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     

Plasticizer structure/performance relationships

Plasticizers for poly(vinyl chloride) may be organized into eight chemical families and by seven key performance criteria. Cost-effective general-purpose phthalates provide a base line for comparing all other plasticizers. The wide range of performance characteristics associated with various phthalate isomers substantiates the large proportion of phthalate esters that are utilized as plasticizers. This article summarizes plasticizer structural/performance relationships using quantitative comparisons of cost, plasticizing efficiency, plastisol solvation characteristics, dryblending, volatility, and low temperature performance properties in PVC. Some generalizations are also made concerning structural effects of the alcohol isomers used in the syntheses of the various types of plasticizer esters.     

Migration of PVC plasticizers into alcohols

The use of labelled plasticizers and radioactivity measurements in conjunction with weight loss, can give quantitative information on the amount of migrated plasticizer, and on the amount of the liquid medium that diffuses into the polymer during the migration process. In the case of PVC plasticized with dibutyl phthalate and dioctyl phthalate and immersed in alcohols, the specimens soon become heterogeneous due to loss in compatibility between the polymer and the mixtures of plasticizer-alcohol high in alcohol. These mixtures are formed in the polymer as a result of continuous migration and diffusion processes. The following factors affecting the migration process were examined: nature of alcohol, nature of phthalate plasticizer, amount of plasticizer, molecular weight of polymer, thickness of specimens, presence of epoxy plasticizers, plasticization process, presence of stabilizers, temperature, and time.     

Rheometric study of the gelation and fusion processes of poly(vinyl chloride‐co‐vinyl acetate) plastisols with different commercial plasticizers

Evolution of the complex viscosity of pastes of PVC‐VA (vinyl chloride‐vinyl acetate copolymer) plasticized with different commercial plasticizers has been studied. Knowledge of the rheological behavior of the formulations allows for better understanding of the gelation and fusion processes. Twenty commercial plasticizers of different types and with different functional groups have been studied and are grouped into five families: phthalate esters with linear chains, phthalate esters with branched chains, adipates (normal and polymeric), citrates, and rest of the plasticizers (carboxylates, alkylsulfonates, and pentaerythritol ester derivatives). Interesting relationships among the observed rheologies and the nature and molecular weight of the plasticizer have been observed. The evolution of the complex viscosity with temperature—at the temperatures where the blowing agents normally used in PVC plastisol foaming processes generate the main amount of gas—has been newly discussed with regard to the chemical structure and molecular weight of all of the plasticizers used. It was found that several different dynamic processes must be synchronized in order to understand the relationships among the chemical structure, plasticization, plasticizer compatibility, rheological properties, and foaming process of such materials. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Poly(vinyl chloride)/plasticizer-mixture interactions. Part I. Phthalate ester mixtures

Flory-Huggins interaction parameters, χ, have been determined as a function of plasticizer composition for poly(vinyl chloride) in various binary mixtures of phthalate ester plasticizers using a method involving the micro-determination of the temperature at which PVC particles in excess plasticizer appear to melt. An optimum composition at which χ goes through a minimum was found to exist for some of the systems. A good correlation between the apparent melting temperature t_m and χ for the neat plasticizers with PVC was also established.     

Dialkyl furan‐2,5‐dicarboxylates,epoxidized fatty acid esters and their mixtures as bio‐based plasticizers for poly(VInylchloride)

Dialkyl furan‐2,5‐dicarboxylates and epoxidized fatty acid esters (EFAE) of varying molecular weights and volatilities, as well as their mixtures, were investigated as alternative plasticizers for poly(vinylchloride) (PVC). The EFAE utilized were epoxidized soybean oil (ESO) and epoxidized fatty acid methyl ester (e‐FAME). All plasticizers were compatible with PVC, with plasticization efficiencies usually increasing with decreasing molecular weights of the plasticizers (except in the case of ESO, which was remarkably effective at plasticizing PVC, in spite of its relatively high molecular weight). In comparison with phthalate and trimellitate plasticizers, the alternatives generally yielded improved balance of flexibility and retention of mechanical properties after heat aging, with particularly outstanding results obtained using 30?50 wt % e‐FAME in mixtures with diisotridecyl 2,5‐furandicarboxylate. Although heat aging characteristics of the plasticized polymer were often related to plasticizer volatilities, e‐FAME performed better than bis(2‐ethylhexyl) 2,5‐furandicarboxylate, and bis(2‐ethylhexyl) phthalate of comparatively higher molecular weights. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42382.     

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.     

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.     

