The decomposition of azodicarbonamide, used as foaming agent in PVC—plasticizer (1/1) plastisols ... more The decomposition of azodicarbonamide, used as foaming agent in PVC—plasticizer (1/1) plastisols was studied by DSC. Nineteen different plasticizers, all belonging to the ester family, two being polymeric (polyadipates), were compared. The temperature of maximum decomposition rate (in anisothermal regime at 5 K min−1 scanning rate), ranges between 434 and 452 K. The heat of decomposition ranges between 8.7 and 12.5 J g−1. Some trends of variation of these parameters appear significant and are discussed in terms of solvent (matrix) and viscosity effects on the decomposition reactions. The shear modulus at 1 Hz frequency was determined at the temperature of maximum rate of foaming agent decomposition, and differs significantly from a sample to another. The foam density was determined at ambient temperature and the volume fraction of bubbles was used as criterion to judge the efficiency of the foaming process. The results reveal the existence of an optimal shear modulus of the order of 2 kPa that corresponds roughly to plasticizer molar masses of the order of 450 ± 50 g mol−1. Heavier plasticizers, especially polymeric ones are too difficult to deform. Lighter plasticizers such as diethyl phthalate (DEP) deform too easily and presumably facilitate bubble collapse.
This study deals with the rheological aspects of poly-vinyl chloride (PVC) plastisol gelation and... more This study deals with the rheological aspects of poly-vinyl chloride (PVC) plastisol gelation and fusion processes in foamable formulations. Here, such processes are simulated by temperature-programmed experiment (5 K min−1) in which complex viscosity components are continuously recorded. Nineteen samples based on a PVC-VAC (vinyl acetate 95/5) copolymer with 100 phr plasticizer have been studied, differing only by the plasticizer structure. The sample shear modulus increases continuously with temperature until a maximum, long time after the end of the dissolution process as characterized by DSC. The temperature at the maximum varies between 345 and 428 K with a clear tendency to increase almost linearly with the plasticizer molar mass, and to vary with the flexibility and the degree of branching of the plasticizer molecule. The shear modulus increase is interpreted in terms of progressive “welding” of swelled particles by polymer chain reptation. The plasticizer nature would mainly affect the friction parameter of chain diffusion.
The foaming of PVC (Poly (Vinyl Chloride)) plastisols is a complex combination of simultaneous pr... more 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), in order 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. In order to confirm such behavior and our hypothesis regarding the possible plasticizer evaporation, the thermal stability of the plastisols, pre-cured 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.
The foaming of PVC-VA (Poly (Vinyl Chloride-co-Vinyl Acetate)) plastisols is a complex combinatio... more The foaming of PVC-VA (Poly (Vinyl Chloride-co-Vinyl Acetate)) plastisols is a complex combination of processes involving the simultaneous curing of the paste with the evolution of gases caused by the decomposition of the chemical blowing agent. The extensional viscosity is a fundamental characteristic of the material, responsible for the behavior of the system when undergoing the extensional stress produced by the released gases. Nevertheless, such changes have not been considered to the same extent as the complex viscosity evolution or the thermal processes suffered by PVC-VA plastisols. The objective of the present work is to study the extensional viscosity of the PVC-VA plastisols prepared with three plasticizers of similar structure, but with different curing and rheological behavior in order to investigate its influence on the quality of the foams obtained. Extensional viscosity measurements under forced prestretch conditions revealed that depending on the structure and consequently on the compatibility of the plasticizer used, each plastisol develops its properties and structure accordingly. DINCH plasticizer (Diisononyl cyclohexane-1,2-dicarboxylate presenting alicyclic ring) seems to be the less compatible compared to the other two studied (both presenting aromatic rings) according to its behavior during the curing and foaming processes and may not be able to withstand the pressure evolved by the released gases during the foaming process yielding foams of poorer quality.
