Fully biobased structural adhesives

Epoxidized natural oils can be cured by cationic polimerisation or polyaddition with anhydrides. Unfortunatly, the properties of the cured polymers are not sufficient for the use as structural adhesives. If cationic polymerisation is used for adhesive curing the properties can be adjusted by polymeric alcohols. Typically polypropylenglycols with two or more alcohol groups are applied for this purpose. Unfortunatly, they lead mainly to softer but less strong adhesives and are not biobased which is a requirement if epoxidised natural oils are used. Therefore, we deverloped a new class of polyols which are biobased and for which we expected pronounced toughening instead of just softening the curdes adhesives. The expectation is based on experiences with artifical crystallisable polyesterpolyols and was verified successfully. Polyolls with different molecular weight and number of alcohol groups based on lactic acid were prepared. This was carried out by ring opening polymerisation of dilactide using different start alcohols. If formulated with epoxidised oils and sufficient curing initiators the new polyols lead to tough structural adhesives which can be cured thermally as well as photochemically. Strength increases with the number of epoxide groups of the applied epoxidised oil.