Soft PVC foams: Study of the gelation, fusion, and foaming processes. II. Adipate, citrate and other types of plasticizers

Abstract

Plasticized poly(vinyl chloride) (PVC) is one of the most useful polymeric materials on an 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 article (part I of this series), we discussed the influence of phthalate ester type plasticizers on the foaming process and on the quality of the foams obtained from the corresponding plastisols. Because the use of phthalate plasticizers has been questioned because of possible health implications, the objective of this work was to undertake a similar study with 11 commercial alternative plasticizers to phthalates. The evolution of the dynamic and extensional viscosity and the interactions and thermal transitions undergone by the plastisols during the heating process were studied. Foams were obtained by rotational molding and were 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, we concluded that foams of relatively good quality could be prepared with alternative plasticizers for replacing phthalates. Several plasticizers {Mesamoll (alkylsulfonic phenyl ester), Eastman 168 [bis(2-ethylhexyl)-1,4-benzenedicarboxylate], Hexamoll [di(isononyl) cyclohexane-1,2-dicarboxylate], Citroflex A4 acetyl tributyl citrate (ATBC), and Plastomoll (dihexyl adipate)} were found to be interesting alternatives in the production of soft PVC foams because they provided very good quality foams with properties similar to, or even better than, those obtained with phthalate plasticizers.

Extensional viscosity measurements and characterization of poly (vinyl chloride‐co‐vinyl acetate) plastisols and foams

“…Further important data should be considered, which is the difference between the decomposition temperature of the azodicarbonamide ( T ADC ) and the temperature of the maximum complex viscosity ( T η*max ). This data provides relevant and useful information about the stage of development of the polymer matrix at the moment of the gas generation 26. The larger this temperature difference, the more developed the properties and melt strength of the studied plastisol.…”

“…The benzene derivatives (EHBDC and DINP) are planar and present aromaticity, while DINCH has a chair conformation because of the non‐aromatic (alicyclic) cyclohexane ring. In previous papers,25–28 we studied 20 plasticizers of 8 different chemical families and found certain correlations between the molecular structure of the plasticizer used and the structural changes undergone by the corresponding plastisols, as well as the foaming and foam quality. Taking those results into consideration to discuss such correlations and provide a better insight into these changes and processes became interesting.…”

“…Moreover, we have not found any reference dealing with the extensional viscosity in the processes of foaming of PVC‐VA plastisols. In previous papers, we studied the effect of different plasticizers in such processes and we reported data on the extensional viscosity of the corresponding pastes at given temperatures 25, 26. The effect of the extensional viscosity on the behavior of the system was not as clear as the effect of the complex viscosity or other properties of the system.…”

“…It is important to consider the data, obtained from the DSC measurement along with the results of the complex viscosity measurements, for a better understanding of the foaming of a dynamic system such as the plastisols studied 25, 26. The foaming has to be synchronized with the viscosity evolution as well, thus it is very convenient to study the relationship between the thermal transitions and the complex viscosity.…”

“…In previous works,23–26 we studied the effect of the nature of different plasticizers in the properties and morphology of the foams obtained from foamable PVC plastisols by rotational molding process. We studied the evolution of the complex viscosity during the curing process,27 the extensional viscosities,25, 26 the thermal effects during the swelling of the resin and the decomposition of the ADC,28 as well as the morphology and characteristics of the foams obtained 25, 26. Interesting relationships were obtained among all these properties and the foams obtained, showing that once cured, these systems behave in a similar way to other nonreactive systems.…”