Suspension Polymerization Of Vinyl Chloride Research Articles

Computer-aided design of initiator utilization strategies for vinyl chloride suspension polymerization with constant reaction rate

From the viewpoint of polymer reaction engineering (PRE), polymerization with constant reaction rate is beneficial for reducing manual operations and promoting production efficiency. Using vinyl chloride (VC) suspension polymerization as a model system, manipulating the radical concentration by radical concentration-dependent optimization (RCO)-based initiators mixing (IM) strategy or continuous initiator dosing (CiD) strategy enables the polymerization with constant reaction rate. Case studies have been done to illustrate how the RCO-based IM strategy works for binary initiator combination screening and how to conduct VC suspension polymerizations with different reaction rates using RCO-based IM strategy. Importantly, decomposition kinetic parameters estimated for virtual initiators can be used for guiding the design of the capable initiators. Moreover, in the single initiator systems, the applicability of the RCO-based CiD strategy has been demonstrated by conducting VC suspension polymerization with different reaction rates and different temperatures. Optimal dosing rate profiles of the initiator can be provided for the cases demonstrated. It is expected that both RCO-based IM and CiD strategies can be extended to other free radical polymerization systems.

In‐silico vinyl chloride suspension polymerization: Kinetic modelling, thermal runaway prediction, and prevention

AbstractIn the present study, a combined kinetic and heat transfer model was developed to study the kinetics and predict thermal runaway of vinyl chloride (VC) suspension polymerization. Reactor temperature, monomer conversion, mole of initiator, radical concentrations in the two phases (i.e., VC‐rich phase and PVC‐rich phase), and average molecular properties were mapped during non‐isothermal processes. Meanwhile, the risk of thermal runaway was evaluated using S–Z (divergence) and H–J criteria. Simulation results show that a lower jacket temperature Tj and a larger heat transfer coefficient U are able to postpone or even avoid the risk of thermal runaway. Both of the criteria serve well for the prediction of thermal runaway during non‐isothermal processes. To prevent the occurrence of thermal runaway to the greatest extent, model‐based design of strategies for an isothermal polymerization process was done. Specifically, either jacket temperature Tj or heat transfer coefficient U can be fine‐tuned to maintain a 50°C isothermal process.

In situ suspension polymerization of vinyl chloride/3-(trimethoxysilyl) propyl methacrylate (MPTMS)-intercalated Mg-Al-hydroxide layered double hydroxide: I. Grain properties

Suspension polymerization of vinyl chloride (VCM) was carried out in the presence of particle of both pristine Mg-Al layered double hydroxide (LDH) and LDH intercalated by 3-(trimethoxysilyl) propyl methacrylate (MPTMS-LDH) in a pilot-scale reactor. The experiments were conducted at different concentrations of each type of the particles (0, 1, 3, 5, 7 wt. % of VCM). The pure LDH and MPTMS-intercalated LDHs were used as co-monomer for fabrication of LDH or MPTMS-LDH/PVC nanocomposites; the particles were directly pre-dispersed in monomer phase before dispersing in the continuous aqueous phase and starting the suspension polymerization. The basal spacing obtained from the X-ray powder diffraction (XRD) showed that the reaction between VCM and MPTMS-LDH was effective, with a further intercalation of PVC chains in the interlayer space. The molecular characterization showed that the polydispersity index (PDI) and molecular weight of the poly (vinyl chloride) (PVC) resin do not change in the presence of the pristine LDH. The MPTMS-LDH, however, decrease the molecular weight and increase the PDI of PVC resin. Also, from the morphological point of view, scanning electron microscopy (SEM) showed that PVC grains produced with high particles content had a smoother surface with more regular shape. Moreover the incorporation of nanoparticles in the VCM suspension polymerization, made particles with a narrower size distribution. The LDH results in the formation of smaller primary particles with higher internal porosity whereas, the larger primary particles with lower internal porosity in the presence of modified particles was observed.

Numerical Simulation of Reaction Efficiency of Vinyl Chloride Suspension Polymerization Reactor

This paper establishes a mathematical method for calculating the polymerization process of industrial vinyl chloride suspension polymerization reactors. The polymerization rate, weight average molecular weight (WAMW), number average molecular weight (NAMW), monomer conversion rate and pressure are displayed throughout the reaction. Applying this model to existing experiment in the literature, the results are close. The final simulation results will be used to guide the industrial production of polyvinyl chloride (PVC).