Castor Epoxy Fatty Acid Alkyl Ester Estolides as Bioplasticizers for Poly(Vinyl Chloride)

Epoxy fatty acid alkyl ester estolides were synthesized from castor oil to be used as biobased plasticizers for poly(vinyl chloride) (PVC) as a safer replacement for phthalate plasticizers. Initially, castor oil was transesterified with methanol or n-butanol to quantitatively yield castor fatty acid alkyl esters. Acetylation of hydroxyl function with acetic anhydride led to the formation of estolide. The unsaturation was epoxidized, resulting in a bifunctional epoxy fatty acid alkyl ester estolide. The bioplasticizers were compounded with PVC and were evaluated for their functionality and compared with commercial phthalate plasticizer diisononyl phthalate (DINP) and nonphthalate 1,2-cyclohexanoic acid diisononyl ester (DINCH). The bioplasticizers showed excellent gelation, efficiency, and compatibility, as well as plastisol viscosity and thermal properties, comparable to or better than the plastisols prepared with commercial controls DINP and DINCH. The volatility of the methyl ester was inferior to the butyl ester. Both compounds showed low water resistance properties. Further evaluation of the butyl ester under tropical conditions of high temperature and humidity confirmed limited compatibility. This indicates that the castor epoxy fatty acid ester estolides would be better suited for applications that do not come in contact with water for prolonged periods, such as flooring, artificial leather, wiring, or wall coverings.     

Influences of contents and molecular weights of LDPE on DOP plasticization of PVC

Influences of contents and molecular weights of low‐density polyethylene (LDPE) on dioctyl phthalate (DOP) plasticization in the poly(vinyl chloride) (PVC) plastisol (PVC/DOP/AO = 100/30/6.5) were investigated using DMA and DSC. The plasticization effects of DOP on the PVC plastisol were found to decrease with increasing LDPE content. A negligible plasticization effect of DOP on the PVC plastisol was found when the LDPE content was equal to or higher than 75 parts per 100 parts by weight of LDPE and PVC together. Based on thermal fractionation experiments, a favorable interaction between LDPE and DOP was developed during melt blending of LDPE and the PVC plastisol. The present interaction enabled the incorporation of DOP into LDPE and decreased the plasticization effects of DOP on the PVC plastisol. A further decrease in the plasticization effects of DOP on the PVC plastisol by the presence of LDPE was found with increasing LDPE molecular weights. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2548–2555, 2002     

Emissivity values for poly(vinyl chloride) with varying plasticizer compositions

The emissivity of plasticized poly(vinly chloride) (PVC) containing varying compositions and amounts of plasticizer was investigated. The four plasticizers examined were dibutyl phthalate (DBP), dioctyl phthalate (DOP), diisodecyl phthalate (DIDP) (Phthalic acid type), and dioctyl adipate (DOA) (adipic acid type). The emmissivity of plasticized PVC film increased almost equally with the difference in the compositions between DOP and DOA. It was also clear that the emissivity of the plasticized PVC film decreased gradually with the molecular sequence length of DBP, DOP, and DIDP.     

Plasticizers derived from cardanol: synthesis and plasticization properties for polyvinyl chloride(PVC)

Two natural plasticizers derived from cardanol (CD), cardanol acetate (CA) and epoxidized cardanol acetate (ECA), were synthesized and characterized by ¹H NMR and ¹³C NMR. The plasticizing effects of the obtained plasticizers on semi-rigid polyvinylchloride (PVC) formulations were also investigated. Two commercial phthalate ester plasticizers, dioctyl terephthalate (DOTP) and diisononyl phthalate (DINP), were used as controls. Mechanical and thermal properties, compatibility, thermal stability, microstructure, and workability were assessed by dynamic mechanical analysis (DMA), mechanical analysis, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and dynamic stability analysis, respectively. Results indicated that the natural plasticizer ECA had overallsuperior flexibility, compatibility, thermal stability, and workability comparable to both controls. The obtained CA and ECA have lower volatility resistance and similar extraction and exudation resistance than that of DOTP and DINP. The CA was further blended with DOTP in soft PVC films. Results of DMA, TGA and mechanicalanalysis indicated that CA can serve as a secondary plasticizer to improve the related properties of soft PVC formulations. These CD derived plasticizers show promise as an alternative to fully or partially replace petroleum-based plasticizers.     

