Scientists develop flexible new polymer blends for 3D printing smart textile devices

Scientists from the GEMTEX research laboratory have worked with the Swedish University of Borås and China’s Soochow University, to develop a new range of polymers for printing directly onto fabrics. 

The researchers designed a series of customized, reinforced, polymer blends consisting of Carbon Black (CB), Polypropylene (PP) elastomers, and Carbon Nanotubes (CNTs). When the plastic combinations were 3D printed onto cloth using a two-step extrusion process, the resulting additive attire exhibited enhanced strength qualities and were less prone to breakage than existing polymer-infused wearables. 

The team’s new range of conductive 3D printing materials could enable the development of a new generation of smart textiles, with more complex geometries than are currently possible.  

The research team's two-step extrusion technique (pictured), turned their polymers into pellets before being 3D printed onto fabrics. Image via the Polymers journal.
The research team’s two-step extrusion technique (pictured), turned their polymers into pellets before 3D printing them onto fabrics. Image via the Polymers journal.

Additive manufacturing in the textile industry 

FDM is the world’s most widely-used 3D printing technology, and while it’s often leveraged as a means of producing prototypes, it’s increasingly being utilized to fuse conductive polymers into textiles as well. Using FDM, it’s possible to deposit thermoplastics in patterns or layers, and numerous researchers have managed to print sensors, antennas and other objects into textiles in recent years. 

One of the more difficult aspects of printing directly onto fabrics is maintaining the tensile properties of the original material and a high level of adhesion after several washes. Previous research at Moi University in Kenya, has shown that deposition into clothing affects the qualities of PET plastics more than it does PLA, meaning that material composition is vital to success in textile 3D printing. 

The Kenyan researchers also found that in order to combat the fragility featured in wearable plastics, an improvement in the stresses and strains of the polymer’s individual layers was needed. As a result, the joint research team began searching for ideal polymers to 3D print with. Low-Density Polyethylene (LDPE) showed potential because its texture is soft and rubbery, and polyethylene (PE) is already used within other textile applications. 

Other plastics such as Conducting Polymer Composites (CPCs) are electrically-charged and have been used to produce sensors before, but their exposure to different temperatures is known to affect their resistance capabilities. To make CPCs easier to process, and make them more stable, the researchers hypothesized that they could be blended into an immiscible elastomeric polymer.

The researchers' co-polymer was formed using a combination of PBE and LDPE plastics. Image via the Polymers journal.
The researchers’ co-polymer was formed using a combination of PBE and LDPE plastics. Image via the Polymers journal.

Creating enhanced blended polymers for 3D printing 

The researchers aimed to improve the flexibility, stress-resistance qualities, and electrical conductivity of LDPE and PBE polymers when 3D printed into textiles. To achieve this, the team produced a number of immiscible CNTs and used a highly-structured CB known as Ketjenblack (KB) to fill a low-density LDPE/PP elastomer (PBE) blend.

In order to examine the features of their new polymeric combination more closely, the team created four samples, with varying levels of fill, and therefore different levels of conductivity. Then another five specimens were made, which also had different weights, but these were used to assess the rheological properties of the CPC-PBE, and to optimize the percentages of each component polymer. 

Testing the research team’s polymeric samples involved depositing them into rectangular pieces of polyester using a Pollen AM Pellet Additive Manufacturing (PAM) 3D printer. Once all the test subjects had been processed, the researchers conducted a series of rheological analyses, in an attempt to assess the tensile properties of their new class of materials. 

Evaluations showed that increasing the level of KB and CNT within the polymers,  increased its electrical conductivity because the fillers began to build networks between them. What’s more, using a two-step extrusion technique (which turned the plastics into pellets before printing), had the opposite effect, limiting the amount of polymeric networks formed, thus reducing conductivity. 

In terms of the strength of the team’s new polymer blends, PBE-intensive formulations proved to be more resistant to strain than those without it. The rheological makeup of PBE allows for highly structured networks between its KB and CNT fillers, which provides enhanced strength while maintaining a natural flexibility and elasticity. 

Overall, the team’s 3D printing approach had allowed them to tailor their combined thermoplastics and create highly-structured polymer networks while maintaining the flexibility of an elastomer. Conductivity, resistance at strain, and elasticity were all demonstrably improved using PBEs, and the researchers concluded their materials to be a viable potential basis for 3D printed wearables in future. 

3D printed garments in the fashion industry 

Recent advances in the formulation of flexible polymers and elastomers have increasingly enabled their use within the fashion industry, as well as the textile sector as a whole. 

Stratasys has developed its novel direct-to-textile PolyJet printing Technology, which also allows digital designs to be printed directly onto materials. In a recent field test with fashion designers Ganit Goldstein and Julia Koerner, the company managed to 3D print a range of trendy additive clothing lines. 

GE Additive and Protolabs achieved something similar in their partnership with American fashion designer Zac Posen, which saw them fabricate dresses for the 2019 Met Gala. The “Glass Slipper” dress, which was worn at the show, took Protolabs over 200 hours to create, due to its printing, sanding, and coating steps. 

Elsewhere, Mingjing Lin and Tsai-Chun Huang, Ph.D. candidates in Fashion and Textile research at the Royal College of Art London used leveraged 3D printer manufacturer Sinterit’s flexible TPUs to 3D print costumes for the Beijing Opera. By utilizing additive manufacturing, the duo was able to produce highly-complex geometries and tailor the outfits to each individual wearer. 

The researchers’ findings are detailed in their paper titled “Development of Flexible and Conductive Immiscible Thermoplastic/Elastomer Monofilament for Smart Textiles Applications Using 3D Printing.” The paper was co-authored by Prisca Eutionnat-Diffo, Yan Chen, Jinping Guan, Vincent Nierstrasz, Aurélie Cayla and Christine Campagne. 

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Featured image shows the first phase of the researchers’ two-step extrusion technique. Image via the Polymers journal. 

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