Thermal behaviour of styrene butadiene rubber/poly(ethylene-co-vinyl acetate) blends

The thermal behaviour of styrene butadiene rubber (SBR)/poly (ethylene-co-vinyl acetate) (EVA) blends was studied by using thermogravimetry (TG) and differential scanning calorimetry (DSC). The effects of blend ratio, cross-linking systems and compatibilization on the thermal stability and phase transition of the blends were analyzed. It was found that the mass loss of the blends at any temperature was lower than that of the components, highlighting the advantage of blending SBR and EVA. The addition of compatibilizer was also found to improve the thermal stability. DSC studies indicated the thermodynamic immiscibility of SBR/EVA system even in the presence of the compatibilizer. This is evident from the presence of two different glass transition temperatures, corresponding to SBR and EVA phases in both compatibilized and uncompatibilized blends.     

Photosensitized dehydrochlorination of poly(vinyl chloride)

The mechanism of the benzophenone-photosensitized degradation of films of poly-(vinyl chloride) was studied, both under vacuum and in the presence of oxygen. Initial rapid increases in absorption in the 340 nm region strongly implicate the ketyl radical in the initiation process which involves the abstraction by triplet benzophenone of a methylenic hydrogen from poly(vinyl chloride). Dehydrochlorination then occurs by a chain mechanism, and the conjugated polyene structure produced photosensitizes further initiation and, in the presence of oxygen, photo-oxidation of the polymer.     

Thermo-oxidative dehydrochlorination of rigid and plasticised poly(vinyl chloride)/poly(methyl methacrylate) blends

The aim of this work was to study the thermo-oxidative dehydrochlorination of rigid and plasticised poly(vinyl chloride)/poly(methyl methacrylate) blends. For that purpose, blends of variable compositions from 0 to 100 wt% were prepared in the presence (15, 30 and 50 wt%) and in the absence of diethyl-2-hexyl phthalate as plasticiser. Their miscibility was investigated by using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). Their thermo-oxidative degradation at 180 ± 1 °C was studied and the amount of HCl released from PVC was measured by a continuous potentiometric method. Degraded samples were characterised, after purification, by FTIR spectroscopy and UV-visible spectroscopy. The results showed that the two polymers are miscible up to 60 wt% of poly(methyl methacrylate) (PMMA). This miscibility is due to a specific interaction of hydrogen bonding type between carbonyl groups (CO) of PMMA and hydrogen (CHCl) groups of PVC as shown by FTIR analysis. On the other hand, PMMA exerted a stabilizing effect on the thermal degradation of PVC by reducing the zip dehydrochlorination, leading to the formation of shorter polyenes.     

Thermal dehydrochlorination of poly(vinylidene chloride)

The kinetics of the early stages of thermal degradation below 1% dehydrochlorination of emulsion-polymerized poly(vinylidene chloride) (PVDC) is studied by the variation of the pH value of potassium hydroxide aqueous solution between 160 and 190°C in the presence of air and other gas streams. The results turned out that the thermal degradation of PVDC can be divided into three stages, which correspond to an induction period, a period with conversion below 0.1% dehydrochlorination, and that with conversion ranging from 0.1 to 1%. For the induction stage, the induction time depends upon the types of environment gas and degradation temperature. Both of the second and the third stages are zero-order reactions, which also result in the discoloration and crosslinking of the neat polymer. The average apparent activational energy of the zero-order degradation reaction was about 21 kcal/mol, which is independent of the types of environment gas. The whole degrading kinetics data can be well explained by the mechanism of a free-radical-induced dehydrochlorination. The viscosity of the degraded sample increases rapidly with degradation and becomes insoluble in regular solvents. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2035–2044, 1999     

Morphology and properties of poly(vinyl chloride)–poly(butadiene-co-acrylonitrile) blends

The objective of this research was to study the structure-property relationships of two poly(vinyl chloride) (PVC)–poly(butadiene-co-acrylonitrile) (BAN) blends which exhibit differences in blend compatibility. Studies were carried out utilizing differential scanning calorimetry, dynamic mechanical testing, stress–strain, transmission electron microscopy (TEM), and infrared dichroism experiments at different temperatures. The BAN 31/PVC (BAN containing 31% acrylonitrile) system is considered to be nearly compatible as evidenced by T_g shifts, stress–strain results, orientation characteristics, and TEM micrographs. Similar experiments indicate that the BAN 44/PVC system is incompatible, and contains a mixed phase of BAN 44-PVC and a pure BAN 44 phase. The extent of heterogeneity in the compatible BAN 31/PVC system, however, plays an important role in the orientation characteristics of the blends.     

