Crosslinking of rigid poly(vinyl chloride) with epoxysilane

Crosslinking is an effective way to improve the properties of poly(vinyl chloride). A crosslinking agent consisting of R‐glycidoxypropyltrimethoxysilane (KH560) has been used for the first time in order to introduce crosslinking into rigid poly(vinyl chloride). Different thermal stabilizers (organotin, Ca/Zn stearate, and Ba/Zn stearate) as well as sodium bisulfite were tried in order to promote grafting of the epoxy group and enhance the degree of crosslinking. Fourier transform infrared (FTIR) spectra showed that grafting and crosslinking of KH560 with poly(vinyl chloride) could take place, and that a gel content of 40% could be obtained when more than 10 phr of epoxysilane was used with a 2:1 (weight) ratio of BaSt₂/ZnSt₂ and a 1:1 molar ratio of NaHSO₃/KH560, while premature crosslinking was avoided. The Vicat softening temperature of crosslinked PVC could be increased by about 10°C when 5 phr of epoxysilane was added, and thermal degradation could be delayed with increasing gel content. Therefore, epoxysilane‐crosslinked PVC has the potential for extensive applications. J. VINYL ADDIT. TECHNOL., 13:103–109, 2007. © 2007 Society of Plastics Engineers.     

Crosslinking of poly(vinyl chloride) with bismaleic compound. I. Crosslinking mechanism

Crosslinked poly(vinyl chloride) (PVC) was obtained by using bismaleic compound (BMC). Styrene, as auxiliary crosslinker, can markedly promote the crosslinking course. After having carefully studied the gelling behavior of PVC in crosslinking, and the reactivity of styrene and BMC with PVC, the crosslink mechanism was suggested. The main crosslink reaction is the bridging of bismaleic compound between PVC macroradicals, which were created by thermal degradation of PVC and disproportionation of PVC with initiator radicals and styrene radicals. The first step of crosslink reaction was the BMC grafting on PVC macroradicals. Then styrene copolymerizes with active center bearing on bismaleic compound to propagate graft chain, which make bridging reaction easier to take place. At last, PVC^* reacted with another double bond possessed by grafted BMC to form network structure     

Stabilization of poly(vinyl chloride) by elemental sulfur

The process of stabilization of a poly(vinylchloride) elemental sulfur in thermal and thermooxidative destruction conditions is investigated. The high stabilizing efficiency of elemental sulfur is revealed at the destruction of plasticized poly(vinylchloride) compared with the efficiency of phenolic antioxidants. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effects of copper and molybdenum oxides on the pyrolysis of model compounds of poly(vinyl chloride)

Numerous transition metal compounds can be added to poly(vinyl chloride) to decrease the smoke evolved during burning or smoldering conditions. Model compound pyrolysis experiments have been carried out to investigated the mechanisms by which smoke retarder additives function in PVC. Three models were used: 3-chloropentane, 2,4-dichloropentane, and 2,4,6-trichlorohenptane. The additives MoMO₃ and Cu₂O both enhanced the rate of dehydrochlorination and promoted the formation of crosslinked products (oligomers) during model compound pyrolysis, but their mechanistic pathways were found to be different. The choice of model compounds also was an important influence in determining the observed decomposition pathways. While much of the pyrolysis chemistry can be explained by Lewis acid catalysis, other effects also appear to be important. The pyrolysis results are interpreted in terms of an “early crosslinking” mechanism of smoke retardation in PVC. In this mechanism the metal smoke retarder works primarily by catalytically promoting early crosslinking of decomposing PVC chains to yield char as a residue.     

Crosslinking of plasticized poly(vinyl chloride) by substitution and free radical reaction

Two new methods to obtain crosslinking plasticized poly(vinyl chloride) (PVC) are shown. One is by the substitution reaction of PVC with the sodium salt of γ-mercaptopropyl trimetoxysilane and the other is by the free-radical reaction of azide-modified PVC with γ-acryloxypropyltrimetoxysilane and vinyltri(2-metoxyetoxy)silane. The content of gel and the number average molecular weight between crosslinking (M_c) were determined by Soxhlet extraction and by using the Flory-Rehner equation. The reactions of PVC with the above organosilanes under normal processing conditions of the polymer lead to high gel contents and, therefore, low M_c. The ultimate tensile strength and elongation at break at 110°C of these polymers are greatly enhanced over those of the uncrosslinked polymer. The results are improved compared to those taken from literature for similar systems. © 1996 John Wiley & Sons, Inc.     

