BioPSA: Bio-based pressure-sensitive adhesives

Based on the joint project “BioPSA: hotmelt pressure-sensitive adhesives based on renewable raw materials“, the basic formulations of hot-melt pressure-sensitive adhesives based on renewable raw materials are to be further developed and adapted to suit different areas of application. Fraunhofer researchers researched the PLA primary polymeric ingredient (PLA: polylactic acid) in a preliminary project before optimizing it with the best properties on a laboratory scale and examining it with a view to possible large-scale production.

A pressure-sensitive adhesive (PSA) is an “adhesive that is permanently tacky when dry at room temperature and easily adheres to surfaces under brief, low pressure“[1]. It is usually applied to various substrates and is often used in self-adhesive tapes and labels. A hot-melt pressure-sensitive adhesive is a pressure-sensitive adhesive that is processed from a melt. In general, pressure-sensitive adhesives are based on four components: primary polymeric ingredient, tackifier, plasticizer, and other additives. The primary polymeric ingredient – also called the base polymer – is a cohesion-determining component (cohesion or “internal cohesion: state in which the parts of a substance are held together by primary or secondary valence forces“[1]). It is responsible for the adhesive strength of a pressure-sensitive adhesive.

Economical production of primary polymeric ingredients

The demand for adhesive products based on renewable raw materials has risen sharply in recent years due to the changed awareness of sustainability and environmental protection. The development of bio-based adhesives is becoming increasingly important.

In order to maintain market access for these products and to secure market shares in a timely manner, the economical production of primary polymeric ingredients is essential for companies in the adhesives industry. Since the properties of PLA differ significantly from those of the polymers used in the adhesives industry to date, it is necessary to develop a completely new formulation. The most important groups of primary polymeric ingredients in the pressure-sensitive adhesive market today are polyacrylates and styrene block copolymers.

Fraunhofer UMSICHT produces various PLA-based primary polymeric ingredients on a laboratory scale. The modified polymer backbone should provide the materials with important adhesive elastomeric properties as well as cohesion capability in the desired range. One challenge is the large number of ingredients in the adhesive formulation (tackifiers, plasticizers, and other mixture components). A further factor is the complexity of the possible interactions with the primary polymeric ingredient.

The use of the newly developed primary polymeric ingredient PLAColl-1 will initially be investigated. In particular, its low thermal stability needs to be improved. In addition to further formulation approaches, the researchers must also examine the properties of the base polymer in detail. This is followed by a timely scale-up of the manufacturing process from a laboratory to an industrial scale. This allows industrial-scale coating trials to be carried out at an early stage in the project. At the same time, the formulation trials will be continued based on the findings of the preliminary project. When selecting the adhesive components, cost, availability, toxicology, sustainability, and environmental aspects are taken into account in addition to technical suitability.

New bio-based raw materials provide various starting points. Design-of-experiments (DOE) methods are used in a targeted manner to optimize properties efficiently.

The use of the new adhesives is to be transferred to various applications and marketed while taking into account licensing. Based on the results of up-scaling to an industrial scale, a commercial production of the base polymer will be investigated and strived for. The scientific results will be used for further research into bio pressure-sensitive adhesives and the development of future applications for PLA copolymers.

[1] DIN EN 923:2008-06. Adhesives - Terms and definitions; German version EN 923:2005+A1:2008

• Jowat SE
• Logo tape Gesellschaft für Selbstklebebänder mbH & Co. KG
• Henkel AG & Co. KGaA
• Westfälische Hochschule Gelsenkirchen, Bocholt, Recklinghausen, Fachbereich Wirtschaftsingenieurwesen in Recklinghausen