Application of new oligomeric plasticizers based on waste poly(ethylene terephthalate) for poly(vinyl chloride) compositions

In this study, chemical recycling products of waste poly(ethylene terephthalate) with oligoesters were used as new plasticizers for poly(vinyl chloride) (PVC). The preparation conditions of the dry blend mixtures of the suspension PVC containing synthesised plasticizers were similar to the conditions of the preparing mixtures with commercial plasticizers. The plasticization efficiency of PVC plasticizers was then examined by analysis of the mechanical, physical and chemical properties, as well as the thermal resistance and migration of plasticizer molecules from polymer matrix. Test results proved that compositions with synthesised oligomeric plasticizers possessed similar or better properties than those containing commercial oligomeric plasticizers and much better properties than those having monomeric plasticizers. Thermal stabilities of the proposed plasticizers were higher than those of the commercial plasticizers either monomeric (bis(2-ethylhexyl)phthalate) or oligomeric, despite the fact that the synthesised oligoesters did not contain any antioxidant. The best properties, especially low volatility, very good mechanical properties, low migration were resulted of the transesterification of the waste PET with oligoesters based on adipic acid, triethylene glycol and 2-ethylhexanol which were selected as plasticizers synthesised on the technical scale. The tested plasticized PVC compositions possessed very good tear resistance, tensile strength, decrease of weight loss after 168 h at 80 °C and low migration. Processing properties of PVC compositions containing these synthesised plasticizers confirmed their effectiveness in these compositions for extrusion process.     

Benzyl ester of dehydrated castor oil fatty acid as plasticizer for poly(vinyl chloride)

The poly(vinyl chloride) (PVC) industry plays an important role in today's total plastics industry. The major volume of PVC is used as soft and plasticized PVC. PVC applications consume approximately 80% of the total production of plasticizers. Most of the common plasticizers are aromatic esters of phthalic acid. In the majority of countries, phthalate plasticizers are banned due to their carcinogenic properties. The concern raised about toxicity led to a large demand for bio‐based non‐toxic plasticizers. Hence, there is an increasing interest in replacing the phthalate plasticizers with those produced from simple bio‐based materials. Dehydrated castor oil fatty acid (DCOFA) is a renewable resource which can be esterified and used as an environment friendly plasticizer for PVC. Benzyl ester (BE) was prepared by reacting DCOFA with benzyl alcohol in the presence of catalyst at 170–180 °C. Esterification was further confirmed by acid value, hydroxyl number, ¹H NMR and Fourier transform IR spectroscopy. The modified plasticizer was used in various proportions as a co‐plasticizer in PVC for partial replacement of dioctyl phthalate (DOP). With an increase in the proportion of BE in PVC samples, a good plasticizing performance was observed. The incorporation of BE also resulted in a reduction in viscosity and viscosity pick‐up and improved mechanical, exudation, thermal degradation and chemical resistance properties. The presence of BE showed a reduction in the whiteness index due to presence of conjugated double bonds in the structure. The results of DSC, XRD and Shore hardness studies showed no significant variation in properties compared with those of DOP‐plasticized sheets and thus we can conclude that BE can be used as a co‐plasticizer in PVC. © 2013 Society of Chemical Industry     

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.     

Effect of liquid plasticizers on crystallization of PCL in soft PVC/PCL/plasticizer blends

In this work, poly(ε-caprolactone) (PCL) and liquid plasticizer were combined used to plasticize poly(vinyl chloride) (PVC), and the possibility of using PVC/PCL/plasticizer blends to fabricate soft PVC with enhanced migration resistance was investigated. Through partial replacement of liquid plasticizers in soft PVC by equal quantity of PCL, flexibility was maintained while extraction loss of plasticizer by organic solvent was reduced significantly. Furthermore, crystallization of PCL in PVC/PCL/plasticizer blends with low PCL content was observed, and crystallization rate of PCL was found to be influenced by plasticizer contents and structures. For instance, crystallization rate of PCL in PVC/PCL/diisononyl phthalate (DINP) (100/40/100) was 3.7 times faster than in PVC/PCL/DINP (100/40/80), while crystallization rate of PCL in PVC/PCL/dioctyl adipate(DOA)(100/40/100) was 8.3 times faster than in PVC/PCL/diisononyl cyclohexane-1,2-dicarboxylate (DINCH) (100/40/100). Low-field ¹H NMR test manifested that different crystallization rate of PCL in PVC/PCL/plasticizer blends with different plasticizer structures was triggered by difference in plasticizers' compatibility with PVC, that is, the number of interaction point between PVC and plasticizers. It is concluded that PCL crystallization favored by liquid plasticizers in PVC/PCL/plasticizer blends was induced by interaction competition between PVC/plasticizer and PVC/PCL. As plasticizer content increases or its compatibility with PVC decreases, interaction competition becomes more intense and consequently faster crystallization of PCL occurs. Thus, to obtain soft PVC products with improve migration resistance while avoiding PCL crystallization, the total content of plasticizer (including both liquid plasticizer and PCL) should be lower than 66 phr (40 wt %). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48803.     