Thermal conductivity of poly(vinyl chloride)/polycaprolactone blends

Thermal diffusivity, heat capacity, and density of polyvinyl chloride/polycaprolactone (PVC/PCL) blends were measured by the laser flash method, DSC, and pycnometry, respectively. The thermal conductivity of the PVC/PCL blends was determined from the results. The miscibility of the blend and crystallinity of PCL were determined by DSC. The effect of blend structure on thermal conductivity is discussed. The phase compositions of the PVC/PCL blends are of three types depending on PCL content: i.e., up to 33%, from 33 to 70%, and above 70% PCL by weight. Thermal conductivity, thermal diffusivity, and heat capacity of the PVC/PCL blends are strongly affected by the phase composition of the blend, which changes in a complicated way with PCL content. © 1994 John Wiley & Sons, Inc.     

Thermal properties of poly(vinyl chloride)/polyurethane blends

Blends of poly(vinyl chloride) and a polyurethane elastomer were investigated by DSC and tensile testing. Up to 30 wt% single glass transition was found. It was concluded that the polyurethane forms partly a true blend and is partly disperged in the continuous blend phase.     

Thermal degradation studies in poly(vinyl chloride)/poly(methyl methacrylate) blends

The miscibility, morphology, and thermal properties of poly(vinyl chloride) (PVC) blends with different concentrations of poly(methyl methacylate) (PMMA) have been studied. The interaction between the phases was studied by FTIR and by measuring the glass transition temperature (T_g) of the blends using differential scanning calorimetry. Distribution of the phases at different compositions was studied through scanning electron microscopy. The FTIR and SEM results show little interaction and gross phase separation. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800 °C at different heating rates varying from 2.5 to 20 °C/min. The thermal decomposition temperatures of the first and second stage of degradation in PVC in the presence of PMMA were higher than the pure. The stabilization effect on PVC was found most significant with 10 wt% PMMA content in the PVC matrix. These results agree with the isothermal degradation studies using dehydrochlorination and UV-vis spectroscopic results carried out on these blends. Using multiple heating rate kinetics the activation energies of the degradation process in PVC and its blends have been reported.     

Photosensitized dehydrochlorination of poly(vinyl chloride). III. Reaction of thermally degraded poly(vinyl chloride) with hydrogen chloride

Films prepared from thermally degraded poly(vinyl chloride) were photolyzed in the presence of hydrogen chloride. When the light was filtered through a Pyrex disk, the absorbance in the region between 270 nm and about 415 nm decreased and reached a minimum value but the absorbance increased at wavelengths shorter than 270 nm and longer than 415 nm. Maximum bleaching occurred at a wavelength which depended on that of the irradiating light. When the Pyrex filter was omitted, an additional slower photodehydrochlorination reaction was superimposed on the photobleaching reaction. Photolysis of hexane or ethanol solutions of 1,8-diphenyloctatetra-1,3,5,7-ene and hydrogen chloride showed a similar reaction involving bleaching of the absorption of the polyene structure. The problems of using absorbance as an indication of the extent of the photodegradation of poly(vinyl chloride) are discussed.     

