PVC Particles Research Articles

Rigid PVC/(layered silicate) nanocomposites produced through a novel melt‐blending approach

AbstractOn the basis of the fusion behavior of poly(vinyl chloride) (PVC), the influence of compounding route on the properties of PVC/(layered silicate) nanocomposites was studied. Four different compounding addition sequences were examined during the melt compounding of PVC with montmorillonite (MMT) clay, including (a) a direct dry mixing of PVC and nanoclay, (b) an addition of nanoclay at compaction, (c) an addition of nanoclay at the onset of fusion, and (d) an addition of nanoclay at equilibrium torque. Both unmodified sodium montmorillonite (Na+‐MMT) and organically modified montmorillonite (Org.‐MMT) clays were used, and the effect of the addition sequence of the clay during compounding on its dispersion in the matrix was evaluated by X‐ray diffraction and transmission electron miscroscopy. The surface color change, dynamic mechanical analysis, and flexural and tensile properties of PVC/clay nanocomposites were also studied. The experimental results indicated that both the extent of property improvement and the dispersion of nanoparticles in PVC/(layered silicate) nanocomposites are strongly influenced by the degree of gelation achieved in PVC compounds during processing. The addition of nanoclay to PVC must be accomplished at the onset of fusion, when PVC particles are reduced in size, in order to produce nanocomposites with better nanodispersion and enhanced mechanical properties. Overall, rigid PVC nanocomposites with unmodified clay (Na+‐MMT) were more thermally stable and exhibited better mechanical properties than their counterparts with organically modified clay (Org.‐MMT). J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers

The influence of temporal cake moisture content on a discontinuous washing process in the centrifugal field

AbstractIn solid/liquid separation processes, filter cake washing is an essential step in improving the quality of particulate products by elimination of impurities. During cake washing and dewatering, the cake saturation changes depending on the flow conditions and it cannot always be measured and controlled accurately. This article deals with investigations on the influence of the initial and temporal cake saturation on washing PVC and silica sand particles in the centrifugal field. It was found, that high initial saturation levels and high maximum saturations during the washing process had a positive impact in inducing a high hydrostatic pressure for advective flow and enabling a homogeneous distribution of the wash water inside the cake. This was achieved by increasing the wash water flux and/or decreasing the g‐factor. A good method to obtain low final impurity quantity is the combination of washing at a low g‐factor and dewatering at a high one. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Separation of PVC and Rubber from Covering Plastics in Communication Cable Scrap by Tribo-Charging

Triboelectrostatic separation of PVC and rubber from covering plastics in communication cable scrap has been performed. In this work, particles charged as positive (+) and negative (−) according to the difference of work function of each material after tribo-charging can be separated through an opposite electric field. In charger material selection tests using a vertical-reciprocation charger, PVC and rubber particles in the covering plastics were charged with the opposite polarity in the charger material made of PP, HDPE, or PET. The difference of charge density (charge to mass ratio, nC/g) of the PVC and rubber was higher in the tribo-charger made of HDPE. Furthermore, in lab-scale triboelectrostatic experiments for separating the PVC and rubber, the charging efficiency of the mixed PVC and rubber increased when the air velocity was adjusted to over 8.2 m/s. The charge density, the electrode potential, and splitter position needed for the separation of the PVC were determined to be 25 nC/g, 30 kV and +2 cm, respectively. In the optimum conditions, we developed a separation technique that can separate up to 99.8% PVC grade with 95.0% of recovery from the covering plastics.

Ball Mill-Assisted Dechlorination of Flexible and Rigid Poly(vinyl chloride) in NaOH/EG Solution

Both flexible and rigid forms of poly(vinyl chloride) (PVC) were effectively dechlorinated in NaOH/ethylene glycol (EG) solution during ball mill pulverization. The high degree of dechlorination obtained was attributed to the increased surface area of the crushed PVC particles and the resulting enhancement of contact between the PVC and dissolved hydroxide ions. The common additives diisononyl phthalate and CaCO3 were easily separated from the PVC bulk during the dechlorination reaction. The reaction proceeded under chemical control, with degrees of dechlorination for both flexible and rigid PVC increasing with temperature with apparent activation energies of 110 and 80 kJ/mol, respectively. This reaction was accurately represented by a modified shrinking-core model.

