Suspension Polymerization Of Vinyl Chloride Research Articles

A Self-Adjustment Optimization Method of Composite Initiator Concentration for Vinyl Chloride Suspension Polymerization

The productivity of batch processes is related to the time required to complete each batch. A self-adjustment optimal method for the vinyl chloride (VC) suspension polymerization is proposed for minimizing polymerization time. By optimizing the concentration of the composite initiators, the polymerization reaction proceeds smoothly so that the cooling capacity of the reactor is fully utilized and the polymerization time is minimized accordingly. In this work, a thermodynamic model is presented to estimate both online reaction advancement and the heat transfer characteristic of the reactor; a kinetic model of composite initiators is referenced to predict the polymerization rate; and a parameter adjustment model is applied to adjust the initiator partition coefficient of the kinetic model for ensuring the prediction performance and compute the maximum limiting polymerization rate for updating the constraints of optimization model. Results show that by choosing the optimal concentration of composite initiators under the constraints of reaction kinetics, maximum limiting polymerization rate, etc., a significant reduction in the total processing time is achieved.

Particle configuration and properties of poly(vinyl chloride)/halloysite nanotubes nanocomposites via in situ suspension polymerization

Poly(vinyl chloride) (PVC)/halloysite nanotubes (HNTs) nanocomposites were synthesized by in situ suspension polymerization of vinyl chloride (VC) in the presence of HNTs. The microstructure, mean particle size, and cold plasticizer absorption (CPA) of these resins and the rheological property, mechanical properties and thermal properties of PVC/HNTs nanocomposites were investigated. The results show that the mean particle size, the degree of porosity, and the CPA of PVC resins decrease with the addition of HNTs. The plasticization time and the equilibrium torque of PVC/HNTs nanocomposites are found to be longer and higher than that for the neat PVC. HNTs are uniformly distributed in the PVC matrix and effective in toughening and stiffening PVC nanocomposites when the addition of HNTs is 4.0 wt% or less. The glass transition temperatures of the PVC/HNTs nanocomposites were nearly identical to that of pure PVC. POLYM. COMPOS., 35:856–863, 2014. © 2013 Society of Plastics Engineers

Modelling and simulation of suspension polymerization of vinyl chloride via population balance model

A detailed population balance model is presented for suspension polymerization of vinyl chloride in an isothermal batch reactor perfectly mixed on macrolevel. Coalescence and breakage of monomer droplets, as well as mass exchange of species between the droplets induced by collisions, termed micromixing, are also included into the model forming a complex three-scale system. The resulted population balance equation is solved by coupling the deterministic continuous time computation of polymerization reactions inside the droplets with the random coalescence and breakage events of droplets using Monte Carlo simulation. The results obtained by simulation revealed that aggregation, breakage and micro-mixing of species induced by droplet collisions affect the process significantly.

Modelling and Simulation of a Batch Poly(Vinyl Chloride) Reactor

A population balance model for batch suspension polymerization of vinyl chloride is presented. Break up into two equal volumes of droplets, binary aggregation and random mass exchanges between the colliding droplets are assumed, while the kinetic data of vinyl chloride polymerization are taken from the literature. The model and the process are analyzed by simulation applying a novel Monte Carlo method taking into account breakage and aggregation of droplets as well as micromixing induced by droplet binary collisions as stochastic discrete event processes. The results revealed that this method of modelling describes phenomena in suspension polymerization of vinyl chloride properly.

Modelling of heat exchange between drops in suspension polymerization of vinyl chloride

A population balance model is presented for suspension polymerization of vinyl chloride in a batch reactor to investigate the thermal properties of the system. Reactions are described using a simplified reaction model focusing on the heat generation of the highly exothermic polymerization reactions. The temperature of the continuous phase is assumed to be homogeneous over the reactor and the effects of some temperature rise of droplets due to the exothermic polymerization reactions and the possible heat exchange because of the coalescence/redispersion process are analysed. The population balance equation is solved applying a Monte Carlo method by coupling the deterministic polymerization reactions inside the droplets with the discrete event process induced by collisions of droplets. The results obtained by simulation show that rise in the temperature of droplets over the mean temperature of continuous phase lead to acceleration of the process. The possible size distribution of droplets and no smooth distribution of the initiator in those decrease the process efficiency.