Thermal and radiation-induced dehydrochlorination of poly(vinyl chloride). II. Head-to-head structures

The mechanism of dehydrochlorination of 2,3-dichlorobutane and chlorinated polybutadiene which are model compounds of head-to-head poly(vinyl chloride) has been investigated by pyrolysis, thermal, and ultraviolet-induced decomposition. The activation energy of dehydrochlorination for head-to-head poly(vinyl chloride) in nitrogen was 23 kcal/mole at temperatures of 150–190°C, which is slightly smaller than that (29 kcal/mole) for head-to-tail poly(vinyl chloride). The conjugated double bonds were formed by thermal and radiation decomposition of head-to-head poly(vinyl chloride), similar to head-to-tail poly(vinyl chloride). The probability of polyene formation by radiation-induced dehydrochlorination is larger than that by thermal decomposition and is affected by the conformation and the molecular motion of the main chain. This may be due to the alternative mechanism of dehydrochlorination in the thermal and radiation decomposition. The amount of head-to-head linkage of poly(vinyl chloride) samples prepared with various catalysts is dependent on polymerization temperature rather than the kinds of catalyst. Commercial poly(vinyl chloride) has 6–7 head-to-head linkages per 1000 monomeric units.     

Electrical conductivity of thermally degraded poly(vinyl chloride)–polyacrylonitrile blends

Finely powdered blends of poly(vinyl chloride) (PVC) and polyacrylonitrile (PAN) have been thermally degraded at 275°C for 24 h in an inert atmosphere to effect complete de-hydrochlorination of PVC to a conjugated polyene structure and simultaneous internal polymerization of nitrile groups in PAN to a conjugated polyimine sequence. The room temperature d.c. conductivity of the degraded blends showed clear synergistic behavior. A maximum conductivity has been observed with a blend of 60 PAN/40 PVC which is about 4 orders of magnitude over the linearly weighted average conductivity of the individual degraded homopolymers. The results have been interpreted in terms of a possible donor-acceptor interaction between the degraded homopolymers leading to mutual doping and, hence, an enhanced electrical conductivity. © 1995 John Wiley & Sons, Inc.     

Miscibility of poly(vinyl chloride) with styrene/acrylonitrile copolymers

Poly(vinyl chloride) (PVC) is shown to be miscible with styrene/acrylonitrile copolymers (SAN) having AN compositions from 11.5 to 26%. Blend samples were prepared using several methods, including solution casting, melt mixing, and precipitation of solutions by a nonsolvent. It is shown that the blend phase behavior is affected by preparation method due to the solvent effect, or Δ_χ effect, and lower critical solution temperature (LCST) behavior. The intramolecular repulsion between styrene and acrylonitrile units in SAN is shown to be the cause of miscibility using heats of mixing obtained from low-molecular-weight analog compounds. An FTIR analysis supplements the above results.     

Thermal, ozone and gamma ageing of styrene butadiene rubber and poly(ethylene-co-vinyl acetate) blends

Ageing behaviour of SBR/EVA blends due to the effects of heat, ozone, and gamma radiation was studied with reference to blend ratio, three crosslinking systems (sulfur, peroxide and mixed) and a compatibiliser (SEBS-g-MA). It was found that an increase in the EVA content of the blends enhanced the ageing characteristics. Among the different crosslinking systems, a peroxide cured system exhibited the best retention of properties even after severe ageing. Tensile strength of peroxide cured SBR/EVA blends increased slightly after ageing for three days at 70 °C due to continued crosslinking, whereas tensile strength of all blends decreased on ageing at 100 °C. Compatibilisation with SEBS-g-MA improved the thermal, gamma and water ageing resistance of SBR/EVA blends.     

Thermal degradation of poly(vinyl chloride)/poly(ethylene oxide) blends: Thermogravimetric analysis

Thermal stability of poly(vinyl chloride)/poly(ethylene oxide) (PVC/PEO) blends has been investigated by thermogravimetric analysis (TGA) in dynamic and isothermal heating regime. PVC/PEO blends were prepared by hot-melt extrusion (HME). According to TG analysis, PEO decomposes in one stage, while PVC and PVC/PEO blends in two degradation stages. In order to evaluate the effect of PEO content on the thermal stability of PVC/PEO blends, different criteria were used. It was found that thermal stability of PVC/PEO blends depends on the blend composition. The interactions of blends components with their degradation products were confirmed. By using multiple heating rate kinetics the activation energies of the PVC/PEO blends thermal degradation were calculated by isoconversional integral Flynn–Wall–Ozawa and differential Friedman method. According to dependence of activation energy on degree of conversion the complexity of degradation processes was determined.     

