Mixed metal vinyl stabilizer synergism. II: Reactions with zinc replacing cadmium

The study of kinetics of displacement of reactive chlorine from a model compound, cinnamyl chloride, has been extended from barium/cadmium to barium/zinc and calcium/zinc carboxylate blends. With carboxylate ligands, the specificity of mixed metal complexes in yielding alkaline earth, rather than Lewis acid, chlorides is not as great with zinc as with cadmium. In the case of barium/zinc blends, this may be compensated for by complexing the metals with a ketoenolate ligand, e.g., benzoylacetone. In a mixed benzoyl-acetone/butyl acetate solvent, barium/zinc carboxylates yielded reaction rates with cinnamyl chloride comparable to barium/cadmium blends.     

New insights into the degradation mechanism of poly(vinyl chloride), based on the action of novel costabilizers. I.

Recent legislation introduced to limit the use of heavy metal stabilizers (cadmium based) in poly(vinyl chloride) (PVC) has necessitated the use of organic costabilizers as adjuncts to alternative main stabilizer systems (barium/zinc or calcium/zinc). It has been suggested in the literature that costabilizers substitute allylic chlorine by a C‐alkylation reaction; costabilizers act as reverse catalysts for the initiation of degradation by complexing the π‐electron sites that would otherwise have an activating affect on labile chlorines; and costabilisers destroy carbonylallyl active sites by proton donation. To rationalize this debate, the focus of this paper is to elucidate the type of interactions that occur between a model compound for PVC and the novel costabiliser N‐phenyl‐3‐acetylpyrrolidin‐2,4‐dione (P24D). The model compound chosen was 4‐chloro‐2‐hexene (4C2H), which simulates the in‐chain allylic chlorine impurities present in PVC and are considered the most labile defects present in the polymer. Results suggested that stabilisation involves concerted reactions involving metal complexes rather than a series of stepwise reactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2731–2743, 2004     

Effect of zinc maleate/zinc oxide complex on thermal stability of poly(vinyl chloride)

In this study, zinc maleate (ZnMA) and zinc oxide (ZnO) complex (ZnMA/ZnO) was prepared by two methods, namely, by the reaction of maleic acid (MAH) with excess ZnO in aqueous solution and by direct mixing of ZnMA and ZnO at 180°C. The chemical structure of the complex was analyzed by X‐ray diffraction, thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy. The thermal stabilizing effect of the complex on poly(vinyl chloride) (PVC) was evaluated through static and dynamic stability methods. Compared to calcium and zinc soaps and ZnMA alone, the complex exhibited better thermal stabilizing effect on PVC. The stabilization mechanism was also investigated by ultraviolet–visible spectrometer, FTIR, TGA, and gel content analysis. The results indicated that the complex which involved the replacement of labile chlorine atoms hindered the formation of conjugated double bonds in PVC chains via Diels–Alder reaction, and ZnMA/ZnO complex also exhibited the ability to absorb hydrogen chloride. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41464.     

Synergism in thermal stabilization of polyvinyl chloride

Plasticized polyvinyl chloride was thermally stabilized by barium, cadmium, and zinc laurates, epoxidized soybean oil, and monoalkyl diaryl phosphite, and by combinations of these stabilizers. Of 26 possible combinations, 18 showed some improvement, 8 showed useful improvement, 7 showed marked improvement, and 3 systems were outstanding. Of the 26 combinations, 10 showed distinct synergism, based mainly upon combinations of Group II-B metals with Group II-A metals, “secondary” stabilizers, or both. Combinations of Group II-B metals with “secondary” stabilizers were particularly interesting and promising.     

Stabilization of poly(vinyl chloride). VIII. Synergisms between epoxy compounds and metal soaps

Effects of bisphenol A type epoxy compounds involving various average molecular weights on the zinc stearate/calcium stearate and the cadmium stearate/barium stearate synergetic soaps induced thermal stabilization of poly(vinyl chloride) (PVC) were investigated by colorimetry. The remarkable stabilization effects of epoxides could not be observed on the PVC films without synergetic soaps, while the stabilization of PVC was markedly enhanced by combined use of epoxides and synergetic soaps. The appearance of excessive coloration of cool color producing metal chloride–polyene complexes which were an origin of abrupt discoloration of stabilized PVC was retarded by using epoxides together with synergetic soaps. Moreover, as for PVC with or without synergetic soaps, the epoxy compounds did not inhibit the formation of longer polyene chains which were a chromophore for yellow orange of aged PVC. Further colorimetries and IR or X-ray photoelectron spectroscopies on the various PVC containing epoxy compounds and zinc chloride indicated that the epoxy groups caught the zinc chloride. The synergetic effect between epoxy compounds and synergetic metal soaps is ascribed to the action that the epoxides serve as an acceptor for the excessive cool color producing metal chloride produced from zinc stearate and cadmium stearate to retard the abrupt discoloration of stabilized PVC.     

