Effect of plasticizer type on gelation and fusion of PVC plastisol,dialkyl phthalate series

Different grades of PVC resins and a variety of plasticizers are used to adjust processability and properties of plastisol. The plastisol, which is a dispersion of fine particles of PVC in plasticizer, is coated on a substrate and heated in an oven to gel and fuse. In the gelation stage the resin particles become swollen with plasticizer and then, in the fusion stage the entire system fuses to become one homogeneous phase. The finished products are flexible PVC such as coated fabrics and surgical globes. Different plasticizers, because of the difference in solvent power, affect the process of gelation and fusion, and hence, processability. This paper examines such an effect systematically by employing a homologous series of plasticizers, dialkyl phthalates. The progress of gelation and fusion are followed by the measurements of dynamic moduli and by the observation with a scanning electron microscope. As it may be expected, the shorter the alkyl chain, the higher the solvent power of the plasticizer.     

In situ,quantitative characterization of gelation and fusion mechanism in poly(vinyl chloride) plastisols by small angle light scattering (SALS)

The present paper explores an effective means of characterizing structural changes of poly(vinyl chloride) (PVC) particles during gelation and fusion of PVC plastisols with small angle light scattering (SALS). The SALS method was shown to provide an in situ observation of swelling of PVC particles as well as quantitative information of average size of swollen particles while they are in progress of gelation and fusion. In addition, the SALS method enabled one to evaluate the relative solvent power of plasticizers from the manner of increase in the correlation distances.     

Gelation and fusion profiles of PVC dispersion resins in plastisols

Poly(vinyl chloride) (PVC) plastisols are used for coatings, films, sheets, foams, and rotational castings. In order to satisfy the requirements for the different applications, a variety of PVC dispersion resins are manufactured. The requirements for the plastisols are many: for example, good air release, viscosity stability, fine particle size, foamability, and good heat stability. Processability is another important requirement, which emphasizes the rheological behavior at room temperature and the gelation—fusion behavior. This paper documents research to fingerprint the gelation and fusion profiles of various PVC dispersion resins. The viscoelastic measurements were used to continuously monitor the changes of moduli during gelation and fusion under a heating rate which simulates the temperature profile of the processes. The effects of molecular weight, resin type, and copolymer on the gelation–fusion behavior are discussed.     

Viscoelastic measurements of PVC plastisol during gelation and fusion

This work is concerned with the change of viscoelastic properties of poly(vinyl chloride) (PVC) plastisol during heating. The system changes from a suspension of solid particles in a liquid medium to a swollen gel and further to a fused state as the temperature is raised. The Rheometrics mechanical spectrometer was used in the oscillatory mode at 0.1 Hz. The temperature of the sample was raised in a controlled manner to 195°C. During gelation, the viscosity increased rapidly about three decades. There was a similar increase of the elastic modulus. After reaching a maximum, both viscosity and elastic modulus decreased rapidly with the progress of fusion. The viscoelastic properties depended somewhat on the heating rate. At 170-195°C, it took a few minutes for the moduli to reach steady values. Continued heating, for several minutes at 195°C, did not change the moduli any further. The temperature range of the decomposition of a blowing agent in the plastisol foam formulation was determined. Over this temperature range, the viscoelastic properties change very rapidly. Quantitative estimates were made for the decrease of moduli during this period.     

Gelation and interaction in plasticizer/PVC solutions

Gelation of PVC solutions is generally agreed to result from network formation. The proposed network linkages include crystallites, hydrogen-bonds, and entanglements brought about by spinodal decomposition. The objective of this work is to relate the phase behavior or compatibility of PVC/plasticizer solutions to their gelation behavior. The thermoreversible sol-gel transition of plasticized PVC was studied using a simultaneous light scattering and dynamic viscoelastic analysis technique, in parallel with a thermal optical analysis (TOA). PVC solutions of 1% to 15% in different types of phthalate and sebecate plasticizers were used. Preliminary results suggest phase separation in the less compatible plasticizer during gelation process while more compatible plasticizer/PVC solutions gel without phase separation. This suggests that the gelation process can be relatively independent of the liquid-liquid phase equilibria in the system.     