Effect of the phase ratio on the particle properties of poly(vinyl chloride) resins produced by suspension polymerization

AbstractThe effects of the dispersed phase to continuous phase ratio (weight of VCM (gr)/weight of water (gr) (φ = gVCM/gwater)) on the particle properties of a poly(vinyl chloride) (PVC) suspension were investigated experimentally. A series of experiments were performed with different φ values in a pilot‐scale reactor. The cold plasticizer absorption of the resin decreased with φ. Scanning electron micrographs showed that by the reduction of φ, many of the produced particles had a regular shape, a smooth surface, and greater porosity. An increase in φ caused a wider and multimodal particle size distribution of the produced PVC particles. The mean particle size and bulk density also increased with φ, whereas the molecular weight and polydispersity index did not change. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A rheological study of the ageing of emulsion and microsuspension‐based PVC plastisols

AbstractA PVC plastisol is a homogeneous dispersion of PVC resin in a liquid continuous phase consisting basically of a plasticizer and a thermal stabilizer; the PVC resin being usually a fine powder is polymerized by emulsion or microsuspension processes. Plastisol rheology is affected by many aspects of the plastisol formulations, such as type and amount of each ingredient, the mixing procedure, temperature, and the effect of PVC resin properties. In this work, the ageing behavior of PVC plastisols with different resin types was studied, with the results showing an unexpected behavior in the elastic modulus, probably originating from plasticizer adsorption at the surface of the PVC particles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Experimental study of particle concentration fluctuations in a turbulent steady flow

AbstractSpecific features of the physics of blown sand and PVC particles were investigated in wind-tunnel experiments. The fluctuations in particle concentration over time were derived from image processing of high-speed films (500 Hz). Spectral analysis of these time series showed a slowly decreasing slope within a frequency range that could be larger than the inertial sub-range of the free stream. A specific transport regime also appears in the lower part of the flow for frequencies less than 10 Hz. The role of turbulence in the generation of this regime is discussed using a simple theoretical model able to describe the aerodynamic behavior of a particle.

Merrifield-like resin beads by acid catalyzed incorporation of benzyl chloride into dehydrochlorinated PVC

A method is presented for preparing Merrifield-like resin beads starting from poly (vinyl chloride) (PVC) in spherical bead form. In this method, first, PVC is partially dehydrochlorinated in boiling methanolic KOH (20%) solution to create minute amounts of allylic carbon centers. Those centers trigger the un-zipping process and make further dehydrochlorination possible at relatively low temperatures (180–200 °C), while retaining the bead shapes. Acid catalyzed reaction of the dehydrochlorinated PVC particles with benzyl chloride at 180 °C yields crosslinked spherical bead polymers possessing chloromethyl benzene functions as high as 3.4 mmol g −1. Experiments showed that, high yields of benzyl chloride insertions can be attained by using PVC samples with 40–50% of unsaturations. In the study transformation yields in each step were followed by conventional analytical methods and IR spectrometry. It was also demonstrated that modification of the chloromethyl groups either with KCN or sodium acetate proceeds with nearly quantitative yields, as in the case for chloromethylated styrene-divinyl benzene resins.

Theoretical and experimental investigation of biodegradation of hydrocarbon polluted water in a three phase fluidized-bed bioreactor with PVC biofilm support

The aerobic treatment of hydrocarbon polluted groundwater was performed experimentally in a three phase fluidized-bed bioreactor (FBBR) using mixed culture of living cells immobilized on PVC particles. The characteristic of the living cells immobilized in FBBR were identified and the kinetic parameters of the biochemical reaction were evaluated. A steady-state biofilm model was developed based on porous pellet model which considers the diffusion and reaction of hydrocarbons within biofilm, axial dispersion coefficient in bioreactor and external mass transfer resistance between biofilm and completely mixed liquid phase. The developed model assumes a first-order biochemical reaction within biofilm. Experimental results were used to test the validity of the proposed model. A reasonable agreement between the experimental and theoretical results was found.