Stabilization of poly(vinyl chloride). I. Change in color of poly(vinyl chloride) compounded with some metal soaps

Poly(vinyl chloride) (PVC) with one or more metal salts added was colored by the action of heat to investigate the stabilization mechanism. The coloration and the color difference of heated PVC compound films varied according to the metal salt added. The decoloration of the colored compound films was advanced markedly in THF, DMF, acetone, and ammonia. On the other hand, the heated achromatic PVC film containing Cd/Ba soaps underwent an opposite change, from colorless to yellow orange, in the above materials. This means that the coloration of heated compound films may result from the formation of some complex (for example, π complex of the polyene with the metal chloride). Furthermore, the colored film with cadmium stearate was decolored by roll mixing with the colored film containing barium stearate. These results indicate that the stabilization with metal soaps may be founded on a physical phenomenon such aa an effect of complementary color.     

Crosslinking reaction of poly(vinyl alcohol) with glyoxal

Crosslinking reactions are one of the most commonly used techniques to improve physical properties of polyvinyl alcohol (PVA). Commonly used crosslinkers for these reactions are di-functional compounds, such as glutaraldehyde and glyoxal. The hydroxyl groups of PVA react with aldehydes via formation of acetal bonds hence corsslinking could take place. Quantitative analysis of glyoxal crosslined PVA will be described in this report. A convenient FTIR method has been established to analyze degree of crosslinking in PVA. Analysis by ¹H NMR spectroscopy methods will also be described.     

Hydrogen chloride evolution from the heating of poly(vinyl chloride) compounds

The dehydrochlorination and the thermal decomposition of five PVC materials was studied using two techniques: a batch analytical method, combining ion chromatography and atomic absorption and continuous thermogravimetry. The temperatures studied ranged from 60°C to 120°C, over a period of almost one year (50 weeks). It was found that a very large proportion of the soluble chloride emitted early on by the PVC materials into the liquid phase is not hydrogen chloride. None of the five materials tested emitted significant amounts of HCl at temperatures lower than 105°C. The emissions at 90°C after 50 weeks ranged from <0.01 Φg/g to 23.62 Φg/g. Furthermore, one of the materials tested emitted virtually no HCl, even at 105°C, as the amount of HCl measured was almost indistinguishable from the normal background of the analytical instruments (37.30 Φg/g after 50 weeks). Numerical calculations of kinetic reaction rates and extrapolation of the results to use temperatures (40°C) indicate that properly stabilized PVC compounds will be unlikely to lose 1% of the mass of PVC as HCl until 2 billion years have passed. This number has no physical meaning as such and may be incorrect by a vast margin, but it clearly indicates that a 1% loss of HCl is unlikely to occur during the useful lifetime of a commercial product into which the PVC material has been fabricated. This is a conservative estimate, which ignores the much higher activation energy for dehydrochlorination at temperatures below the glass transition temperature (ca. 85°C). Copyright © 2005 John Wiley & Sons, Ltd.     

Miscibility in poly(vinyl chloride)/chlorinated poly(vinyl chloride) blends,and blends of different chlorinated poly(vinyl chlorides)

Blends of poly(vinyl chloride) with chlorinated poly(vinyl chloride) (PVC), and blends of different chlorinated poly(vinyl chlorides) (CPVC) provide an opportunity to examine systematically the effect that small changes in chemical structure have on polymer-polymer miscibility. Phase diagrams of PVC/CPVC blends have been determined for CPVC's containing 62 to 38 percent chlorine. The characteristics of binary blends of CPVC's of different chlorine contents have also been examined using differential calorimetry (DSC) and transmission electron microscopy. Their mutual solubility has been found to be very sensitive to their differences in mole percent CCl₂ groups and degree of chlorination. In metastable binary blends of CPVC's possessing single glass transition temperatures (T_g) the rate of phase separation, as followed by DSC, was found to be relatively slow at temperatures 45 to 65° above the T_g of the blend.     