One-pot polyvinyl chloride preparation utilizing polyacrylate latex with tertiary amine groups for improved thermal stability, toughness, and reduced reactor scaling

In this paper, crosslinked polyacrylate latex with tertiary amine groups (ACLN) and base latex without tertiary amine groups (ACL) were prepared by emulsion polymerization using butyl acrylate as the monomer and 1,4-butanediol dimethacrylate as the crosslinker. Composite resins of polyvinyl chloride (PVC), ACL/PVC and ACLN/PVC, were prepared by suspension polymerization of vinyl chloride in a 20 L high-pressure reactor by adding ACL and ACLN as modifiers. The inner pressure of the reactor and initiator concentration as a function of reaction time during suspension polymerization were studied. Morphology of resin particles, processing properties, thermal stability and mechanical properties of ACL/PVC and ACLN/PVC products were investigated. A commercial PVC product named PVC-SG5 was used as the control sample for comparison. It was found that compared with typical PVC-SG5 preparation, ACL/PVC fabrication took less time while initiator concentrations needed to be increased to 2400 ppm in ACLN/PVC preparation in order to complete the polymerization within the same time. Reactor scaling occurred during ACL/PVC preparation, but could be avoided in ACLN/PVC preparation owing to the hydrophilicity of ACLN. The morphology of ACL/PVC and ACLN/PVC particles was smooth microspheres and mosaic particle shapes, respectively, the diameter of which were all smaller than PVC-SG5 particles. The covalent-bonding existing in ACL/PVC and ACLN/PVC, and ionic-bond formation of quaternary ammonium in ACLN/PVC composite resins, between tertiary amine groups in ACLN and chlorine atoms in PVC, contributed to the dramatic increase in thermal stability. ACLN/PVC exhibited the shortest plasticizing time and the longest elongation at break, followed by ACL/PVC. The toughness of both ACL/PVC and ACLN/PVC were greatly enhanced without affecting the tensile strength and softening temperature of the resin. Thus, three issues, namely, low thermal stability, low toughness and reactor scaling during polymerization of PVC have been comprehensively solved by introducing ACLN to PVC through a one-pot method.

The effects of initiators mixture on suspension polymerization of vinyl chloride and its comparison with other productivity-enhancing procedures

Molecular and morphological properties of poly(vinyl chloride) (PVC) grains produced by suspension polymerization of VCM in the presence of a mixture of fast, mild and slow initiators (named as Cok process) was experimentally investigated in a pilot-scale reactor. In contrast to nonisothermal and fast initiator dosage process, using initiators mixture has the smallest influence on molecular weight and polydispersity index compared to the control process. It is found that Cok-PVC grains have the lowest cold plasticizer absorption and porosity among productivity-enhancing processes. Scanning electron microscopy showed that the particles produced by Cok process are more regularly shaped, with a smoother surface compared with the control resin. All three productivity-enhancing techniques lead to an apparent quality enhancement, higher flowability and greater bulk density of final grains when compared with control resin grains. While both nonisothermal and fast initiator dosage polymerization process broaden the particle size distribution (PID) of final PVC grains, applying Cok process produces particles with the same PID as a control process. In comparison with nonisothermal trajectory and continuous fast initiator dosage system, the Cok polymerization process leads to the most delay of motionless conversions, fusion time and the formation of a three-dimensional skeleton of primary particles as well.

Morphology, mechanical property, and processing thermal stability of PVC/La‐OMMTs nanocomposites prepared via in situ intercalative polymerization

Poly(vinyl chloride) (PVC) nanocomposites were prepared via an in situ intercalative suspension polymerization of vinyl chloride with four organic carboxylic acid salts (montmorillonite [MMT] units) containing thermally stable lanthanum ions. The effects of different lanthanum organic montmorillonites (La‐OMMTs) on the particle features and molecular weight were investigated. The transmission electron microscopy data indicated the formation of partially exfoliated or intercalated PVC/La‐OMMTs nanocomposites. The effect of different functional groups on the mechanical properties and processing thermal stability of PVC/La‐OMMT nanocomposites were investigated. Tensile testing and two‐roll mill processing results showed that La‐OMMTs could enhance the dynamic thermal stability and mechanical properties versus PVC pure resin and PVC/I.30P nanocomposites (composed of PVC and I.30P). This suggested that the double bond and amidogen group in La‐OMMTs could promote the dispersion of La‐OMMTs in the PVC matrix and also improve the adhesion between the La‐OMMTs and PVC matrix. The results have potential value in the industrial development of PVC/La‐OMMTs nanocomposites. J. VINYL ADDIT. TECHNOL., 26:97–108, 2020. © 2019 Society of Plastics Engineers

Effect of Initiator Rate on Kinetics of Reaction and PVC Grains Features in Continuous Dosing of Fast Initiator During Vinyl Chloride Suspension Polymerization