Über die hitzestabilisierung von PVC durch blei-, barium- und cadmiumoctoat

The following reactions between carbonic acid salts of bivalent metals as heat-stabilizers and PVC take place during heat-treatment:

• Chemical HCI-bonding by stabilizers (HCI-acceptance);
• esterification of isolated allylic chlorine atoms in the polymer chains, starting from a complex formed by stabilizer molecules and labile chlorine atoms:
• the stabilizer inhibits formation of longer polyene sequences by exchange reactions of the allylic chlorine atoms with the ester groups of the stabilizer.

Reaction (a) prevents an autocatalytic acceleration of the HCI splitting off by HCI. Reaction (b) eliminates ?labile”? chlorine atoms of the polymer which are responsible for the thermal instability of PVC. Reaction (c) prevents the formation of longer polyene sequences, which absorb in the visible range of the spectrum.     

The action of tridecyl phosphite in the stabilization of poly(vinyl chloride) with metal soaps

The effect of tridecyl phosphite on the stabilization of the thermal degradation of poly(vinyl chloride) under nitrogen by cadmium and zinc stearates has been studied. The rate of evolution of hydrochloric acid from solutions of the polymer with stabilizers in dioctyl phthalate at 190°C has been measured. Tridecyl phosphite absorbs HCl and is converted into the phosphonate which reduced the deleterious action of the cadmium and zinc chlorides formed from the stearates.     

True stabilization: A mechanism for the behavior of lead compounds and other primary stabilizers against PVC thermal dehydrochlorination

A free-radical mechanism by which lead compounds are thought to inhibit thermal dehydrochlorination of polyvinyl chloride (PVC) is described. This mechanism is called “true stabilization” in order to distinguish it from simple hydrogen chloride (HCl) scavenging, which is a well-known and sometimes important function of all primary stabilizers used in PVC. In true stabilization, it is thought that stearate or other aliphatic carboxylate groups (initially from lubricants) react with reservoirs of basic lead compound such as the carbonates, dibasic lead phosphite, the phthalates, or the sulfates, to give mobile carboxylates of lead. These latter salts then react with chlorine atoms released by the hot PVC, giving chlorides of lead and aliphatic carboxylate free-radicals. Hence the chlorine atoms are trapped and unable to propagate free-radical dehydrochlorination. Also it is thought that the aliphatic carboxylate free-radicals esterify PVC molecules at methylenic carbon atoms (from which hydrogen atoms have been removed by chlorine atoms giving HCl and free-radical sites in the polymer chain). Thus, unpaired electrons on the carboxylate free-radicals and on these methylenic carbon atoms in the PVC molecules are paired, so that the neighboring chlorine atoms in polymer chloromethylenic groups are stabilized. Hence loss of chlorine atoms in the free-radical dehydrochlorination of PVC is prevented. The pendant aliphatic carboxylate groups dissociate from the PVC molecules taking chloromethylenic hydrogen atoms to form acid molecules, and leaving chlorine atoms in relatively stable vinyl type groups. The aliphatic carboxylic acids react with more of the basic lead compound reservoir, giving mobile carboxylates of lead which can enter further reactions as just described. Thus, the true stabilizing mechanism is continuous and cyclic, while the reservoir of basic lead is available, and the PVC thermal dehydrochlorination will be retarded to almost negligible rates in favorable circumstances. It is thought that the behaviors of metal soaps and of organo-tin stabilizers may be encompassed within the general true stabilization concepts of free-radical exchanges and PVC esterifications described above. In these ways they also would retard PVC thermal dehydrochlorination. However, they are neutral compounds and have no basic reservoir which can react with carboxylic acids in the manner described above for lead stabilizers. Hence they are not able to confer long term stability on PVC in the way that basic lead stabilizing regimes do.     

