Radiation protection of poly(vinyl chloride) by N-methyl dithiocarbamate substitution

The effect of N-methyl dithiocarbamate substitution on the radiation stability of poly-(vinyl chloride) (PVC) films was studied. PVC containing between 2 and 11 mole-% N-methyl dithiocarbamate (PMD) was irradiated with γ-rays from a ⁶⁰Co source at 40°C and the evolved gaseous products were measured and analyzed with a mass spectrometer. The apparent G values for gas evolution for PMD decreased remarkably. For example, a G value of 0.28 was obtained for a PMD which contains 11 mole-% dithiocarbamate group compared with a G value of 10.8 for unmodified poly(vinyl chloride). Furthermore, the mass spectrum of the evolved gas from the same PMD sample (PMD-44) with 10 Mrad irradiation showed no hydrogen chloride to be present. The external protection was studied using polymer-blended films of PVC and PMD-44. The stabilization coefficients for internal protection and external protection in polymer blends were calculated. The ESR spectrum of the irradiated PMD-44 showed a strong anisotropy with high g values which differed significantly from the spectrum of the irradiated PVC. A suggested mechanism for radiation protection of PVC against γ-rays irradiation by the N-methyl dithiocarbamate group is discussed.     

Radiation crosslinking of poly(vinyl chloride)

The mechanism of the electron irradiation crosslinking of poly(vinyl chloride) (PVC) with polyfunctional acrylic monomers has been investigated as part of a program to develop an insulation for distributing-frame wire. These monomers were found to undergo rapid polymerization to form a rigid, three-dimensional network onto which PVC was grafted. Polyfunctionality was necessary for crosslinking to occur, since butyl methacrylate, containing only a single unsaturated bond, did not crosslink readily. On the other hand, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate, each containing three unsaturated groups, gave extremely rapid crosslinking. Trimethylolpropane triacrylate showed 40 times the radiation sensitivity of tetraethylene glycol dimethacrylate, a diunsaturated compound. The rate of disappearance of unsaturation was related inversely to the rate of gel formation. This was attributed to immobilization of unreacted pendant double bonds in the rigid crosslinked network. In the triunsaturated monomers, half the vinyl groups were left unreacted when all of the PVC was insoluble.     

Chemical modification of rigid poly(vinyl chloride) by the substitution with nucleophiles

The reaction of rigid poly(vinyl chloride) (PVC) with iodide, hydroxide, azide, and thiocyanate as nucleophiles (Nu) in ethylene glycol (EG) resulted in the substitution of Cl by Nu additional to the elimination of HCl, leading to the dehydrochlorination of the rigid PVC. High substitution rates were observed for hydroxide, azide and thiocyanate, while the addition of iodide accelerated predominately the elimination of HCl. The substitution by thiocyanate resulted at 150°C in both thiocyanate and isothiocyanate structures, whereas at 190°C, only isothiocyanate was observed in the polymer. The dehydrochlorination yield increased with an increasing molar SCN/Cl ratio, resulting in a maximum substitution at high molar SCN/Cl ratios. When EG was replaced by diethylene glycol (DEG) as solvent, the dehydrochlorination was found to be accelerated. It was assumed that DEG has a higher compatibility with PVC, making it easier to penetrate the rigid PVC particle. For triethylene glycol (TEG), the rapid dehydrochlorination resulted probably in the coverage of the surface of the PVC particle by methyl methacrylate/butadiene/styrene (MBS), preventing the penetration by the solution. The substitution/dehydrochlorination ratio decreased in the order of EG > DEG > TEG because of the declining polarity of the solvent, stabilizing the activated S_N2 complex. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

Radiation yield of hydrogen chloride in gamma-irradiated poly(vinyl chloride) stabilized by epoxy compounds

The G_HCI values of γ-irradiated PVC mixtures were studied after addition of various amounts of three epoxy stabilizers: diglycidyl ether of 2,2-bis(4-hydroxy-3-methylphenyl)propane (I); diglycidyl ether of 1,1-bis(4-hydroxyphenyl)cyclohexane (II), and butyl-cis-9,10-epoxystearate (III). The results indicated that two processes are essential for the stabilization: HCI capture by the epoxy groups, and an external protective effect, due to the remaining part of the stabilizer molecule. The role of the benzene rings in stabilizers I and II, as compared with the protective effect due to the long chains of stabilizer III, is not as dominant as one would expect.     