In order to investigate how the continuous dosage of a fast initiator can affect the kinetics of polymerization and the properties of PVC grains, a series of vinyl chloride monomer suspension polymerization experiments were carried out in which a fast initiator was dosed into the reactor in different ways (non‐continuous, intermittent, and continuous) and different rates. It was found that in the case of polymerization with continuous dosage of the fast initiator, the polymerization time decreased and critical conversion increased with increasing in the initiator dosage level. While the molecular weight of the final PVC was only slightly decreased. Morphological analysis showed that the porosity and particles size increased with initiator dosage level, while the bulk density was also decreased. Other methods of initiator dosing, i.e., intermittent and non‐continuous dosage of the fast initiator reduced the efficiency of the fast initiator compared to the corresponding continuous dosage polymerization at the same initiator value. J. VINYL ADDIT. TECHNOL., 24:367–375, 2018. © 2018 Society of Plastics Engineers

Agitating transformation during vinyl chloride suspension polymerization: aggregation morphology and PVC properties

In this study, the effect of agitation rate on the aggregation morphology of the suspension poly(vinyl chloride) (PVC) grains, especially their primary particles, at different conversions was investigated.

Continuous dosing of fast initiator during vinyl chloride suspension polymerization: Thermal stability of PVC resin

ABSTRACTThermal stability of poly(vinyl chloride) (PVC) produced using continuous dosages of a fast initiator method was investigated in terms of morphological and microstructural characteristics. The results were compared with the properties of the PVC prepared by conventional polymerization method. The Brabender® Plastograph and DSC results showed a lower fusion time, higher stable time, and greater degree of fusion for PVC obtained by polymerization using initiator continuous dosage method. Also, chemical analysis indicated that the PVC produced under an initiator continuous dosage system have lower structural defects, that is, branch numbers, internal double bonds, labile chlorine, and tacticity index, thereby improving the thermal stability of PVC resin. The results obtained from dehydrochlorination and thermogravimetry analysis confirm the improvement of thermal stability of PVC chains synthesized with continuous dosages of a fast initiator. Moreover, it was found that the concentration of microstructural defects and the dehydrochlorination rates of the PVC samples prepared by both processes increase with monomer conversion, particularly after critical conversion. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44480.

Continuous dosing of fast initiator during vinyl chloride suspension polymerization: Polymerization rate and PVC properties

ABSTRACTContinuous dosing of a fast initiator during the suspension polymerization of vinyl chloride has been carried out in a pilot‐scale reactor. The kinetics course of this polymerization and the particle features of the resulting grains were discussed and compared to the conventional polymerization with the same conversion and maximum reaction rate. It was found for the system used that a suitable dosage trajectory allows the reaction rate to remain constant during polymerization. This decreases the polymerization time up to 53% compared with the conventional suspension polymerization, while the molecular weight distribution and molecular weight of the final grains remained almost unchanged. SEM micrographs revealed that PVC grains prepared using this polymerization process had irregularly shaped, uneven particle surfaces and larger particle sizes. The grains also featured high porosity with loosely aggregated smaller primary particles that led to low levels of residual unreacted monomer. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44079.

Continuous Dosing of a Fast Initiator during Suspension Polymerization of Vinyl Chloride for Enhanced Productivity: Mathematical Modeling and Experimental Study

An adopted mathematical model was developed to reduce the batch time required for the suspension polymerization of vinyl chloride in order to improve the productivity by continuous dosage of a fast initiator during polymerization reaction. The model was accompanied by a particle swarm optimization (PSO) algorithm, so as to optimize the initiator dosage rate during the process for a certain conversion. A pilot scale reactor was employed to verify the mathematical model predictions. This showed that the model predictions are in very good agreement with the experimental data. A proper initiator dosage trajectory during the course of the reaction was obtained in such a way that the reaction rate over the course of polymerization was constant and corresponded to the maximum rate in the conventional case (non-continuous addition of a mild initiator). The maximum reduction in reaction time relative to conventional polymerization for the predefined conversion was 53%. Analyzing the molecular characteristics of the samples showed that the molecular characteristics of the final poly(vinyl chloride) (PVC) product remained relatively unchanged under an optimum initiator dosage trajectory compared with the conventional process.