In‐Line Monitoring of Vinyl Chloride Suspension Polymerization with Near Infrared Spectroscopy, 2 ‐ Design of an Advanced Control Strategy

AbstractNear infrared spectroscopy (NIRS) may constitute a powerful tool for in‐line monitoring of morphological properties of PVC particles in suspension polymerizations. It is shown that dynamic trajectories of morphological properties, as predicted with NIR‐based calibration models, change smoothly along the batch; thus, these trajectories can be used as references for process monitoring and control. It is also shown that modification of operation variables during the batch leads to modification of the final morphological properties of the powder. This indicates that the morphology of PVC grains can be manipulated along the batch and that advanced NIR‐based control procedures can be implemented for control of the morphological properties of PVC resins, as illustrated through simulation.magnified image

In‐Line Monitoring of Vinyl Chloride Suspension Polymerization with Near‐Infrared Spectroscopy, 1 – Analysis of Morphological Properties

AbstractIt is demonstrated that during suspension polymerizations it is possible to monitor morphological characteristics of PVC resins such as bulk density, cold plasticizer absorption and average particle diameter in‐line and in real time using NIR spectroscopy. NIR spectra are obtained at different experimental conditions, showing that the spectra are sensitive to changes in the PVC properties. Standard mathematical procedures (partial least squares regression) are used to build empirical models and correlate the morphological properties with the obtained NIR spectra, allowing for monitoring of the PVC morphology in‐line and in real time.magnified image

Microkinetic Modeling of Structural Properties of Poly(vinyl chloride)

The free radical suspension polymerization of vinyl chloride is modeled at the elementary reaction level, systematically taking into account diffusion limitations. By deriving balances for structurally distinct polymer and radical species the formation of structural defects can be followed: monomer conversion, averages of the molar mass distribution and the structural defects content can be calculated as a function of polymerization time for industrially relevant conditions. A good agreement between literature reported and calculated values for these properties is obtained for a polymerization temperature range of 325-340 K, a dicetyl peroxydicarbonate and dimyristyl peroxydicarbonate initiator concentration range of 0.00069-1.0 wt %, and a monomer conversion range of 12-96%. The increase of the branching content and the decrease of the terminal double bond content at high monomer conversions can be explained in terms of a favoring of monomolecular reactions and the increasing importance of addition reactions to unsaturations at these conditions.

On‐line acoustic attenuation spectroscopy of emulsions stabilized by vinyl alcohol–vinyl acetate copolymers: a model system for the suspension polymerization of vinyl chloride

AbstractBACKGROUND: Poly[(vinyl alcohol)‐co‐(vinyl acetate)] (PVA) copolymers obtained by partial hydrolysis of poly(vinyl acetate) are currently used as industrial stabilizers in the suspension polymerization of vinyl chloride monomer (VCM). Their molecular characteristics, mainly the average degree of hydrolysis (DH) and average degree of polymerization (DPw), have a major influence on the monomer droplet size and the properties of the final poly(vinyl chloride) resin.RESULTS: The average droplet size and size distribution of chlorobutane/water emulsions, as a model system for VCM/water emulsions, were studied using acoustic attenuation spectroscopy on‐line with an agitated laboratory reactor. The emulsions were stabilized by PVA with DH values between 73 and 88 mol% and DPw values between 450 and 2500. The effects of agitation speed, stirring time and concentration of the PVA copolymers were investigated. An attempt was made to correlate the interfacial tension and the droplet size.CONCLUSION: On‐line acoustic spectroscopy appears to be a suitable technique for the real‐time control of the droplet size of monomer suspensions. The advantages and limitations of the technique are outlined. The validity and the application limits of the commonly cited correlation between the droplet size and the Weber number are established for polymeric surfactant‐stabilized emulsions. Copyright © 2009 Society of Chemical Industry

Initiator efficiency modeling for vinyl chloride suspension polymerization

A unified methodology is developed to calculate the fraction of initiator derived radicals that initiates the polymerization, i.e. the initiator efficiency, as a function of polymerization time and polymerization conditions. In the presented approach the most important reactions that initiator derived radicals undergo are taken into account. All involved parameters have a clear physical and fundamental meaning and no adjustment to experimental data is required. The presented methodology is applied to diacyl peroxide initiators that are commonly used in industrial vinyl chloride suspension polymerization processes: dodecanoyl peroxide and benzoyl peroxide. Validation is performed by comparing calculated and experimental data for the monomer conversion and averages of the molar mass distribution within a polymerization temperature range of 323–333 K and an initiator concentration range of 0.26–4.2 wt% based on the monomer.

