 agglomeration at high contents leads to a reduction in impact toughness.

Effect of calcium stearates and zinc stearates on polyene formation of poly(vinyl chloride) under degradation

The effect of calcium stearates (CaSt2) and zinc stearates (ZnSt2) on polyene formation of poly(vinyl chloride) (PVC) was investigated by gel content, ultraviolet (UV)–visible, Fourier transform infrared and static stability analyses. The linear polyene sequences are preferred to form in pure PVC and the PVC/CaSt2 mixture during degradation, and while crosslinking polyene is found in the PVC/ZnSt2 and PVC/ZnSt2/CaSt2 mixtures. The gel content increases with first high slope of 39.80 and second low slope of 7.37 in the PVC/ZnSt2 mixture. The crosslinking degree reaches 41.62%, when adding 3 phr ZnSt2. For the PVC/ZnSt2/CaSt2 mixture, the crosslinking reaction is delayed by CaSt2 because of their synergistic effect.

The Effect of High Intensity UV Irradiation on Color Behavior of Poly(Vinyl Chloride)

A detailed study of color change in poly(vinyl chloride) (PVC) sheets due to high intensity ultraviolet (UV) irradiation was undertaken, focusing on the first 50 h of change. Color changes were monitored with a Datacolor check spectrophotometer and compared with a set of controls. Measurements were taken after 1, 3, 5, 10, 15, and 20 h of irradiation, then at 10 h intervals for the next 40 h. Further measurements were conducted at 100, 240, and 480 h. Data were analyzed using the reflectance spectra (350–800 nm) as well as the CIE (International Commission on Illumination) L* a* b* color values (L*, a*, and b* are lightness value, redness-greenness value, and yellowness-blueness value, respectively) and the total color change (ΔE). The majority of color changes were found to occur within the first 50 h. After 50 h, the color change slowed and began to reverse toward 480 h. Surface microstructure properties, such as morphology, surface tension and oxidized products, were characterized to allow a comparison of sensitivity between the color monitoring methods and a comprehensive understanding of the color change. The results show that color evolution was attributable to the competition between the formations of polyene sequences (dehydrochlorination reaction) and their subsequent oxidation (photobleaching), which was slightly different from the behavior under a xenon arc lamp. According to the color behavior and the microstructure analysis a general scheme accounting for the mechanism of ageing behavior of PVC under high intensity UV irradiation is proposed.

Gamma irradiation aging of NBR/CSM rubber nanocomposites

The effect of gamma-irradiation on the acrylonitrile butadiene/chlorosulphonated polyethylene rubber blends (NBR/CSM) based nanocomposites containing carbon black (CB) and silica filler (Si) were investigated by TG-DTG and ATR-FTIR techniques. The silica (with primary particle size of 22nm) was added in content of 0, 10, 20 and 30phr and carbon black (with primary particle size 40–48nm) was added in content of 30phr and rubber blend compounds were prepared. The obtained elastomeric materials were aging to different γ-irradiation doses (100, 200 and 400kGy). The cure and mechanical properties of obtained nanocomposites were determined. Incorporating 20phr of silica to the control NBR/CSM rubber blends containing 30phr CB resulted 152% increase in tensile strength, 116%, in elongation at break and 142% modulus at 100% elongation, according to synergistic effect between the fillers. FTIR measurements of aged samples estimated the formation of alcohols, ethers and small amounts of lactones, anhydrides, esters and carboxylic acids after exposure to lower doses of γ-radiation (100kGy). On the basis of the obtained spectra the formation of shorter polyene sequences and aromatic rings in aged elastomeric samples are assumed. The results show that 30phr of carbon black (CB) and 20phr of silica are needed for the best gamma aging resistance of NBR/CSM rubber nanocomposites. The result of radiation exposure is decrease in mechanical properties. The dose at which ultimate mechanical properties decreased was at 200kGy. TG-DTG measurements estimated decrease in thermal stability of gamma-irradiated NBR/CSM rubber blend based nanocomposites. Silica reinforced NBR/CSM rubber blend had better radiation resistant than carbon black. Rough and heterogeneity of fracture surfaces has been observed for NBR/CSM rubber blends filled with silica. More uniform morphology of fracture surfaces according to high polymer–filler interaction and low filler–filler interaction has been observed for CB/Si filled NBR/CSM rubber blend.

Structural and thermal stabilizations of PVC and wood/PVC composites by metal stearates and organotin

Structural and thermal stabilizations of poly(vinyl chloride) (PVC) and wood/PVC (WPVC) composites were studied using lead stearate (PbSt2), calcium/zinc complex (Ca/Zn) stabilizers, and methyl tin mercaptide (MT). Thermal and structural stabilities of PVC and WPVC composites were assessed using FTIR spectrometer, thermogravimetric analysis (TGA) and UV-Vis spectrophotometry. The results indicated that the additions of thermal stabilizers into PVC and WPVC composites could promote the thermal stabilities under both un-aged and thermally aged conditions. The presence of wood particles resulted in increases in polyene and carbonyl sequences during processing and decreases in the decomposition temperature (Td). The presence of wood was found to accelerate the thermal degradation in PVC, and suppressed the efficiencies of the thermal stabilizers used. By increasing the stabilizer dosage, the thermal degradations of PVC and WPVC were moderated. Under thermally aged condition at 177oC, the additions of thermal stabilizer could decrease the increase in yellowness index (YI) and discoloration at different ageing times. In this work, MT was found to be the most suitable and promising stabilizer for PVC and WPVC composites, considering the polyene and carbonyl contents, Td, the shift of derivative thermogravimetric (DTG) curves, and changes in YI value and visual color.