Dynamic mechanical analysis of poly(vinyl chloride) compounds and blends

PVC is one of the most versatile and cost effective commercial polymers. A main limitation of PVC is optimizing its fabrication characteristics and end use properties with minimum adverse effect on either. PVC compounding technology is supersensitive due to effect of subtle variations in formulations causing “inspec” products during one production run and “out-of-spec” products in another. Large variations in properties are frequently due to improper mixing. Dynamic mechanical analyses provides a method of monitoring variations in mixing and their affect on morphological structure deviations which can lead to poor processing and end use properties.     

Stabilization of poly(vinyl chloride). V. Synergism between metal soaps and polyols upon stabilization of poly(vinyl chloride)

The marked discolorations observed on aged poly(vinyl chloride) (PVC) containing synergetic metal soaps, in the early heating stage, were due to the excessive coloration of π complex of metal chloride and double bonds in the polyene chain. These excessive colorations were inhibited by masking the excessive metal chloride with some masking agents, thereby slowing down the abrupt discoloration of PVC. In this paper, the masking effect of various alcohols such as 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, hexylene glycol, glycerol, 1,2,4-butanetriol, trimethylolethane, trimethylolpropane, meso-erythritol, pentaerythritol, sorbitol, and dipentaerythritol is investigated. The polyhydric alcohols, except dihydric alcohols, showed superior masking effect and markedly improved the thermal stabilization effects of synergetic metal soaps. The mechanism for the synergetic effects between polyols and metal soaps should be based on the masking effect of polyols, owing to the formation of the colorless complex of polyols with excess metal chlorides obtained from the metal soap.     

Polyene formation in poly(vinyl chloride) stabilised with pre-heated metal stearates

Summary PVC stabilised with mixtures of pre-heated metal stearates are degraded thermally for specific periods of time, in order to determine their influence on the production of polyenes by uv spectroscopy. Additionally, the PVC samples are treated with NaBH₄ to reduce the carbonylic groups produced during the thermo-oxidative process. Important differences in the polyene formation trends are observed, between the reduced and non-reduced samples, indicating that the carbonyl groups attached to polyenes shift the absorbance maxima and alter considerably the quantification of the double bond conjugations. Received: 14 September 1998/Revised version: 28 January 1999/Accepted: 28 January 1999     

Interaction effects and property retention in poly(vinyl chloride) compounds

The influence of thermodynamic interactions among the components of a polymer system on mechanical properties and their retention on aging has been investigated. The systems considered involve plasticized poly(vinyl chloride)(PVC), and CaCO₃ fillers. Inverse gas chromatography was used to measure interaction parameters, and to express these in terms of acid-base concepts. Interaction data were obtained over a wide temperature range. It was shown that the volume of plasticizers retained by the PVC correlates with the measured interaction parameters. Similarly, the interaction parameters identify a CaCO₃ filler preferred for reinforcing rigid PVC, and a different CaCO₃ filler for use in given PVC-plasticizer combinations. The mechanical properties of filled PVC (up to 40 phr CaCO₃), and particularly the ultimate properties of the compounds, correlate with interaction concepts, as do property retention data after accelerated aging of the compounds at 100°C. It is concluded that component interaction parameters may provide useful guidelines to the formulation of compounds with superior properties and reduced property losses due to aging.     