Mixed metal vinyl stabilizer synergism—reactions with model compounds

An allylic model compound for degrading PVC, cinnamyl chloride, was found to react with metal carboxylates in n-butyl acetate at 50°C with rates first order in each component. The corresponding metal chlorides and a mixture of rearranged and unrearranged allyl esters were isolated. With cadmium carboxylates, the rate constant is of the order of 300 × 10^?5 sec^?1; with barium carboxylates, two orders of magnitude slower. In the presence of excess barium carboxylate, the rate of reaction is first order in cadmium and independent of barium concentration; the product is, however, barium chloride. Under such conditions, only unrearranged allyl ester is recovered. These observations are interpreted in terms of a rapid step leading to formation of a carboxylate-bridged barium/cadmium intermediate. It is proposed that such intermediates displace chloride from allylic carbon by a concerted mechanism, generating chloride-bridged reaction products that collapse exclusively to barium chloride.     

Metal soaps under the view point of sustainability—One vision

Poly(vinyl chloride) (PVC) products accompany us throughout our lives, from toys to potable water pipes. In many instances, this is enabled by the capacity of PVC to deliver benefits over a very long lifetime with barely diminished functional efficiency and operational reliability. However, people today are often misled by marketing claims such as products being “green,” “bio‐based,” or “environmentally friendly.” This willful or unintended misleading of public opinion is enabled by an often vague or imprecise understanding of what is meant by the term “sustainable.” The European PVC industry has recently published a renewed commitment to sustainability under the VinylPlus program 1 . It is to progress and promote this ongoing commitment to sustainable development‐‐‐measures to make practical progress toward the goal of sustainability, which we decided to publish in this paper, in which we have sought to evaluate data relevant to sustainability challenges within the PVC industry and the societal lifecycle of the plastic. We have done this by applying a science‐based sustainability framework to evaluate a category of PVC additives that can make a significant contribution toward fully sustainable products. Metal soaps such as stearates, oleates, 12‐hydroxy stearates, laurates, octoates, and benzoates of lead, barium, calcium, magnesium, aluminum, zinc, and cadmium were and are partially still playing an important role in PVC applications. Owing largely to the ubiquity of calcium, magnesium, zinc, and aluminum in the natural environment, salts of these metals formed with organic acids already have a higher potential to become fully sustainable. J. VINYL ADDIT. TECHNOL., 23:125–134, 2017. © 2015 Society of Plastics Engineers     

Stabilization of poly(vinyl chloride). VI. Synergetic effects of aminopolycarboxylates or nitrogen-containing agents with zinc stearate/calcium stearate soap

Discoloration such as zinc burning was observed in aged poly(vinyl chloride) (PVC) compounded with synergetic soaps. This discoloration was caused by excessive formation of cool color-producing π complexes formed between double bonds in polyene chain and zinc chloride or cadmium chloride produced from the corresponding metal soap. The appearance of excessive color of the π complexes was reduced by adding some masking agents into PVC admixed with synergetic soaps. In the present study differences in masking effects results by adding solid or an aqueous solution of aminopoly-carboxylates such as glycine, ethylenediaminetetraacetates, and nitrilotriacetates to PVC stabilized with zinc stearate/calcium stearate synergetic soap. The mechanism of synergetic effect between nitrogen-containing agents and synergetic soaps upon the stabilization of PVC is also investigated by colorimetry. The aqueous solution of aminopolycarboxylates exhibits a greater masking effect than the solid. The masking effect of aminopolycarboxylates depends on the ease with which they are fnely dispersed into PVC. Colorimetry indicated that the masking effect of aminopolycarboxylates and other nitrogen-containing agents depends on forming the colorless complex compound with the excessive cool color-producing metal chlorides.     

Inhibition of the degradation of poly(vinyl chloride) by its modification with 5-pyrimidine carbonitrile (1,2,3,4- tetrahydro-4-oxo-6-phenyl-2-thioxo)

The reaction of poly(vinyl chloride) (PVC) with 5-pyrimidine carbonitrile (1,2,3,4-tetrahydro-4-oxo-6-phenyl-2-thioxo) has been studied. The thermal stability of the modified polymer is improved markedly compared with the unmodified polymer. The stability improvement is attributed to the replacement of the labile chlorine atoms by more stable thio groups. The modified polymer also showed a lower extent of discoloration against ultraviolet rays compared with the unmodified PVC. © 1998 SCI.     