Modification of pitches by poly (vinylidene chloride) and poly (vinyl chloride)

Poly(vinylidene chloride) — PVDC — and poly(vinyl chloride) — PVC — reacted with pitches at elevated temperature with an increase in the yield of residual carbon; the greater the aromaticity and ‘fixed carbon’ of the pitch, the greater the increase. PVDC especially had a remarkable effect. This increase of residual carbon may be due to an increase in the molecular weight of pitch produced by its reaction with PVDC or PVC via dehydrochlorination. This tends to elevate the softening point and increase the insolubility in solvents. It is clearly indicated from i.r. spectra that reaction takes place mainly between aromatic hydrogen in the pitch and chlorine in PVDC. X-ray diffraction profiles of the reaction products show that the pitch forms hard (non-graphitizing) carbon as the PVDC content in the mixture increases.     

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.     

Radiation yield of hydrogen chloride in the poly(vinyl chloride) foils irradiated by accelerated electrons

The G_HCl values of PVC foils, containing 18% of dioctylphthalate, irradiated with accelerated electrons were studied after addition of various amounts of the stabilizers: (I) ethylene glycol bis-β-aminocrotonate, (II) calcium/zinc laurate + epoxy compounds, (III) calcium/zinc stearate, (IV) dioctyltin bis(octylthioglycolate). The effect of stabilization turned out to be very good, especially when stabilizer I was used. In the case of soft PVC foils in contact with water, elution of hydrogen chloride occurs. This creates difficulties in preparing PVC foils sterilized radiatively for medical purposes, especially if the foils are expected to be in contact with water.     

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.     

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.     

Preparation of modified poly(vinyl chloride) containing N,N-di(β-hydroxyethyl)dithiocarbamate and its reaction with metal ions

Reaction of N,N-di(β-hydroxyethyl)dithiocarbamate ion with poly(vinyl chloride) (PVC) was undertaken, and the reaction with metal ions of the polymer obtained was investigated. The effect of γ-irradiation on the reaction with metal ion was also studied. The modified PVC (PHDC) obtained from the reaction with N,N-di(β-hydroxyethyl)dithiocarbamate ion is pale yellow even after reaction at 100°C for 5 hr in dimethylformamide (DMF); it is soluble in dipolar solvents and its chlorine content is decreased considerably. This polymer reacted well with acetate salts of copper(II), nickel(II), zinc(II), and silver(I) heterogeneously in aqueous solution because of the introduction of hydrophilic groups (two hydroxy groups). The reactivity of the metal ions toward the polymer was of the order Ag(I) ? Cu(II) > Ni(II) > Zn(II). From the result of the reaction of γ-irradiated polymer with cupric ion, the polymer was judged to have fairly good antiradiation property.     

Dehydrochlorination of poly(vinyl chloride)

PVC has been dehydrochlorinated with alcoholic alkali in soution at 7°C for different lengths of time. At early stages of dehydrochlorination the dominant reaction is intramolecular removal of HCl and this gives rise to two intense Raman bands at ～ 1126 (ν₁) and ～ 1518 cm^?1 (ν₂) and following UV irradiation, to a quadruplet ESR spectrum. Increasing polyene sequence length and intermolecular removal of HCl at later stages of reaction alters the quadruplet signal to a singlet, shifts ν₁ and ν₂ to lower frequencies and increases the molecular weight. The presence of polyene units stiffens the chain and increases the elastic modulus. The T_g is, however, lowered slightly due to the removal of bulky chlorine atoms which relieves steric hindrance and dipole interaction between neighboring chains. The β-transition is also rendered less distinct.     

Degradation of poly(vinyl chloride)

The decomposition of poly(vinyl chloride) below 155°C has been examined by thermogravimetric analysis. Degradation is enhanced by irradiation with 1 MeV electrons. Later stages of isothermal weight loss for thermal and radiolytic decomposition follow 3/2-order kinetics and a similar reaction scheme is inferred. A free radical mechanism for dehydrochlorination involving allyl and polyenyl radicals is postulated.     