The evolution of complex viscosity of pastes of PVC-VA (poly-vinyl chloride-vinyl acetate copolym... more The evolution of complex viscosity of pastes of PVC-VA (poly-vinyl chloride-vinyl acetate copolymer) plasticized with twenty different commercial plasticizers has been studied. The knowledge of the rheological behavior of the formulations allows for better understanding of the gelation and fusion processes. Twenty commercial plasticizers with different types and functional groups have been studied, grouped into five families such as phthalate esters with linear chains, phthalate esters with branched chains, adipates (normal and polymeric), citrates, and the group of the rest of 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 gases – has been newly discussed regarding the chemical structure and molecular weight of all the twenty plasticizers used. It was found that several different dynamic processes must be synchronized in order to understand the relationship between the chemical structure, plasticization, plasticizer compatibility, rheological properties, and foaming process of such materials.
In this paper the characterization of the thermal behavior of foamable PVC (Poly (vinyl chloride)... more In this paper the characterization of the thermal behavior of foamable PVC (Poly (vinyl chloride)) plastisols from 20 different plasticizers has been studied by differential scanning calorimetry (DSC). The interactions among the resin and the plasticizer as well as the decomposition of the azodicarbonamide (ADC) - the chemical blowing agent (CBA) used - have been analyzed. The latter process has a crucial importance for the knowledge of plasticized PVC flexible foam formation. Clear effects of the chemical nature of the plasticizers and their molecular weight (Mw) have been observed, both in the interactions (swelling and early stages of gelation) among the resin and the plasticizer, as well as in the temperature of the ADC decomposition and the shape of the DSC peak.
Keywords: DSC, PVC, chemical blowing agent, decomposition, characterization.
The use of foamed plastics gains more and more interest every day. Flexible PVC (Poly(Vinyl Chlor... more The use of foamed plastics gains more and more interest every day. Flexible PVC (Poly(Vinyl Chloride)) 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 the present work, 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 (CBA), and the foam production by rotational molding. In addition, we have characterized the foams obtained by thermomechanical analysis (TMA), 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.
Plasticized PVC is one of the most useful polymeric materials at industrial scale, because of its... more Plasticized PVC is one of the most useful polymeric materials at industrial scale, because of its processability, wide range of obtainable properties and low cost. PVC plastisols are used in the production of flexible PVC foams. Phthalates are the most used plasticizers for PVC, and in a previous paper (part I), we studied the influence of phthalate ester type plasticizers on the foaming process and on the quality of the foams obtained from the corresponding plastisols. Since, the use of phthalate plasticizers has been questioned because of possible health implications; the objective of the present work is to undertake a similar study with eleven commercial alternative plasticizers to phthalates. The evolution of the dynamic and extensional viscosity, as well as the interactions and thermal transitions undergone by the plastisols during the heating process have been studied. Foams were obtained by rotational molding and characterized by the determination of their thermomechanical properties, density, and cell size distribution. Correlations were obtained between the molecular weight and structure of the plasticizer and the behavior of the corresponding plastisols. After the characterization of the final foamed product, it can be concluded that foams of relatively good quality can be prepared with alternative plasticizers for replacing phthalates. Several plasticizers (Mesamoll (ASE), Eastman 168 (EHBDC), Hexamoll (DINCH), Citroflex A4 (ATBC) and Plastomoll (DHA)) have been found as interesting alternatives in the production of soft PVC foams, since they provided very good quality foams with properties similar to, or even better than those obtained with phthalate plasticizers.