Real time monitoring of the quiescent suspension polymerization of vinyl chloride in microreactors – Part 2. A kinetic study by Raman spectroscopy and evolution of droplet size

This paper regards the experimental study on the polymerization of vinyl chloride droplets in quiescent state using microreactors. As presented in a previous work performed with methyl methacrylate monomer, this work presents results on the reaction kinetics of vinyl chloride (VCM) polymerization monitored by Raman spectroscopy and on the evolution of VCM droplets as captured by charge-coupled device (CCD) camera in a microcapillary. Different experimental recipes were proposed using commercial initiators in order to compare the system performance when initiated with monofunctional and bifunctional peroxides. For the first time in the open literature the evolution of VCM droplets is shown up to high conversions (>90%) in quiescent state. It is also shown how the pressure drop can modify the PVC particle morphology at the end of polymerization. Finally, it is shown that the Raman technique is able to monitor the reaction kinetics at different conditions, being possible to identify four different characteristic stages during the vinyl chloride polymerization reactions.

Influences of initiator addition methods in suspension polymerization of vinyl chloride on poly(vinyl chloride) particles properties

Vinyl chloride suspension polymerization was carried out in a pilot‐scale reactor to study the effects of different methods of initiator addition on poly(vinyl chloride) (PVC) resin properties. The experiments used different arrangements for adding the initiator to the reactor, whereas other reaction conditions were the same: (i) initiator was added to the continuous aqueous phase and then monomer was dispersed in it (conventional method); (ii) initiator was predissolved in monomer before dispersing in the continuous aqueous phase; and (iii) suspending agents along with initiator were added to the monomer before polymerization. The PVC resin prepared by method of (i) had a higher monomer conversion and a higher Sauter mean diameter of grains with a narrow particle size distribution comparable to that of PVC resins by other methods. Scanning electron microscopy showed more uniform particles and fused primary particles in the grains, which confirms lower porosity and lower cold plasticizer absorption (CPA) for PVC grains produced by procedure of (ii). The results showed that when the suspending agents were also predispersed in monomer along with initiator (iii), CPA increases dramatically due to internal porosity of the grains. Simultaneously, a marked decrease in Sauter mean diameter was apparent. Scanning electron microscopy micrographs show that primary particles in the interior of PVC grains prepared by the latter method are looser, and there is more free volume between primary particles resulting the high internal porosity and consequently higher CPA. Mercury porosimetry analysis also confirms these results. K value as a molecular weight characteristic for all methods was the same. J. VINYL ADDIT. TECHNOL., 24:116–123, 2018. © 2016 Society of Plastics Engineers

Mechanistic investigation of nonisothermal suspension polymerization of vinyl chloride

Vinyl chloride suspension polymerization using different temperature trajectories was carried out in a pilot scale batch reactor. Detailed understanding of the conversion at which the primary particles become motionless (Xm) and the key effects of Xm on morphology development of PVC grains were provided. Motionless conversion is estimated for poly(vinyl chloride) (PVC) grains prepared with different temperature trajectories by cold plasticizer absorption measurements. The porosity of PVC grains (prepared isothermally and nonisothermally) shows a maximum at a certain conversion that is considered motionless conversion. With increasing monomer conversion, the cold plasticizer uptake decreases dramatically with conversions greater than motionless conversion until the monomer phase is completely exhausted (Xf) and continues to slightly decrease after Xf. The decrease in cold plasticizer absorption is more pronounced for PVC grains produced nonisothermally by lower initial temperature. The results obtained by scanning electron microscopy and Brabender® plastography showed that the changes in internal structure and fusion behavior of PVC grains after Xm would be much lower when early aggregates of primary particles are formed. Scanning electron microscopy photographs indicate that applying the variable temperature with negative slope accelerates networking between the primary particles inside the polymerizing monomer droplets. The Brabender® plastograph measurements indicate a lower time and temperature of fusion and a higher degree of gelation for nonisothermally produced resin in which the temperature trajectory follows a greater negative slope. J. VINYL ADDIT. TECHNOL., 24:84–92, 2018. © 2015 Society of Plastics Engineers

Fabrication and characterization of a novel hydrophobic CaCO3 grafted by hydroxylated poly(vinyl chloride) chains

The hydroxylated PVC (PVC-OH) was successfully synthesized by a suspension polymerization of vinyl chloride (VC), butyl acrylate (BA) and hydroxyethyl acrylate (HEA). Novel hydrophobic CaCO3 was then prepared by a urethane formation reaction between methylene diphenyl diisocyanate (MDI) and the OH groups both in the PVC-OH chains and on the surface of pristine CaCO3 particles. The effect of the PVC-OH content on the grafting ratio of treated CaCO3 particles was extensively investigated. Combining the result of Fourier transform infrared (FTIR) with that of water contact angle, it can be concluded that the hydrophobicity of CaCO3 had been efficiently improved by the PVC-OH segments grafted on the surface of CaCO3 particles. X-ray diffraction (XRD), thermal gravity analysis (TGA), scanning electron microscope (SEM) and transmission electron microscope (TEM) were also used to study crystalline behaviors, thermal stability and surface morphology of the modified CaCO3 particles, respectively. The change of specific surface area implying surface modification was investigated as well.