Thermal degradation of poly(vinyl chloride)

This paper presents an initial attempt at describing poly(vinyl chloride) (PVC) thermal degradation through a semi-detailed and lumped kinetic model. A mechanism of 40 species and pseudocomponents (molecules and radicals) involved in about 250 reactions permits quite a good reproduction of the main characteristics of PVC degradation and volatilization. The presence of the two step mechanism—the first step of which corresponds to dehydrochlorination and the second to the tar release and residue char formation—are correctly predicted both in quantitative terms and in the temperature ranges. The model was validated by comparison with several thermo gravimetric analyses, both dynamic at different heating rates, and isothermal. When compared with the typical one step global apparent degradation models, the approach proposed here spans quite large operative ranges, especially when it comes to predicting product distributions. The initial results of these product predictions, even though quite preliminary, are encouraging and confirm the validity of the model.     

Study of the thermal dehydrochlorination of poly(vinylidene chloride) and poly(vinyl chloride) by ESR spectroscopy

The evidence for a radical elimination of hydrogen chloride during the thermal degradation of homopolymers and copolymers of vinylidene chloride is summarized and confirmed by an ESR spectroscopic study of the degradation residues. However, sufficient differences in the degradation characteristics exist between these polymers and those of vinyl chloride to suggest that a radical process alone is not sufficient. No evidence of a radical process can be obtained from an ESR spectroscopic analysis of the elimination. The paramagnetic character of the degraded polymer is attributed to the polyene structure produced on dehydrochlorination.     

Combined relaxation study of poly(vinyl chloride) blends with chlorinated poly(ethylene), hydroxyl-terminated poly(butadiene), and ethylene-propylene-diene terpolymer

A number of blends based on suspension poly(vinyl chloride) and stabilizers with poly(ethylene) chlorinated in a fluidized-bed reactor containing 21.8% chlorine, hydroxyl-terminated poly(butadiene), and ethylene-propylene-diene terpolymer have been studied using such methods as thermally stimulated current depolarization and dynamic mechanical analysis. Some dielectric and thermodynamic parameters (τ_max, τ_o, E_a, ΔH^*, ΔS_E^*, ΔG^*, μ_eff) have been determined. Blends containing randomly chlorinated poly(ethylene) exhibited dipole–dipole interactions between the macromolecules of poly(vinyl chloride) which decreased at the expense of the long sequences of nonchlorinated methylene groups. Simultaneously, an increased physical interaction between poly(vinyl chloride) and the additives was observed in blends containing chlorinated poly(ethylene) and/or hydroxyl-terminated poly(butadiene), and ethylene-propylene-diene terpolymer. On the basis of the data of dynamic mechanical analysis obtained a heterogeneous structure of the blends is suggested. The development of a boundary interfacial layer with a proper region of relaxation proves the formation of compatible structures between the components. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1595–1608, 1998     

Radiation-induced graft polymerization of styrene to poly(vinyl chloride)

The radiation-induced graft polymerization of styrene to poly(vinyl chloride) (PVC) was investigated. Relations between the rate of grafting and the dose rate when the polymer is irradiated in liquid monomer or in monomer vapor, and between the rate of grafting and monomer concentration absorbed in the polymer have been investigated. The rate of grafting in monomer vapor was found to be far larger than that in liquid monomer. A high rate of grafting in monomer vapor was thought to result from a lower concentration of monomer in PVC during irradiation. An experiment carried out on PVC containing the monomer at various concentrations showed that the rate is largest at a monomer concentration of about 3.5 mole/l. and is smaller for higher and lower concentrations. On the assumption that the theory of homogeneous homopolymerization can be applied to this grafting reaction, the value of k_p²/k_t has been obtained, where k_p and k_t are propagation constant and termination constant, respectively. The value of k_t greatly increases when the monomer concentration exceeds 3.5 mole/l. This increase of k_t can be accounted for if it is assumed that the monomer absorbed in the polymer works as a plasticizer and increases the molecular motion of the polymer. A measurement of the elastic modulus of PVC containing the monomer at various concentrations showed that this is, in fact, the case.