THE ADVANTAGES OF DIMER FATTY ACID-BASED CO-POLYAMIDES AND THEIR HIGH CONTENT OF RENEWABLE SOURCES COMPARED TO STANDARD CO-POLYAMIDES CONVINCED SIPOL® TO INVEST IN THE PRODUCTION OF THIS CATEGORY OF HOT-MELT ADHESIVES
MACPLAS INTERNATIONAL FAKUMA 2017
The core business of SIPOL®, a privately owned Italian company, is the polymerization of high performance polymers for both the adhesive and the engineering plastics segments. The traditional activities of the company were the development and manufacturing of specialty co-polyesters (hot-melt and TPC-ET). However, in 2012 the company made an investment to add co-polyamides to its product portfolio because the main market segments where SIPOL® operates with hot-melt adhesives (footwear, filter bonding and textile lamination) often use both co-polyesters and co-polyamides. Therefore, the R&D team developed some proprietary polyamides molecules and scaled them up to a new polymerization plant which started operations in 2015. Nowadays, thanks to its complete portfolio of co-polyesters and co-polyamides, SIPOL® operates in several fields, such as automotive, footwear, packaging and electronics.
Dimer fatty acid co-polyamides
The best known and most common polyamides are often called “Nylon” (the trade name given by the first manufacturer, DuPont) and these are aliphatic polyamides (e.g. PA 6, PA 6.6, PA 12), widely used in engineering plastics for various applications. They are obtained from the condensation reaction of lactams, diamines and dicarboxylic acids. On the other hand, polyamides hot-melt adhesives are a small niche of the bigger polyamide world, and they can be divided into two categories:
- co-polyamides, built with lactams, diamines and short chain dicarboxylic acids, similar to “Nylons”;
- dimer fatty acid-based co-polyamides.
The Italian company SIPOL® focused on dimer fatty acid-based co-polyamides because of their unquestionable innovation content. In fact, these kinds of polyamides are synthesized combining dimer acids with other short chain dicarboxylic acids and various diamines. The nature and the relative molar amount of each component (co-monomer) influence the properties of the polymer (e.g. softening point, viscosity, mechanical performances, and adhesion behaviour).
Hot-melt polyamides provide an excellent adhesion on porous substrates (leather, paper, wood), some synthetic materials (treated polypropylene and polyethylene, ABS, PVC and other vinyl resins) and also metals (heat pre-treatment needed). Polyamides, ensuring high thermal stability and good chemical resistance to solvents, plasticizer and oils, find application in the automotive, textile and electronic industries. In addition, one more specific advantage, among others, provided by polyamides versus other hot-melt adhesives is their higher mechanical flexibility on glued junctions. In comparison to standard hot-melt polyamides (“Nylon” type), dimer-based polyamides have a much higher content of monomers from renewable sources and they are lactam-free (lactams bring some limitation in the VOC emission tests). In fact, dimeric acid comes from dimerization of ricinoleic acid, obtained by hydrolysis of vegetable oils. This is why all these polyamides have a content of renewable sources higher than 70%. Table 1 shows an overview of the properties between Nylon 6 (PA 6) and dimer-based co-polyamides.
The described features make hot-melt polyamides an ideal adhesive in the following fields:
- automotive: designed for air, oil and diesel filters (figure 1); also used in encapsulation, overmoulding, electrical insulation and interior trim;
- footwear: used in lasting and folding operations, together with toe puff printing operation (figure 2);
- electronics: used for credit cards and waterproofing connections;
- telecommunications: used in electric or telecom cable;
- metallic packaging: bonding and seaming;
- wood assembly: thread coating, knots repair and edge-banding;
- textile lamination: for car interiors, apparel, flooring.
Polyamide granules can be extruded in films, webs and rods, coated and also applied in powder (powder scattering).
TECHNIPOL® PA and SIPOLTEX® PA
SIPOL® portfolio of polyamide adhesives covers a range of viscosity from 0.5 Pa·s to 50 Pa·s (230°C) with softening point from 100°C to 210°C.