A new family of sustainable tackifying agents with adjustable glass transition temperatures was prepared via torrefaction of outer birch bark waste. The application of the obtained betulin esters as a tackifier was tested in combination with a semicrystalline ethylene vinyl acetate (EVA) copolymer in a standard hot-melt adhesive formulation. Three torrefied birch bark products with different glass transition temperatures (23, 45, and 66 °C) showed excellent compatibility with the EVA copolymer in a 1/1 (w/w) mixing ratio. A high Tg tackifier resin (66 °C) was prepared with a rotary tube furnace in a continuous production process at 240 °C. High product yields of about 25% (w/w) could be obtained after solvent extraction of the torrefied bark with acetone. The birch bark tackifying agents change from a stiff, brittle material below Tg to a low viscosity fluid at higher temperatures accompanied by a change of storage and loss modulus over several decades. The Tg of the adhesives could be exactly tailored by the choice of the birch bark tackifier. The resulting adhesives showed excellent lap shear strength on zinc-plated steel and on wood, shifting to values up to 10 MPa with increased Tg of the archaeoinspired adhesives.     «

A new family of sustainable tackifying agents with adjustable glass transition temperatures was prepared via torrefaction of outer birch bark waste. The application of the obtained betulin esters as a tackifier was tested in combination with a semicrystalline ethylene vinyl acetate (EVA) copolymer in a standard hot-melt adhesive formulation. Three torrefied birch bark products with different glass transition temperatures (23, 45, and 66 °C) showed excellent compatibility with the EVA copolymer i...     »