Radiation crosslinking of poly(vinyl chloride)/epoxidized natural rubber blend: effect of lead stabilization of the poly(vinyl chloride) phase

The irradiation crosslinking of 50/50 poly(vinyl chloride)/epoxidized natural rubber blend was investigated in the presence of 1–5 parts per hundred resin (phr) tribasic lead sulfate (TBLS) with blends prepared at various mixing temperatures. The blends were irradiated using a 3.0 MeV electron accelerator at 0, 100 and 200 kGy irradiation doses. Changes in tensile strength, elongation at break and stress‐strain curves of the blends with the increase TBLS content and blending temperatures were observed before and after irradiation. The results on the tensile properties revealed the inhibition of the irradiation‐induced crosslinking by the TBLS although it stabilizes the blend against thermal and irradiation‐induced degradation. The Fourier transform infrared spectroscopy studies further confirmed these observations. Control on the thermal degradation of the blend during blending found to be crucial in achieving maximum enhancement in blend properties upon irradiation. Evidence from dynamic mechanical analysis was also used to support this contention. Addition of 2 phr TBLS and blending at 150 °C found to be adequate in order to achieve the best enhancement in blend properties through irradiation‐induced crosslinking. © 2001 Society of Chemical Industry     

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). XXXIV. Crosslinked poly(vinyl chloride) via paste-processing

A novel PVC-crosslinking technique using 6-dibutylamino-1,3,5-triazine-2,4-dithiol (DB) was applied for a paste processing to produce a crosslinked PVC product. The paste formulation recommended in the present study consisted of 100 parts of PVC (Zeon 121), 60 parts of dioctyl phthalate, 0.2 parts of MgO, and 6 parts of a 50% solution of DB-Na in butylcarbitol, which gave a highly crosslinked and transparent sheet with an excellent stability for thermal discolouring. The increasing viscosity behaviour of the paste during storage is explained by the effect of interparticle attracting forces of DB-Na which coordinates to the ether oxygen atoms in the glycol derivatives adsorbed on the surface of PVC particles. The increased viscosity can be reduced by addition of 3 parts of N-butyl-benzene-sulfonamide. The tension-distortion properties at elevated temperatures were remarkably improved at the crosslinked product compared with the uncrosslinked. The mechanical properties of the two crosslinked products produced via paste processing and roll-blending are compared in regard to the differences of the uniformity of crosslinking units.     

Surface protection of poly(vinyl chloride) by photografting of epoxy–acrylate coatings

UV-curable epoxy–acrylate coatings were used to protect poly(vinyl chloride) against superficial degradation. With α-hydroxy–acetophenone photoinitiators, the crosslinking polymerization develops in the ms time scale; 50% degree conversion is reached after irradiation times of 2.5 ms in a nitrogen atmosphere and 17 ms in air. The adhesion of the coating on to the PVC substrate can be greatly improved by inducing a photochemical grafting process. The best results are obtained by incorporating the photoinitiator into the top layer of the PVC sheet. Highly crosslinked epoxy–acrylate coatings are very stable toward UV radiations and chemical agents like organic solvents and strong acids. By their light-screening effect they provide an excellent protection against photodegradation for light-sensitive polymeric materials.     

Photostabilization of poly(vinyl chloride) by protective coatings

The light stability of poly(vinyl chloride) plates has been substantially increased by protecting their surface with a UV‐cured acrylic clearcoat containing both a UV absorber and a HALS radical scavenger. To ensure a long‐lasting adhesion, the coating was photochemically grafted onto the PVC substrate. The coated PVC sample remained transparent, non‐colored, and glossy upon accelerated QUV‐B weathering for up to 3000 hours. An additional advantage of this method of photostabilization is to improve some of the surface properties of the coated polymer, such as its resistance to solvents, abrasion, and scratching. The method was also successfully used to recover highly photodegraded PVC and make it even more weathering‐resistant than the original polymer.