INFORM November/December 2025

22 • inform November/December 2025, Vol. 36 (10)

Apparent viscosity of different PVC plastisols with CNSL-C2 esters at 25 °C. Source: Gartili, A., et al. , JAOCS , 102, 8, 1141, 2025.

viscosity can be attributed to the onset of gelation between plasticizer and PVC at room temperature due to the mechan ical force applied to the mixture. The epoxy derivatives ESBO and ELO have many polar groups, which facilitate the gelling process, as does B-C2, which has two ester groups. For PVC plastisol plasticized with A-C2 or CNSL mixture-C2, a relatively linear viscosity profile with an increase in shear gradi ent is observed. This behavior is interesting as it suggests a pre dictable and consistent response of the material to shear stress variations. Thus, CNSL and cardanol derived plastisol maintain a certain level of fluidity while reacting stably to changes in shear gradient, which can be useful in certain applications. Plastisol containing CNSL derivatives or A-C2 has lower viscosity (5 Pa s) than those plasticized with phthalates (20 Pa s) or biobased epoxidized oils, which can reach 100–400 Pa s. The gelation process of a plastisol is complex, involv ing the swelling of PVC particles and aggregates to form a gel structure. This process is influenced by diffusion laws and is highly dependent on temperature and compatibility with the plasticizer. The rheological analysis involving measuring the complex viscosity’s changes as the temperature increases pro vides valuable insights into the plasticizer absorption within PVC particles. A sharp increase signals the onset of gelation, caused by PVC particle swelling due to plasticizer absorption at T onset . Then, as particle size grows, coalescence occurs, reaching a maximum viscosity (η max ) at T endset . The maximum viscosity, η max , is directly linked to the quantity of plasticizer absorbed by soft PVC. A higher η max value signifies a greater degree of plasticizer absorption by PVC particles. As soft PVC absorbs plasticizer, it undergoes swelling, resulting in an increase in

viscosity. Hence, the rise in maximum viscosity serves as an indicator of intensified plasticizer absorption by PVC particles. Then, the viscosity peak is followed by a decrease as the gelation rate slows and the temperature rises. The material begins to degrade and viscosity may increase again. Interestingly, initially ESBO, ELO, and phthalates have higher viscosity than CNSL derivatives, and plastisol containing cardol derivatives also has higher viscosity than cardanol ones. It may be attributed to the constraint on molecular mobility and the reduction in available free volume resulting from the interactions between the plasticizer and PVC. PVC plasticized with ESBO and ELO has depicted very high viscosity compared to the other plasticizers. Indeed, ESBO and ELO are more viscous plasticizers than CNSL ones. ESBO and ELO plasticizers can limit the molecular mobility of PVC through epoxy groups, fostering additional intermolec ular bonds. Furthermore, B-C2-based plasticizers, possessing more polar groups than A-C2, may contribute to the observed increase in viscosity, acting as a pseudo-crosslinker with PVC. Notably, PVC plasticized with the mixture of cardanol and car dol exhibits lower viscosity compared to B-C2 alone, under scoring once again the intriguing properties of CNSL-based plasticizers. Based on the rheology analysis, the entanglement of chains and intermolecular interactions with PVC are less pronounced for the mixture of A-C2 and CNSL plasticized PVC. In general, the efficiency of a plasticizer can be assessed by comparing its viscosity curve with that of the DEHP or DINP plastisol. The closer the viscosity of CNSL derivatives plasti sol was to that of references plastisol, the better the plasticiz ing efficiency. B-C2 and CNSL enriched in cardol derivatives exhibit similar viscosity behavior to the reference ones. It was