Keywords: alternative plasticizers, citrates, adipates, flexible PVC foam, characterization
The decomposition of azodicarbonamide, used as foaming agent in PVC—plasticizer (1/1) plastisols ... more The decomposition of azodicarbonamide, used as foaming agent in PVC—plasticizer (1/1) plastisols was studied by DSC. Nineteen different plasticizers, all belonging to the ester family, two being polymeric (polyadipates), were compared. The temperature of maximum decomposition rate (in anisothermal regime at 5 K min−1 scanning rate), ranges between 434 and 452 K. The heat of decomposition ranges between 8.7 and 12.5 J g−1. Some trends of variation of these parameters appear significant and are discussed in terms of solvent (matrix) and viscosity effects on the decomposition reactions. The shear modulus at 1 Hz frequency was determined at the temperature of maximum rate of foaming agent decomposition, and differs significantly from a sample to another. The foam density was determined at ambient temperature and the volume fraction of bubbles was used as criterion to judge the efficiency of the foaming process. The results reveal the existence of an optimal shear modulus of the order of 2 kPa that corresponds roughly to plasticizer molar masses of the order of 450 ± 50 g mol−1. Heavier plasticizers, especially polymeric ones are too difficult to deform. Lighter plasticizers such as diethyl phthalate (DEP) deform too easily and presumably facilitate bubble collapse.
This study deals with the rheological aspects of poly-vinyl chloride (PVC) plastisol gelation and... more This study deals with the rheological aspects of poly-vinyl chloride (PVC) plastisol gelation and fusion processes in foamable formulations. Here, such processes are simulated by temperature-programmed experiment (5 K min−1) in which complex viscosity components are continuously recorded. Nineteen samples based on a PVC-VAC (vinyl acetate 95/5) copolymer with 100 phr plasticizer have been studied, differing only by the plasticizer structure. The sample shear modulus increases continuously with temperature until a maximum, long time after the end of the dissolution process as characterized by DSC. The temperature at the maximum varies between 345 and 428 K with a clear tendency to increase almost linearly with the plasticizer molar mass, and to vary with the flexibility and the degree of branching of the plasticizer molecule. The shear modulus increase is interpreted in terms of progressive “welding” of swelled particles by polymer chain reptation. The plasticizer nature would mainly affect the friction parameter of chain diffusion.
The foaming of PVC (Poly (Vinyl Chloride)) plastisols is a complex combination of simultaneous pr... more 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), in order 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. In order to confirm such behavior and our hypothesis regarding the possible plasticizer evaporation, the thermal stability of the plastisols, pre-cured 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.
The foaming of PVC-VA (Poly (Vinyl Chloride-co-Vinyl Acetate)) plastisols is a complex combinatio... more The foaming of PVC-VA (Poly (Vinyl Chloride-co-Vinyl Acetate)) plastisols is a complex combination of processes involving the simultaneous curing of the paste with the evolution of gases caused by the decomposition of the chemical blowing agent. The extensional viscosity is a fundamental characteristic of the material, responsible for the behavior of the system when undergoing the extensional stress produced by the released gases. Nevertheless, such changes have not been considered to the same extent as the complex viscosity evolution or the thermal processes suffered by PVC-VA plastisols. The objective of the present work is to study the extensional viscosity of the PVC-VA plastisols prepared with three plasticizers of similar structure, but with different curing and rheological behavior in order to investigate its influence on the quality of the foams obtained. Extensional viscosity measurements under forced prestretch conditions revealed that depending on the structure and consequently on the compatibility of the plasticizer used, each plastisol develops its properties and structure accordingly. DINCH plasticizer (Diisononyl cyclohexane-1,2-dicarboxylate presenting alicyclic ring) seems to be the less compatible compared to the other two studied (both presenting aromatic rings) according to its behavior during the curing and foaming processes and may not be able to withstand the pressure evolved by the released gases during the foaming process yielding foams of poorer quality.
The evolution of complex viscosity of pastes of PVC-VA (poly-vinyl chloride-vinyl acetate copolym... more The evolution of complex viscosity of pastes of PVC-VA (poly-vinyl chloride-vinyl acetate copolymer) plasticized with twenty different commercial plasticizers has been studied. The knowledge of the rheological behavior of the formulations allows for better understanding of the gelation and fusion processes. Twenty commercial plasticizers with different types and functional groups have been studied, grouped into five families such as phthalate esters with linear chains, phthalate esters with branched chains, adipates (normal and polymeric), citrates, and the group of the rest of 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 gases – has been newly discussed regarding the chemical structure and molecular weight of all the twenty plasticizers used. It was found that several different dynamic processes must be synchronized in order to understand the relationship between the chemical structure, plasticization, plasticizer compatibility, rheological properties, and foaming process of such materials.
