Hot-melt adhesives (HMAs) offer a gamut of advantages over their contemporary water-based and solvent-based adhesives. With their excellent adhesion, ease of use and quick set time they have a critical advantage of fast processing in various industrial applications. Apart from the lucrative benefit, HMAs provide a more eco-friendly alternative due to their solventless formulation. In recent years, efforts have been devoted to making these formulations completely bio-based and biodegradable. The need for this stems from two factors- The escalating market share of HMAs, prompting to reduce their dependence on dwindling petroleum resources and the enormous use of HMAs in packaging areas that demand 100% recyclability. In this endeavor, replacements to the base polymers have been found mainly from soy, modified starch, polylactides and vegetable oils. The most popular approach has been the use of poly(lactic acid) (PLA) and its blends due to their excellent hot tack, moderate setting time and cost effectiveness. Polyamides and polyesteramides from seed oil and soy-derived dimer fatty acids have been reported to provide strength comparable to best HMAs. Work has also been reported on the use of starch esters and ethers as components in low melting, high flexibility HMA formulations for packaging applications.
The enormous amount of research going on in the field of bio-based polymers has still not reached its complete potential in the field of HMAs. In this review article HMAs based on bio-based polyamides, poly(lactic acid), soy protein and starch are discussed.
Key words: Bio-based polymers, hot-melt adhesives, biodegradability, lactic acid, soy protein, polyamides, starch