"Mass customization" is a megatrend for the future. The individualization of customer requirements, however, presents manufacturers with new challenges. Neenah Gessner GmbH, Feldkirchen-Westerham/Germany, and Covestro AG, Leverkusen/Germany, teamed up to cooperate in product development, beginning with nonwovens with a shape memory effect. The material is manufactured using the meltblown process and is characterized by its ability to temporarily store a structural change until it returns to its original, memorized form by means of a temperature increase.
Key to the unique shape memory nonwovens is the base material used, a thermoplastic polyurethane (TPU) with a specially tailored molecular structure. Unlike common TPUs, the plastic has a crystalline soft phase that changes to an amorphous state at about 40-50 °C, allowing deformation at low force. This state is retained by cooling until a renewed increase in temperature leads to a return to the permanent form.
In practical terms, this effect means that the nonwovens can temporarily remain in a stretched shape and only shrink to original size at temperatures above 50 °C. In addition, the nonwovens have all the properties that generally characterize TPU nonwovens: the fabric consists of fibers with a diameter of about 10 µm, making it highly permeable to air. The material can be produced in a wide range of mass per unit area, which makes it possible to control the strength and the force applied when the material shrinks. It also exhibits elasticity with good recovery even when cold.
The combination of shape memory effect and fibrous structure allows the nonwovens to be used in countless applications. In addition to the properties of the material itself, it can be combined with a wide variety of other materials. The lamination technologies allow extensive possibilities to combine 2 or more layers without losing functions such as air permeability.
Support bandages are an example for an application of the new nonwovens field. Fig. 3 shows the shape memory nonwoven material in its temporary form, which was created by stretching at approx. 60 °C and then cooling under tension. It can be loosely pulled over the hand, significantly simplifying dressing. When heated with a blow-dryer to temperatures above 50 °C, the bandage shrinks as shown in Fig. 4. At the same time, it retains its porosity and air permeability, which helps to prevent skin irritation caused by moisture. The elasticity allows for good mobility of the arm.
With nearly 60 years of experience in research, development and production of specialty technical papers and filter materials for industrial and automotive applications, Neenah is one of the leading manufacturers of filtration solutions, as well as an expert in the production of meltblown nonwovens applications.
The use of different technologies and raw materials enables the company to meet the needs of customers. Depending on the choice of polymer and additives, the nonwovens can be functionalized with many different properties. Meltblown materials with weights ranging from 25-600 g/m2 can be produced. Alternatively, meltblowns can be applied directly to a carrier medium, creating combination media in one step.
In addition, many other options are available to customize meltblown nonwovens: Fiber diameter, thickness, basis weight, food compliance, surface design, chemical resistance, heat resistance, compostability, dust loading, UV protection, antibacterial properties, colors and electret charge are some of those.