The solubility of vinyl chloride in poly(vinyl chloride)

The solubility of vinyl chloride monomer (VCM) in PVC powders has been studied by equilibrium vapor pressure and microbalance gravimetric techniques at temperatures from 30 to 110°C. At temperatures and VCM concentrations above the glass transition, the solubility closely follows the Flory-Huggins equation with χ = 0.98 and is independent of temperature and of the PVC type, molecular weight, or history. In the glassy state, the VCM solubility is higher than the Flory-Huggins value and shows pronounced dependence upon time and the PVC history. These results have been interpreted through the dual-mode sorption concept of Michaels, Vieth, and Barrie: Normal dissolution follows the Flory-Huggins relation, and the additional glassy-state solubility represents the contribution of a hole-filling process. Changes in solubility with time and sample history parallel well-known volume relaxation processes, indicating that vapor solubility measurements offer a direct and sensitive measure of the free-volume state of glassy polymers.     

Blends of plasticized poly(vinyl chloride) and waste flexible poly(vinyl chloride) with waste nitrile rubber powder

Blends of poly(vinyl chloride) (PVC) with varying contents of plasticizer and finely ground powder of waste nitrile rubber rollers were prepared over a wide range of rubber contents through high‐temperature blending. The effects of rubber and plasticizer (dioctyl phthalate) content on the tensile strength, percentage elongation, impact properties, hardness, abrasion resistance, flexural crack resistance, limiting oxygen index (LOI), electrical properties, and breakdown voltage were studied. The percentage elongation, flexural crack resistance, and impact strength of blends increased considerably over those of PVC. The waste rubber had a plasticizing effect. Blends of waste plasticized PVC and waste nitrile rubber showed promising properties. The electrical properties and LOI decreased with increasing rubber and plasticizer content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1552–1558, 2004     

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.     

Reactive extrusion of poly(vinyl chloride) compounds with polyethylene and with ethylene-vinyl acetate copolymers

The mechanical properties of poly(vinyl chloride)/polyethylene blends can be improved by a reactive extrusion process in the presence of an organic peroxide and a coupling agent. With a judicious loading of dibenzoyl peroxide and triallyl isocyanurate coupling agent, such blends generally exhibit significantly greater ultimate tensile strengths and dynamic moduli. The nature of the sample posttreatment after compression molding is shown to have a major impact upon the relative magnitude of these differences. Evidence is also presented to suggest that such improvements result from a superior physical interlocking between blend components, rather than through the formation of co-crosslinked graft segments (which would, presumably, impart a compatibilization effect). Similar extrusion trials with a poly(vinyl chloride)/poly(ethylene-stat-vinyl acetate) mixture revealed a general worsening of material properties with increasing dibenzoyl peroxide levels. These observations can be rationalized by examination of the degradation reactions that likely occur in these reacting systems.     

Effect of compatibility between solvent and poly(vinyl chloride) on dechlorination of poly(vinyl chloride)

In this study, the use of diethylene glycol (DEG), triethylene glycol (TEG), n-C₁₀H₂₁OH, and ethylene glycol (EG) as solvents for NaOH in the dechlorination of poly(vinyl chloride) (PVC) was investigated. In the early reaction time, the degrees of dechlorination for DEG, TEG, and n-C₁₀H₂₁OH were notably higher than that for EG. Further, the high compatibility between PVC and the solvents was considered to result in the easy penetration of the solvent and OH⁻ into PVC particles, leading to the acceleration of dechlorination in the early reaction stage. An improvement of the dechlorination was actually observed for DEG and TEG compared with EG. The solvent with the best compatibility to PVC, n-C₁₀H₂₁OH, however, showed little improvement due to the formation of a protective polyene layer on the surface of the PVC particles.     

Modification of poly(vinyl chloride). XIX. Electroplating of poly(vinyl chloride)

As a preliminary treatment in the PVC-electroplating procedure, treatment with dimethylformamide followed by sensitization leads to a finely roughened and a highly hydrophilic surface with reducing power. This is caused by the formation of an ionic complex compound between dimethylformamide and tin(II) chloride absorbed in the PVC surface. A much more finely and deeply etched surface which exhibits higher adhesion through the mechanical interlocking effect is obtained with the PVC blends containing the plasticizer with a low value of interaction parameter and with a solubility parameter approximate to that of PVC. Adhesion of the metal layer to the PVC surface thus obtained is improved about 1.5 times by thermal aging at 120°C for 20 min.