Importance of Radical Transfer in Precipitation Polymerization: The Case of Vinyl Chloride Suspension Polymerization

AbstractThe importance of radical transfer between the reactive phases in precipitation polymerization processes is investigated with the vinyl chloride suspension polymerization as an example. A two‐film model that accounts for a mass transfer resistance in both the monomer‐rich and the polymer‐rich phase is constructed and applied. Equilibrium is assumed at the interphase boundary. Based on model calculations using intrinsic rate coefficients obtained by regression to experimental data the effect of accounting for radical transfer between the reactive phases on the simulated monomer conversion and total moments of the molar mass distribution is demonstrated. It is found that the effect of radical transfer between the reactive phases is most pronounced at low polymerization temperatures.magnified image

Thermal stability, smoke emission and mechanical properties of poly(vinyl chloride)/hydrotalcite nanocomposites

Poly(vinyl chloride)/hydrotalcite (PVC/HT) nanocomposites were prepared through vinyl chloride suspension polymerization in the presence of HT nanoparticles surface modified with alkyl phosphate (AP). The thermal stability, smoke emission and mechanical properties of PVC/HT nanocomposites were investigated. It was found that AP molecules were effectively absorbed by HT particles with no intercalation into the interlayer of HT. The dispersion morphologies of PVC/HT nanocomposites were observed by transmission electron microscopy showing that the majority of HT particles were dispersed in the PVC matrix in the nanoscale. The Congo Red measurement and thermogravimetric analysis showed that the thermal stability time, and the temperatures at 10% weight loss and at the maximum weight loss rate of PVC resins increased as the weight fraction of HT in the composite resins increased. The well-dispersed nano-sized HT showed an obvious smoke suppression effect on PVC. The maximum smoke density decreased about 1/3 and 1/2 when 2.5 wt% and 5.3 wt% nano-sized HT were incorporated into PVC, respectively. Furthermore, PVC/HT nanocomposites exhibited greater tensile strength and impact strength than the pristine PVC.

On the prediction of internal particle morphology in suspension polymerization of vinyl chloride. Part I:: The effect of primary particle size distribution

The present study provides a comprehensive investigation on the determination of the primary particle size distribution in the suspension “powder” polymerization of vinyl chloride. The primary particle size distribution inside the polymerizing monomer droplets is determined by the solution of a population balance equation governing the nucleation, growth, and aggregation of the primary particles. The stability of the colloidal primary particles is expressed in terms of the electrostatic and steric stabilization forces. The primary particle stability model includes the effects of agitation, temperature, electrolyte as well as primary and secondary stabilizer concentrations. It also includes both diffusive and shear-induced particle destabilization mechanisms. The proposed stability model is shown to accurately describe existing experimental data on particle number, mean particle size and particle size distribution for both bulk and suspension vinyl chloride polymerizations. The primary particle population balance model can predict the critical monomer conversion at which massive particle aggregation occurs leading to the formation of a continuous network of primary polymer particles inside the polymerizing monomer droplets. A detailed investigation on the predicted critical monomer conversion is carried out including its dependence on the rate of agitation, temperature, electrolyte concentration, as well as the concentrations of the primary and secondary stabilizers.

Modelling the formation of structural defects during the suspension polymerization of vinyl chloride

The free radical suspension polymerization of vinyl chloride is modelled at the elementary reaction level, systematically taking into account diffusion limitations. The resulting kinetic model enables the quantitative description of conversion, molecular mass distribution and the formation of structural defects as a function of polymerization time for a wide range of industrially relevant conditions. By deriving population balance equations for structurally distinct radical species the formation of structural defects could be determined. From model calculations it follows that structural defects are predominantly formed at conversions higher than 75% as the rates of the monomolecular reactions responsible for the formation of structural defects are not limited by diffusion and thus become favoured at higher conversion. This threshold value for the monomer conversion is in good agreement with experimental observations.