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 (X_m) and the key effects of X_m 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 (X_f) and continues to slightly decrease after X_f. 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 X_m 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     

Plastisols of poly(vinyl chloride); particle size distribution,morphology, rheology,and mechanism of aging

Plastisols of poly(vinyl chloride) (PVC) are suspensions of fine resin particles in plasticizer with about a 50% resin volume fraction. Typically, the gross particle size ranges from about 15 to 0.2 μm and smaller, where the common practice of spray drying these resins dictates that the size ranges include agglomerates as well as the ultimate particles. In this work we have related the particle size distribution to the dynamic mechanical behavior with model plastisols prepared from various particle-size fractions of a commercial resin. This relationship, together with the microscopic observation of the particle dispersions, provided an interpretation of the plausible mechanisms of the viscoelastic response. The morphological observation of the particle aggregates, the changes of the particle size distribution during the aging, and the above viscoelastic study have established that deagglomeration is the dominant cause of the increase of viscosity during aging.     

Effect of the sol fraction and hydrostatic deformation on the viscoelastic behavior of prestrained highly filled elastomers

This study focuses on the relations between the microstructure and the viscoelastic behavior of an industrial solid propellant belonging to the class of highly filled elastomers. Precisely, the study aims at determining the impact on the viscoelastic behavior of the presence of the sol fraction inside the polymer network. The sol fraction is the part of the binder that a good solvent can extract. The solid propellant is swollen to various extents by solutions of plasticizer and polymer molecules. This swelling leads to a hydrostatic deformation of the polymer network, corresponding to an extension or contraction loading for each specimen. Prestrained dynamic mechanical analysis tests, superimposing a small oscillating strain on a prestrain, characterize the viscoelastic behavior. The degree of swelling of the network and the effective filler fraction drive the viscoelastic response. In addition, the mechanical behavior does not depend on the chemical nature of the introduced sol fraction. Moreover, a nonlinear behavior, i.e., an increase in both storage and loss moduli with increasing prestrain, is initiated at low prestrain. This nonlinearity depends on the contraction or extension of the network and could result from particles aligning with prestrain, which is expected in such highly filled materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

微悬浮法PVC增塑溶胶凝胶化和熔化特性的研究

用HAAKE转矩流变仪测定了微悬浮法聚氯乙烯(PVC)增塑溶胶的凝胶化和熔化特性,探讨了树脂品级、增塑剂类型和混合树脂对凝胶化和熔化速率的影响。实验还表明,单丝的拉伸强度和相对伸长率与它的加工温度、形态和熔化程度有密切的关系。     

Fusion behavior of plastisols of PVC studied by ATR-FTIR

The behavior of PVC plastisols during gelation and fusion was studied by the ATR-FTIR technique (Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy). DBP, DOP, and DIDP, three common phthalate plasticizers for PVC, were used in plastisols formulations. Three heating rates—5, 10 and 15°C/min—and formulations with different plasticizer concentrations were studied. The IR spectra of a plastisol coincides with the IR spectra of the plasticizer except for the bands at 1435 and 613 cm^?1 from the PVC (CH₂ wagging and C—Cl stretching, respectively). When the plastisol is heated, a progressive decrease of the plasticizer bands areas can be observed, while bands from PVC increase their intensity, probably because of the adsorption of the plasticizer by the resin. On cooling, the area of all bands follows the same path as when heating, but the paths separate at a certain temperature, showing the irreversible nature of this process. The analysis of the band at 1280 cm^?1 (C(O)—O from plasticizer) during heating and cooling, shows that the temperature of separation areas (T_s) takes place at temperatures coherent with plasticizer compatibility. Studies at different heating rates and different plasticizer content are in good agreement with results using other techniques, available in the literature.     

