Natural formulations are a well known stalwart of the adhesive industry, with highly specified applications that include around 30 percent of the market for adhesives that do not use volatile solvents.1 Equally well known are the limits of natural adhesives, frequently including weak bonds and slow curing. During the 20th century advances in chemistry have brought a rapid expansion in the use of synthetic polymers in adhesives, but now interest in natural feedstocks is being renewed as "sustainability" becomes a watchword. Thankfully, the chemical lessons learnt in decades of polymer chemistry can now be applied to helping natural adhesives challenge their perceived limitations.
Most natural adhesives don't cure by a crosslinking chemical reaction. Instead, they are complicated systems of entangled natural polymers made mobile and then allowed to set into a solid, cohesive layer. Bitumen adhesives are examples of this, with the basic bitumen feedstock itself being a mix of complex longer chain organic polymers and various shorter chains that can act as solvents.