Sustainable pressure sensitive adhesives based on biobased epoxies and dicarboxylic acids

TEPER MARINELLI, LAUTARO G.; RUSECKAITE, ROXANA A.; CIANNAMEA, EMILIANO M.

Buenos Aires

Congreso; 11th WORLD CONGRESS OF CHEMICAL ENGINEERING; 2023

Asociacion argentina de ingenieros Quimicos

Pressure-sensitive adhesives (PSAs) are a special category of polymeric materials that are permanently tacky at the operating temperature and can adhere to any given substrate under a slight pressure in a short time, without any chemical reaction, phase change or solvent evaporation [1]. Renewable resources can be used as feedstock to manufacture PSAs that can compete with those derived from petrochemical sources [1]. The motivation of this study was the design of completely renewable PSAs with tunable properties based on epoxidized soybean oil (ESO, EEW=233.47) and dicarboxylic acids. Two types of bifunctional acids were used: sebacic acid (SA) and a linear polymeric diacid (PD) synthesized from SA and a flexible bifunctional epoxy resin Cardolite NC-514 (EEW=456).Polymeric diacids (PD) were synthesized by mixing SA and NC-514 using different acid/epoxy equivalent ratios (1.23, 1.5 and 1.76). The polymers were designated PD1.X, where x refers to the equivalent ratio. The reaction was carried out in a silicone thermostatic bath at 140°C with mechanical stirring for 2 hours. The acid equivalent weights were obtained by titration for each polymeric diacid: PD1.23, AEW=1405,45 g/eq; PD1.5, AEW=860,08 g/eq; PD1.76, AEW=709 g/eq. PSAs were obtained from the reaction between ESO and diacids (SA and PDx) in stoichiometric equivalent ratio. Curing time (tgel) of PSAs were determined by pot-life test at 160°C, 170°C and 180°C. In base of the results the adhesives were cured in a convection oven for tgel + 5 min at 160°C.Thermal-gravimetrical analysis (TGA) was used to determine the thermal stability of the raw materials, polymerics diacids and PSAs. Dynamic calorimetry (DSC) was employed to determine reaction temperatures of uncured mixtures and the glass transition temperature (Tg) of PSAs, in order to determine their potential applicability as commercial adhesives. Rheological properties were measured in an Anton Paar MCR 301 rheometer by means of frequency sweeps at room temperature to stablish the Chang viscoelasticity window [2] and determine the potential applications of these materials as pressure-sensitive adhesives. Mechanical measurements were made to determine the peel strength according to the ASTM D3330 Test Method A standard and compared with commercial synthetic PSAs.The Tg of a PSA must be 25–45 °C below the usage temperature [1]. Therefore, the low Tg observed for the synthesized polymers (~ -22°C) indicates that these could be used as PSAs at room temperature. According to Chang, the obtained adhesives have a potential use as renewable PSAs at a large range of temperatures. Moreover, obtained PSAs showed a good balance between peel and tack. Particularly, ESOPD1.5 showed the best balance of properties. The measurement of peel strength was near to 1 N/cm, being comparable with commercial PSAs (i.e. Scotch tape 3M), demonstrating the potential of these renewable adhesives.