In this paper the characterization of the thermal behavior of foamable PVC (Poly (vinyl chloride)... more In this paper the characterization of the thermal behavior of foamable PVC (Poly (vinyl chloride)) plastisols from 20 different plasticizers has been studied by differential scanning calorimetry (DSC). The interactions among the resin and the plasticizer as well as the decomposition of the azodicarbonamide (ADC) - the chemical blowing agent (CBA) used - have been analyzed. The latter process has a crucial importance for the knowledge of plasticized PVC flexible foam formation. Clear effects of the chemical nature of the plasticizers and their molecular weight (Mw) have been observed, both in the interactions (swelling and early stages of gelation) among the resin and the plasticizer, as well as in the temperature of the ADC decomposition and the shape of the DSC peak.
Keywords: DSC, PVC, chemical blowing agent, decomposition, characterization.
The use of foamed plastics gains more and more interest every day. Flexible PVC (Poly(Vinyl Chlor... more The use of foamed plastics gains more and more interest every day. Flexible PVC (Poly(Vinyl Chloride)) 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 the present work, 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 (CBA), and the foam production by rotational molding. In addition, we have characterized the foams obtained by thermomechanical analysis (TMA), 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.
Plasticized PVC is one of the most useful polymeric materials at industrial scale, because of its... more Plasticized PVC is one of the most useful polymeric materials at industrial scale, because of its processability, wide range of obtainable properties and low cost. PVC plastisols are used in the production of flexible PVC foams. Phthalates are the most used plasticizers for PVC, and in a previous paper (part I), we studied the influence of phthalate ester type plasticizers on the foaming process and on the quality of the foams obtained from the corresponding plastisols. Since, the use of phthalate plasticizers has been questioned because of possible health implications; the objective of the present work is to undertake a similar study with eleven commercial alternative plasticizers to phthalates. The evolution of the dynamic and extensional viscosity, as well as the interactions and thermal transitions undergone by the plastisols during the heating process have been studied. Foams were obtained by rotational molding and characterized by the determination of their thermomechanical properties, density, and cell size distribution. Correlations were obtained between the molecular weight and structure of the plasticizer and the behavior of the corresponding plastisols. After the characterization of the final foamed product, it can be concluded that foams of relatively good quality can be prepared with alternative plasticizers for replacing phthalates. Several plasticizers (Mesamoll (ASE), Eastman 168 (EHBDC), Hexamoll (DINCH), Citroflex A4 (ATBC) and Plastomoll (DHA)) have been found as interesting alternatives in the production of soft PVC foams, since they provided very good quality foams with properties similar to, or even better than those obtained with phthalate plasticizers.
Keywords: alternative plasticizers, citrates, adipates, flexible PVC foam, characterization
Uploads
Papers by Agnes Zoller
Keywords: flexible PVC-VA foam, DEP - DIDP mixed phthalate plasticizers, plasticizer evaporation
Keywords: PVC, DINP, HEXAMOLL DINCH, EASTMAN 168, Extensional Viscosity, Foaming
Keywords: PVC; Gelation; Plasticizers; Rheology, Viscoelasticity
Keywords: DSC, PVC, chemical blowing agent, decomposition, characterization.
Keywords: phthalates, flexible PVC foam, characterization
Keywords: alternative plasticizers, citrates, adipates, flexible PVC foam, characterization
Keywords: flexible PVC-VA foam, DEP - DIDP mixed phthalate plasticizers, plasticizer evaporation
Keywords: PVC, DINP, HEXAMOLL DINCH, EASTMAN 168, Extensional Viscosity, Foaming
Keywords: PVC; Gelation; Plasticizers; Rheology, Viscoelasticity
Keywords: DSC, PVC, chemical blowing agent, decomposition, characterization.
Keywords: phthalates, flexible PVC foam, characterization
Keywords: alternative plasticizers, citrates, adipates, flexible PVC foam, characterization