A brief overview of theories of PVC plasticization and methods used to evaluate PVC‐plasticizer interaction

This paper reviews the most widely used models for explaining how plasticizers render PVC flexible. These models include the gel, lubricity, and free volume theories; kinetic theories; and mathematical models which predict on the basis of plasticizer structure how much a plasticizer will lower the polymer glass transition in a flexible PVC compound. Since plasticization results from interactions between plasticizer and polymer, methods which have been used to study either the strength or the permanence (or both) of those interactions are also briefly discussed. Tools which have often been used to study plasticizer‐PVC interactions include infrared and nuclear magnetic resonance spectroscopy, compression and humid‐aging tests, dynamic mechanical analysis, torque rheometer tests, plasticizer‐resin clear point temperature measurements, plastisol gelation/fusion by hot stage measurements, and others. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Soft PVC foams: Study of the gelation,fusion, and foaming processes. I. Phthalate ester plasticizers

The use of foamed plastics gains more and more interest every day. Flexible poly(vinyl chloride) (PVC) foams have excellent mechanical properties and low price, thus their application is extensive. Foams are produced from plastisols, which are based on the suspension of the PVC resin in a plasticizer. Phthalates are the most used plasticizers in flexible PVC foam formation. In this study, we have studied the influence of the phthalate ester‐type plasticizers on the foaming process and the quality of the foams obtained from the corresponding plastisols. For the plastisols prepared with the nine phthalate plasticizers considered, we have studied and discussed the complex and extensional viscosities; the thermal behavior (DSC) including the decomposition of the chemical blowing agent, and the foam production by rotational molding. In addition, we have characterized the foams obtained by thermomechanical analysis, density, and bubble size distribution. As expected, clear correlations have been obtained between the molecular weight and structure of the plasticizer with the rheological behavior of the plastisols. The knowledge of the gelation and fusion processes and evolution of the extensional viscosity of the plastisols combined with the study of the thermal decomposition of the blowing agent in each plastisol allows for better understanding of the complex dynamic behavior of these foaming systems. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Meaningful evaluation of plastisol gelation and fusion temperatures by dynamic mechanical analysis

In most PVC plastisol processing operations, gelation and fusion characteristics of the plastisol are critically important. For example, in chemically foamed plastisols, plastisol fusion temperature and blowing agent decomposition temperature must be carefully coordinated. In rotomolded parts, rates of gelation may determine the quality of the finished parts. For plastisol products made by any process, the final fusion temperature determines the processing temperatures required to give the finished product acceptable mechanical properties. For a variety of reasons, the methods commonly used to characterize plastisol gelation and fusion (hot bar test, resin in plasticizer clear point, torque rheometer measurements, etc.) provide comparisons between plastisols but do not provide temperatures that are easily related to actual industrial processes. With dynamic mechanical analysis (DMA), one can characterize, under low shear conditions, the temperatures at which gelation begins, gelation ends, and complete fusion occurs. Additionally, it is possible to record plastisol viscosities (and other dynamic mechanical properties) over the processing temperature range. We used a multiple linear regression program to analyze the DMA data for plastisols heated from 30 to 210°C and containing either 70, 80 or 90 phr of Jayflex dihexyl phthalate (DHP) or Jaylflex di-isodecyl phthalate (DIDP). Further, we determined the plasticizer phr dependence and the reproducibility of gel and fusion temperatures given by data analyzed in this manner. Finally, for comparison, we analyzed the reproducibility of initial and final plastisol gel temperatures and fusion temperatures, which were determined by visually analyzing the DMA data for plastisols containing 70, 80, and 90 phr of Jyflex plasticizers DHP, Jayflex 77, diisononyl phthalate (DINP), and DIDP. Precise characterization of plastisol gelation and fusion behavior will, undoubtedly, facilitate substitution of plastisol ingredients as is often required by those who manufacture and process plastisols.     

Effects of dry blending on morphogy of PVC powder particles

Mass and suspension PVC were blended on a Fielder mixer and changes in powder morphology and additive distribution investigated. The techniques used to characterize and assess processing behavior have included microscopy, density, size analysis, torque, and capillary rheometry. The particulate structure of PVC remained intact, and there were no pronounced differences in the processability of blends discharged at different temperatures. In the absence of shear PVC particles are largely unchanged in character. Solid additives do not appear to enter into resin particles while liquid stabilizer readily does so.     

Panel 1: PVC Resins—past,present and future

PVC Resin behavior vs VCM control; processing differences pre- and early control vs current VCM standards. Differences in fusion, bulk density, output rates—lot to lot variations; differences in plasticizer absorption and response; nature of resin particles surface; drift in K value; static charge; viscosity differences in dispersion resins; S-PVC vs M-PVC; quality control, ASTM D 1755 resin classification.     