Electrical conductivity of prelocalized graphite‐filled blend of polyvinyl chloride/styrene acrylonitrile composites in relationship to morphology and hardness

AbstractAt present there is a greater need to design conducting polymeric composites that suit particular application with little compromise on mechanical properties. This work deals with the study of electrical conductivity and mechanical strength of graphite‐filled blend of polyvinyl chloride/styrene acrylonitrile (PVC/SAN) composites. Samples were prepared by prelocalization of graphite onto the particles of PVC and SAN with subsequent compression molding. At a fixed volume ratio of 1:1 of PVC/SAN, percolation threshold of 0.0063 volume fraction of graphite has been observed. SAN has improved the D‐shore hardness of composites. Composites with more than 3 wt% graphite content have good conductivity and still preserve a reasonable mechanical strength. Conductivity patterns suggest higher affinity of graphite for PVC as compared to SAN. Scanning electron microscopy (SEM) micrographs indicate the widening of graphite layers with increasing graphite content. The electrical conductivity of composites has been explained in terms of percolation theory. The universal exponent t is found to be 3.09 for a best‐fit value of percolation threshold of 0.0057 volume fraction of graphite. There is good agreement between calculated and experimental values. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Compatible Polyethylene/Polyvinyl Chloride Particle Hybrids Prepared by in‐situ Polymerization

Polyethylene/polyvinyl chloride (PE/PVC) hybrids were successfully prepared by a polymerization‐filling method. The catalyst for ethylene polymerization was supported on PVC particles, and ethylene was then polymerized in‐situ on the surface of the activated PVC. PVC particles could be well segmented and dispersed during in‐situ polymerization, and the prepared hybrids had an additional tangent peak between the glass transitions of polyethylene and PVC, indicating the formation of a compatible interlayer between nascent polyethylene and PVC during polymerization.

Experiments and Analysis of Effect of Calender Gaps on Melting of PVC Powders in an Intermeshing Counter-rotating Twin-screw Extruder

Abstract Our ultrasound in-line monitoring studies revealed that dispersion or dissipation melting mechanism played a dominant role during melting of unplasticized polyvinyl chloride (uPVC) in an intermeshing counter-rotating twin-screw extruder. It is found that calendering effect between two screws contributes to the melting of PVC particles, and results in dispersion or dissipation melting. Thus, in this paper, a dispersed melting model in calender gaps is considered to predict polymer melting length in terms of numbers of calender gaps. Effects of screw geometries (channel depth, calender gap clearance) and processing conditions including screw speed and leakage flow on melting length are discussed for particle-filled fluid models. The calculated results are compared with experimental observations by both “screw pulling out” method and ultrasound in-line monitoring method. Ultrasound in-line monitoring provides a solution to overcome the time delay occurred in screw-pulling out method.

Visual determination of nitrite and nitrate in waters by color band formation method

A spot test for aqueous nitrate and nitrite for controlling nitrogen removal performance in small-scale wastewater treatment facilities is proposed. In this method, NO 2 - ion in water samples was allowed to react with sulfanilic acid and 1-naphthol to form an anionic azo dye. The resulting colored solution was introduced onto a mini column (similar to a gas detecting tube) packed with PVC particles coated with benzyl cetyl dimethyl ammonium chloride (BCDMA) and biphenyl. The NO 2 - – N concentration was determined visually by measuring the color band length (CBL) in the column. The CBL correlates linearly with nitrite concentration in the 4–20 mg-N l −1 range. The concentration of nitrite + nitrate was determined after reduction to nitrite with zinc. The concentration of NO 3 - – N species was calculated by difference. This method was used to visually determine the concentrations of NO 2 - – N and ( NO 2 - + NO 3 - ) – N in domestic wastewater samples with maximum suspended solid (SS) and chemical oxygen demand (COD) concentrations of 114 mg l −1 and 73.9 mg l −1, respectively.

Flow regime transition pointers in three-phase fluidized beds inferred from a solid tracer trajectory

Trajectories of solid radioactive tracers freely moving in a 3D gas–liquid–solid fluidized bed are analyzed from a data mining approach and using tools of symbolic dynamics. The trajectories are obtained by the radioactive particle tracking (RPT) technique, employing solids of different densities (glass beads and hydrophilized PVC particles), tap water as the fluidizing media and filtered air as the gas phase. Different gas velocities are examined to span the homogeneous and the heterogeneous flow regimes. The aim is to define parameters that can act as flow regime pointers. Hence, particular features of the particle motion are examined in detail to relate them to the underlying flow regime. In addition, by means of data symbolization, it is found that the recurrence of specific patterns of the tracer trajectories leads to higher frequencies of certain symbol sequences. Estimated frequencies are strongly influenced by the flow regime and may allow for regime identification.