Effects of copper‐containing layered double hydroxide on thermal and smoke behavior of poly(vinyl chloride)

AbstractThermal and smoke properties of poly(vinyl chloride)/copper‐containing layered double hydroxide (MgCuAl‐LDH) composites were studied in this article. Highly crystallized LDH with platelet size at micrometer scale was prepared via urea hydrolysis and further intercalated with a variety of anions. X‐ray diffraction results indicated an enlargement of basal spacing to 2.54 nm for dodecylsulfonate‐intercalated LDH. The effects of LDHs on thermal stability and degradation behavior of PVC were investigated by Congo Red tests and thermogravimetric analysis (TGA). By incorporating 3 wt % LDHs, the thermal stability times of carbonated MgAl‐LDH and MgCuAl‐LDH/PVC composites were even three and five times of that of neat PVC. The TGA showed an increase of polyene sequences and char residues formed during PVC pyrolysis. MgCuAl‐LDH/PVC composites gave the best reduction in maximum density of smoke, i.e., 25% lower than that of MgAl‐LDH/PVC composites. However, the organomodification of LDH by anion exchange gave no contribution to improvement of thermal stability of PVC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Stabilizations of molecular structures and mechanical properties of PVC and wood/PVC composites by Tinuvin and TiO2 stabilizers

AbstractThree different UV stabilizers, 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐ditertpentylphenol (Tinuvin XT833), 2‐(2H‐benzotriazol‐2‐yl)‐p‐cresol (Tinuvin P), or rutile–titanium dioxide (TiO2) were incorporated into poly(vinyl chloride) (PVC) and wood/PVC (WPVC) composite, and mechanical and physical properties and photostabilities were monitored. The polyene and carbonyl sequences of PVC increased with UV weathering time and with presence of wood flour. The yellowness index increased because of polyene and carbonyl productions, whereas the brightness increased because of the photobleaching of lignin in wood. The photostabilities of PVC and WPVC could be improved through the use of UV stabilizers. Tinuvin P was recommended in this work as the most effective stabilizer for PVC and WPVC composites. The stabilization effect was interfered by presence of wood particles. The mechanical property changes corresponded well to the structural changes under UV for neat PVC. For WPVC composites, the presence of wood particles played more significant effect on the mechanical properties during UV aging than the UV stabilizer. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Evaluating PVC Degradation Using UV and Raman Spectroscopies

While the world growth in PVC consumption continues (currently ~35 million tonnes per annum), its poor thermal stability, remains an issue due to restrictions on the use of stabilizers containing heavy metals such as lead. Monitoring degradation in PVC is important, and this work is concerned with the detection of PVC degradation using UV and Raman spectroscopies. The bands which appear in the Raman spectra of PVC samples after thermal degradation at around 1100 and 1500 cm-1, are the result of a resonance Raman effect. Optimization of the PVC degradation assessment process using laser-Raman is crucial to minimize the effects of additive interference and the fluorescent background. The most important factor is the wavelength of the exciting laser source, as it should fall within the absorption range for polyene sequences in degraded PVC. Laser-Raman spectroscopy has been shown to be an appropriate method for the quantitative determination of the polyene length distribution in lightly degraded PVC samples. The application of this method for various degraded PVC samples is reported. Ageing of compounds containing various heat stabilizers were considered, in order to assess their effectiveness. Additives studied included calcium zinc stabilizers and two commercial grades of hydrotalcite (Sorbacid 911 and Alcamizer P93).

Synergistic combination of metal stearates and β‐diketones with hydrotalcites in poly(vinyl chloride) stabilization

AbstractA synergistic effect of synthetic hydrotalcites as long term stabilizer with metal soaps (the mixture of calcium and zinc stearate) and metal acetylacetonates on dehydrochlorination of PVC has been studied. A proper balance between color stabilization and HCl scavenging capacity has been obtained. Hydrotalcite was prepared by hydrothermal treatment and characterized by EDX, XRD, FTIR, TGA, and SEM techniques. The material is reasonably crystalline and suggests a relatively well ordered sheet arrangement with crystallite size 24.87 nm. The interlayer water content was calculated from the TGA curves and the suggested formula is Mg0.76 Al0.24(OH)2(CO3)0.12·0.5H2O. Synergism in PVC stabilization has been studied by measuring the HCl evolution during the processing at 180°C. Oven aging method was used to study the color stabilization at higher temperature. PVC sheet with different formulation was prepared using Labcoater and subjected to oven for different time interval. The color development (polyene formation) on oven ageing was recorded using UV–visible spectroscopy. UV–visible studies shows that an average sized polyene gives pale yellow color, whereas red or brown color was developed due to long range polyene (n = 10–14) sequences. Hence, the HCl evolution depends on the rate of dehydrochlorination but color depends on the kind of polyene formed. Mechanism of stabilization suggests that adsorption and ion exchange, both phenomenon, are responsible for hydrotalcites as long term stabilizers. The acetylacetonate complex too substitute allylic chlorides and inhibit formation of long polyene responsible for darkening. A clear effect of synergism has been observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009