Soft polyurethane elastomers with adhesion properties based on palm olein and palm oil fatty acid methyl ester polyols

Soft polyurethane (PU) elastomers with >70% bio-based content and with properties characteristic of pressure sensitive adhesives were prepared from an equimolar ratio of a polyol derived from palm oil fatty acid methyl ester (PolyFAME-EG polyol) and palm olein polyols (Pioneer E-135 and Pioneer M-60) cured with 2,4'- and 4,4'- diphenyhnethane diisocyanate isomeric mixture at isocyanate to hydroxyl equivalent weight ratio (Isocyanate Index) of 1.02 and 0.73. FTIR. analyses of the resulting elastomers indicate high levels of free non-hydrogen bonded urethanes, indicating phase mixing of hard and soft segments, which explains the transparent nature of the elastomers. The physical properties of the elastomers were correlated with the crosslink density of the palm olein polyols and Isocyanate Index. Elastomers produced at an Isocyanate Index of 1.02 ranges in hardness from 21 to 67 Shore A which correlated with the average polyol functionality. However, at an Isocyanate Index of 0.72 the resulting elastomers were very soft with hardness ranging from 1 to 4 Shore A and with T-peel adhesion to polypropylene in the range from 2.27 to 1.98 N/25 mm. Based on these results, a polyurethane matrix with a high renewable content of palm oil polyols can be used as a platform for the development of transparent elastomers that can be used as soft energy-absorbing materials with potential use in pressure sensitive adhesives.