Soft PVC foams: Study of the gelation,fusion and foaming processes. III. Mixed phthalate ester plasticizers

The foaming of PVC (poly(vinyl chloride)) plastisols is a complex combination of simultaneous processes, involving the curing and structural changes of the plastisol, the gas generation and the foam formation. Our comprehensive study of such processes and of the influence of plasticizer on the foam quality has shown that all the processes involved have to be adequately synchronized to obtain foams of the required quality. A series of plastisols prepared by mixing a high and a low compatible phthalate ester plasticizer in several proportions (100/0, 75/25, 50/50, 25/75, 0/100 ratios) has been studied and characterized (by means of rheology, calorimetry, thermal stability, thermomechanical properties, density, and foam morphology), to study the influence of the plasticizer in such processes with changing compatibility. We found expectable rheological and calorimetric behavior regarding the plastisols without curing; however we experienced nonlinear (unexpected) behaviors in cases of foams and plastisols being cured. To confirm such behavior and our hypothesis regarding the possible plasticizer evaporation, the thermal stability of the plastisols, precured samples and foams have been studied by themorgravimetric analysis (TGA). According to our results it can be deduced that the plasticizer loss occurring in some cases during the production of the foams or the specimens being characterized, plays an important role in the foaming process and also influences the foam quality. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of ketal group in castor oil acid-based plasticizer on the properties of poly(vinyl chloride)

Two castor oil acid esters containing a ketal or ketone group (KCL or CL), as alternative plasticizers for poly(vinyl chloride) (PVC), were prepared. The structures were confirmed by ¹H NMR and FTIR spectroscopies. The effects of the presence of a ketal or ketone group in these compounds on PVC plasticization were examined. The DMA and SEM results showed that both plasticizers were miscible with PVC and exhibited excellent plasticizing properties, compared to those of dioctyl phthalate (DOP). The PVC plasticized by KCL displayed a lower T_g value of 20.6 ° C, which was lower than that of PVC plasticized with DOP (22.3 ° C) and PVC plasticized with CL (40.5 ° C). Tensile tests indicated that PVC plasticized using KCL showed a 37% higher of elongation at break than PVC plasticized by CL and 30% higher than PVC plasticized by DOP. The plasticizing mechanism was also investigated. Moreover, exudation, volatility, and extraction tests, along with TGA indicated that the presence of ketal groups effectively improved the migration resistance of plasticizer and the thermal stability of PVC blends. Taken together, introducing ketal groups into plasticizer might be an effective strategy for improving its plasticizing efficiency.     

Optimizing performance of benzoate and phthalate blends for vinyl applications

To achieve required performance, blends of plasticizers are commonly used in flexible vinyl applications. Typically, when fast fusion is required, high solvating phthalates have been utilized in plasticizer blends. Benzoate esters are high solvators and can also be used in these blends. However, even though benzoate plasticizers offer additional performance benefits that can complement general‐purpose phthalate performance, most of the literature does not include the use of benzoate plasticizers in blends with phthalates. The purpose of this article is to demonstrate the performance benefits of blending benzoate and phthalate plasticizers. The approach selected to accomplish this task was to develop performance data by utilizing a mixture design approach with DOE (design of experiments) software. A resilient flooring plastisol formulation was selected as the model. The following properties were obtained: degassing, low and high shear viscosity, viscosity stability of the plastisol, gel and fusion characteristics, tensile strength vs. temperature, vinyl heat stability, stain resistance, volatility, and UV stability. The data indicate how to utilize the advantage of benzoates as “process aids” to speed production rates and improve product quality. J. VINYL. ADDIT. TECHNOL. 11:150–154, 2005. © 2005 Society of Plastics Engineers     

Structure and properties of poly(vinyl chloride)‐triallyl cyanurate plastisols

Triallyl cyanurate (TAC) has been used as a reactive plasticizer to promote the high‐temperature creep resistance of poly(vinyl chloride) (PVC) plastisols. The resultant crosslinked structure is characterized using gel content and swell ratio measurements as well as Fourier transform infrared spectroscopy. The crosslinking reaction was initiated using peroxide. The effect on the network structure of using a free radical scavenger in the formulation has also been studied. The gel yield and crosslink density in the gel increase with increasing TAC concentration in the plastisol, while the grafted PVC fraction and the residual unsaturation of TAC behave in the opposite way. Introduction of TAC into the plastisol promotes creep resistance at high temperatures, and the logarithmic creep rate was found to decrease linearly with increasing crosslink density.