Effects of 6-anilino-1,3,5-triazine-2,4-dithiol,zinc stearate,and barium stearate on the thermal stabilization of PVC

Individual action and synergistic effect in the combination of 6-anilino-1,3,5-triazine-2,4-dithiol (AF), zinc stearate, and barium stearate on the color stabilization of PVC were investigated. In this system, AF selectively reacts with allylic chlorine atoms in PVC. Consequently, unstable allylic chlorine units were converted to thermally stable allylic structures, thus retarding the development of polyene sequences. Zinc stearate accelerated the reaction of AF with allylic chlorine atoms in PVC, forming the zinc salts of AF (AFZ_nSt, St?C₁–H₃₅COO? ) by reacting with AF. Barium stearate reacted with ZnCl₂ which is formed in the above reaction to give St₂Zn and BaCl₂. Consequently, barium stearate led to the selective reaction of AF with allylic chlorine atoms in PVC and the remarkable retarding effect of discoloration of PVC.     

The solubility of heavy metal soaps in co-solvent mixtures of chloroform and propylene glycol

Summary The solubilities of the myristates, laurates, palmitates, and stearates of magnesium, lead, calcium, barium, and zinc have been measured at 25° C. in chloroform and in propylene glycol and in their mixtures. Even where they are sparingly soluble in the solvents separately, they dissolve freely in mixtures of the two. For each metal the solubility is greatest for laurate and least for stearate and it is very low for zinc soaps, particularly zinc stearate. Heavy metal soaps may be directly titrated with acid in mixtures of propylene glycol and chloroform using thymol blue as indicator (yellow to pink).     

Formations and controls of HCl and PAHs by different additives during waste incineration

This study employed a laboratory-scale fluidized bed incinerator to investigate the formations and controls of hydrogen chloride (HCl) and polycyclic aromatic hydrocarbons (PAHs) by adding different additives in the feedstock during waste incineration. The effects of different organic and inorganic chlorides on the formation and control of HCl and PAHs were also studied. Additionally, the thermodynamic equilibrium modeling was also carried out to interpret and compare with the experimental results.Experimental results showed that the formation of HCl was related to the potential of chlorine released from the combustion of different chlorides. Organic chloride PVC had greater potential to form HCl than inorganic chloride NaCl. The performances of additives were affected by incineration temperature. Increasing temperature decreased the control efficiency of additives because the emission yields of HCl and Cl₂ were increased with temperature. The control efficiencies for HCl and Cl₂ by calcium based additives (Ca(OH)₂, CaO, CaCO₃) were better than that by magnesium based additive (Mg(OH)₂) and CaO was the best additive. The control efficiencies of PAHs by adding CaO in the feedstock were not apparent because the fluidization quality in the fluidized bed incinerator was decreased.     

The mechanism of stabilization of poly(vinyl chloride). II. Cleavage of organotin sulfur compounds by anhydrous hydrogen chloride

A number of organotin compounds of the type R_nSn Y_4–n, where R = alkyl or aryl; Y = alkylthio, arylthio or carbothiolate; and n = 1, 2, 3 have been prepared and treated with hydrogen chloride at 180°C in o-dichlorobenzene solution. The organotin compounds were also tested at 190°C as thermal stabilizers for PVC. Cleavage of tin–carbon bonds by hydrogen chloride was demonstrated in some cases by analysis of the organotin–hydrogen chloride reaction products. The formation of monoalkyl(aryl)tin chlorides or stannic chloride, or both, in the model system was shown to correspond to a catastrophic mode of degradation in the polymer. The use of stabilizers with fewer than two alkyl or aryl groups on tin also gave this mode of degradation.     

Recent research advances in the chemistry of poly(vinyl chloride)

Summarized briefly here are some new observations that relate to the polymerization chemistry of vinyl chloride (VC) and to the thermal degradation, thermal stabilization, fire retardance, and smoke suppression of poly(vinyl chloride) (PVC). During polymerization, head-to-head VC emplacement leads to β-chloroalkyl radicals that can transfer chlorine atoms directly to VC. Another mechanism for transfer to monomer is responsible, however, for the polymer molecular-weight reductions that occur at high VC conversions. This transfer process involves the abstraction of methylene hydrogen from the polymer by an ordinary macroradical and the subsequent bimolecular donation of a chlorine atom to VC. The propagation steps of the polymerization do not become diffusion-controlled at VC conversions near 90%, and hydrogen abstraction from the polymer by ordinary macroradicals leads to the structural defects that cause thermal instability. The thermal dehydrochlorination of PVC involves ion pairs or four-center concerted transition states that are highly polarized. Reversible thermal stabilization of the polymer by organic metal salts occurs by the Frye-Horst process, and the reductive coupling of PVC chains may suppress both smoke and flame. This coupling can result from reactions of the polymer with zero- or low-valent transition-metal species that are formed in situ from appropriate additives.     