Transition metal-doped titanium(IV) dioxide: Characterisation and influence on photodegradation of poly(vinyl chloride)

The effects of transition metal dopants (V(IV), V(V), Mn(II), Cr(III), Mo(V), and W(V)), introduced into TiO 2, upon the rate of photodegradation of poly(vinyl chloride) (PVC) films containing TiO 2 have been measured. The rates were determined mainly by monitoring carbonyl group formation. In another set of experiments, the rates of chloride ion release from irradiated PVC particles suspended in water undergoing agitation with air or O 2 in the presence of particles of doped TiO 2 were measured electrochemically. The doping of TiO 2 (rutile) with Cr(III), V(V) or Mn(II) reduces the photoactivity of the pigment, while doping by Mo(V) or W(V) enhances its photoactivity; the results obtained from carbonyl index measurements are paralleled closely by those from chloride ion release. Even the most aggressive doped pigments were less reactive than Degussa P25 pigment, while the greatest protection to PVC film was offered by TiO 2 particles coated with Al 2O 3 or SiO 2. Overall, the photoactivity of doped TiO 2 is a complex function of dopant concentration, the energy levels of the dopants in the TiO 2 lattice, their d electronic configuration and their local distribution. Photoactivity is also linked to other factors such as crystal type, particle size distribution and surface area. There is a clear relationship between the tendency of the dopant to induce the rutile-to-anatase transition and its effect in enhancing the photoactivity of the pigment. The characterisation of the doped pigments was achieved using X-ray powder diffraction, EPR spectroscopy, diffuse reflectance UV–vis spectrophotometry, scanning optical and electron microscopy and particle size analysis using LALLS.

Porownanie wplywu wybranych handlowych stabilizatorow suspensji na niektore wlasciwosci ziarna poli(chlorku winylu). Cz. I. Wplyw na rozklad wymiarow ziarna

The effects of the compositions of binary mixtures of selected commercial suspension stabilizers on suspension PVC particle size distribution (r.w.z.) and some other properties (K-value, bulk density, plasticizer absorption) were compared. The subjects of investigations were: 3 primary poly(vinyl alcohol) (PVAL) stabilizers of very similar hydrolysis degree (71-72 %), one secondary PVAL and methylhydroxypropylcellulose derivative classified as primary stabilizer. Binary mixtures differing in types and parts of components were prepared from these products. Suspension polymerization of vinyl chloride was carried out in laboratory scale at temperature dependent on required K-value of a polymer (53 °C, 57 °C and 64 °C). PVC particle size distribution has been investigated (Figs. 1-11) and the properties mentioned above (Tables 1-3) for the polymers prepared at each temperature. The mixtures of stabilizers allowing producing the products showing most advantageous (from the processing point of view) granulometric characteristics, that is, of most narrow r.w.z. and possibly minimal part of oversized and undersized grain, were picked. The results show that commercial stabilizers of even very similar characteristics can not be swapped because only the proper choice of their types and amounts let produce PVC of good processing properties.

Rotational Moulding of PVC Plastisol

Abstract The viscosity during the earlier stages of the gelation process of plastisols formulated with 15 different commercial plasticizers has been obtained. Plastisols prepared were rotomoulded and mouldings obtained were characterized according to their wall thickness distribution. This parameter strongly depends on the minimum viscosity and on the rate of viscosity change during gelation (slope of the curves during the viscosity increase), and also on the temperature where no more flow of the plastisol is observed (gelation temperature). These variables are conditioned by the characteristics of the plasticizer and PVC employed, among other variables. The effect of plate and arm velocity and rotation rate on the wall thickness distribution was also studied. A simple model has been proposed to correlate the initial stage of the gelation of PVC plastisols formulated with the phthalate plasticizers. The suggested model assumes that the plastisol is a suspension constituted by a continuous phase (initially pure plasticizer) and a discontinuous phase constituted by PVC particles. It has been considered that the viscosity of the plastisol is influenced by the average mass molecular weight of the continuous phase and the temperature. The quantity of PVC dissolved in the continuous phase has been calculated by using a generic n-order kinetic equation for PVC dissolution rate. Additionally, a swelling process of the PVC particle by the plasticizer has also been considered and its effect on the viscosity of the suspension has also been accounted for. The model proposed provides a very good fitting of the sharp viscosity increase observed and is useful to predict the evolution of the viscosity of the parts in a rotomoulding process.

