Synthetic chemicals are used in most pressure sensitive hot melt adhesives. Lower cost synthetic components are being substituted for higher cost synthetic materials by adhesive manufacturers to insure the availability and consistent pricing of hot melt pressure sensitives.
Some manufacturers are claiming incorrectly that they are switching to “Synthetic” materials when they are simply switching from one synthetic component to another. Many of these companies also give the impression that they are switching from “Natural” materials. Most HMPSAs are composed of tackifiers (either synthetic or natural resins), mineral oils, and a small amount of antioxidant.
Adhesive manufacturers will replace Styrene-Isoprene-Styrene block copolymers (SIS) with SIBS or SBS, both isoprene and butadiene used for making SBCs which are all synthetic materials starting from petroleum. None of these are natural materials. In fact, almost all the ingredients, including natural tackifying resins such as rosin and terpene derivatives, used for HMPSAs are all considered to be synthetic materials. Natural materials are obtained directly from paper mills or live trees, cannot be used as is and all require further synthesis to be useful tackifiers.
Isoprene or 2-methyl-1,3-butadiene is a colorless liquid organic compound. It is available industrially as a by-product of the thermal cracking of naphtha or oil. The isoprene yield is approximately 2 to 5% of the ethylene yield. About 95% of isoprene production is used to produce cis-1,4-polyisoprene (also known as Isoprene Rubber, IR)- a synthetic version of natural rubber (NR); 2%, to produce butyl rubber (isobutene-isoprene copolymer, IIR); and only 3%, to produce SIS.
Due to dramatic petroleum price increases and the imbalanced supply-demand of isoprene feedstock in the past couple years, the cost of making SIS is rather high while the availability of isoprene is always very limited. Since butadiene (most of the time it refers to 1,3-butadiene) feedstock is cheaper and readily available at most SBC (Styrenic Block Copolymer) manufacturers, a series of new hybrid version of SIS and SBS (Styrene-Butadiene-Styrene), named SIBS (Styrene-Isoprene/Butadiene-Styrene), is then developed as an alternative for SIS. The SIBS is structurally tailored to be performed like that of conventional SIS. Another alternative for SIS is the high % di-blocks SBS.
The selling prices of these newly developed “synthetic” block copolymers, SIBS and high % bi-block SBS are less than that of SIS currently. In order to maintain a stable raw material cost and resource, introducing these new SBCs into their HMPSA is needed.