Investigation of the effects of nonisothermal suspension polymerization of vinyl chloride on the fusion and degradation behavior of poly(vinyl chloride)

Thermal stability of poly(vinyl chloride) (PVC) samples polymerized under a temperature trajectory was studied from the point of view of morphological and microstructural characteristics. The results are compared with those of the PVC samples obtained by polymerization at constant temperature having the same K value. The Brabender® plastograph data indicated that the final PVC synthesized with the temperature trajectory showed lower fusion time and higher thermal stability time. The nonisothermal condition also increased the degree of fusion of the final PVC resin, reflecting lower temperature/time required to process it. It was found that the thermal stability of nonisothermally produced PVC as characterized by dehydrochlorination rate decreased (improved) with the increasing monomer conversion until a minimum value was reached that corresponded to the conversion at the pressure drop. However, the dehydrochlorination rate remains almost constant with conversion for an isothermal grade PVC resin. Although the evolution of the number of internal double bonds as well as extent of discoloration of PVC with conversion shows a decreasing trend, the labile chlorine concentration exhibits a maximum at early conversion. The reason for the former can be explained by the temperature dependence of reactions forming defect structures, which are kinetically controlled and thus favored at higher temperatures. The latter, however, can be explained because of the increasing importance of transfer reactions to polymer with increasing polymer concentration. Finally, the results from differential thermogravimetry verify an improvement in thermal stability of the final PVC prepared by using a temperature trajectory during vinyl chloride monomer suspension polymerization. J. VINYL ADDIT. TECHNOL., 23:259–266, 2017. © 2015 Society of Plastics Engineers

Investigation of the effects of nonisothermal suspension polymerization of vinyl chloride on resin properties

Molecular and morphological properties of suspension poly(vinyl chloride) produced by nonisothermal polymerization was experimentally investigated in a pilot‐scale reactor. Although molecular weight and polydispersity index of the nonisothermally produced poly(vinyl chloride) is almost the same as the equivalent isothermal polymerization, there are differences in morphological characteristics. The cold plasticizer absorption of the resin produced nonisothermally is greater than that of the equivalent isothermal product. Scanning electron microscopy showed that nonisothermally produced particles are more regularly shaped, with a smoother surface, and had greater porosity compared with the product of isothermal polymerization reaction. Applying temperature trajectory produces particles with slightly wider particle size distribution relative to the particles produced isothermally. The evolution of particles with conversion is characterized by processing images obtained by scanning electron microscope. Applying a variable temperature trajectory accelerates the formation of a three‐dimensional skeleton of primary particles relative to the isothermally produced particles. J. VINYL ADDIT. TECHNOL., 23:267–274, 2017. © 2015 Society of Plastics Engineers

Nonisothermal suspension polymerization of vinyl chloride for enhanced productivity

In the present study, a mathematical model is developed to numerically predict nonisothermal batch suspension polymerization of vinyl chloride. Free volume theory was used to consider diffusion‐controlled reactions. Model predictions were validated against field data obtained in a pilot scale stirred tank reactor. Variable temperature trajectory was considered during the course of the reaction to improve productivity by reducing the polymerization time for a certain conversion. Variable temperature during the course of the polymerization was successfully implemented by considering the predefined K value. By using variable temperatures during the course of the reaction, the density of the short branches per 1,000 monomer units as a criterion for structure defect remained relatively unchanged. Maximum reduction in reaction time relative to the isothermal case with the same K value and final conversion was 44% for the best temperature trajectory. J. VINYL ADDIT. TECHNOL., 22:470–478, 2016. © 2015 Society of Plastics Engineers

Stochastic Simulation of Droplet Interactions in Suspension Polymerization of Vinyl Chloride

In this paper a population balance based mathematical model is presented for describing suspension polymerization of vinyl chloride. The properties of the polymer product and the behaviour of the stirred batch polymerization reactor are investigated by simulation. Two-phase kinetics model of free radical polymerization is used, and heat balance is also included into the model. Beside the coalescence and breakage phenomena, are taken interchanges of species and heat between the droplets induced by collisions into account forming a complex threescale system. The motion of droplets in the physical space of the polymerization reactor, the breakage, coalescence and coalescence/ redispersion processes are simulated by using a coupled continuous time – Monte Carlo method.