Small-angle X-ray scattering study of modified porous suspension-poly(vinyl chloride) particles

Small-angle X-ray scattering (SAXS) was ap- plied to investigate the microstructure of unmodified and modified porous commercial suspension-type poly(vinyl chloride) (PVC) particles. The modified PVC particles were prepared by an in situ stabilizer-free polymerization/ crosslinking of particles absorbed with a monomer/ crosslinker/peroxide solution. The modifying polymers in- clude styrene with or without divinyl benzene (DVB) as a crosslinker and methyl methacrylate (MMA) with or with- out ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The SAXS method was used to highlight the effect of polystyrene (PS) on the microstructure of PVC particles and to evaluate the characteristic lengths, both in the PVC/PS and the PVC/XPS (PS crosslinked with 0 and 5% DVB, respectively) systems. A model is suggested, where during the synthesis modification process, swelling of PVC by styrene and styrene polymerization occur simulta- neously. PVC swelling by styrene causes destruction of the PVC subprimary particles, whereas styrene polymerization leads to phase separation resulting from incompatibility of the polymers. It was further suggested that because of PVC swelling by styrene, structure of the subprimary particles is lost. Therefore the characteristic lengths of PVC/PS and PVC/XPS, as calculated from the SAXS measurements, were attributed to the size of the phase-separated PS and XPS inclusions, respectively. The SAXS method also shows that PMMA and XPMMA do not influence the PVC microstruc- ture. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1024 -1031, 2005

Structure of reactively extruded rigid PVC/PMMA blends

A novel route for producing polymer blends by reactive extrusion is described, starting from poly (vinyl chloride)/methyl methacrylate (PVC/MMA) dry blend and successive polymerization of MMA in an extruder. Small angle X-ray scattering (SAXS) measurements were applied to study the monomer's mode of penetration into the PVC particles and to characterize the supermolecular structure of the reactive poly(vinyl chloride)/poly(methyl methacrylate) (PVC/PMMA) blends obtained, as compared to the corresponding physical blends of similar composition. These measurements indicate that the monomer molecules can easily penetrate into the PVC sub-primary particles, separating the PVC chains. Moreover, the increased mobility of the PVC chains enables formation of an ordered lamellar structure, with an average d-spacing of 4.1 nm. The same characteristic lamellar structure is further detected upon compression molding or extrusion of PVC and PVC/PMMA blends. In this case the mobility of the PVC chains is enabled through thermal energy. Dynamic mechanical thermal analysis (DMTA) and SAXS measurements of reactive and physical PVC/PMMA blends indicate that miscibility occurs between the PVC and PMMA chains. The studied reactive PVC/PMMA blends are found to be miscible, while the physical PVC/PMMA blends are only partially miscible. It can be suggested that the miscible PMMA chains weaken dipole–dipole interactions between the PVC chains, leading to high mobility and resulting in an increased PVC crystallinity degree and decreased PVC glass transition temperature (Tg). These phenomena are shown in the physical PVC/PMMA blends and further emphasized in the reactive PVC/PMMA blends. Copyright © 2005 John Wiley & Sons, Ltd.

Finite volume approach for solving multiphase flows in vertical pneumatic dryers

In the present study, a finite volume approach for solving two‐dimensional, two‐fluids flows with heat and mass transfer was developed for predicting the flow of particulate materials through pneumatic dryer. The model was solved for a two‐dimensional steady‐state condition and considering axial and radial profiles for the flow variables. A two‐stage drying process was implemented. The numerical procedure includes discretization of calculation domain into torus‐shaped final volumes, solving the gas phase conservation equations by a modified semi‐implicit method for pressure‐linked equations algorithm, and the conservation equations of particulate phase were solved by the explicit forward difference algorithm. The mass momentum and energy coupling between the phases were considered by principles of the Interphase slip algorithm. In order to validate the theoretical and the numerical models, the developed models were applied to simulate the drying process of wet PVC particles in a large‐scale pneumatic dryer and to the drying process of wet sand in a laboratory‐scale pneumatic dryer. The predictions of the numerical simulations were compared successfully with the results of independent numerical and experimental investigations. Following the models validation, the two‐dimensional distributions of the flow characteristics were examined.