Preparation and characterization of colloidal dispersions of vinyl alcohol–vinyl acetate copolymers: application as stabilizers for vinyl chloride suspension polymerization

AbstractWell‐defined colloidal dispersions of vinyl alcohol–vinyl acetate copolymers (PVAs) with different degrees of hydrolysis (DH) were prepared by a coacervation technique. Colloidal particles in the size range 150–250 nm, with an acetate‐rich core and a hydrophilic PVA corona, were obtained using a combination of a hydrophobic PVA (PVA II) having an average DH ($\overline{DH}$) value of 43 mol% with a ‘blocky’ hydrophilic PVA (PVA I) with a $\overline{DH}$ value of 72 mol%. The core–shell structure of these particles was demonstrated using 1H NMR and using fluorescence‐labelled PVA I. The stabilization efficiency of PVA I and PVA II and their combination was examined for 1‐chlorobutane–water emulsions, as a ‘model solvent’ for vinyl chloride–water emulsions. Preliminary tests of vinyl chloride suspension polymerization confirmed the beneficial effect of PVA I and PVA II combinations as stabilizers on the granulometry and the porosity specifications of the poly(vinyl chloride) grains. Copyright © 2006 Society of Chemical Industry

Polymerization of vinyl chloride in the presence of nanofillers - effects on the shape and morphology of PVC grains

Suspension polymerization of vinyl chloride has been carried out in the presence of various types of nanofillers chosen from clays, silica (pure or functionalized), silicone polymer or hybrid core/shell ones. Nanofillers used in VC polymerization significantly influence the structure and shape of PVC grain: from typical one in case of control sample and in the presence of silica to cake-like in case of functionalized silica, sea-shells with silicone polymer use or and dented balls - not typical for suspension PVC - in the presence of hybrid core/shell particles. The last ones look just as emulsion PVC although were prepared in suspension polymerization process. It has been found, using SEM and TEM methods, that distribution of nanofiller in polymer was rather uniform. MMT is semiintercalated/semiexfoliated in PVC grain. Some regions showing mesoporosity were also found (especially in the presence of silica) suggesting the formation of more ordered structures in the grain. We can foresee that not only the presence and distribution of nanofillers in PVC grain but also the change of PVC grain shape caused by them can both influence the final properties of PVC and its processability.

Estimation of intrinsic rate coefficients in vinyl chloride suspension polymerization

The pre-exponential factor and the activation energy of the intrinsic rate coefficients for propagation, chain transfer to monomer, chain initiation by a Cl radical and termination in the suspension polymerization of vinyl chloride are estimated by regression of experimental data for the monomer conversion, ranging from 3 to 85%, and for the moments of the molecular mass distribution as a function of batch time over the temperature range of 308–338K and for initiator (tert-butyl peroxyneodecanoate) concentrations from 0.026 to 3.0wt%, based on the monomer. Termination by combination is the dominant termination mechanism. Cl radicals, formed in the chain transfer to monomer, contribute to the termination by recombination with macroradicals and, hence, attenuate the gel effect. Physically meaningful and statistically significant estimates for the pre-exponential factors and activation energies, 24.9kJmol−1 for propagation and 54.3kJmol−1 for chain transfer, allow to describe the experimental data over the full range of investigated conditions.

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.

New Insight into the Formation of Structural Defects in Poly(Vinyl Chloride)

The monomer conversion dependence of the formation of the various types of defect structures in radical suspension polymerization of vinyl chloride was examined via both 1H and 13C NMR spectrometry. The rate coefficients for model propagation and intra- and intermolecular hydrogen abstraction reactions were obtained via high-level ab initio molecular orbital calculations. An enormous increase in the formation of both branched and internal unsaturated structures was observed at conversions above 85%, and this is mirrored by a sudden decrease in stability of the resulting PVC polymer. Above this threshold-conversion, the monomer is depleted from the polymer-rich phase, and the propagation rate is thus substantially reduced, thereby allowing the chain-transfer processes to compete more effectively. In contrast to the other defects, the chloroallylic end groups were found to decrease at high conversions. On the basis of the theoretical and experimental data obtained in this study, this decrease was attributed to copolymerization and abstraction reactions that are expected to be favored at high monomer conversions. Finally, a surprising increase in the concentration of the methyl branches was reported. Although a definitive explanation for this behavior is yet to be obtained, the involvement of transfer reactions of an intra- or intermolecular nature seems likely, and (in the latter case) these could lead to the presence of tertiary chlorine in these defects.

Calorimetric study of polyvinyl alcohols used as emulsifiers in suspension polymerization of vinyl chloride

The heat effects of dissolution of two pairs of polyvinyl alcohols used as emulsifiers in suspension polymerization of vinyl chloride and the optical transmission of their stirred aqueous solutions as a function of time were determined.