Soft thermoplastic polyurethanes can win roles in applications where touch and feel are important but maintaining softness can be challenging. Ingevity’s new polyol product line for soft TPUs, the Capa S series, could help.
There is high, but untapped, market demand for soft TPUs with good mechanical properties. They are particularly desirable in applications such as wearable devices like smart watches and fitness trackers, and also automobile dashboards, seating and door panels. These are products where consumers want functional long-lasting products that are also comfortable and aesthetically appealing.
Ingevity has two new polyols, Capa S 22X and Capa S 23Y, that are designed to help formulators produce materials that stay soft, and minimise cracking during a product’s functional lifetime. They could also simplify formulations, and lower production costs.
In applications where softness is required for extended periods, the market is currently dominated by the more expensive fluoroelastomers and silicone elastomers.
Polyurethanes have been able to compete, but need to be plasticised to overcome the problem of cold hardening – the slow crystallisation of the soft polyol blocks of the polyurethane over time.
Although plasticisation is a well-known process used to produce polymeric compounds that are more flexible and softer than their unplasticised homologues, adding plasticisers to formulations can generate a number of challenges. First, plasticisers must be added to the formulation, which can involve an extra processing step and additional cost. Once incorporated into the polymer, plasticisers can migrate from the compound into surrounding materials and the environment. This can lead to unwanted chemical exposure and a gradual stiffening of the part over time.
Keeping polyurethanes soft
By modifying the crystallinity in soft blocks in the finished TPU, we believe Capa S can help fill the gap between plasticised TPUs and premium soft elastomeric materials. Our technology uses carefully branched monomers which act as internal plasticisers for TPUs. Here, the branches can disrupt packing and crystallinity in soft blocks.
Since the soft block chains are more mobile than customary polyols, it is possible to produce polymers that are intrinsically softer than similar polyurethanes. At the same time, the hard blocks retain the crystallinity needed to make injection moulding a viable process. There is a balance between the crystallinity of the soft segment and the ability to process the materials. These Capa polyols are characterised by a lack of by-products, very low acid values and water content, 100% primary hydroxyl content, and a narrow and consistent polydispersity.
This technology is flexible, and a wide range of polyols can be generated using a variety of hydroxyl-functionalised initiators. Additionally, co-monomers can be integrated into the polyol, often leading to synergistic effects. The Capa product portfolio includes materials that can be used as polyurethane soft segments and chain extenders. The ability to tailor the structure of these polyols gives customers the ability to differentiate their products.
Capa S 22X and Capa S 23Y are polycaprolactone diols with a structure tailored for use in polyurethane materials of hardness less than 70 Shore A. They have molecular weights of 2000 g/mol and 3000 g/mol respectively.
Compare and contrast
We compared the effectiveness of two new polyols Capa S 22X and 23Y (Slide 27) against an equivalent grade 2210A from our range and a group of competitive materials including silicone elastomer, flroroelastomer, thermopolastic polyolefin, thermoplastic vulcanisate and a styrene butadiene copolymer.