Plasticizer factors influencing take-up by PVC resins

The ease with which plasticizer is combined with poly(vinyl chloride) resin is a measure of processing characteristics critical in the dry blending of suspension PVC and the gelation of plastisols. By using commercial grade plasticizers, this study developed predictive equations for the following processing parameters of dialkyl phthalates in PVC:

• Relative dry-blend rates in suspension PVC as a function of plasticizer viscosity.
• Relative initial gelation temperatures in plastisols as a function of plasticizer molecular weight and solvating strength.
• Relative final gelation temperatures in plastisols as a function of plasticizer solvating strength.

This information allows one to predict the relative processing characteristics of any dialkyl phthalate plasticizer for PVC on the basis of its chemical and physical properties.     

Processing of precipitated nongranular PVC in the brabender measuring mixer

The structure and properties of processed poly(vinyl chloride) (PVC) depend on temperature, shear rate, operations time, and morphology of the PVC grains. The aim of our research was the preparation of a nongranular PVC and the examination of its processing during kneading in a Brabender plastographometer in comparison with the processing of commercial PVC. It was stated that grains of virgin PVC‐S61, a commercial suspension resin, cause a self‐heating of the compound during kneading in such a way that point X of the plastograms occurs at a temperature 15°C lower than that of precipitated PVC (i.e., PVC without grains). As a result of self‐heating, time of compound processing needed to reach point depends largely on the grain morphology of the PVC. The less compact structure, the smaller bulk density, and the greater absorption of plasticizer, result in a longer processing time. Homogeneous, loosely packed particles of powder and the crystalline structure of precipitated PVC are different from PVC‐S61 morphology and cause a high degree of gelation and low melt flow rate values for compounds processed at 175°C and higher. J. VINYL ADDIT. TECHNOL., 18:147–152, 2012. © 2012 Society of Plastics Engineers     

Viscoelastic characterization of PVC plastisol melts for foam applications

Melt rheology and its time-temperature dependence have long been known to be fundamental properties associated with satisfactory expansion characteristics in vinyl foam. Since much is known about the relationship between rheology and material variables like polymer morphology and system composition, adequate rheological characterization should be quite helpful in polymer design and plastisol compounding. Earlier attempts to study the melt rheology of plasticized PVC foam systems were only partially successful because instrument limitations required that the material be studied at too high shear rate or temperature, or that behavior of specific compositions be extrapolated from data obtained at considerably higher plasticizer level. This paper deals with measurement of the viscoelastic behavior of melts from actual azodicarbonamide foam compositions. The Rheometrics Mechanical Spectrometer was used in the orthogonal mode to study both elastic modulus and loss modulus (viscosity) in the range of shear rates and temperatures which actually occur during commercial utilization of PVC foam compounds. The effects of changing vinyl resin types and plasticizer types and levels were explored.     

Studies of molecular weight distribution,particle morphology,and rheological behavior of ultra-high molecular weight suspension PVC

In this paper, the particle characteristics and rheological behavior of ultra-high molecular weight PVC (UHMWPVC) produced in both Japan and mainland China were studied. The molecular weight and its distribution of UHMWPVC were measured by GPC. By means of a series of techniques such as SEM, the measurement of surface pore size, plasticizer absorption, and photographic analysis, the morphology and general characteristics of UHMWPVC particles were investigated. A model of particle structure was proposed. It was found that compared to general PVC, UHMWPVC resins are more porous, having better plasticizer absorption properties. Similarly, compared to UHMWPVC made in mainland China, UHMWPVC made in Japan possesses particle characteristics preferred in PVC processing. In the studies of rheological behavior, the programmed temperature Brabender torque rheometer was used to study and compare the melting process of UHMWPVC resins and their plasticized systems under the same shear stress. The capillary rheometer and Brabender extrusion-rheometer were applied to investigate the rheological and extrusion properties of the plasticized systems mentioned above. The results showed that in melting and extrusion process, the particle characteristics of UHMWPVC result in the easy breakage of particles and the formation of “molecular flow,” On the other hand, the high molecular weight is unfavorable to processing. Generally speaking, much more research work is needed to improve the flow properties of UHMWPVC.     

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

A 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