Metal formates as potential stabilizers for vinylidene chloride copolymers

Vinylidene chloride copolymers have a number of superior properties, most notably, a high barrier to the transport of oxygen and other small molecules. As a consequence, these materials have assumed a position of prominence in the packaging industry. At processing temperatures these copolymers tend to undergo degradative dehydrochlorination. The dehydrochlorination reaction is a typical chain process with distinct initiation, propagation, and termination phases. It has been demonstrated that initiation of degradation is strongly facilitated by the presence of unsaturation along the backbone. Such unsaturation may be introduced via interaction of the polymer with a variety of agents which might commonly be encountered during polymerization or processing. The presence of an unsaturated unit within the polymer generates an allylic dichloromethylene, which may function as a major defect (labile) site for the initiation of degradation. The conversion of these dichloromethylene units into nonreactive groups would interrupt propagation of the dehydrochlorination reaction and lead to the stabilization of the copolymer. Potential stabilization in the presence of metal formates has been examined using a vinylidene chloride/methyl acrylate (5 mol%) copolymer and thermogravimetric techniques. The effect of the metal formate on the stability of the polymer reflects the relative halogenophilicity of the metal cation present. Metal formates of low cation acidity [sodium, calcium, nickel(II) and to a lesser extent lead(II), cadmium, manganese(II) and magnesium] may be expected to be ineffective as stabilizers for vinylidene chloride copolymers. At the other extreme, metal formates that contain cations sufficiently acidic to actively strip chlorine from the polymer backbone, e.g., zinc formate, will function to enhance the degradation process. An effective carboxylate stabilizer must contain a metal cation sufficiently acidic to interact with allylic chlorine and to facilitate its displacement by the carboxylate anion. Copper(II) formate may possess the balance of cation acidity and carboxylate acitvity to function as an effective stabilizer for vinylidene chloride copolymers.     

Formation of anomalous structures in PVC and their influence on the thermal stability: 2. Branch structures and tertiary chlorine

Branch structures were determined in fractions of a commercial suspension of PVC (S-PVC) and experimental PVC samples obtained at subsaturation conditions (U-PVC). The analyses were performed with ¹³C n.m.r. spectroscopy at 50.31 MHz after reductive dehalogenation with tributyltinhydride. With increasing monomer starvation U-PVC was found to have an increasing amount of butyl and long chain branches (LCB). A polymer prepared at 55°C and 59% of the saturation pressure of vinylchloride had 3.4 butyl branches and 2.0 LCB per 1000 monomer units. In the S-PVC series the total content of these two structures varied between 0.5 and 1.0 per 1000 monomer units. By using tributyltindeuteride as reducing agent the structure of the butyl branches could be determined as ～CHClCH₂CCl(CH₂CHClCH₂CH₂Cl)CH₂CHCl～. A major part of the LCB points also contained tertiary chlorine. The formation of LCB is suggested as occurring after abstraction of hydrogen from the polymer chain by macroradicals and chlorine atoms. The latter will lead to LCB points with tertiary hydrogen and internal double bonds. The rate of dehydrochlorination at 190°C in nitrogen could be related to the amount of tertiary chlorine (correction coefficient=0.97). It was assumed that tertiary chlorine is the most important labile structure in PVC.     

Use of N‐(N′‐arylamino)maleimides to improve the thermal properties of poly(vinyl chloride) through chemical modification and graft copolymerization

The reaction of poly(vinyl chloride) (PVC) with N‐(N′‐arylamino)maleimide derivatives was studied. The thermal stability of the modified polymer was improved markedly when compared with that of the unmodified polymer. The stability improvement was attributed to the replacement of the labile chlorine atoms by more stable organic groups. The modified polymer also showed a lower extent of discoloration when compared with that of unmodified PVC. In order to introduce a polymeric stabilizer into PVC, the dienophilic monomer was chemically grafted onto the polymeric chains. The mechanism of the chemical modification as well as that of the graft copolymerization are discussed. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.